Phyllosticta leaf spot, fruit blotch, and canker of the apple : its etiology and control

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UNIVERSITY OF ILLINOIS

Agricultural Experiment Station

BULLETIN NO. 256

PHYLLOSTICTA LEAF SPOT, FRUIT BLOTCH,

AND CANKER OF THE APPLE: ITS

ETIOLOGY AND CONTROL

By EMIL FREDERICK GUBA

CONTENTS OP BULLETIN No. 256

PAGE

THE DISEASE 481

Names Applied 481

Historical 481

Probable Origin 484

Distribution and Prevalence in Illinois 485

Plants Affected 487

ETIOLOGY 488

Morphology of the Pathogene 488

Pycnidia 488

Pycnospores > '. 490

Conidiophores 491

Mycelium 491

Nomenclature 492

Physiology 494

Cultural Characters 494

Factors Involved in Growth and Pycnosclerotia Formation 496

Spore Production in Culture 498

Spore Germination 500

Life History 505

Inoculation and Infection 505

Sources of Inoculum 506

Time of Infection 507

Conditions Associated with Natural Infection 517

Development of the Fungus 519

Varietal Susceptibility 526

Dissemination 528

CONTROL MEASURES 530

Historical : Methods That Have Been Advocated 530

Dormant Spraying 533

Experiments with Dormant Sprays 535

Effect of the Fungicide 539

Experiments with Summer Sprays 541

Summer Spraying : Conclusions 548

Other Aspects of Control 550

Soil Treatments 550

Pruning 550

Surgery 551

Protective and Preventive Measures 551

Selection and Location of Varieties 552

Recommendations for Control 552

LITERATURE CITED . . 554

PHYLLOSTICTA LEAF SPOT, FRUIT BLOTCH,

AND CANKER OF THE APPLE: ITS

ETIOLOGY AND CONTROL1

BY EMIL FREDERICK GUBAb

The increasing prevalence and seriousness of apple blotch in Illinois
and thruout the United States, and the inadequacy of present control
measures emphasize the need of detailed study of the life history
and habits of the causal organism, Phyllosticta solitaria E. & E. Since
the first published account of the disease on the commercial apple in
1902, valuable observations and isolated facts have been presented by
many investigators. Existing publications on the disease, however,
show a lack of knowledge of many important phases of nje organism
necessary for its successful control.

THE DISEASE
NAMES APPLIED

Before anything definite was known about apple blotch, fruit
growers regarded it as an unusual stage of apple scab or apple bitter
rot. Up to 1907, the disease was known variously as "apple blotch,"
' ' fruit blotch, " ' ' dry rot, " ' < black scab, "" late scab, " " cancer, " ' ' tar
blotch," "Phyllosticta," ' ' Phyllostictose, " "star fungus," "Phyllos-
ticta spot," or ' ' Phyllosticta on the apple." As more was known
about the disease it came generally to be referred to as apple blotch,
and this is the name that will be used in this bulletin.

HISTORICAL

*£*' £$>

Specimens of fhe disease were first collected in October, 1893, by
L. M. Underwood92 on the leaves of the American crab apple (Pyrus
coronaria L.) in Montgomery county, Indiana. They were submitted
for examination to J. B. Ellis, who determined the causal organism
to be a Phyllosticta, to which he gave the name Phyllosticta solitaria;
in 1895, he furnished a meagre description of it. A few months pre-
vious to the publication of the description of Phyllosticta solitaria, by
Ellis and Everhart,30 M. B. Waite, pathologist of the Bureau of Plant
Industry, U. S. Department of Agriculture, photographed blotched

aThe results presented in this bulletin form part of a thesis submitted by
the author to the Graduate School of the University of Illinois in partial fulfilment
of the requirements for the degree of doctor of philosophy in botany, May, 1923.
The writer wishes to express to Dr. H. W. Anderson, Assistant Chief in Pomol-
ogical Pathology in Horticulture, and to Dr. F. L. Stevens, Professor of Plant
Pathology in Botany, his appreciation for their supervision of the study and for
their suggestions and criticisms in the preparation of the manuscript. He is
indebted to Dr. C. F. Hottes, Professor of Plant Physiology in Botany, for the
use of his laboratory and for suggestions in the study of the temperature rela-
tions of the fungus in culture, and to others who have shown interest in the work.

b Formerly Assistant in Pomology and Fellow in Botany in the Graduate
School.

481

482

BULLETIN No. 256

[February,

fruits of Malus Mains L. collected from localities about Washington,
D. C., and identified the causal organism as a species of Phyllosticta
(Fig. 1). Owing to the uncertainty which existed at that time con-
cerning the causal agent of the frog-eye apple leaf spot, Waite sup-
posed that the fruit blotch and the frog-eye leaf spot were the results
of the same organism, but was in no way certain of his hypothesis. So

FIG. 1. — APPLE BLOTCH

Specimens collected at Garrett Park, Montgomery county,
Maryland, by M. B. Waite; (A) 1897, (B) 1895 (photographs by
M. B. Waite).

many Phyllostictas on the apple were then known that he was un-
willing to make any statement as to the causal fungus further than
that it was a species of Phyllosticta.* In 1902 Clinton17 gave the first
published account of the disease on the commercial apple and called
attention to its prevalence in the apple regions of southern Illinois.
Clinton cultured the organism and described its microscopic char-
acters. He considered the fungus a new species of the genus Phyllos-

•Information obtained from personal correspondence. These collections by
M. B. Waite represent the earliest record of apple blotch on the commercial apple.

APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 483

ticta. At about the same time Faurot31 of Missouri had his attention
called to the disease by growers who had mistaken it for a dormant
condition of bitter rot.

What appear to be the first experiments involving the control of
apple blotch were conducted in 1903 by C. S. Crandall23 of the Illinois
Agricultural Experiment Station in the investigation of the compara-
tive efficiency of Bordeaux dust and liquid Bordeaux in the control of
apple insects and diseases. The first investigation directed primarily
toward the control of apple blotch was conducted by Scott and Quaint-
ance77 in 1906 in Benton county, Arkansas. Their spraying experi-
ments resulted in the use of a spray schedule, which at that time gave
satisfactory control of the disease.

To Sheldon86 we are indebted for knowledge of the fact that
Phyllosticta solitaria E. & E. on the leaves of Pyrus coronaria is iden-
tical with the organism producing the bark canker, leaf spot, and the
fruit blotch of the commercial apple. Sheldon did not attempt cross
inoculations, and type specimens of the fungus were not examined.
His conclusions, however, were generally accepted.

At the same time Scott and Rorer,78 at Bentonville, Arkansas,
established by isolation of the fungus, comparison of its growth in
culture, and by inoculation of the host with spores from natural
sources, the identity of the organism causing the bark canker, leaf
spot, and fruit blotch of the apple.

Stevens 87> 88 in 1907 found blotch for the first time in North Caro-
lina. In 1908 Garman37 reported it in Kentucky, Morris and Nichol-
son52 cited its prevalence and seriousness in Oklahoma, and Orton and
Ames56' 57 reported its general distribution in the region extending
from Maryland and the Carolinas to Arkansas and Missouri. Doug-
lass26 in 1909 and McCormack53 in 1910 reported its prevalence in
southern Indiana, and in 1910 Selby82 and Gloyer39 recorded it for
Ohio ; Orton8 found it in Pennsylvania, and Beach* in South Dakota.
As early as 1912, according to Cook,22 apple blotch was common in
New Jersey.

Scott and Rorer79 in the period 19Q6 to 1909 conducted the first
general study of the apple blotch fungus. Their study dealt briefly
with the etiology of the disease, the cultural and morphological char-
acters of the fungus, its life history, and control.

Since 1912 some attention has been directed to the control of
apple blotch with dormant sprays. Such a possibility was originally
conceived by growers in Illinois, was first given experimental atten-
tion by Watkins106' 107 of Illinois, and later was taken up on several
occasions by the Agricultural Experiment Stations in Illinois and
Indiana.

•Information obtained by personal correspondence.

484 BULLETIN No. 256 [February,

Lewis51 in 1913 presented an extensive account of apple blotch
embodying descriptions of the disease on various varieties of apples
and the results of his experiments in its control.

Since the publication of the paper by Scott and Korer,79 experi-
mental work on blotch control has been concerned particularly with
the relative merits of Bordeaux and lime sulfur, and the time of the
applications. In connection with this experimental work the results of
Lewis,51 Blair et al.,8 Gunderson,42'45 Cooper,20 Roberts,67'69 Beach,5'7
Brock,9- «• 13'15 and Selby82- 83 should be noted. The results of Beach5'7
demonstrated the value of a spray two weeks after petal fall, supple-
mentary to applications recommended by previous investigators. The
probability of primary infection earlier than three weeks after petal
fall had been suggested previously by Lewis51 of Kansas, Cooper20 of
Nebraska, Rolfs71' 72 of Oklahoma, Brock13 of Illinois, and Stover et
al.90 of Ohio.

In 1917 Roberts67 confirmed the previous inoculation work of
Scott and Rorer by successfully inoculating the host with spores from
pure culture. In 1921 Roberts68 demonstrated by artificial inocula-
tion that only the current season's growth is susceptible to blotch
infection.

In 1920 Anderson3 reported the distribution of the disease in
Illinois and outlined a plan embodying exclusion, prevention, quar-
antine, and inspection measures, whereby he believed it possible to
restrict the disease to its confines in Illinois at that time, and thus
prevent its northward migration.

In 1922 Gardner35 of Indiana found that most of the apple blotch
cankers are the direct result of petiole and bud scale infections. He
reported that the mycelium from the basal petiole lesions crosses the
absciss layer before leaf fall, invades the bark and produces a canker
about the bud which, in the majority of cases, becomes conspicuous
the following spring. Lewis,51 and Scott and Rorer78 observed that
cankers originated in this manner, but the seriousness of this method
of infection was emphasized by Gardner.

In 1923 Gardner and Jackson36 suggested surgical measures to
eradicate cankers from young apple stock and thus avoid an increase
of new cankers in young orchards.

The timely reports of the Plant Disease Survey, U. S. Department
of Agriculture,93'102 from 1917 to the present, have been exceedingly
valuable as a source of information on the annual prevalence, distri-
bution, and losses from this disease.

PROBABLE ORIGIN

Collections of apple blotch from widely scattered localities (see
page 481) prior to 1902 establish the proof of the wide distribution of

1925}

APPLE BLOTCH: ITS ETIOLOGY AND CONTROL

485

the fungus even at that early period and support the contention that
the disease did not arise locally on the commercial apple.

The original host of this fungus was probably the native crab
apple (Pyrus coronaria} and during the past few years in Illinois
and Indiana the fungus often has been found on this host. Sheldon86
found it on this species of native crab apple in West Virginia, and
Scott and Rorer79 in Pennsylvania. The fungus still exists in a severe
form on this host, but in a less serious degree than on susceptible vari-
eties of commercial apples. This may be explained thru the fact that

FIG. 2. — DISTRIBUTION OF APPLE BLOTCH IN THE UNITED STATES,
1916-1923

the native crab may have gradually developed partial immunity dur-
ing its long period of susceptibility in its native habitat. With the
rise and development of commercial fruit growing in the eastern half
of the United States, the extensive planting of -varieties susceptible to
the apple blotch fungus, and favorable climatic conditions, the fungus
adapted itself to growth on the commercial apple and developed into
a serious disease producer.

The disease first became seriously destructive in the Ozark apple
region. During the period 1900 to 1902 in southern Illinois, Arkansas,
and southern Missouri it was generally prevalent and serious. In the
time which has since elapsed it has spread over most of the eastern
half of the United States (Fig. 2).

DISTRIBUTION AND PREVALENCE IN ILLINOIS

•Clinton17 stated that apple blotch was found in a number of places
in southern Illinois by Burrill in 1901 ; that growers were aware of

486 BULLETIN No. 256 [February,

its presence earlier, and that it was present in an orchard at Dubois,
Washington county, for some time previous to 1901. Since its first
reported appearance, it has developed into epidemic form in the cen-
ters of apple production.

No information is available to show the periodic progress of the
disease northward. Crandall,23 in 19'03, found apple blotch prevalent
on Ben Davis trees south of Olney, in Richland county, and in 1912
Ruth8 reported infection of approximately 70 percent of the apples
on unsprayed Ben Davis and Jonathan trees in an orchard at Flora.

The accounts of the spraying experiments of Crandall23 in 1904,
and of Foglesong32 in 1909 at Griggsville, Pike county, do not include
data on apple blotch. Likewise, the absence of any statements con-
cerning apple blotch in the accounts of the spraying experiments of
Gunderson8 in Ben Davis orchards in Pike county in 1911 and 1912.
indicates that apple blotch was not present or at least was not serious
in southwestern Illinois in this period.

The account of the spraying experiments of Watkins8 with fifteen-
year-old Ben Davis trees at Neoga, Cumberland county, for three
seasons, 1910 to 1912, does not mention apple blotch. Blotch, evi-
dently, was not present in the orchard and very likely not established
in the vicinity.

With the meager information available, together with a knowledge
of the development of fruit growing in Illinois, it seems probable that
the fungus came into Illinois from the apple-growing region to the
southwest, and that the disease appeared at about the same time in all
of southern Illinois coincident with the extensive development of the
apple industry. The Pike-Calhoun apple section, being of recent de-
velopment and with different conditions, remained relatively free of
blotch until 1913.

Knowledge of the disease in central Illinois is limited to recent
years. Evidence points to the appearance of the disease on North-
western Greening in the University orchards, Champaign county, in
1917. It appeared at about the same time on Northwestern Greening
at Lilly, Tazewell county, at Yates City, Knox county, and near Dan-
ville, Vermilion county. At Lilly the disease may also be traced to
infections of 1917 on Ben Davis, Missouri Pippin, and Duchess vari-
eties. In 1921, in the Lilly orchards, 90 percent of the fruit of North-
western Greening trees was affected with blotch, which indicates that
epidemic development of the disease after its first appearance at Lilly
was but a matter of a few years.

In 1920 the disease was found on Red Astrachan in Peoria county,
on Northwestern Greening and Duchess in Ogle county, and on
Duchess in Kendall county. In Ogle and Kendall counties the epi-
demic development of blotch on Duchess trees in a home orchard lends

WSS5} APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 487

support to the belief that the disease may have been present since
1917-1918. In 1921 the prevalence of apple blotch was observed on
Northwestern Greening at Eome, Peoria county. In the same year
a trace of it was found on the same variety near Galena, Jo Daviess
county. The appearance of this disease in isolated regions in central
and northern Illinois within the last few years suggests that its dis-
tribution in this region is comparatively recent.

Apple blotch to-day is present thruout Illinois. South of the 40th
parallel, i.e., south of the tier of counties extending east and west
approximately from Adams to Vermilion counties, it is very preva-
lent and is a limiting factor in the commercial production of sus-
ceptible varieties of apples. In the Pike-Calhoun apple section,
however, the disease is generally much less severe and less prevalent
than in the more central and southern sections of this area. In the
area of the 41st parallel, i.e., extending east of Henderson, Hancock,
and the northern half of Adams counties, apple blotch is now rather
generally present and well established on Duchess and Northwestern
Greening and is rapidly passing to other less susceptible varieties.
Its progress in this section has been comparatively slow in the absence
of extensive plantings.

In northern Illinois apple blotch is local and found only in scattered
places. Severe cases of it have been found in home orchards, where
spraying and the culture of the apple often are neglected.

PLANTS AFFECTED

Apple blotch is strictly a disease of certain species of the genus
Malus of Hall. The disease has never been found on any other host,
altho recently Seaver81 has named Crataegus sp. as a host for the
fungus.

The confusion existing in the nomenclature of our native mid-
western crab apples renders an accurate designation of the susceptible
species difficult. In Illinois, Malus lancifolia Eehd. and Malus coro-
naria L. are very susceptible and Malus angustifolia Michx. is mod-
erately so. The disease has been found occasionally on Malus angusti-
folia in Union county, and on Malus lancifolia and Malus coronaria
in central Illinois and central Indiana. The common prairie crab
apple (Malus ioensis Britt.) and its varieties are resistant; the dis-
ease never has been found on them.-

488 BULLETIN No. 256 [February,

ETIOLOGY

MORPHOLOGY OF THE PATHOGENE
Pycnidia

The pycnidia vary in size and form according to the organs of the
plant affected. They are smallest on the leaf spots, being globose or
sub-globose and with a thin wall. On the petioles they are similar
in form, but somewhat larger. On the fruit they are considerably
depressed and elliptical, with thick lateral walls. On the bark they
are very large and the carbonaceous walls are more extensively de-
veloped than elsewhere.

On the leaf spots the pycnidia have a small, Tostrate ostiole which
measures 9 to 12/x long and 7 to 12/* wide (Plate 1, Fig. H, I). The
pycnidia vary in diameter from 60 to 95/x. The pycnidial wall is
comparatively thin, generally1 consisting of one or two layers of dark-
colored cells and measures 6 to 7/t wide. The wall is much thicker
at the top and after the formation of the ostiole the thickened wall
is retained around the short neck. Next to the wall within are the
narrow sporogenous layers of hyaline parenchyma cells bearing
conidiophores.

The pycnidia on the petioles are commonly larger than those
formed on the leaf spots and measure 62 to 119/x, in diameter, and
have a definite, thin, dark-colored, and regular wall (Plate 1, Figs. D,
G, J). About the ostiole the walls are broader and the cells are
denser than at the sides and base of the pycnidium. The beak meas-
ures 12 to 14/x long and 9 to 12u wide. Within the narrow dark-col-
ored wall the larger hyaline sporogenous cells with conidiophores ap-
pear in sharp contrast.

On the fruit the pycnidia are black, punctiform, and prominent
(Plate 1, Figs. E, F). They may be aggregated and fused, but usually
their individuality is retained. They are decidedly depressed or
elliptical and almost twice as wide as deep. The lateral walls are 14 to
16/u, thick and the basal wall is about 4.75/t thick. The ostiole is in-
definite, without a neck, and usually the wall around it is as broad as
the lateral walls. The diameter of the stoma varies from 12 to 23/*.
The wall is regular and definite, and adjoining it within are the hyaline
cells of the thin sporogenous layer. The pycnidia on the fruit vary
in size, from 57 to 95/* deep and 107 to 166/x wide. Upon the dis-
charge of spores in summer the sporogenous tissue lining the interior
of the pycnidium is rejuvenated and eventually fills the entire cavity
while the ostiole is closed by the growth of the wall cells. During
the fall and winter months the interior is occupied by pseudo-paren-

PLATE I.— SECTIONS THRU PYCNIDIA OF P. solitaria, SHOWING THE VARIATION IN

SIZE AND FORM

(A, B) From bark cankers, the original pycnosclerotia ; (C) from the ad-
vancing area of the canker formed in the spring; (D, G, J) from petioles:
(E, F) from the fruit in June and July; (H, I) from the leaf blades.

1925]

APPLE BLOTCH: ITS ETIOLOGY AND CONTROL

489

chyma tissue enclosed in a thick carbonaceous wall. Extensive en-
largement of the pycnidium occurs and often results in the fusion of
the pycnidia. Such fruits with dense, thick, carbonaceous walls, en-
closing a hyaline parenchyma context have been named pycnosclerotia
(Fig. 3) by Eeddick.66- "

On the bark two types of fruiting bodies are recognized : first, the
pycnidia which form and function in the same season; and second,
the pycnosclerotia which form in the late summer, pass the winter
in a dormant condition, and function the following spring (Plate 1,
Figs. A, B, C, and Fig.
3). Both forms at first
resemble the pycnidia on
the fruit in form and
shape ; depressed, wider
than long, and with thick
lateral and thin basal
walls. The pycnidia usu-
ally develop a distinct
ostiole and the thickness
of the wall is more or
less limited. In pycnos-
clerotia, the ostiole is
usually indefinite and re-
sults from the rupture
and removal of a part
of the thick protective
apical wall.

Pycnosclerotia formed
in late summer are in
the following spring

comparatively large, with thick, carbonaceous walls and without a
definite ostiole. Spore formation commences in the center of the
pseudo-parenchyma early in the year and the sporogenous layer which
is formed gradually progresses outward. When sporulation is complete
only the dark wall cells remain, enclosing the spores. Apically and
laterally the walls are broader than at the base. The apical wall
measures from 23 to 48/i thick ; the lateral wall from 35 to 47/*, and
the basal wall from 7 to 28/x. The pycnosclerotia are globose or sub-

FIG. 3. — SECTION THRU A PYCNOSCLEROTIUM OF

P. solitaria FROM A CANKER COLLECTED

IN DECEMBER

Note the dense, carbonaceous wall and the
hyaline interior parenchyma context.

* Eeddick first used the term pycnosclerotium referring to a pycnidium with
a thick carbonaceous wall enclosing a pseudo-parenchyma context of large hyaline
cells which gives rise to a perithecium. Since perithecia have never been found to
result from the differentiation of the pycnosclerotium of P. solitaria, the word is
here used in a slightly different sense from that of Reddick, altho the form and
structure of the fruit is in all respects the same.

490

BULLETIN No. 256

[February,

globose. The ostiole measures from 23 to 59/x wide. The pycnosclerotia
measure 155 to 274/x, wide and 107 to 238/u, deep.

Pycnospores

The pycnospores are ovoid or broad-elliptic, unicellular, hyaline,
multi-guttulate, with a smooth wall which occasionally is partly cov-
ered at the broad end by an elongated, gelatinous appendage (Figs.
4, 9 A1). The guttules are ordinarily uniform in size and form and
evenly distributed in the cell tho often they are fused to form broad.

greenish, irregular bands. In
immature spores commonly
one large guttule may almost
fill the entire spore cell. The
spores range in size from 7
to 11/u, long and 6 to 8.5ju, wide.
The spores of Phyllosticta
solitaria from the pycnos-
clerotia bear a gelatinous,
hyaline appendage which is at
first very long and narrow,
and considerably broadened
at the base. It envelops about
one-half of the spore at the
broad end. The appendage
may appear as a thick cap
over the broad pole of the
spore. This gelatinous cap or
appendage has never been
observed on spores from
pycnidia which form and
function in the same season ;
however, it is constant on the
spores in the pycnosclerotia in the host and in artificial culture.

Other Phyllostictas show morphological characters similar to those
of Phyllosticta solitaria, e. g., the imperfect forms of Guignardia
bidwellii (E) V. & R. and Guignardia vaccinii Shear. Shear84 in the
study of the above forms noted the gelatinous appendage on the spores
of Guignardia bidivettii. He described and figured similar append-
ages on the imperfect spores of Guignardia vaccinii.

Stewart89 has described and illustrated similar appendages on the
imperfect spore form of Guignardia aesculi (Pk.) Stewart. These
descriptions agree with the character of the appendages on the spores

FIG. 4. — SPORES OP P. solitaria FROM PURE
CULTURE

1925] APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 491

of P. solitaria from pure culture and from the pycnosclerotia in the
host cankers.

ConidiopJiores

The conidiophores arise from a hyaline sporogenous layer of cells
which is supported by a colorless pseudo-parenchymatous sheath lin-
ing the dark wall of the pycnidium (Plate 2). Sometimes the pycni-
dial membrane is not sharply limited, but appears gradually to dif-
ferentiate, on the interior, into hyaline pseudo-parenchyma tissue.

A

FIG. 5. — MYCELIUM OP P. solitaria FROM PURE CULTURE
(A) From margin of a young colony, (B) from an old culture.

This tissue does not react readily with common stains and appears
more or less hyaline and somewhat obscure in stained sections.

The sporogenous layer is composed of very small and narrow cells
from which the conidiophores arise. The conidiophores are simple,
unicellular, excepting in the pycnosclerotia, where in the early stages
of differentiation they are long and septate. They may be filiform,
long, obclavate, and irregularly curved or straight; or they may be
short, broad, straight, columnar, and almost as wide as the supported
spore. They usually measure from 4 to 11/u, long and 1 to 3ju, wide.
Commonly they taper, being broader at the base than at the apex.

Mycelium

The mycelium in culture is composed of septate, pale green hyphac
which branch irregularly. The mode of branching, the irregular form,
size, and the bulging of the cell walls are very characteristic.

The young, long, slender, and actively-growing hyphae measure
about 2 to 3^, in diameter; septa are rare and the walls are not con-
stricted (Fig. 5, A). Occasional bulging lateral walls mark the begin-
ning of new filaments. Anastomosis is frequent along the walls.
Transversely in the cells there are definite, rather large, irregularly-
shaped, colorless vacuoles and bands of a pale olivine substance. The

492 BULLETIN No. 256 [February,

color of the young colonies in culture is due probably to a colored
pigment in the globules and bands of the substance along the walls
and across the cells.

In the old mycelium the cells are short and thick, 6 to 8/* wide and
occupied by large globules of a greenish color; septation is frequent
and the walls are prominently constricted at the septa and at the
bases of the short, stout branches that arise at irregular angles (Fig.
5, B). The anastomosis of these stout cells produces a very irregular
network.

NOMENCLATURE

The original description of Phyllosticta solitaria was published
by Ellis and Everhart30 in 1895, as follows:

"Phyllosticta solitaris E. & E. On leaves of Pyrus eoronarw, Crawfordsville,
la., Oct., 1893. Prof. L. M. Underwood. Spots minute, 1 millimeter, round
pale-white, with a darker border. Perithecia epiphyllous, solitary, one in the
center of each spot, 75/x diameter. Sporules sub-globose, hyaline, nudeate, 5 to 6/t
diameter. ' *

The locality of this collection has been misrepresented by many.
Sacearado74 refers to the collection from "Iowa, Amer., bor.," but this
misrepresentation is due to Ellis' incorrect abbreviation of Indiana,
namely "la." on the original packet. Saccardo changed the ending
of the specific name "solitaris" to "solitaria," since the gender of
Phyllosticta, by common usage, is feminine.

Type specimens of the fungus were not available for personal
study. Thru the kindness of Professor H. M. Fitzpatrick, the
specimen in the Everhart herbarium (Vol. 2, p. 57) at Harvard Uni-
versity was examined and compared with specimens of the fungus
on apple foliage from Illinois. He writes, "I feel no hesitancy in
saying that your material agrees with the type in external appear-
ance. ' ' Scott and Rorer79 examined the type specimen of Phyllosticta
solitaria from the New York Botanical Gardens and found that the
spores were identical with those of the apple blotch fungus.

The genera Phoma and Phyllosticta are very large, the former
comprizing approximately 1,700 form-species and the latter more than
1,100 form-species. Allescher2 calls attention to certain differences
between these genera, such as the small, sometimes indistinct papilla,
and filiform, sometimes short or indistinct conidiophores in Phoma,
and the relative absence of the small papilla, and the very short, rarely
distinctly developed or absent conidiophores in Phyllosticta. They are
further segregated in that Phyllosticta is only leaf-inhabiting while
Phoma occurs on branches, twigs, stems, pedicels, petioles, and on
the needles of the conifers. In practice it is customary to regard a
species as a Phyllosticta if on the leaves, and as a Phoma if on the
stems. This artificial classification is unsatisfactory and worthless.

PLATE 2. — SECTIONS THRU PYCNIDIA FROM DIFFERENT ORGANS OF THE HOST
SHOWING THE SPOROGENOUS LAYER

(A) From the leaves (blades) ; (B) from the petioles; (C) from the fruit;
(D) from the advancing area of the canker.

1925] APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 493

It is evident that the species at present in the genera Phoma and
Phyllosticta should be critically examined in order to segregate them
into several genera on morphological grounds.

In 1916 Sydow91 created the genus Phyllostictina based on the
type Phyllostictina murrayae Syd., occurring on living leaves of
Murrayae koenigii, from Dehra Dun, India.

Von Hohnel48 later studied the type specimen of Phyllostictina
murrayae Syd., and contends that its characters closely agree with
those of Phoma uvicola B. & C., and comments that he found no trace
of conidiophores altho he assumes that they were originally present
and had dissolved. He claims that both of these fungi belong to
the same form genus and to receive them he emends the description
of the genus Phyllostictina.

Professor Sydow furnished the writer with type specimens of
Phyllostictina murrayae for study. The outstanding characters are
the globose pycnidia with dark brown, thin parenchyma-like walls
composed of two layers of thin-walled cells, with usually a definite
ostiole surrounded by a slightly thickened ring of wall cells. The
spores are ovate, or broadly elliptical, and contain numerous, uniform
round globules. From microtome sections of the specimen these spores
appear to be formed by the histolysis of the gelatinous parenchyma-
tous context, without conidiophores.

Phyllosticta solitaria is certainly not a typical Phyllosticta and
also cannot be regarded as a Phyllostictina since it does not agree with
the type nor with the original description altho it does agree with
the emended description of von Hohnel. It is evident that von
Hohnel 's emended description is applicable to Phoma uvicola and to
Phyllosticta solitaria but not to Phyllostictina murrayae. It is the
belief of von Hohnel that all forms similar to Phoma uvicola are the
conidial stages of Guignardia which indeed has been found to be true
of Phyllosticta paviae Desm. (Guignardia aesculi (Pk.) Stewart) and
of the imperfect form of Guignardia vaccinii Shear, lately named
Phyllostictina vaccinii Shear.85 It is also probable that Phyllosticta
solitaria E. & E., Phyllosticta congesta Heald and Wolf and other
forms like Phoma uvicola are related to Guignardia. Shear,85 however,
adhering to the view of von Hohnel, has regarded Phyllosticta solitaria
E.&E. as a good Phyllostictina. Roberts'70 study of Phyllosticta
congesta Heald and Wolf shows the very close relation of this fungus
with P. solitaria E.&E.

In Phoma uvicola and Phyllosticta solitaria the conidiophores are
always present (Fig. 6). The pycnidial membrane of both of these
forms is similar altho variable; occasionally thin, and at times thick-
ened laterally or only in the region- of the ostiole. The pycnosclerotia
are often somewhat stromatic and always have thick, dense dothid-

494

BULLETIN No. 256

[February,

eaceous membranes. Their mode of spore formation differs so much
from our present conception of the genus Phyllosticta that these forms
might rightfully be established under a new form genus in the main
like the emended description of Phyllostictina. The presence of a
gelatinous cap or appendage on the spores of the pycnosclerotia of
these species is a character of added value for supporting the seg-
regation.

The question therefore
arises whether to create a new
genus for Phoma uvicola B. &
C. (not Phyllostictina uvicola
(B. & C.) v. Hohnel) and
Phyllosticta solitaria E. & E.,
embodying the essential char-
acters of the emended descrip-
tion of Phyllostictina as given
by von Hohnel, or to retain
these forms in the form genera
Phoma and Phyllosticta until
critical examination of the
species in these and other re-
lated genera is possible. The
latter course appears to be ad-
visable ; therefore, for the

FIG. 8. — SECTION THRU A PYCNOSCLEROTIUM

FROM CULTURE
Note gelatinous threads connecting spores

present, the original name
Phyllosticta solitaria E. & E.
has been retained.

PHYSIOLOGY
Cultural Characters

Phyllosticta solitaria grows readily upon almost any type of arti-
ficial media, but it grows well upon a medium rich in carbohydrates.
In the study of the cultural characters of the fungus, the following
types of media were employed: apple-bark corn-meal agar, Czapek's
agar, apple agar, apple corn-meal agar, corn-meal agar, prune agar,
sterile apple twigs, apple-bark agar, oat agar.

Apple agar was prepared by heating 150 grams of chopped apples
in distilled water in a boiling water bath for thirty minutes, then
filtering and adding to the filtrate 20 grams of granulated sugar. The
volume was made up to 1,000 cc. and 20 grams of agar added. Apple-
bark agar was prepared similarly; the cortex of water sprouts and
petioles, and leaves being employed in the preparation of the mixture.
Combinations of these media were prepared by mixing together equal
parts of separate media. The other types of media were prepared
according to standard formulae.

19 IS 5]

APPLE BLOTCH: ITS ETIOLOGY AND CONTROL

495

Growth is manifested as a spreading, flat, white, round colony,
growing superficially upon the medium and only slightly penetrating
it (Fig. 7). The colony may advance evenly in all directions, or in a
wavy-bordered fashion. An olivaceous coloration appears very early
in the center of the colony, and increases in area with the increase
in area of the colony. On oat agar, and frequently on corn-meal agar,
the olivaceous coloration fails to appear. Growth is commonly
olivaceous and with age becomes black-olivaceous and almost com

FIG. 7. — APPLE BLOTCH FUNGUS IN CULTURE
Note the flat, spreading character of the growth

and the numerous black pycnosclerotia. Growing on

apple agar at 25° C. in Petri dish.

pletely black in the interior. With the appearance of the dark
olivaceous coloration in the center and the light olivaceous coloration
about the center, the colony becomes over-grown by a short, floccose,
erect, and olivaceous aerial growth, arising first in the center of the
colony and advancing outward.

The production of pycnosclerotia (Fig. 8) occurs upon almost all
types of artificial media. Apple agars, sterile apple twigs, prune agar,
and Czapek's agar, are very favorable for their production. Carbon-
aceous, coal-black pycnosclerotia form over the entire inner surface
of the colony giving the surface a crusty, coal-black appearance
(Plate 3).

On Czapek's agar, prune agar, and commonly on apple agar, the
fungous growth eventually becomes ' a high, irregular, carbonaceous

496 BULLETIN No. 256 [February,

mass of mycelium and pycnosclerotia. This type of growth appears
commonly on agar slants on the above types of media, but rarely in
plates on these media excepting on Czapek's medium on which the
colony always grows in a high, irregular fashion. On corn-meal or
oat agar, on the other hand, growth is always flat and spreading.

Factors Involved in Growth and Pycnosclerotia Formation

In the experiment dealing with the relation of temperature and
light on growth and pycnosclerotia formation various types of media,
previously mentioned, were employed. The organism was transferred
to agar plates and tubes, and placed in the open in constant tempera-
ture chambers of 5°, 10°, 15°, 20°, 25°, and 30° C. An equal number
of plates and tubes of each medium were placed in black, cardboard,
light-proof boxes, consisting of box and lid which permitted of easy

t,

FIG. 8. — SECTION THRU PYCNOSCLEROTIA FKOM CULTURE
Note character of the pseudo-parenchymatous interior
and thick outer coat.

aeration. These temperature chambers were located in greenhouses
and protected against direct sunlight. Constant temperatures were
maintained by the circulation of brine, cooled by the expansion of sul-
fur dioxid. The brine was circulated thru the chambers by an elec-
trically driven pump, and the temperatures were kept constant and
uniform in the chambers by thermostats and electrically driven fans.
The humidity factor was not under control, but since the differences
in growth and production of pycnosclerotia were apparent long before
any drying of the media occurred, the effect of different temperatures
on growth and pycnosclerotia formation may be regarded as relatively
accurate.

The results obtained from this study bear evidence that growth
and pycnosclerotia formation of Phyllosticta solitaria are not affected

•

PLATE 3. — CULTURES OF P. solitaria, SHOWING TYPE AND MANNER OF GROWTH ON
DIFFERENT SOLID MEDIA AND THE BLACK, CARBONACEOUS PYCNOSCL.EROTIA

Tube 17, on Czapek and prune agar mixed; 20, on Czapek and apple-bark
agar mixed ; 21, 22, on apple agar ; 23, 24, on apple-fruit and apple-bark agar
mixed; 25, 26, on Czapek and apple-fruit agar mixed.

1925}

APPLE BLOTCH: ITS ETIOLOGY AND CONTROL

497

TABLE 1. — INFLUENCE OF DIFFERENT TEMPERATURES UPON THE RATE OF APPEAR-
ANCE OF GROWTH IN OPEN AND IN LIGHT-PROOF BOXES

Temperature

5°C.

10°C.

15°C.

20°C.

25°C.

30°C.

35°C.

Open boxes

Number of days after planting

No growth
No growth

25-30
30-35

10-15
10-12

4
4

3

2-3

3
2-3

No growth
No growth

Light-proof boxes

TABLE 2. — INFLUENCE OF DIFFERENT TEMPERATURES UPON THE BATE OF
PYCNOSCLEROTIA PRODUCTION IN OPEN AND IN LIGHT-PROOF BOXES

Temperature

5°C.

10°G.

15°C.

20°C.

25°C.

30°C.

35°C.

Open boxes

Number of days after planting

No growth 1 30-35
No growth | 30-40

23

18-25

13
11-13

5-10
5-8

5-7

5-8

No growth
No growth

Light-proof boxes

by light. The colonies on agar plates and tube slants in the open,
and in the light-proof boxes, from all appearances developed and
produced pycnosclerotia at the same time. There was no evidence
to show that constant darkness had a repressive effect upon growth or
pycnosclerotia formation. According to Coons18 light is a decisive
factor in the reproduction of Plenodomus fuscomaculans regardless of
the richness or poverty of the substrata in nutrients. With that
organism there is also a strong tendency for increased growth in the
dark. The results of Coons and Levine19 and Levine50 indicate that
among the genera of Sphaeropsidales many species are definitely light
positive to pycnidia formation while many are indifferent, producing
pycnidia under all conditions. Their results also show that the species
of one form-genus do not necessarily behave alike. Phyllosticta soli-
taria may be classed among those species which are indifferent to light.

The constant presence of pycnidia on the upper sides of the leaf
blades is not due to any light reaction, but, as histological studies
show, to the construction of the leaf and the supply of food. The
organism grows and fruits as well in the cavities of the apple, on the
pedicels, and on the bud scales, as elsewhere on the host. These tis-
sues are shaded much more than are other parts of the host, yet
fruiting does not seem to be affected.

The relation of temperature to growth and pycnosclerotia forma-
tion is significant (Tables 1 and 2). At 5° C. growth is completely
suppressed. At 10° C. growth is very slow and does not become
perceptible on the surface of agar until twenty-five to thirty-five days
after planting; the first pycnosclerotia are apparent from thirty to
forty days after planting. At 15° C. the organism grows slowly altho
better than at 10° C. ; the earliest apparent growth is between ten
and fifteen days after planting. At 20° C., growth is manifested in

498 BULLETIN No. 256 [February,

four days and the pycnosclerotia are apparent in eleven to thirteen
days.

The optimum temperature for growth and pycnosclerotia forma-
tion lies between 25° and 30° €., 25° C. being slightly more favorable
than 30° C. At both temperatures growth is evident in two to three
days and pycnosclerotia formation in five to eight days after planting.
At 35° C. the fungus does not grow, showing that the maximum tem-
perature for growth lies between 30° C. and 35° C. (Table 1).

Results show that pycnosclerotia production occurs at all tempera-
tures favorable to growth, and that where growth is slow the forma-
tion of pycnosclerotia is slow. At the extreme temperatures pycno-
sclerotia production is less in proportion to growth than at the more
favorable temperatures, which indicates that growth of P. solitaria
occurs at slightly wider limits than the production of pycnosclerotia.

Thruout this study it was evident that corn-meal and oat agars,
i.e., media rich in protein, were not favorable for pycnosclerotia pro-
duction, whereas all of the other media employed induced them
abundantly.

Spore Production in Culture

In spite of the rich masses of pycnosclerotia formed on artificial
media spores were rarely produced. In regard to spore formation of
P. solitaria Clinton17 states: "Cultures made by taking diseased tis-
sues from the interior of affected apples produced a characteristic
dark olive-green mycelium that formed patches of rather slow growth
on the medium and had not, after two months development, given any
sign of the formation of a spore stage." Scott and Rorer79 remark.
"The fungus does not fruit freely on culture media, and so far, the
writers have been able to secure spore-bearing pycnidia only on steril-
ized apple wood and corn meal agar. Pycnidia-like bodies are formed
in great abundance on all media, but these are, for the most part,
sterile. In apple-wood cultures, the fungus generally fruits well, pro-
ducing little groups of pycnidia rich in spores." Lewis51 says, "No
spores were produced on prune or potato agar or on potato cylinders,
but apple wood cultures produced spores abundantly." Roberts67
states in a discussion of cultural relations of the blotch fungus,
"Phyllosticta solitaria will produce pycnidia on all of the ordinary
solid culture media. These pycnidia, however, do not produce
spores. ' ' He was able to grow the fungus with the formation of both
pycnidia and spores only on sterile apple wood, and even on this
medium, two to three months elapsed before mature spores were pro-
duced. Stewart89 working with Guignardia aesculi found that cul-
tures from ascospores and from diseased horse chestnut leaves de-
veloped small sclerotia-like bodies and "altho the fungus from these
two sources was cultured for a period of twelve months on various
media no fruiting bodies ever developed."

1-925] APPLE BLOTCH: ITS ETIOLOGV AND CONTROL 499

The writer cultured the organism repeatedly on different media
and under various conditions. Pycnosclerotia production always
occurred, but spore production could never be expected, or predicted
with any measure of certainty. The pycnosclerotia were examined for
spores at short intervals for a period of two months. Spores were very
rarely found. In 1919 the writer secured spores on a corn-meal agar
slant at 25° C. in seven days from the date of planting. A few
pycnosclerotia formed on the colony, but on sectioning them, it was
found that only a few contained spores and that the remainder were
sterile. During this study spore production occurred a few times — on
one occasion at 30° C. in plates on a mixture of Czapek's and apple
media and again at 25° C. on oat agar. It occurred about twenty-six
days after planting and the medium then was completely dry and
hardened.

In February, 1921, the fungus was isolated from cankers on vari-
ously aged bark and transferred to tubes of a mixture of Czapek's
and apple agar, and to corn-meal agar containing prune juice. Spore
production occurred abundantly in several of these cultures. The
age of the canker and season of the year in which the isolations were
made seemed, at that time, to have some influence upon spore bearing.
In the earlier cultural studies most of the isolations from the host
lesions were made in autumn and winter while the organism was in
an inactive condition, but no spore-bearing cultures were obtained.
Further attempts early in the season in later years and in the spring
of 1923, with mycelium from old cankers on the same medium and
under the same conditions failed to obtain fertile pycnidia.

Since it is a common biologic principle that suppression in growth
generally leads to reproduction, the writer grew the organism on media
in "roll cultures." The "roll cultures" were prepared by rapidly
rolling tubes containing lOcc. of warm mediurii in a vertical position
between the palms of the hands with the base of the tube in cold water.
In such tubes the medium is shallow, and consequently the mycelium,
by coming in direct contact with the glass wall of the culture tube,
would eventually become starved, a condition which would suppress
growth and affect fruiting. The "roll cultures," however, did not
induce spore production, but the production of pycnosclerotia was as
common as usual.

Repeated attempts were made to obtain sporulation by subjecting
the pycnosclerotia to alternating high and low temperatures (freezing
them and restoring them to warm temperature). The results, how-
ever, were all negative. Spores were obtained abundantly only once
in pure culture, and then under the fluctuating conditions of a labora-
tory. The factors favorable to sporulation in culture remain unknown.

There is no evidence of spore-bearing strains in culture. The spore-
bearing cultures obtained by the writer have never given rise to others,

500

BULLETIN No. 256

[February,

altho the same medium was used and the organism was incubated in
the same laboratory.

Spore Germination

Germination (Fig. 9) is first manifested by a small, round pro-
tuberance occurring most commonly on the narrow end of the spore.

FIG. 9. — COMPARATIVE DEVELOPMENT OF TUBES OF GERMINATING
SPORES AT THE END OF FORTY-EIGHT HOURS AT

CONSTANT TEMPERATURES

(A) Mature spores at 10° C., (Ai) immature spores bearing
conspicuous gelatinous cap, (B) at 15° C., (C) at 20° C., (D) at
25° C., (E) at 30° C.

In practically 85 percent of the germinations the germ tube arises
from the narrow pole, about 10 percent arise from the sides of the
spore, and the remaining 5 percent or less arise from the broad pole.

1925] APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 501

The broad pole of the spore bears the gelatinous appendage which
evidently serves to attach the spore to the substratum it is capable
of infecting. The primary germ tube issues usually from the oppo-
site ,end. In the course of time a second germ tube arises commonly
from the broad end of the spore. The cap or appendage is eventually
dissolved ; it is inconspicuous on mature spores.

In contrast to the successful germination of spores from culture,
the spores from natural sources have never been induced to germinate
regularly or in any large quantity. During the spring and summer
of 1920 and 1921, from April 15 to July 15, repeated attempts were
made to germinate spores secured from pycnidia on leaves, fruit, and
bark. The pycnidia were crushed in sterile, tap, or rainwater, and
drops of the suspension were placed on slides in moist Petri dishes and
kept at room temperature. Similar mounts to which crushed pieces
of apple peelings, leaves, or bark were added were made during the
spring and summer of 1920 and 1921, in the hope that these might in
some way facilitate spore germination. The percentages of germina-
tion were small, irregular, and generally insignificant. Occasional
mounts showed a trace of germination and rarely high percentages of
germination, but since the conditions under which the high percentages
of germination occurred were the same in all respects as those where
none occurred, it is difficult to explain the failures. Roberts67 tested
the germination of spores of P. solitaria from bark cankers and ob-
tained germination in distilled water after May 23, 1914. On May
13, 1915, he found that 10 percent, and after May 24, 75 percent had
germinated.

The conditions necessary for spore germination are moisture,
nutrition, favorable temperatures, and maturity of the spores. Sterile
distilled water is not a favorable medium for vigorous and successful
germination since the germ tubes grow slowly to about three to four
times the length of the spore and then collapse from want of
nutrient. In sterile distilled water the percentage of germination
is small; in sterile tap water it may reach 100 percent. In a weak
solution of apple or prune extract, the germ tubes appear early and
grow vigorously, and finally give rise to mycelium.

The spores do not germinate well unless they are fully matured.
This is shown by attempts to germinate spores from natural sources
before the occurrence of natural infection, or from pycnidia from the
outer living portions of the cankers, even after primary infection has
taken place. Spores formed in the pycnosclerotia on the overwintered
cankers require about three to four months to mature, that is, from
the time differentiation begins to time of spore-discharge. Spores from
young spore-bearing cultures fail to germinate even in a nutrient
medium at the optimum temperatures. The best germination was ob-

502

BULLETIN No. 256

[February,

tained from spore-bearing cultures one to one and one-half months old.
From a culture sixteen days old the germination was less than 1 per-
cent under the most favorable conditions. Spores from a culture forty-
six days old under similar conditions gave 100 percent germination.
In spore germination the temperature is of extreme importance.
Pycnidia were taken from fertile cultures and crushed in sterile dis-
tilled water, or in a weak, sterilized, nutrient solution, such as prune
or apple fruit extract, and the volume of the liquid was then increased
five to ten times in order to avoid crowding the spores. The prune
extract was prepared by cooking two or three prunes in 200 cc. of
distilled water; the apple extract was made similarly from fresh
apples. The extracts were filtered and sterilized before using. The
spores were germinated on slides in Petri dishes at constant tempera-

•i*.<;?.-.^. :;_••)? K;; - : : -jyl
TABLE 3. — BATE AND PERCENTAGE OF GERMINATION, AT DIFFERENT TEMPERATURES,

OF SPORES FROM CULTURE 32 DAYS OLD
Spores suspended in a weak sterilized solution of apple extract

Hours after sowing

10 20

32

45 | 70

95

117

Temperature

Percentage germination

41°F. : 5°C...

0
0
t
1
2
0

0
t
1
2-3
5
1

0
t
1-5
15-20
25
1

0
1
5,
20
30
1

0
1

10-15
50
50

(Practici

t
5-10
20
50

50-60
lly no gerr

,;:-.t; f
10
20-25
50
50-60
r nation)

50°F. : 10°C

58°F. : 15°C

68°F. : 20°C

77°F. : 25°C

86°F. : 30°C

t = trace.

-,.;: - • . . -•;,) ,-; ..• :•<.•.. .". •{ ;•:.;• . : .- =...:•

tures. Drops of the spore suspension were placed on slides and two
slides were placed in each dish on glass rods with moistened filter
paper in the bottom of the dish with sufficient water to maintain
moist conditions.

The results in Table 3 are based on spores from a culture thirty-
two days old. The percentage of germination is not high, evidently
owing to the immaturity of the spores. After an exposure of 167
hours, the Petri dishes in the 5°, 10°, and 15° C. chambers were trans-
ferred to the 20° C. chamber where, within 132 hours, 40 to 60 per-
cent of the spores had germinated and developed hyphae.

The results in Table 4 were obtained with spores from a culture
forty-six days old. They show that with this increased age of the
pycnidia there was increased percentage of germination. At 15°, 20°,
25°, and 30° C., 100 percent germination was eventually present, but
the rate of development of the germ tubes was most extensive and
rapid at 25° and 30° C. After an exposure of 101 hours at 5° and
10° C. the Petri dishes were placed in the 25° C. chamber, where at the
end of thirteen hours about 80 percent of the spores had germinated,
and at the end of twenty -five hours from 80 to 100 percent.

1925}

APPLE BLOTCH: ITS ETIOLOGY AND CONTROL

503

TABLE 4.— BATE AND PERCENTAGE or GERMINATION, AT DIFFERENT TEMPERATURES,

OF SPORES FROM CULTURE 46 DAYS OLD
Spores suspended in a weak sterilized solution of apple extract

Hours

after sowing

7

17

31

42

73

Temperature

Percentage germination

41°F.

5°C...

0
0
0
0
t
30-40

0
0
3

40-50
95
90-100

0

t
30-40
90-95
95-100
9.5-100

0

t
80
95-100
(Excellent g
(Excellent a,

0

t
90-100
100
ermination)
ermination)

50°F.
59°F.
68°F.
77°F.
86°F.

10°C
15°C

20°C
25°C

30°C

t = trace.

The results in Table 5 are based on spores from a culture thirty-
four days old. The spores were suspended in sterile distilled water.
The germination was low at first, altho it increased later even at the
lower temperatures. The growth of the germ tubes was checked early.
After 132 hours the Petri dishes in the 5° C. chamber were trans-
ferred to the 20° C. chamber and good germination resulted, altho the
germ tubes were poorly developed.

TABLE 5. — BATE AND PERCENTAGE OF GERMINATION, AT DIFFERENT TEMPERATURES,

OF SPORES FROM CULTURE 34 DAYS OLD

Spores suspended in sterile distilled water

Hours after sowing

12

21

35

59

108

Temperature

Percentage germination

41°F. 5°C

.0
0
t
t
1
2-4

0
0
t

1

10
50

0
t
1-2

10
15
50

0
t
20-30
30
30-40
50

0
t

25-30
30-40
40-50
60

50°F. 10°C

59°F. 15°C

68°F. 20°C
77°F. 25°C

86°F. 30°C

t = trace.

In Table 6 the mounts were made from a culture forty-eight days
old. Petri dishes exposed to 5°, 10°, and 15° C. respectively for
seventy-one hours were transferred to 25° C. and at the end of four-
teen hours some germination had occurred at 5° C., and 50 to 60 per-
cent at 10° and 15° C.

In Table 7 the germinations were conducted in a laboratory where
the temperatures fluctuated between 13° and 24° C. The spores were
from a culture thirty-four days old.

The data in the above tables show that the optimum temperature
for spore germination lies around 30° C. (86° F.), and that the rate
of growth of the germ tubes is greatest at 25° C. (77° F.) and
30° C. (86° F.). At the lower temperatures, namely 15° C. (59° F.)

504

BULLETIN No. 256

[February,

TABLE 6. — RATE AND PERCENTAGE or GERMINATION, AT DIFFERENT TEMPERATURES,

OF SPORES FROM CULTURE 48 DAYS OLD
Spores suspended in sterile distilled water

Hours after sowing

11

17

34

46

71

Temperature

Percentage germination

41°F. 5°C...

0
0
0
0
0
5-10

0
0
0
0
30
40-50

0
0
t
30-40
50-60
60-70

0
0

t
40
60-70
60-70

0
0
t
40-50
60-70
70

50°F. 10°C

59°F. 15°C

68°F. 20°C

77°F. 25°C

86°F. 30°C

TABLE 7. — RATE AND PERCENTAGE OF GERMINATION, UNDER LABORATORY TEMPERA-
TURES, OF SPORES FROM CULTURE 34 DAYS OLD

Hours after sowing

12

24

36

60

Media used

Percentage germination

Sterile water

t
t
0
t

50
60
0
90

50
70-90
2-10
100

95
100
25-35
100

Weak sugar solution

Apple-bark extract

Apple fruit juice

t = trace.

and 20° C. (68° F.), the amount of germination at first is small and
the growth of the germ tubes is slow, altho with longer exposures 100
percent germination is obtained in nutrient solutions, including sterile
tap water (Fig. 9, B and C). At 15° C. (59 F.) branching and
anastomosing of the germ tubes are rare, while at 20° C. (68°F.),
altho growth is slow, hyphae ultimately appear. At 5° C. (41° F.)
and 10° C. (50° F.) germination rarely occurs and then growth never
exceeds twice the length of the spore (Fig. 9, A).

The spores remain viable in moisture for some time under tempera-
tures low enough to inhibit germination. Since spores from pure cul-
ture were rarely obtained, no studies could be undertaken to deter-
mine the longevity of the spores under various conditions; however,
the above results show that when spores are exposed to a tempera-
ture of 5° C. (41° F.) for one week they remain viable and germinate
normally when introduced into higher temperatures. Undoubtedly
the spores can survive much longer periods under these conditions.
This is significant since under natural conditions in prolonged periods
of rain and low temperatures spores may remain viable and produce
infection when favorable temperatures are obtained.

1925] APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 505

LIFE HISTORY
Inoculation and Infection

Scott and Rorer79 report the successful infection of the leaves and
fruit of the apple with spores obtained from bark cankers and apple
blotches. Numerous small blotches were found on the fruits, leaf
blades, and petioles in one month, but no bark cankers resulted. One
tree which was atomized with sterile water as a check showed no signs
of the disease. The experiment of Scott and Rorer is far from con-
clusive since they report the results of but a single experiment with-
out the use of pure culture and in a territory where blotch was seri-
ously prevalent.

Roberts67 infected successfully the foliage, fruits, and twigs of
the Missouri Pippin with spores of Phyllosticta solitaria obtained from
pure culture. The spores were suspended in sterile water and sprayed
upon the host in early July. The disease appeared a month later.
His attempts to infect the fruit of the Missouri Pippin and Ben Davis
after August 1 were unsuccessful. Roberts68 states, " Infection can
take place only on the young branches of the current year's growth.
Vigorously growing water sprouts are especially susceptible."

The writer has been unsuccessful in securing artificial infection.
In the winter of 1921 spores were obtained abundantly on artificial
media and when properly matured, as indicated by the high per-
centages of germination, they were suspended in water, sprayed with
an atomizer, and sprinkled on potted one-year-old Duchess apple
trees in inoculating chambers. The trees were grown in the green-
house for a month or more and the foliage was abundant. Clusters
of leaves were also atomized and enclosed in transparent parchment
paper bags. In each sack moist, absorbent cotton was placed in order
to insure moist conditions. All such attempts were unsuccessful. The
failure to obtain spores in quantity in pure culture eliminated all
hope of conducting artificial inoculations with spores under aseptic
conditions.

During two seasons' work in southern Illinois, many attempts
were made to produce the disease artificially with spores obtained from
host lesions. One-year-old Duchess trees were secured from a northern
nursery and planted in pots. Pycnidia were crushed in sterile water,
tap water, or rain water, and the spore suspension was applied to the
new growth with an atomizer. Transparent parchment paper bags
containing moist cotton were then placed over the atomized foliage
and the bags were moistened frequently. Despite the many attempts
no infections resulted.

Similar efforts were made to infect the healthy fruit and foliage
of bearing Duchess and Benoni trees with spores obtained from
natural sources. Before natural infection occurred transparent parch-

506 BULLETIN No. 256 [February,

ment paper bags were placed over and tied around the new growth of
foliage and fruit as a protection against natural infection. Fre-
quently, thruout the season, some of the bags were removed and the
healthy growth atomized with a water suspension of spores, this being
done when possible before rains and in the evening. After atomiza-
tion a handful of wet absorbent cotton was placed around the stem
and the growth was covered by a fresh bag, and moistened. For
every group of protected growths atomized with spores, two or three
bagged growths were atomized with sterile water to serve as checks.
Similar trials were made using glass flasks and chimneys containing
moist cotton in place of the parchment paper bags. Infections were
never obtained.

The difficulty of securing spores in pure culture and artificially
infecting the host likewise has been encountered with Guignardia
bidwellii, G. aesculi, and G. vaccinii. Reddick66 was unable to obtain
successful infections of the grape with pycnospores of Guignardia
bidwellii; he states, ' ' The writer is utterly at a loss to understand his
failures to obtain infections. ' ' Shear84 was unable to infect the cran-
berry artificially to thereby discover exactly when and in what manner
infection of the leaves and fruit takes place. He found that the
majority of cultures of Guignardia vaccinii were either entirely sterile
or produced only pycnosclerotia.

Sources of Inoculum

The fruiting bodies in the central areas of the cankers are matured
and free of spores earlier in the season than those in the outer areas.
Primary infections, therefore, are evidently the result of spores from
pycnosclerotia confined to the older areas of the canker, the pycnidia
on the outer areas serving as sources of inoculum for later infections.
Owing to the slow advance of the cankers during the late spring and
summer, inoculum from the cankers during the season is practically
limited to the fruiting bodies formed prior to the fall of the bloom.
The irregular and continued discharge of spores from the pycnidia
on the cankers is responsible for repeated infections thruout the spring
and summer. After August, infections from these sources cease, for
the supply of spores becomes exhausted and only pycnosclerotia are
formed. The new cankers, which appear in August, likewise bear only
pycnosclerotia which function the following spring.

After leaf petioles, blades, pedicels, and fruit are infected, the
sources of inoculum later in the season are naturally increased many
times. The pycnospores from the lesions on the leaves infect the same
leaves and, as new lesions appear on the fruit and leaves, new sources
of inoculum arise. Infections resulting from inoculum from these

1985] APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 507

sources cease in August, since the supply of spores becomes exhausted,
and the organism produces only pycnosclerotia.

The pycnosclerotia also overwinter on the mummies and fallen
leaves. In the spring these pycnosclerotia either remain sterile or
produce pycnospores, but in the absence of evidence, the significance
of these spores is uncertain. In view of the location of mummied
fruit and decaying leaves, and the adhesive quality of the spores when
exuded under moist conditions it would seem that the influence of
gravity and washings from rain would carry the spores away from
the action of wind and a favorable substratum.

The relation of the location of diseased fruit and foliage to the
location of the cankers supports the view that the inocula causing
primary infections arise from the bark cankers. This relationship is
best observed on lightly infected trees. With the first appearance of
the disease on the leaves and fruit, close observations show that the
first symptoms of the disease are always close to, and associated with,
the bark cankers. A very clear ease of such a relationship was found
at Mount Morris (111.) in 1920. On only one tree in a Northwestern
Greening orchard, did the writer find a cluster of blotched apples on
a spur, accompanied by infected leaves. A lone canker was on a
branch directly above. In no instance has it been possible to trace
primary infections to any source but the cankers, a fact which is
universally recognized in the literature on this disease.

Time of Infection

The periods of infection have been studied for three years at vari-
ous localities in Illinois. The plan involved the daily presence of the
writer in the orchard under observation, bagging of fruit and foliage,
compilation of daily weather data, spraying, and other orchard opera-
tions. The results obtained with bags correlated with weather data
have made it possible to arrive at valuable information regarding the
dates of primary infection and the frequency of infections during
the season.

The bags were of white, stiff, transparent, parchment paper bear-
ing a disk at the upper end to whichj a string was attached for tying.
Two sizes were employed, H/o by 5V4 inches for the fruit, and 141/2
by 8 inches for water sprouts and terminal twig growth. When the
bags were first used it was found that often in rainy weather the
glued edges came apart. An application of hot paraffin to the edges
of the bags before use insured their security during rainy weather.

The bagging operations were conducted as follows: A few days
after petal fall, in dry, fair weather, several bags were tied over the
fruit and twigs of severely cankered trees. At regular intervals
thereafter, until the first symptoms of the disease on the fruit and
foliage became apparent, additional bags were placed on other fruits

508

BULLETIN No. 256

[February,

and twigs. Likewise, at regular intervals, bags were removed during
the course of the season tho many bags were left on until September
to serve as cheeks. But one apple and a few leaves were limited to

FIG. 10. — BAGS USED TO DETERMINE TIME AND DURATION OP

NATURAL INFECTION

Above, on Duchess trees; below, on Sops of Wine trees.
Anna, May, 1921.

a single small bag. When more than one apple was present on the
spur the others were removed, thus allowing for the better develop-
ment of the apple and avoiding the danger of breaking the bag. The
larger bags allowed covering of entire fruit clusters. To facilitate

1925]

APPLE BLOTCH: ITS ETIOLOGY AND CONTROL

509

placing and tying the bag about the fruit and twigs, the leaves on
a few of the nodes of the preceding season's growth were removed.
Because of the stiffness of the parchment paper when dry, tearing
cannot be avoided in opening and tying unless the bag is first moist-
ened. A short wetting before opening and tying permits of firm
tying about the twig and thus avoids any danger of infection enter-

FIG. 11. — COMPARATIVE SIZE OF FOUR SUSCEPTIBLE VARIETIES OF
APPLES AT THE TIME OF FIRST HEAVY INFECTIONS

AT ANNA, 1921

Upper left, Duchess; upper right, Sops of Wine; lower left,
Ben Davis; lower right, Benoni.

ing the bag at this point. The bag is placed over the growth and
the upper portion is gathered together and wrapped evenly about the
twig, and the string is wrapped a few times below the disk, then at
the base of the new growth and a few times about the disk. The
tyings must not be too tight and care must be taken to exclude any
portion of the previous season's growth, since the presence of cankers
in the bag would destroy the value of the experiment. On drying,
the bags become stiff and if the tying is done properly, growth pro-
ceeds as with the unbagged fruit (Fig. 10). The protected fruit

510

BULLETIN No. 256

[February,

matures somewhat earlier than the unbagged fruit, but this does not
vitiate the accuracy of the data since infection is possible even when
the fruit and foliage are nearly mature.

Season of 1920 at Anna. — The bagging was conducted on the
Duchess variety (Table 8). The first bags were put on May 1 and 2.
Petal fall (75 percent fallen) occurred on April 25 and 26 and the
calyx spray was applied on April 26 and 27. The first infections of
the season occurred during the rains of May 11, 12, and 13, or fifteen
to eighteen days after the recorded period of petal fall. Further
infections occurred during the rains of May 16, 17, and 18, May 30

FIG. 12. — THERMOGRAPH AND PRECIPITATION RECORDS IN ANDERSON ORCHARD,

ANNA, MAY 9 TO 17, AND MAY 29 TO JUNE 4, 1920
Time periods for Duchess variety; precipitation for twenty-four hour
period, evening to evening.

and 31, and June 3. The first spray for blotch was applied on May 14
and 15, and spraying was continued at weekly intervals during May
and June. The failure to apply the first blotch spray ahead of the
rainy period of May 11 to 13 resulted in poor control in every plat.
In bags that were put on May 12 and 13, and removed on June 11,
there was present, with one exception, an abundance of fruit and
petiole infection. This shows that primary infections occurred be-
tween May 2 and May 14, and from a study of the local weather
records (Fig. 12) the primary infection of Duchess fruit and foliage
must have occurred on May 11, 12, and 13. The disease was found
on May 27 for the first time in the season.

The data show (Table 8) that the disease was not present on foliage
protected up to June 4, when examined on July 15. However, growth
protected up to June 4 and examined on September 11, revealed seri-
ous infection of the petioles. Study of the weather after June 4
shows that small precipitations occurred on June 19, 21, 22, July 2,
5, and that heavy rain occurred on July 13 and July 18. Since two to

70

19S5]

APPLE BLOTCH: ITS ETIOLOGY AND CONTROL

511

TABLE 8. — EESULTS OF BAGGING EXPERIMENTS ON DUCHESS TREES, ANDERSON

ORCHARD, ANNA, 1920

No. of
bags

Date put
on

Date taken
off

Infection

Second examination

Date

Infection

5

May 1 and 2

June 4

_

July 15

_

7

—

Sept. 11

S.p.i.

1

"

—

M.p.i.

3

June 6

—

July 15

—

7

—

Sept. 11

S.p.i.

1

44

—

—

5

June 8

—

July 15

—

3
3

.!

I

Sept. 11

Sp.i.
M.p.i.

1

"

—

5

June 11

—

July 15

—

2

—

Sept. 11

—

6

"

—

S.p.i.

5

June 16

—

July 15

—

5

"

—

Sept. 11

S.p.i.

5

June 20

—

July 15

—

5
0

June 25

—

Sept. 11
July 15

S.p.i.

2

—

Sept. 11

—

5

44

—

S.p.i.

2

July 2

—

S.p.i.

5

—

—

5

July 9

_

S.p.i.

3

"

— '

—

2
1

July 13

I

S.p.i.
M.p.i.

1

"

—

20 (checks)

Sept. 11

Found in 1 bag

8

July 2

—

July 15

—

4

May 12

June 11

S.f. & p.i.

1

*'

41

—

3

May 13

44

S.f. & p.i.

3

May 14

44

S.f. & p.i.

1

44

—

3

May 17

44

S.f. & p.i.

1

44

S. p. i.

6

May 21

14

S.f. & p.i.

1

0

May 23

S.f &p.i.

( - )=: disease not
ate petiole infection ;

present ; S.p.i. = severe petiole infection ; M.p.i. = moder-
S.f. & p.i. = severe fruit and petiole infection.

three weeks are required for the symptoms to become apparent on
fruit and foliage, it seems that the small precipitations between June
4 and July 15 were insignificant and not favorable for infection. The
precipitations of July 13 and 18 were large enough for infection, and
the constancy of the disease on the foliage when examined on Sep-
tember 11 indicates that infection occurred during these rains, as
well as during the heavy rains of August 8 to 10 and 15. The re-
maining days of these two months were marked by dry weather and
occasional short rains unfavorable for infection. When the bags were
removed at intervals during the period June 4 to July 13, and the fruit
and foliage examined on July 15, the disease was universally absent,
and when this same growth was examined on September 11, the dis-
ease, with a few exceptions, was universally present. Heavy infections,
therefore, occurred during July and August.

Season of 1921 at Anna. — The bagging experiments in this season
were conducted on the Duchess variety (Table 9). The season was

512

BULLETIN No. 256

[February,

TABLE 9. — RESULTS OF BAGGING EXPERIMENTS ON DUCHESS TREES, MILLER
ORCHARD, ANNA, 1921

No. of
bags

Date put
on

Date taken
off

Infection

Second examination

Third examination

Date

Infection

Date

Infection

2
2

April 18

May 23

-

Sept. 7
July 15

S.p.i.

3

"

May 25

—

"

44

2

May 28

—

**

44

1

"

—

M.p.i.

Sept. 7

S.p.i

4

"

May 31

—

44

S.p.i.

1

—

Sept. 7

4

1

June 4

—

July 15

44

1

•

"

—

M.p.i

M.p.i.

1

*

June 10

—

"

S.p.i.

Defoliated

2

•

—

Sept. 7

3

1

!

June 21

—

July 15

—

S.p.i
M.p.i.

1

*

June 28

—

*4

—

S.p.i

3

•

—

Sept. 7

M.p i.

1

July 8

—

S.p.i

2

*

July 15

—

14

M.p»i.

1

*

—

44

S.p.i.

1

•

July 28

_

44

M.p.i.

1

*'

Trace

44

S.p.i.

8 (checks)

•

Sept. 9

—

1 (check)

April 21

"

—

1

April 22

July 15

—

44

M.p.i.

1

"

'*

—

44

S.p.i.

2

11

July 28

—

44

7

April 25

June 16

—

44

1

"

July 15

—

44

1

*'

Trace

2

"

July 28

—

44

M.p.i.

1

*'

44

Trace

44

Sp.i.

1

April 26

July 15

S.p.i.

44

1

44

—

4

1

"

July 28

Trace

4

1

"

"

—

4

3

April 27

June 16

—

4

1

"

Trace

4

1

May 2

July 28

—

4

1

**

S.p.i.

4

1

"

"

Trace

4

1

May 3

S.p.i.

2

•*

**

Trace

1
1

May 5

June 16

July 15

Sept. 7

S.p.i.

1

**

"

—

Sept. 7

1

July 28

Trace

1

May 7

July 8

—

July 15

—

44

Trace

1

H

July 15

—

Sept. 7

M.p.i.

1

11

July 28

—

1

**

44

Trace

44

S.p.i.

2

May 12

June 16

S.p.i.

July 15

1

**

4

May 16

"

'

4

May 19

*4

*

1

May 31

1

July 15

*

1

July 28

2

June 4

Scot. 7

(-)=

ate petiole

: disease not present ; S.p.i. = severe petiole infection ; M.p.i. =: moder-
infection.

abnormal. The trees bloomed very early and three successive frosts
destroyed the major portion of the crop. In the absence of much
fruit, only twig growth with leaves could be bagged; but since both
leaf and fruit infection occur at the same time and under the same
conditions, the data obtained are applicable to fruit infection as well.
Petal fall for the Duchess orchard was recorded for April 6 and 7.
The first bags were removed and new ones put on at intervals of two

1925] APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 513

or three days. The first bags were put on April 18, and, as the
data show (Table 9) the disease was not present when these bags were
removed at various intervals from May 23 to September 9, indicating
that no infection occurred prior to April 18. Of a total of thirty-four
bags put on during the period April 25 to May 7, twenty-one growths
were disease-free, thirteen showed disease, three of which showed
severe infection, and ten traces of infection. The primary infections,
therefore, could not have been heavy. A study of the weather records
shows that ideal conditions for infection occurred on April 26 and 27,
about nineteen days after petal fall. The disease was apparent on
Duchess fruit and foliage on May 19. The first heavy infections, how-
ever, occurred during the period May 9 to 12; a period five weeks
after petal fall, marked by continuous damp, foggy weather, and
precipitations amounting to 1.58 inches. As the season was abnormal
no significance can be attached to the relation of the time elapsing
between petal fall and infection (Fig. 11). The data (Table 9) fur-
ther show that growth covered at intervals during the period May 12
to June 4 was severely diseased on examination later in the season.

Heavy infections occurred again in June. The data show (Table 9)
that when bags were applied April 18, and removed at intervals from
May 23 to June 10, no disease was present, and that when this same
growth was examined on July 15 disease was universally present. A
study of the weather after May 9 to 12 shows that infection could
only have happened on June 19 to 21 during a precipitation of 3.7
inches, 2.99 inches of which fell on June 19 (Fig. 13) . The fruit and
foliage of many varieties some weeks after revealed a large increase
in the disease even on mature apples. The infections for this period
were even greater than those of May 9 to 11.

The month of July was dry with the exception of a precipitation
of .68 of an inch on July 10. The month of August was characterized
by heavy rainfall, amounting to 7.58 inches near Anna. Healthy
growths exposed from June 28 and July 8, 15 and 28 for the rest
of the season showed disease when examined on September 7. New
lesions of the disease on the foliage and fruit were common in Illinois
in September of 1921, the result of infections favored by the weather
of August. The data do not reveal to what extent the conditions of
July 10 were favorable for infection (it is probable that some infec-
tions occurred at this date at Anna). Heavy infections occurred in
August, a significant fact in that the literature so far has always
borne testimony against the probability of late infections.

Season of 1922 at Lilly and Other Points. — In this season the writer
had opportunity to note the primary period of infection and the first
appearance of the disease on several varieties in several sections of the
state. The bagging experiment was conducted on Northwestern

514

BULLETIN No. 256

[February,

Greening trees in the Lilly orchards (Table 10). The trees, however,
were not generally diseased.

Petal fall for the Northwestern Greening occurred on May 5 and 6
and the first bags were put on May 17, eleven days after petal fall.
The bags were removed at intervals from May 29 to July 20, and the
growth was free of disease, indicating that no infection occurred on
this variety at Lilly prior to May 17. Growth that was bagged
on May 29 and June 1 and examined July 20 showed disease, indi-
cating that primary infection occurred during the period May 17 to
May 29. Heavy rains occurred at Lilly during the period May 23 to

Sundar I : Hcniay • I Tuadav I YMntsday / Thursday I Wi

wf? ,»/,* ,•;.« • ,w.^.v/,vf ,»;£."? •.•/.' " ,* >•*.•: .v.v.1 •• :,w; .v.V.'r vw

Slauiay I • Monday 1 Tuesday [ VUHnaday I Tniirsaa.

"" '' «•«•«:.»•»•««« "* •• > '<« • »>*• • -**'• «»•«« < 4

FIG. 13. — THERMOGRAPH AND PRECIPITATION RECORDS IN MILLER ORCHARD,
ANNA, JUNE 18 TO 23, 1921

Time periods for Duchess variety; precipitation for twenty-four hour
period, evening to evening.

26, approximately two and one-half weeks after petal fall. These
dates for primary blotch infections are further supported by the fact
that the first symptoms of the disease were apparent on June 7 to 8,
or fifteen to sixteen days later. The period required for infection to
become evident agrees closely with that of previous years for other
varieties in Illinois. The month of June was relatively dry and
unfavorable for infection. Of eighteen growths protected up to June
8, 16, and July 1, seven were diseased when examined again on July
20. This infection was associated with the heavy rains of July 1.
Further infections occurred later in the summer. Of thirty-one
growths bagged on May 17 and free of disease on July 20, fifteen
showed symptoms of disease on October 15, indicating infection periods
after July 20. Because of the small number of cankers on these trees,

19S5]

APPLE BLOTCH: ITS ETIOLOGY AND CONTROL

515

the data are not as complete as would be expected from heavily in-
fected trees. The experiment, however, gave valuable information
regarding the time of primary infections and further demonstrated
the fact brought out in previous years that heavy infections occur
under ideal conditions as late as August.

Data on the dates of primary infection and the appearance of the
first symptoms were also obtained from Anna, Olney, Urbana, Tonti,
and Hillview. At Urbana, petal fall for the Duchess variety occurred
on May 3, and for the Ben Davis and Northwestern Greening on
May 5. Blotch first appeared on the fruit and leaves of the Duchess
variety on June 4 and on the Northwestern Greening on June 6.

TABLE 10. — RESULTS OF BAGGING EXPERIMENTS ON NORTHWESTERN GREENING
TREES, LILLY ORCHARDS, LILLY, 1922.

No. of
bags

Date put
on

Date taken
off

Infection

Second examination

Third examination

Date

Infection

Date

Infection

1

May 17

May 29

—

Oct. 15

+

1

"

—

July 20

—

Oct. 15

M.f. & p.i.

1

—

—

S.f. & p.i.

1

—

+

1

4

44

—

**

—

44

1

"

—

—

1

June 8

—

—

+

1

—

Oct. 15

—

1

"

—

July 20

—

44

S.f. & p.i.

1

—

11

—

Trace

1

June 16

—

"

—

M.p.i.

1

'

"

—

"

+

1

"

—

S.f. & p.i.

1

—

—

1

1

"

—

"

M.pi.

1

"

—

+

2

July 1

—

—

—

1

—

—

44

S.p.i.

2

—

M

+

1

.Oct. 15

—

2

11

—

July 20

+

1

*

*'

—

"

—

+

1

"

—

—

1

July 10

—

Oct. 15

—

1

1

"

—

July 20

—

S.p.i.

3

—

—

2

—

41

—

+

1

"

—

Oct. 15

—

1

—

S.p.i.

1

—

July 20

—

S.p.i.

5

1

July 20

—

Oct. 15

—

1

—

Trace

3

—

"

—

8 (checks)

Oct. 15

—

5

May 29

July 20

+

1

M.p.i.

1

—

1

+

Oct. 15

+

4

June 1

"

+

•' ,'^

1

"

—

—

6

June 8

"

+

1

"

"

M.p.i.

1

Oct. 15

S.f. &p.i.

1

June 16

July 20

—

44

S.f. & p.i.

6

+

( — ) = disease not present ; S.p.i. = severe petiole infection ; M.p.i. — moder-
ate petiole infection; S.f . & p.i. •=. severe fruit and petiole infection; (-)-) — dis-
ease present but degree not determined; M.f . & p.i. •=. moderate fruit and petiole
infection.

516 BULLETIN No. 256 [February,

It was first found on the Ben Davis, on June 8. The heaviest pre-
cipitation of the month of May occurred on May 25 and 26 (Fig. 14).
The first infections of the season at Urbana also occurred at this time,
or about three weeks after petal fall. Precipitations occurred fre-
quently in the middle and early part of May, but since they were
slight, conditions were unfavorable for infection; no precipitation
occurred later in May.

The data from Anna are interesting and confirm the results of the
previous seasons. The period of petal fall and of the calyx spray
was April 17 to 20. Blotch was found on Yellow Transparent,
Duchess, and Benoni for the first time in the period May 16 to 18,
approximately four weeks after petal fall. Heavy rains occurred at
Anna during the periods April 25 to 28 and May 2 and 3, and the
conditions were ideal for infection, but the conditions in the latter
period were responsible for the first infections as revealed by the

PRECIPITATION .01 .10 1.76 .34

FIG. 14. — THERMOGRAPH AND PRECIPITATION EECORDS IN UNIVERSITY

ORCHARD, URBANA, MAY 22 TO 28, 1922
Precipitation for twenty-four hour period, morning to morning.

results from several demonstration orchards for blotch control in
Union county for the season of 1922. Eight orchards were selected
and the spraying schedule called for applications at intervals of
two, three, four, and six weeks after petal fall. This work was
supervised by the assistant farm adviser in cooperation with the
growers. In seven of these orchards the two-weeks spray was applied
by May 2, but in the remaining orchard difficulty was encountered and
the two-weeks spray was not applied until after the rainy period, with
the result that the fruit and foliage of this orchard were heavily in-
fected, while in the other seven orchards control was excellent. In
the Miller orchard at Anna, the application of the two-weeks spray
in the Benoni orchard was interfered with by rains of May 2 and 3,
and the fruit from the trees which failed to get this application on
time was diseased, while the fruit from trees sprayed before this
period was clean. The data therefore indicate that the first infections
occurred at Anna in the period May 2 and 3, or approximately two

1925} APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 517

weeks after petal fall. The disease was noted generally for the first
time during May 16 to 18, or approximately two weeks after primary
infection took place.

At Olney on Ben Davis, petal fall occurred April 18 and 19, and
the disease was first found on May 21 and 22. Primary infection was
traced to the heavy precipitation of May 3 and 4, about two weeks
after petal fall. At Tonti, fifty miles west of Olney, the initial blotches
on Ben Davis, Benoni, Grimes Golden, and Duchess fruit were found
May 20 to 22. Petal fall for these varieties occurred on April 25 and
26. At Hillview, blotch was found on late varieties for the first time
on May 24 and 25 ; petal fall was recorded for April 22 and 23.

The evidence obtained from three years of field work shows that
primary blotch infections did not occur prior to two weeks after petal
fall. It is certainly possible for primary infections to occur earlier in
exceptional seasons, and no doubt a field study of the fungus over a
period of years will bear out this statement. It is interesting to note
that in southern Pennsylvania in 1922, according to Walton and
Orton,105 primary infection of the fruit occurred earlier than two
weeks after petal fall. The results from this study also show that
severe cases of fruit and leaf infection may occur in August under
conditions existing in Illinois.

Conditions Associated with Natural Infection

The pycnidia do not swell and discharge their spores unless they
are moistened. Study of the weather during the growing season has
shown that heavy precipitation is required to bring about infection,
since considerable wetting is necessary to soften the pycnidia suffici-
ently to lead to the expulsion of the spores, and to maintain moist
conditions a sufficient length of time for spore germination. The
pycnidia in the dead inner portions of the canker are the first to-
discharge spores, yet these may retain their spores until late in the
summer notwithstanding the heavy rains earlier in the season.

Moisture alone is insignificant since the spores cannot germinate
unless the temperature is favorable. Mature spores germinate early
at the higher temperatures, that is, 25° C. (77° F.) and 30° C. (86° F.)..
The percentage of germination is ultimately as great at the lower
temperatures, that is, 15° C. (59° F.) and 20° C. (68° F.) altho the
rate of growth of the germ tubes is much less. It is safe to assume that
if germination occurs normally at the low temperatures, infection
may occur also at these temperatures as indicated by the conditions
associated with primary infections. In the past three seasons, the
primary infections have occurred during prolonged periods of mois-
ture, accompanied and followed by low temperatures, and the sum-
mer infections in shorter periods of heavy rains and high temperature.
Moist conditions during the night resulting from rains during the

518 BULLETIN No. 256 [February,

day prolong the conditions favorable for spore germination and thus
obviously for infection. There is ample evidence that light rains of
short duration, even with warm temperature are not favorable to
infection.

In 1920 at Anna the earliest infections occurred in the periods
May 11 to 13 and May 16 to 18. The weather on May 11 was marked
by continuous rains which were particularly heavy early in the after-
noon. The maximum temperature of 22.8°C. (73°F.) occurred at
5 p. m., and rain continued thruout the night, and until 8 a. m. of
May 12 (Fig. 12). May 12 was cloudy from 8 to 11 a. m., followed
by hot sunshine, with thunder showers from 2 to 4 p. m. On May
13 the weather was cloudy and windy, the temperature was low, and
rain fell again in the evening. For three days prior to May 11 the
temperature was near 26.6°C. (80°F.) at midday, and the weather
was fair and dry. Repeated examinations of the pycnidia during
this period revealed that the spores were mature. The wet period
of twenty-eight hours from noon May 11 to 4 p. m. May 12 was ideal
for spore germination. Low temperatures prevailed during the period
May 13 to 17, cloudy and windy weather from May 13 to 15, and
heavy rains on May 16, 17, and 18. On May 19 and 21 the atmosphere
was very humid, high temperatures prevailed at midday, and rains
and thunder showers in the evenings. The precipitation for! the
period May 11 to 21 amounted to 6.13 inches. Prolonged wet weather
of this kind is common in Illinois in the latter part of April and in
May before the dry season begins.

The bagging results for 1920 on the Duchess variety at Anna show
that further infection occurred in the period from May 30 to June 4
(Fig. 12). The weather for this period was as follows: thunder
showers early in the morning of May 30, rain all day, amounting to
.78 of an inch with intermittent periods of warm, bright sunshine,
thunder showers at night and early in the morning of May 31, fol-
lowed by clear weather and high temperatures for the day; cloudy
on June 1 and 2, with high humidity ; thunder showers in the evening
of June 2 and rain all day on June 3, continuing until 11 p. m.,
and amounting to 1.54 inches ; cloudy and high humidity on June 4.
For one week prior to this period, and two weeks after, the weather
was fair and dry.

The conditions associated with the first heavy infections in 1921 at
Anna in the period May 9 to 12 were similar to those of the preceding
year (Fig. 13). The precipitation during this period amounted to
1.58 inches, the days were cloudy and foggy, and the rains were pro-
longed and drizzly, interrupted by heavy showers. There was no
sunshine during the entire period and the temperature was compara-
tively low. For almost two weeks prior to May 9 the weather wa?
relatively dry and clear. After May 12, no rain occurred until May

1925} APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 519

27. Blotch was found on the fruit and foliage on May 28, as a result
of the infection of this period, and was also found generally distrib-
uted in the county.

Extensive infections occurred on June 19, 1921, at Anna during
heavy thunder showers from 7 a. m. to 3 p. m. (Fig. 13). The rain
was forceful and amounted to 3 inches within the period of eight
hours, thus drenching the orchard so thoroly that the leaves remained
wet thruout the night. The temperature rose from 21.1°C. (70°F.)
when the showers began, to 33.3°C. (92°F.) at 2 p. m., and remained
above 21.1°C. (70°F.) for sixteen hours, that is, from 8 a. m. to
12 p. m. Both moisture and temperature, therefore, were favorable
for rapid and early spore germination. The extensive infections of
this period wrere evident about two weeks later. For many days pre-
ceding the thunder showers of May 19 the weather was clear, and for
many days after it was dry, except for traces of rain on June 23, 24,
and 25. The conditions of June 19 demonstrated the fact that with
high temperature and heavy rain, infection occurs in a shorter time
than in the spring when the temperature is low.

In the season of 1922 at Urbana heavy infections occurred during
the wet period of May 25 and 26 (Fig. 14). The weather conditions
during this period were as follows: continuous rains on May 25,
.amounting to 1.76 inches for the twenty-four hour period from 7 a. m.
May 25 to 7 a. m. May 26, cloudy in the evening of May 25 and moist
conditions thruout the night ; cloudy weather on May 26 with occa-
sional rains amounting to .34 of an inch. On both days there were
thunder showers and the weather was continuously moist, while the
temperature was never below 15.5° C. (60° P.). The heavy precipita-
tion was ideal for infection, which was generally apparent on all
susceptible varieties by June 9.

The rains and wet periods of the types described for May and
June are responsible usually for the heaviest infections of the season.
It is obvious, then, that sprays must be applied frequently in this season
of the year. In the summer months the frequency of infection is less
in the dry period which often extends thru the entire summer ; con-
sequently, spraying in this period for apple blotch is necessary only at
wide intervals.

Development of the Fungus

Pycnidial Stage (a) in the Bark. — The twig growth of infected
trees reveals in August, for the first time in the season, small purplish
cankers, particularly noticeable at the nodes, and sometimes at the
internodes. They are very common on the water sprouts.

Bark cankers are the result of two different modes of infection.
First, they may result from the growth of the fungus from the
•diseased basal portion of the petiole across the absciss layer and into

520 BULLETIN No. 256 [February,.

the cortex of the twig. The majority of the node infections occur in
this manner. Second, they may result directly from spore infections.
The internode cankers are the results of such infections.

The pycnosclerotia appear rapidly with the enlargement of the
canker, and their growth in size causes the rupture of the epidermis,
and their exposure. Many, however, are not exposed until the follow-
ing spring.

In Illinois the conditions in August and September are favorable
for the growth of the fungus. These conditions prevail only for a
short time, for usually in the latter part of September and early in
October growth ceases, and the cankers remain nearly dormant thru-
out the winter. The inhibition of the fungus during the winter months
is due to the prevailing low temperature and to the presence of an
absciss layer of cells inside of the diseased region.

In March of the following year, the interior cells of the pycnosclero-
tium begin to differentiate and spores appear in the center. Spore
formation continues until all of the pseudo-parenchyma context has
become differentiated. First, a distinct sporogenous layer appears
lining the small central cavity; this increases in size as the sporo-
genous layer progresses outward to the dense dothideaceous membrane.
The conidiophores are of various lengths and frequently distinctly
septate. The spores are produced acrogenously, each cell below the
ejected spore giving rise to another spore. The pseudo-parenchyma
context is gelatinous and in the process of spore formation some of the
gelatinous substance is retained on the broad pole of the spore in the
form of an appendage, but is dissolved with the maturity and germina-
tion of the spores (Fig. 9Ai).

Early in April, the vegetative growth of the fungus in the canker
is resumed and the cankers increase rapidly in size. The formation
of new cankerous areas about the original canker continues actively
thruout April and early May. With warm, dry weather, and with
the formation of absciss layers by the host, the progress of the fungus,
is inhibited again, and the cankers remain relatively quiescent during
the summer months. Simultaneously with the enlargement of the
canker, true pycnidia appear over the surface. There are present in
the canker at the beginning of the season, therefore, two distinct
sources of spores, first, the pycnosclerotia of the original canker, and
second, the pycnidia formed with the advance of the canker.

With age the older portions of the canker become hard and dry,
and rifting and exfoliation of the bark occurs. The canker becomes
marked by definite growth areas and the tissues become dessicated
and cracked. After the pycnidia have discharged their spores, the
cankers become occupied by saprophytic fungi, notably of the genera
Phoma and Septoria. Under the dead exfoliating bark, the periderm

APPLE BLOTCH: ITS ETIOLOGY AND CONTROL

521

layer, formed in advance of the fungus, develops to the extent of
starving the fungus and repairing the wound.

In August and September the fungus grows rapidly, and simultane-
ously produces pycnosclerotia. New cankers now appear for the
first time in the season and bear only pycnosclerotia. They appear
to be the result of the same inocula which cause infection of the fruit
and foliage, the incubation period being unusually long.

The fungus grows year after year in the bark, causes the increased
annual enlargement of the cankers, and produces pycnidia in the
spring and summer, and pycnosclerotia late in the summer. Growth,

TABLE 11. — ISOLATIONS OF P. solitaria FROM BRANCHES OF DUCHESS VARIETY
Two TO FIVE YEARS OLD

Pure cultures,
successful

Contaminated cultures,
unsuccessful

Total number of
cultures

Two-year wood
Three-year wood

edge ....
/edge....

3
3

4
2

7
5

Four-year wood

(.center. . .
(edge

3

4

1
3

4

7

Five-year wood

' ' \center. . .
/edge. . . .

4
5

1

2

5

7

' ' (center. . .

0

7

7

however, is much slower after the first year and the rate decreases
with age. Previous investigators of apple blotch concede that the
fungus is inhibited in its growth within three or four years and that
the cankers disappear at the end of this period. This may be true
for some varieties and under certain conditions, but it is not true
generally for all varieties. The fungus may live indefinitely in the
bark.

In order to establish proof of the longevity of the organism in the
bark, isolations were made both from the advancing and the central
portions of cankers from Duchess trees.

Table 11 shows the results of isolations from cankers on Duchess
branches made February, 1921. The bark varied in age from two
to five years. The unsuccessful cultures bore saprophytes. These
saprophytes exist largely in the dead central portions of the cankers,
but may also occur in the raised marginal living tissue of the canker.
In March, 1921, isolations were again made from cankers on Duchess
branches with the results presented in Table 12.

Later in March further isolations were made from edges and
centers of cankers on twelve-year-old bark. Of nine isolations from
the central areas, two gave pure cultures, and of thirteen isolations
from the edge, six gave pure cultures.

These facts demonstrate that the fungus may continue its per-
ennial habit in the bark for many years on this variety. Other varie-

522

BULLETIN No. 256

[February,

ties very susceptible to bark infection likewise manifest the long-
lived character of the fungus, i.e., the Benoni, Chenango, North-
western Greening, and Missouri Pippin. Other less susceptible varie-
ties like the Ben Davis, Yellow Transparent, and Rome Beauty, may
support the fungus for only three or four years.

(b) In the Fruit. — The infections responsible for the initial
blotches usually occur in May, ordinarily between two and three weeks
after petal fall, tho they may occur even five weeks afterwards. In
some years they may occur in the latter part of April, as in 1921.

TABLE 12.-

-ISOLATIONS OF P. solitaria FROM BRANCHES OF DUCHESS VARIETY
FOUR TO EIGHT YEARS OLD

Pure cultures,
successful

Contaminated cultures,
unsuccessful

Total number of
cultures

Four-year wood

f edge ....

3

3, >

6

Five-year wood

' ' \center. . .
/edge....

0
3

3
3

3

6

Six-year wood

\center. . .
/edge....

3
3

3
3

6
6

Seven-year wood

\center. . .
f edge ....

3
2

3
4

6
6

Eight-year wood

' ' ' ' \center. . .
/edge....

1
4

5
2

6
6

\center. . .

0

6

6

Symptoms appear two to three weeks after initial infection. The in-
cubation period of the disease on the apple may vary according to
climatic conditions and in some seasons may be shorter for early
varieties, such as Duchess and Yellow Transparent, than for late
varieties such as Ben Davis.

The pycnidia are usually present on the first appearance of the
blotches, at first sparse and then many, but always definite and dis-
tinct. The pycnospores are produced rapidly and microscopic ex-
amination shows that they are present simultaneously with the ap-
pearance of the pycnidia. Usually within ten days after the first
evidence of the lesions, the pycnidia are black and upon being crushed
emit a mass of loose, distinct and apparently mature spores. The
rapidity with which the pycnidia develop and form spores is remark-
able. Oozing of spores from these pycnidia occurs in June and
July, under favorable conditions leading to secondary infections of
the fruit and foliage.

All of the pycnidia are not emptied under the first favorable
conditions. The repeated infection of the new growth causes much
increase in the disease on the fruit and foliage, which later serve as
sources of further infections. The spores from the pycnidia on the
primary blotches may reinfect the same apple. Examples of this are
common in the summer. The new lesions are small and numerous
and often appear directly below the large blotches.

1925]

APPLE BLOTCH: ITS ETIOLOGY AND CONTROL

523

The blotches increase in size with age. Late blotches resulting
from late infections develop slowly and usually remain small. On
early maturing varieties, such as the Duchess and Yellow Transparent,
the blotches are small, while on the late maturing varieties, such as
Ben Davis, Northwestern Greening, and Rome Beauty, they become
quite large. As the blotches develop, the affected tissue becomes hard
and dry, the growth of the underlying tissue is stunted, and the
tension that arises from growth of the surrounding tissues results

FIG. 15. — SECTION THRU PYCNOSCLEROTIA FROM APPLE IN COLD
STORAGE, FEBRUARY 10, 1920

in the cracking of the apple across the lesion. On the early ma-
turing varieties the cracks are usually small, narrow, or absent, but
on later maturing varieties they are quite large and deep. Pycnidia
commonly form inside the cracks on the fleshy pulp.

The blotches increase in size and produce pycnidia as the apple
develops. In August only pycnosclerotia are formed; the pycnidia
formed previous to August also become pycnosclerotia by the rejuvena-
tion of the sporogenous layer. Their walls become thick, carbonaceous,
and the pycnosclerotia sometimes coalesce and become somewhat
stromatic (Fig. 15). No pycnidia with spores, therefore, are present
on the blotches after September. Early in the following spring the
pseudo-parenchyma cells of the pycnosclerotia differentiate and by
April or May many of the pycnosclerotia contain distinct and appar-
ently mature pycnospores. Attempts to germinate the pycnospores
obtained from these sources were generally unsuccessful.

524 BULLETIN No. 256 [February,

(c) In the Foliage. — The disease is apparent two to three weeks
after infection. Pycnidia with spores appear very early and can be
recognized on the youngest lesions, maturing within a few days.
In Illinois under favorable conditions these pycnospores are liberated
in June, resulting in new infections of the fruit and leaves ; these,
then serve as additional sources of inoculum. After the spores are
expelled, the pycnidia cease functioning. The lesions resulting from
late infections both on the blades and petioles bear pycnosclerotia as
on the fruit and pass the winter in this resting stage and usually
produce pycnospores the following spring. Pycnosclerotia from over-
wintered foliage have been examined in the spring and frequently
pycnospores have been found. Pycnosclerotia are more common on
the petioles than on the blades, because the growth of the fungus 011
the petioles continues late in the season.

The development of the disease on the petioles offers a serious
aspect. At first the petiole canker is small. and ellipitical, and during
the course of the season the fungus grows downward across the leaf
scar into the cortex of the twig, usually girdling the petiole. As
early as 1909 Scott and Rorer79 were aware of the serious aspect of
petiole infection. The significance of these petiole lesions was again
emphasized by Gardner,35 who thus explained the occurrence of so
high a percentage of cankers at the nodes.

The initial lesions on the petioles commonly occur on the lower
side. Growth is rapid at first and usually by August, particularly if
infection occurs at the base of the petiole, the fungus has extended
across the absciss layer, and by the latter part of August or early
in September the canker is evident, usually adjacent to the bud.
Frequently the hyphae do not cross the absciss layer until late in the
season and the infection at the node is not evident until the following
spring. The mycelium may grow downward within the petiole and
across the absciss layer before the leaf falls. Not all cankers about
the nodes are the result of these basal petiole infections. The axil of
the leaf furnishes a convenient place for lodging spores and water
and thus for infection, resulting in frequent infection of the bud
scales, and the direct infection of the bark of the twig around the
bud. In Illinois 75 to 90 percent of the bark cankers are the result
of node infections, resulting either from the direct infection of the
bark, or indirectly by the vegetative growth of the fungus from the
infected bud scales, buds, and petioles.

Serious petiole infection causes early leaf fall. In the season of
1921, in the general absence of a crop, no spraying was done for
blotch, and petiole infection was severe. In southern Illinois, on the
Duchess variety, girdling of the petioles was completed in late July

1925} APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 525

and early in August and the lower branches of the trees were con-
spicuously defoliated by the latter part of August.

Ascigerous Stage. — The morphology, development, and life history
of P. solitaria and of the imperfect stage of Guignardia bidwellii show
many interesting analogies.

In the development of black rot of grape, as reported by Reddick,66
the pycnospores are produced in large numbers on the mummied
berries from June until early August. They are discharged under
favorable conditions and may produce new infections. In August,
pycnosclerotia and spermogonia are produced on the new spots on the
berries. Early in the spring some of these pycnosclerotia become
perithecia, and others, true pycnidia. The simultaneous production
of pycnosclerotia and spermogonia indicates the approach of the
ascigerous stage.

In the development of P. solitaria on the leaves, only the late
appearing lesions bear pycnosclerotia ; the pycnidia which formed and
functioned earlier in the season on early lesions terminate their ex-
istence after the pycnospores are discharged. On the. fruit, pycnos-
clerotia are likewise present on late appearing blotches; but the
pycnidia formed early in the season on blotches also become pycnos-
clerotia after spore discharge and pass the winter in this resting
condition. All the fruiting bodies on the apple, therefore, pass the
winter as pycnosclerotia (Fig. 15). A similar development has been
reported for black rot on the grape berry by Prillieux,61 Jaczewski,49
Perraud,60 and Prunet.62 They report that pycnidia on the fruit pass
into the resting stage in the autumn, and that the ascigerous stage
may follow during the next spring. Quoting from Jaczewski :

"When grapes affected with black rot are dried or exposed to a
low temperature (8° to 10° C.), the formation of stylospores ceases
completely and the pycnidia fill up with a white compact pulp which
consists of polygonal cells very rich in oil drops. The over-wintering,
resting pycnidia, when exposed to the moist weather of the spring,
differentiate again. In them, there develops a new activity of the
pulp cells which leads to the formation of ascospores. The pycnidia
therefore become, in this way, perithecia. It must be noted that all
of the perithecia do not reach their full development and Prunet has
already observed that the resting pycnidia (so-called sclerotia) in
nature, transform more readily into pycnidia with stylospores than
into perithecia."

The development is similar to P. solitaria on the fruit and, altho
no ascigerous stage has yet been found, the indication is that its
occurrence and formation is like that of the black rot fungus.

In the spring many of the pycnosclerotia of P. solitaria form
pycnospores and many remain sterile. Attempts by the writer to

526

BULLETIN No. 256

[February?

discover the ascigerous stage among overwintering fruit and leaves
have been unsuccessful altho doubtless it may eventually be found as
one of the final stages of the pycnosclerotium.

VARIETAL SUSCEPTIBILITY

The relative susceptibility of varieties of Malus Malus to apple
blotch has been measured in the past largely by the severity and pre-
valence of the disease on the fruit. This method, however, does not
measure the relative susceptibility of varieties nor the amount and
severity of the disease on the bark since the bark shows a much
wider variation to infection than the fruit. The comparative sus-
ceptibility of the bark is more significant also because the amount of
infection on the fruit depends on the prevalence , and distribution of
the cankers on the tree. The Jonathan variety is a typical example,
the bark of which is resistant under Illinois conditions. When this
variety grows at a distance from infected Duchess or Ben Davis
trees for example, spraying for blotch is unnecessary, but growing

TABLE 13. — RELATIVE SUSCEPTIBILITY OF APPLE FRUIT TO Phyllostwta solitaria

Very Susceptible

Arkansas Black

Gilpin

Paradise Sweet

Arkansas Red

Harvest Pippin

Red Astrachan

Ben Davis

Hawthornden

Rhode Island Greening

Benoni

Huntsman Favorite

Rome Beauty

Bentley Sweet

Krauser

Royal Pearmain

Chenango

Lansingburg

Schockley

Clayton

Lawver

Smith Cider

Doraine

Limbertwig

Sops of Wine

Duchess

Maiden Blush

Stark

Early Harvest

Mann

Tolman Sweet

Ewait

Missouri Pippin

Wagener

Fameuse

Northwestern Greening

White Winter Pearmain

Gano

Oliver (Senator)

Yellow Transparent

Moderately Susceptible

Aiken Red

Baldwin

Bradford

Champion

Fink

Golden Russet

Ingram

Mammoth Black Tv.ig

May of Myers

McAfee

Mclntosh

Minkler

Northern Spy

Rails Gennett

Rrunbo
Roman Stem
Salome
Shannon
Willow Twig
Yellow Bellflower
Yellow Newton

Resistant or Slightly Susceptible

Delicious
Grimes Golden

Jonathan
Red June

Stayman Winesap
Wealthy

York Imperial
Winesap

1925] APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 527

adjacent to such susceptible varieties the fruit of the Jonathan be-
comes infected.

The fruit of practically all the important commercial varieties
of apples in Illinois is susceptible. Observations indicate that the
Winesap variety as a whole is resistant, yet the fruit of this variety
may be found infected under favorable conditions as is true of the
fruit of many other varieties whose bark is resistant, such as, Sops
of Wine, May of Myers (Rheinish May), Wealthy, Jonathan, Early
Harvest, York Imperial, and Grimes Golden. Lewis51 found under
Kansas conditions that the Winesap and York Imperial are most
resistant but that occasionally the fruit becomes infected.

In an orchard near Anna, several Benoni trees are partly top-
worked with the Miller variety. In the absence of sprays, the apples
on the trees become infected and there seems to be no wide difference
in the susceptibility of these two varieties of apples. Only the Benoni

TABLE 14. — RELATIVE SUSCEPTIBILITY OF APPLE BAKK TO Phyllosticta solitaria

Very Susceptible

Benoni
Bentley Sweet
Chenango

Duchess
Fameuse
Lawyer
Mann

Missouri Pippin
Northwestern Greening
Smith Cider

Moderately Susceptible

Baldwin
Ben Davis
Gano
Limbertwig

Maiden Blush
Mclntosh
Oliver (Senator)
Red Astrachan

Rhode Island Greening
Rome Beauty
Stark
Yellow Transparent

Resistant or Slightly Susceptible

Aiken Red

Ingram

Red June

Champion

Jonathan

Sops of Wine

Delicious

Mammoth Black Twig

Stayman Winesap

Early Harvest

May of Myers

Wealthy

Fallawater

Minkler

Willow Twig

Fink

Northern Spy

Winesap

Grimes Golden

Rails Genett

Yellow Newton

Huntsman

Rambo

York Imperial

Susceptible to Bark Infection but Degree of Susceptibility Doubtful

Arkansas Black Golden Russet Salome

Arkansas Red Harvest Pippin Schockley

Bradford Hawthornden Shannon

Clayton Lansingburg Tolman Sweet

Domine McAfee Wagener

Gilpin Roman Stem White Winter Peru-main
Royal Pearmaiu

528 BULLETIN No. 256 [February,

twigs and branches, however, were cankered. The fruit of the Miller
trees located at a distance from Benoni trees was always free of
blotch even when unsprayed. Similarly Adams1 in Pennsylvania re-
ports an instance where Smith Cider was extremely susceptible to
canker infection while Grimes Golden growing adjacent was but
slightly infected and on the York Imperial it was impossible to find
cankers. The fruit of the last two varieties, however, was badly
infected. These and other observations warrant the statement that
the infection of the fruit of any variety is directly associated with
its proximity to infected bark. It seems then that in selecting varieties
for the orchard, the susceptibility of the bark rather than of the
fruit is worthy of most consideration. Planting of susceptible varieties
of high commercial value may be recommended, but their location in
relation to bark resistant varieties should be planned carefully.

A limited number of varieties in Illinois are seriously susceptible
to bark infections. About an equal number are moderately so, while
the majority are resistant or only slightly susceptible. The Duchess,
Smith Cider, Northwestern Greening, and Missouri Pippin are ex-
amples of varieties whose fruit and bark are extremely susceptible.
The fruit of the Yellow Transparent is very susceptible but to a
less degree than the fruit of the Smith Cider and Ben Davis. The
bark of the Ben Davis is more susceptible than the bark of the Yellow
Transparent and frequently the latter is quite resistant. The fruit
of the Rome Beauty is very susceptible, but according to the suscep-
tibility of the bark this variety is in the class with the Ben Davis.
The Jonathan, Grimes Golden, and York Imperial varieties might
be classified alike because of the resistance of the bark and because
the fruit is less than moderately susceptible. The variations in the
susceptibility of the fruit and bark in different localities prevent
satisfactory separation of varieties into more than three classes of
susceptibility. (Tables 13 and 14.)

DISSEMINATION

When bark-resistant and bark-susceptible varieties are growing
in adjacent rows the fruit of the bark-resistant varieties becomes in-
fected usually only on the side exposed to the infected trees and within
the drip of the infected branches. This indicates that the dissemina-
tion of spores is limited to a comparatively short distance during
periods when conditions are favorable for infection. The constant
proximity of the fruit and foliage lesions to the cankers on the same
tree also indicates that the infectious material is carried only a
relatively short distance under these conditions. The washing rains
associated with infection carry the spores downward to the lower half

1925] APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 529

of the tree as is always evidenced by the relative absence of the disease
high up on the tree and the abundance of it on the lower branches.
The splashing rains and washings assisted by wind carry the fungus
into the adjacent rows.

In Knox county, in September, 1921, the disease was found con-
fined to a few trees in a block of Northwestern Greening and the ex-
amination of the twigs showed that a few isolated cankers were pres-
ent on the preceding season's growth. A similar instance was found
in the same season at Mount Morris, Ogle county, on a single tree in
the center of a block of twenty-year-old Northwestern Greening. A
thoro examination of the orchard revealed a single canker. " Both of
the above orchards are located in counties where serious isolated cases
of the disease are known.

The spores, which are extruded in gelatinous masses, may retain
their vitality for some time and dried fragments of the exudate and
individual spores may be carried by wind currents for some distance.
Ordinarily, pycnospores are short-lived, but in the case of PJioma
uvicola, a very closely related organism, according to Scribner80 the
pycnospores may germinate after six months under dry conditions.
According to Rathay65 the dissemination of the pycnospores of the
black-rot fungus is effected by water and wind, the former freeing
the binding substance of the cirrhi. Viala, according to Rathay65
(p. 311), observed that on. continued drjdng the slimy cirrhi shrivel
and crumble away and that the wind blows away small fragments
holding three to four pycnospores. The dissemination of the spores
of P. solitaria under dry conditions by the wind, as the above authors
report for black rot, may account for out-croppings of apple blotch
in healthy orchards at some distance from disease centers.

Man is the most important agent of dissemination. Apple blotch
is frequently found in Illinois on young apple trees in shipments from
nurseries in the blotch infested area of the United States. Adams1
has noted several instances of its presence in Pennsylvania on nursery
stock from the Middle West.

The great danger of infesting the nurseries lies in the nursery-
man's use of infected American-grown apple-seedling stock. The
great bulk of the apple seedlings come from the region between Ross-
ville and Perry in the Kaw valley of Kansas. Apple blotch has been
prevalent in Kansas since 1903. Conclusions have been reached to
the effect that American-grown apple seedlings, especially those grown
in localities where apple blotch is prevalent, are an important means
of distributing the disease, especially when the practice of budding
is followed. There is sufficient evidence that the disease is frequently
present on seedlings coming into the eastern states from sections west
of the Mississippi river.

530 BULLETIN No. 256 [February,

In Illinois only a relatively small percentage of the seedlings are
budded; the majority are grafted. In both cases, however, even tho
the stock is healthy, the danger of making diseased trees is obvious
since 80 to 90 percent of the infection appears at the buds, which
sometimes is not evident until the spring following infection. Since
the disease is so prevalent on susceptible varieties in the east and
south-central regions of the United States, the chances of selecting
disease-free buds here is not very great and if the seedlings are grafted,
the probabilities of selecting disease-free scions is less. There is no
danger of disseminating the disease on seedling stock provided it is
used only for grafting purposes, topping back to the root is practiced,
and healthy scions are employed.

HISTORICAL : METHODS THAT HAVE BEEN ADVOCATED

In the earliest experiments on the control of apple blotch, con-
ducted by Crandall,23 Scott and Quaintance,77 and Scott and Rorer,78
measures were recommended which at that time gave satisfactory
control of the disease. Crandall23' 2* found that apple blotch yielded
quite readily to applications of liquid Bordeaux. In 1907 Scott and
Quaintance77 reported that the periods of infection were about the
same for blotch as for bitter rot and recommended the same treatment
for both diseases ; namely, four applications of Bordeaux at intervals
of two weeks, beginning six weeks after petal fall. This schedule
was modified later by Scott and Rorer78 under the belief that the
principal infections occurred from four to six weeks after the petals
had fallen. Consequently, they recommended four applications of
Bordeaux, beginning three to four weeks after petal fall, again four
weeks later, and the third and fourth applications at intervals of three
weeks thereafter. The second and succeeding applications cor-
responded with the treatment for bitter rot, so that one course of
treatment controlled both diseases. Hewitt46- 47 recommended prac-
tically the same schedule for blotch and bitter rot in Arkansas. The
idea of applying a spray three weeks after petal fall for blotch orig-
inated with Dickens and Headlee25 of Kansas. The most satisfactory
results were obtained with three applications of Bordeaux applied at
petal fall and again at three and ten weeks later. Lewis,51 in 1913,
confirmed these results and recommended an identical spraying
schedule.

Many of the earlier investigations on apple blotch control have
been concerned with the study of tbe relative merits of Bordeaux and
lime sulfur. In 1913 Lewis51 reported that lime sulfur was less
effective than Bordeaux for blotch control, and that by the continued

1925} APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 531

use of Bordeaux during successive seasons the disease could be almost
completely eradicated from the orchard. These results coincided with
those of Scott75' 76 in Virginia in 1910. The results of Blair et al8
like those of Scott, and Lewis, showed a greater efficiency from the
use of Bordeaux. The treatment which seemed to be of most value,
however, when russet and foliage injury are considered, involved the
use of lime sulfur for the early applications and Bordeaux for the
later applications. On the basis of their results, it seemed that ap-
plications at intervals of ten days after petal fall, two to three weeks
later, and ten weeks after petal fall were worthy of recommendation
in Illinois, using lime sulfur for the first two applications and Bor-
deaux for the ten-weeks spray. In 1915 Gunderson42 recommended
the substitution of lime sulfur for Bordeaux for the early applications
in order to avoid injuries to the fruit and foliage. He recommended
applications at three weeks after petal fall and at sufficient frequency
thereafter until July 1 to keep the fruit coated. In 1916 Gunderson43
considered Bordeaux superior to lime sulfur for blotch and stated
that applications at intervals of three, five, and seven weeks after
petal fall were the important sprays. Walton104 offered the same
recommendations for Ohio, with the exception that where the disease
is light or there is danger of injury from Bordeaux, lime sulfur should
be used. The results of the spraying experiments of Gunderson44 in
1917 and 1918 showed that the lime sulfur and Bordeaux sprays were
equally effective and that the three- and five-weeks sprays were the
most important.

In 1918 Brock10 employed a schedule consisting of applications
three, five, seven, and nine weeks following the bloom, and reported
inconclusive and disappointing results, stating that it was impossible
to bring blotch under satisfactory control in a neglected, susceptible
orchard in one or two years. Brock believed that very susceptible
varieties should receive applications of lime sulfur or Bordeaux at
intervals of three, four, five, and six weeks after the bloom. He12
considered the six-weeks application generally unnecessary and con-
sequently recommended the three-, four-, and five-weeks applications
under the belief that no infections occur later than five weeks after
petal fall.

The results of Gunderson45 for the three-year period 1916 to 1918
showed that applications three weeks and five weeks after petal fall,
with additional sprays under conditions of heavy rains, successfully
controlled apple blotch and that the results from Bordeaux and lime
sulfur were practically equal.

In Nebraska, Cooper,20 working on the assumption that the primary
and greatest infections occur during the four- to five-weeks period after
petal fall, recommended a schedule involving applications of Bordeaux

532 BULLETIN No. 256 [February,

three weeks after petal fall, again when spraying for the second-
brood codling moth, and an additional intermediate spray five weeks
after petal fall for heavily infected orchards. Cooper's results also
claimed the superiority of Bordeaux over the lime sulfur.

In Oklahoma,55 on the basis of five years' work, the Experiment
Station reports the worthlessness of the lime sulfur spray for apple
blotch control. For effective control, applications of Bordeaux mix-
ture are recommended at intervals of 2, 4, 5, and 7 weeks after the
petals fall.

Ballou and Lewis4 of Ohio, on the basis of one season's work, ob-
tained excellent control of blotch with Bordeaux sprays following a
2, 4, 10 weeks schedule. The same schedule with lime sulfur was
much less effective but produced the only really smooth, bright, and
attractive apples. It is interesting to note, however, that where the
2, 4, 6, 10 weeks schedule with lime sulfur was followed, the results
were as good as with the Bordeaux sprays.

With the introduction of dusts as substitutes for sprays attempts
were made to control apple blotch with dusts. The first experiments
by Crandall23' 24 with Bordeaux dust demonstrated that the dust was
inefficient in controlling the dominant apple fungi among which
P. solitaria was included ; a conclusion which was likewise reached by
Fromme8 et al34 from two years' experiments with Bordeaux dusts in
Virginia, contrary to the earlier report of Fromme and Ralston33 that
control with Bordeaux dust was as striking as it was unexpected. In
1918 Brock11 reported the failure of sulfur dusts to control apple
blotch in Illinois, and Giddings,38 experimenting with various types
of dusts, stated that dusts could not be recommended in West Vir-
ginia for the control of apple blotch or any of the dominant apple
fungi.

A new era appeared in the history of apple blotch control when
the spraying results of Rolfs72 in Oklahoma, Brock14 in Illinois, Stover
et al54> 90 and Beach5'7 in Ohio, emphasized the need of applying a
spray somewhat earlier than the three-weeks application. On the
basis of their results, the two-weeks spray has been recommended in
many states as the first spray in the schedule for the control of this
disease. In Illinois, Brock14 observed that better control was possi-
ble with the application of the two-weeks spray of either lime sulfur
or Bordeaux. The results convinced him that blotch infections
must occur in many seasons prior to three weeks after petal fall.
Beach's results from the two-, four-, six-, and ten- weeks spray schedule
with hydrated lime-Bordeaux demonstrated the possibility of obtain-
ing perfect control of apple blotch in Ohio under the most severe
cases of infection. We are indebted to Rolfs,72 however, for first

•Information obtained from personal correspondence.

1925] APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 533

emphasizing the necessity of an application at two weeks after petal
fall. He states, "The spring of 1918 was unusually wet and we
failed to get our second spray on the trees until about the middle of
the third week. Consequently fully 50 percent of the apples became
infected with the blotch organism (Phyllosticta solitarium). The
results . . . show that the second spray if applied in three weeks is
not soon enough to prevent the early blotch infections ..." This
has also only recently been found to be true for Pennsylvania
conditions.89

Supplementary to the use of fungicides for the control of apple
blotch many investigators have stressed pruning of the cankered
branches, for it has been known from the earliest investigations that
the cankers serve as the annual sources of inocula. Others have
recommended a general thinning-out pruning before the spraying
season begins in order to facilitate more thoro and general distribution
of the sprays.

Beach,5 in 1922, suggested fertilization of weak and badly diseased
trees with nitrate of soda or sulf ate of ammonia to induce an abundance
of new growth which could be kept free from cankers by spraying
and which would gradually build up a healthy fruit spur system.

Dormant Spraying

As early as 1910 apple growers in some sections of southern Illi-
nois observed that dormant applications of lime sulfur or copper sul-
fate were of some value in reducing the amount of apple blotch on
the fruit. No experiments, however, had been undertaken to deter-
mine this point. Watkins106' 107 as early as 1912 stated from field
observations that the difference in the amount of infection on trees
receiving and not receiving the winter lime-sulfur application was
not sufficient to attract attention and yet, without the confirmation
of any experiments, he felt that winter applications of lime sulfur
should reduce the amount of infection by permitting less potential
inocula. Watkins strongly urged upon the growers the necessity of
this spray primarily for scale, but his great confidence in it as a
bark spray, and his desire to see growers acquire the practice of
dormant spraying, led him to recommend it as • well for superficial
bark diseases like bitter rot and blotch. Wallace,103 experimenting on
this phase of blotch control in Indiana, claimed remarkable results
with an application of strong lime sulfur and stated, ' ' It seems prob-
able that this disease which costs Indiana growers as much as any
other apple disease will eventually be controlled by winter spraying. ' '
The assumption was also made that there would be fewer fungus
spores left to start infections. Later, Douglass27-29 claimed that one
dormant application of a very strong lime-sulfur solution "would

534 BULLETIN No. 256 [February,

eat its way into the shallow canker and kill the fungus in its strong-
hold. ' ' Gunderson 's44> 45 results show that dormant applications of
copper sulfate, lime sulfur, or Scalecide have no effect upon the growth
of the cankers or upon pycnidial formation and "altho no examina-
tions were made for spores, it is reasonable to conclude that these
were produced." Brock,14 from the results of several experiments,
and Oskamp58 have also reported no apparent blotch control from
dormant sprays.

The failure to recognize the merits of certain dormant sprays for
blotch control has resulted from the fact that investigators have
measured the effect of these sprays entirely by the amount of blotched
fruit. Their effort was directed primarily to the extermination of
the organism from the living tissues by external applications of toxic
substances, not realizing the close association between fungus and
host, and the existence of the fungus in the raised margins of the
cankers securely protected from the influence of any chemical. None
of these investigators used the microscope in the field to determine
the actual condition of the spores after the applications.

In the absence of such microscopic evidence they were at a loss
to explain their negative results. The fact that there was no apparent
difference in the percentage of control on trees receiving only the
regular summer sprays and trees receiving the dormant spray in
addition is obvious. Indeed, in some seasons during these years,
growers occasionally observed a marked difference in infection on
trees receiving and not receiving the dormant spray, and their results
led them to continue the practice of late dormant spraying. The
diversity of results among growers and investigators was due to the
varied conditions of spraying, that is, the kind of spray, the time
and frequency of the applications, the thoroness of the applications,
and the amount of infection, and to other factors inherent in the
habit of the cankers.

The Department of Botany of the Purdue Agricultural Experi-
ment Station63' 64 found from laboratory tests that a strong lime-
sulfur solution killed the spores of the fungus in exposed pycnidia
and not the mycelium in the tissues of the bark, but their field ' ' results
of 1919 indicated that the dormant spray does not in any way diminish
blotch infection on the fruit and foliage." The writer40'41 claimed
that for reasons connected with the habit and life history of the
fungus it is possible to destroy a percentage of the season's infections
with late, strong applications of copper sulfate or lime sulfur, but that
the extermination of the fungus by spraying is impossible. This report
also stated that the summer sprays were absolutely necessary to con-
trol the disease. In confirmation of this report, Brock16 recently has
stated, "Heavy applications of lime sulfur at winter strength applied
at the delayed dormant stage are partially effective in reducing the

1985] APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 535

percentage of infection, altho their use alone would not be considered
as approaching control."

EXPERIMENTS WITH DORMANT SPRAYS

As has been mentioned previously, the cankers remain relatively
dormant during the winter months, altho their increase in size and
the formation of pycnosclerotia occur during this period under warm,
moist conditions. In the spring after the buds swell and open, a rapid
enlargement of the canker is effected and true pycnidia are formed
whose spores play an important part in the season 's infections.

Previously it has been stated that differentiation of the pycno-
sclerotia begins in March and that distinct spores are present in
March and April. The pycnosclerotia may become exposed at the time
of their formation in autumn, in winter, or in the following spring.
Obviously the nearer the development of the pycnosclerotia approaches
the period of blossoming and initial infection, the greater is the number

TABLE 15. — APPROXIMATE NUMBER OF EXPOSED AND UNEXPOSED PYCNOSCLEROTIA

ON CANKERS EXAMINED AT INTERVALS DURING SPRING

OF 1923 AT URBANA

Number of cankers
examined

Date of
examination

Number of
pycnosclerotia

Number
exposed

Number
unexposed

Percentage
exposed

21
26

February 7 . .
March 23

1039
1017

245
491

794
526

23.6
48.3

of exposed pycnosclerotia. In other words, before the dormant season
for the host terminates some of the pycnosclerotia are covered, some
exposed, and no matter how late the strong dormant spray is applied
not every pycnosclerotium can be touched. It is common to find
pycnosclerotia on the outer, purplish areas of the older cankers cov-
ered even late in the dormant' season, because the thickness and
strength of the bark prevents their exposure. One-year wood and,
particularly, water sprouts show many exposed pycnosclerotia be-
fore the winter begins. Table 15 shows the relative number of exposed
and covered pycnosclerotia on cankers in February and March, 1923.
In order, therefore, to get the greatest advantage from dormant
sprays for blotch control, it is necessary to delay the application as
late as the trees will tolerate it without injury. Growers frequently
apply the dormant spray when the buds are beginning to show pink
color. This late application would be very desirable since most of the
pycnosclerotia are then exposed, were it not for the fact that the trees
cannot then be drenched without causing some injury. Therefore, the
application should be made a little earlier when the buds are swelling
and are green, even tho not as many prospective infections are likely
thus to be suppressed.

536

BULLETIN No. 256

[February,

TABLE 16. — DIFFERENCE IN THE NUMBER OF APPLE BLOTCH INFECTIONS ON

DUCHESS APPLES AS THE RESULT OF DORMANT SPRAYS

AT ANNA, JUNE, 1920

Dormant treatment

Number of apples
examined

Total number of
infections

Scalecide

15

327

Lime sulfur (1-8)

15

217

Hcaleoide

15

257

Lime sulfur (1-4)

15

120

Scalecide

15

275

Lime sulfur (1-8)

15

213

Another factor which deserves emphasis is the need of thoroness
in the applications. Every exposed pycnosclerotium must be covered
by the fungicide if it is hoped to kill the spores within. Slipshod

methods of spraying, appli-
cations from one side of the
trees, and incomplete cover-
ing of the trees have been in
part responsible for the con-
tradictory results. Every por-
tion of the bark must be cov-
ered.

The nature and strength
of the spray is of fundamen-
tal importance. Late in
March, 1920, at Anna, Duch-
ess and Benoni trees were
sprayed with commercial lime
sulfur (32° Baume, l-4y2)
and others with copper sul-
fate ( 1-41/2). Both sprays
effective in killing the

NOSCLEROTIA FROM CANKERS SPRAYED . , .

WITH COMMERCIAL LIME SULFUR 32° spores. In a neighboring or-
BAUME, 1-8, LATE DORMANT SEASON chard Duchess trees were

sprayed with commercial lime

sulfur (32° Baume, 1-8) on March 29 and 30 with the same results.
Scalecide applied at the same time and at the rate of 4 gallons of
Scalecide to 50 gallons of water had no apparent effect upon the
spores. In tallying the amount of infection on the trees receiving
and not receiving the effective dormant sprays no difference was
apparent in the amount of infected fruit, altho counts of the num-
ber of infections on apples from trees sprayed with Scalecide and
from trees sprayed with lime sulfur, showed that there was a differ-
ence in the number of infections, and that the difference was greater
on the apples from trees which received the double strength of lime
sulfur, as is shown in Table 16.

19 S5}

APPLE BLOTCH: ITS ETIOLOGY AND CONTROL

537

Since Scalecide had no toxic effect on the spores the trees receiving
only this spray may be regarded as unsprayed so far as blotch infec-
tion is concerned. The apples from which the data in Table 16 were
obtained were picked at random from the trees and the picking was
done blindfolded. The percentage and number of seriously and
slightly infected apples from these pickings are found in Table 17.

TABLE 17. — NUMBER AND PERCENTAGE OF INFECTED DUCHESS APPLES FROM TREES
SPRAYED WITH SCALECIDE AND WITH LIME SULFUR

Dormant treatment

Number of apples
examined

Apples seriously infected

Apples slightly infected

Number

Percentage

Number

Percentage

Scalecide

45
45

37
29

82
64

8
16

18
36

Lime snlfur

In these tables "slightly infected" is interpreted to mean less than
six infections per apple, "seriously infected," more than five infec-
tions. Commonly, the seriously infected fruit bore as many as fifty
or more infections. Of forty-five apples examined from the trees
receiving Scalecide, twenty apples showed more than twenty infec-
tions, eight of which showed more than forty infections; while of

TABLE 18. — EFFECT OF DORMANT SPRAY UPON AMOUNT OF APPLE BLOTCH ON
DUCHESS APPLES (after W. S. Brock")

Percentage affected

Serious

Slight

Total

Free

Double strength lime sulfur

35.2

48.5

83.7

16.3

No dormant

76.7

2.2

78.9

21.1

forty-five apples examined from the trees receiving lime sulfur, twelve
showed more than twenty blotches of which only three showed more
than forty blotches. Brock16 recently has reported some control of
apple blotch with dormant lime sulfur (Table 18). The real differ-
ences in the number of infections appear in the percentage of slightly
and seriously infected fruit.

On March 22, 1921, at Anna, three Benoni trees were given a heavy
application of homemade lime sulfur (31° Baume, 1-S1/^). At the
time of the application, the fruit buds were showing pink color and
the young leaves were well exposed. The spraying was done under
windy conditions and altho drenching was resorted to, microscopic
examination of the spores on March 31, and later in the season, showed
that generally they were not killed, even in cankers which were
specifically marked and heavily covered with the spray. This led the
writer to lose confidence in homemade lime sulfur for dormant spray-
ing of apple blotch control. In another portion of the same orchard,
Duchess, Ben Davis, and Rome Beauty trees were sprayed late with
the lime sulfur (com. 33° Baume, 1-8) and examinations of the

538

BULLETIN No. 256

[February,

pycnidia from these trees on April 10, 1921, revealed the dead col-
lapsed condition of the spores, altho several pycnidia were found full
of apparently normal spores. Other blocks of Duchess trees in the
orchard were sprayed in December, and again in March with lime
sulfur (com. 32° Baume, 1-8) and no pycnidia could be found with
normal spores on March 22, 1921. However, since the fungus was
not killed, the cankers enlarged in April and a new source of in-
fection arose. Nevertheless, the fruit on these trees was relatively

TABLE 19. — EESULTS FROM TREATMENT OF CANKERS WITH CHEMICALS LATE IN THE
DORMANT SEASON, URBANA, 1922

Treatment

First application

Second application

Resultt

Strength

Date

Strength

Date

\\i-50
4-50
6-50
20-50
1-5

April 3

1 qt.-15 gals.
3^-50 , <
3^-50
13-50
(Not duplicated)

April 15. . .

+

Aoril 3

April 13

Spra-Mulsion

April 3

April 13

April 3

April 13 ...

Copper sulfate

April 13

1 ( — ) indicates that the spores were not affected; (+) indicates that the spores were affected.

free of blotch when the orchard was examined on May 27, while
in a neighboring Duchess orchard where the dormant spraying
was only partially effective in killing the spores, and where the trees
were much less severely cankered, the apples were quite heavily in-
fected. Similar results have often been observed by growers.

In the spring of 1922, dormant spraying experiments were under-
taken on Northwestern Greening trees in the University Orchards
at Urbana. The materials used were Phenolene, Sealecide, Spra-
Mulsion, copper sulfate, and dry lime sulfur. Two dormant appli-
cations were made with each solution excepting with copper sulfate,
as noted in Table 19.*

On April 23 and June 5, cankers from the trees receiving these
applications were brought into the laboratory and it was found that
the pycnidia and spores from the trees receiving the strong copper-
sulfate spray were dead. All other sprays applied had no effect upon
the fungus. No data were taken upon the relation of these dormant
sprays to the amount of infection upon the fruit, since the trees were
adjacent to one another in the same row. In a near-by orchard a
heavily cankered tree was sprayed on April 3 with copper sulfate in
the proportion of 1 pound of copper sulfate to 15 gallons of water
and the examination of the pycnidia later in the season showed the
toxic effect of the fungicide.

The evidence obtained from these experiments with dormant sprays
indicates that it is possible to reduce the amount of the season 's inf ec-

"The Phenolene, Spra-Mulsion, and dry lime sulfur were furnished by the
Sherwin-Williams Company; the Sealecide by the Pratt Fungicide and Insecti-
cide Company.

19S5] APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 539

tion by dormant spraying with commercial lime sulfur or copper
sult'ate. It seems from these results that a dilution of commercial
lime sulfur (32° Baume, 1-8) recommended for San Jose scale in
Illinois orchards is strong enough to kill the spores in the exposed
pycnidia. The experiments also show that copper sulfate (l-4!/2 and
1-15) produces the same effect. Until more definite evidence is secured
a solution of copper sulfate prepared in the proportion 1-10 can be
applied with the assurance of success, since the greater the concentra-
tion, the greater the deposit, and the less rapidly the material is likely
to wash from the branches or become too diluted before accomplishing
its effect. The practice of applying two dormant sprays for bark-
susceptible varieties of apples has been followed by some southern
Illinois orchardists and is a sound one. For the purpose of suppressing
as much prospective infection as possible, it is particularly desirable
to spray as late as possible. The spring applications are also more
effective than the autumn applications for the control of San Jose
scale. It is suggested that the entire orchard be sprayed with com-
mercial lime sulfur (32° or 33° Baume, 1-8) primarily for scale, and
the blotch-cankered varieties again very late with copper sulfate (1-
10). With the present cheap price of copper sulfate and the value
that can be derived from this spray, southern Illinois growers can
well afford its application. If the duplicate application is not pos-
sible, then the application of commercial lime sulfur only (32° or
33° Baume, 1-8) for the bark-susceptible varieties should be post-
poned as late as the trees will tolerate it.

The writer claims that the dormant spray reduces the season's
infections, but since the remaining infection that does not come within
the reach of the dormant spray may be large, the difference between
the amount of disease on the fruit of those trees receiving and those
not receiving the application may not be sufficient to attract attention.

Effect of the Fungicide

The difference in the appearance of the spores affected by chemicals
and the normal spores is very striking. In contrast to the normal
turgid, broadly elliptical spores containing large globules (Fig. 9 A),
the affected spores are collapsed, like irregularly shaped rods or clubs,
usually retaining the attached collapsed appendage (Fig. J6). The
original globules in the spore cell are united into an irregular, homo-
geneous mass and their individuality lost. The pycnidia affected by
the fungicide are brittle, rigid, and inflexible, and the dead spores
can be pressed from them only with difficulty. In the summer, the
contents of these pycnidia are dry and collapsed into a hard mass
and the individual spores lose their identity (Figs. 17, 18).

540

BULLETIN No. 256

[February,

The pycnidia are conspicuously larger after rains than during dry
periods, due to the swelling of the concentrated food materials in the
gelatinous matrix. When cankers are covered with lime sulfur or
copper sulfate it is evident that these chemicals in solution over the

FIG. 17. — SECTIONS THRU PYCNOSCLEROTIA, SHOWING THE EFFECT
OF DORMANT SPRAY

(A) Collected June 7, 1920, from canker sprayed with copper
sulfate; (B) higher magnification of A, showing the dead,
irregular content of the pycnosclerotium.

cankers are carried into the matrix of the exposed pycnosclerotia.
Therefore, during wet periods, the effect of these substances may be
expected to be at the maximum. Cooper21 found that the stromata of
Nummularia discreta absorbed copper sulfate and lime sulfur readily

1925]

APPLE BLOTCH: ITS ETIOLOGY AND CONTROL

541

in solution, with the result that the quantities of spores expelled and
the percentage of germinations were considerably reduced. The
greatest effect was obtained with copper sulfate. He suggested spray-
ing the cankers with copper sulfate at the rate of 1 pound to 2 gallons
of water as one means of preventing the dissemination of ascospores
in the spring. For use on apple blotch cankers the copper sulfate
seems to be more desirable than lime sulfur. The fact that it is

FIG. 18. — SECTIONS THRU PYCNOSCLEROTIA

(A) From canker receiving dormant spray, collected April 18, 1920; (B) from
an unsprayed canker, collected March 21, 1920.

readily soluble, and that the solution readily passes into the fungus
and the dead tissues of the canker, and that it persists in these por-
tions long after the application, gives it an added advantage.

To illustrate the need of moisture to produce the maximum effect
with the fungicides, the following observations are noteworthy. On
March 30, 1920, at Anna, Duchess trees were sprayed with commer-
cial lime sulfur (32° Baume, l-4i^>). On the night of March 31 there
was a heavy rain and the following morning pycnidia from these trees
were examined and the contents found to be dead. Four young
Duchess trees in another orchard at Anna were drenched with copper
sulfate (l-4Vk) and on the following day most of the spores appeared
normal, no precipitation occurring between the time of application
and the observation. A few days later a heavy rain fell and when the
spores were examined on April 8 after the rain they were dead
(Plate 4). It seems then, that the spray alone is not sufficient to carry
the chemicals into the pycnidium and that a wetting is necessary to
soak and soften the carbonaceous membrane.

EXPERIMENTS WITH SUMMER SPRAYS ..

The plan of the spraying experiments has been based largely on
the life history of the fungus. The results of the treatments con-

542

BULLETIN No. 256

[February,

TABLE 20. — PLAN OF APPLE BLOTCH CONTROL EXPERIMENT, ANDERSON DUCHESS

ORCHARD, ANNA, 1920

Plat
No.

Treatment

Applications

Calyx

2 wks.

3 wks.

4 wks.

5 wks.

6 wks.

7 wks.

1

2
3
4

5
6

7
8
9
10
11
12

13
14

15
16

17
18

19

X

X

X

X

X

X

X
X

X

X

X

X

X

X

Check

X

X

X

X

..

Lime sulfur

X
X

X

X
X

X

X

X

X
X

X

Lime sulfur

X

X

X

X

X

X

Lime sulfur

X

X

X

X

X

X

Lime sulfur

X

X

X

X

X

X

Lime sulfur

X

Bordeaux

X

X

X

X

X

Lime sulfur

X

Bordeaux

X

X

X

X

X

..

Lime sulfur

X

Bordeaux

X

X

X

X

X

X

Lime sulfur

X

Bordeaux

X

X

X

X

X

X

X

X
X

X
X

Bordeaux

X

X

X

X

X

Bordeaux

Lime sulfur

X

X

Bordeaux

Lime sulfur

X
X

X
X

X
X

X
X

X

Lime sulfur

Bordeaux

Lime sulfur

X

X

X

X

Bordeaux

Lime sulfur. . .

X

X

X

NOTE. — All Bordeaux was of the 3-4-50 formula. All lime sulfur was of the
1-50 formula, commercial 32° Baume. All sprays combined with powdered arsenate
of lead 1-50.

ducted by growers under the supervision of the writer, and the re-
sults of the experiments of the writer are based on field work of three
seasons at several localities in Illinois. The control work has been
largely of a demonstrative nature and on a small scale, and while
extensive data have not been obtained, the results are sufficiently con-
clusive to warrant the statement that successful control of the disease
with sprays is possible in even the most seriously infested orchards.

PLATE 4. — SECTIONS THRU PYCNOSCLEROTIA

(A, C) From cankers sprayed late in the dormant season with copper sulfate;
(B, D) from cankers not sprayed in dormant season, Anna, May, 1920.

1925] APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 543

In 1920 at Anna

The spraying experiments for the control of apple blotch were
conducted in a block of Duchess trees in the Anderson orchard. The
trees were about fifteen years old, in good vigor, and they seemed
not to be weakened from apple blotch altho cankers were sufficiently
abundant to cause severe injury to the entire apple crop in the ab-
sence of sprays. In June, it was found that on unsprayed trees sixty
apples picked at random showed on each apple an average of eighteen
blotches.

The orchard was divided into plats of four trees each. Various
schedules with applications of Bordeaux 3-4-50 and lime sulfur 1-50
with arsenate of lead were employed (Table 20). The schedules called
for applications at two, three, four, five, six, seven, and eight weeks
after the fall of the petals. Certain applications were omitted in
some plats, since the purpose of the experiment was to determine
which schedule and treatment would give most satisfactory control.
A sufficient number of unsprayed trees was left for adequate compari-
son. The spraying was done with a power sprayer and bamboo rods
were used for all of the summer sprays.

The dormant spray of lime sulfur was applied when the buds were
opening and showing green (March 28 and 29), the cluster-bud spray
of lime sulfur (1-40) was applied on April 17 and 18, and the calyx
spray of lime sulfur and lead arsenate on April 26 and 27 when the
petals were 75 percent fallen. The spray two weeks after petal fall
(commonly called the first blotch spray), was delayed until seventeen
to nineteen days after the fall of the petals (May 14 and 15). No
difficulty was encountered in the application of the remaining sprays.

The fruit was harvested July 5 and since poor control was obtained
in all of the plats, no attempt is here made to present the results of
the treatments, altho the study of the results afforded a means of ex-
plaining the failures and gave evidence regarding the time and con-
ditions associated with infection. The failure to apply the first blotch
spray on time — two weeks after petal fall and prior to the rainy period
of May 11 to 13 — and the fact that rains were continuous during the
period May 11 to 21, favored extensive infection of the fruit and
foliage. Even from plats receiving all of the other sprays in the
schedule the percentage of blotched fruit was almost equal to that
from unsprayed trees altho the number of infections on the fruit was
considerably less. The results emphasized the fact that the most ex-
tensive infections of the season may occur prior to the three-weeks
application. The serious injury to the fruit from early applications
of Bordeaux, i.e., at petal fall and two weeks after petal fall, and the
absence of injury from treatments of lime surfur at these intervals,
demonstrated that lime sulfur is the more desirable spray for early
applications.

544 BULLETIN No. 256 [February,

In 1921 at Anna

In 1921, spraying for apple blotch control was conducted in a
block of Benoni trees thirty-five years of age in the Miller orchard.
The trees were badly cankered and the fruit had been blotched
severely in previous years in the absence of sprays. The age of the
trees necessitated renovation, which consisted in the removal of many
of the top branches, dead wood, and crowding branches ; a more uni-
form distribution of the sprays thus being possible. Unfortunately
late frosts killed most of the blossoms; however, a sufficient amount
of fruit set to warrant the continuation of the experiment.

Bordeaux, hydrated lime-Bordeaux mixture, and homemade lime
sulfur testing 31° Baume were used as sprays, and all of the applica-
tions were combined with powdered arsenate of lead in the proportion
of 1 pound to 50 gallons of water. The spraying was done with a
power sprayer at a pressure of 250 pounds and rods were used ex-
clusively.

The dormant spray was applied to all of the plats on March 20
when the fruit buds were beginning to show pink. It served the pur-
pose of both the dormant and cluster bud sprays. The treatment was
homemade lime sulfur testing 31° Baume used in the proportion of
1 gallon of lime sulfur to 7 gallons of water. The calyx spray was
applied on April 9, three days after the recorded date of petal fall
(April 6) with the same fungicide in the proportion of 1-35 and with
the addition of powdered arsenate of lead (1-50). The season was
abnormal and the fall of the petals occurred unusually early.

The treatments were made at intervals of two, three, four, five, six,
and seven weeks after petal fall. Various omissions, and alternations
between lime sulfur and Bordeaux, were made in the spray schedule
(Table 21). It was intended originally to omit the two-weeks spray
in Plats 2, 6, 12, and 15, but because of the high wind prevailing
two weeks after the fall of the petals it was impossible to spray the
rest of the orchard without spraying the trees in these plats, especially
on the leeward side of the trees. The remaining summer sprays
were applied under ideal weather conditions. Six trees were main-
tained as checks, three of which, isolated from the orchard by a peach
orchard, had been treated earlier in the season with homemade lime
sulfur (31° Baume, 1-31/2). As previously stated, this -spray had
relatively no effect upon the spores, because of the weakness of the
fungicide and its poor application under conditions of strong wind.
Consequently, these three trees have been considered in the same class
with the trees in Plat 15, which were not sprayed at all.

Because of the late frosts, the fruit was thinned out severely and
the result of this, combined with heavy pruning, had the effect of

1925}

APPLE BLOTCH : ITS ETIOLOGY AND CONTROL

TABLE 21. — PLAN OF APPLE BLOTCH CONTROL EXPERIMENT,
MILLER ORCHARD, ANNA, 1921

Plat
No.

Treatment

Applications and dates

2wks.
Apr. 21

3wks.
Apr. 27-28

4 wks.
May 3-4

5 wks.
May 12

6 wks.
May 18

7 wks.
May 29

1

2
3

4
5

6

7

8
9

10
11

12

13
14

15

Hydrated lime bordeaux. . . .
Lime sulfur

X

X
X

X
X

X
X

X
X

X

X

X

X

X

X
X

X

X
X

X
X

X
X
X

X
X

X
X

X
X

X
X
X

X
X
X
X

X
X

X

X
X

X

X
X

Hydrated lime bordenux. . . .

Hydrated lime bordeaux. . . .
Lime sulfur

Hydrated lime bordeaux. . . .

Bordeaux

Lime sulfur

X

Bordeaux

Bordeaux

Lime sulfur

X

Bordeaux

Lime sulfur

X

Bordeaux

Lime sulfur

X
X

Lime sulfur

Bordeaux

Lime sulfur

X

Bordeaux

Lime sulfur

Lime sulfur

X
X

Lime sulfur

Check. . .

NOTE. — All hydrated lime Bordeaux was of the 3-5-50 formula. All Bordeaux
was of the 3-4-50 formula. All lime sulfur was of the 1-36 formula (homemade
31° Baume). All sprays combined with powdered arsenate of lead 1-50.

producing large apples. Approximately eighty bushels of apples were
harvested from the forty-seven trees in the orchard, altho some trees
bore no fruit. The apples from the sprayed trees were free of dis-
ease and spray injury, and the control of apple blotch was perfect.
The fruit from the check trees and the drops from these trees were
gathered and sorted into three classes, namely, blotch free, slightly
blotched, and seriously blotched (Table 22).

The records of natural infection for the season of 1921 at Anna
show that a light primary infection occurred as early as April 26
and 27, or nineteen to twenty-one days after petal fall, but since all
of the trees in the orchard received spray two weeks after petal
fall (April 21) infection was prevented. The next — the first heavy
infections — occurred in the period May 9 to 11. Prior to this many
of the plats had already received three blotch sprays, namely two
weeks (April 21), three weeks (April 27 and 28), and four weeks

546

BULLETIN No. 256

[February,

(May 3 and 4) after petal fall, and since every plat received the two-
weeks spray and either the three-or four-weeks spray as the plan of
the experiment shows, (Table 21), no infections resulted.

TABLE 22. — RESULTS OF THE SPRAYING EXPERIMENT FOR THE CONTROL OF APPLE

BLOTCH, ANNA, 1921

Number apples
examined

Number blotch-
free

Number blotched

Slightly

Severely

Total

Percentage

Unsprayed. . . .
Sprayed

1,379

186
Perfect control in all
plats

446
0

747
0

1,193
0

86.5
0

In 1922 at Urbana

The Urbana orchard consisted of several winter varieties of apples,
some trees of which were severely cankered with apple blotch and
black rot. The trees were about thirty years old, high, and bore a
considerable amount of dead wood. In order to improve the trees
for spraying a heavy pruning was resorted to in the dormant season.
The setting of fruit in 1922 was small and altho some trees bore
heavily, the amount of fruit on others was insignificant, and too small
for the purposes of the experiment.

The spraying was done with a power sprayer and both guns and
rods were employed. The dormant spray of commercial lime sulfur
(33° Baume, 1-8) was applied; late in the dormant season, on April 3

TABLE 23. — TREATMENTS AND TIME OF APPLICATION OF SPRAYS IN THE WEBBER

ORCHARD, URBANA, 1922

Application

Treatment

Time of application

Cluster bud

April 12

Calyx

Lime sulfur (1—50) lead arsenate (1—50)

May 2 (Petals fallen 75%)

Two weeks

Lime sulfur (1—50) lead arsenate (1—50)

May 15

Three weeks. . . .

Lime sulfur (1—50) lead arsenate (1—50)

May 23

Four weeks ....

May 31

Six weeks

Lime sulfur (1—50) lead arsenate (1—50) lime (1—50). . .

June 13

Ten weeks

Lime sulfur (1-50) lead arsenate (1-50) lime (1-50). . .

July 11

(Table 23). Three trees were left unsprayed excepting for the dor-
mant, cluster bud, and calyx applications.

On July 23, a record was taken of the amount of blotch on dropped
apples from the check trees (Table 24). There were no dropped
apples from the sprayed trees and careful observations of these trees
in the latter part of July testified to the absence of blotch on the fruit
and foliage. On the unsprayed trees the fruit and foliage chiefly on
the lower branches were infected. The orchard was given no attention
after July and since a serious outbreak of codling moth, combined

1985]

APPLE BLOTCH: ITS ETIOLOGY AND CONTROL

547

with black rot infection, occurred in August, much of the fruit was
wormy and infected with black rot at harvest time. Undoubtedly the
application of an insecticide in August would have protected the fruit
against the third-brood codling moth, and its combination with a fungi-
cide would have safeguarded the season 's growth against late infections
of apple blotch, had the weather conditions been favorable. In Sep-
tember and October, and again in March, 1923, the season's twig
growth was examined for bark cankers. These were found largely
on the water sprouts, and only on the unsprayed trees. The two-,
three-, four-, six-, and ten-weeks spray schedule, therefore, demon-
strated its efficiency in controlling apple blotch in this orchard in
1922. The exclusive use of lime sulfur in all of the sprays and the

TABLE 24. — NUMBER OF DROPPED BLOTCHED AND BLOTCH-FREE APPLES FROM CHECK
TREES IN THE WEBBER ORCHARD, URBANA, 1922

Total number
apples examined

Number blotch-
free

Number blotched

Slightly

Severely

Total

Percentage

2 trees, undetermined
variety

860
326

741
121

97

77

22
128

119
205

13.8
63

1 tree, Ben Davis. . . .

absence of spray injury on the fruit testified to the decided effective-
ness of lime sulfur for the control of apple blotch.

In 1922 at Lilly

The main purpose of the work at Lilly was to demonstrate con-
trol of apple blotch with the proper spray schedule. The trees were
of the Northwestern Greening variety on which the disease was mak-
ing serious progress. Attempts by the owner to control the disease
had failed every season since its first appearance in 1917. In 1921
the fruit from many of these trees was ruined by blotch. Approxi-
mately twenty-five trees were used in the plan of the experiment and
two of these were not sprayed.

The calyx spray was applied on May 5 and 6, when 75 percent of
the petals had fallen. The spraying was done with a power sprayer
and both spray gun and rods were employed (Table 25). The orchard
was visited on July 20 and no blotch could be found on the fruit and
foliage of the sprayed trees, but it was common on the unsprayed
trees. During the period May 23 to 26, seventeen to twenty-one days
after petal fall, heavy infections occurred at Lilly, symptoms of which
were apparent on the fruit and foliage by June 7 and 8. The ab-
sence of the disease on the sprayed trees indicated that the two-weeks
spray (May 19) was applied at the right time. The perfect results
demonstrated the success of the two-, three-, four-, six-, and ten-weeks
spray schedule.

548 BULLETIN No. 256 [February,

At Rome a control demonstration was undertaken on six North-
western Greening trees as a cheek on the results at Lilly. Local help
was relied upon to apply the two- and three-weeks sprays of lime sulfur,
but no accurate information could be obtained as to the time and
manner of these applications. The writer applied the four-weeks
(June 9) and six- weeks (June 23) sprays of Bordeaux. No attention
was given to the orchard after June 23 (six- weeks spray) and conse-
quently no data were obtained on the condition of the crop at harvest
time. There was a considerable amount of disease on the fruit and
foliage as early as June and the infections were traced to the condi-

TABLE 25. — TREATMENT AND TIME OP APPLICATION OF SPRAYS
AT LILLY ORCHARDS, 1922

Application

Treatment ,

Time of application

Lime sulfur (1—40) lead arsenate (1—50)

May 19

Lime sulfur (1—40) lead arsenate (1—50)

May 26

Lime sulfur (1-40) lead arsenate (1-59)

June 2

Bordeaux (3-4-50) lead arsenate (1-50)

June 16

Bordeaux (3—4-50) lead arsenate (1-50)

July 20

tions of May 23 to 27, or two and one-half to three weeks after petal
fall. It was evident that the early infections were not suppressed,
altho spraying had the effect of reducing the amount of infection
more than in previous years.

SUMMER SPRAYING: CONCLUSIONS

While the spraying experiments have not been extensive and on
a large scale, the results, together with the knowledge of the life his-
tory of the fungus, make it possible to arrive at recommendations for
the successful control of the disease with sprays.

The infections are most frequent in the spring and consequently
the application of sprays must be frequent at this time of the season
in order to keep the growth protected, and as the summers are usually
dry, applications are necessary only at wide intervals. Since the pri-
mary infections usually occur from two to three weeks after the petals
have fallen, the first spray for apple blotch must be applied between ten
days and two weeks after petal fall and not later than two weeks after
petal fall. This recommendation applies to all varieties of apples. It
is the critical application of the season and the production of blotch-
free apples depends upon the timely and thoro application of the
first spray. The suppression of the first infections is significant in
that it prevents the multiplication of the disease in the orchard.

In addition to the two-weeks spray, later sprays must be applied
in the order of three, four, six, ten, and fifteen weeks after the petals
have fallen, the last two applications conforming to the period of the

APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 549

second- and third-brood codling moth. They are particularly necessary
for susceptible fall and winter varieties of apples. In view of the
duration of the infection period the need of so many sprays is obvious.
Since the spraying with arsenate of lead for the second- and third-
brood codling moth is generally practiced, the addition of a fungicide
at these intervals is only a matter of some small expense compared with
the value of the returns. The two-, four-, six-, ten-weeks schedule of
Beach5 of hydrated lime-Bordeaux (3-5-50), the preliminary schedule
of Rolfs72 of Bordeaux at two and four to five weeks and arsenate of
lead at seven to eight weeks after the fall of the petals cannot be
recommended in Illinois since the period between the two- and four-
weeks applications is entirely too long and since no provision is made
for late infections, and further because under Illinois conditions Bor-
deaux cannot safely be used ordinarily at two weeks after the fall of
the petals. Likewise, the two-, three-, four-, five-, seven-, ten-weeks
schedule of Brock16 of early applications of lime sulfur and summer
applications of Bordeaux, makes no provision for late seasonal infec-
tions. It is more profitable, and as effective, to omit the five- and
seven-weeks applications and to make an application at six weeks after
petal fall, especially for early varieties like the Duchess, Benoni, and
Yellow Transparent, which usually require from nine to ten weeks
to mature. Ordinarily, the conditions are dry in Illinois after four
weeks after petal fall and with the protection afforded by the two-,
three-, and four-weeks applications it is unnecessary to make the next
application until six weeks after petal fall. The six-weeks applica-
tion for early varieties also is as effective as the seven-weeks applica-
tion for the protection of the growth until harvest.

The time of the applications is of more importance than the nature
of the spray. Lime sulfur and Bordeaux are still considered the
standard and dependable sprays for Illinois orchards. They have
been employed repeatedly by the writer in the control of apple blotch
with equal and highly favorable results, thus verifying earlier litera-
ture. However, because of the greater adhesive quality and toxicity
of Bordeaux this fungicide is the better spray for long periods;
nevertheless, with the schedules employed, lime sulfur alone has given
perfectly satisfactory results. Both of these fungicides should be
employed in the proportions recommended under Illinois conditions;
namely, lime sulfur 32° Baume, 1-40 and Bordeaux 3-4-50. The se-
lection of either one of these fungicides for any particular applica-
tion depends upon the variety and the prevailing weather conditions.
The moist cool weather of the spring months in Illinois prohibits the
use of Bordeaux and the hot dry weather of the summer prohibits the
use of lime sulfur. The general fungicidal effect without burning can
successfully be obtained by employing lime sulfur for the first one or
two blotch sprays — at two weeks and three weeks after petal fall—

550 BULLETIN No. 256 [February,

and Bordeaux for the remaining applications. The results of the
writer, and those of growers, with hydrated lime-Bordeaux have dem-
onstrated that its efficiency for apple blotch control is equal to that
of the ordinary Bordeaux prepared from slaked lime and that its
use also must be restricted to applications later than two and three
weeks after petal fall.

The success in controlling apple blotch lies in keeping the surface
of the fruit, foliage, and growing twigs covered with spray during
the growing season. The failures have been, and are, due to delay
in the first application, and to making the applications too far apart.
A power sprayer furnishing pressure of 225 to 300 pounds is neces-
sary to apply the spray forcibly (as a fine mist), in order to reach
every portion of the tree.

OTHER ASPECTS OF CONTROL
Soil Treatments

The results in Illinois from fertilization of blotch infected orchards
with sodium nitrate or ammonium sulfate gave no evidence of in-
creased resistance of the bark to apple blotch nor any reduction in the
amount of the disease. Rather the opposite was true, since the in-
creased succulence of the growth as the result of soil treatments was
favorable for infection and for the growth of the fungus.

Fertilization, however, is necessary for the rejuvenation of badly
infected trees and the spraying program for the control of blotch
in badly infected orchards should include some attention to the needs
of the soil, cultivation and the use of nitrogenous fertilizers being
desirable. Since the trees respond actively to soil treatments they
must be sprayed regularly in accordance with the recommended spray
schedule in order to maintain growth free of infection. Following
such a procedure, some varieties of trees may eventually be freed of
bark cankers.

Pruning

The removal of infected branches and twigs, primarily to decrease
the amount of apple blotch infection, is impracticable and seems never
to have been adopted by growers. The practice causes excessive prun-
ing and involves much time and expense.

Pruning for the .purpose of removing dead wood and crossed
branches, thus opening the trees to uniform distribution of the spray,
is a worthy practice. The succulent growth which may be induced
as the result of this pruning can be maintained free of infection
by spraying.

1925] APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 551

Surgery

Even tho histology of the bark cankers shows that removal of the
fungus from nursery stock or young trees in the orchard by cutting
is a simple operation, the method cannot be recommended since the
cankers are frequently too numerous, and often too small to be de-
tected by the growers. The method is tedious and impracticable, re-
quiring reinspection of the trees and repetition of the process, for
which reasons growers cannot be induced to undertake the practice.

It is more desirable to reject diseased trees from the nursery and
thus keep the fungus from the orchard.

Protective and Preventive Measures

The means of avoiding apple blotch in the young orchard rest
largely with the nurserymen. Nurserymen grow and sometimes sell
diseased trees, and it is known that they have received blotch-infected
apple seedlings from localities where apple blotch is seriously preva-
lent. It is desirable, therefore, that measures be enforced in the
separate states that will insure rigid inspection of all apple seedlings
and the exclusion from shipment of all stock that is infected.

In order to insure disease-free apple seedlings the seedling growers
should be required to spray the nursery rows during the growing
season. This is a protective measure for the thousands of growers
and nurserymen in the United States who are necessarily dependent
for their stocks upon the American growers of seedlings.

In the second place, local nurserymen must protect themselves
against the receipt of infected seedling stock from the seedling growers,
and the steps which they may wisely take will consist of rigid inspec-
tion of the seedlings and the rejection of all infested stock intended
for budding. If the seedling stock is used for grafting there is no
danger of distributing the disease provided healthy scions are em-
ployed. Unless it is possible to obtain blotch-free American grown
apple seedlings, it may be wise for nurserymen to use foreign-grown
seedling stock.

Local nurserymen must be cautious in the selection of buds and
scions, and as a measure of safety should select them from trees which
they know are free of blotch cankers. As long as spraying is directed
primarily for the protection of fruit, infections of the bark will occur ;
thus the danger of selecting diseased buds and scions is evident,
especially among early varieties, such as Yellow Transparent, Benoni,
and Duchess. Since the fungus persists for many years in the bark
of some varieties, the policy of destroying cankered trees in the
nursery rows should be followed rigidly in order to safeguard other
trees from infection.

552 BULLETIN No. 256 [February,

The growers can save themselves much expense and unnecessary
losses later in the fruiting period of the trees by carefully examining
the young trees upon receipt from the nurseries and rejecting those
which show evidence of cankers. The planting of healthy trees
is strongly recommended and is most economical in the end. If the
grower is not sure of obtaining blotch-free trees from nurserymen in
the blotch area it may be wise for him to buy from nurseries in states
where the disease is known not to exist.

Selection and Location of Varieties

It is imperative to select varieties which are bark-resistant, and to
plant them at a distance from bark-susceptible varieties.

Growers are divided in their opinions as to the selection of vari-
eties, even among those seriously susceptible to fungi. In the central
and western sections of the state, commercial growers still favor the
Ben Davis in spite of the fact that all our serious apple maladies are
common on this variety, blotch, blister canker, and scab being espe-
cially so. In southern Illinois, owing to this susceptibility, the Ben
Davis has become unpopular and is no longer planted. Likewise, there
is difference of opinion in regard to the Duchess variety, which in
Illinois ranks among those most susceptible to apple blotch ; yet some
growers realize that control is possible and they feel that the high
market value of this apple warrants planting it. It must be empha-
sized, however, that the more susceptible the variety the more ex-
pensive its culture, and unless growers feel that they can care for
the trees in the proper manner they should select varieties which are
relatively bark-resistant, and by all means reject varieties very sus-
ceptible to bark infection (Table 14).

The writer opposes the selection of bark-susceptible varieties, since
it is obvious that the control of insects and fungi is a serious problem
to be avoided when possible. However, if a grower insists upon plant-
ing these varieties he should separate them well from resistant ones
so that he may concentrate his spraying, especially during the busy
seasons, within a relatively small area and thus save time and labor.

RECOMMENDATIONS FOR CONTROL

The recommendations for the control of apple blotch may be con-
sidered under two headings — pruning and spraying.

In pruning, aim to remove crowded and dead branches in accord-
ance with general pruning methods so that the sprays may reach
every apple. Remove surplus water sprouts: they are particularly
undesirable since they are very susceptible to infection. In renovat-

1925] APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 553

ing the orchard, leave only those water sprouts which are expected to
be of some use in developing the framework of the trees.

All pruning should be done prior to the dormant spray.

Trees must be sprayed uniformly. The practice of applying the
spray from one side of the tree with the wind, or from one side of the
tree for one application and from the opposite side for the succeed-
ing application, cannot be recommended. Either guns or rods may
be employed with disc nozzles having small openings. High pres-
sures of 225 to 300 pounds are desirable to force the spray into the
trees as a fine mist. It is necessary to apply the sprays on time with
reference to the time the petals have fallen (75 percent fallen) and
in accordance with the following schedule.

Dormant Spray. — This application should be made late in the dor-
mant season, preferably when the tips of the buds are showing green
(delayed dormant), using commercial lime sulfur 32 or 33° Baume
in the proportion of 1 gallon of lime sulfur to 8 gallons of water, or
copper sulfate in the proportion of 1 pound to 10 gallons of water.
Spray thoroly and if severely cankered, drench the trees.

First Blotch Spray. — Apply a few days earlier than two weeks
after petal fall and complete the application by two weeks after petal
fall. Use lime sulfur in the proportion of 1 gallon of lime sulfur to
50 gallons of water; and for every 50 gallons of spray solution, add
1 pound of powdered arsenate of lead.

Second Blotch Spray. — At three weeks after the fall of the petals,
use the same treatment as for the first blotch spray.

Third Blotch Spray. — At four weeks after the fall of the petals,
use Bordeaux in the proportion of 3 pounds of copper sulfate, and
4 pounds of slaked lime* to 50 gallons of water.

Fourth Blotch Spray. — At six weeks after the fall of the petals,
use the same treatment as for the third blotch spray.

Fifth Blotch Spray. — At nine or ten weeks after the fall of the
petals, use the same treatment as for the third blotch spray, adding
1 pound of powdered arsenate of lead for every 50 gallons of spray.
The time of this application corresponds to that of the second-brood
codling moth.

Sixth Blotch Spray. — Apply in the middle of August. The time
of this application corresponds to that of the third-brood codling moth.
Use the same materials as for the fifth blotch spray. This is the last
spray for apple blotch and is intended to protect the fruit of late
varieties against late infections. Its application in some seasons for
blotch may not be necessary, depending upon the weather.

• If hydrated lime is used instead of rock lime use 5 pounds to 50 gallons.

554 BULLETIN No. 256 [February,

For early varieties, such as Yellow Transparent, Duchess, and
sometimes Benoni, only the two-, three-, four-, and six-weeks applica-
tions are necessary to protect the fruit until harvest. Usually for
the Benoni and other varieties that are harvested around ten weeks
after blooming an application eight weeks after the fall of petals
is desirable in seriously cankered orchards. For late summer vari-
eties the ten-weeks spray is desirable for blotch, as well as for the
second-brood codling moth. It is impossible to make any definite
recommendations of late sprays for every orchard and every section
of Illinois. The need of these late sprays should be determined by
the grower, and his decision should be guided by the weather peculiar
to his section and by the amount of infection in the orchard.

In addition to pruning and spraying, soil treatments in the form
of cultivation and fertilization are particularly necessary in old and
weakened orchards.

In planting the orchard, varieties should be selected which are
relatively resistant to bark infections. If bark-susceptible varieties of
high commercial value are desirable they should be planted at a dis-
tance from bark-resistant varieties.

All infected trees from the nursery should be rejected.

LITERATURE CITED

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3. ANDERSON, H. W. The northward advance of apple blotch and how it may

be checked. Trans. 111. State Hort. Soc., n.s., 54, 234-237. 1920.

4. BALLOU, F. H., and LEWIS, I. P. Spraying . experiments in southeastern

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L. E., and GUNDERSON, A. J. Field experiments in spraying apple
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Hort. Soc., n.s., 54, 184-190. 1920.

1925} APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 555

16. The control of blotch and scale. Trans. HI. State Hort. Soc., n.s.,

56, 432-446. 1922.

17. CLINTON, G. P. Apple rots in Illinois. 111. Agr. Exp. Sta. Bui. 69, 190-192.

1902.

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Sta. Bui. 106, 217-218. 1906.

25. DICKENS, A., and HEADLEE, T. J. Spraying the apple orchard. Kans. Agr.

Exp. Sta. Bui. 174, 283-284. 1911.

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92-101. 1909.

27. Orchard and garden. Federal Publishing Co., Indianapolis, Ind.,

85-86. 1918.

28. - — War and the fruit grower. Country Gent., Sept. 14, 1918. 7.

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31. FAUROT, F. W. Eeport on fungous diseases occurring on cultivated fruits

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32. FOGLESONG, L. E. Eesults from spraying experiments, 1909, in Pike County.

Trans. 111. State Hort. Soc., n.s., 43, 365-371. 1909.

33. FROMME, F. D., and EALSTON, G. S. Dusting experiments in peach and apple

orchards. Va. Agr. Exp. Sta. Bui. 223. 1919.

34. FROMME, F. D., EALSTON, G. S., and EHEART, J. F. Dusting experiments in

peach and apple orchards in 1920. Va. Agr. Exp. Sta. Bui. 224. 1921.

35. GARDNER, M. W. Origin of apple blotch cankers. Phytopath. 12, 55. 1922.

36. and JACKSON, H. S. New aspects of apple blotch control. Phyto-
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37. GARMAN, H. Spraying apple trees. Ky. Agr. Exp. Sta. Bui. 133, 65. 1908.

38. GIDDINGS, N. J. Orchard spraying vs. dusting. W. Va. Agr. Exp. Sta. Bui.

167. 1918.

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40. GUBA, E. F. The effect of dormant sprays on the control of apple blotch.

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42. GUNDERSON, A. J. Spray schedules and formulas for apples and peaches in

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43. — — Spraying experiments in 1916 for the control of apple blotch.

Trans. 111. State Hort. Soc., n.s., 50, 248-251. 1916.

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556 BULLETIN No. 256 [February,

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1913.

52. MORRIS, B. S., and NICHOLSON, J. F. Orchard spraying. Okla. Agr. Exp.

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53. McCORMACK, E. F. Fungous diseases of the apple. State Entomologist of

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1925} APPLE BLOTCH: ITS ETIOLOGY AND CONTROL 557

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70

AUTHOR INDEX

559

AUTHOR INDEX

Bakluf, W. V., and Flint, W. P.
Calcium Cyanide for Chinch-
Bug Control 71-86

Boughton, I. B., and Graham,
Robert. Clostridium botuli-
num Type C : A Pathogenic
Anaerobe Associated with a
Limberneck-Like Disease in
Chickens and Ducks 1-34

Burlison, W. L., Holbert, James
B., Koehler, Benjamin, Wood-
worth, C. M., Dungan, George
H. Corn Boot, Stalk, and
Ear Bot Diseases, and Their
Control Thru Seed Selection
and Breeding 235-478

Case, H. C. M., and Mosher,
M. L. Increasing Farm
Earnings by the Use of
Simple Farm Accounts . . . 147-82

Crandall, Charles S. Blooming

Periods of Apples 111-46

Dungan, George H., Holbert,
James B., Burlison, W. L.,
Koehler, Benjamin, Wood-
worth, C. M. Corn Boot,
Stalk, and Ear Bot Diseases,
and Their Control Thru Seed
Selection and Breeding. .235-478

Graham, Bobert, and Boughton,
I. B. Clostridium Botulinum
Type C: A Pathogenic Ana-
eroOe Associated with a
Limberneck-Like Disease in
Chickens and Ducks 1-34

Guba, Emil Frederick. Phyllos-
ticta Leaf Spot, Fruit Blotch,
and Canker of the Apple:
Its Etiology and Con-
trol 479-558

Flint, W. P., and Balduf, W. V.
Calcium Cyanide for Chinch-
Bug Control 71-86

Harding, H. A., and Prucha,
M. J. Elimination of Germs
from Dairy Utensils: III.
Steaming Cans Over a
Jet 227-34

Holbert, James B., Burlison,
W. L., Koehler, Benjamin,
Woodworth, C. M., Dungan,
Georgo H. Corn Boot, Stalk,

PAGE

and Ear Eot Diseases, and
Their Control Thru Seed Se-
lection and Breeding 235-478

Koehler, Benjamin, Holbert,
James B., Burlison, W. L.,
Woodworth, C. M., Dungan,
George H. Corn Boot, Stalk,
and Ear Bot Diseases, and
Their Control Thru Seed
Selection and Breeding. .235-478

Mitchell, H. H., and Bice, John
B. The Value of Mineral
Supplements in Swine Feed-
ing 87-110

Mosher, M. L., and Case, H. C. M.
Increasing Farm Earnings by
the Use of Simple Farm
Accounts 147-82

Nevens, W. B. The Sunflower as
a Silage Crop : Feeding
Value for Dairy Cows ; Com-
position and Digestibility
When Ensiled at Different
Stages of Maturity 183-226

Overman, O. B., and Tracy, P. H.
A Modification of the Bab-
cock Test- for the Determi-
nation of Fat in Butter-
milk 63-70

Prucha, M. J., and Harding,
H. A. Elimination of Germs
from Dairy Utensils: III.
Steaming Cans Over a
Jet 227-34

Bice, John B. Feeding Pigs on

Pasture 35-62

Bice, John B., and Mitchell, H. H.
The Value of Mineral Sup-
plements in Swine Breed-
ing 87-110

Tracy, P. H., and Overman, O. B.
. A Modification of the Bab-
cock Test for the Determina-
tion of Fat in Buttermilk . . 63-70

Woodworth, C. M., Holbert,
James B., Burlison, W. L.,
Koehler, Benjamin, Dungan,
George H. Corn Boot, Stalk,
and Ear Bot Diseases, and
Their Control Thru Seed Se-
lection and Breeding 235-478

INDEX

561

INDEX

(The headings in capitals are subjects of entire bulletins')

PAGE
Accounts, see Farm accounts and

Farm earnings
Alfalfa pasture, Feeding pigs

on 43-47, 50-59

Aplanobacter stewarti (E. F. S.)

McCul 272-74, 421, 434-^3

Apple bitter rot, see Apple blotch

Apple blotch 479-557

Bibliography 554-57

Control measures

methods previously advo-
cated 530-35

protective and preventive

measures 551-52

pruning 550, 552-53

recommendations 552-54

selection of resistant va-
rieties 552, 554

soil treatments 550, 554

spraying experiments, dor-
mant 535-41

effect of fungicide 539-41

spraying experiments, sum-
mer 541-50

conclusions 548-50

surgery 551

Dissemination 528-30

Distribution and prevalence in

Illinois 485-87

History of 481-84

Life history 505-26

development of fungus. . . .519-26
inoculation and infection . . 505-06

natural infection 517-19

sources of inoculum 506-07

time of infection 507-17

Morphology 488-92

conidiophores 491

mycelium 491-92

pycnidia 488-90

pycnospores 490-91

Nomenclature 492-94

Origin 484-85

Physiology 494-504

cultural characters 494-96

growth and pycnosclerotia

formation 496-98

spore germination 500-04

spore production in cul-
ture 498-500

Plants affected by 487

Varietal susceptibility 526-28

PAGE

Apple scab, see Apple blotch
Apples, Blooming periods of. .111-45
Records at 111. Sta. .113-16, 120-43

amount of bloom 131-39

amount of bloom and distri-
bution of varieties into

time-groups 139

blooming period of 1910. .124-26

character of records 114-15

comparison of periods of

1904 and 1910 126-29

early blooming varieties. .122-23
full flowering records for all

varieties 120-22

late blooming varieties 123-24

summary 144-45

temperature and distribution

of bloom 140-41

variation in varietal blooming

periods 141-43

varietal flowering periods. . 130-31
Records of other localities. .116-20

England 118-20

New York 116-17

Oregon 118

Virginia 116

Variability in flowering per-
iod 115-16

Ascaridia perspicilli in chicken.. 5

Aspergillus flamts Link 271

Aspergillus niger 271

Asperqillus spp 271-72

BABCOCK TEST, A MODIFI-
CATION OF FOR THE DE-
TERMINATION OF FAT IN

BUTTERMILK 63-70

Conditions limiting use of. ..66-68
Comparison with normal Butyl

alcohol method 68-69

Comparison with Roese-Gottlieb

method 68-69

Conclusions 70

Directions for operating 70

Bacteria in milk cans, see Milk

cans
Bacterial wilt, see Aplanobacter

stewarti

Black scab, see Apple blotch
Black -bundle disease, see Cephal-

osporium a-cremonium
BLOOMING PERIODS OF AP-
PLES, see Apples

562

INDEX

PAGE

Blue grass, Feeding pigs

on 40-42, 59-60, 100-05

Botulinus, see Clostridium botuli-

nus, Type C
Buttermilk, Determination of fat

in, see Babcock test
Butyl alcohol method compared

with Babcock test 68-69

CALCIUM CYANIDE FOB
CHINCH-BUG CONTROL... 71-84

Care in handling 84

Forms used 74

Methods of using 74-77

alone as a barrier 81-84

in strips at right angles to
creosote or coal-tar bar-
rier 74-76

on trap crops 79-81

with creosote or coal-tar bar-

iers 76-77

Summary of experiments 72

Calcium gain in pigs on corn and

supplementary feed 92

Cancer, see Apple blotch

Capital invested in farming in

Illinois 149

Cephalosporium acremonium

Corda 267, 269-71,

292, 351, 353, 359, 360, 383-84,
391, 406, 421-24, 426-27, 432-43
see also Corn rot diseases
Chickens, limberneck-like disease
in, see Clostridium botuUnum
type C
Chinch-bug control

Coal-tar barrier for 78-79

Creosote barrier for 77-78

Trap crops for 77-78

see also Calcium cyanide for

Chlorida obsoleta 271

Clostridium botulinum types A

and B 3-4, 6, 8, 17, 33

CLOSTRIDIUM BOTULINUM
TYPE C: A Pathogenic An-
aerobe Associated with a Lim-
berneck-Like Disease in Chick-
ens and Ducks 1-34

Antitoxin 28-31

Cultural characters differentia-
ting types A and B from C
and Parabotulinus of Sed-

don 12

Cultures of (plates) 9-10

In horses and cattle 28-29

Presence in soil.. 12, 23, 28, 29, 34
Specimens 2770, 2771, and

2772 5-7

Speciments 3419 and 3420 8-15

bacteriologic examination ... 8
cultural characters in various
media 8-12, 13-15

PAGE

gross pathology 8

history 8

Specimens 3421, 3422, and

3423 ..16-23

bacteriologic examination... 17

clinical symptoms 16

gross pathology 16-17

history 16

pathogenesis 17-23

Specimens 3466, 3467, and

3468 23-28

Summary 32-34

Toxin in shelled corn 31-32

Corn

Boil smut of, see Ustilago seae
Brown smut of, see Physoderma

zeae-maydis
Downy mildew of, see Scleros-

pora spp, '
Ear characters of as related to

yield, literature on 240-43

Feeding with, see Pigs on pas-
ture, Feeding; also Swine
feeding, Value of mineral
supplements in

Germinator for testing 357-58

Head smut of, see Sphacelo-

theca reiliana
Improvement of, Program

of 447-69

pure-line method 455-68

probable uses of methods . . 468—69

selection method 448-55

Mosaic disease of 282

Purple-leaf sheath disease of.. 282
CORN ROOT, STALK, AND
EAR ROT DISEASES, AND
THEIR CONTROL THRU
SEED SELECTION AND

BREEDING 235-478

Corn rot diseases

Bibliography 472-78

Economic importance of .... 346—53

estimate of losses 239, 353

experiments to determine loss

thru infected seed 346-53

Cephalosporium infected. . 351

Diplodia-infected 347

Fusarium-inf ected 347-51

scutellum rotted 346-47

extent of infection on 111.

farms 353

Environmental factors affect-
ing 283-328

crop sequence 323-28

injurious constituents in soil

solution 319-23

effect of limestone appli-
cations 319-23

plant-food materials in soil
solution 309-18

INDEX

563

PAGE

soil aeration 307-09

soft moisture 304-07

soil temperature and time of

planting 283-303

Experimental conditions and

methods 354—66

experimental plots 354—56

germination and selec-
tion 357-60

harvesting methods 362-63

planting and cultural meth-
ods 360-62

statistical analysis 363-66

strains of corn used 356-57

Genetic factors affecting. . . .328-45
differences in root sys-
tems 329-39

Parasitic factors of 245-82

bacterial wilt 272-74

black-bundle disease 269-71

corn rust and other diseases. . 282

corn smut 279-81

Diplodia 251-64

Fusarium 265-68

Gibberella 274-79

miscellaneous ear rots and

molds 271-72

miscellaneous soil-borne dis-
eases 281

Summary 470-71

Susceptibility and resistance

to 393-446

differences i n commercial

strains 406-11

influence of endosperm. . .403-06
influence of parent plants. . 393
physical characters associa-
ted with 411-30

value of physical appearance

in selection 431-46

limitation of physical se-
lection 443-46

Corn rust, see Puccinia sorghi
Corn, Seed ears of

Performance of germinator-

selected 366-67

Physical appearance of germi-

nator-selected 368

Physical characters associated
with infection and non-
infection 366-92

Relation of appearance to con-
dition 368-82

ear-tip covering 371-73

general discussion 376-82

kernel indentation 373

luster of ear 369

luster of kernel 376

nature of endosperm 373-75,

Plate IV between pp. 372-373

PAGE

shank attachment 369-71,

Plate IV between pp. 372-373
Value of single ear characters

in seed selection 382-92

coloring of cob interior. .384— 85,
Plate V between pp. 378-379

luster of kernel 389-92

nature of endosperm

386-89, 390, 392

shank attachment 382-86

Corn, Self-fertilization of, see

Improvement, Program of
Corn silage vs. sunflower sil-
age 185-87, 190-91,

193-98, 204, 206, 208-10, 213, 215
Corn smut, see Ustilago zeae
Crop acres worked per horse.

Effect on earnings 165-67

Crop acres worked per man,

Effect on earnings 163-64

Crop rotation, Effect on corn rot

diseases 323-28

Crop yields, Effect on earnings

of good and poor 157-60

Dairy cows, Feeding value of

sunflower silage for 183-225

DAIEY UTENSILS, ELIMINA-
TION OF GERMS FROM : III
Steaming cans over a jet... 227-34

Bibliography 234

Diplodia root rot, see Diplodia,

zeae

Diplodia zeae (Schw.) Lev. . . .251-64,
265, 267, 272, 286, 287, 291-93,
296-302, 305-07, 314-16, 318, 320-23,
347, 358, 359-60, 361, 369, 371,
373, 374, 377, 379, 381, 382, 384-86,
391, 396, 401, 405, 415, 421, 470
see also Corn rot diseases
Dry rot, see Apple blotch
Ducks, Limberneck-like disease
in, see Clostridium botulinum
type C

ELIMINATION OF GERMS
FROM DAIRY UTENSILS,
III. Steaming Cans Over a

Jet 227-34

FARM ACCOUNTS, INCREAS-
ING FARM EARNINGS BY

THE USE OF SIMPLE 147-82

Benefits realized from keep-
ing 152-55

Summary of study of 148

Woodford county's method of

conducting work on 151

summary of records kept in

(tables) 174-81

Farm earnings

Effect on of crop yields. .. .157-60

564

INDEX

PAGE
Effect on of farm organization

and management 155-57

Effect on of use of live-
stock 160-63

Effect on of crop acres worked

per horse 165-67

Effect on of crop acres worked

per man 163—64

Importance of thrift 167-69

Increase of on well balanced

farms 169-73

see also Farm accounts

Farm organization and manage-
ment

Effect of on farm earn-
ings 155-57

Measuring success of farm .... 182
Profit in well balanced
farms . . 169-73

Farming, Capital invested in
Illinois 149

FEEDING PIGS ON PAS-
TURE . 35-60

Frog-eye apple leaf spot 482

Fruit blotch, see Apple blotch

Field peas and oats, Feeding
pigs on 43, 45-47, 59

Fusarium moniliforme Sheldon. .
265-68, 272, 291, 294, 308, 311,
312, 314, 316-17, 318, 347-51, 359,
3J60, 369, 374, 376-79, 381, 382,
385-86, 391, 396, 401, 415, 421
Plate I between pp. 250 and 251
see also Corn rot diseases

Fusarium root and ear rot, see
Fusarium moniliforme

Fusarium spp 265,

267, 271, 373, 379, 406

Germs in milk cans, see Milk cans

Gibberella root and seedling
blight, see Gibberella saubinetti

Gibberella saubinetti (Mont.)

Sacc 243, 267,

274-79, 284, 329-30, 339, 343, 393,
396, 397, 399, 404-05, 421, 422,
423, 424-26, 432-33, 434-43, 470

Helminthosporium 281

Hogs, see Swine

lodids for farm stock. . 89-90, 95

Late scab, see Apple blotch

Limberneck, see Clostridium bo-
tulinum

Limestone, influence on corn rot
diseases 319-23

Livestock, Effect on earnings of
use of 160-63

Milk cans

Safe number of bacteria
in., ..232-33

PAGE
Study of elimination of germs

from 228-34

bacterial count of steamed. 231-32
bacterial count of un-

steamed 230-31

methods of study 228-30

Time and steam pressure for
sterilizing ... ... .228-30, 233-34

Mineral requirements of ani-
mals 89-90

Mineral supplements in swine
feeding, see Swine feeding

Parabotulinus organism

4, 29-30, 32-33

Pasteurella avium 17

Pasture crops for pigs,
Comparative value of var-
ious 38, 45, 51-52, 53, 55, 57

One vs. two . '. 57-59

Penicillum spp 271-72

Phyllosticta, see Apple blotch
PHYLLOSTICTA LEAF SPOT,
FEUIT BLOTCH, AND
CANKER OF THE APPLE:
Its Etiology and Control. .479-557
Phyllosticta solitaria, see Apple

blotch

Phyllostictose, see Apple blotch
Physoderma zeae-maydis Shaw.. 282
Pigs

Carrying fall pigs thru sum-
mer on pasture 59-60

Feeding on dry lot... 50-52, 54-56
Feeding on pasture

comparative value of various

pasture crops

38, 45, 51-52, 53, 55, 57

corn, different amounts, with

middlings and tankage . .48-50
corn, different amounts, with

tankage 43-47

corn, medium rations, with

and without tankage .... 40-42
corn and tankage in self-
feeder 50-57

without concentrates . 43, 47, 48-49
one vs. two pasture crops.. 57-59

plan of experiment 39-40

purpose of experiment 39

summary 37-38

see also Swine

Pseudomonas dissolvens 273

Pseudomona-s spp 273

Puccinia sorghi Schw 282

Pyrus coronaria 485

Rape, Feeding pigs on. .40-60, 98-100
Red clover pasture, Feeding pigs

on 52-54

Ehizopus spp 245, 246, 393

INDEX

565

PAGE

Eoese-Gottlieb method compared
with Babcock method 68-60

Sclerospora spp 282

Scutellum rot 245-50,

286, 291-94, 297, 299-302, 311,
314-15, 318, 323-27, 346-49, 359,
360, 369, 374, 377, 380, 382,
383, 391, 396, 401, 402, 415, 420
Plate I between pp. 250 and 251
see also Corn rot diseases

Self -feeder, used for minerals. .98-106
Used with pigs on pasture. . .48-57

Soybean pasture, Feeding pigs
on 43, 45-47

Spacelotheca reiliana (Kiihn)
Clinton 281

Star fungus, see Apple blotch

Statistical analysis used in corn
experiments 363-66

Stewart's disease, see Aplano-
bacter stewarti

SUNFLOWER AS A SILAGE
CROP: Feeding Value for
Dairy Cows; Composition and
Digestibility When Ensiled at
Different Stages of Ma-
turity 183-225

Aero yield of digestible nu-
trients 210, 215

Bibliography 216-17

Composition of 203-10, 215

Digestion trial of at different

stages 211-13, 215, 221-25

Effect upon composition of

milk 213-14

Effect upon flavor of milk 214

Growing and ensiling 188

Plan of feeding trial 189-93

Results of feeding trial 193-202

detailed data (tables) 217-21

economy of milk and fat pro-
duction. .193, 196-98, 200, 214

gain or loss in weight

193-98. 199, 201

PAGE

general discussion 200-02

milk and fat production ....

193, 194-95

palatability. .198-99, 200-01, 214

physiological effects . 199-200, 214

Review of previous work. . .185-87

Summary 214-15

Sweet-clover pasture, Feeding

pigs on 40-42, 54-55

SWINE FEEDING, VALUE OF
MINERAL SUPPLEMENTS

IN 87-110

Economic value of mineral

feeding 96-97

Experiments 97-109

conclusions 110

for pregnant and lactating

sows 106-09

in self-feeder to pigs on

pasture 100-02

with corn, linseed oil meal,
and middlings with blue-
grass pasture 102-05

with corn, middlings, and
tankage with and without

rape pasture 98-100

Improving calcium retention on

grain rations 91-92

Improving quality of bone on

grain rations 92-93

Mineral mixtures — homemade

and commercial 95-96

Mineral problem in 91

Review of experiments at

other stations 93-95

Value of different minerals as

supplements 93-95

Tar blotch, see Apple blotch
Vstilago zeae (Beckm.) Ung.. 279-81
Woodford county

Study of farm accounts in . . 147-82

Type of farming in 150-51

Seed corn from 406-11

see also Farm accounts

THE LIBRARY OF THE
OCT 2 I 1931

UNIVERSITY OF ILLINOIS,

UNIVERSITY OF ILLINOIS-URBANA