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; R Qs U. S. DEPARTMENT OF AGRICULTURE,
BUREAU OF PLANT INDUSTRY—BULLETIN NO, 217.

B. T. GALLOWAY, Chief of Bureau,

ROOT-KNOT AND ITS CONTROL.

ERNST A. BESSEY,

Professor of Botany, Michigan Agricultural College, and
Collaborator, Bureau of Plant Industry. :

IssurpD NovemMBER 21, 1911.

WASHINGTON :
GOVERNMENT PRINTING OFFICE.
1911.

Class

Bok” RWB 5

U. S DEPARTMENT OF AGRICULTURE.
BUREAU OF PLANT INDUSTRY—BULLETIN NO. 217.

B. T. GALLOWAY, Chief of Bureau.

ROOT-KNOT AND ITS CONTROL.

BY
) of

ERNST a! BESSEY,

)
Professor of Botany, Michigan Agricultural College, and
Collaborator, Bureau of Plant Industry.

IssueD NovEMBER 21, 1911.

WASHINGTON :
GOVERNMENT PRINTING OFFICE.
1911,

BUREAU OF PLANT INDUSTRY.

Chief of Bureau, BEVERLY T. GALLOWAY.
Assistant Chief of Bureau, WimLtIAM A. TAYLOR.
Editor, J. E. ROCKWELL.

Chief Clerk, JAMES E. JONES.

COTTON AND TRUCK DISEASE AND SUGAR-PLANT INVESTIGATIONS.
SCIENTIFIC STAFF.

W. A. Orton, Pathologist in Charge.
H. A. Edson and J. B. Norton, Physiologists.
W. W. Gilbert, L. L. Harter, H. B. Shaw, F. J. Pritchard, F. A. Wolf, and H. W. Wollenweber, A ssis¢-
ant Pathologists.
C. F. Clark, G. F. Miles, Clara O. Jamieson, Ethel C. Field, W. B. Clark, and A. C. Lewis, Scientific
Assistants.
E. C. Rittue, Joseph F. Reed, J. Rosenbaum, and L. O. Watson, Assistants.

217
2

LETTER OF TRANSMITTAL.

U. S. DeparTMENT OF AGRICULTURE,
Bureau or Pranr Inpustry,
OFFICE OF THE CHIEF,
Washington, D. C., April 10, 1911.
Srr: I have the honor to transmit herewith and to recommend
for publication as Bulletin No. 217 of the series of this Bureau a manu-
script entitled ‘‘ Root-Knot and Its Control,” by Dr. Ernst A. Bessey,
professor of botany, Michigan Agricultural College, formerly a plant
pathologist in this Bureau and now a collaborator of the Bureau of
Plant Industry. This bulletin presents the results and conclusions
of studies made by the author while in the service of the Bureau.
Root-knot, which is widespread through the warm temperate and
tropical zones of the whole world, is especially prevalent in this
country in the South, and, as the bulletin shows, it is present even in
the cold parts of the Northern States. It is also a very serious dis-
ease of greenhouse plants all over the country. Fortunately, it is
almost exclusively confined to the lighter types of soils, causing little
or no damage in stiff clays. Dr. Bessey has worked out under field
conditions a practical method of holding the pest in check. The
means of its control in greenhouses had already been worked out,
so that the methods presented here for controlling the pest in green-
houses offer little that is new. The list of plants susceptible to this
disease is more complete than any previous list published, contain-
ing more than double the names of any other list.
Respectfully,
Wn. A. Tay Lor,
Acting Chief of Bureau.
Hon. JAMEs WILson,
Secretary of Agriculture.

217

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CONTENTS.

Page

DRE NOY CATS OS BE oe 7
Sas TRA FN LOTTIE PRREIO IN Obs ae sim ceeralarm ccna win dp fen alat nah) ais sce ASerai nas wwe ORS z
“2 TEEEOAPRD LEADS a 010) NOPE het eke ote ee ne 8
“STIS SM ERE CG revel On git C1 6010) ae Be eee OOS ane ee ne a 10
Pani potiaiected by NOOt-KNOt: soa ccc-e<5 4 etc. nse cee wee case ete ee ees 21
Cross-inoculation experiments............-.-- 2 rt SPA 22
Ppa HinoM ON TOOL MOU -6 spat eat ne eat = 5 Almaicino see Delite De alaeloe Pe. Ss 23
TH) CET OFT 2 S12 Se ee Oe ee ee ee ee 25
LE OY el SP EDI Soe ME EP Res Ro Pe a 26
[LATE WiSease HEE OS ASS ct UA ee ae aR ert Sec ie, Oe Se 27
GSE N Ae SUTTER SS S25 aI aaa in Ce egal st ea 32
LDU ce Piogols Sd eS Aa Rs Sa ge NR 34

CU RRSTLRAC/TLLDL SY 11a al RAN et 3 8 Se 36
Companion with, Heterodera schachtit. 002... coo ou mo oy acs ee ees ae dy 36

Pe peti aGEn Es ROR ae nse ais eet ig Ses Sete on ce Nee Sinks ae ls ae 37
URES MC HO te ee ee oes Sn el a ee ne ae aa es a on ie aes 39
PAMatnORG AV Oni TOOU-KNOL. -2c2 toca fsck. Se omiccs soles lee ee bese ce ecee 41
Oe ee a eee ee eee re Sepa a rr een Coe ee nee 41
BOROHR REN CS se Meet See 098 aR ae yt St ets sped aa Rin cet bid 3 See. gt 42
TESPPEY D3 Pn AUG le abet Mi Soot ht a te eA ae NR ARE STOMP Sr 42
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Creenhouses seed! DeEdseelenn ene eee ee oe tue ae einen ela hr we 44
IBA yiete beaten nae oe ER eet FER ee Rae ee oh aes toe 44
ECS A SOM esa tee tee ey ey Go Joe. 2 PS eS Zi ahS cheba 45
Hormaldielyglenas seen ea ete R ie. Beets le tip eha meek Ubeam ela 46
Mase eM mecimec ne teas nto See ee hes aS oes eile A MU 48
Control of root-knot in the field on perennial crops..........--..---------- 48
Kei mit eal eran ere ace Ae ia. Hala enes Naw atuee Sook REE Re 49
Parhonybisubp hid 224s ene en. at eek ew OS kL ene. 49

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Ler CHOHM CANS eae ees Re me oe eS Bo oe eS ees Pe eee 51

I GRGMIZOTH seers ee aah Mae Don LETC Di ete Wee ae Ee 52

EP Le ocliricrapaeto esha bone cee, arse Ne th Ng or die Sa Luk Se eee 52

Control of root-knot in the field when no crop is present...............---- 53
SO Cayo (te een. 2 RRO SRT ey ae Ee 53
Carbon bisillphidss) Saucon cee ae ee eee es ee a a 53
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217

CONTENTS

Control of root-knot—Continued.
Control of root-knot in the field when no crop is present—Continued.

SDTA CHOPS! cnn 5 -ee ws bacon see ree olee = nae oa pee ae

Nonsuscepible crops: ....5.£1. . 2st. eee ee ee oo ees Bene

Recommendations for freeing a field from root-knot......................----
Breeding strains resistant to root-knot....-..022 22s a.e+e sues os Jose neeweenees

Summary

bib lipeTaA PW yc: . cee os see be esc ou nines sonar eee eee oe nee eee Oe ee

Puate I.

TELUS TRATIONS:

PLATES.

Stages in the development of Heterodera radicicola (Greef) Miill., etc.

. Fig. 1—Root-knot on sugar beet. Fig. 2—Root-knot on squash... ..-

Fig. 1—Root-knot on carrot. Fig. 2—Root-knot on clover..........-
TEXT FIGURES.

Heterodera radicicola. Half-grown female (?) individual shortly
betore the dinalimoltys sso: oo ae ae ooo eee a eee eee

. Anterior portion of same nematode shown in figure 1...-.......-...-

itarvarotHeterogeramaqicicolasas ce. = sees see coe eee ee
217

Page.
61
63
64
65
69
71
72
76
82
83

Page.
82
82
82

28
29
29

B. P. 1.—667.

ROOT-KNOT AND ITS CONTROL.

INTRODUCTION.

The disease of plants known as root-knot, beaded root-knot, root-
gall, eelworm disease, big-root, and probably under other names has
been present in the United States for many years and has caused
losses whose extent can not be calculated. Although more abundant
in the South, it is present, at least sporadically, in all but the most
Northern or Northwestern States as an out-of-doors pest and is every-
where distributed in greenhouses.

SYMPTOMS OF ROOT-KNOT.

The presence of root-knot becomes noticeable when the affected
plants become dwarfed or begin to die, but it is often present and
causing a great reduction in the crop yield without the grower’s
knowledge. Indeed, it is probable that greater actual loss occurs
from the form of the disease where, to the untrained eye, no signs are
visible than in the case where the plants are actually killed, for a
farmer soon learns by experience not to plant in infected regions those
crops liable to total destruction, while he fails to notice a reduction in
yield, especially if the disease be well established and not a recent
introduction, so long as the affected plants do not show too great
dwarfing or discoloration.

Aside from the killing or dwarfing of the plants in severe cases
or the reduction of yield in less serious infections there are no very
noticeable symptoms apparent on those parts of the plant above
ground. If rainfall has been rather scanty during the summer, the
affected plants first show the lack of sufficient water, while sometimes
the wilting is apparent when the sun is hot, even with abundant soil
moisture. Occasionally no discoloration is noticeable, but usually
plants that are badly affected show a lighter shade of green than un-
affected plants. Since, however, the disease usually occupies large
areas when it has been long established, there would be no opportunity
ordinarily to compare affected with unaffected plants in mass, so that
this difference would be readily overlooked.

On the roots, on the contrary, very marked structural changes
are apparent. Instead of being smooth and of uniform or slowly

217

=
(

8 ROOT-KNOT AND ITS CONTROL.

decreasing diameter toward the tip, they show irregular enlargements
which involve the whole root if it be small or sometimes only one side
of a large root. (Pls. If and III.) These are not superficial swell-
ings only slightly attached to the root, as in the case of the bacterial
tubercles of leguminous plants, but are integral parts of the root itself.
On small roots these swellings may vary from only slightly greater
than the thickness of the root to twice as thick, and spherical to spindle
shaped; on larger roots they are usually lateral, or in bad cases may
involve all sides, making a gall many times the normal diameter of
the root and covered with furrows and seams until the root loses all
semblance of its normal appearance. Such compound knots may
reach a diameter of 3 or, rarely, even more centimeters and a length
many times as great.

HISTORY OF ROOT-KNOT.!

Root-knot has been known for many years both in the United
States and abroad. It was apparently first mentioned in print by the
famous mycologist Rev. M. J. Berkeley,? who described and figured
roots of plants affected by this disease and recognized the animal na-
ture of the organism causing it. The galls were observed by Greef on
grass roots in 1864, but it was not until 1872 that the parasite received
a name,? Anguillula radicicola Greef, after it had been observed sev-
eral times on a number of different plants. In 1879 Cornu described
this species, observed by him on sainfoin in 1874, as A. marion. In
1882 and 1885 the well-known plant pathologist, Prof. A. B. Frank,
described it as a serious enemy of a number of cultivated plants in
Germany. In 1883 and 1884 C. Miller made a careful study of the
organism causing the disease and placed it in the genus Heterodera
under the name of Heterodera radicicola (Greef) Miller. He showed
it to be a close relative of the destructive sugar-beet nematode Hete-
rodera schachtiit Schmidt, which has caused so much injury to the beet-
sugar industry in Europe and which the writer found in 1907 in
scattered localities in the United States. Treub in 1885 described as
a parasite of sugar cane in Java what he considered to be a new
species, naming it Heterodera javanica. ‘This is considered now by
most authors to be a synonym of H. radicicola.

In the United States the root-knot early attracted the attention of
greenhouse men as a serious pest of roses, violets, and other plants.
J. N. May states ¢ that he saw the disease, which he calls ‘‘club-root,”’
on violets in 1876. We find the florists’ papers full of references to

1 The full titles of all papers mentioned in this bulletin will be found in the “ Bibliography,’ pp. 76-81.
The a, b, c following a date, if given, refer to the first, second, and third papers published if more than one
paper in that year is referred to.

2 Berkeley, 1855.

3 Greef, 1864 and 1872.

4 May, 1888.

217

— Ss ha

HISTORY OF ROOT-KNOT. 9

. this trouble in the late eighties and early nineties. The first extensive
investigation in this country was undertaken by Dr. J. C. Neal,!
of the Florida Agricultural Experiment Station, for the Division of
Entomology of the United States Department of Agriculture. Owing
to lack of access to literature he did not identify it with the pest
previously described in Europe, but gave it the name Anguillula
arenaria. Dr. N. A. Cobb,” then of New South Wales, in the absence
of specimens from America, provisionally accepted Neal’s species
as distinct from the European species, renaming the former
Tylenchus arenarius and the latter 7. radicicola. He described the
injury caused by it in New South Wales, and gave recommenda-
tions as to treatment. In 1889 Prof. G. F. Atkinson, then connected
with the Alabama Polytechnic Institute, at Auburn, Ala., described
the disease, paying special attention to the life history of the parasite,
which he correctly identified with the European species. In 1898
Stone and Smith, of the Hatch Agricultural Experiment Station,
published the most complete account yet written of the treatment
of the trouble in greenhouses, at the same time giving some excellent
illustrations of the parasite in various stages of development.

In 1892 Géldi described a nematode parasitic on the roots of coffee
in Brazil under the name Meloidogyne exigua. This proved subse-
quently to be identical with Heterodera radicicola. Finally, in 1901,
Lavergne, evidently misled by an erroneous statement as to the
dimensions of Heterodera radicicola, described this species from Chile
as Anguillula vialae.

The foregoing is by no means a complete list of the publications
on the subject but embraces the papers that bear on the question
of its synonymy and its occurrence in this country.

The synonymy of the causal parasite is, then, as follows:

Heterodera radicicola (Greef) Miiller, 1883.
Syn. Anguillula radicicola Greef, 1872.
mariont Cornu, 1879.
arenaria Neal, 1889.
vialae Lavergne, 1901.
Heterodera javanica Treub, 1885. (?)
Tylenchus arenarius Cobb, 1890.

radicicola Cobb, 1890.
Meloidogyne exigua Géldi, 1892.

The writer’s investigations of the subject were begun in 1900,
but were soon interrupted for a period of years. Not until 1905
was the work resumed in earnest and pursued with various inter-
ruptions untilits completion. The work was done partly at Washing-
ton, D. C., but mainly at Miami, Fla., at the Subtropical Laboratory
and Garden of the Bureau of Plant Industry, and at Monetta, S. C.,

1 Neal, 1889. 2 Cobb, 1890.
217

10 ROOT-KNOT AND ITS CONTROL.

the majority of the field experiments being made at the last-named
place. In addition to this, trips were made to the various parts of
the country where the disease occurs or was suspected to occur.

The caring for the experimental plats at Monetta, as well as the
making of many of the observations on these experiments, was
performed by Mr. J. M. Johnson, without whose services much of
the writer’s work would have been impossible. At Miami the
cooperation of Mr. P. J. Wester, at that time gardener of the Sub-
tropical Laboratory and Garden, was also of considerable assistance,
although the experiments there were not on so large a scale as at
Monetta.

PLANTS AFFECTED BY ROOT-KNOT.

The nematode causing root-knot seems to be one of the most
omnivorous known. Neal, in 1889, reported about 65 species of
plants as more or less subject to attacks by this pest. Reports by
other investigators in different parts of the world and extensive
experiments and observations by the writer have increased this
number to 480 species and subspecies. Of this total number the
writer has personally observed it on 291. The most complete list
hitherto is that of Dr. Kati Marcinowski,’ who lists 235 species
(after subtracting hosts reported under two names). Almost all of
the more important families of flowering plants are present in the
list, as well as one gymnosperm and a fern. The plants include
monocotyledons and dicotyledons, herbs and woody plants, annuals
and perennials. Most of the garden plants are affected, as are many
field crops.

The list of plants shown in Table I is sure to be largely added to as
investigations of this disease are carried on, and is not to be looked
on as being in any way final. It is true that the writer has made
many hundred examinations of plants in badly infested soil that did
not take the disease, but such a list is of far less value than that of
plants known to be susceptible. In the list are given (1) the scientific
name of the plant;’ (2) in parenthesis, the name under which it was
reported, if different from the name now used; (3) the common English
name, if any; (4) the name of the person first reporting it on that host;
(5) the date of observation; and (6) the degree of injury. Where the
disease is reported on the host for apparently the first time, the name
of the first observer is omitted, the observation having been made
by the writer. In all cases where the writer has seen the plant

1 Marcinowski, Kati, 1909.

2 The nomenclature followed is that used by the systematic botanists of the Bureau of Plant Industry.
The list was submitted to the Office of Taxonomic Investigations of that Bureau, where it was revised by
Mr. Homer C. Skeels. In a number of cases it would have been impossible, without seeing specimens, to

determine to which of several segregates of a species the plant listed might belong, and in that case the
original species name was retained, if still valid.

217

PLANTS AFFECTED BY ROOT-KNOT. 11

affected, whether previously reported or not, the name in the first
column is preceded by an asterisk (*). In the last column the letters
indicate the degree of injury only on those plants observed by the
writer, the severest injury observed being reported, even though less
severe cases have been observed—a=severe injury; b=nematodes
abundant, but injury apparently not great; c=nematodes not abun-
dant and no injury observed. It must be understood that under
different circumstances many plants marked ‘‘a’’ would show little
injury, while plants observed as uninjured and noted as ‘‘c” might
easily be severely harmed under different conditions. Too much
dependence can not, therefore, be laid on this column. In a number
of cases the writer has grown in very badly infested fields plants
reported by others as susceptible to root-knot, without the slightest
signs of infection. Such cases are indicated in the list by a dagger ({).
Some of these cases may be of species that are susceptible only under
special conditions, while others may be due to erroneous observation
on the part of the first observer or perhaps to the confusion of the
bacterial root tubercle with the nematode gall. The former surmise
may explain why the writer during a three years’ residence in a part
of Florida where the disease is very abundant failed to find it in any
species of Citrus. Dr. H. J. Webber and Prof. P. H. Rolfs, who have
studied plant diseases in Florida for many years, confirm this. Yet
Dr. J. C. Neal? reports it as occurring on lemon, orange, and bitter-
sweet orange, while a similar report is made by Lavergne from Chile?
In the list those names added on the authority of Marcinowski *
are indicated by a double dagger ({) before the name of the plant.

TaBLE I.—Lust of plants susceptible to root-knot.

[An asterisk (*) is used to show those plants which the writer has found affected with root-knot, and a
dagger (t) those which he has grown in infested fields without infection, while a double dagger ({) shows
the names of susceptible plants added on the authority of Marcinowski. In the last column a=severe
injury; b, nematodes abundant, but injury apparently not great; c, nematodes not abundant and no
injury observed.]

Date of | Charac-

Name of plant. Name of observer. observa- | ter of
tion. injury.
* Abelmoschus esculentus (L) Moench. Okra....| Neal.........-.-..-- 1889 a
ROMO LONE LG PRE ak iets a iene a eo Ses Phd Se = RES Re cis ere St ar ee NSE b
SAbrus precatorus bi: Paternoster beatle.- 22 Jc)t 22. fe Goose oes Oe c
*Abutilon avicennae Gaertn. Chinese hemp....|...............2.--c{0e------ b
£21 TESTIS 3 a NAA AE Atkinsoms. 222. TSS ee S .
erremria women Links 2 ca pea teen brs corns aftee we do ee eee Be eee oak b
epee, several species from Australia. Wat- | C. P. Lounsbury‘..} 1908 |......
tle.
PMA TE WES BIS 3 os: 3. «2 «ae anon seks sew Neale a5. aecceenae UBSQMs er
Aigeranum comjzotdes Vj.:...2.2....cccerccens Breda de Haan..... SOO) eae.
VEG AEUTETITN GOS aR EE Zimmermann ...... TL90O=T ete.
Agropyron repens (L) Beauv. ( Triticum repens).| Greef...........--- LST OVE.
Quack-grass.
1 Neal, 1889. 2 Lavergne, 1901. 3 Marcinowski, 1909. 4Tn letter.

217

12 ROOT-KNOT AND ITS CONTROL.

TaBLeE [.—List of plants susceptible to root-knot—Continued.

*Allium ascalonicum L. Shallot.............- ope teaca a) bs. cesee se Cpl she eee b

Se nL COPE Lae (OMIM 35 es Bee as a ee, Fae Ree See a ene Boe. Soe b

*Allium fistulosum L. Welsh onion......-.---- [claro ene ener rae ic eee er b

7 Alan Porrimels:*vseSkre sis So st SER | ee ee ee c

“A linaen. roeed (1s) Caw: ss HMoliyhock .2: 1/2 .cc.cla ss 3h) See ee a

SA MURTAIIULS OLTOPUT PUTEUS HOKU. «occ s cece celac sez ee ofc ee ee nee eee c

*Amaranthus caudatus L. Love-lies-bleeding..|.........-....-.---+-|---+----- e

“AMGrantus graecizans ly (AL Qi0US rece DUM oe in oso 6 ee |e b

bleweed.

*Amaranthus hybridus L. Slender pigweed....|....-....-.----2-.--.|-.------ €

*Amaranthus hybridus forma hypochondriacus |..-....-----------+-|--+----- c

(L.) Rob. Prince’s feather.

*Amarontiow palmer ay WaIaen siadis Ser Pao Gk LOE Se eS ee c
Amaranthussretrofienus Na. = sc 4s oe oe Adkindos2 os. 4 1889. y4le: oa

*Amaranthus spinosus L. Spiny amaranth....| Neal. .......-...-- 1889 c

*Amaéranthusiricotor Ei.3. os), Lip Ck NG OIRO. PRE. SE eee a

“AMI COPMCHMD Wis 445) co AS Ree Peo hee ee ee c
Amygdalus communis L. (Prunus communis). | Neal. ...---.------ TS80— = |seeeee

Almond.

ATU CEALUA: Neraicd 17,°° (Peace 2b, ..c-2,. store Sateen donses wate 1889 a

Anis Sin0iUs SCHULG, 1. 3: Pineapples: .ctc a scladce «ees oo cee 3 eee b
Andropogon schoenanthus L............-.---- Breda de Haan....| 1899 |..----
AREMONE ODENNING ti. < Gis esc pase nd. ae ee ade Tiitiert. 22s) p 2. 1905=A "ep, Jae

PANE Gravearentesy las Toit. £2.55 cere airs Sater sek oases cae oe he eee c
Angelica archanpelea Lt jiscae ta. 22.022) Eseopolt ign... 1800 Ve eee
An gelicarsulvestrts Nica): Pen kesele cae ad oo pee clemeat dares ane ee MoV WAM lames cc

ARUCLOMIA GOranet Loo keke aes. is Seen ees ae indie, Jac cle OS aeaane a

*Aaithpavis woul Lis». Mrwreed ey. Gack 2s) ea De EE eee eRe ee b

*Antrrkinum magus U. Suandrasdm.? 22) .ssile. Jk ota. aetee eee ae a

*Apium graveolens L. Celery...............- Janse, ce ae eee 1892 a

{Atachis hypogaea... Peanut >on Neal: eee ee 1889: |o ose
Archum sp. Burdoek2222) 2. Seas ea Selby: 7s eee: 1896: 1623822

Argunevd nervosa: (purm:) ojer So.e2 2. bee | ek a ns es b
PATISIDUOCI De CLOTAUOS Nae on Sa. a ale paerenativs wees Bret oct een ae 1896 72/2 cee ae

*“Arrhenatherum, | elatwus Gu.) Beavis Tall is .ci so. se ote ee soles tee G

meadow oat-grass.

LArtemisia absinthium L............-- eae Ee Cobbs as eee TOO seer
ATLENUISTD COUNOI MICUK to loin he een Neale ets tsar me TSSO "22 ee
Asclepiasiaph | Milkweed). 2225.22.60... 2.225. Prank: 2ee fies 1896. iseeizes

SARparep ie Ojainale le SASPatAe Us. 26): oie. | ene Se ee b
sla apts) CR aes pe ag Re me ng Anan B lead Us Stumsines- ose ones 1893° "| asee

SAStranid COrmiouca WUlie = = one ooh ee ae Dalla Torre......... 1892 0s aeeee

LAstrantme major li. a. jo. slanted. by: eee ee Os. es ave 1892): )|/i-Ae

ele semibacctata-R.. Br. Australian salt- |....../.c.asecel: os SON c

ush.

SAnena pind le. SOAs os: a oak Basilsted . 234.25) Somes 1891 c

*Basella twbra L.. Weart-leaved Babel .......0:00.).. 0.c22--s+200sse0eioeeewee a
Begonia coccinea Hooker. (B.rubra).......... Selby. .........2eeeee 1806 sjouek?.
Begomaaetal tien lr Sint. £60). nha et - lestee dowvik see: 1896 clout...
Begonia olbia Kuntze. (B. olvia)............)..... do... eee 1896 Woke.
PBCHORAGIAL.E Wie scp carci 2 AER s bn cncoeoc Molliandieaesewes. 33 1900 "(sc38.

Bethe permits 1s. Waidy sels leat oi... <1... |20. 2 = eee eee ee ae b

*Benincoseeryera Pave. Waxigattd . ....:........|.. Seaenes es teee a cok ee eee a
Berberis-wulgoris LL. . Barberry sci). .4412. 939i) Wem pee! 828 1885) qr. -

"Rela Wil guria’ Win EOP t sna aes ccc <b. 2 oe 3 2c ee 6 eat any 1885 a
Bihai pulverulenta (Lindl.) Kuntze. (Helico- | Ross..............- at? Bild Fee

nia pulverulenta).
217

PLANTS AFFECTED BY ROOT-KNOT. bs

TasLE I.—List of plants susceptible to root-knot—Continued.

Date of | Charac-
Name of plant. Name of observer. observa- | ter of
tion. injury.

Boerhaave accumoens Vabl-2:222 0... : 22222222). - 2-2 - eee sess et efedeeee ss c
Boerhaavi erecla by... 225-2222: -2- 2-55: PIRES Pea M soos. 34 Sele wae ate’ c
Bosea amherstiana (Moq.) Hook. f. (Rodetid).| Trotter. . ..22....2- 1905=2: |o02 52
* Boussingaultia basselloides H. B. K. Madeira | Neal... ......-.--- 1889 b
vine.
ME UATHIMIED = (2'= <.-0 asin Sse e-- -s cioee ee Mosseri. fash. 2: BOOS): Leas.
*Brassica campestris L. Rutabaga.....-------- PA EK BOM: 22 2\..2:2/3: a 1889 c
*Brassica juncea (L.) Cass. Chinese mustard..-|..-.-.-..--.--------|-------- c
phrasscamepus Ly. Rape... ii:22..-22:-222:|-<-++-2sss5 ES USES oa SUN aa a
ermsnenguera 1. Mustard .:J52....- <<: ::: =< :|2--- 22-2205 2 bee. s|bs 22 222 c
* Brassica oleracea boirytis L. Cauliflower, broc- |...-----------------|-------- b
coli.
* Brassica oleracea capitata L. Cabbage....-.--- NGHEMis 298. Co0Ss 2 1889 b
* Brassica oleracea viridis 11. Kale, collard .....|.---- 70 CPP ea ae 1889 b
*Brassica pekinensis (Lour.) Skeels. Chinese |...--.-.------------]+------- b
cabbage. |
Sbrasmcanapa W, Turnip....0.>--'.-.<=2:-+-< Atkinson.J2222:7 - 4: 1889 c
PRAIA BO n- con Cases SSNS. eect ieee? Néabavet is... Sa BESO ones.
Bursa bursa-pastoris (L.) Britt. (Capsella |..... Seta! STA HSCS SR.
bursa-pastoris). Shepherd’s purse.
Cajon modicum Spreng Pigeon pea......--:2-|..-<-2--+22225-05+2-|Piseses- ae
Cananga odorata (Lam.) Hook. and Thom. | Breda de Haan...-| 1899 |...-.-.-
Ylang-ylang.
*Canavals ensiforme (L:) DC. Jack bean.....:.|.... 2.25. ..-222 iss 2.[b2. 2222] *b
*Capriola dactylon (l.) Kuntze. Bermuda | Mosseri....-..-.---- 1903 c
Tass.
Opsioum annuum L. (including C. cordiforme)., Neal... ......----- 1889 a
Red pepper. |
*Cardiospermum halicacabum LL. Balloon vine.|............--...-.--|..---++- fore
*Carica papaya L. Papaya or melon pawpaw..|_.....-....--225--+:|2.---5+- a
P@anase Dispinosa (Iu:) Desf... 22 2..-:--....-.- |eeae tn aS cua» Wa ce eS c

Mar pimus betulus 1. -Beech...:..-222..5. <2. <- Trovter-2i5) 2.38 LOND oan
Peer imusntncorius L,. Satllower: so... . 2-122 22 oe PS Lote Se c
mearum cary li. Caraway: ..:2::-------~---- Frankee9-32iaiss. 2 2 1885 c

ANID MUINOSOIMES Lio rw ehu eee ties tie oe. soe G. AWG hmm! 5k W908) ib ee...
{Cassia tora L. (C. obtusifolia). Wild senna, | Atkinson .......... USES ase

coffee bean.

Castanea sativa Miller (C. vesca). Chestnut-..| Trotter.............. 1905-2 |......
*Catalpa speciosa Warder. -Catalpa........----|...----2-:--- “ane ePaper Rese a
pGcesomen palinata: Wilds s+. ..0x 0022 2—- 502.22. [ets ee Sk See c
Rocwminearcvanwus L. ‘CormilOwe? 4. .2.0.52055|e22 sb Ya). oe bopese dt Wastes a

Centratherum reticulatum (DC.) Benth ...-..--- Gu A iG@amaie }ss2.h W908. joes.
*Ceratoma siliqua Li. Carob or St.-John’s- |.....205 8. ....222sc) 3.52203 c

bread.
*Chaetochloa italica (Lu.) Scrib. German millet.|................----]..------ c
*Chenopoavum album L. Lamb's quarters... .|...22s2352i22--2022-feeiess.s] €
*Chenopodium anthelminthicum L. Wormwood.) Atkinson.........-- 1889 c
*Chenopodium boscianum Moq....-..--- RasaradoWestsawetorecehes cua oeeeed ve c

Chenopodium botrys L. Jerusalem oak.....-. Néal weiestonccenaes SSO fers. -
*Chenopodiumsp. (Notany of the preceding). .|.................2--[eeceeeee c

aisy. ard.
*Chrysanthemum sap. Chrysanthemum.........)..22... 2025252. scesfbece sees b
Urrouamemmwum 1: Chick-pea.....:ctsssco.schindav ct Os a. 0 SUEUR Bak Soke b
*Cichorium endivia L. Endive....-.-.-.-.--.. Kamerling.........- 1903 a
Cichorium intybus L. Chicory...........----- Ligopeli. 62.) datas BOTT Mie.
Cinchonasp. Peruvian bark............-...-- Datberiiiis.s-.....- FOOD San!

1 Tn letter.
2G

14 ROOT-KNOT AND ITS CONTROL.

Tas.eE I.—List of plants susceptible to root-knot—Continued.

Date of | Charac-

Name of plant. Name of observer. observa- | ter of
tion. injury.

Coreaca ptermedia Mmbrh. .. ..2 5-2 -= =i == see Tischiler...2..2-se-6e. 1902 oj seeeees

Circaea lutetiana L. Enchanter’s nightshade.|..... G02. 5:30 1902; | oaeee
*Citrullus vulgaris Schrad. Watermelon.......| Neal.....-.-..-.---- 1889 a

Citrus aurantium L, (C. vulgaris). Bitter |..... do. 102 eA 1889... |sseniae

orange.

Citrus aurantium sinensis L. (C. aurantium). |..... dOn soe ee as 18895 sloaseee

Sweet orange.

Cirus inmonum aAvisso.. Lemon. 5. -- lise 2.)s ex dO: . a6 bane ASS +s laiawmiee
pOlematis flomaa Thin: scscc2 coos tes sss = = Chifflot 2 2a23%- oe 1900 w|anentas
TG ei EMO Sir 1.7 Ba 8 Fe) a ey AS AN (Re do... Saseneecee 1900 -lemsetee
{Clematis lanuginosa Lindl. and Paxt..........|...-- dO: cs) gateenae 1900 5 ste sayarctere
= (Clemans. paniculata VOUnba3 12 25 ae oie oe]: oe ads os 22 ae ee a
{Clematis patens Morr. and Decais.........-...- Chifflot =. 2 45a eee<2 1900 = |\eouee

Clemariswialba Na. : aos caceenee anne ees eee Gormus 2223. seeuces 1879-2 |....e0
EClematis witiceia Ty's. Sass wos ss oe eee EEE Chifllot ase}. 382 | M900 oo. tveictanece

CLEMGHISISD ware Beet een ee Sehr eee eee Moller isc seen ce oouae 1884, looaeee
*Cojea arabica I. Coffee: 22. -.122-2-2-2---- = =|) VOWETL. = aera a 1878 a

Coffea liberica Hiern. Liberian coffee........ Bouquet de la GEye: 1899) |: ase

Coffea robusta Hort. Robusta coffee........-.- Cramer. 222-2 2 dle A906. |eaeeee

Coleus blumei Benth. (C.verschaffelti). Coleus.| Frank..........-.-... 188) aula

Coleus scutellarioides (L.) Benth. Coleus..... Breda de Haan....- 1905. “|ya cree

Coleus sp. (Coleus var.sp.). Coleus......-.-- Neale. fjeceeao oe LSS 9e)| eee 4
= Conchorus OMOniUs Ay, . IUt6s sid ncnncee sae ct ee]. sels eee eee ee b
*Conandrum sativum V.. ‘Coriander... 5 U..5 22-4 see. ERE ees eee c 4
+ Coronopus procumbens Gills ccc. fos - obser loa -eieeee 65> 6. ee eee c |

Conjlus avellana ta. Palbpert:. <262.<60. 25-2222 | Oasaline 5 aes oe meer 1898 plosemion }
*Cosmos bipinnatus Cav. COSMOS. 2: £2242 54\-e ed eee ee ee eee eee eee :

Crepis _leontodontoides Allioni. Hawk’s- | Trotter............ 1905-1 |......

beard.
RCTEDISpUlChnG Wao). Aree to. ction eae eee Dae and ;Hou-'| 1901) |a.qsee
ard.
*Crotalaria juncea L. Sunn hemp.....-.-------|-----------2-00-----=:|s2==-=== c
* Croton glandulosus stmpsoni, Were...) 2.52). eo See ae. - oc) 2 ae eee c
*Cucumis melo lu.. Muskmelones=2%< 3.2.1.2 22 Neal .2- see see ee 1889 a
*Cucumis sativus L. Cucumber. ..5..---2...--2 Berkeley -..2 2-258 1855 a
*Cucurbita maxima uch. (Squash*.... #2. 2... 095. (ene eee ee a eee a
* Cucurbita moschata Duch. (Squash... -:.222-:2-|--- 2-5. -22-=2 eee | eee a
*Cucurbtta pepo L. Pumpkin, squash....-....|..--..-.------------|-----+-- a

Cuminum cyminum L. Cumin.........------ Frank. - = asfvec 2%) 4 A885 pee
*OCyamopsis tetragonoloba (..) Taub,” Guar s)|..6 522 4 eee eee b
{Cyclamen europaeum L. Cyclamen......------ Peglion® sc). -. 9252 1902, jcineee

Cyclamen persicum Mill. Cyclamen......-.--. Osterwalder....--.-- L901 sees
*Cydonia oblonga Mill. Quimce.-. ..5.22-2255e4\5. -5= - ee eet a? facie ee b
* Cyperus escilentusola, 2ORUIA. <6. 252 oc csecis Solem eer em gan ate sees se (cote ee c
* Dactylis glomerata 1a. Orchard prasa..: </2/2Genje2e6). - .ds2a6 (- ee ee ee Cc

Dahlia pinnata Cav. (D.variabilis). Dahlia...| Neal.....-...--..--- 13890) |saiteer

Datista cannaving Nis... .agseeeeeee = stereo Trottersaaet estes 1902, jae = s
* Daucus canowa t1.. Carrot ncc5- cscs bes sme ee Licopoli:s.cc22.ceee| plo a

DEST OAS! oxime bina aoe Os sine ee oe Barbers... 226-8 ESOL.) s0,26%i0
*Deuizia crenaia:‘S. and Z. Deutzia... 2 s.5)ecees-< 4) S = Vase Se eee a
“Dianthus barbatus L. “Sweet William. 222. {.2|2.2 «<< <-> Soest eee ae c
*Dianthus caryophyllus L. Carnation......... ee i nl is ‘cues
*Dianthus chinensis heddewigi Regel. Pink....|.......------------slecsenee b
*Dianthus plumarive GL. .Pink:..:-.-...-...-2=|-25 sseeePeeeee. ---= tee eee b
{Drei entrthinispe =, cons see oe ete =o cele = <a s Schlechtendal...... 1886) see
+ Dioscorea allustrata Hort. “Yams. :...... «| (Qeyaeeee. ~.5- tie Ubi) Nee aac
*Diospyros kaki L. i. Japanese persimmon . o salbeesss Seeu kien ee dl ee a
*Diospyros virvimiana L, “Persimmon......2. cele es.c.s 48 a06 ss soe eee leeeee sae c

217

PLANTS AFFECTED BY ROOT-KNOT.

Tasie I.—List of plants susceptible to root-knot—Continued.

Name of plant.

Dipsacus fullonum LL. Teasel......-..-..----
elensacus sylvestris Huds....-..-.-----=------
DT UREONOLUCTLGLUS i santste te 3 ars) Sela ele 3 = 222 Se
*Dolicholus intermedius (T. and G.) Vail....-...
BEROSOLILOTUS. Lio. sca e nc sce a ote aes ones
*Dolichos lablab L. Hyacinth bean or Bona-
vist bean.
*Dolichos umbellatus Thunb..........----------
Dracaena rosea Hort. Dragon tree........--.--
*Hclipta alba (L.) Hask.......-
mbicockaris palustris (L.) R. Br...-/...-..-----
*Fleusine coracana (L.) Gaertn. Ragi millet... -
*Bleusine indica (L.) Gaertn. Wire-grass. ..-..
*Elichrysum bracteatum (Vent.) Andr. Im-
mortelle.
Elymus arenarius L. Downy lyme-grass
*Emilia sagittata (Vahl.) DC. Scarlet tassel

flower.
*Hruca sativa Mill. Roquette............-...--
*Erythrina americana Mill. Coral tree.......--
PMUNTUNUE CHISTAGQUUY Vi oo cera ois oo = = ==
*Fschscholtzia californica Cham. California
poppy: ee
Eupatorium capillifolium. (Lam.) Small.
(E. foeniculaceum).
Euphorbia cyparissias L. Cypress spurge. .- - -
Peephorurd wilens Wag... 2. 2..-2----s------
Euphorbia peplis L. Leafy spurge..-..--.--..-
EP pnoTora Diwliperd, We... = mae «242 =< --
* Fagopyrum vulgare Hill. Buckwheat.......--
* Festuca elatior L. Meadow fescue......-.-.-.---
* Festuca ovina L. Sheep fescue. ..-.- eee te eae
*Ficus aurea Nutt. Strangling fig. Wild
rubber plant.
SOP UGICAT VCH tac: VENI ae = oc 2 oi ye Bates ce niajeia an
* Ficus elastica Roxb. Rubber plant..........
SEomeapl (irom Natal) ceca. 2 <252- 5.2 ee os
seruernp.- (arom Mexic0) 22. 2h... 2+ .<.5- <<:
Filicinae, genus and species not stated. Fern.
* Foeniculum vulgare Hill. Sweet fennel.....-.
*Fragaria chiloensis (L.) Duches. American
strawberry.
Fragaria vesca L. European strawberry. . ..--
eH Cone He SEU CHSIA. toe os 52.2 > «o'er s
Galinsoga parviflora Cav.....-.---.----------
*Gardenia jasminoides Ellis (G. florida). Cape

jasmine.
‘Gudowessp. ‘Gladioluss...c.. 2-4. 2----- s--'
*Glycine hispida (Moench) Maxim. (Soja bean.)
Soy bean.
*Gossypium barbadense L. Sea Island cotton. .
*Gossypium hirsutum L. Upland cotton.....-.
pGreuouspia guauce Hort........-.sess.<0-----
*Hardenbergia monophylla (Vent.) Benth.
Australian sarsaparilla.
*Hedysarum coronarium L. Sulla.......-...--
Helianthus annuus L. Sunflower. .....-.-----
* Helianthus debilis Nutt. Sunflower.........-.-
* Helianthus tuberosus L.

Name of observer.

Date of
observa-
tion.

Charac-
_ter of
injury.

Hieronymus.......-
Greele sec. eer.

Mr oGbers 425 12 -
Ui Koy! (2) 3 ht Nee

(teyanainiss Sob abeo se

isaneelerany Grok noe |b wae eee Ie be ee

1 According to Ritzema Bos (1900-1) this injury is due to another nematode, Tylenchus hordei.

2 Species distinct from the preceding.

91294°—Bul. 217—11 2

ROOT-KNOT AND ITS CONTROL.

TaBLe I,—List of plants susceptible to root-knot—Continued.

Name of plant.

Name of observer.

Heliotropium sp. Heliotrope............-.- :
pale pan ly i ahi} SO cea a6 aeior = Be Seon 35 = - |
Hibiscus coceineus Walt. Rose mallow
* Mibiscus rosa-sinensis L. Hibiscus
*Mibiscus sabdariffa L. Roselle

* Hibiscus syriacus L. Rose of Sharon
*Hicoria pecan (Marsh) Britt. Pecan
Hordeum sativum. Barley
Hypericum perforatum L. St.-John’s-wort
Hyssopus sp. Hyssop.. ves Bh
Iberis umbellata L. Candytuit.. Bee eel Sites Mace ta
*Ilysanthes dubia (L.) Barnh..
Impatiens balsamina L. (Balsamina hortensis).
Balsam.
Impatiens kleinit Wight and Am...........--
*Tpomoea batatas (L.) Poir. Sweet potato
Ipomoea bona-nox L. Moonflower..........--
*Ipomoea cathartica Poir. Wild morning-glory.
*Ipomoea fuchsioides Griseb. Fuchsia-flowered
morning-glory.
Ipomoea lacunosa L.. ¢
*Ipomoea purpurea L. Roth. | “Morning- -glory..
*Tpomoea quamoclit L. Cypress vine.........-
POMBE ScvOSh Ker) S7hc Leen eae sees
eenee syringaefolia Meissn. Tree morning-
giory
*Ipomoea sp.?_ Indian potato.........-...-.-.-
*Tresine paniculata (L.) Kuntze
MTiaipe ARIS See peat oe Seta ee ty Sees Oe
Ov CiQUred TAO 2 so nae eee ee See
Ixvora chinensis Lam.

ETORONCTHOCEO ERG US ee Oe ee eon ene :

LGOr a TOsery ELON Seiya ae ae eh Le

PORES Oe a oe SEO ee
Jacquemontia tamnifolia (L.) Griseb. " (Ipo-
moea tamnifolia.)

Juglans cinerea L. _ Butternut......-.-.-....-
* Juglans regia L. Persian (English) walnut. .
* Juglans rupestris Engelm. Arizona walnut. .
{Jiineus-gerardvlioisel. 3.45 2225-2 os. oo ee

Kadsura sp. _ (Cadsura) ..
*Konig maritima (L.) R. Br.
* Kraunhia sinensis (Sims) Greene.
*Zactuca sativa L. Lettuce..
*Lagenaria vulgaris Ser. Gourd .
*Lamium amplexicaule L. Dead nettle... .....

Lantana horrida H. B. K. Lantana...........
*Lathyrus cicera L. Lesser chick-pea.........-
*Lathyrus odoratus L. Sweet pea.............-
*Lathyrus sativus L. Bitter vetch
*Lathyrus tingitanus L. Tangier pea........-.-
*Dens esculenta Moench. Lentil

Leontodon hastilis L. Hawkbit.

Sweet ‘alyssum.
Wistaria. .

tLepidium sativum L. Garden peppergrass. .

i depen bicolor Turcz. Bush clover.........

Lats pea striata (Thunb.) Hook. Japan
clover

1Tn letter.
QA,

.| Stone and Smith. . .

Wee ao © a 6 ale © 6 a Sin efeie «ow

Waete Teegit

Darboux and Hou-
ard.
Cornu.

2 Species distinct from the preceding.

Date of
observa-
tion.

Peer eens

1879-1

Charaec-
ter of
injury.

PLANTS AFFECTED BY ROOT-KNOT.

TasBLE I.—List of plants susceptible to root-knot—Continued.

Date of
Name of plant. Name of observer. observa-
tion.
eamesirim ovalijolum ~Hassk, California |i2. 2522 .:.....52..22}.35e2.5-
privet.
mn enarme concdens:s (E.) Dumont Toadflax+.|).as22-52 2s: ose si sheds.
Linum angustifolium Huds........----------- Prottiers s+ 6 thse 22 1905-1
*Linum usitatissimum L. Flax .........------ | SOrawers2=s sss. 2 =. 1906
*Lippia nodiflora (L.) Michx. Frog-fruit. . - - - - Peepers Sieh Sera ee
00 AE GWE AS OS ordieicicito 6 Gus SoUSSdos ae = Seb ieee oc a aeng Gacoe see
whenicerd japonica Thunb. Japanese horméy=|.......-.....2:..--.fs.0.. 22:
suckle.

*Lotus corniculatus L. Bird’s-foot trefoil... -- AtkaneOn. . 225.522: 1889
Mes se cies re a eeiinccide oe se ee Pretters 222.2 255939... 1905-2
pereacna ginuce (Is.) Bente 22-2225: == == 22>) 2 222 2222 asset fee oe =
eiucumarvvicoa angustifolia Miq. "Ty-ess:...-.|......... 220) 22.e5e [eee eee ee
peagacyenares (Is.) Roem. Sponge gourd:').|:-.22-..-:-..2:.225:}...22 22.
perpieraibus I. White lupime.-2:-5- 2:52: .|- 162522823... 2 222 eee sie 2:
ene emrmamguAlipolius lr. 22-2. == 2222222 |sene 2 2 cia seas ele ce oe
*Tupinus luteus L. Yellow lupine.. Dsl ee a 58 Rts SEE SS,
imaparee tOriivee Lb OFSIEs 5 sack nor soeesi ss sek ees ee toe ees Pee Tepe ee 2:

*Lycopersicon esculentum Mill. 'Tomato......-.. Neat ers. 2. 2528 1889
Malus sylvestris Mill. (Pyrus malus). Apple..| Selby......------- 1896
* Malva rotundifolia borealis (Wallm.) Masters. |........-..--.------|----.-:-

Wild mallow.
“Manihot utilissima Pohl. Cassava...........-| Neal-..........--. 1889
* Marrubium vulgare L. Horehound......------ Atkinson. .:-2:,-- 1889
* Medicago sativa L. Alfalfa, or lucern......-. Bramst 210954 2032 1882
+ Meibomia mollis (Vahl) Kuntze. Florida bes? | Rolist 52-222. <.- 1898
garweed.
DOM RtICLa (EUISH) KUntZe S225 2). Les 2S 2 s2 ee eee ee
eeneuccasrach\.- Wmbrella tree... 2220520: o 0 aoe i I
* Melilotus alba Desr. White sweet clover, or | Atkinson......... 1889
Bokhara clover.
eRe CARTS UREA LH ly a) Aden = he egy ne eke le ee ts Ptcss Me SYED ee
SMPlOn ML CrOSST OLE SMA le une. ae seers cL [oss e+ 22 see ccs 2. oe a[om seme
Mesembryanthemum sp. Fig marigold......... Nea? Soe 1889
Modiola caroliniana (L.) Don. ( M. multifida)..| Atkinson....-...- 1889
Mollugo pentaphylla L. (M. stricta)......--- G. A. Gammie!....} 1908
* Mollugo verticillata L. Carpet weed. .::...2.)o2s22.ese222552-2--ehaeecee:
“Momordica charantia Li: -Balsamiapple:.<2.- 2.4: s:2225. 22-2 223-2 les ee eee
* Morus aloa muliveaulis (Perr.) Loud. Mul- |...-.2::5:.2-.-2-.-2s|252-223:
berry.
= Morumaloa tatarica (Is.) Loud. Mulberty:..-:|-22:---4-22--.25 220-222 252:
See nmanmitar a im MID ErhY: os 158 26s. o teat ol tuo ae ees teen sowie esse
* Morus rubra L. Mulberry... bneiline yee ee eh oe ESE
Mulgedium macrophyllum (Willd. aN DOr ec baller Meet A: - 1884
Musa cavendishat Lamb. (Musa chinensis). Ossineae 2. SaaS 1883
Dwarf banana.
"Musa e..scte Gmael.” Bruce’s batiana. .....==.=|s2s-c- sos. 22senesessseeeeet
Musa paradisiaca dacca (Horan) Baker (M. | Ross............- 1883
dacca). Dacca banana.
Musa paradisiaca sapientum (L.) Kuntze. | Delacroix........ 1904
Banana.
MMUSaTOSHOM JACQ sessesseessee secede eee eke Miller. ..2:..22:: 1884
= Musacenuie wee. Manila hemp. sc25.222i52¢.|-25c2 2250550505 eeRceeaser
<Nicohanasanderae- Hort. = 2.0..200 208525 tethers ete os Pe P22 PS. Lee Pee spose ee
* Nicotiana tabacum L. Tobacco... seac cet) Wemse =o. 2. dss 1892-2
INOLONGISPeamcrameees fae oo eece ses tee nan NOMS. ail 2 sah: 1889-1
*Ocimum basilicum L. Basil........-.....-..-| Breda de Haan... 1899
Giionlandia spoasseess tees 625. 3. EA G. A. Gammie?!....} 1908
Onobrychis viciaefolia Scop. Sainfoin.....-..- Cornus... saccete 1879-2

1Jn letter.
217

Charae-
ter of
injucy.

ROOT-KNOT AND ITS CONTROL.

TABLE |.—List of plants susceptible to root-knot—Continued.

Name of plant.

*Ornithopus sativus Brot.
*Ozxalis corniculata L.
Oral Strichitlns tee soccss erate Seis = eee
PEE ORI SP MRE BOM e ats ores msec Sasser
* Paliurus spina-Christi Mill. Christ’s-thorn....
*Panax quinquefolium L. Ginseng......-.-----
Papaver rhoeas L. Poppy :
Papyrius Bea ra(L.) Kuntze (Broussonettia
papyrifera). Paper ee
* Passiflora incarnata L. Passion flower.......-
* Passiflora pfordit (=X P. alato-caerulea Lindl. )
Passiflora sp
SPasinoce sate Lic Parsnip’. sos 222 ese Seas
* Pelargonium zonale (L.) Ait. Geranium......
* Pentagonia physalodes (L.) Hiern.............
* Peritla frutescens (i.) Britt. Perilla. 9.2% ..-
{Persea gratissima Gaertn. f.
*Petroselinum satiwwum Hoffm. Parsley........

*Petumalyornda Vilm. -Petunian. a ses 22

eels aconitifolius Jacq. Aconite-leaved
ean.
* Phaseolus angularis (Willd.) Wight.
bean.
* Phaseolus calcaratus Roxb. Seeta bean.......
* Phaseolus lunatus L. Lima bean.. ee
*Phaseolus max L. Green gram, or mung bean .
*Phaseolus radiatus L. Green gram ...........
* Phaseolus retusus Moench. Metcalfe bean...
*Phaseolus vulgaris L. (incl. P. nanus). Bean.
Physalis peruviana L. Cape Boe pety, aes 4
Physalis sp...

Adsuki

Poles americana L. (2. ‘decandra). ‘Poke-
wee
*Pilea serpyllifolia (Poir) Wedd. Artillery

plant.
Piper betle L. Betel pepper..
Piper nigrum L. Pepper BD)
* Piriqueta tomentosa (Willd, s HieBe KA ad
> Pisin arvense la. SHield pease 25-2 k
*Pisum sativum L. Garden pea.. 2
*Pithecolobium saman (Jacq.) Benth. Rain
tree.
Plantago lanceolata L. Rib-grass..............
Plantago major’. ePlanitaime st: ech sss. 25 48
*Plantago sp ”
Plgtanisisps ee laneyreOrnaseeessee eres eae
PEC ANIUSIED osc gone = ei see nee es ees
* Pluchea purpurascens (Swartz) DC.........-..-
*Plumbago capensis Thunb. Cape leadwort....-
Poaannua L. Annual bluegrass..............
tPoa pratensis L. Kentucky bluegrass... ...--
Podranea ricasoliana (Tanf.) Sprague
coma mackennit).
*Polianthes tuberosa L. Tuberose............--
Polygate-olepere MAOre. a3 hs eee tes aco =. <2
* Polygonum hydropiperoides Mich......-.------
Polygonum 8

| Date of

Name of observer.

observa-
tion.

C. P. Lounsbury !
Cin Sones sae ee

.| Zimmermann ......-

Delacroix. ---eeeee

iHramilesee ase Virvint a

Greet . ae ee

Seradella.:.lcc.en eee oe cee eee
Sheep sorrel . 4. [2 ee peters 4 5 oe eee

*Portulacasorandijlora Hook.) Portulaca, ..---22!2e- 2: 22----<2-- 2-2 eee

1Tn letter.
217

2 Species distinet from the preceding.

Charac-
ter of
injury.

fe > at. a

PLANTS AFFECTED BY

ROOT-KNOT.

TaBLE I.—List of plants susceptible to root-knot—Continued.

1h)

Name of plant.

Name of observer.

{
Date of
observa-
tion.

Charac-
ter of
injury.

PPortvaies overacea Lia, Purslane.. 225. 222 vas) Neal a. ine. es - 2
eRIMMLanaUuricwla ky, ETIMTOBC 52-1... 2 2-5-2255 Dallaywlomess--25-5-
{Primula carniolica Jacq. Primrose...........|...-- dow te <2 Se

Prunus armenica Li... Apricot....---...------| INGEN ee oe Ate ae ears

Prunus cerasifera Ehrh. (P. myrobalanus) ....|..--- Cloighene ee core

erinus Gomestica Iie) PLUM. -Sseccce aint. ee =|- = oe Mone eee a

Prunus japonica Thunb. (P. nana and P. |..... do tases 3. ha

lanceolata).
eerie inoomand Ln. *Chokeveherry. .-22s2')-|. + «2-28 gens act
SPrinusspe (irom Mexico). \Cherry.....<---s)2 32 =---200-25- 6-205:
SISO TUITION UG ait, CrUAV Desc ina = tape caren) eee tata eee = n|veyte Ame tear
Erunicagrancuun: Ue Pomepramate...5.-22-25-|. sees 2. 2s ace ee
nies COMMITS. lr. -PCAn... Bisete 5-555 23 pata kee: See et ts

Ouercusisuvene Conk Oak: -2a=e2+ see 22 es << Duwcometees.- 2 ee
*Radicula armoracia (L.) Robinson. Horse- |..........--....-.--

radish.
erodeiita walters (Til.) Greene. 22 ons ons, «<3 Resta -2 -oleos sates
eRapnanus sativus Iu. Radish...........---=-=- Neal-fae2s)= -t e
Bescamoaorane lus Mienonette. 2. o.25 2-2 -< mseicl2 = eee 2 =. 4-5ee
tRhinanthus cristagalli L. Rattlebox..........| Darboux and Hou-
ar
iipes Minium. Currant. i.25- 2% - 2 Cobbs ete sees aut
*Rosa chinensis manetti Dippel. Manetti rose..|.............-------
=hosa laevigata Mich. Cherokee nose... 22. /sea|2 be 222 ke eee - Ae
Siioemescrigena MICHX OTROS. 2utbet). oo cede S-laeie a teen Ee

MO sERA EE OSCS apie miontacins wclro mie oe nee heey Malsted agus tse

Rubusidaeus L. Raspberry. .+....---------- Selbyescet sak wee

Rubus subuniflorus Rydb. (R. villosus). Black- | Neal.........-------

berry.

Pppustiruiniis: MACH onss oc.) yore nee sie kel ers does yk See
Bue CTAAECIOSE) Liew, SOIC Wiz sche eetsic 2 iat Reese Sel vs ieee ALES
BIC, UOC Kiam os saan eit eat = wie cena SE es See 2 ig eee
*Saccharum officinarum L. Sugar cane.....--. Breda de Haan.....-

Salix babylonica L. ‘Weeping willow...-.----- INGEN Petes oe cote ee

ANAS ZIMSI 9 SSIES a eae nr ORs es a Rnen ola aaa Peer Geer,
{Sanicula europaea L. Wood sanicle .........- Cormmufaent Poe

SCAUTOSE COUNMDATIG Views es easier iteokicm 2 oes WOORAMETE I... 2.1 Reet.

Schizonotus sorbifolius (L.) Lindl. (Spiraea sor- | Neal......-..-.-----

bifolia).
*Scolymus hispanicus L. Spanish oyster plant.|.......-.........-..
*Scorzonera hispanica L. Black salsify...:-25.\... 020. 5...--<--21-2-

Sedum (several species)....--..- Biaras vee eats 8 Greehteta2 52 eee

Demperowumglaucum TEM)... 4.9. vehon a5 <i Wicopolre. e.--2
SIS ETL PEN UUD LIM ALEC LONIUTID: Wi pape ora ale, nn eassyn'e winel\pas Se dO. 5 25 es

IS CNECVOMMAGUT ta reece senna et bwe ni) ate rotten: wirek hws
BSesbanvispimiosa: (aca!) (Steudaxa so 325. x Jee ce oe OS2 Sa 28k
ASAT ATE (ONY f (LOR O10 11 OYUN AL PER oo al ge

Sesuvium maritumum (Walt.) B.S. P. (S. pen- , Neal........-..-.---

tandrum).
PS eel DOTLLACOSETUM, Lis 2 Bele iain otc int A Ue pee eee te
PGT HONUU GLUE Lic oo sotic atoms rhe eaiese = eval sles aetteres «ae eae
PS cKa DINO SO l2.. 020s... ose ee eee = Se At cmsonee. £542 aap
STL EAOLOUICO NV Glib 2,32 sia) nccrcin mie neue essai, PSE ators = << 1 5 ES
“Solanum canolimense Ii. . Horse mettle 255-2. o|saseacie eects oe see a

Solanum dulcamara L. Bittersweet.....-.-.--- Mosserts aS 3322. 2e
*Solanum melongena L. Eggplant.........-.-- Atkamsonssss: 028
Zolaniwnmnuignu mene Nightshade... hepa ee eats os ss yaini= «2.2 Sheol
msolanum rosiretume: Wun... Buffalo. Dur cps es Aloe 5 operas opine ae cain
*Solanum tuberosum L, Potato...........-.--- INCRE eo ce an teres

1 Species distinct from the preceding.

217

90 ROOT-KNOT AND ITS CONTROL.

TABLE I.—List of plants susceptible to root-knot—Continued.

Date of | Charac.
Name of plant. Name of observer. observa- | ter of
- tion. injury.
* SolagumMm Gp) <i. sen cheese eect PERRIS ER Pee oon b
Sonchus arvensis L. Sow thistle............--- Larnanit 0.2-. 2.2280 4808) Wosscee
Sonchustolaraceys Vi... casa= Sede nn scss ss vsao se) MOREE. 2 Oe LESS ese
*Spergula arvensis L. Spurry Meee B ets awe See ccc PUN Epte ot te ene
Spermadictyon suaveolens Roxb. (Hamiltonia | Cornu............--- 1879-1 |......
spectabilis).
*Spineciaereracea. ly... Spmachi........2..\) 2. Oia a. tee ee b
* Spr ged CANLOMENSIs LiOUT.. ISP. 2-152 Hiss | eels. sae toe oe a ee b
*Spondiasluies x, oc plam': -... <2 22.22. d/ eee. eee a
LSE PNGROLSSP eR ee. 2. 2s Sei taer eee si std Woes... (ees eee SOO: ieee
*Stizolobium pachylobium. Piper and Tracy...|.....-.-..-.--------|.-.----- b
{Stizolobium pruriens (L.) Medic.....-.--.---- -| Piper and Cobb?....| 1910 b
TStizolobium deeringianum Bort ( Mucuna utilis). | Rolis........--.--- 1868: ieee
Velvet bean.
Strelitzia nicolai Reg. and Koern. Bird-of- | Ross............... PSSS) il tose
paradise flower.
*Syncorpia-giomulijera (Sim.). Naedenz... -......|- 5 catieSe | See See e
*Tamerwndus indies W; : DMamarind: i 25 25 3.2 =32\..< 20 28 sees ee Se eee c
*Tanacetum vulgare L. Tansy. atid, lncest = oft SER ae ee b
Taraxacum officinale Weber. Dandelion... ... licopoli-: 32: s4ays82 AST hee
*Terapanaz papyrier (Hook.)\Kech. | Japanese |:.22-52.22.-825-2- leon aoe a
paper plant.
THEM BtRONME La DOR ooo. ies ceee aa eee Barheay: 065. sas NOQTA cleans
tTheobroma cacao LL. Chocolate or cacao....... Ritzema Bos.....-... 1900 lesa S.
Theophrasta crassipes Lindl... aeectns.3 bee WAU DEIS emer 75 caer ROVOS1 |e cetk
* Thunbergia fragrans Roxb.. SPEEA Sees enya seta hey a
*Tragopogon porrifolius L. Salsify.. 32 oh Atkinson 5.25 1889 a
* Trichosanthes cucumeroides (Ser. ) Maxine Saluatdtie 2 1 dea Hl oneal peteanee a
*Trjolum alerandrmum L. “Eeyptian clovers |.- 22.) <-<22-c-2-4se1h eee ee c
Berseem.
* Trifolium incarnatum L. Crimson clover.....- Erank:-5o5eeteee 1885 a
*Prvoluum pratense In.) Red clovers:s>...20222+|..-.—2 dd: ...ia4c ee 1885 a
* Trifolium repens L. White clover.. iz. ot J Shekden..-2 pape 1905 a
* Trigonella foenum-graecum L. Fenugreek Sam oO ti Sees ar b
Triticum aestwwum L. (T. sativum). Wheat...| Sorauer.......----- L006. okies =
Triumfetta rhomboidea Jacq. ........--------- G, A; Gammie 2...) BOS Neseee-
*Tropacotum majue Ll. Nasturtium... ....-~..|.22. 22-2 2-+ 2-1 eee ec
*Tropacolum minus Ls... Dwarf nastur tama. )\4615 5 yt 4 ee ee c
*Uims campestris Li Tauropeam elms.) sie oe er | ea a
* Verbascum thapsue L:. Moulleim' 27053 Sai ae aes eo Se pa ee oe ce
Verbesina occidentalis (L.) Walt. Crownbeard..| Neal........-..-.-.- itself
*Verbesina virginica L. (V. sinwata). Crown- |..... 6-33 eee 1889 c
beard.
* Veroniea peregrina l.-Speatwell.. 2.2.22 0.2.5|scneioecnce Se ees eee c
* Veronita tournejorin Guieline tit 20 e222 Sal cece eceeee nel eee e
tViburnum lantana L. Wayfaring tree......-- Bronk) Ss) 32: LOGS AAs
tViburnum tinus L. Laurestine............-. Keller. . Sapte cee AOOL Weeee es
* Vicia airopur pura: Dest... 02 eae se ee eee c
*Vicia faba L. Horse beans. chs, qaudemmee oct ese. cee b
* Vicia fulgens Battand. mre ae VOtCh ...2.552-.). - ek. od. eo ee ere c
* Vicia wirsita (1.) So MGraye S25 epee Ss SS a eee b
* Vicia monanihos (.) Dests.0: 23.4.2... -2-|.-- <1 4- eee eeeeees a
* View nanbonensis lu. Narbonne -vetch..... -: . . <\2.:..<ceeeeeeee eee een ee b
* Vicia, pseudocracen Bertol, ..3.22.<-..2-- - --</|-ie Sane See eee oars c
* Vicia sateia 1). Neteh.. . u.josveceue dss: =... - - >| oes ee aioe otek b
* Vicia vitiosa ‘Roth. Hainneeneh.-s,- :)...2.:.- |; ane et eee alosee See b
* Vigna: 2epens Wears» asa crcecnisis. abo <i eae oe ee Oa ek cee b
1 Species distinct from the preceding. 2Tn letter.

217

PLANTS NOT AFFECTED BY ROOT-KNOT. Dal

TaBLE I.—List of plants susceptible to root-knot—Continued.

Date of | Charac-
Name of plant. Name of observer. observa- | ter of
tion. | injury.

*Vigna unguiculata (L.) Walp. ( Vigna catjang, | Neal..........-..--. 1889 a

Dolichos catjang). Cowpea.

Viole edaraia L..\ |) Vidlet.os308 222202. 5.22 aleted ose 28 1891 a
Vitis aestivalis Michx. Grape .....-.-....... (NE | ae ee ene ee CC er
PR tao rere hy. GTADS asses 2 2-242 omc ee PACQDOM. == 2.22, ---) yA B87T oo...
Vitis serianaefolia (Bunge) Maxim. (Cissus | Cornu..............- 1879-2 |.22.2.

aconitifolia).

* Vitis vinifera L. Old World grape. .......... 1 |S ie ate ea a 1899 a

*Washingtonia filifera microsperma! Beccari. |.......-....----.-.-|.....--- b

California fan palm.

OSM MOPANAR GTACHIS © Parish. /o)2. 22 nce sles. ancy <ca ns Maen cloccevess b
Willughbaea scandens (L.) Kuntze. (Mikania | Neal................ TSO8 fe 2 OO,
scandens).
Ey TESTA HDEGOI TNT) Us 2 a awe (Ah a Re (NS b
~Zea mays L. Maize or Indian corn..........- Neal. ee oS TBS9F Se

1 Seed received under this name from Dr. O. Beceari.

PLANTS NOT AFFECTED BY ROOT-KNOT.

Among the plants grown by the writer in infected land without
their becoming infected with root-knot in the slightest degree were sev-
eral species of Stizolobium, the genus to which the velvet bean belongs,
viz, Stizolobium lyoni, S. pruriens, S. hirsutum, and the velvet bean and
one or more other unidentified species of this genus.1_ Many of the
grasses seem to be resistant. Thus the writer has failed to find the
nematode on crab-grass (Syntherisma sanguinalis), redtop (Agrostis
alba), Johnson grass (Andropogon halepensis), some varieties of oats
(Avena sativa)—but some are susceptible—Bromus schraderi, Eusta-
chys petraea, some varieties of barley (Hordeum vulgare), Lolium
perenne, Japanese barnyard millet (Hchinochloa frumentacea), broom-
corn millet, or proso (Panicum miliaceum), pearl millet (Pennisetum
sp.), timothy (Phleum pratense), rye (Secale cereale), the various forms
of sorghums, milos, Kafir corn, ete. (Andropogon sorghum), wheat
(Triticum aestivum), but see list of susceptible plants. The same is
true of corn (maize, Zea mays) as of wheat. Euchlaena luxurians
was also free. Several Composite seem to be free from the trouble
even where the nematodes are very abundant in the soil. Thus,
Bidens leucantha and B. bipinnata always were found free. (na-
phalium purpureum, Helenium tenuifolium, species of Solidago, Zinnia,
etc., were also free. The absence of nematodes in the plants above
enumerated is far less significant than their presence in other plants,
for conditions may have been unfavorable, and yet under other con-

1 Rolfs, however, 1898, reports root-knot on the velvet bean, and recently Prof. C. V. Piper has found it in
abundance on plants of Stizolobium pruriens, S. P. I. 21566, grown in a greenhouse in Washington, D. C.
Evidently under certain conditions some strains may be susceptible, but as a rule it is immune.

217

22. ROOT-KNOT AND ITS CONTROL.

ditions they might have shown root-knot. However, it is probable
that the above-named plants will show themselves nematode resistant
in most cases.

CROSS-INOCULATION EXPERIMENTS.

It has been suggested by several investigators that Heterodera
radicicola, like Tylenchus dipsaci, may show the development of
strains preferring certain hosts and exhibiting a reluctance to attack
others, although these different strains are morphologically indis-
tinguishable.! This explanation has been suggested for the fact
recorded by Stone and Smith? that lettuce often is not attacked in
beds in greenhouses where other crops suffer great mjury. The
writer accordingly made a number of cross-inoculation experiments
to determine, if possible, to what extent the nematodes of certain
generally grown crops were interchangeable. The experiments
were performed as follows: Pots of soil were sterilized in an autoclave
for about an hour and a half, sometimes longer, at a temperature of
125° C. While this was perhaps not long enough to kill all bacterial
spores in the center of the pots, the temperature attained showed
itself to have been high enough to kill all nematode larve or eggs.
In the sterilized soil were placed affected roots of the plant used as a
source of the nematodes. These roots were first carefully washed
(sometimes in water containing a small amount of formaldehyde) to
remove all adhering dirt in which conceivably larvee or eggs of other
strains of nematodes might be present. These pots were planted with
seeds of plants to be tested as possible hosts of the nematode, either
at the same time or a few days after the roots were put into the pots.
Except when it was certain that the water was nematode free, it was
boiled and cooled before using it to water the pots. Experiments
made in this manner showed that the root-knot nematodes were
mutually interchangeable in the following plants: Red clover (Tri-
folium pratense; Pl. III, fig. 2), white clover (7. repens), crimson
clover (T. incarnatum), cowpea (Vigna unguiculata), strawberry
(Fragaria chiloensis), tree morning-glory (Ipomoea syringaefolia),
sunflower (/Telianthus debilis), horse bean (Vicia faba), ginseng
(Panaz quinquefolium), purslane (Portulaca oleracea), fig (Ficus carica),
papaya (Carica papaya), catalpa (Catalpa speciosa), tomato (Lyco-
persicon esculentum), and Old World grape (Vitis vinifera). ‘These
all also affect the following, for which the reverse inoculation experi-
ments were not made: Lettuce (Lactuca sativa), green gram (Phase-
olus radiatus), tobacco (Nicotiana tabacum), squash (Cucurhita
moschata), cucumber (Cucumis sativus), and muskmelon (C. melo).

1 Prof. J. Ritzema Bos (1900) reports that Tylenchus dipsaci becomes so adapted toa host plant after
growing on that species only for several generations that it will not attack with any severity the species
upon which it grew before until several generations have passed.

2 Stone and Smith, 1898, p. 30.

217

DISTRIBUTION OF ROOT-KNOT. 93

The various families of plants represented in the foregoing list and
the fact that the infections were obtained easily and very pronouncedly
would seem to indicate that the nematode causing root-knot of the
plants experimented with, including some of those most generally
affected in the field, is not as yet very markedly differentiated into
strains peculiar to certain hosts. It is still possible, and indeed quite
likely, that had seeds of the same host as that furnishing the roots
from which the nematodes came been sown in the pot along with the
other seeds the latter would have shown less infection than the other
plants. Unfortunately, however, various circumstances prevented
this line of experiments from being carried out.

Observations in the field seem to bear out the results of the pot
experiments. The writer has been unable to detect any special adap-
tation to any one species of plant. Indeed, peaches were attacked
very badly when planted where cowpeas had been grown for several
years. Figs and the Old World grape are the plants through which
the parasite has been introduced into many new districts, which could
hardly have been done so thoroughly and rapidly if the nematode
had become in a manner specialized upon them.

DISTRIBUTION OF ROOT-KNOT.

Root-knot was first observed by Berkeley ' on greenhouse plants
in England [t was next reported by Greef ? on out-of-doors plants
in Germany. Since then it has been observed in many parts of
Germany, France, Italy, Austria, Holland, Sweden, and Russia.
In Africa it is abundant in parts of Algeria, occurring even in some
of the Saharan oases, Egypt, German East Africa, Transvaal, Cape
Colony, and Madagascar; in Asia it occurs widespread in India,
Ceylon, and to some extent in China and Japan. In the East Indies,
Java and Sumatra are badly infested. No authentic reports have
been received of the presence of this pest in the Philippines, but it is
probably to be found there. Several of the Australian States are
infested, and the pest is not unknown in New Zealand. In South
America it has been reported from Chile, Argentina, and Brazil. It
seems also to be widespread throughout the West Indies. In Mexico
it is prevalent at many points.

In the United States the root-knot is to be found in sandy soil now
or previously in cultivation in most parts of North Carolina, South
Carolina, Georgia, Florida, Alabama, Mississippi, Louisiana, and
Texas, as well as at many points in California. It is not abundant
in New Mexico or Arizona, although proving destructive in some of
the irrigated districts of the latter. It is very evidently of recent
introduction there, as in many parts of Texas. In the interior of the

1 Berkeley, 1855. 2 Greef, 1864.
217

24 ROOT-KNOT AND ITS CONTROL.

West the writer has observed it, only sporadically it is true, in Utah
and Colorado and at one place in Nebraska. It is reported, and the
writer has seen specimens, from Arkansas. Oklahoma, Tennessee,
and Kentucky have no reports of it in the open, but it is probably
present to some extent, since it is found along the Ohio River in
West Virginia and also in northern Pennsylvania. It occurs, but not
in great abundance, in Delaware, Maryland, and Virginia The New
England States appear to be almost free from the trouble, so far as
outdoor plants are concerned, although it has been observed in Con-
necticut and Rhode Island. The most northerly points where it has
been observed out of doors in this country are at various points in
New York State, on ginseng and alfalfa; northern Indiana; Menomi-
nee, in the Upper Peninsula of Michigan; and the locality in Nebraska
already mentioned. In the last three instances all the evidence indi-
cates that the disease was directly imported from other localities and
was not indigenous to that locality. The important point is, how-
ever, and this will be reverted to, that this nematode is able to main-
tain itself in regions where the winter’s cold may be very intense

All of the localities named above are those in which the root-knot
nematode has been found out of doors, not merely on plants par-
tially protected during the winter, but in soil not at all protected
from the severest winter cold. In addition to these localities it is
almost universally present in this country in greenhouses and has
in a number of instances become more or less established out of
doors in their immediate vicinity, where it is protected by compost
heaps, etc., from the extreme cold. In the most northern States it
need not be feared that the pest will ever become widely distributed.

A careful study of the distribution of the disease convinces the
writer that root-knot is of comparatively recent introduction in the
regions west of the Mississippi. Indeed, it is possible to trace its
arrival in parts of Texas, Arizona, and southern California, it having
appeared in recent years after the land had been in cultivation for
a long time with no signs of injury from such a pest. In Texas the
introduction and spread of the nematode has been accomplished
almost entirely by means of infected nursery stock, mainly figs,
mulberries, and peaches; in Arizona and California figs and the
Old World grape seem to be the responsible plants. The scattered
localities in the North where the trouble occurs often reveal, on care-
ful inquiry, the source of the infestation. Ginseng has been respon-
sible for several ‘outbreaks, the nematodes doubtless having been
introduced in the moist earth in which the seeds were packed. In
other cases nursery stock, such as peaches or even apples, has been
responsible; sometimes the soil thrown out from greenhouses has

217

THE CAUSAL PARASITE. 25

spread the trouble, and in some cases the manner of introduction
can not be determined.

Close analysis of all the earlier reports and of the existing distribu-
tion of root-knot has convinced the writer that we have to deal with
a pest originally tropical or subtropical in its distribution and not
native to any part of the United States. In this the writer comes
to a conclusion at variance with that of Neal, who believed that it
was native to the Southern States. If that were the case, however,
it ought to be found on uncleared land where no crops have ever
been grown, but that is not generally the case. Indeed, it is the
general practice, when nematode-free land is needed, to go to un-
cleared land. To be sure, nematodes are occasionally found in such
land, but almost always it can be shown to have been previously in
cultivation, perhaps many years ago, or to be so situated that soil
from infested fields could be washed upon it.

The general trade in exotic plants which began over a hundred
years ago and grew rapidly, in the course of which ornamental and
useful plants from the Tropics, especially of the Americas, were car-
ried to Kuropean conservatories and gardens and also to ourshores,
may very probably have served to introduce the pest into the tem-
perate regions of both the Old World and the New World. In all like-
lihood the Spaniards introduced this nematode into Florida directly
from the West Indies or Central America, for it is found in parts of
southern Florida that were in cultivation more than 75 years ago,
but where now dense forests have grown up, as well as in clearings
with no signs of recent cultivation. Yet even here it does not seem
to occur in land absolutely unused in the past.

Whether the Old World or New World Tropics were the original
home can not be decided now, as it is widely distributed in both.
Perhaps its wide distribution in Africa, India, the East Indies,
China, and Japan and the fact that another species of the same genus
(Heterodera schachtit Schmidt) is apparently native in Europe would
warrant the conclusion that it is probably of Old World origin.

THE CAUSAL PARASITE.

Upon breaking across a medium-sized or large knot and holding
the broken surface so as to reflect the light a close observer will often
see one to many clear to almost pearly white rounded bodies, con-
siderably smaller than half the diameter of a pinhead, projecting
from the surface. With a hand lens they are easily seen, but for the
unaided eye they are sometimes very difficult to detect, on account
both of their minuteness and of their transparency. In knots
that have been cut across they are usually not visible, as they col-

1 Neal, 1889.
217

26 ROOT-KNOT AND ITS CONTROL.

lapse when touched by the knife. These objects are the mature
females of the nematode Heterodera radicicola (Greef) Miller. Each
is capable of laying several hundred eggs, more than 500 having been
counted by the writer in one case where the nematode was still
actively laying eggs.

EGG.

The eggs (Pl. I, figs. 1 and 2) are ellipsoidal bodies, sometimes
symmetrical, more often slightly curved, and therefore somewhat
kidney shaped. They are usually a little over twice as long as broad.
Out of 71 different lots of egg masses measured by the writer, repre-
senting nematodes from 63 different hosts, the length varied from
67 to 128 » and the width from 30 to 52.5 yw. The greatest ranges
observed in any one lot of eggs were 67 to 108 by 33 to 42 y, 88 to
128 by 33 to 44 yw, 81 to 112 by 33.5 to 40 yp, and 84 to 119 by 35 to
52.5 uw. These represented in each case eggs from the same nema-
tode, showing how variable in size they may be. The average range
of all measurements was 85 to 98 by 34 to 40 yw with an absolute
average of more than 500 eggs measured of 92 by 38.4 w. These
dimensions agree closely with those given by Miiller,t who studied
this nematode in Germany, his figures being 94 by 38 ». On the
other hand, Frank,? also working in Germany, gives the figures as
80 by 40 ». Stone and Smith * give the length as 100 yp.

When the writer first examined the eggs from different hosts he
thought that there might be a possibility of distinguishing different
races of the nematode by the variations in the size of the eggs, but
the variability in size, even among the eggs from the same nematode,
soon demonstrated that no results of value could be obtained in
this direction. It seemed to be true, however, that the smaller,
less strongly developed females often produce the smaller eggs.
Thus, a nematode situated near the surface of a root, where the
pressure was not so great, was often larger and had larger eggs, but
this rule has so many exceptions that it can not be considered as
being in any way general.

The egg consists of a densely granular body in which a lighter
spot, the nucleus, can occasionally be seen, inclosed in a tough, elastic,
transparent coat, or shell, probably chitinous in nature. When the
mother nematode is so situated that she has plenty of room to de-
posit her eggs so that they are not laid with difficulty, they usually
leave her body unsegmented. On the other hand, if the eggs as
they are laid are crowded together so that considerable force has to
be used to lay each egg, the oviposition is delayed and segmenta-
tion begins before the later eggs leave the body. Only exceptionally,
however, do the eggs develop so far as to contain fully developed

1 Miiller, 1883. 2 Frank, 1885. 3 Stone and Smith, 1898.
217

THE CAUSAL PARASITE. Oy.

larvee by the time they are laid. Where this does occur it is mostly
only the last eggs produced and which the mother nematode has not
had the strength to force out against the large mass of eggs already
laid. In this the root-knot nematode differs quite markedly from
the sugar-beet nematode (Heterodera schachtii1 Schmidt), in which a
comparatively large part of the eggs produced remain within the
body of the mother and undergo segmentation and finally escape
from the shell, eventually escaping to the outside through the open-
ings in the body wall after the death of the old nematode.

Segmentation of the eggs begins very soon in any case and proceeds
rapidly. It was not determined exactly how long the embryonic
development required, but it is apparently not over two or three
days in warm weather (much longer in cool).

The eggs were laid at the rate of 10 to 15 a day in the cases
observed by the writer, although in some cases egg laying may pro-
ceed even more rapidly. They are surrounded by a slimy or gelati-
nous substance, which incloses them and evidently acts as a pro-
tection. This is secreted by the nematode with the eggs, as was
observed on isolated mature females under the microscope. It
is at first quite liquid and colorless, but soon becomes rather firm
and light brown in color toward the outside. This is the structure
that has been called by some investigators the egg sack (Kiersack) ;
for example, Voigt! and Strubell. The latter applied the term to
the similar structure in the sugar-beet nematode (Leterodera
schachtii), and, erroneously, denied its occurrence in LH. radicicola.
Occasionally the remains of the male may be found entangled in this
slimy mass. It is probable in such cases that after fertilizing the
female the male died and when the eggs were laid the egg mass sur-
rounded his remains. The eggs at the outer portion of the mass are
usually either hatched or contain larve, while those next to the body
of the nematode are not segmented.

This egg mass is sometimes as large as the adult female and can be
seen, readily when the latter partly projects from the root.

LARVA.

The larva (PI. I, figs. 3 and 4) emerges from the egg through a hole
which it pierces in the shell, usually at one end. It is a slender,
cylindrical animal, blunt at the anterior and tapering at the poste-
rior end to a pointed tail. The larve when they emerge from the
egg are 375 to 500 » in length*® and about 12 to 15 y» in greatest

1 Voigt, 1890.

2 Strubell, 1888.
3 Stone and Smith (1898) give the length of the larva as 350 », but this is considerably less than the meas-

urements made by the writer. They give the egg length as 100 », showing that they were not dealing
with eggs below the normal size.

217

98 ROOT-KNOT AND ITS CONTROL.

thickness. The average length is 420 to 475 ». The structure of the
larva is comparatively simple, consisting essentially of a tube (the
alimentary canal) within a tube (the body wall), the space between
(the body cavity) being filled with a liquid and minor structures
(fig. 1). The body cavity has no opening to the exterior. The ali-
mentary canal opens anteriorly at the end of the body, but posteri-
orly it opens in the median ventral line about one-eighth of the dis-
tance forward from the tip of the tail
(i. e., 50 to 65 w). The body wall con-
sists of an external cuticle and a dermal
layer of cells beneath which are the
four “fields’’ of obliquely longitudinal
muscle cells. Longitudinal tissue
Masses springing inward from the der-
mail layer at the median dorsal, ventral,
and lateral lines separate the muscles
into the four “muscle fields’? men-
tioned. Only occasionally the opening
of the excretory canal can be made out
in the larva, but it is quite distinct in
the mature male. It is in the ventral
median line, opposite or slightly pos-
terior to the esophageal bulb. These
details of structure are clearly shown in
the accompanying text figures (figs. 1,
2, and 3), contributed by Dr. N. A.
Cobb.
The alimentary canal consists first of
. a buccal spear (PI. I, fig. 4) 10 to 15.»
%250 ke long (usually about 12 »), a chitinous
Fic. 1.—Heterodera radicicola, Halt-grown organ, pointed at the anterior end and
female (?) individual shortly before the with three small knobs at the posterior
final molt: a, Anterior end; b, spear; c, : : 5
esophagus; d, esophageal bulb; e, nerve @Xtremity and pierced its whole length
ting; f, excretory pore; g, gland; h, thick hy a fine canal. Connected with the
wall of alimentary canal; i, body wall; 5 C
j, beginning of reproductive organs; k, basal knobs are retractile and exsertile
anus. Magnified 250 diameters. Drawn wyscles. This spear is used by the nem-
by W. E. Chambers. F : ci
atode in boring its way out of the egg
and through plant tissues, and through it the nourishment is apparently
drawn, for its canal is continuous with the lumen of the remainder of
the alimentary canal. This spear lies in a cavity, the buccal cavity,
from which it may be exserted. At the base of the spear begins the
slender esophagus, 40 to 50 long, which expands then into the thick,
muscular-walled esophageal bulb (figs. 2 and 3). This is a stout,
muscular body, often nearly spherical, but more often a little longer
217

mei a Eins Ngee” te

THE CAUSAL PARASITE. 29

than broad, about 10 by 7 ». The thick walls inclose a small lumen
which can be expanded and contracted by the muscular action, thus
acting in the manner of a pump in connection with the esophagus
and spear (fig. 3). The expansion and contraction of the bulb are
often synchronous with motions of

the spear. Immediately behind the
bulb the alimentary canal is rather
narrow for a very short distance and
then widens out rather abruptly into
the comparatively thick-walled di-
gestive portion which fills the body

x 700

Tie. 3—Larva of Heterodera radicicola: a, An-
terior end; b,c, and e, spear; d, buccal cavity;
jf, esophagus; g and h, outer and inner por-
tions, respectively, of esophageal bulb; 3,
nerve ring; j,excretory pore; k and 7, lumen
and thick wall, respectively, of alimentary
eanal; m, fat globule (?); , anus; 0, pos-
terior extremity. Magnified 700 diameters.
Drawn by W. E. Chambers.

x 700

Fic. 2—Anterior portion of the same nematode
shown in figure 1: a, Anterior end; b and c, free
and inclosed portions, respectively, of spear; d,
esophagus; e, outer wall, and, f,central portion
of esophageal bulb; g, nerve ring; h, second
bulb; i, thickened wall of alimentary canal;
j, excretory pore; k, gland. Magnified 700
diameters. Drawn by W. E. Chambers.

cavity and continues unchanged toa
point shortly anterior to the anus.
The anterior part of this digestive por-
tion is not clearly marked off as a
second bulb, as is the case in some
species of Tylenchus. Immediately

behind the esophageal bulb, surrounding the short, narrow portion, of
the canal, can be seen occasionally the nerve ring. About 25 to 40
anterior to the anus the walls begin to become thicker and the canal
tapers, the anal opening itself being rather small.

217

30 ROOT-KNOT AND ITS CONTROL.

Except anterior to the digestive portion of the alimentary canal
the body cavity is small. There are no signs as yet of the repro-
ductive organs, nor can the sexes be distinguished.

The larve are actively motile, but not so active as many of the free-
living forms. Unlike the larve of some nematodes parasitic upon
plants, for example, Tylenchus tritici, T. dipsaci,? and a species of
Aphelenchus discovered by Dorsett * on the violet and studied by the
writer, the larve of Heterodera radicicola are not very resistant to
unfavorable conditions. The other nematodes mentioned are unin-
jured by desiccation for long periods, by cold, many acids, etc. Thus,
the wheat nematode has been revived after having been left dry for 27
years. The Aphelenchus referred to remained alive in kerosene
emulsion for two days in contact with a drop of kerosene. Osmic-
acid fixatives killed it but slowly, as was true of chromic acid, mer-
euric chlorid, and other strong poisons. On the other hand, the
larvee of Heterodera radicicola, although able to remain alive in water
for a few days, soon die and decay, although damp or wet soil, pro-
vided the air supply is good, is favorable to their existence. Drying
out is usually fatal to them in a comparatively short time.

The larvee of the root-knot nematode are able to remain alive in the
soil for months without entering upon a parasitic existence. The
writer has been unable, however, to find any evidence that they take
any nourishment from the soil; at least they undergo no development
until they enter the roots of some plant, for if the soil be kept free from
vegetation for two years they all die. Even one year without food is
sufficient to kill large numbers of them.

In the normal course of development the larve, having encoun-
tered a root, seek its growing point and batter their way into it by the
aid of the buccal spear (PI. I, fig. 17). They then take up a position
entirely within the root and parallel to its longitudinal axis, the
anterior end pointing away from the root tip. This position may be
in the plerome, or perhaps as frequently, if not more often, in the
periblem. In the former case the nematode lies within the central
cylinder as the root develops, in the latter case in the cortex. In
either case the anterior end of the nematode is usually in close con-
nection with the cells surrounding the conductive tissues. In the
case of larvee which hatch from eggs produced within the root, some
bore their way out into the surrounding soil and enter new roots, as
described above, while others burrow along in the tissues of the root
and settle down, usually in the fleshy cortex. Thus an old nematode
gall will contain nematodes in all stages of development and at a

2 Ritzema Bos, 1892.
3 Dorsett, 1899.

217

THE CAUSAL PARASITE. OL

depth below the surface of the root of even 5 or more centimeters.
The latter has been observed by the writer in roots of sweet potato
(Ipomoea batatas) at Miami, Fla.

Within the tissues the larva becomes fixed in position and remains
quiet except for occasional movements of the spear and esophageal
bulb. Whether all the nourishment is taken through the hollow
spear or some is absorbed directly through the skin was not deter-
mined. It seems probable, however, that the former is the case,
especially in view of the fact that the female occasionally bursts the
surrounding tissues of the root, so that she lies outside the latter
except for the anterior portion, which remains buried in the tissues.

Growth begins almost immediately. This is mainly, however, in
thickness and only slightly in length (PI. I, figs. 5, 6, 7, and 8). By
the time a gain of 10 per cent in length has taken place the thickness
has increased five to ten fold. This increase in thickness is confined
to the region anterior to the anal opening and in the main posterior
to the esophageal bulb. The alimentary canal posterior to the bulb
becomes greatly enlarged. In a week or ten days the larve of both
sexes are spindle shaped. By the end of the fifteenth to twentieth
day the diameter is about a fourth of the length and the differentiation
of the sexes becomes apparent (PI. I, figs. 9 and 13). According to
Stone and Smith! the female nematode sheds her skin four or five
times during the course of development, the first time just before
leaving the egg and the other two or three times before the final molt,
when she becomes sexually mature. The writer has been unable to
confirm this statement. In none of the specimens examined was any
sign of shedding the skin apparent on leaving the egg, although on
this point the evidence is slight, as special attention was not given to
it. On the other hand, no trace of old skins could be found sur-
rounding the developing larvz within the galls up to the time of dif-
ferentiation of the sexes. It seems possible that the investigators
referred to may have been misled by the fact that an injured nematode
sometimes secretes a new cuticle underneath the old or on account of
the circumstance that the molting may commence at one point long
before it is visible elsewhere. If these extra molts do actually occur
it seems strange that no signs are to be found of the cast-off skins
around the nematode.

The writer’s observations lead him to the following conclusions:
The sexes are alike (externally at least) up to about the fifteenth
day, or sometimes longer. Then a new skin becomes visible under-
neath the old, from which it becomes separated at various points.
In the female the most marked change is that of the shape of the
posterior end of the body, which no longer possesses the tail it had

1 Stone and Smith, 1898, p. 22.
91294°—Bul. 217—11——3

32 ROOT-KNOT AND ITS CONTROL.

before the new skin was formed. At first the remnants of the old
skin are visible as an empty skin attached to the rounded posterior
portion of the nematode (Pl. I, fig. 9), but soon the growth of the
latter obliterates the cavity left and all signs of it disappear. The
anus, which before this time occupied a median ventral position some
distance anterior to the tip of the tail, now becomes terminal, and
immediately ventral to it but also occupying a position almost ter-
minal on the rounded posterior portion appears the prominent genital
opening, a horizontal opening with two rather thick and prominent
lips (Pl. I, fig. 10). The anterior portion has undergone but little
change. Apparently fertilization must take place at about this
time, for soon the external genitalia become so modified that this
would become impossible. The lips become smaller, the opening less
prominent, and eggs begin to develop.

Up to the last molt the larve of both sexes are alike, at least ex-
ternally. The writer’s very numerous observations do not allow
him to confirm the statement of Atkinson! that the female can be
distinguished before this period by the lack of a pointed tail, that of
the male being pointed. In all the writer’s observations, as pre-
viously described, the larve are indistinguishable until the last
molt. Then the still small but sexually mature female may be seen,
without a tail, in the old larval skin which has a tail.

ADULT FEMALE.

The mature female rapidly increases in thickness, becoming
eventually flask shaped to pear shaped with a length of 400 to 1,300 p
and a thickness at the point of greatest diameter of 270 to 500 yp,
or even 750 » (PI. I, fig. 12). The average of many measurements
is about 800 » for the total length, 500 » at the point of greatest diam-
eter, the length of the less enlarged anterior portion being 240 pu
and its diameter just before the region of great thickening begins
150 ». This not greatly enlarged anterior portion usually extends to
a little posterior to the bulb. The body then enlarges abruptly,
this posterior portion being approximately spherical.

Up to the last molt the spear of the female retains the dimensions
and shape it had in the larva. As is characteristic of all spear-
bearing nematodes, the old spear is shed with the cuticle at the time of
molting, a new spear being formed in its place. This new spear is
usually smaller both in length and thickness than the larval spear,
and the knobs at its base are less prominent. It is usually 10 to 12 4
long as against 12 to 15 » (rarely 10 »), characteristic of the larva.

1 Atkinson, 1889.
217

THE CAUSAL PARASITE. 33

The fully mature egg-laying female is of a glistening pearly
white color. The enlarged posterior portion is smooth and shows
no markings, except that the internal organs are visible where they
approach the surface. The comparatively little enlarged anterior
portion shows faintly the transverse cuticular markings so charac-
teristic of the mature male.

The bulk of the body of the sexually mature but not yet egg-
laying female is occupied by the enormously dilated alimentary canal
(Pl. I, fig. 11). The anus is a small round terminal opening, while
the genital opening is a transverse slit slightly ventral to the anus
and bordered by two more or less well-marked lips. This opens into
a short, thick-walled vagina about 16 to 20 » in diameter (including the
walls). At its upper end it is abruptly contracted into a tube 8 to
10 » in diameter, which soon divides into two tubes, the uteri. These
are at first slender but slightly coiled tubes, leading forward (usually
lateroventrally) and gradually increasing in diameter. Just before the
ovary is reached each uterus expands into a spherical portion, about
16 “in diameter, apparently the receptaculum seminis. Above this
lie the cylindrical ovaries filled with the rudimentary eggs in the
form of a sort of parenchyma. At this time the whole reproductive
system if straightened out would not be more than 300 to 400»
long. After fertilization the uteri undergo a most remarkable elonga-
tion and become very much coiled and tangled as they become
filled with the fertilized ova. Although the body of the nematode
increases rapidly in thickness, the increased space thus afforded is
not sufficient, the alimentary canal becomes pushed to one side, and
much of the space originally occupied by it is occupied by the uteri.

Egg laying had already begun, in the earliest cases observed by
the writer, 29 days after the seed of the host plant (Pisum sativum,
the garden pea) in these experiments was planted in soil known to
be infested with the nematodes. Since germination of the seed is
not immediate it is probably safe to assert that during warm weather
the period from the time the larva enters the root until it begins
egg laying is not over 25 days. This is somewhat longer during
cooler weather, i. e., in the early spring and in autumn.

In most cases the greater part of the eggs are laid in an unseg-
mented condition. However, if the nematode is buried deeply in
the tissues so that their pressure impedes egg laying, the eggs may
develop and the larve escape still within the body of the mother, so
that the latter may be viviparous. The last few eggs often develop
in a similar manner, the nematode having evidently become so weak
that she could not deposit them before they underwent development.

217

34 ROOT-KNOT AND ITS CONTROL.
MALE.

The development of the male after the larval stage differs greatly
from that of the female. Within the old larval cuticle a new cuticle
is formed. The nematode pulls itself away from the old skin, remain-
ing inclosed by it, however. The tail is rounded here, too, but the
anus is ventral instead of terminal. The whole body now elongates
very rapidly, becoming correspondingly slender (PI. I, figs. 13 and 14).
This necessitates a coiling in order still to remain within the old skin,
until it is coiled two or three times. When this development is com-
plete (Pl. I, fig. 15) it breaks its way out of the old cuticle, which has
retained its larval shape, and passes through the tissues and probably
even outside of the root in search of a female. Just prior to leaving
the old larval skin after undergoing this metamorphosis the nematode
does not molt again, as some assert.

The mature male differs greatly in many particulars from its appear-
ance just previous to the last molt. The form is about like that of
the larva on emerging from the egg, 1. e., long and slender, differing,
however, in the greater size and in the short, rounded tail. The
length is usually 1,200 to 1,500 y, the thickness 30 to 36 ». The tail
is short and rounded, not tapering, the distance from the anal open-
ing to the posterior end of the body being not more than 13 to 18 yp.
The cuticle over the whole body is very distinctly marked with trans-
verse rings extending entirely around the body and 2 to 2.5 y apart
(shown in section in PI. J, fig. 16). Except in profile it is only the
furrows between the projecting segments of cuticle that are visible.
These cuticular rings, which are also visible on the anterior portion
of the mature female, are not visible, at least at ordinary magnifica-
tion, in the Jarve.

The alimentary canal is essentially as in the young larva. The
spear, however, deserves special notice. It is larger than in the larval
stage or than in the mature female, being usually about 24 » in
length (rarely as short as 18 » or as long as 28). The knobs at its
base are prominent. Above the knobs the sides are parallel for about
half way and then taper to the finely pointed tip. The canal through
the spear is rather distinct. The body wall is about 1.5 » thick.
However, at the truncate anterior end it is between 5 and 6 » thick.
The anterior 2.5 » of this is a sort of hood, or cap, set off from the
rest of the body by a sharp furrow. Lying in the terminal body
wall, well below this hood and projecting but slightly into it, is a
series of six radiating perforated lamellae (apparently chitinous in
nature), narrow at their anterior ends and broad basally. Viewed
from the side they are approximately right triangles, the hypotenuse
being somewhat wavy. The bases of the lamelle radiate from a

217

THE CAUSAL PARASITE. 85

common center, and the upright legs of the triangle surround a canal
through which the spear passes. The bases are united into a small
ring just around this canal and another ring unites the outer ends of
the basal legs (Pl. I, fig. 16). Looked at from the anterior or pos-
terior direction this apparatus resembles a wheel with six spokes.
Distinct muscle strands run from the rim of this wheel to the knobs
of the spear, as well as to the point where it begins to taper. It is
probable that this peculiar organ is to help support and guide the
spear as the male is battering his way through the tissues. A similar
apparatus is present in Heterodera schachtw, the sugar-beet nematode.
It was imperfectly described by Strubell,' but the writer’s observa-
tion shows it to be essentially the same as in the root-knot nematode.
It has also been reported, but not correctly described, for a Tylenchus
species.

The reproductive organs of the male consist in all cases examined
by the writer of a single testis, a tube blind at the anterior end and
running parallel to the alimentary canal, into which it opens just
before the anal opening is reached. Atkinson reports that there are
two of these reproductive organs, as is the case with some other
nematodes. In all the specimens examined by the writer, however,
including specimens from Indiana, South Carolina, and Florida, using
the oil immersion lens and viewing the nematodes from different
sides, there was not the slightest evidence of a second testis. Cobb ?
also mentions its presence, and as both he and Atkinson are accurate
observers it must be that sometimes this occurs. In fact, Atkinson
himself later found specimens in which the testis was single.* Accord-
ing to the writer’s own observation the right testis is the one that is
missing, as the one present is placed somewhat asymmetrically, lying
nearly in the left half of the body.

Lying on either side of the posterior portion of the alimentary canal
and with their points entering the cloacal chamber are two peculiar,
somewhat sickle-shaped bodies, the spicules. These are curved bodies,
tapering toward the posterior end, about 35 » long, measured on the
chord connecting the two ends. No accessory piece is present,
although a thickening near the apical portion may represent one fused
with the spicules. These spicules are of use only during the sexual
process.

The excretory canal is plainly visible in the left lateral line, open-
ing ventrally in the median line 160 to 170 » from the anterior end
of the body.

It seems probable that the mature males take little or no food
and that they perish after having performed their function. The
reason for this supposition is the fact that one often finds still actively

1 Strubell, 1888. 2 Cobb, 1902. 3 Atkinson, 1889; see also Atkinson, 1896.
217

36 ROOT-KNOT AND ITS CONTROL.

moving males in which the alimentary canal posterior to the bulb,
or even includingit, has entirely disintegrated, leaving the body cavity
filled with a granular disorganized mass except for the long testis,
which extends nearly to the esophageal bulb. The large buccal spear
with its complicated guiding apparatus is doubtless to enable the
animal to batter its way through the root tissues in its search for the
female, as a much smaller spear serves the female for obtaining the

necessary food.
OVERWINTERING.

The stage in which this nematode overwinters was made the object
of considerable study. In the galls on annual plants examined in
November it was found that in almost all cases the mature or partly
developed nematodes, as well as the eggs, were dead, in many cases
being filled with fungous threads. Larve, however, alive and
actively motile, were found in abundance in and around the galls.
It is probable, therefore, that it is in the larval stage that the nema-
todes from annual plants pass the winter, probably descending into
the lower levels of the soil to avoid the cold. This latter point,
however, was not determined. In cases where the death of the top
of the plant had caused the death of the roots, the nematodes in the
roots soon died also.

In roots of perennial plants, for example, European grape, fig, etc.,
the writer has repeatedly found living female nematodes in nearly
or quite complete development at various periods in the winter and
early spring, showing that in such roots the nematodes may survive
not only in the larval stage, as previously described, but also as
mature females ready to begin egg laying as soon as the weather
becomes favorable.

COMPARISON WITH HETERODERA SCHACHTII.

In view of the fact that some authors! have questioned the correct-
ness of keeping separate the two species Heterodera schachtu, the
sugar-beet nematode, and H. radicicola, the cause of root-knot, it
will be well to give briefly an account of the points of difference,
especially since the writer has found the former to be a serious pest
at several points in California and Utah, while the latter has been
found as a serious sugar-beet pest at some other points. In tabular
form the main differences are easy to point out.

1 Stone and Smith, 1898; Atkinson, 1896.
217

THE CAUSAL PARASITE.

TaBLE II.—Differences between Heterodera schachtti and H. radicicola,

Points. Heterodera schachtii.

Effect on host........... No galls.
Location of mature fe- | External, anterior end only within
male. tissues of root.

Shape of female, external
appearance, etc.

Mostly lemon shaped, dull and flaky
in appearance, no trace of transverse
rings.

Heterodera radicicola.

Produces galls on roots.

Usually entirely within tissues of root,
more rarely the posterior portion,
very rarely nearly the whole body
external.

Pear or flask shaped, glistening and
pearly white, transverse rings of
cuticle often visible on anterior por-

tion.
All but the last few deposited outside

RP ESM eS coe teres Part deposited outside body, but most
developing within it. the body.

ADV ACs ees secrete ese Buccal spear about 25 » (PI. I, figs. 18 | Buccal spear 10 to 15 », mostly 12 to 15 »
and 19). (Pl. I, figs. 3 and 4).

Mature male............ Buccal spear about 30 » (according to | Buccal spear mostly about 24 p.

Strubell, 1888).

That these nematodes are not the same is readily seen when they
occur on the sugar beet. The one causes no conspicuous galls while
the other makes the galls so characteristic of root-knot (PI. II, fig. 1).
Both are very destructive pests of this host, and there is not much
choice as to which is the more harmful. Another difference not
mentioned above is that H. schachtii, perhaps by virtue of its more
powerful spear, is able to thrive and spread in stiffer soils than does
H, radicicola. In Plate I the figures for the larve of Heterodera
radicicola (figs. 3 and 4) and H. schachtw (figs. 18 and 19) are drawn
to the same scale, respectively. The difference between the two
species was emphasized in tabular form by Voigt in 1890.

METHODS OF SPREAD.

The larva of Heterodera radicicola is capable of active movement
in the soil, and in this manner doubtless the disease is slowly spread.
From some experiments made by Frank?‘ he estimated the rate of
progress at about 3 cm. per week. This would amount, during the
warm weather, in which infection occurs, say May 1 to September
15, to about 75 cm., or about 30 inches. These figures are probably
far too low. However, it is not through their own efforts that these
nematodes are mainly spread. There are many means of transporta-
tion at their disposal. A very frequent one is running water. Thus,
a field previously free from the pest sometimes shows its presence
in those spots where surface water at a time of heavy rains has
deposited a lot of soil from an infested field lying higher up. In this
way the pest has been carried from infested fields even to uncultivated
woods, as observed by the writer at one place. It has been suggested
that heavy winds carrying large quantities of soil from one field to
another may also transfer the nematodes, but in view of their sus-
ceptibility to injury by drying, this seems little likely. Especially is

1 Frank, 1885.
217

388 ROOT-KNOT AND ITS CONTROL.

this unlikely since the larve shun dry soil, and so would not be
present in that part of the soil which is dry enough to be transported
by the wind. More effective as means of transportation are the
hoofs of animals, wheels of vehicles, farm implements, and men’s
boots. Itis difficult to see how it would be possible to avoid conveying
living nematode larve from one field to another on farm implements
if they are left, as is too often the case, uncleaned on being trans-
ferred from one field to the next. Thus, a wagon and horses going
from one field to another would, if the soil were at all damp, carry
some of the damp earth, probably containing nematode larve, with
them.

The foregoing explains the spread of nematodes after they have
once been introduced into a locality. The introduction of nematodes
into a new locality, however, must have some other manner of accom-
plishment. This seems to be in most cases along with nursery stock.
Thus, the writer found that in parts of Texas the nematode appeared
first in the soil near fig and mulberry trees obtained from farther
east, which were noticed at the time of planting, several years ago,
to have knotted roots. In this way the soil near the trees became
infested and thence the disease spread, as previously described, to
different points in the locality. Perhaps east of the irrigated districts
the fig, mulberry, and peach are responsible more than any other
plants for the spread of the disease. Since the putting into effect of
good nursery inspection much of this source of infection has been cut
off. In the irrigated districts of Arizona and California the vine was
observed in several cases to be the plant at fault. The strawberry
has been observed at a few points in the East as the plant upon which
the pest was introduced. It is often badly affected without showing
much injury. <A case has been called to the writer’s attention in
which the disease was introduced into a garden in Washington, D.C.,
by asparagus roots from an infested field. The wide distribution of
the disease in ginseng plantations is doubtless due to the setting out of
small rooted plants from infested regions, as well as to the practice.
of some growers of packing the seed in damp earth. Should this
come, as is natural, from the vicinity of the ginseng bed and this
be affected by nematodes, the danger of sending nematodes along
with the seeds is very great. The dirt used for packing is naturally
thrown out at the point where the seeds are planted, and thus the
larve, if present, are able to enter the soil and infect the young gin-
seng seedlings. Seed potatoes are also another known source of
introduction of the disease.t| In a personal communication Dr. N. A.

1 Lounsbury (1904) regards the potato as perhaps the chief source of introduction and spread of this dis-
ease in South Africa.

217

THE CAUSAL PARASITE. 39

Cobb expresses the same opinion based on his observations in New
South Wales."

For the North, where root-knot is mostly confined to greenhouses
and hotbeds and their vicinity, perhaps one of the chief sources of
infection is the soil that is thrown out of these beds at the end of the
season. This soil, if infested, will spread the disease in the imme-
diate vicinity, especially if it be put near some manure pile or compost
heap which keeps the ground damp and warm during the winter.

EFFECT ON THE HOST.

The effect upon the root of the presence within it of the young
nematode is usually the hypertrophy of some of the tissues. The
parenchyma cells become abnormally large and multinucleate,?
sometimes only a few, at other times a great many cells being involved
in this hypertrophy. This abnormal enlargement of the cells leads
to a displacement of the various tissue elements, so that the tracheary
cells and vessels become separated and also show lateral displace-
ment and often much distortion. Often in bad cases individual cells
of a tracheary nature will occur entirely separated from others of the
same kind. The amount of hypertrophic enlargement of the root
depends upon the host on the one hand and upon the number of
nematodes entering the root in the same vicinity on the other. In
some roots the swelling is barely noticeable and is so small that as
the female nematode enlarges she eventually is inclosed in the root
only by the narrow anterior third of the body, the remainder being
entirely external, in this particular showing great similarity to the
sugar-beet nematode, whose galls are always of this nature. More
often, however, the hypertrophy is so pronounced that the mature
female is entirely concealed or reaches the surface only at the extreme
posterior portion of the body. If many nematodes are present in
the same general region of a susceptible root, the gall may be many
times the normal size of the root (PI. II, fig. 2). These galls are at
first of soft tissues, but in some woody plants, the European elm, for
example, some of the hypertrophied cells become lignified, inclosing
the female nematode in a woody prison from which in all probability
the larvee would be unable to escape should egg laying continue
after the lignification has begun. The structure of such a gall is like
that of the burls that often occur on various trees.

A very frequent phenomenon, but one that is by no means uni-
versal or characteristic of any one group of plants, is the formation
of numerous lateral rootlets above the gall. This is doubtless due

1 The writer’s attention has been called to the fact that in certain of the irrigated districts of the West
this nematode has become a very serious potato trouble. On one occasion several carloads of potatoes
were rejected on account of being infested with it. :

2 Tischler, 1902.

217

40 ROOT-KNOT AND ITS CONTROL.

to the disturbed and to a large extent interrupted water supply
and to the accumulation above the gall of food substances which
would normally pass on to the root tip. They accordingly are made
use of in the formation of lateral roots at that point. It is probably
not different in its nature from the adventitious root formation in cot-
ton and other plants just above the point of entry of the wilt fungus
( Neocosmospora vasinfecta)' or, in fact, from that occurring when
the end of a root is cut off or mechanically injured. The shape
or size of the gall does not seem to depend upon the place the plant
occupies in the current schemes of classification. The statement
of Frank ? that the galls of the dicotyledons are mostly of the round,
tuberlike type, with lateral rootlets, while those of the monocoty-
ledons are mostly spindle shaped, without lateral rootlets, is not
confirmed by the writer’s observations. Galls of both types may
be found on the same plant (PI. III, figs. 1 and 2) and appear to
owe their differences to the number of nematodes entering at a given
point, to the age and rapidity of growth of the root, and perhaps to
other causes. On both the beet and the radish, as well as on many
other plants, both types of galls and all gradations between may be
found. Entrance to the plant by the larve is not confined to root
tips or to passage from galls to the adjacent healthy tissues, although
these are the usual ways by which a nematode reaches the point
where it undergoes its subsequent development. Nematodes are
also able to bore from the outside directly into the tender tissues
of other parts of the roots, and even into stems. Thus, not only are
the roots of potatoes attacked but even the tubers, while some-
times the prostrate stems of tomato plants as well as those buried
beneath the ground in setting out the young plants are badly
knotted. Indeed, Sefor Romulo Escobar, of the Mexican Ministry
of Agriculture, informs the writer by letter that in the State of Nuevo
Leon the roots, stems, leaves, and even fruits of the watermelon are
attacked when they are in contact with the ground. This is excep-
tional, however, and is possible only where the nematodes are very
abundant and when the surface of the soil is constantly moist, so-
that they are in its uppermost layers.

Through the kindness of Mr. W. K. Winterhalter, then consulting
agriculturist of the American Beet-Sugar Co., at Rocky Ford, Colo.,
analyses were made of sugar beets badly affected with root-knot
and of healthy beets from the same field. Strange to say, in six
samples each of healthy and diseased beets the average sugar
content differed less than one-fifth of 1 per cent of the total weight
of the beet, while the percentage of purity was equally as close in
the two lots. In these points there also seems to be a marked dis-

1 Orton, 1902, p. 10, fig. 1. 3 Frank, 1885.
217

CONDITIONS FAVORING ROOT-KNOT. 41

tinction between the root-knot nematode and the true sugar-beet
nematode (Heterodera schachti), for the latter’s presence not only
reduces the size of the affected beets, but also greatly reduces their
sugar content and usually lowers also the purity.

The greatest depth at which Frank observed nematode galls was
33 centimeters (about 13 inches). On the other hand, the writer
finds that they may occur more than a yard below the surface of the
soil. To be sure, these are only scattering galls, for the great major-
ity of the nematode galls occur in the first foot of the soil. Indeed,
in practical culture it has been found that if trees can be forced to
root extensively at a depth of 16 inches or more they suffer but
little from root-knot ,

CONDITIONS FAVORING ROOT-KNOT.

SOIL.

Root-knot is essentially a disease of light soils. Wherever the
soil is sandy or contains a fairly large proportion of sand, other con-
ditions being favorable, the root-knot nematode may be expected
to thrive when once introduced. In heavy soils, on the other hand,
the disease seems never to be serious. In some of the writer’s
experiments affected plants were planted in pots of stiff clay soils,
and not only was it almost impossible to obtain infection of sus-
ceptible plants placed in close proximity in the same pots, but even
on the diseased plants the new roots remained free from the trouble.
Similar experiences have been reported to the writer from various
parts of the country where diseased trees were set out in stiff soil
and after a few years seemed to be entirely free from the trouble.
Contradictory statements sometimes find their way into print, but
they are explicable in most cases when one understands the great
popular confusion in the use of the words “heavy,” ‘‘stiff,’’ and
“light”? as applied to soils. Thus, in parts of Florida and South
Carolina a very sandy, yellow soil containing only enough clay to
hold it together while moist, is called “clay” or ‘‘heavy soil.” It
is clayey, to be sure, compared with some of the soils thereabouts,
for sometimes the latter are almost pure sand. “Light” and
“heavy” in the sense used in this bulletin have reference to those
soils containing, respectively, little and much clay. Soils that dry
out rather quickly, that do not cake hard on drying, and that are
easily crumbled to a fine granular mass are favorable to these nema-
todes, while the reverse is the case for the difficultly permeable,
hard-caking, clayey soils. This applies only to the root-knot nema-
todes, as the writer’s investigations have not gone into this point
with reference to other sorts. It is known that the sugar-beet
nematode will thrive in some of the heavier as well as in light soils.

217

42 ROOT-KNOT AND ITS CONTROL,
MOISTURE.

A certain degree of moisture is necessary for the maintenance of the
life of the nematode in the soil. Experiments by the writer, Frank,!
and others have shown that the larve of the root-knot nematode,
unlike those of many other nematodes, are destroyed by being dried
in the laboratory. Observations by the writer in New Mexico, Ari-
zona, and California confirm this abundantly, for in those communi-
ties the root-knot is practically confined to the irrigated land. This
does not mean that the soil must be wet, for that is not necessary.
The soil, however, must have sufficient moisture in it to be properly
called a moist soil, though not enough to fill the air spaces and inter-
fere with proper aeration. Thus, we have reports from South Africa,?
Argentina,® and Chile * which state that the nematodes grow only in
wet soils. This, in the light of conditions existing in America, evi-
dently means not what we would call wet, but merely moist, in the
eastern and southern part of the United States, but what many people
in irrigated districts would not hesitate to call wet in contradistinc-
tion to the dry, unirrigated soils. Prof. P. H. Rolfs,> Dr. N. A. Cobb,
and others report experiments which would seem to prove that dry-
ing of nematode-containing soil does not entirely kill out the Hetero-
dera radicicola. This will be discussed more in detail later.

On the other hand, soils that are water-logged for a considerable
part of each year are usually free from the trouble. Some observa-
tions on the effects of floods on nematodes led the writer to believe
that flooding for a few days would destroy them, but field experiments
in Arizona and California showed that keeping the soil submerged for
five days was not sufficient to kill out the nematodes, at least not
those inclosed within the root galls of the trees and vines growing in
the fields. Yet it is certain that very wet soils are free where this is
long continued, and long periods of flooding kill out the nematodes.
Thus, in the Everglades of southern Florida there occur islands, parts
of which are never flooded and parts of which are out of the water
ordinarily, but submerged for two to six months of the year. Truck
growers occupy some of these islands and find that the root-knot
nematode is abundant above the high-water level—i. e., where the
land is never flooded, but absent in the zone that is flooded every year.

TEMPERATURE.

As long as the soil is not too dry, the higher the temperature the
more actively the nematodes seem to develop. On the other hand,
they seem to become practically inactive when the soil temperature
falls below 50° F. Yet they are capable of remaining alive when

1 Frank, 1885. 2 Lounsbury, 1904. 8 Huergo, 1902, 1906. ¢ Lavergne, 1901. 5 Rolfs, 1894.
217

CONDITIONS FAVORING ROOT-KNOT. 43

exposed to great cold. The writer saw root-knot abundant on gin-
seng in a slat shed in Menominee, Mich., where the soil a year or so
before froze to a depth of more than 3 feet and where outside the
shed water pipes 6 feet beneath the surface were frozen, so the writer
was informed. In spite of this cold the nematode injuries were bad
the next year. In York, Nebr., where the temperature goes below
zero every year and sometimes reaches nearly or quite to —30° F.,
this nematode survived the winter in peony roots which remained
out of doors without protection. In New York State ginseng and
alfalfa are both more or less affected with root-knot, while in West
Virginia, along the Ohio River, clover is badly affected. It thus
becomes apparent that cold alone does not destroy the pest in the
soil. To be sure, Bailey! placed soil containing root-knot nematodes
in boxes and set some of the boxes out of doors through the winter.
In the spring the boxes kept indoors still had living nematodes, as
shown by gall formations upon plants grown from seeds sown there,
while the boxes left out of doors were free from nematodes. It seems
probable that the soil in this case dried out in the freezing process
sufficiently to kill the nematodes. Ordinarily, however, the frozen
soil remains in connection with soil moisture below, and so the drying
out and consequent destruction of nematodes does not occur.

The root-knot nematode does not become active in the soil and
begin to penetrate the roots of susceptible plants until the soil begins
to be warm. In the tropical and subtropical regions plants are sub-
ject to attack the year around, but the farther north one passes the
longer is the winter period of comparative immunity from injury by
this pest. Thus, in Miami, Fla., there is no dormant period for the
nematode. In northern Florida, however, crops planted in the latter
part of November or in December show comparatively little injury,
nor does the injury begin to be severe until the middle of February or
early in March. On the other hand, plants sown in October are in-
fected before the soil becomes cool and are badly injured, the nema-
todes continuing to develop and spread within the tissues when it is too
cool for them to spread outside through the soil. At Monetta, S. C.,
about half way between Columbia and Augusta, Ga., in the writer’s
experiments no infection by nematodes could be obtained before the
middle of April, while it was the middle of May before they became
really active. By the end of September or the middle of October
their activity had begun to decline.

Frank ? assumed that the chief period of infection was in the spring.
He was in error in this statement, for the writer’s experiments show
that the nematodes are more active in midsummer and that infec-

! Bailey, 1892, pp. 157-158. 2 Frank, 1885.
217

44 ROOT-KNOT AND ITS CONTROL.

tions occur more freely the warmer the weather, except where lack of
rain permits the soil to dry out, in which case both plants and
nematodes cease to thrive.

CONTROL OF ROOT-KNOT.

The problem of the control of root-knot is one that varies much
according to the place infested, the kind of plants grown, the methods
of culture followed, etc. We may distinguish between small, inten-
sively cultivated lots of soil, such as we find in greenhouses, hotbeds,
and seed beds, and field culture. Each group may be subdivided in
accordance with the answer to the question whether the crops are
annual or long lived. For the first great division, owing to the value
of the crops raised and the amount of capital invested, methods of
combating a disease may be used that would be barred from field
crops or other crops on larger areas of land, because the expense would
not be justified in view of the comparatively low earning power of
the land. Furthermore, the actual monetary loss to the crop due to
a given disease may be far greater in the restricted areas of intensive
culture than in large fields where each plant is of relatively less
value. So, for example, root-knot may affect a field of cowpeas
and actually reduce the crop one-half, but unless the field were very
large that might not equal the loss sustained by a grower of cucumbers,
lettuce, or tomatoes whose whole greenhouse crop has been totally
destroyed by the same pest.

GREENHOUSES, SEED BEDS, ETC.

LIVE STEAM.

Probably the most satisfactory method for destroying the root-
knot in greenhouses and seed beds is the use of live steam under
considerable pressure. This has been advocated by various persons,
viz, May, Galloway, Selby, and Rudd,’ but it was as a result of care-
ful experiments by Stone and Smith * that it became generally used.
The method recommended by them is a modification of that. recom-
mended by Galloway and others. The scheme is essentially as fol-
lows: At the bottom of the bench or bed are laid either iron pipes
perforated with g-inch holes every few inches or drain tiles. Live
steam is passed into these and escaping from the holes of the iron pipes
or between the ends of adjacent tiles heats the soil to such a degree
that all animals and most plants (except, of course, bacterial spores)
are killed. The pipes must be placed at intervals short enough to
permit the spaces between the rows of piping to be thoroughly per-
meated by the steam. This distance varies with the soil, but 12

1 May, 1896; Galloway, 1897; Rudd, 1893; Selby, 1896. 2 Stone and Smith, 1898.
217

CONTROL OF ROOT-KNOT. 45

inches is close enough for all general purposes, and even 2 feet is not
too far in deep beds if the sterilization is kept up long enough. The
bed should be covered with straw, boards, sacking, or something of
the kind to permit the upper layer of soil to become heated through.
The pipes or tiles in the soil should be arranged lengthwise in the
beds, with the steam inlet in a crosspiece of piping running across the
bed, from which the longitudinal rows take their origin. A similar
crosspiece at the other end may be used, but is not absolutely neces-
sary. There should be no open ends of pipes or tiles; otherwise all
the steam will escape out of these and not through the cracks or small
holes. Depending upon the pressure of steam used, the time neces-
sary for sterilization will vary from half an hour to even two hours
when the pressure is poor.

A method often recommended to determine whether the steam has
passed long enough, and one that has considerable merit, is to bury
raw potatoes at the surface of the soil underneath the covering of
straw, boards, or sacking. When all these potatoes are found to be
cooked the steam can safely be turned off. Stone and Smith recom-
mend the use of a special boiler so that steam at fairly high pressure
can be used, not under 40 pounds per square inch, preferably more.
Even 80 to 100 pounds pressure is not too high if obtainable, as it
shortens the time necessary and also prevents the soil from becoming
as wet as with lower pressure.

Not only are all nematodes killed by this treatment, but also all
insects and other noxious animals, as well as all fungi and their spores.
Many bacteria are killed, too, but not all of their spores, the survival
of the latter being desirable in view of what we know of the value
of soil bacteria.

This method has some disadvantages. Thus, it can not be used
for beds occupied by living plants. Furthermore, care must be
taken on the one hand not to leave the soil soggy and on the other
not to dry it out too much. The latter is, however, a much less seri-
ous matter than the former.

FRESH SOIL.

For greenhouses, cold frames, seed beds, etc., where a steam-heating
plant is lacking and where it would not pay to incur the expense
of installing a boiler for the purpose of using it for soil sterilization,
the desired results can be obtained by the use of fresh soil each year.
This should be taken from some place in the woods or from a field
where the nematode is known not to occur. The old soil should be
placed where it can do no harm in the way of spreading the disease.
If it can be allowed to become perfectly dry for some weeks before
taking it out, the danger from the old soil is greatly reduced. The

217

46 ROOT-KNOT AND ITS CONTROL.

framework of the beds should be thoroughly whitewashed with strong,
hot whitewash, freshly made from good quicklime, or it may be
painted with formaldehyde or some other disinfectant of this nature.
This is to kill all larve or eggs that might be in the dirt adhering to
the cracks. In selecting new soil it will always be well to examine
the roots of susceptible plants growing where the soil is to be obtained
in order to determine. whether or not root-knot is present. This
method has given good satisfaction where carried out in the North.
It is applicable, however, only to small greenhouses that do not
require much new soil. Large greenhouses can be far better taken
care of by sterilizing the soil in the benches.

It often happens that to obtain fresh soil is not desirable in view
of the character of the soil in the vicinity. Perhaps it has taken
some years to bring up the soil in the beds to the desired lightness,
humus content, etc., and to have to take new soil every year would
bea hardship. In such cases steaming should be made use of if pos-
sible. If it is not feasible, a formaldehyde solution has shown itself
of considerable value.

FORMALDEHYDE.

The formaldehyde method consists essentially of treating the soil
with a weak solution of commercial formaldehyde (or formalin). It
has been found that a solution of 1 part commercial (36 to 40 per cent)
formaldehyde in 100 parts water is effective against the root-knot
nematode in shallow beds when applied at the rate of 1 to 14 gallons
(or more in the case of very absorbent soils) to every square yard of
soil surface. For deep beds the quantity must be increased. Care
must be taken that all parts of the soil are reached and thoroughly
wetted by the solution. Upon the thoroughness with which it is done
depends largely the success of the process. After the formaldehyde
solution has soaked in the soil should be thoroughly stirred, so that
all parts may be exposed to the disinfectant. Before setting into the
soil any plants or sowing any seeds the excess of formaldehyde must
be allowed to escape by evaporation or, if necessary, be washed out by
flooding the bed. The former is preferable. The writer has not found
the germination of seeds interfered with when 10 days are allowed to
elapse between the treatment and the sowing of the seeds, especially
if the soil be allowed to become rather dry and be stirred in the mean-
while.

This formaldehyde treatment has been used with success at the
Ohio Agricultural Experiment Station ! in the forcing house and seed
beds. It was applied primarily to prevent certain damping-off fungi
from destroying the seedlings, but it was found that the nematodes
were sometimes destroyed also or greatly reduced in numbers. How-

1 Selby, 1906.
217

CONTROL OF ROOT-KNOT. 47

ever, as a means of combating nematodes it is not recommended by
Prof. Selby. The strength of the solution used there was about 1 to
14 parts commercial formaldehyde to 400 of water, which is less than
that found to be really effective against this nematode.

The treatment of living plants in the greenhouse to destroy root-
knot is fraught with considerable difficulty. Means that will destroy
the nematodes are mostly injurious to the plants containing them.
Thus, steaming or drying and freezing the soil can not be thought of,
as these processes are fatal to the plants. So, too, the use of carbon
bisulphid has in a similar way proved not feasible. It is still possible,
however, that certain plants less susceptible to this chemical, if per-
fectly dormant and rather dry, might escape without serious injury
when enough of it was used to kill the nematodes present. This must
be determined by experiment. Under certain conditions the use of
the formaldehyde solution has been found efficacious with some kinds
of roses. Many plants are killed outright by the treatment, but roses,
at least some sorts, are less susceptible to injury. The first experi-
ments in this line were performed in February, 1902, in the green-
houses of Mr. Loosé, a florist of Alexandria, Va., under the direction
of Mr. A. F. Woods, of the Bureau of Plant Industry. The writer
cooperated in so far that he examined the roots for nematodes after
the experiment. The following extracts from Mr. Loosé’s report of
the experiment indicate the methods used:

In the early part of February a bed of Bridesmaids, 150 feet long and 3 feet wide,
4 inches soil, was thoroughly saturated, using 50 gallons of the 1 per cent mixture.
The plants did not seem to suffer from the application, and one week later we were
able to see young healthy roots making their appearance, while the old fibrous roots
were entirely decayed. We then treated in the same manner Bride, Kaiserine,
Chatanays, Nephetos, Beauty, Liberty, and Meteor with equal success as to freeing
the soil of the pest.

Some strong-growing varieties, however, such as Beauties, Chatanays, and Kaiser-
ine, suffered and lost much of their foliage. Even some of the soft growth wilted
during the sunny part of the day. My experience in this treatment is that care
should be taken to harden the plants by lower temperature and keeping the beds
dry, being careful, however, to give the plant a good watering 12 hours before apply-
ing the mixture. * * * The cut of roses on February 10, at the time when we
applied the remedy, had dwindled down to 250 a day. It remained practically sta-
tionary during the four following weeks. We were able, however, to notice that the
foliage was regaining its normal color and the plants were starting strong growths. By
April 1 our cut had increased to 500 daily, mostly prime stock, and by the middle of
April it had resumed its normal cut of 1,000.

Asa matter of experiment we left a few plants untreated at the ends of some of the
benches, and to-day, May 10, they are practically worthless, showing effectually that
the spring weather had nothing to do with the improvement. The roots of the un-
treated plants looked like a ball of fern roots used for orchid potting, full of galls and
matted, plants making a weakly growth, foliage pale, and flowers insignificant. On
the contrary, the plants treated last February have healthy strong roots, making fine
growth and the foliage of the very best color.

91294°—Bul. 217—11——_4

48 ROOT-KNOT AND ITS CONTROL.

The mixture was applied with the hose connected to a force pump at the rate of 4
pounds of formaldehyde to 50 gallons of water, the treating of 15,000 plants requiring
200 pounds of formalin, worth about 18 cents a pound, making the treatment quite
inexpensive considering the result.

Since this experiment this method has been tried in a number of
places and with success where the proper precautions were taken.
Doubtless other plants might be treated similarly, but the method
should be tried with caution, even for roses, until it is ascertained
that the plants will not be killed.

MISCELLANEOUS.

Plants for which the formaldehyde treatment can not be used can
often be benefited by the following treatment: Remove them from the
soil, wash the roots clean, and cut away every diseased root, burning
them. Top the plant to correspond with the amount removed from
the roots and plant in nematode-free soil. Such severe treatment is
too injurious to some plants, and about all that can be done then is to
give them plenty of well-aerated soil with an abundance of fertilizer, so
as to stimulate root growth to more than counterbalance the roots
that are reduced in value by the entry of the nematodes into them.

It is possible that by transplanting diseased plants to stiff clay soil
the number of nematodes will be so reduced that a subsequent trans-
plantation to more suitable soil will find them free from the disease.

On purchasing rooted plants, unless they come from a place known
to be free from root-knot, it will always be best to put them into a
quarantine bench for several months. If at the expiration of this
time they show no signs of the trouble, they can safely be removed to
their permanent quarters. Of course the soil in the quarantine bed
must be renewed whenever it becomes infested with the nematodes.

Moderate quantities of soil can be freed from the pest by putting
it at the beginning of winter in a place where it will be exposed to the |
cold and subject to drying out at the same time. Thus, it can be
thrown upon boards in a comparatively thin layer. The boards will
keep the nematodes from passing downward into the ground as the
soil dries out. At the same time the boards keep the moisture from
the soil beneath from passing by capillarity up into the soil from the
beds. The continued drying and freezing, especially if the soil be
occasionally stirred, is fairly effective in killing off the nematodes.

CONTROL OF ROOT-KNOT IN THE FIELD ON PERENNIAL CROPS,

The treatment of perennial crops in the field is of a greatly different
nature from that of plants in the greenhouse, cold frame, or seed bed,
for a process that could be applied with profit to such valuable soil
as that in greenhouses, etc., might, indeed mostly does, prove too

217

CONTROL OF ROOT-KNOT. 49

expensive for ordinary use in large fields where the crop value per
given area is far lower. The methods to be applied differ according
to whether the land is used for annual or short-lived crops or is pos-
sessed by a long-lived crop, such, for example, as fruit trees. In the
former case the treatment can be begun after the crop is off, while in
the latter it must be of such a nature that the trees present do not
receive injury. The latter problem will be discussed first.

In the South the trees most generally affected seriously are the
peach, fig, mulberry, and walnut, while in California and Arizona
the Old World grapevine is seriously affected in addition. Many
other plants are subject to great injury elsewhere, such as coffee in
Biazil, Mexico, and the East Indies; papaya (Carica papaya) in
Florida and the Tropics; shrubs like tea in Ceylon and India, etc.
By consuiting the list of plants subject to the disease it will be seen
that many are woody plants and that of these a number besides those
mentioned are seriously injured by the disease.

CHEMICALS.

Of the various treatments proposed, the use of chemicals has offered
a wide field for investigation and one that is by no means thoroughly
explored as yet. The more promising chemicals tested by the writer
are mentioned in the following paragraphs:

Carbon bisulphid.—This has been used in Europe for the phyl-
loxera on vine roots where the plants were dormant, without serious
injury to the vine. The writer’s experiments, however, lead him to
look upon it with suspicion. Many plants were very quickly killed
by it and others seriously injured. Its use should not be attempted
without first testing its effect upon one or two trees. These should
preferably be dormant, at least not in an actively growing condition.
The root hairs are killed outright, so the plant must not be where
it will actively transpire until new root hairs are formed. The usual
method of procedure is to make holes in the ground to a depth of
several inches or a foot or more, the carbon bisulphid being poured
or injected into these holes and the latter covered up with dirt before
the liquid volatilizes. The fumes penetrate the soil and destroy
nearly all living things. Extreme care must be used in handling
this chemical, as its fumes are poisonous and exceedingly inflammable,
being explosive when enough air is mixed with them.

Carbon bisulphid will doubtless be of value in an orchard or grove
where it is desired to replace certain trees or fill vacant places with
new plants. By its use the spots where the old trees stood or where
vacant places are to be filled can be thoroughly disinfected. After
a week or two the trees can be set out and, the soil being free from
nematodes, can make quite a start before the nematodes from the

217

50 ROOT-KNOT AND ITS CONTROL.

soil outside of the disinfected patch can get to their roots. In deep
sandy soil the writer found not all the nematodes destroyed by the
use of 2 ounces of carbon bisulphid per square yard, but when 4
ounces were used they were exterminated. The size of the area to
be treated depends upon the size and rapidity of growth of the trees
to be planted, the faster they grow the smaller being the area to be
treated. For the best results the chemical must be placed at a depth
of several inches below the surface, the opening being firmly closed
so that the vapors will have to diffuse throughout the soil. In France
special forms of apparatus have been devised for this purpose in
combating phylloxera. They consist of a reservoir for the liquid and
a hollow rod which can be inserted to any desired depth, a measured
quantity of the liquid then being forced out into the soil. In the
writer’s experiments, however, use was not made of these rather
expensive contrivances, but of a simple dibble consisting of a pointed
piece of broomstick. Holes were made to the depth of a foot to the
number of eight or nine to the square yard. The desired amount of
carbon bisulphid was poured into them, each being closed at once by
the foot and the earth firmly pressed down to prevent the escape of
the vapors into the air. About a teaspoonful to each hole is sufficient,
or about 4 ounces to the square yard.

Potassium sulphocarbonate.—Potassium sulphocarbonate in the form
of a solution of 1 part, by weight, to 5 parts of water to be applied in
little trenches dug around the diseased trees is recommended by Gan-
dara.!. According to him, 4,000 liters of the solution suffice for a
hectare—i. e., about 425 gallons per acre. His experiments were with
nematode-affected coffee. This treatment he reports as being success-
ful, but too expensive for general use. The writer’s results, however,
were not so successful. Papaya plants (Carica papaya), about 18 to
20 months old and with roots badly affected with root-knot, were used.
The chemical, diluted as directed by Gandara, was applied to some
trees in little ditches and to some in numerous holes about a foot deep.
After it had all soaked in, the soil was watered thoroughly, as it was
very dry, so that the chemical might the better soak evenly through
the soil. In a day or two some of the old leaves dropped, showing
that the roots had suffered some injury; but at the expiration of a
few weeks the roots were found to be as badly knotted as ever, prov-
ing that for the papaya, at least, this process is ineffective. The
high cost of the chemical, moreover, would make its use utterly
impracticable.

Formaldehyde.—In view of the comparative success obtained with
formaldehyde solution on roses it was tested on papaya trees out of
doors. A ridge of earth was made around each tree at a distance of

1GAndara, 1906.
217

CONTROL OF ROOT-KNOT. 51

about 5 feet, so as to retain the solution. One part of commercial
formaldehyde (about 40 per cent strength) was mixed with 100 parts
of water. About 25 gallons were applied to each tree—i. e., about 3
gallons to the square yard. In some cases water was applied after-
wards to cause the solution to penetrate deeper; in other cases no
water was added. A few of the older leaves turned yellow and
dropped off a day or two after the treatment, but no further injury
was noticeable. In two weeks the nematode root galls, containing
living nematodes, were found to be almost as numerous as ever,
although a good many of the galls on the roots nearest the surface
were found to contain dead nematodes. These and other experi-
ments lead the writer to believe that where the soil is rather deep and
the liquids applied can drain through instead of remaining in the
immediate vicinity of the roots this formaldehyde treatment is not
likely to prove very effective.

Calevum carbid.—The use of calcium carbid was also recom-
mended by Gandara.‘ His instructions were to mix 4 parts of it
with 1,000 parts of water. After letting it stand half an hour this
milky solution is to be injected into the soil in five holes per square
meter, 10 grams to a hole. Through lack of other trees suitable to
test it on, papaya trees were also used in testing this method. A
modification was also made in that about an ounce of the calcium
carbid, without previous treatment with water, was placed in the
bottom of 8-inch holes, which were promptly plugged with earth,
about eight or ten holes being made to the square yard. Afterwards
the soil was thoroughly watered. In this case a strong odor of acety-
lene was noticeable for two days. No damage was done to the trees
and the nematodes in the galls were not killed by either treatment.

Other chemicals.—Various other chemicals recommended have the
disadvantage that they are poisonous to living plants or too expen-
sive. It is still possible, however, that some easily volatilizing liquid
may be found whose vapors while fatal to the nematodes will not
seriously injure the plants harboring them. Of those already men-
tioned carbon bisulphid has many desirable qualities; but its poison-
ous effect on vegetation is against it. It is possible that by applying
it only during the dormant season of the plant and carefully regulat-
ing the quantity applied it may prove as effective as it is claimed by
some investigators to be against phylloxera in the vine. The writer’s
experiments were mainly carried on at Miami, Fla., where there is
no dormant season; hence this point could not be well determined.
It is also conceivable that after a period of dry weather the chemical
might be less harmful, as the trees would then be in a less actively

1 Gandara, 1906.
2G,

52 ROOT-KNOT AND ITS CONTROL.

erowing condition and perhaps, therefore, less injured when the root
hairs were killed by the chemical. Further experiments on this line
should be carried out.

FERTILIZERS.

It is the result of general observation that if trees affected by root-
knot can be forced into rapid growth, especially in the early part of
the season, so that the roots penetrate deeply into the ground and
form a widely branching system, they will thenceforward usually
develop normally and cease to show much injury from the nematode.
This is particularly the case with the peach. Many growers now on
setting out an orchard where the pest is present fertilize the trees
very highly, so that they may start right into growth and keep ahead
of the nematode injury. As shown on page 41, the nematodes are
mostly confined to the upper 12 to 16 inches of soil, so that if the
roots can be forced to grow rapidly and deeply enough they will
escape much injury. To accomplish this, it is necessary that the soil
be prepared to a good depth before setting out the trees and that an
abundance of nitrogenous fertilizers be given. The various potas-
sium salts, too, are apparently very beneficial in the Southeastern
States, so much so that some people believe that they destroy the
root-knot nematode. Perhaps in the naturally rather potash-poor
soils of many of the Southern States the addition of potassium is
simply another factor in bringing the plant to its normal resistant
power. At any rate, in the writer’s experiments plants given an
excess of potash suffered less from root-knot than those not so fer-
tilized. It has been found in Germany that the sugar-beet nema-
tode removes the mineral salts from the roots about equally. If,
however, the soil is not much overstocked with potash it would be
exhausted in the plant sooner than the others, for, being less abundant
in the soil, it would be taken up less rapidly by the roots. The same
would be true of any other of the necessary minerals. This may
explain the effect of potash in combating this disease.

FLOODING.

In view of the fact that root-knot injury never seems to be severe
in soils that are flooded for a part of each year it seemed reasonable
to suppose that flooding might have a beneficial effect when applied
to affected trees. Unfortunately, however, through a misunder-
standing of instructions the experiments arranged to be carried out on
this line failed to be performed. It is certain, however, that great
care must be taken, for many trees are killed by having their roots
submerged even a few days.

217

CONTROL OF ROOT-KNOT. 53
CONTROL OF ROOT-KNOT IN THE FIELD WHEN NO OROP IS PRESENT.

Land known to contain the root-knot nematode and not occupied
by a permanent crop like an orchard, grove, etc., may be freed from
the pest far more readily than land so occupied. The methods are
the same, whether the land is to be planted subsequently to annual
crops or to trees. The only difference is that land destined for
perennial crops must be more thoroughly cleared of the root-knot
nematode than that destined for simply one-year crops.

CHEMICALS.

Carbon bisulphidCarbon bisulphid is undoubtedly the most
efficient chemical for the destruction of the nematode in fields.
Experiments were made by the writer at Monetta, S. C., in 1906 and
repeated in 1907, which showed that when used as previously described
at the rate of 4 ounces per square yard of surface the nematodes were
practically exterminated, being found only at the edges of the plats,
where they could have come in from the surrounding untreated land.
Two ounces per square yard did not prove so effective, although the
nematodes were largely destroyed by even this application. In
view, however, of the quantity required and of the high price of this
chemical it is very evidently out of the question to apply it on a
large scale. Even in bulk the crude carbon bisulphid costs 10 to
15 cents a pound. At 4 ounces a square yard the cost for an acre,
not including cost of the labor required, would be from $120 to $180.
Nearly all the chemicals that have been suggested have the same
fault. Yet for small patches when it is desired, perhaps, to destroy
the nematode where a tree is to be set out, or in a small spot where
the pest has appeared but has not spread badly, it would probably
be found very effective.

Formaldehyde.—Formaldehyde was tested at Monetta, S. C., in
both 1906 and 1907, and at Miami, Fla., as well, in 1906. Itwasapplied
as a solution of 1 part commercia! formaldehyde (36 to 40 per cent)
in 100 or 200 parts of water. The solution was either sprinkled directly
on the surface or poured into deep furrows, which were leveled off after
the solution had soaked in. From 1 to 2 gallons per square yard of
surface were used. As a whole, the treatment did not recommend
itself. In no case were the nematodes entirely destroyed, although
they were considerably reduced in numbers. The plants grown on
these plats after the treatment showed the presence of root-knot
galls on their deeper roots, although most of the upper layer of soil
seemed to be free from the pest. This would indicate that a larger
quantity would perhaps penetrate deeply enough to kill all the
nematodes in the soil. With formaldehyde at 20 cents a pound,
wholesale, the cost of treating an acre with the stronger solution,

217

54 ROOT-KNOT AND ITS CONTROL.

2 gallons per square yard, would be about $150 exclusive of labor,
which would include the hauling of 5,000 to 10,000 gallons of water.

Calcium carbid.—At Monetta, S. C., experiments were made with
calcium carbid. It was strewn in furrows which were then covered
over so that the resulting acetylene gas should penetrate throughout
the soil, or it was applied as a solution in water. The amount of root-
knot was reduced, but in all cases where the reduction was great the
injury to the crops, especially to tomatoes, was also great. Better
results were obtained from the dry application in 2-inch furrows than
from the solution. Planting was not undertaken for a week or two,
but still the results were such that in spite of replanting a second and
even a third time the test crops—okra, beans, tomatoes, and cowpeas—
were badly killed out. The odor of acetylene was perceptible for sev-
eral days. The fairly effective amounts were 1,500 pounds per acre,
dry, in shallow furrows or a solution of 5 pounds per 100 gallons of
water applied in deep furrows, 1 to 2 gallons per square yard. In
view of the high cost of the treatment (at 10 cents a pound this would
be $150 per acre exclusive of labor for the dry application and $25 to
$50 for the solution) this method can not be recommended. The
injury to vegetation is also against it.

Potassium sulphocarbonate.—This salt is obtained commercially as
a concentrated dark-brown solution, smelling strongly of sulphureted
hydrogen. Gandara‘ states that it has been tried against phylloxera
in France and recommends it for root-knot, at arate of 1 part
of potassium sulphocarbonate to 5 parts of water. Accordingly, the
following experiments were outlined. Plats of land were laid off as
follows: (1) Check, no treatment; (2) 10 parts of the chemical to
90 parts of water, 2 quarts per square yard in holes which were quickly
filled; (3) 1 part to 99 of water poured on the surface at a rate of
2 gallons per square yard, that being the quantity necessary to wet
the surface thoroughly; (4) a similar quantity of a solution of 1 part
to 199 of water; (5) check. After a few days beans, tomatoes, okra,
and cowpeas (New Era) were planted. In all cases where the
chemical was used, both weak and strong, the tomatoes, okra, and
beans were to a large extent killed, but the cowpeas were not hurt.
Root-knot was present, however, even where the solution was the
strongest. As a fungicide, too, this chemical had little value, for
Rhizoctonia was very abundant at the crowns of all the plants.

For field use, then, this chemical is not to be recommended as a
means of combating the root-knot nematode.

Ammonium sulphate—Van Breda de Haan? recommended against
the nematode on tobacco in the Dutch East Indies the use of am-
monium sulphate followed by quicklime. The latter sets free the

1 Gandara, 1906. 2 Breda de Haan, 1905.
217

CONTROL OF ROOT-KNOT. 55

ammonia, which that author supposed might have value in destroy-
ing the pest. The writer’s experiments at Monetta, S. C., were as
follows: Plats of nematode-infested land 10 feet by 70 feet and 10 by
140 feet were laid off, separated from one another by ditches 2 feet
wide. The chemicals were scattered on the surface and worked in
with a cultivator or hoe. The rate per acre of the applications is

here given, not the actual quantity put on the particular plats.
~ (1) Water-slaked lime (quicklime put in a hole in the damp earth and
left several days until slaked to a powder) 2 tons per acre, ammonium
sulphate 1 ton per acre; (2) quicklime 2 tons, ammonium sulphate
1 ton; (3) slaked lime 2 tons; (4) quicklime 2 tons; (5) check. Sum-
mer squashes were planted on one half of each plat and New Era
cowpeas on the other half, both these crops being very susceptible to
nematodes.

Plats 3 and 4, respectively, slaked lime and quicklime, showed a
very great abundance of root-knot, even more than plat 5, the check.
The plants were pale in color and weak. Evidently lime in the
quantities used is not effective against root-knot. In plats 1 and 2,
ammonium sulphate plus slaked lime and quicklime, respectively, the
squash roots were fairly badly knotted, especially in plat 1, but not
nearly so badly as in plats 3 and 4 or in the check plat (5). The cow-
peas were very dark green in color and very vigorous, and only moder-
ately affected with root-knot, far less than plats 3 or 4, perhaps
about like the check. The two plats with ammonium sulphate
ripened their seed earlier than any other of the experimental plats.
The next year these plats were again planted, this time to cowpeas,
okra, tomatoes, and beans. The chemicals were not added, but
observations were made to determine whether any beneficial effect
might show the second year. The ammonium-sulphate plats were
distinctly better than the check or those with lime alone, and were
only moderately affected with root-knot, although by no. means free
from it.

Experiments similar to these but on a very much smaller scale were
made in Miami, Fla. Quicklime, even at the rate of 5 tons to the acre,
did not suffice to prevent nematode injury, while root-knot was quite
abundant in a plat treated with quicklime at the rate of 2 tons per acre
with 2 tons per acre of ammonium sulphate dissolved and poured over
the surface.

We must then conclude that these chemicals are not of special value
for the combating of nematodes.

Abbey! recommends using silicofluorid of ammonium at the rate
of 1 ounce to asquare yard. It must not be applied to soil containing
living plants, as it will kill them. It soon decomposes and then is

1 Abbey, 1898 and 1899.
217

56 ROOT-KNOT AND ITS CONTROL.

harmless. Abbey also recommends 3 ounces of Little’s soluble pheny]
in 3 gallons of water applied around affected roots. Dyke! and
Iggulden? also tried the latter, but Dyke found it a failure, claiming,
however, that kainit was effective.

FERTILIZERS.

Closely related to the use of chemicals may be considered the effect
of various fertilizers on the development of root-knot. At Monetta,
S. C., the following fertilizers were tested in 1906, mostly in one-
twentieth acre plats separated by ditches (or rather very deep furrows)
2 feet wide, the numbers in parentheses referring to the field numbers
of the plats: (12) Kainit, 1,000 pounds per acre; (13) ammonium sul-
phate, 667 pounds per acre; (14) kainit, 500 pounds per acre; (15)
high-grade potassium sulphate, 1,000 pounds per acre; (16) check; (17)
high-grade potassium sulphate, 500 pounds per acre; (18) 17 per cent
acid phosphate, 1,000 pounds per acre; (19) 17 per cent acid phosphate,
1 ton per acre; (20) check. In 1907 the following tests were made:
(1) Kainit, 1,000 pounds per acre; (2) kainit, 1,500 pounds per acre;
(3) high-grade potassium sulphate, 667 pounds per acre; (4) high-grade
potassium sulphate, 1,333 pounds per acre; (5) ammonium sulphate,
1,000 pounds per acre; (6) muriate of potash, 1,000 pounds per acre;
(7) potassium magnesium carbonate, 667 pounds per acre; (8) potas-
sium magnesium carbonate, 1,333 pounds per acre. The checks
received no numbers in 1907. The plats of that year and the checks
were planted to tomatoes, okra, beans, and New Era cowpeas, all of
which are very susceptible to root-knot. The last year’s plats (1906
experiments) were also replanted in 1907 with these four plants. In
1906 the fertilizer plats were planted with New Era cowpeas and
summer squashes. To all of the fields was applied each year, at the
rate of 500 pounds per acre, a special brand of commercial fertilizer
in common use in that vicinity, the soil being so poor that without
some complete fertilizer nothing would grow well. The experiments
were intended to show the effect, if any, of an excess of some par-
ticular fertilizer over the normal quantity applied.

The 1906 plats showed plainly the beneficial effects of potash fer-
tilizers on the sandy soil of the experimental field. All the plats
treated with kainit and potassium sulphate were darker green and the
plants were far more vigorous than on the other plats. In fact, plats
12 and 15, respectively, kainit and potassium sulphate, both 1,000
pounds to the acre, were, so far as the cowpeas were concerned, hard
to excel anywhere. The squashes did not show much difference in
any of the plats. They were badly infested with the squash bug,

1 Dyke, 1897. 2 Iggulden, 1898.
217

€

CONTROL OF ROOT-KNOT. 57

which killed the plants out in some of the plats. The cowpeas in
plat 12 showed no nematodes and but few were present in the squashes.
Plat 14 had a fair amount of root-knot in the cowpeas and from few
to many on the different squash plants. The rest of the plats did
not differ materially from the check plats which were fairly badly
affected, in spots very badly.

The plants grown on these same plats in 1907 without the addi-
tion of the fertilizers again were badly affected except in plat 12, and
somewhat in plat 15, which remained fairly free, showing a residual
effect.

In the 1907 fertilizer experiments the following results were
obtained. The kainit applications were injurious to the germina-
tion of the seeds, both the 1,000 as well as the 1,500 pound applica-
tion, but naturally the latter more markedly. The amount of root-
knot, however, in these plats was slight. Potassium sulphate at 667
pounds per acre was not injurious, but at twice that amount it so
injured the germination of the cowpeas and beans that they required
replanting. Root-knot was fairly abundant and, strangely, more so
in the more highly fertilized plat. In both plats the growth of the
plants was very vigorous. The sulphate of ammonia at the rate used
exerted a very harmful effect on germination, requiring several
replantings. The plants that did grow, however, were very vigor-
ous, dark green, and rather free from nematodes. The muriate of
potash injured the germination of the beans and cowpeas, while the
nematodes were fairly abundant. The potassium magnesium car-
bonate gave the best and most vigorous plants of all, without injury
to germination. Root-knot was present in most of the plants, but
not abundant.

Judging from these experiments, it is clear that fertilizers alone
can not be depended upon to exterminate root-knot. On the other
hand it is also plain that some fertilizers exert a beneficial effect upon
the plant and enable it to make a good crop in spite of nematodes.
Perhaps they may also increase the resisting power of the plant
against the entrance of the nematodes into the roots. The potash
fertilizers seem to be most favorable for this purpose, so far as the
experiments at Monetta and observations elsewhere go. However,
it will not be safe to conclude that they will be equally beneficial
everywhere. In the sandy, rather potash-free soils of South Caro-
lina and Florida the application of potash in amounts not too large
seems to be followed by favorable results.

According to Stift,! Hollrung, in Germany, has shown that ferti-
lizing highly with potash alone is not of much benefit to beets attacked
by the sugar-beet nematode. Wimmer has shown that the nema-

1 Stift, 190s.
217

58 ROOT-KNOT AND ITS CONTROL.

todes remove the different minerals almost equally, so that only
where one element is rather deficient will the addition of that alone
be of benefit. The sugar-beet nematode removes large quantities
of mineral food from the roots, so that unless these minerals are
present in the soil in considerable excess over that naturally needed
by the crop the plants will suffer from lack of that mineral which is
not sufficiently superabundant. Thus, an amount of potash sufficient
for a healthy crop may be insufficient if the sugar-beet nematode is
present, and the symptoms of potash hunger can be averted only by
applying an excess of potash. Probably this is also true of the root-
knot nematode. The sandy soils of South Carolina are rather potash
poor, so that a diseased plant will suffer from potash hunger, while
the other elements may be in sufficient abundance. At any rate,
the addition of potash in excess proved helpful. The nitrogen-
containing fertilizers when not in too great excess also benefited the
plants somewhat, but not so markedly as the potash. This is to be
expected, as nitrogen is not any too abundant in those soils. The
phosphatic fertilizers, however, showed no benefit at all.

Caution must be taken not to apply too much potash. In 1907,
in fact, kainit at 1,000 pounds per acre was harmful in that many of
the young seedlings were killed, necessitating replanting several times
in order to get a fair stand. This quantity was not harmful in 1906
on another plat, showing that the danger limit is probably not far
below that amount. Muriate of potash at the same rate was very
harmful in 1907, as was also the same amount of ammonium sulphate.
Potassium sulphate, 667 pounds to the acre, and potassium magnesium
carbonate, 667 and 1,333 pounds to the acre, were absolutely harm-
less, while the latter amount of potassium sulphate was only
slightly harmful.

In spite of the high fertilization a field continually plata to
nematode-susceptible crops will, if the nematode is present, eventually
become so infested with that neraite that it will be impossible to
make paying crops. However, it can not be denied that for special
occasions it is of value to reduce part of the evil effects of the nematode
infestation by high fertilization.

FLOODING.

The objections to flooding the soil that would apply in the case of
land occupied by permanent crops do not hold good in fields devoted
to annual or short-period crops. In the former case the soil can not
be kept submerged longer than a few days or the roots are killed.
In the latter case, however, the fields can be flooded for as long a
period as desired before the crops are planted. There is no doubt
that under such conditions flooding has value. This has already

217

CONTROL OF ROOT-KNOT. 59

been mentioned, reference being made to the conditions in the Ever-
glade islands, where the never submerged tops of the islands are full
of root-knot and the annually submerged sides are free from it. The
writer has records of fields in Georgia badly infested with the root-
knot nematode that were free from the trouble after a spring freshet
that kept the ground submerged several days.

Apparently flooding, unless possibly of long duration, will not kill
the nematodes inclosed within the root galls, so that if such knotted
roots of perennial plants are present the flooding must be continued
much longer. In Yuma, Ariz., under the writer’s directions a field was
flooded. It had once been a vineyard of Old World grapes, but these
had become unprofitable owing to the ravages of the root-knot, and
the vines had been cut down or pulled up. Many of the roots, however,
were leftin the ground. The next year the field was planted to melons.
When the writer saw the field in May, 1907, the young cucumber
and melon plants were dying from root-knot and the pest was found
in the old living grape roots. The field was flooded the following
winter, but root-knot was again prevalent the following spring,
although apparently not so abundant. It seems likely that the vine
roots may have harbored and saved from destruction many nema-
todes, or perhaps the flooding was not continued long enough. That
under some circumstances even three weeks is insufficient appears to
be the conclusion to be drawn from an experiment performed at. the
writer’s suggestion by a fruit grower and nurseryman in California.
He kept submerged for three weeks his field of sandy alluvial soil
which was badly infested by nematodes. Afterwards grape cuttings
and peach seedlings were set out in it. The grapes (a resistant sort,
Rupestris St. George) showed no root-knot, but the peaches became
knotted. This period seems excessive in view of laboratory results,
and is not entirely free from doubt as to other possible means of in-
fection, yet, until disproved, three weeks should be regarded as not
enough time to exterminate the nematode by flooding.

It is of interest that flooding the soil is claimed by Stift! to be of no
value against the closely related sugar-beet nematode.

Flooding, then, can not be recommended as a certain means of ex-
terminating root-knot under all circumstances. Probably the soil
should be flooded at least 25 days; in the laboratory the nematode
larve usually succumbed much sooner when isolated and placed in
water. Furthermore, no roots of perennial susceptible plants must be
present. When water is expensive or means of flooding are not at
hand, or when the soil is too porous, it will be out of the question to
try this method. The subject is one, however, that needs further
investigation. It will be of interest to call attention to the phenom-

1 Stift, 1903.
217

60 ROOT-KNOT AND ITS CONTROL.

enon often observed that a sloping field may have nematodes at its
upper or middle portion and be free from them at the lower end where
the soil is water-soaked part of the year.

DRYING.

Laboratory experiments by the writer seem to show that the root-
knot nematode can not withstand the drying out of the soil. Thus,
two pots of badly infested earth, containing badly knotted plants,
were allowed to remain without watering from June 4 to September
22,1908. The soil became very dry and dusty. It was then watered
and seeds of susceptible plants were sown. ‘These remained entirely
free from root-knot. It is certain that the adults are killed by drying
out, they being, indeed, very susceptible to injury of that kind. The
foregoing experiments led the writer to the conclusion that thorough
drying was fatal to larve and eggs as well. This was strengthened
by the observation that in his cross-inoculation work where carefully
washed root-knot roots of various plants were planted in sterilized
pots of soil and seeds of the desired plants sown in the pots, infection
was obtained wherever the roots used were fresh, while whenever
they were somewhat wilted, not even dry, no infection was obtainable.
Frank! and Stone? were also of the opinion that drying out was fatal
to these nematodes.

On the other hand, there are several recorded observations which
would seem to indicate that the opposite is true, at least sometimes.
Thus, Géldi* dried the roots of coffee affected with root-knot, both in
the sun and in the shade. After two months he wet them up and soon
found, with the aid of the microscope, numerous nematode larve,
which he considered to be those of the root-knot nematode. A second
case was as follows: Prof. P. H. Rolfs, of tlte Florida Agricultural
Experiment Station,’ kept some sandy soil in the laboratory for 10
months. It became dry long before the expiration of that period.
The soil was watered and tomato seeds were sown. The radicles of
the seedlings became swollen and cedematous in a manner resembling
the work of the root-knot nematode. No nematodes were found
within the roots, but clinging to the outside were found nematodes
which he identified as Heterodera radicicola.

Géldi’s conclusions may have been erroneous, for there are many
nematodes, almost indistinguishable from Heterodera radicicola in the
larval state, that endure drying out for long periods. If they were
examined only with the microscope and not tested in connection with
livmg plants on which they could be grown to maturity, it would be
almost impossible to tell whether those seen by Géldi were the one or
the other. Prof. Rolfs, on the other hand, is not likely to have made

1 Frank, 1885. 2 Stone, 1899. 3 GOldi, 1892. 4 Rolfs, 1894.
217

CONTROL OF ROOT-KNOT. 61

a mistake of this nature, performing the experiment as he did. Still
it is not certain that he had Heterodera radicicola unless he actually
had the mature nematodes, but on this point he says nothing. There
are some other nematodes besides this species that cause root galls,
and it is barely possible that it may have been one of these, not the
root-knot nematode that Prof. Rolfs had, since this latter species is
rarely even partially external in the tomato. Yet with the confirma-
tion of these reports by Dr. Cobb’s observations, it can hardly be
doubted that under some circumstances some of the root-knot
nematodes may survive drying out of the soil.

Whether the drying out of the soil kills all the root-knot larve or
not, there is no doubt that their activity ceases and there is no injury
by them in fairly dry soils. In a letter to the writer, C. P. Lounsbury,
entomologist of the Department of Agriculture of the Cape of Good
Hope, states that the nematode occurs only in loose soils well sup-
plied with moisture. Badly knotted grapevines set out in rather dry
soil not only recovered, at least in part, but the nematodes did not
spread to surrounding susceptible plants. Lavergne' in Chile,
Gandara?’ in Mexico, and Huergo * in Argentina also point out that
dry soils are unfavorable to the development of root-knot. The
writer has repeatedly sought for these nematodes in susceptible plants
in dry soil outside of but in close proximity to badly infested irrigated
fields in the semiarid parts of the country, but without success.

In view of the foregoing facts, it is probable that deep plowing, so as
to loosen up the soil quite deeply without harrowing to pulverize it,
would permit it to dry out sufficiently in a dry season to reduce
greatly the injury from the pest. Of course, this is possible only
_ where the climate is dry and the rainfall slight. In irrigated districts
it could probably be carried on, such fields not being irrigated for
some months after plowing. Of course this will not have much effect
if underground seepage or rains keep the soil moist. Unfortunately
the writer was unable to test the eflicacy of this proposed method by
direct experiment. It is a method that should be tested at the earliest
opportunity in those regions where it can be carried out.

TRAP CROPS.

After Kihn, the great German agriculturist, had demonstrated *
that the so-called Ribenmiidigkeit (beet tiredness) of sugar-beet
fields was due to a nematode, Heterodera schachtw, he devised *® a
method of reducing the injury based upon the principle of trapping the
nematodes in some susceptible plant and destroying the latter before
the larvee which had entered the roots had reached maturity. For his
trap crop he used a sort of summer rape. This was sown closely and

1 Lavergne, 1901. 2 Gandara, 1906. 3 Huergo, 1902, 1906. 4 Kuhn and Liebscher, 1880.
6 Kiihn, 1881, 1882, 1886-1, 1886-2, 1891.

217

62 ROOT-KNOT AND ITS CONTROL.

when the plants had grown long enough so that the first nematodes
that entered the roots were not yet mature but were in the nonmotile
stage they were plowed up and either removed and destroyed or
turned under with the tops down and roots up. The plants treated
in the latter manner died quickly and the nematodes in the exposed
roots died within a few hours. By repeating this process several
times (three to five) in a season the number of nematodes was found
to be so reduced that good crops could be grown again for several
years. In using this method extreme care must be taken to plow
under or remove the plants at the right time, for if left too long the
nematodes will reach maturity in the roots and lay eggs, thus increas-
ing instead of diminishing the number of nematodes in the soil.

Frank! and others have also recommended this method for com-
bating the root-knot nematodes. The writer has found no record of
any such experiment having been tried. He made experiments on this
line two different years at Monetta, 8. C., but with no success. A
badly infested field was separated from adjacent plats by a shallow
ditch, 2 feet wide. The plat was sown very thickly to Whippoorwill
cowpeas, a variety susceptible to root-knot. Roots from numerous
plants were examined microscopically at short intervals to determine
the stage at which the nematodes first entering the roots had become
motionless and were approaching sexual maturity. At that stage
the plants were destroyed, on one plat by plowing them under, on
another by loosening the roots and removing and destroying the
plants, roots and all. The time necessary to reach that stage was
found to be from 19 to 21 days after the sowing of the seed. As soon
as the trap crop was removed or turned under, the soil was made ready
and resown with cowpeas, the process being repeated. This was done
until four or five crops of cowpeas had been removed in this manner.
The next year through these plats and the check plat were planted
rows of tomatoes, beans, okra, and New Era cowpeas. Some of these
plants remained free, while some were slightly affected and some
very badly affected by root-knot, no difference being noticeable be-
tween the trap-crop plats and the check plats. This was true both in
the experiments of 1906-7 and of 1907-8, which were conducted on
another field.

The cause of the failure of this method can not be that a sufficiently
susceptible host plant was not chosen, for the variety of cowpea used
is very susceptible. Furthermore, cowpeas had been grown fre-
quently on that land, so that the nematodes were, so to say, accus-
tomed to that crop. The period of growth allowed was carefully
checked by microscopical examinations so as to avoid any chance of
letting the development of the nematodes progress too far, for if that

1 Frank, 1885.
217

CONTROL OF ROOT-KNOT. 63

were permitted and egg laying were started the number of nematodes
would be increased instead of diminished. Probably such large num-
bers were present that only a part entered the trap plants and were
destroyed, enough remaining in the soil to infest badly the next year’s
crop. It is possible that some other crop would have done better, but
it could not have been clover, as Frank suggested, for that did
not do well where the experiments were being carried on. The
requisites of a good trap plant are fairly cheap seed, great susceptibility
to nematode attacks, a wide-spreading root system, and rapid growth.
All these are possessed by the cowpea to a greater or less extent.

STEAM.

It has been seriously proposed to use steam to destroy nematodes
in the field in view of the success with its use in the greenhouse, cold
frame, and seed bed. The writer has made no experiments along this
line, owing to the expense of the undertaking. It is seriously to be
doubted whether a large field, producing a crop selling at $25 to $50
or even $100 net per acre, could be profitably piped for steam sterili-
zation. Small fields isolated from danger of reinfection by deep
ditches, water, stiff soil, or other obstacles and devoted to the inten-
sive culture of some very remunerative crop might be so treated with
profit. For a large field a very large boiler and many hundred feet
of perforated pipe would be necessary to steam the soil by the green-
house method.

Several schemes for sterilizing the soil in a field by means of movy-
able apparatus have been devised, some of which have proved
effective under certain conditions. Thus, for combating the Thielavia
root-rot of tobacco, Gilbert 1 recommends the inverted-pan method
of steam sterilization. This was devised by Mr. A. D. Shamel, of
the Bureau of Plant Industry, for sterilizing nematode-infested soils
in Florida. The following description is taken from Gilbert’s account:

The apparatus consists of a galvanized-iron pan, 6 by 10 feet and 6 inches deep,
which is inverted over the soil to be sterilized and the steam admitted under pressure.
The pan is supplied with steam hose connections, has sharp edges, which are forced
into the soil on all sides to prevent the escape of steam, and is fitted with handles for
moving it from place to place, the weight of the entire pan being not over 400 pounds.
The soil is prepared as in the greenhouse method, a few potatoes being buried at a
depth of a foot to gauge the degree of heat attained. A soil thermometer may also be
used if desired. The steam should be kept at as high a degree of pressure as possible,
80 to 100 pounds being best, and the treatment should continue for one to two hours,
depending on the pressure maintained. In experiments conducted in the spring of
1907, one hour’s steaming at 80° C. under 100 pounds pressure gave best results in
killing both the fungus and the weed seeds. When one section of the bed is treated,

the pan is lifted and carried to an unsterilized portion and the operation repeated
until the entire bed is steamed.

1 Gilbert, 1909, pp. 35-36.
91294°—Bul. 217—11——_5

64 ROOT-KNOT AND ITS CONTROL.

The great objection to this method, and one that makes it imprac-
ticable except for use on small spots, is the smallness of the area that
can be treated at one time. Even with a pan of twice the area of that
described, and allowing only one hour’s sterilization each time, it
would require more than 15 days, working day and night, to sterilize
the soil on one acre of land. Furthermore, for deep soils, where, as
already explained, the nematode sometimes is present at a depth of
more than a yard, it is extremely doubtful whether the steam would
penetrate deeply enough to destroy all the nematodes. This last
objection applies to all methods of sterilization where an attempt is
made to kill the nematode by heat or poisons.

FALLOW.

It is self-evident that if a field be kept free from all vegetation for a
long enough period all the plant-parasitic nematodes within the soil
will die from starvation. This is the principle involved in the use of
the bare fallow. The field is plowed and kept free from weeds and
other plants by frequent cultivation. In those localities where the
winter is cold enough to prevent the further development of the
nematodes during that period, it does no harm if grass or weeds grow
up after the weather has become decidedly cool. This date might
safely be put at November 1 for North Carolina, South Carolina,
northern Georgia, Alabama, Mississippi, northern Louisiana, and
northern Texas. In central and southern Florida and probably the
southern portion of Texas and Louisiana, however, the nematode is
active the year around, so that it would be necessary to keep the
ground bare the whole time until the nematodes had died. In the
early spring, where vegetation was allowed to grow in the winter,
the cultivating to keep down the weeds must be taken up again before
the soil begins to warm up. The length of time necessary to remain
in fallow is not certainly known. Mr. A. D. Jackson, of Denison,
Tex., found that 15 months in fallow was not sufficient to rid a field
of root-knot nematodes entirely, although the number was greatly
diminished. On the other hand, two whole years seem to be amply
sufficient.

This method has some objections which make it impossible to use
in some localities. The land is idle and not only not productive, but
requires the expenditure of time and labor to keep the vegetation
down. Furthermore, the light soils where the nematodes abound
are easily leached out when there is not a covering of vegetation.
Then, such soils are subject to bad washing during heavy rains when
they have no plant roots to bind them in place. A further objection
is the destruction of humus in the soil exposed directly to the action
of the fierce summer sun. The use of this method therefore can not
be universal, although it is successful where it can be put into effect.

Phy

CONTROL OF ROOT-KNOT. 65
NONSUSCEPTIBLE CROPS.

The most promising method, and the one that has given the best
results wherever carefully tried, is that of growing crops that are not
subject to root-knot until the nematodes causing the disease are starved
out. To carry out this method successfully several things are requi-
site: (1) The crops planted must be free from nematode attack, so
that the larvee in the soil may not be able to find any nourishment
to sustain their life and enable them to undergo their development.
(2) The crop grown should at least pay the expense of working the
land, as well as the rent, taxes, etc. (3) At the same time, if possible,
the crops should enrich the land, or at least not impoverish it. (4)
The plants must make such a vigorous, dense growth as to choke out
all weeds or other plants that might harbor nematodes and permit
them to develop and produce their numerous eggs.

On referring to the list of susceptible plants it will be seen that with
few exceptions none of the ordinary farm crops fulfill the first require-
ment. However, the following plants appear to be free from nematode
attack, at least under most conditions: Cowpea (the Iron variety), all
species tested of Stizolobium (the velvet bean and close relatives),
Florida beggarweed (Meibomia mollis), peanut (Arachis hypogaea),
rye (Secale cereale), most varieties of winter oats (Avena sativa), crab-
grass (Syntherisma sanguinalis), and possibly a few others. Webber
and Orton * first called attention to the nematode-resistant quality of
the Iron cowpea and recommended its use in combating root-knot.
The velvet bean and beggarweed have been recommended by Rolfs,?
of the Florida Agricultural Experiment Station, who has also pointed
out the value of crab-grass in a plan of rotation for reducing the num-
ber of nematodes. Thus, he found the nematodes far less abundant
the next year after an infested field was allowed to grow up to crab-
grass for one year.

The following rotations were planned by the writer for his work at
Monetta, S. C., there being four plats measuring, respectively, 0.152,
0.217, 0.217, and 0.166 acre:

TasLE III.—Rotation of crops planned for four experimental plats at Monetta, S. C,

Season. Plat 1. Plat 2. Plat 3. Plat 4.
Whiter: oo... Abruzzes rye..-.... Abruzzes rye...... Virginia winter oats...) Virginia winter oats.
Summer....... Beggarweed......- Velvet bean.......| Velvet bean........... Beggarweed.

This experiment was planned for three years. It was begun in the
fall of 1905. It was planned to keep careful records of all yields, etc.,
but in some cases the records are lacking. Unfortunately, the soil

1 Webber and Orton, 1902. 2 Rolfs, 1898.
Al

66 ROOT-KNOT AND ITS CONTROL.

proved so very poor for the oats that forit was substituted Abruzzes
rye in succeeding years. Once each yearthe land was fertilized with
the special commercial fertilizer previously mentioned at the rate of
500 pounds per acre.

The grain was harvested when mature, thrashed, and measured.
As soon as the land could be put into proper condition the beggarweed
and velvet bean seed were sown. In October a measured part of each
field was carefully mowed and the vines cured to hay and weighed, thus
permitting an approximate estimate of the actual yield per acre. The
erain was sown as soon as the hay crop was cut and the land prepared.
Unfortunately it was impossible, in addition to the substitution of rye
for oats, to carry out the rotation just as planned, for in 1907 the beg-
garweed seed obtained germinated so poorly that those plats were
resown to velvet beans, as it was then impossible to get good beggar-
weed seed.

In the summer of 1908 across the south edge of the field rows of
tomatoes, beans, okra, and New Era cowpeas were planted to test the
degree to which the nematode infestation had been reduced by two
years of these rotations. In the spring of 1909 another strip was
sown to the same four kinds of plants, the remainder being planted with
two varieties of cotton, viz, Triumph and Columbia. A similar area
to the north of the rotation fields was also sown to the same sorts of
cotton, while to the east was a field of Peterkin cotton belonging to a
renter and not planted with reference to the experiment. The choice
of the field to the north was made through an unfortunate misunder-
standing. It was not discovered until the planting was done and the
plants above the ground that that field too had undergone somewhat
of a rotation, viz, 1906, cotton; summer of 1907, Iron cowpea; winter
of 1907-8, rye; summer of 1908, Iron cowpea; winter of 1908-9, rye.
The field to the east, which was sown to Peterkin cotton, was in cotton
for the third successive season.

The experiments were further interfered with by torrential rains
which were harmful in two particulars, viz, they washed out much of
the cotton and brought soil from nematode-infested fields and depos-
ited it on parts of the rotation plats.

217 : ,

CONTROL OF ROOT-KNOT. 67

The yields on the plats were as follows:

Taste IV.— Yield of crops on four experimental plats at Monetta, S. C.

Season and year. Crop. Actual yield. | Yield
per acre.
Spring of 1906.....-. {gets Oa is Gc Sa a come OE ce cad a hoi oe pashels | PN OS ore Bila Gk 549
f Noch HeHMnay. (Hale. pedi, DEI corms: About 4, 900 11, 300
Fall of 1906.........| (Regzarweed ayia She aber as etek gst toe eee dos: About 1,575 5, 000
Spring of 1907...... Revie Re Stee 80s OS ea te Se 8 I eS bushels. - 104 14
Fall of 1907 \f Vi ay et bean hay on own plat................-- ounds..| About 1,600 3,700
tac \Velvet bean hay sown late on beggarweed plat ...do....| About ae 2,300
Spring of 1908.....- [REV.Gk, eee Eee Ree REARS eee A) SRE DOR bushels 1. 01 14
lyVelvet bean hay.......-.-- SOI Fes get Stes pounds..| About 3, gin’ 8, 850
oe of 1908. ......-- {esearw {Sea TCN pape BA Od ARR a> TMS TEN GR a Be do....| About 560 1,770
Spring of 1909...... IR yieiey eee eee es cee Sas he eee SA eee ita (ee eee ora eee tine aatae eiciale

1204 bushels on 14 acres; therefore estimated at 104 bushels for that field, 0.752 acre.
2 Cut before ripening to allow cotton to be planted.

At the prices current at Monetta, S. C., for hay (about $18 per ton)
and grain ($3 per bushel in 1909 for seed, but here estimated at $1 per
bushel) the value of the hay produced in the three years amounted to
about $117 and that of the grain to $22.50, a total of $139.50, at the
rate per acre of $156, $30, and $186, eee ie an average of $62
per acre per year. While these yields are probably considerably more
than enough to pay for working the land and the rent of the land
besides, as well as payment for the seed, velvet beans having cost about
$4 per bushel, it must not be concluded that the experiment was a
failure in that the yields were not greater, for the primary purpose of
the rotation was to reduce the nematode infestation while improving
the land, or at least keeping it from deteriorating, and yet to make
enough money to pay for the labor and seed used.

To test to what extent, if any, the land was improved was the pur-
pose of planting a plat of cotton at the north of the rotation plat.
Unfortunately, so many plants in each section were washed out by the
heavy rains that a very poor stand was obtained, with the result that
the yield per acre on the rotation and check plats could not be deter-
mined. The yields of the unginned cotton on the rotation plat were at
the rate of 1 pound of cotton for 6 plants of Triumph and 6.1 plants of
Columbia, while on the control plat to the north it took 6.9 and 7.25
plants, respectively, to make a pound. The Peterkin plants to the
east were not half as large and yielded even less.

The soil which at the beginning was very poor in humus, so poor
in fact that the rye would scarcely grow and the oats did not pay for
cutting, gave a much better appearing field of rye the following
years. The foliage of the cotton on it had a good color, showing that
the leguminous crops had increased the nitrogenous content of the
soil.

217

68 ROOT-KNOT AND ITS CONTROL.

From the standpoint of nematode extermination the results were
very satisfactory. Both in 1908, after two years of this rotation,
and in 1909, after three years, the susceptible plants on part of the
plat remained free from root-knot except as specified below. These
plants were, as in previous tests, tomatoes, okra, beans, and New
Era cowpeas, all extremely susceptible to root-knot attacks. Sev-
eral rows of each were planted in 1908 along the southern edge of
the plat, and in 1909 on the part just adjacent to that on the southern
part of that portion’ of the field which had had a rotation of three
years. Every plant was carefully dug up and all its roots examined
after freeing them from the adhering soil. Every such plant was
recorded as free, slightly affected, or seriously affected, a separate
record being kept of all the plants in each hill.

The field slopes very gradually toward the south from higher,
somewhat nematode-infested land on the north. Two slight de-
pressions lead somewhat diagonally from the northwest to the south-
east. In the spring of 1908 and again in the early summer of 1909
Monetta was visited by torrential rains which flooded and very badly
washed the fields. Considerable soil from the fields to the north,
and especially the badly infested field to the west, was washed down
these depressions, settling on them and in the lower (southern) edge
of the rotation field. Where these deposits of dirt occurred, and con-
fined to these areas, some of the plants showed more or less nematode
injury, most near the middle and least along the edges of the depres-
sions. Furthermore, a few plants at the edges of the field, 1. e., at
the east and west ends of the rows, showed nematodes where they
were probably introduced from the adjoiming land in cultivating,
plowing, etc. All the rest of the plants remained nematode free,
although this field was badly infested before the experiment began.

In accordance with suggestions of the writer, Mr. A. D. Jackson,
of Denison, Tex., made some rather similar experiments, using Iron
cowpeas and rye as his rotation. Certain fields were very badly
infested, so badly, indeed, that the crops on them were almost a
total failure. By growing the cowpeas two seasons with rye as the
winter crop the nematodes were so: reduced in number that only
20 hills of cantaloupes out of half an acre were affected with root-
knot and the crop of melons was excellent. Under date of July
10, 1909, Mr. Jackson wrote as follows:

T am well pleased with the Iron pea. While I have not eradicated the pest entirely
by growing the pea two seasons, I have enriched my soil, have grown a large crop of
feed, and the succeeding crop of vegetables has not in any case been materially af-
fected (by nematodes).

In Mr. Jackson’s fields the writer’s and Mr. Jackson’s conclusions
were that the few nematodes surviving were those that were pro-

217

FREEING A FIELD FROM ROOT-KNOT. 69

duced on the few weeds whose presence it was impossible absolutely
to prevent in the cowpeas. Thus, the weed known as careless weed
(Amaranthus sp.) was found to have root-knot in the field of Iron
cowpeas the second season these were grown.

Mr. Jackson also made the experiment of using summer fallow in
combination with winter rye, as follows: The preceding crop was
taken off the summer of 1906, being badly knotted. The field was
then kept in bare fallow from August, 1906, until the fall of 1907,
when it was sown torye. This was turned under when about mature,
and in July, 1908, the field was sown to tomatoes (which are especially
‘susceptible to root-knot). A fine crop of tomatoes resulted, the
only nematodes present being in a small part of the field where Irish
potatoes were badly attacked in 1906 and where volunteer potatoes
came up in 1907. The remainder of the field remained free the
succeeding year also (1909).

Prof. P. H. Rolfs* recommends letting the field grow up to crab-
grass (Syntherisma sanguinalis) after the crops are removed, first
taking up and burning or otherwise destroying the plants to avoid
infection from them. According to him this method when used even
for only one year greatly reduces the number of nematodes present.
Dr. Neal? recommended the use of beggarweed, Japan clover, or
Mexican clover. Regarding the latter the present writer knows
nothing, but the first two are practically, if not entirely, immune
and so ought to be valuable for this purpose.

This method was used with complete success by Schroeder? in
Germany against the stem nematode (Tylenchus dipsaci) after all
other practicable methods had failed. He planted infected fields for
a series of years with crops not susceptible to the nematode. After
this period the fields gave again their normal yields of susceptible
plants.

RECOMMENDATIONS FOR FREEING A’ FIELD FROM ROOT-KNOT.

In view of the results of the experiments described, the writer
would make the following recommendations for freeing a field from
root-knot. If the situation is one where the winters are cold and
cool weather sets in in October, it will not be necessary to give
attention to the subject during the fall and winter or in the spring
before the ground begins to warm up. Under such conditions it
would probably suffice to plow the land in the autumn, so as to have
it in good condition for as early planting as possible in the spring.
In the spring the field should be kept free from vegetation by cultiva-
tion or harrowing until the ground is warm enough to plant cowpeas.
The field should then be planted thickly with Iron cowpeas, this

1 Rolfs, 1898. 2 Neal, 1889. ® Schroeder, 1902.
217

70 ROOT-KNOT AND ITS CONTROL.

variety being usually sufficiently resistant to the root-knot to permit
its use for this purpose. In the fall this can be cut for seed or hay.
The ground should then be plowed up and the process repeated the
next season. Except in exceedingly bad infestations, two seasons
devoted to Iron cowpeas should be sufficient to free the land from the
pest. If desired, some winter grain, preferably rye or perhaps wheat,
may be sown in the fall, the cowpeas not being planted until the crop
is harvested early the next summer, following them by grain again.
Where the weather remains warm rather late in the fall it would be
desirable always to do this and so prevent the growth of weeds
which might harbor the nematode in the fall and winter. Where
the summer is long enough, velvet beans or Florida beggarweed are
perhaps preferable to cowpeas, as they give a denser growth that more
completely smothers out all weeds. Special care must be taken that
in the summer time no weeds are allowed to grow in the field, as it
will be seen by reference to the list of susceptible plants that many
of the common weeds harbor the nematode. Their presence in the
field, therefore, would serve to perpetuate rather than kill the
nematode. ;

Where practicable, the surest results can be attained by keeping
the ground absolutely bare of all vegetation for two years. This can
not be done on some soils, owing to the danger of the destruction of
humus by the hot sun or of washing by heavy rain.

Where the field is free from roots of perennial plants which might
shelter the pest and is so situated that it can be submerged easily
for long periods, it may pay to flood the land for three or four weeks, or
perhaps during the winter. This would be impracticable except in a
few locations. Furthermore, in many soils it would leach out all the
plant food and make the soil poor, but where an impermeable layer
will hold the water and keep it from leaching out it is conceivable
that this method might be found very satisfactory. A short period
of flooding or attempting to do this while the soil contains perennial
roots containing the nematode will hardly prove successful.

In the irrigated districts of the West, special care should be taken
to avoid the introduction of this nematode into lands devoted to
potato raising. To this end only perfectly sound, clean potatoes
should be used; no potatoes from suspected regions should be planted,
even should the individual potatoes appear perfectly healthy, with-
out a preliminary sterilization with formaldehyde solution to destroy
any nematodes present in the adhering soil.

Should none of the foregoing methods be feasible, high fertiliza-
tion, especially with that element (potassium calcium or phos-
phorus) which is most nearly deficient in the soil, will prove helpful,
although it will not kill the nematodes. When, as is often the case in

217

BREEDING STRAINS RESISTANT TO ROOT-KNOT. yar

the sandy soils of the southern United States, the soils are already
deficient in potash, rather strong applications of some of the potash
fertilizers—for example, kainit, potassium magnesium carbonate,
sulphate of potash, ete.—are very helpful. Care should be taken
not to apply enough to prevent the germination of the seed.

BREEDING STRAINS RESISTANT TO ROOT-KNOT.

As already mentioned, Webber and Orton have shown! that the
Tron variety of cowpea is practically immune to root-knot and wilt
(Neocosmospora vasinfecta), while most other sorts are exceedingly
susceptible to both diseases. The latter investigator has continued
his breeding experiments, using the Iron cowpea as one of the parents,
and has produced several varieties more prolific than that sort in
which the resistant characteristics are present. Similarly in the
breeding of tobacco, Shamel and Cobey? obtained a strain resistant to
nematodes. Certain sorts of figs—for example, Celeste and Pou-
lette—are said to be less subject to injury by nematodes than other
kinds. Among grapes, so far as the writer’s observations go, the
Old World species (Vitis vinifera) seems to be especially liable to
injury by root-knot, although the different sorts vary greatly in their
susceptibility. Thus, Zinfandel and Muscat appear very subject to
this trouble, while Sultanina (erroneously called Thompson Seedless)
is apparently not so easily injured. Some of the phylloxera-resistant
hybrids and pure American sorts are practically immune to root-
knot as well as to phylloxera, although some American sorts are quite
badly affected by the nematode. These observations of the writer
are confirmed by Lavergne, who states * that the European varieties
are very susceptible to Anguillula vialae, as he calls the root-knot
nematode, while those of American origin that are resistant to
phylloxera are also resistant to root-knot. Of the watermelon-
citron hybrids bred by Mr. Orton with resistance to wilt as the main
aim, it was found by the writer that of one strain only 4 out of 333
plants showed root-knot, i. e., 1.2 per cent, while in two other strains
28 and 51.9 per cent, respectively, showed root-knot. The presence
of such marked differences shows that it would be entirely feasible
to breed a watermelon variety that would be practically immune to
root-knot as well as to wilt. Bouquet de la Grye* points out that
Coffea liberica is less susceptible to root-knot than C. arabica and
recommends grafting the latter upon the former. To obtain a firm
union, this must be done by an approach graft with seedlings.

Simple selection can be and ought to be practiced by everyone who
erows his own seed; more complicated breeding work, unless per-

1 Webber and Orton, 1902. 2Shamel and Cobey, 1907. 3% Lavergne, 1901. 4 Bouquet de la Grye, 1899.

PAT |

72 ROOT-KNOT AND ITS CONTROL.

formed by men who can devote considerable time to it, hardly pays
for the time and expense required.

In carrying out simple selection we must remember that no new
characters are originated by this method. We simply select and
strive to fix in one strain certain characters that are present as
variations in the plants we are working with. Thus, if we find in a
field badly infested with nematodes that a certain proportion of the
plants are free from root-knot while the rest succumb, it would
probably pay to begin selecting seed from the unaffected plants. It
is better still if we can inbreed or intercross similar resistant plants.
On the other hand, resistance to nematodes seems sometimes net to
be one of the variations occurring in a plant. Such a plant can not
be selected, as there is no foundation on which to build. However, by
crossing it with some nearly related nonsusceptible sorts, some of the
progeny may possibly show desirable qualities of resistance while at
the same time preserving the best qualities of the parent sorts.

In all such breeding it must be borne in mind as a very important
principle that this work should be done in badly infested fields. If
naturally infested fields are not available, provision should be made to
do this work where the disease is abundant.

No attempt will be made here to describe the methods of selection
or hybridization. These are known to all seed growers and breeders.
They can be found described in detail in many publications.

Every farmer ought to be able at least to carry on this simple
selection: When any plants in an infested field show special vigor and
freedom from root-knot they should be marked and the seed collected
before the main crop is gathered. This should only be done, how-
ever, if these resistant plants are also up to standard in all other
features.

SUMMARY.

(1) The disease known as root-knot, characterized by enlargements
of the roots and often leading to the death of the plant affected, is
caused by a nematode (Heterodera radicicola (Greef) Miull.). This
was probably originally native in the Tropics (of the Old World 2),
but has spread into nearly every part of both Temperate Zones.

(2) The plants recorded as more or less subject to attack number
almost 480 species and varieties, including nearly all of the larger
families of flowering plants. Probably many more are actually
susceptible, but have not been reported yet as hosts. Most of the
important field and garden crops and ornamental plants are more
or less subject to root-knot.

1 Hays, 1901; Bailey, 1906; Orton, 1909; Reed, 1909; Salmon, 1907; Spillman, 1909; Wilcox, 1903; Oliver,
1910.
yh iy ¢

SUMMARY. 73

(3) The life cycle of this nematode, from egg to egg, may take place
in four weeks, or longer, depending upon the temperature of the soil.
The larval stage is that in which entry into the host takes place.
It then becomes motionless and soon enlarges and undergoes a sort
of metamorphosis, the males eventually recovering the original
worm shape, while the females become pear or flask shaped and very
much enlarged in their transverse dimensions. Each female lays
500 or more eggs. The winter is passed probably most frequently
in the larval stage in the soil, but in the case of galls on perennial
roots the nematodes may overwinter in these in a more advanced
stage, even as practically mature and perhaps already fertilized
females.

(4) For the rapid multiplication of the root-knot nematode the
following conditions are necessary: (@) A certain degree of warmth
of the soil. Thus, in southern Florida this nematode is active the
year round, in part of South Carolina the active season is from
April 20 or May 1 to the middle or end of October, while farther
north the period is still shorter. (6) Loose-textured soil. Only
sandy or at least light soil is favorable to its spread. (c¢) Moisture.
The drying out of the soil is frequently fatal to the nematode and in
any case prevents it from doing any harm. Apparently the moister
the soil as long as it is well supplied with air, the more favorable it
is to the nematode’s development. However, wet soil, i. e., soil in
which the air spaces are filled with water, is at length fatal to the
nematode. (d) Food supply. The larve are able to exist in the soil
for more than one year, but apparently not for two years, without
the presence of living plants into which to enter. They are apparently
unable to develop beyond the larval stage unless they enter a suitable
host plant.

(5) The nematode is distributed in several ways: (a) The
larvee move through the soil by their own motion, but the distance
traversed thus is probably not more than 6 feet or so a season.
(b) They are carried from field to field in the earth clinging to imple-
ments, the hoofs of animals, the shoes of laborers, wagon wheels, etc.
(c) They are conveyed in the soil that is washed from one field to
another by heavy rains, a very common mode of distribution of this
pest. (d) Itis possible that heavy winds may carry larve or eggs with
the soil blown from one field to another, but probably most would be so
dried out in the process that this is not much to be feared. (e) They
are introduced into new places in the roots or in the dirt adhering to
the roots of nursery stock, in rooted cuttings, potted plants, etc.,
especially those of the peach, grape, fig, mulberry, potato, ginseng,
etc.; also in the dirt in which some seeds are packed. (jf) They are

217

74 ROOT-KNOT AND ITS CONTROL.

sometimes brought to a field in manure if the manure pile has stood
on infested soil.

(6) The following methods of control in greenhouses and seed beds
may be used: (a) The most efficient method is the use of live steam
at fairly high pressure. The steam is forced through a system of per-
forated pipes laid at the bottom of the bed or bench. (6) The old
infested soil may be entirely removed and the benches thoroughly
cleaned out. ‘Then noninfected soil may be put in its place. This
method is not advisable in regions where the nematode occurs out
of doors in the vicinity. (c¢) Infected soil, when it is desired to save
it and steaming is impracticable, may be freed by allowing it to lie
through the winter in a place where it will be exposed to alternate
freezing and thawing, and especially to drying. (d) Soil containing
perennial plants can be nearly if not quite freed from nematodes by
the use of an abundance of a solution of formaldehyde (1 part of com-
mercial formaldehyde to 100 parts of water). This solution is fatal
to many plants and can be used only with great caution.

(7) For the control of the nematode in the field where the land is
occupied by perennial crops no entirely satisfactory chemical applica-
tion can be recommended. Places where trees are to be reset should
be freed from nematodes by the use of carbon bisulphid at a rate of
3 or 4 ounces per square yard placed in about nine holes per square
yard, these holes being about 6 to 12 inches deep and to be filled with
dirt as soon as the chemical is placed in them. Carbon bisulphid can
not be used with safety around living trees. Flooding the land seems
to be unsatisfactory, as flooding long enough to kill the nematodes
is usually fatal to the trees. High fertilization and constant culti-
vation to induce growth often so help the trees that they are able, as
it seems, to outgrow the trouble, the roots either penetrating to
levels where the nematodes are less abundant or being formed faster
than the galls can be produced. Avoid growing susceptible cover
crops, like the ordinary nonresistant varieties of cowpeas, for exam-
ple, for these multiply the nematodes in the soil manyfold. In pre-
paring the land for setting out a perennial crop the soil should be
freed from nematodes by the use of the methods suggested below.

(8) For land infested with nematodes and not bearing a perennial
crop, the following methods may be recommended: (a) Keeping
the land free from vegetation of all kinds for two years. This is
the most effective method, but it is not practicable in many cases.
(6) Planting the land to nonsusceptible crops for at least two (perhaps
better three) years, using in the winter small grains, such as wheat,
rye, or oats, and in the summer the velvet bean, Florida beggarweed,
the Iron cowpea, or even peanuts, scrupulously destroying all weeds
that might harbor the nematodes. (c) Making heavy applications of

217

SUMMARY. 15

fertilizers, especially those containing potash, except where the soil
already contains this in abundance. This treatment often reduces
nematode injury greatly. (d) Flooding the land for a period of
some weeks. (¢) Where rain is not likely to interfere, plowing and
allowing the soil to dry out for several months. (f) Preventing, by
the use of embankments, ditches, ete., the washing of soil from infested
fields to the field which it is desired to free from the pest. The intro-
duction of the pest by tools, wagons, farm animals, etc., should be
avoided. The trap-crop methods and the use of various chemicals
have not proved practicable as tested by the writer. The former
needs, perhaps, further trial.

(9) The ideal procedure is to develop nonsusceptible strains of
plants, so that the expense and trouble of exterminating the pest
may be avoided. Such strains may be obtained by the selection
of more resistant plants or by crossing with resistant strains followed
by the careful selection and breeding of the progeny.

Norr.—While this bulletin was in press, there appeared a note in
Science,! by L. N. Hawkins, describing the occurrence of Heterodera
radicicola in the roots of Typha latifolia near Ithaca, N. Y.

The writer has just received from Mr. G. L. Fawcett, plant patholo-
gist of the Porto Rico Experiment Station, Mayaguez, P. R., speci-
mens of the bark near the base of a 15-year-old coffee tree. Mr.
Fawcett writes: ‘The disease is characterized by a roughening of the
bark at the base of the coffee tree, extending from the surface of
the soil upward for a foot or two. No doubt it injures the tree, but
such injury must be slight. I have seen no sick tree the bad condi-
tion of which could clearly be ascribed to this nematode; only a
small percentage of the trees in any plantation are infested. It is
perhaps more common in moister and more shady places. Older trees,
say, those of 15 years or more, are the only ones noticed with this
disease.” The living portion of the cortex was found to be very
densely infested with mature females of Heterodera radicicola. It
seems probable that these nematodes must have passed upward
through the soft tissue of the cortex from some original infection in
the root. It is worthy of note that sometimes in herbaceous plants,
such as tomato, the writer has found nematodes 6 inches or more
above the level of the ground within the cortical tissue of the stem.

1 Science, n. s., vol. 34, no. 865, July 28, 1911, p. 127.
217

BIBLIOGRAPHY.

Papers seen by the author are indicated by an asterisk (*).
All not so marked have been accepted on the authority of other
writers. Only those titles to which reference has been made in the
text are included in this list. This is not, therefore, a complete
bibliography of all papers pertaining to this nematode.

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Eelworm in vine roots. Journal of Horticulture, London, ser. 3, vol. 38, Janu-
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* ATKINSON, GEORGE F. A preliminary report upon the life history and metamor-
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caused by it upon the roots of various plants. Science Contributions from the
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ie Diseases of cotton, Bulletin 33, Office of Experiment Stations, U. S. Dept.
of Agriculture, 1896, pp. 279-316.

*BarLey, L. H. Some troubles of winter tomatoes. Bulletin 48, Cornell Agricul-
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<3 Plant-breeding; being six lectures upon the amelioration of domestic plants,
4th ed., New York, 1906, 483 pp., illustrated.

Baker, H. Employment for the microscope, London, 1753, chap. 4, p. 250.

Barer, ©. A. A tea-eelworm disease in South India. Department of Land Rec-
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pp. 227-234, 3 pls.

* BERKELEY, M. J. Vibrio forming cysts on the roots of cucumbers. Gardeners’
Chronicle, London, 1855, p. 220, 2 figs.

* BouqUETDELAGRYE. La régénération des plantations de caféiers dans les Antilles.
Bulletin des Séances de la Société Nationale d’Agriculture de France, Paris, vol.
59, 1899, pp. 683-687.

* BREDA DE Haan, J. vAN. Levensgeschiedenis en bestrijding van het tabaks-aaltje
(Heterodera radicicola) in Deli. Mededeelingen uit ’s Lands Plantentuin, Bata-
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* Wortel-ziekte bij de peper op Java. Verslag omtrent den Staat van ’s
Lands Plantentuin te Buitenzorg over het Jaar 1904, Batavia, 1905, pp. 21-39.

* Brick, ©. Bericht tiber die Tatigkeit der Abteilung fiir Pflanzenschutz fiir die
Zeit vom 1 Juli, 1904, bis 30 Juni, 1905. Jahrbuch der Hamburgischen Wissen-
schaftlichen Anstalten, vol. 22, 1904, p. 299-311. 1905.

Casati, ©. L’Heterodera radicicola Greef nelle radici del nocciuolo. Giornale di
Viticoltura e di Enologia, vol. 5, 1898, p. 4.

CurrrtoT, J. La maladie noire des clématites 4 grandes fleurs causée par |’ “‘ Hete-
rodera radicicola Greeff.’?! Semaine Horticole, 1900, pp. 535-537. Bulletin de la
Société des Sciences Naturelles de Saone-et-Loire, n. s., vol. 6, 1900, pp. 128-134.

1 The name of Greef is misspelled, as shown in the title of the paper cited.
PA br

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* Root-gall. The Agricultural Gazette of New South Wales, September, 1901,
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* Cornu, Maxime. Sur une maladie nouvelle qui fait périr les Rubiacées des serres
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* Cramer, P.J.S. Nematoden in ropusta-koffie. Teysmannia, vol. 17, no. 3, 1906,
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1892, pp. 90-172.

* Darpoux, G.,and Hovarp,C. Catalogue systématique des Zoocécidies de I’ Europe
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» vue de Vhistoire naturelle et de l’agriculture, Mémoire couronné par l’institut
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* Enfermedad radicular de la vid causada por la Heterodera radicicola 6 Angui-
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* Kutun, J. Die Ergebnisse der Versuche zur Ermittelung der Ursache der Riiben-
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vol. 2, no. 6, 1886, pp. 163-175. (1886-1.)
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91294°—Bul. 217—11——_6

80 ROOT-KNOT AND ITS CONTROL.

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217

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pp., 21 figs.

217

DESCRIPTION OF PLATES.

Puate I. Stages in the development of Heterodera radicicola (Greef) Miill., etc. Figs.
1 and 2.—Eggs in two different stages of development, X 350. Fig. 3.—Larva
immediately after escaping from egg, x 105. Fig. 4.—Anterior portion of
same, X 410. Figs.5 to 8.—Developmental stages of larvee before sexual differen-
tiation is apparent, 105. Fig. 9.—Molt in which sexual differentiation first
becomes apparent, female nematodes approaching sexual maturity, x 105.
Fig. 10.—Sexually mature female nematode, a somewhat more advanced stage
than shown in figure 9, X 105. Fig. 11.—Posterior portion of sexually mature
female nematode somewhat compressed, X 220: a, Anal opening; b, alimentary
canal; c, genital opening; d, vagina; e, e, uteri; f, f, ovaries. Fig. 12.—Egg-
bearing female nematode, X 47: a, Alimentary canal; 6, loop of uterus; ¢,
genital opening. Fig. 13.—First visible stage in differentiation of the male
nematode (compare with fig. 9), X 105: ¢, t, Testis. Fig. 14.—Mature male still
within larval skin, X 85. Fig. 15.—Mature male, X 85. Fig. 16.—Anterior
portion of adult male, showing spear and peculiar structure for guiding its
movements, X 930. Fig. 17.—Larva entering root of clover, x 100. Fig. 18.—
Larva of Heterodera schachtii Schmidt just escaped from egg (compare fig. 3),
X 105. Fig. 19.—Anterior portion of same, X 435.

Puate II. Fig. 1.—Root-knot on sugar beets grown at the Subtropical Laboratory,
Miami, Fla. 1907. Photographed by E. A. Bessey. Fig. 2.—Root-knot on
squash, from Beeville, Tex. 1904. Photographed by W. A. Orton.

Puate III. Fig. 1.—Root-knot on carrot, from Morrison, Ill. 1908. Photographed
by W. W. Gilbert. Fig. 2.—Root-knot on red clover grown in a pot of sterilized
soil inoculated with affected roots of Ipomoea syringaefolia, Subtropical Labora-
tory, Miami, Fla., 1908. Photographed by E. A. Bessey.

217

ais ei

Bul. 217, Bureau of Piant Industry, U. S. Dept. of Agriculture. PLATE I.

STAGES IN THE DEVELOPMENT OF HETERODERA RADICICOLA (GREEF) MULL., ETC.

Bul. 217, Bureau of Plant Industry, U. S. Dept. of Agriculture. PLATE II.

Fic. 1.—ROOT-KNOT ON SUGAR BEET.

Fig. 2.—ROOT-KNOT ON SQUASH.

Bul. 217, Bureau of Plant Industry, U. S. Dept. of Agriculture. PLATE III.

Fic. 1.—ROOT-KNOT ON CARROT.

Fic. 2.—ROOT-KNOT ON CLOVER.

mepey.(Cr.,0n Control of root-kMOpe osc .\iem see ene. Bask Use ee 3 55-56, 76
Manica German: Hast: Occurrence Ol TOOL-KNOt: = 2 ssnsee soe aa anee ate tee te Sete 23
OCCUTTENCE OF TOOt-RMOG I. too aise eine cine wine BEM ede 23, 25, 38, 42
Soubnr. occurrence of rogt-knOti 22-2252. <csc05 ae a hs ee ES 23, 38, 42
Agrostis alba. See Redtop.
AUT ACONnGiilONSs Ta VvOraplestomootekn ote eee tse es fal fa cteresieia daisies Aas 42-44
See also Moisture, and Temperature.

mianama. ‘occurrence of root-knot: 9.2) -2e2es sss. + cae. Fe Lis Aa os: 23, 64

mlexondria. Va. iInvestications!ol reot-knots - =... ssuydeee2 5s emeiis Joere as. 02 47

Miia asnsceptibility to\root-KnOtioe. 55.2. 4s0ch's eee ts ce Ue Sondet Seek 17, 24, 43

ml geria soceurrence of root-knots sas 2.6 yadse26 20. Ieee Jake ee ed 23

Amaranthus spp., susceptibility to root-knot.............--..--------- Kyaw aie 12, 69

Ammonium silicofluorid, application for control of root-knot............-.-.--- 55-56

sulphate, application for control of root-knot.......--.-.-- 54-56, 57, 58

Andropozon spp., susceptibility to root-knot..-..c.00sso0 su ogediieee 2 ee 12, 21

Anguillula spp., synonyms of parasite causing root-knot..............------- 8,9, 71

Animals arency: in spreading root-knot.-. 2-2 ---26-.04doUdsusrb se shauely.- 38,73

ip melanchtis sp. uvilaliiyutestsy 22598. 5 fs oe, Jess's Sole Sv wa ase set 30

AUD ES RNIBCe PLllol lity bO TOOt-KaObs <vastme seae Mos eee ONS PaaS Sua wel oe BSS 17, 24

Pr pentine. occurrence or TOOt-KNOb. cs <--> Sos sede 2 Os SL AO Abe «ahs te. ALOR4ABE OL

Anan occurrence of root-knots 2. 98. .to Lissa .d eee dele. «os 23, 24, 38, 42, 49, 59

PERE OCCUITCHCO:OL TOOL-KNOKs <2) 5si)- Foes ALO Sites bia est 2

MBtaAMOrenIreuCe OL TOOt-KMOLS 2.02.58 ec2 <,- oSS s ulate CS See 23, 25, 49

MEpataais, Susceptibility, to root-Knote.20.0 -)..2e8salut ye. A Eee ee 12, 38

iKimson. Ge. Hon TOot-KnObs2s..os44<c 92. 3, 165,17; 18,195 20532) .35, 365.76

MU At LAA OCCULTEN CE OL TOOL KINO Letee eee iene a ley ee epee ee ea, ever 23

ATISUTI AT OCCUBLENCE Ol TOO KM Olesen tere rete ane Saal gale eI SA cs 23

Bailey; LL: H., on methods of control of root-knot.:- 22622282 5. Sse Weis 43, 72, 76

iBakerrheOonoccurrenceronhme»matodesucs sans so. 2 serene ate AO ope, 30, 76

Barbers 2 Aeon occurrence: of root-knot-eyss2 a2 See ae aes: 13, 14, 20, 76

Barc ausceptibuity torcotsknot.. 50... le tae 8! we Seek Sok Seo. 16, 21

Beaded root-knot. See Root-knot, beaded.

Bean, experiments for control of root-knot..-...-..---------- 54, 55, 56, 57, 62, 66, 68
OTSe | SUSCEPUULLY tO, LOOL-KMOt. a Wir se Sos eels aoe we Ben icliclees 4 jes see 20, 22
velvet, susceptibility to root-knot......................-.. 20,21, 65-67, 70, 74

Beet, sugar, affected with root-knot, analyses, study..........--------------- 40-41

nematode. See Heterodera schachtil.
BuSceptibility to rootsknot-)-s eee ees 232 12, 39, 40-41, 52, 57, 61, 82
tiredness, disease due to Heterodera schachtil...............---------- 61

Begegarweed, Florida, resistance to root-knot..............------- 17, 65-67, 69, 70, 74

Berkeley, M. Ji.,.on oceurrence of root-knot. ...-/.. 0.028 Ubasoe on PIS a es. 8, 14, 23, 76

Bessey, 1, A... in vesticationsof root-kmlot sss anseneese ule Ns 2S. 82

Bibltopraphy. partial,.of coot-kmObse.. uc neenes tees eee nae} eee oe oe 76-81

Bidens:spp resistance to Toot-kmotsice <6. x. sere ges cs Se OL a Wa neon 21

Big-root, variant name for root-knot...............2...- pa ke Aly C3 Vc aiid AT a 7

Bouquet de la Grye, on susceptibility of Coffea spp. to root-knot..........- 14, 71,76

rail hOCCUITeEN CCL OlTOOt-KMO bet eee Ey nae ete eee eee a 9, 23, 49

Breda de Haan, J. van, on root-knot..............- 11, 12, 13, 14, 16, 17, 18, 19, 54, 76

Breeding. See Root-knot, breeding resistant strains.

Bricks CP onvoccurrence Of LOOt- kn Ober a4 eet aa ema NaS oy Sure Lidar bUl ais 16, 76

Bromits'sehradern, resistance to root-kmot!)22-!.. 25.22.2002. selh. cede eens 21

Calcium carbid, use in experiments for control of root-knot..............---- 51, 54

Califorma occurrence: of) root-knot.. 22 ceee soe ae ees 23, 24, 36, 38, 42, 49, 59

Cane), sigdn susceptibility to root-knote ss. ose! SONA Wiel ae as HS 8, 19

217 83

84 ROOT-KNOT AND ITS CONTROL.

Page.
Cape Colony, ,oceurrence/of root-knot.. . .. ../-.-|- 22. ee ce es = 2 eee ome 23
Carbon bisulphid, use in experiments for control of root-knot.. 47, 49-50, 51-52, 53, 74
Careless weed. See Amaranthus spp.

Carrot, susceptibility to xoot-kmot) 2 ...2- 3c) SS oe eee eee 14, 82
Casali; 'C-. ontoccunrence of root-kmot . <2.) 2/4: eg ate on Cael ee emia ee acto 14, 76
Catalpa, susceptibility HO WOOe-KMNObS. LLL OSE EE RSE” ie es a 13, 22
Ceylon: occurrence orroot-kmot .5. 2. 5.<-2<'.02 ob see os 6 ee Pt 23, 49
Chambers, W. E., drawings illustrating root-knot nematode.................-- 28, 29
Chemicals, use in experiments for control of root-knot...........-.-.- 49-52, 53- 56, 74
CGhifflot, J.,.om occurrence of root-knot. .. . .. . s.:.-./9025 200 2 ees 14, 76
Chile; occurrence of root-knot... 5. -.../ 00 AAS 9, 23, 42, 61
China, occurrence of root-knot. . 2). 522. 2. sented eee ee Oe et ee es
Climate, relation to rootskmot 2. teal otra Se ee eee aoe 24, 42-44, 48, 73
Clover, Japan; resistance'to root-knot..... 2.2.2... 2/325 .9 a ee 16, 69
Mexican, employment for reduction of root-knot............--..-....-. 69
species resistant to rootsknot.. .......... 42a etus iw), ileal yO Ga 63, 69
susceptibility to\root-kmote: ose. soc. Dee 16, 17, 20, 22, 43, 69, 82
Chub=-root, waniant name formoot-knot: 222 22208 Vis pan NE ee ie ee aga 8
Cobb: Di Ay Hom root-kmot. (ceo ee ious ee: 9, 12, 19, 20, 28, 35, 38-39, 42, 61, 77
Cobey, W. W., and Shamel, A. D., on strains of tobacco resistant to root-knot - 71, 80
Coftee, susceptibility £0 TOOT sons ec Mucha 1 RMN 9, 14, 49, 50, 60, 71, 75
Colorado, occurrence of roobt-knob!t 20-2 YU) N99 Wek. OO Le a 24, 40
Connecticut, OCCUIrEeNnceof TOOt=KMOb AY TN EL, OS CPR ER 24
Corn; Indian,, resistance to. root-knotw..-. Shs eo) A te 21-22
Cornu, Maxime, on occurrence of root-knot........-.------ 8, 14, 16, 17, 19, 20, 21, 77
Cotton, relation to root-knot-......--- Spee rer eee ee CPA Geyer | de | 15, 66, 67
Cowpea, relation, to TOOt-kMOts 22 soe ejrreye cree 2, 23, 54-57, 62, 65, 66, 68-69, 70, 71
Crab-grass, susceptibility to root- knot Sectors ate aiiolatoe ae ele Neha ee Rae 21, 65, 69
Cramer /P.'J:.8., on occurrence of root-knot..01<.. 20k 2 Se 14, 77
Crops, nonsusceptible, rotations for control of root-knot..............-...-- 65-69, 74
perennial, root-knot, control infield -.5.025. 1082 eee 48-52, 74
trap, use im. contro! of root-knots~. + 2. cpy ae. 6 ee ISIS IO eee 61-63, 75
Cucumber, susceptibility to root-knot...2 <5. 2 22a Ot ae Pe 14, 22, 59
Dalla Torre, K. W. von, on occurrence of root-knot.........-.-----5.-2.--- 12,19) °77
Darboux, G., and Houard, C., on occurrence of root-knot......-.... 13, 14, 16, 19, 77
Davaine. iC. J.,/on occurrence) of mematodess.:4: 5/4... 225. occ eee emer 30, 77
Delacroix, Georges, on occurrence of root-knot........-.----.----.------- LUGS ANSE (7
Delaware, occurrence of root-knot.......-.-.-.-.-.--- eRe SAE S 1) APE EY TEER OR A ‘24
Dorsett,\P2 H., on oceurrence.ol mematodes: ies hive ty see ee nae eee 30, 77
Drying, effect on root-knot, investigations... . - 30, 37-38, 42-44, 45, 48, 60-61, 73, 74, 75
Ducomet, V., on occurrence of root- rlenot (iu ana dchcun Suan Ae eteere 19, 77
Dyke, W., ancontroliof rootckmnot,... ....... .asasleek Ws tence eel 56, 77
Hast indies) cccurrence of root-knot...)). ..)-2s2 eee ek ee eee 23, 25, 49, 54
Echinochloa frumentacea. See Millet, Japanese.
Eelworm, variant name for nematode causing root-knot............---------- 7
Egg of root-knot nematode. See Heterodera radicicola, egg.
Beypt, occurrence of root-kmot. ..Sc-dibes ascberseherl os 2s ee Ee eee 23
Elm;;Huropean, susceptibility to root-knot.<..: os: -J-<ssulelses - Ah28e See 20, 39
England, occurrence of root-knot:. 2. 2... 4485-20 hi wees ee 23
Escobar, Romulo, on root-knot infestation of watermelon............-.------- 40
Euchlaena luxurians, resistance to root-knot.........220+0.0see002eeeeeeeeee 21
Burope, eceurrence of root-kmnot....5..-2/... 1.2... Aepecece ee eee ee 23
European elm. See Elm, European.
Eustachys petraea, unaffected by root-knot .....-...-....2....-.-.222--+------ 21
Everglades, occurrence of root- AM Ob. ood seheweseec ps otRe Ee ee re 42, 59
Experiments, cross inoculation, for testing adaptation of root-knot nema-
fod@s 222252. ecece oss tota 5. sb eee eee. Be eee ee eee 22-23, 82
See also Root-knot, methods of control.
Fallow, bare, use in control of root-knot.......-...geeeseee= 2s =< = 0 64, 69, 70, 74
Fawcett, G. L., on root-knot infestation of the coffee tree. ......--..--------- 75
Fertilizers, use in control of root-knot in fields.......-.---..-.---- 52, 56-58, 70, 74-75
Fields, root-knot eradication and control, . .....Jegee-ters <)- -ctie-e eee 48-71, 74-75

217

INDEX. 85

Page.
Rieirelationso root-knote esis 24 15, 22, 23, 24, 36, 38, 49, 71, 73
Flooding, method of control of root-knot........------------- 42, 52, 58-60, 70, 74, 75
Florida beggarweed. See Beggarweed, Florida.
DEGURLENCCOLTOO LaKAIO tse en tee Rete ere ase ape ai aisioiave ois

11, 23, 25, 31, 35, 42, 43, 49, 51, 53, 57, 59, 60, 63, 64, 73, 82
root-knot investigation. See Miami, Fla.
Formaldehyde, use in experiments for control of root-knot.... 46-48, 50-51, 53-54, 74
Formalin. See Formaldehyde.

Hrance, experimonts for control of phylloxera.....:-.-5-.-52 2-22.52. 2262. 54
OCCUTFENCO OL TOOU- KO. 0. any ce eee iae aes aye Mag BOR A Le 23
Bank’ A.B. 'on root-knot.../..0..0. 0000 8, 12-20, 26, 37, 40, 41, 42, 43, 60, 62, 63, 77
Freezing. See Temperature.
Galloway, B. 'T’., on occurrence of root-kmot.-.. <2... =.= ..2)):=.- eee ae ene 44,77
Calis TooL-kiot, depth of eccurrence im soll: ope ee ks Soa sia inf gels oblate o's 41, 52
ra =ts/ hos 0 (0) 0 SRY Rat tora RE RR VR PIN AO NA CO) en ee ES 7-8, 39-41
Game, G;. -A:., On OCCUrrence: Of LOOt-KNO b=. <6 1). on aysiaiia = Cea =i A- = = = 13, 16, 17, 20
Gandara, Guillermo, on occurrence of root-knot..........-------- 18, 50, 51, 54, 61, 77
Gardens, in Florida, root-knot investigations. .....-.....---- 9-10, 31, 43, 51, 53, 55, 82
Ceoroia GECUIrenCe. OL TOOt-kMObaser sos ate eee to tocta ew Se es ss 23, 59, 64
German East Africa. See Africa, German East.
Germany, occurrence of root-knot or other nematodes. .......-.-..-- 8, 23, 26, 52, 57, 69
Gailbertw Wi. iW -,, On Studies. of root-knols.< 22.6 .<tas 2 sey onl se ets aS aie) y= Be 63, 77, 82
Gansene, occurrence of root-knobte): A422 eee cee: fee 2d es 22 18, 22, 24, 38, 43, 73
Gnaphalium purpureum, resistance to root-knot...-.-.-......../:---2----..-- 2
Golai, . A... on root-knot parasite of coliee. 1. 1... 2.2... 22225. - saws ctss 229, 60,77
Gransarelationto,controlot root-knot...). 92.2 sane 2k en 21-22, 74
See also Barley, Corn, Oats, Rye, Wheat, etc.
Gram seneen. susceptibility to root-knot.aue YIUh eta vest ea Poe Sk 18, 22
Grapevine, relation to root-knot..........----.... 21, 22, 23, 24, 36, 38, 49, 59, 61, 71, 73
Grasses; relation tovroot-knot-) 223. 52425226255 452225: 8, 11, 12, 13, 14, 15, 18, 21, 65, 69
Greets)... on, occurrenceloimnoot-knottes-s--2- oes aa eee 2 ae 8, 11, 15, 18, 19, 23, 78
Greenhouses, methods of control of root-knot...-.-..-....------------ 9, 24, 44-48, 74
Gvozdenovic, Franc, on occurrence of root-knot-....-..2..:.....2222-51...-4- 13, 78
Halsted,)Bs D.; onicecurrenceyorroot-knot.. 22.02.2082 nae. 22 SE). 2 T2919, 20 78
ieaiwileins,) 0.) Ni., on occurrence, ofroot-kmotssse. see eh fe See se es 75
Hee iWie NL. on plant breeding soy siseh etic MOSER AO Ao), SOE UE ie -Paks)
Helenium tenuifolium, resistance to root-knot..............-.:.-..-.---.+---- PAL
ennmesRrnst) onyroo tka tase a aaa esas Sete ere eens Senet un iaenen ee 18, 78
Heferodera, javanica, synonym of, EL. radicieola a, Su 4e8 SDN a 8-9
radicicola, cause of root-knot, life history, effects, etc... .-- 25-41, 72, 82
eOO4 MESCRIDLION 6 ce is Ay ie Cae eo 26-27, 73, 82
larva,,descrptionand habits.) 132.4224 - 27-32, 34, 73, 82
mature worms, descriptions sss F220 ese 32-36, 82
measurements of eggs, parts, etc..--.-..--.-.-- 26-29, 32-35, 37
Moline eee ee eee a ee eA Sy. 31-32, 34, 32
origimellehomes seer er eins nas tes sie seein eM ange Zot
ONERWIMbEING ee home eee as s,1 sors ss. a ais ete ia setae: 36, 73
similarity tole. schachtti. > $. 02262) 8, 27, 35, 36-37, 40-4
ENARO ONY COni is Oe epeaoeS Soke ao SES Ce ete Es MAE) or 8-9
See also Root-knot.
schachtii, cause of disease of the sugar beet.................---- ;
95, 27, 35-37, 39, 40-41, 52, 57, 58, 61, 82
Hacronyantiss, Ge onroot-knott i220 26 56 £R SE Se 2 eee weeny sine emotes 15, 78
Historical notes-onistudy of reotacnots: 225-66 ets os eee eee eee cele eos 8-10, 72
to lland occurrence Of ROOt=kmots se sneha eh hee ee See eee ere oe See 23
Hollrung, on the effect of potash on sugar-beet nematodes.......:......------ 57
GO MEN ea vialis: OF HOOT KINO Sacre ees ney te aie) eve ee ce ey se as ae 18, 78
Hordeum vulgare. See Barley.
Horse bean. See Bean, horse.
Host plants. See Plants, host.
Houard, C., and Darboux, G., on occurrence of root-knot.......-..-- 13, 14, 16, 19, 77
Huergo, J. M., studies on root-knot in Argentina..............-....--.-.- 42,61, 78
Hybridization, plant, authorities, note. ............ ae a me aig yl gegs, SA ay 72

217

86 ROOT-KNOT AND ITS CONTROL.

Page
Iggulden, IW ., On, ,conirolo@root-knot...2-6 oc cere ee eee See De eee 56, 78
Diligois, OCCULLemGe, Gi tOGe-KNOG.. 2... Ws \. isa pie tars ie ey aa ier ee 82
Implements, farm, agency im spread of Toot-knoh.. 2. ane -1- 5-4 pees yack a 38, 73
India, occurrence Ohrootmicnate oP! 0. uae ean 235,205 49, 54
I ndiana, OCCUITEREe Ol Oot eRe be. oe). 2 ise pe ee I. ee Oe emia ke eae 4,35
Inoc ulation, cross experiments with root-knot nematodes ............-......- 5083
Tntmduction te Wiles rr ee ear ad 7
Irish potato. See Potato, Irish.
Hinly, occurrence Onwoot-kmot. 08S 2. 2 ose bee Oe Aen tea he 23
Jackson, A. D., experiments for control of root-knot...............-...-.. 64, 68-69
Janse, JM ronlruerkaipee eos eo oe Soe re en eS ae ee 12, 17, 78
Japan, Gecurrenee of roct-kmobe< 0s 2.5.2... 022225222 ea eee 23, 25
clover. See Clover, Japan.
Java, occurrence of ODIs HOES See ve NA ITO EOE Be 8, 23
Jobert.<Cs/on,oceurrenceomroot-kmOt!seec. fee set ao eee ne eee a eee ee 14, 78
Johnson, J. M., assistance in root-knot investigations. ......................- 10
grass. See Andropogon.

Kafir, corn, resistance sto root-kmot.<.....7-8s 514 9S Se 21
Kainit,; application for control, of root-kmot)2 4... {0.29822 2299/9.222 56, 57, 58, 71
Kamerling, Z., om oceurrence|of root-knot. ys. 50). Ae PE ee ee 13, 78
Kentucky, probable presence: of'root-kmott 662i: 61 SS We 24
Ketter s):-Ji., sonsnoot-knote asc. 2 Suc br Se Sa Rea TE ee 20, 78
Kiihn, Julius, and Liebscher, G., on occurrence of sugar-beet nematodes... ... 61,78

on control of sugar-beet nematodes ......................-- 61, 78, 79
Laboratory, Subtropical. See Miami, Fla.
Lagerheim, N. G. von, on occurrence of root-kmot..........+--.---.2/2:+-. 15, 16, 79
Larva of root-knot nematode. See Heterodera radicicola, larva.
laverone) Gaston on-rootekm Otis 23 = 252 ccm -eej2 =f ae 9, 11, 18,42; 6, 74,79
Lemon, susceptibility to root-knot../.. 2b 5.5.) ..5- 2.0 SeGasehe-Ge See 11, 14
Lespedeza spp. (bush and Japan clovers), resistance to root-knot.-.........--- 16, 69
Lettuce: susceptibility to root-knot: ...... S22 se eate seeteies 1 (Ss eee ee 16, 22
Licopoli, G., on occurrence of root-knot-...- 22.4.2... 12, 13, 14, 15, 18, 19, 20, 21, 79
Liebscher, Ga and Kiihn, Julius, on occurrence of sugar-beet nematodes... .. él, 78
Lime, use in control.of noot-knot. |... -.. ..seddearse Sameera uae oe a 54, 55
Little’s soluble phenyl. See Phenyl, Little’s soluble.
Lolium. perenne, resistance to root-knot......-- --,-/.<<2esmsissbe Jone: See 2 ee 21
Iboosé,, J. 1:, on treatment of roses for root-knote: =4-454144 ee eee eee eee 47-48
Hotays Je ie. 400 OCCUITeENn Ce Oh TOO b= Kin O thee 5 io eee a ete ae 14, 79
Touisiana, occurrence of root-knot 2.25555 see so ee eee eee 23, 64
Lounsbury.C. P.; on:root-kiots 5 cp4aut 22 ej ek ee bee aes CAE 11, 18, 38, 42, 61, 79
Madagascan, Gecurrence of Toot-knGt 6263.5 steals = ane eee = ee 23
Macnus cb .. On TOOt-KNOG. saeco sani a Seale a eee eet 18, 79
Manure, infested, relation to spread of root-knot........-....------------- 39, 73-74
Marcinowski, Kati, list of plants susceptible to root-knot...-......-.------ 10;115 79
Maryland; occurrence Of foot-knOte. -. 2 oe es 2 ce eee ee eee res 24
May, J. N., on control of root-knot on greenhouse plants... ..-..-..--------- 8, 44, 79
Meloidogyne exigua, synonym of Heterodera radicicola..............----.-.-- 9
Mexico, occurrence Hise Tie a1 aaa an pagal iinet tad Veg aeenntO aot | 23, 40, 49, 61
Miami, Fla., TOOt-KNOL MM VesuiOntIONB. . -..-.c1. see eee ae 9-10, 31, 43, 51, 53, 55, 82
Michican. occurrence’ of TOOt-KiGi-o=--asace eo ease ee ae eee 24, 43
Millet, Japanese barnyard, resistance to root-knot.............--------------- 21
Millets, susceptibility to root-knots....-.2.-- 2 = 5... eee eee ee ee 13,2
Malo -resistance:-to root-knot:--.4- > =-. ccc ss- 6s Seeker eee ee eee eee Pal
Mississippi, occurrence of root-knot.-.......-.-5 2.5 sqasdqce 35 42 epee eee
Moisture eiect/om root-kn Ot. 4-nc ese Sac eee ee eee ee 42,73

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