ITED STATES DEPARTMENT OF AGRICULTURE
BULLETIN No. 829
Contribution from the Bureau of Plant Industry
WM. A. TAYLOR, Chief
Washington, D. C.
October 29, 1919
MOSAIC DISEASE OF SUGAR CANE
AND OTHER GRASPS
E. W. BRANDES
Pathologist, Office of Sugar-Plant Investigations
History of the Disease 1
Distribution in the United States ... 4
Losses in the United States ... 7
Primary Symptoms 8
Secondary Symptoms 10
Injuries Resembling Mosaic 12
Varietal Susceptibility 12
Varieties Attacked 12
Immune Varieties 14
Other Hosts 15
Nature of the Disease 16
Infection Phenomena 16
Transmission of Mosaic in Diseased
Seed Pieces 18
Nature of the Disease — Continued. Page
Transmission of the Disease by Car-
Soil Relations 19
Relation to Disinfectants 20
Relation to Fertilizers 20
Elimination by Roguing 21
Elimination by Grinding All Cane
and Securing-CIean Seed .... 22
Eradication .... * 23
Elimination by Planting Immune
GOVERNMENT PRINTING OFFICE
Book .M75 j g7
UNITED STATES DEPARTMENT OF AGRICULTURE
BULLETIN No. 829 «
Contribution from the Bureau of Plant Industry
WM. A. TAYLOR, Chief
Washington, D. C.
October 29, 1919
THE MOSAIC DISEASE OF SUGAR CANE
AND OTHER GRASSES.
By E. W. Brandes,
Pathologist, Sugar-Plant Investigations; formerly Pathologist, Porto Rico Agricultural
Experiment Station, Mayaguez, P. R.
History of the disease 1
Distribution in the United States 4
Losses in the United States , 7
Primary symptoms 8
Secondary sjTuproms 10
Injuries resembling mosaic 12
Varietal susceptibility 12
Varieties attacked 12
Immune varieties ^ 14
Other hosts 15
Nature of the disease 16
Infection phenomena 16
Transmission of mosaic in diseased seed
Nature of the disease — Continued.
Transmission of the ■disease by carriers . 18
Soil relations 19
Relation to disinfectants 20
Relation to fertilizers 20
Elimination by rogumg 21
Elimination by grinding al! cane and secur-
ing clean seed 22
E limination by planting immune varieties . 24
HISTORY OF THE DISEASE.
The mosaic disease of sugar cane, the presence of which has
recently been discovered in Louisiana and other Southern States,
is the malady that in epidemic form has occasioned severe losses m
parts of Porto Rico during the past four years. There it has been
variously called matizado, "mottlings;" rayas amarillas, "yellow
stripe;" morida de perro, *'dog bite;" la enfermadad de Arecibo,
"disease of Arecibo;" la enfermadad nueva, "new disease;" etc.
The disease was first noticed in Porto Rico about the middle of
Starting from some point near Arecibo, on the north coast of
Porto Rico, it spread rapidly over the cane fields to the west, down
the west coast to the south coast, and up into the valleys and hilb
4 BULLETIN 829, V. S. DEPARTMENT OF AGRICULTURE.
of transmission was not present or at least not abundant in this
region, it lias spread very little. At Santiago de las Vegas it was
found on plants recently imported from Louisiana and from Tucuman,
Argentina. The latter plants had come originally from Java. The
disease had spread from these plants to an adjoining field of the native
Crystalina cane. In view of this demonstration of its ability to
spread at Santiago, it is very fortunate that the diseased plants were
early observed and destroyed. A slight infection has been found at
Mercedes, also as the result of a recent importation.
Infected cuttings have been received in both Porto Rico and Cuba
from Tucuman, Argentina, but to what extent the disease is prevalent
in Argentina has not been learned. •
Last year the mosaic disease was found in abundance at La Romana
and the city of Santo Domingo, Santo Domingo, and less plentifully
at Samana, La Vega, Monte Cristi, and Bonao.^ Lastly it was dis-
covered at St. Croix, Virgin Islands, on cane imported from Porto
DISTRIBUTION IN THE UNITED STATES.^
The presence of the mosaic disease in the United States was first
suspected when an agent of the Office of Sugar-Plant Investigations
of the LTnited States Department of Agriculture discovered young
diseased cane in Porto Rico from seed cane imported from Louisiana.
The plants were so young at the time that secondary infection seemed
improbable, and it was assumed that the seed pieces were diseased
when shipped from Louisiana. Accordingly another agent of the
same office visited Louisiana and on July 7, 1919, confirmed the
presence of mosaic there. The State authorities were apprised of this
important disclosure, and the Government agent made a hurried
reconnoissance of the Gulf States, which reveajed the fact that the
disease was already quite widely distributed there.
On account of the infectious nature of the malady and the fact that
it has caused severe losses in other cane countries, a complete sur-
vey of the Southern States was immediately instituted to determine
the location of all infested areas and, if possible, to trace the original
importation of the disease and the course of its subsequent spread.
Infested areas have been well delimited. The disease has been found
by inspectors of the United States Department of Agriculture in
Louisiana, Florida, Georgia, Alabama, and Mississippi (fig. 1). It
is most abundant in Louisiana, as would be expected. There the
river district is already badly infested. As far north as Angola, in
West Feliciana Parish, several fields in a large plantation were found
1 Stevenson, John A. The mottling disease of sugar cane. In Jour. Dept. Agr. and Labor, Porto Rico
2 Thanks are due to Mr. W. G. Taggart, vice director of the University of Louisiana Sugar Cane Experi-
ment Station, and to Dr. C. W. Edgerton, pathologist, Louisiana Experiment Station, for courtesies
extended to the writer and suggestions facilitating the survey in Louisiana.
MOSAIC OF SUGAE CANE AND OTHER GRASSES. 5
in wliich 75 per cent or more of the plants had the mosaic disease.
From tliis point south to Donaldsonville, however, the amount of
infection is not heavy. Many pLmtations are entirely free from
mosaic, so far as can be determined by inspection. From Donaldson-
ville to New Orleans an increasing amount of infection was recorded
by the inspectors. Between Lutcher and Keserve, about 75 per cent
of the plants in every plantation were infected. This is by far the
m.ost heavily infested large area in the United States. From this
region to New Orleans and from New Orleans to the lower extremity
of the river district the amount of infection ranges from 4 to 30 per
cent. Just a few fields were visited where no mosaic was found.
Fig. 1.— Map showing the location of diseased areas of sugar cane in the United States.
In the Bayou Lafourche district mosaic was found in only about one
out of four fields visited and where present amounted to only 1 to 8 per
cent of the plants. In the Bayou Teche district no mosaic was
found on plantation cane, although nearly 500 fields were carefully
inspected. A few cases were found in this region on cane recently
distributed by the State Sugar Experiment Station. The imme-
diate destruction of these few sources of infection is a matter of great
importance. No mosaic whatever was found west of Bayou Teche
or in Avoyelles and Rapides Parishes to the north. Thus, a very
considerable part of the sugar-cane lands of Louisiana is stiU free
from the disease, and every efi'ort should be made to keep it free.
In Georgia the worst infested region is in the vicinity of Cairo,
Grady County. There the proportion of infection ranges from less
than 1 to 75 per cent or more in fields where the disease is present.
6 BULLETIN 829, U. S. DEPAETMEIsTT OF AGRICULTURE.
but only about one-fourth of the cane fields in this county harbor
the infection at all. The affected area is quite sharply delimited, all of
the disease being confined at present to farms located on the high-
ways leading out from Cairo. The cane fields in Georgia consist
usually of a few acres grown for sirup making. It is quite possible
that by prompt and energetic action this community could free
itself from the mosaic disease in short order.
Cane fields are distributed over practically the whole State of
Florida, but the crop is grown largely for sirup for home use and
the cane patches are even smaller than those in Georgia. Mosaic
has been widely scattered over the State by the distribution of cut-
tings from experimental plats grown for the purpose of testing
varieties. There are only two points, however, where the disease
has spread so as to include any considerable area, namely, the vicini-
ties of Marianna and Bristol. Other points in Florida where mosaic
has been found include Apalachicola, Tallahassee, Punta Gorda,
Palmetto, De Land, Winterhaven, Chattahoochee, Muscogee, and
Canal Point. These are all purely local, infections, and in some cases
the disease has not j^et spread more than a few rods from the
original plantings shipped in from other States. An eradication
. campaign would be entirely practicable in Florida.
Mosaic has been discovered at only one point, Biloxi, in Mississippi.
From the farm on which it first appeared it spread to one other farm
in the vicinity.
In Alabama similarly, it was found only on one place, near Mus-
cogee, Fla. It was confined to the farm where it first appeared.
Final reports on the results of the inspection in Texas must be
deferred, since the survey is still under way in that State.
The survey has also been very illuminating concerning the prob-
able time of introduction of the disease into this country and the
method of its subsequent spread here. Since 1913 a prohibitory
regulation has been placed upon the introduction of sugar cane into
the continental United States, and it is probable that no cane has
been introduced since that time. Prior to 1913 varieties of sugar
cane were imported naany times by private individuals and by various
Government agencies. The Sugar Experiment Station of the Louisi-
ana State University, at Audubon Park, has been particularly active
in importing new varieties, with the idea of securing some higher in
sugar content and yield than those already grown here. Wliether the
mosaic was introduced by the experiment station or by private indi-
viduals no particular blame attaches to those who are responsible for
the importation of thi& obscure disease. There is no known method
by which the presence of the disease in cuttings can be positiv/ely
established. It is merely pointed out that such an importation
would be practically impossible with the present quarantine against
MOSAIC OF SUGAi; CANE AND OTHER GRASSES. 7
sugar cane. Concerning the probable time of the importation that
was responsible for the present wide distribution of mosaic in Amer-
ica, the survey has brought out the fact that the distribution of cut-
tings by the Louisiana Sugar Experiment Station in 1914 and prior
to that time has not resulted in establishing the disease at the points
where such cane was received. Since 1914, however, every point
receiving seed from the station has become the center of a larger or
smaller infected area. The inference, of course, is that while the
disease may have been present at the station for a few years prior
to 1914, it had not become so widespread that every seed shipment
from there contained some infected cuttings. At the present time,
about 97 per cent of the cane plants at the station have the mosaic
disease. It is probable that private individuals have imported cane
with this disease, but such cane is not likely to be widely distributed,
and its spread, therefore, must depend upon natural agencies, a
much slower process.
Without exception, every infested area in Georgia and Florida can
be directly traced to distributions of seed, cane from the Sirup Field
Station at Cairo, Ga., since 1916, and the infection at this station
dates from the importation of a number of varieties from Audubon
Park in 1915. In nearly every instance where diseased cuttings
have been received from Cairo, it has resulted in secondary infection
of the surrounding native cane.
The above is the brief and much condensed compendium of a large
amount of data collected during July, August, and September,
1919. It has made possible the recommendation of plans of attack
upon the mosaic disease, which vary slightly in the different cane
regions of the country, but all of which, if strictly adhered to by every
cane planter, will bring the disease under control. Its capacity for
rapid spread, as demonstrated in Georgia and Florida, means that
a lapse of one year will result in immeasurably complicating the
problem of ultimate eradication.
LOSSES IN THE UNITED STATES.
Since the mosaic disease had been unrecognized m this country until
the writer announced its presence m July of this year, no extensive
data have been accumulated to determine whether the losses caused
by it in the United States are comparable with those sustained m Porto
Kico. A few figures (Table II) have been obtained in Louisiana,
however, which indicate that we may expect a decrease in yield
almost equal to that in Porto Rico if the disease is permitted to
become as widespread here as it is in that country. Losses here are
held in check somewhat on account of frequent replanting. It has
been noticed that where mfected sugar cane is allowed to ratoon over
a long period of years that losses due to the mosaic are more severe
8 BULLETIN 829, U. S. DEPARTMENT OF AGRICULTURE.
each successive year. The figures m. Table II were ob tamed by
cuttuig all of the cane in approxunately square patches of about
one-tenth to one-fifth of an acre selected in commercial fields and
in the fields at the Sugar Experiment Station, Audubon Park, La.
The stalks cut from such patches were then sorted into two classes,
diseased and healthy, and the average weight of stalks in each class
was determined. The patches were not selected at random, but an
attempt was made to find areas where the mosaic was doing a maxi-
mum amount of damage and at the same time a sufficient number of
healthy plants were present in the patches, growing under identical
conditions, in order to make a fair comparison possible. Since, if
no attempt is made to control the disease in these fields, we may
expect ultimately to find an infection of 100 per cent, the losses wiU
then be equivalent to the figures found in column 5 of Table II.
Table II. — Tests of sugar cane in Louisiana, showing the extent of losses in different
Average weight of
Upon walking between the rows of cane in an affected field, more
or less plants will be seen that are conspicuous on account of a gen-
eral pallor of the leaves. This may be discernible for many rods.
Closer examination of such plants reveals that the pallor is due to
irregular light-colored streaks or spots on the leaves. The affected
leaf areas, in so far as color is concerned, are of two distinct types.
The most common type presents merely a ''washed-out" appearance.
It is, in fact, merely a tint of the normal color, in which the blue and
yellow are present in the same proportions but diluted. In the sec-
ond type, the yellow is predominant, and the affected areas have a
decided yellowish green appearance. The normal and affected areas
are sharply demarked. In other words, there is no gradual merging
of one color into the other. There is a great diversity of patterns
in the different varieties, due to the variation in the amount, size, and
shape of the light-colored areas, but the arrangement is so constant
in any particular kind of cane that the character could be used as an
aid in determining varieties.
MOSAIC OF SUGAR CAI^TE A:firD OTHER GRASSES. 9
Among the cane varieties commonly grown in Louisiana and other
Southern States, some rather constant differences occur in the expres-
sion of the mosaic disease. In L 511 it will be noticed that streaks
are rather scant in newly invaded leaves and on account of their light
color make a great contrast with the normal areas. They are bluntly
pointed and range from one-sixteenth to three-sixteenths of an inch
wide and from one-fourth of an inch to 3 or 4 inches long (PL I, fig. 4) .
Later, the light areas or streaks are more numerous and in most
cases tend to become confluent in well-defined bands of light tissue
extending across the leaf at right angles to the midrib and alternating
with bands where the light streaks remain isolated. These bands are
from H to 2 inches long. The above condition is typical of the
disease as it appears in L 511, but does not invariably occur.
In D 74 the streaks are not usually isolated, even at first, so that
very quickly the coalesced light areas are predominant and the nor-
mal areas appear as irregular, elongated islands 1 thirty-second to
three-eighths of an inch wide and of varying length, from one-fourth
of an inch to several inches, as shown in Plate I, fig. 5. Affected
areas are light green at first, but the tendency for the whole leaf
to become opaque yellow is pronounced.
In purple cane the light areas are elongate and isolated at first, but
later they predominate and coalesce and the normal green shows as
irregular elongated islands, as illustrated in Plate I, fig. 5. The islands
are not of uniform width or length.
In the youngest leaves of Ribbon cane, the light areas are in the
shape of attenuated streaks, usually about one-eighth of an inch wide
and one-half of an inch to 1^ inches long, but the size varies greatly,
some streaks being very minute, and others, by running together at
the ends, form continuous stripes 6 inches or more in length. In
general, the streaks are isolated from one another and uniformly dis-
tributed on the leaf blade as in Plate I, fig. 4. The amount of nor-
mal-colored tissue greatly exceeds the light tissue at this time. Excep-
tionally, the light streaks may be confluent from the first, and this is
more frequently seen near the midrib, leaving the margin normal in color
orwith a fewscattered palestreaks. In slightly older leaves, by growth
and confluence of the light-colored areas the latter becomes predomi-
nant and the whole leaf becomes pallid or even yellow in its general ap-
pearance. The dark-green or normal areas are now very scant, and
they appear as elongated streaks in the pale green, just the reverse of
the condition in young leaves, except that the dark-green streaks
are less regular in outline. The individual streaks vary considerably
in width and direction throughout their extent, streaks perhaps
three-eighths of an inch wide at one end becoming constricted to
1 thirty-second of an inch, then alternately widening and narrow-
ing or becoming oT)lique with the midrib, with no apparent forces
142481°— 19— Bull. 829 2
10 BULLETIl!^ 829, V. S. DEPAETMENT OF AGRICULTURE.
limiting their extent or direction except that in general they are
elongated in the direction of the parallel veins of the leaf.
In D 95 the light areas are predominant from the start (PI. I, fig. 5).
In L 219 the light streaks are isolated near the base of the leaf but
become confluent toward the tip.
In L 226 the streaks are isolated and even in older leaves remain so.
L 231 is very severely injured. The leaves are usually quite yellow,
as shown in Plate I, fig. 6. Practically the entire surface is light
from the beginning. There are exceptions, however. The amount of
injury in this variety is variable.
L 253 is quite tolerant. The lighter areas predominate but are not
yellowish. All plants seen were dark green and vigorous.
Field observations covering a number of years indicate that the
deleterious effects of the mosaic disease are cumulative. The streak-
ing and spotting of the leaves discussed above are the only noticeable
sign in newly infected plants. The disease is never fatal during the
first year and, in fact, it rarely terminates in death even in diseased
plants that have been allowed to ratoon for years. Usually, however,
more serious effects are seen in first ratoons of cane which became in-
fected the previous year or in plant cane originating from diseased
cuttings. At this time another quite distinct leaf symptom appears.
It consists of small white opaque spots and streaks in the light-colored
areas. These streaks are sm.aller than the light areas previously men-
tioned and differ from them in having no pigment whatever. They
range from mere points to elongated irregular streaks several inches
in length. The white streaks may become confluent to a limited
extent. They are for the most part restricted to the light-green areas
of affected leaves, but do not correspond to them in outline and
typically remain more or less isolated from one another. The white
opaque tissue has a dried-out appearance and seems to be quite
functionless. It remains firm, however, and does not become brown
or rot out. The amount of total leaf area occupied by this type
of tissue rarely exceeds 20 to 30 per cent of the whole.
At about the same time, or during the next year, a still more in-
jurious sign of mosaic appears, namely, the striping or cankering of
the stalk. This is much more marked in some varieties than in
others. Ordinarily, it does not become noticeable until the cane is
quite w^eU developed. By tearing away the enveloping leaf bases,
cankers can sometimes be found in the mcipient stage. They appear
as discolored or water-soaked patches or longitudinal streaks on the
internodes. In severe cases these areas become siuiken and the
internodes are spindle shaped and attenuated. Longitudinal cracks
may appear, resulting in the drying out of the cane. There is a
tendency toward shortening of the joints and premature development
U. S. DEPARTMENT OF AGRICULTURE
BUREAU OF PLANT INDUSTRY
THE MOSAIC DISEASE OF SUC
1.— A short piece of healthy leaf of the Immune varietyKavan-
2.— A piece of leaf of variety B-3922, showing isolated, more
or less rounded and irregular patches of normal color on a
background of pallid, affected tissue.
3.— A piece of leaf of variety D-1 17, showing a mosaic pattern
somewhat similar to the above, but finer.
CANE AND OTHER GRASSES.
<+.— « rnrrwT'L'i ivp" '■ r-':v,,ne, irrK:Jji;u streaks Of pallid
green, of unequal length and width but elongated in the direc-
tion of the long axis of the leaf, on a background of normal
green; on leaf of variety Rayada.
5. — A pattern somewhat similar to the above, but with the
colors reversed, so that the pallid green predominates; on leaf
of variety G. C. 1479.
6.— The most injurious of the common types of mosaic. Just
a few streaks or islands of normal green remain on a back-
ground of yellowish green ; on leaf of variety M. P. R. 2.
MOSAIC OF SUGAR CANE AND OTHER GRASSES.
of roots and shoots at the nodes of standmg cane. Figure 2 shows
such a condition in Yellow Caledonia cane. The photograph repro-
duced here was taken at Arecibo, Porto Rico, in 1919, and the
probabilities are that the plant had been infected for at least five
years. These iden-
tical cuttings and
similar ones were
brought to Washing-
ton and planted in
a quarantine green-
house. Most of them
grew, but at the pres-
ent time, five months
after planting, they
are scarcely 1 foot
tali. The opaque
covers practically all
of the leaf area. This
is the most excessive
injury ever observed
by the writer. Most
varieties of cane do
not go to pieces like
this, but rather the
injury to stalks con-
sists merely of re-
Among the well-
however, all grada-
tions in the extent of
injury between these
two extremes are to
When a large pro-
portion of the plants
in a field are infested,
the aspect in general
resembles the effect
of a severe drought.
The foliage of the entire field is yellowish, and the plants are more or less
noticeably stunted. Where a row of some immune variety is planted
in or near a badly infested field, the contrast in color is exceedingly
conspicuous and the dwarfed habit of infected plants is more notice-
FiG. 2. — Canker stage in Yellow Caledonia sugar cane; healthy cane of
the same variety in center.
12 BULLETIN 829, U. S. DEPARTMENT OF AGRICULTURE.
able. It is possible to recognize such fields from a distance of half a
mile or more on account of their sickly, dry appearance.
INJURIES RESEMBLING MOSAIC.
Many types of injury are commonly fomid on cane leaves that
might be confused with this malady by one not familiar with it.
The condition termed chlorosis, which is due for the most part to
soil conditions, expresses itself in many ways, some of which closely
simulate the mosaic disease. The affected areas are white opaque
or yellow, and the most familiar form is a regular striping of the leaves
longitudinally. The stripes usually extend the entire length of the
leaves and may be about one-eighth of an inch wide and numerous,
with normal green stripes of equal width spaced between them, or
the chlorotic areas may be quite wide. Occasionally, the entire leaf
is pure white. Less frequently the areas are in the form of large
spots or blotches, extending inward from the margins of leaves or
situated at the center of the blades anywhere from base to tip.
Another type, which is rare, consists of a very fine irregular white
mottling of the leaves, which, however, is in local patches and does
not involve the whole leaf, as is invariably the case with the mosaic
disease. Many fungi cause spotting of the leaves of cane, but these
can easily be distinguished, as the spots usually turn broAvn and the
leaf tissue dies, which does not occur in the cane mosaic. Since a
pale-green halo is sometimes present surrounding these small spots,
they have the appearance of mosaic from a distance, especially
when quite numerous, but a close examination always reveals quite
distinct differences. Many insects, especially those which feed by
pimcturing the leaf epidermis and sucking the sap from the layere
of cells below, cause a very fuie mottling of the leaves when the
punctures are present in enormous numbers. Ordmarily, the punc-
tures are scattered and can lead to no confusion. This type of in-
juiy can also be determined by close inspection, since the minute
pale area surrounding each individual puncture is almost exactly
circular and has no tendency to elongation in the direction of the
long axis of the leaf, such as is almost invariably the case in true
mosaic. Drought, lack of proper nutrients in the soil, excessive
rainfall, and poor tilth, or combinations of these, sometimes result in
a general pallor or yellowing of the leaves, but this color is always
uniform and can lead to no confusion.
More than a thousand varieties of cane have been determined to be
susceptible to the mosaic disease. Most of these are the progeny of
seedling canes that exist in small variety-test rows or patches at the
MOSAIC OF SUGAR CANE AND OTHER GRASSES. 13
various sugar-cane experiment stations, but the list includes also
practically all of the commercially esteemed sorts grown for the mills
on a plantation scale.
3o far as can be learned, none of the varieties grown in Java is
truly immune, but a high degree of resistance or tolerance of the
disease has been observed in the favorite Java seedling canes grown
in Porto Rico, a probable explanation of which has already been given.
Only Java 56, 100, 228, and 234 have been seen by the WTiter in
Porto Rico, but all of these, though 100 per cent of the individuals
were affected, made a tlu-if ty growth and produced apparently normal
stalks. The leaves arc not noticeably yellowed, but on the contrary
appear to be of uniform dark-green color when viewed from a dis-
tance. Close inspection, however, shows the characteristic streaks,
but the diseased areas are very little lighter than the normal areas.
Probably the damage done to an individual plant is slight, but the
aggregate damage to all of the individuals in a field is a measurable
quantity and has been shown to be quite considerable in Java. In
the different varieties all degrees of tolerance are exhibited, ranging
from the higlily resistant Java canes down to the soft white Otaheite
or Bourbon cane, which is so severely injured that the cane is hardly
worth milling. In addition to the conditions which might be termed
varietal tolerance of the disease, some varieties exhibit decided and
rather constant differences in the percentage of individuals that
become affected under the same conditions. This is brought out in
variety-row tests where the same varieties have been planted at
several points in the same field. Under these conditions it has been
found that some varieties will show a 100 per cent infection of the
individuals in all of the rows, while in others perhaps only 60 per cent
of the plants will be diseased in each of the separated rows or plats.
It seems reasonable to suppose that all varieties were equally exposed
to the contagion in such situations. This fact indicates a possibility
of resistant strains among the individuals of a variety.
The Rayada or Striped cane and- the Crystalina or Wliite Trans-
parent, the two favorite varieties in Porto Rico, are severely injured.
Yellow Caledonia is grown on a large scale in some localities, and
plants of this variety killed by the mosaic disease have been observed.
This is quite unusual, since attacked plants of most varieties become
badly stunted but do not die. All seedling canes from Demerara
and Barbados grown in Porto Rico are attacked. Seedlings of the
Insular and Federal agricultural experiment stations likewise are aU
affected, as are the seedlings originated at Centrals Guanica and Fa-
jardo. Among the varieties planted commercially to a limited ex-
tent the Bambu, Cavengerie, Morada, and, in fact, all the broad-
leaved canes have proved to be susceptible.
14 BULLETIN 829, U. S. DEPARTMENT Ol^ AGRICULTURE.
Ill Cuba all varieties that are exposed seem to become infected,
but since the disease has not become rampant nor spread over any
considerable area no opportunity to observe the reaction of all the
varieties grown there is to be had. Practically aU of the seedlings
origmated in the Harvard Experiment Station near Cienfuegos were
affected, as well as the imported Ja^^^a 228, L 511, and the native
Crystalina at Santiago de las Vegas.
Practically all varieties are attacked in the Hawaiian Islands, and
extensive damage is done.
The common varieties in Louisiana have proved susceptible to
mosaic disease. Louisiana Purple, Louisiana Striped, D 74, D 95,
L 511, L 218, L 219, L 226, L 231, L 253, and hundreds of seedhngs
being tested at the Louisiana Sugar Experiment Station all fall prey
to the ravages of this disease.
Fortunately a few varieties of sugar cane have been discovered
which appear to be entirely immune. Most of them are of the
slender North India type, generally known as Japanese canes. The
Kavangu-e, a variety which, because of its prolific stooling, yields a
very large tonnage and is much esteemed in Argentina for making
sugar has never been observed to be diseased, although it has been
exposed to infection for four years in the worst infested regions of
Porto Rico.^ It is a rather long season cane, however, and for this
reason is probably not suited to Louisiana conditions. Another Jap-
anese cane, Cayana 10, which is becoming prominent in the sirup
sections of Georgia and Florida, is also immune. This variety has
already met with considerable favor on the part of cane growers in
Georgia. All the other Japanese varieties observed, including many
imported by the Office of Foreign Seed and Plant Introduction of
the Bureau of Plant Industry, have been found to be uniformly free
from this disease.
Among the broad-leaved thicker stalked varieties several kinds
have been found that appear to be immune, but our evidence of their
immunity is not so complete as is the case with the Japanese varieties.
Louisiana seedlings 1646, 1606, 1674, and 1797, growing in the
variety test plats at Audubon Park, New Orleans, this year appeared
to be immune. No individuals of these varieties were diseased,
although they were surrounded by other varieties, the individuals
of which averaged 97 per cent diseased.
1 Townsend, C. O. An immune variety of cane. (Abstract of an article by F. S. Earle.) In Science,
n. s., V. 49, no. 1272, p. 470-472. 1919.
MOSAIC OF SUGAE CANE AND OTHER GRASSES. 15
A number of other grass plants are known to be subject to the
mosaic disease, but apparently they are attacked with difficulty
and only under conditions favorable to the disease. Among these
hosts are corn, sorghum, rice, millet, crab-grass, foxtail, and Panicum.
Probably the list of susceptible plants is much larger, but up to the
present time opportunity for testing others has not been had. In
the case of corn, rice, and millet, we have no experimental proof that
the diseases are the same, but must depend upon field observations.
If not the same, the disease must be very similar, since the leaf
symptoms are identical. The characteristic streaked and spotted
appearance of the leaves is present in all attacked plants.
With regard to sorghum, crab-grass, foxtail, and Panicum our
evidence is conclusive and j^roves that the infectious material or virus
is the same for all of these plants. Sorghum seed of the Early
Amber, Sugar Drip, and Japanese Ribbon varieties was sown in a
bed at the quarantine gi'eenhouse at Washington, where diseased
plants of 17 different varieties of sugar cane were growing. When the
sorghum plants were about half grown, practically all of them began
to produce mottled leaves and continued to do so until they went to
The seed was saved from these sorghum plants to determine whether
the disease is transmitted to the next generation in the true seed.^
The leaf symptoms in these greenhouse plants were exactly like the
symptoms on sugar-cane leaves. Plants arising from the same batch
of seed used in the greenhouse experiment cited above but planted
elsewhere and not exposed to the disease did not show the phenomenon
but produced healthy leaves of uniform color. The crab-grass, fox-
tail, and Panicum came up as volunteer plants in the quarantine
greenhouse. Scores of stools of these weeds were allowed to mature
for observation and identification. Every plant became infected
and exhibited the typical leaf symptoms. Some half dozen other
species of wild grasses were present in the greenhouse, but they were
not attacked. All of the wild grasses were abundant outside of the
greenhouse, but in spite of an assiduous search in the vicinity not
a single infected plant could be found. The conclusion to be drawn
from these observations is obvious. We are not dealing with similar
mosaic diseases of these various graminicolous hosts, the viruses of
which are specific for each host, but with one and the same disease.
The existence of other host plants, especially the common wild
grasses, would appear to be one of the most alarming of the recent
developments in the problem. It is needless to say that the control
1 This seed was planted in flats. At the present time, three weeks after germination, no sign of the mosaic
16 BULLETIN 829, U. S. DEPARTMENT OF AGKICULTURE.
of the disease would be immeasurably complicated if it were to be-
come prevalent on such, omnipresent weeds. Fortunately, however,
our observations appear to indicate that the grasses other than, cane
become infected only under conditions favorable to the disease and
in the near vicinity of infect'ed sugar-cane plants. Infected corn,
for instance, has been seen by the writer only in Porto Eico, where
it was growing between the rows of diseased cane stubble. Infected
rice plants were observed there only once, growing just across a
narrow dirt road from a badly attacked cane field. At Audubon
Park, La., attacked sorghum was seen in a similar situation, the
most remote plants being only about 3 rods from the cane, and the
percentage of attacked plants decreased in an inverse ratio to the
distance from the cane. The same was true of crab-grass, which
was abundant in the sorghum field. These observations are en-
couraging and tend to offset the disconcerting facts discussed above.
NATURE OF THE DISEASE.
Sugar-cane mosaic is an infectious chlorosis, similar in many re-
spects to the mosaic diseases of tobacco, cucumber, bean, tomato,
and potato. Evidence of its infectious nature exists in hundreds of
field observations and in the infection of experimental plants under
controlled conditions. The well-defined epidemic in Porto Rico, in
which it has been established that the disease started in a small local
area and gradually spread from this focus of infection, diseased plants
being confined within the limits of the ever-increasing infested terri-
tory and not appearing sporadically at remote points, is convincing.
It leads to the inevitable conclusion that some virus or inoculum is
responsible for the appearance of new cases and that the only source
of inoculum is some plant previously infected with the disease. No
other explanation accounts satisfactorily for the observed facts.
Climatic conditions were at first suggested, but the epidemic has
lasted already for a period of years, during which rainfall, tempera-
ture, sunshine, and the other factors that go to make up climate
have been normal. The wearing out of soils was regarded as a
possible cause, but during the steady progress of the disease it gradu-
ally encroached upon every conceivable type of soil, including the
richest and most productive in the island. Strong support was
given to the idea that it was a case of deterioration or the "running
out" of varieties, but when it became evident that all varieties
present in the invaded district were affected, this idea was aban-
doned. For the same reason the hypothesis that it is a case of bud
variations, or "sports," seems highly improbable, and when the
regular progress of the epidemic is borne in mind, radiating outward
MOSAIC OF SUGAR CANE AND OTHER GRASSES. 17
as it does from a common starting point, there is seen to be notliing
to substantiate this claim.
Only a few specific observations of infection may be cited in the
limited space available. In October, 1918, healthy seed of about 80
varieties was brought into the infested area from disease-free regions
in order to determine whether any natural immunity existed among
the varieties present in Porto Rico. This seed was planted at the
Santa Rita estate, near Yauco. When the seed germinated, the
young plants were seen to be healthy and normal, but within six
weeks to two months practically every plant of all varieties with one
exception (the Japanese Kavangire) showed the unmistakable symp-
toms of mosaic. This was a clear case of secondary infection from
the fields of diseased cane surrounding the test plat.
At Santiago de las Vegas, Cuba, about 200 seed pieces of Java 228
cane imported from Tucuman, Argentina, were planted in two rows,
and two rows of the native Crystalina cane were planted beside them.
The Java cane was 100 per cent infected when it came up, the cut-
tings having come from diseased parent plants. When this planting
was examined in June, 1919, 75 per cent of the Crystalina plants-
were characteristically diseased. The Crystalina seed pieces had
come from a field which was minutely searched and found to be en-
tirely free from disease. No other cases were found in the entire
region, in fact, with the exception of a single stool of L 511 imported
In July, 1919, a field of D 74 stubble cane, grown for sirup near
Cairo, Ga., was found to be healthy with the exception of one corner
near the kitchen garden, where about 80 per cent of the plants had
the mosaic. Investigation revealed the fact that a patch of green
chewing cane had been growing adjacent to the D 74 at that corner
during the preceding year. The green cane was found growing else-
where on the farm this year, and examination showed that every
plant had the mosaic disease. Clearly the D 74 had become infected
last year, the disease had survived the winter in the stubble, and the
shoots were diseased when they appeared again.
At Washington, D. C, 17 varieties of cane, all diseased, are growing
in an insect-proof quarantine greenhouse.^ From time to time
healthy sugar-cane plants in pots have been taken into the greenhouse
and left exposed to the contagion. Invariably they show the incip-
ient symptoms of the disease on the average in 17 days, proving that
the incubation period is from two to three weeks. As has been men-
tioned elsewhere, sorghum and wild grasses taken into this greenhouse
have also become infected. Much more evidence of this kind could
be adduced, but it is believed to be sufficiently clear that infection
' Insects were present in the greenhouse.
18 BULLETIN 829, U. S. DEPARTMENT OF AGEICULTURE,
by some principle present only in dieased plants is responsible for the
appearance of the disease in formerly healthy individuals.
TRANSMISSION OF MOSAIC IN DISEASED SEED PIECES.
Experiments in Porto Rico ^ and elsewhere have repeatedly demon-
strated that cuttings from infected stalks invariably give rise to
infected plants. The young shoots are seen to be mottled as soon as
they appear. These are referred to as primary infections. The
fact is one of far-reaching importance, and to it must be attributed the
spread of the disease to new regions, remote from any infected cane,
by shipments of cane seed. The use of diseased stalks for propagating
results in wider distribution of diseased plants on the same planta-
tion from year to year and insures the survival of the virus, even in
the absence of secondary infections. Transmission of the disease in
cuttings is a fact, the importance of which can not be overemphasized
in view of its obvious bearing on control measures.
TRANSMISSION OF THE DISEASE BY CARRIERS.
It can be proved mathematically that by the law of chance the
percentage of diseased plants in a plantation would tend to remain
stationary from year to year provided there was no conscious or
unconscious selection,^ if the spread of the disease depended wholly
upon the use of infected cuttings. Nature has provided a far more
efficient method for the quick dissemination of the malady. Second-
ary infection, i. e., infection due to the inoculation of healthy plants
during the growing season, goes on at a more or less rapid rate wher-
ever the disease has been observed. Secondary infections are easily
determined as such when the plants are young. In the case of plants
infected in the greenhouse it has been determined that only the leaves
which were immature at the time of inoculation and leaves subse-
quently formed become mottled. When a plant is found with normal
leaves up to a certain point on the stalk and mottled leaves above
that point it is a clear case of secondary infection. Since in older
plants the lower leaves are gradually sloughed off until only a
relatively small terminal tuft of the youngest leaves remain when the
plant approaches maturity, this method is obviously limited to
young plants or to plants with green leaves still present above and
below the point of inoculation.
The rate of spread of the disease, as indicated by these secondary
infections, varies greatly. Fields are frequently seen in which there
has been apparently no secondary infection during an entire growing
1 Stevenson, John A. The "mottling" disease of cane. Porto Rico Insular Exp. Sta. Ann. Rpt. 1916-17,
p. 40-77. 1917. [Literature], p. 7&-77.
2 Selection is employed where the disease is not recognized. During the beginning of the epidemic in
Porto Rico, when sugar was bringing an unprecendented price, it was learned that the manager of one of the
mills was instructed to grind the best cane and save the poorest for seed. The "poorest " was undoubtedly
that attacked by mosiac.
MOSAIC OF SUGAR CANE AND OTHER GRASSES. 19
season. As an extreme case illustrating this point, the fields near
Cienfuegos, Cuba, may be cited. There the disease has merely sur-
vived by the planting of infected seed pieces, and secondary infection,
if it goes on at all, is certainly very limited. Even in Porto Rico,
during the height of the epidemic, secondary infection was at a
standstill in some localities for a year or more. On the contrary,
whole fields of healthy cane became infected in the short space of a
month or two. Such a case was the invasion of the variety test field
at Santa Rita, Porto Rico, previously mentioned. No doubt the
explanation for this great variation in rate of spread by secondary
infection must be sought in the . mechanics of inoculation. Up to
the present no positive proof of the method by which inoculation is
accomplished in nature has been brought forward. Reasoning from
the fact that new cases often appear at some distance from diseased
individuals, it would seem that some agent or carrier is* necessary.
Mere contact of diseased and healthy plants does not serve to com-
municate the infection from the former to the latter. In no case has
the planting of healthy cuttings in the same pots with diseased plants ,
resulted in the new plants becoming diseased. The same holds true
for plants in the field, where healthy plants are often seen with their
leaves mingling freely with the leaves of diseased plants for a time
much longer than the incubation period for mosaic, but with no
evidence of transference of the inoculum. It is evident that special
conditions are necessary in order that the disease can be communi-
cated to healthy plants.
Field observations indicate that acceleration in the spread of the
mosaic disease is accompanied with or preceded by severe insect infesta-
tions. The cane leafhopper (Tettigonia sp.) in particular has been
noticed to accompany the rapid spreading of the disease. This evidence
is incomplete, but it is supported by the fact that 10 healthy plants
placed in insect-proof cages in the greenhouse at Garrett Park, Md.,
did not contract the disease, while five control plants outside of the
cages, but otherwise under identical conditions, all became infected.
Aphids were abundant on the diseased cane in this greenhouse, and
a few leafhoppers were present. A great deal of experimental work
remains to be done before formal proof of the responsibility of any
particular insect or insects for the transmission of the disease can
There has been no indication that the contagion persists in the soil
after a crop has been removed and the stubble plowed up. Fields
that have been veritable hotbeds of infection after being plowed up
and planted with clean seed have only a few scattered cases, which
can be accounted for by faulty seed selection. Healthy cuttings
planted in the soil of pots from which badly diseased specimens had
20 BULLETIN 829, TJ. S. DEPAETMEISTT OF AGRICULTUEE.
just been removed grew witliout any evidence of the disease. The
virus does not live over in the soil and it is doubtful whether it exists
there at any time. In this respect the mosaic does not by any means
present the practical difficulties in the way of control measures to be
met with in root-rot. Root-rot, in fact, is to be regarded as a far
more serious problem for the Louisiana cane planter than mosaic on
RELATION TO DISINFECTANTS.
Treatment of infected seed pieces by soaking in strong Bordeaux
mixture or corrosive sublimate previous to planting has had no effect
on the course of the disease. All shoots were typically mottled as
soon as they appeared. It was hardly to be expected that superficial
disinfection could influence the virility of the infectious principle when
all our evidence indicates that the latter permeates the internal
tissues, or at least the vascular systems of affected plants.
RELATION TO FERTILIZERS.
Many experiments ^ have been performed in Porto Rico to deter-
mine the effect of applying fertilizers, since the claim was made by
many planters that mosaic was due to insufficiency of plant nutrients
in the soil. Filter press cake, sulphate of ammonia, and lime in
various combinations, together with turning under cover crops and
good tilth, had no noticeable effect on the disease as compared with
control plats. Standard complete fertilizers were also tried. Beyond
a slight stimulation in growth and the darker green color of the treated
plants, there was no observed effect. Diseased plants may be expected
to respond to good growing conditions the same as healthy ones,
but the same constant difference between healthy and diseased plants
is maintained under all conditions. The diseased stalks remain below
the average weight for healthy stalks and are just as capable of
spreading the disease. Liming the soil has no more effect on diseased
plants than the application of fertilizers.
It is interesting to note that in Java long experience has demon-
strated that the disease can best be held in check by careful selection
of healthy plants for seed and by replanting fields with cuttings taken
from the same field, in preference to buying cuttings of imknown
origin or moving the cuttings from field to field on the same plan-
tation. The use of such methods practically amounts to tacit
admission of the infectious nature of cane mosaic, although it is
ascribed to "bud variation." The facts wliich have most impressed
the Dutch planters are that cuttings from diseased stalks always
1 Stevenson, John A. The "mottling" disease of cane. Porto Rico Insular Exp. Sta. Ann. Rpt.,
1916-17, p. 40-77, 1917. [Literature] p. 76-77.
MOSAIC OF SUGAR CANE AND OTHER GRASSES. 21
produce diseased plants and that careless importation of seed is
apt to result in increased amounts of the disease.
In the Hawaiian Islands also the disease is controlled by selection
of clean seed and the use of resistant varieties.
Measures for controlling the mosaic disease recommended in the
following pages are not haphazard expedients, but have been used
with very satisfactory results in Porto Rico for more than a year.
Planters there have paid a heavy price to learn them, and it is urged
that planters of sugar cane in the United States cooperate to prevent
a possible epidemic. Indifference to the situation may result in the
cane growers being confronted with the fact that it is too late to prac-
tice seed selection, as is already the case in western Porto Rico.
At present, it will work no particular hardship on the planters to
take steps that will reduce the disease to a minimum.
ELIMINATION BY ROGUING.
Roguing consists of pulling out infected plants, root, stem, and
branch, and throwing them down between the rows. It is based on
the fact that as soon as the plants are wilted they are no longer
dangerous as a source of infection. This method is applicable only
to fields in which the disease has not obtained a strong foothold.
It is not recommended for fields in which the number of infected plants
exceeds 5 per cent in half -grown to mature cane or 20 per cent in young
plants just sprouting. The size of the field and the condition of
surrounding fields with reference to the occurrence of the disease
in them must also be taken into consideration. When the field is
quite small or consists merely of a few rows or plants of a new variety
being propagated for trial on a plantation scale, it should be rogued
even if 100 per cent of the plants are infected. Such plants are a
constant menace to plants in surrounding fields. In large fields
where the proportion of diseased individuals is greater than 20 per
cent, roguing is impracticable, not because the plants are any less
potent as sources of infection, but because diseased plants produce
millable cane, and to destroy considerable quantities of such plants
would probably result in greater financial loss than would be sustained
by the reduction in yield due to new cases. Large fields with a high
percentage of diseased plants should be allowed to mature, but no
cane from such fields should be saved for seed.
It is suggested that the foUowuig schedule of inspections and
roguing be put into operation : In the spriiig, just as soon as all of the
plants have sprouted, the fields should be inspected by passmg up
and down the rows. All diseased stools should be puUed out of the
ground and cast down between the rows. If this fu'st inspection is
carried out in a thorough manner the field will be completely freed
from the disease provided no secondary uifections are going on.
22 BULLETIN 829, U. S. DEPARTMENT OF AGRICULTURE.
Since there are as yet no certain means of determining the latter
fact, a second mspection is essential. It should be made from 25
to 30 days after the first, a lapse of time sufficiently in excess of the
incubation period for mosaic to insure recognition of the disease in
plants inoculated prior to the first inspection. If no diseased plants
are found during the second inspection, it can be assumed that
secondary infection is not in operation and that the remaining
plants will continue healthy. If diseased plants are found, how-
ever, it establishes the fact that secondary infections are going on.
The field should be rogued as before, and a third inspection made
after the same interval, i. e., 25 to 30 days. If the carriers remain
active it may be necessary to repeat the process several times, and
owuig to the impossibility of recognizing the disease in inoculated
plants before the end of the incubation period it is certain that
plants which have become infected just before the inspection is
made will escape detection. This emphasizes the necessity for
making the first inspection early, preferably before leafhoppers or
other sucking insects have appeared on the plants.
This procedure may result in perfect control or eradication of the
disease or in partial control, the element of uncertainty bemg due to
om' inabifity to control the carriers. By it their activity can be
rendered less effective by reducing the sources of inoculum to a
minimiun. It has effectually halted the progress of the disease into
new territory in Porto Rico.
ELIMINATION BY GRINDING ALL CANE AND SECURING CLEAN SEED.
In badly infested sections the problem is manifestly complicated.
Where 25 to 60 per cent or more of the plants in large fields are
diseased, roguing is obviously out of the question. Such plantings
should be allowed to matm-e. Every stalk of it should be ground,
however, and the stubble plowed up and kiUed. This means, of
course, that carefully selected seed must be imported for replanting.
Fortunately there is still an abundance of healthy stock in Louisiana
and other cane sections in the United States. As a result of its
recent exhaustive survey for mosiac disease, the Ofiice of Sugar-
Plant Investigations of the Bm'eau of Plant Industry is in a position
to furnish information on the nearest or m.ost accessible som'ce of
clean seed for any region. Data have been secured on the prevalence
of other diseases and msect pests in all cane regions, so that reason-
able security against the dissemination of other cane maladies is
There are at the present time (October, 1919) a number of large
cane areas in the United States not yet mvaded by the mosaic
disease. Cane planters in these areas should urge the enactment of
MOSAIC OF SUGAR CANE AND OTHER GRASSES.
State legislation prohibiting the importing of cane into them from
any source whatever until such time as it can be accompanied by an
authentic certification of health. Such areas include the entire
Bayou Teche district and the parishes to the north in Louisiana,
consisting of St. Mary, Iberia, Vermilion, Lafayette, St. Martin,
Acadia, St. Landry, Avoyelles, and Rapides. This is, of course,
the most important disease-free area. (Fig. 2.) Other similar
Fig. 3.— Map of Louisiana, sho\ving the location of diseased areas of sugar cauo in that State.
areas are the entire State of Mississippi with the exception of Biloxi;
the entire State of Alabama except a small locality near Muscogee,
Fla. ; the entire State of Georgia except Grady County; and all parts
of Florida other than those indicated in figure 4.
Wliere the disease is present in small amomit and in few well-
defined areas, the possibility of quick and complete eradication
exists. Such conditions are found in Mssissippi, Alabama, and
Florida. (See fig. 1.) The cane in these areas should all be ground'
during the present hai^vesting season -and the stubble plowed up.
As a precautionary measure, some crop other than a grass should
be grown on the land for one year, after which cane may again be
grown with safety. The two small infested areas iii Alabama and
1 In so far as it applies to the regions Indicated, we concur in this suggestion by Mr. Wilmon Newell,
Plant Commissioner of Florida.
BULLETIlSr 829, U. S, DEPARTMENT OF AGPJCULTUEE.
Mssissippi offer no diiE-culty at all. They can be destroyed with
practically no loss to the owners, and the assurance of healthy crops
in the future more than offsets the inconvenience of growing some
other crop on the land now occupied by infected cane. The success
of the measure in Florida is made possible by the present organization
of the State plant board, which has already met the test of success-
fully handling more serious problems.
ELIMINATION BY PLANTING IMMUNE VARIETIES.
Success of the control measures suggested up to the present depends
entirely upon the whole-hearted cooperation of all cane growers.
Fig. 4. — Map of Florida, sho^^•ing the location of diseased areas of sugar cane in that State.
There yet remains a method, applicable only to certain regions, by
which a planter can make himself wholly independent of any default
on the part of his neighbors. A few varieties of sugar cane have been
discovered that are absolutely immune to mosaic under all condi-
tions. Most of them are of the type referred to as Japanese cane.
Their origin is obscure. They have certain characteristics in com-
mon. All are tall growing with slender stalks. They stool abund-
antly, ratoon well, and produce an enormous tonnage. The sucrose
content is not so high as in some of the broad-leaved canes, but in
sugar per acre they take first rank with the best existing varieties.
The Kavangire, Zwinga, Uba, Cayana 10, and numerous others
imported by the office of Foreign Seed and Plant Introduction are
MOSAIC OF SUGAR CAI^E AND OTHER GRASSES.
included among these varieties. The Cayana 10 has already won a
well-deserved popularity among the farmers of the cane-sirup
section in Georgia and northern Florida on account of its high
tonnage and the excellent quality of sirup made from it. The Kavan-
gire is used for manufacturing sugar in Argentina. Its estimable
qualities are brought out in Table III.
Fig. 5.— Kavangire sugar cane (immune), at the left; G. C. 1070 (susceptible), at the center; Java 36 (sus-
ceptible but tolerant), at the right.
Table III. — Yield and analysis of Kavangire sugar cane compared with other standard
Ravada (Louisiana Striped)
Morada (Louisiana Purple (?))
1 Bennett, A. G. Informe de subestaciones para el aflo 1914. In Rev. Indus, y Agr. Tucuman, ano 5,
p. 208-209. 1914.
2 A kilo is the equivalent of 2.2 pounds. 3 ^ hectare is the equivalent of 2.47 acres.
26 BULLETIN 829, U. S. DEPARTMENT OF AGRICULTURE.
Figure 5 shows a row of Kavangire cane on the left; a susceptible
variety, G. C, 1070, at the center; and a diseased but tolerant variety,
Java 56, on the right. Unfortunately, the Kavangire variety is a
long-season cane and therefore not suitable for conditions in Louisiana.
The possibility of breeding more early maturing varieties from these
parents is being investigated.
Several of the broad-leaved varieties of cane originated at the
Sugar Cane Experiment Station at Audubon Park, La., appear to be
immune. Although equally exposed to the contagion, no individuals
of these varieties have becom.e affected, while practically every plant
of the scores of other varieties surrounding them is diseased. They
have been under observation for too short a time, however, to
demonstrate that their apparent immunity is permanent.