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'W^f'» THEIR 


ONION SMUT kills the young seedlings in the 
spring, is common in old onion sections, but can 
he controlled successfully by applying a formalde- 
hyde solution in the row with the seed by means of 
a drip attachment on the seeder. 

Onion mildew blights the leaves in midscason, but 
can be held in check by rotation of crops, good drain- 
age, thorough cultivation, and by spraying the foliage 
thoroughly with Bordeaux mixture before the dis- 
ease becomes widespread in the field. 

Storage rots — smudge, ueck-rot, soft-rot, black- 
mold — are controlled by protecting the crop from 
moisture during and after harvest and by facilitating 
as rapid and thorough curing as possible. 

Bruising due to careless handling, topping, or mill- 
ing should he avoided. 

For storage a well-ventilated warehouse kept at 
32° to 35° F. is preferable. 

Contribution from Iho Bureau of Plant Industry 
WM. A. TAYLOR, Chief 
Washington. D. C. IS'ovcnilior, 1919 



J. C. Walker, 

Assistant Pathologist, Office of Cotton, Truck, and Forage Crop Disease 




Scope of this bulletin 8 

Descriptive key to onion diseases 8 

Diseases primarily Important In the 

Held 4 

Smut ; 4 

Mildew (blight) 0 

Leaf-mold 12 

Fusarlum rot 13 

l'lnk-root 13 

Itoot-knot 14 


Farm practice in relation to storage 

diseases 15 

Diseases primarily important in stor- 
age and transit 18 

Neck-rot 18 

Soft-rot 20 

Mack-mold 21 

Smudge (anthracnose black- 
spot) 22 

Summary of control measures 23 


THE ONION INDUSTRY of the United States is widely dis- 
tributed and of increasing importance. The chief producing 
centers may be grouped into two hirge divisions, namely (1) those 
in the northern and central tier of States, extending from Massachu- 
setts to the Pacific coast, which produce principally a late summer or 
fall erop, and (2) those in the souhern tier of States, extending 
from Florida to southern California, in which a winter or spring 
crop is grown. The wido range of soil and climatic conditions in 
the different sections makes difficult a general discussion of onion 
diseases which may apply to all regions. This bulletin is written 
primarily from the standpoint of onion growing in the North Cen- 
tral and Northeastern States, viz, from Iowa to Massachusetts. 
Recommendations in general, however, will apply to other sections, 
and at certain points special reference will be made to diseases in 
the South and AVest. 


Since certain diseases of onions resemble one another rather closely, 
the following descriptive key will aid in their prompt recognition. 

A. Diseases primarily Important In the field. 

1. Dark pustules appear within the leaves or scales and may later 
split open, exposing black, powdery masses, principally on the young 
seedlings. (See flg. 1) Smut, page 4 


' Bulletin 1060. 

A. Diseases primarily Important in the Hold — Continued. 

2. The leaves turn pale green and yellowish, become covered with 
a violet furry growth, nnd finally collapse; most serious In moist 
weather In mldseason or later. (See fig. 5) Mildew, page 9 

3. A black, moldy growth on leaf tips or seed stalks, often follow- 
ing mildew Leaf-mold, page 12 

4. A rapid dying back from the lips of the leaves, accompanied 

by rotting from the base of the bulb. (See fig. 0) Fusarlum rot, page 13 

5. The roots turn pink In color and die; new roots are attacked as 

they develop, resulting in a marked stunting of the plant— Pink-root, page 13 

0. The leaves become a sickly green ; swellings form on the roots. 

(See fig. 7) Uoot-knot, page 14 

15. Diseases primarily Important In storage and transit. 

1. A rot begins at the neck of the bulb and progresses downward ; 
the tissue shrinks and collapses; a gray to brown moldy growth and 
hard, bhiek kernels later appear on the surface of affected scales. 

(See figs. 8 and 0) Neck-rot, page 18 

2. A rot begins at harvest time or later, but differs from neck-rot In 
that It is softer and more watery, usually with a very offensive odor. 

(See fig. 10) Soft-rot, page 20 

3. A semhvMtcry rot advancing from the base of the scale upward. 

(See fig. 0) Fusarlum rot, page 13 

4. TJiack, powdery masses form, not in definite pustules within the 
scales, as in smut, but on the outer surface of or between the scales. 

(See fig. 11) Black-mold, page 21 

5. Smudgy, superficial black spots made up of fine dots, but with 
no powdery masses, appear shortly before harvest time on the outer 
scales; primarily on white varieties. (See fig. 12) Smudge, page 22 

In addition to these specific diseases there are certain other troubles, 
due to insects, with which they are liable to be confused. 

(1) Thrlps Injury: Small, white, chafed spots appear on the leaves and cause 
them to die prematurely; the minute pale-yellow thrlps which cause the injury 
are commonly present. 

(2) Onion maggots often kill seedlings by feeding upon the roots. Tlds 
Injury is sometimes confused with onion smut, but the absence of pustules of 
black powder distinguishes it from the latter. 



Onion smut appeared in the United States nearly 50 years ago, 
when it was found to be doing damage in the Connecticut River 
valley, and has spread into most of the large northern onion sections, 
including Xew York, New Jersey, Ohio, Wisconsin, Illinois, Iowa, 
sind Oregon. Whan once introduced, it becomes more serious each 
year the crop is replanted on the same soil and spreads slowly to ad- 
joining areas. 


The disease appears soon after the seedlings como above ground. 
Brown to black elongated blisters form within the scales or leaves, 

Onion Diseases and Their Control. 


the latter usually being- slightly thickened mid often curved down- 
ward abnormally. Not uncommonly the leaf splits, exposing n pow- 
dery black mass of spores in the interior of the blister (fig. 1). Many 
of the young seedlings are so severely attacked that they die within 
three to five weeks after germina- 
tion. In others, which may sur- 
vive until midseason or harvest, the 
new leaves and scales continue to 
he attacked as they develop. A 
very few outgrow the disease. Al- 
though most of the infected bulbs 
are so small and imperfect that they 
are thrown out at harvest time, oc- 
casional ones are of sufficient size 
to escape notice and thus reach the 
warehouse or market. Such speci- 
mens are characterized by the 
slightly raised brown to black pus- 
tules most prevalent near the base of 
the bulbs and usually occurring as 
deeply as the third or fourth scale. 
Smut does not cause a storage rot, 
but smutted bulbs shrink more 
rapidly and are more subject to the 
attack of other organisms than 
healthy ones. 


Smut is due to a fungous para- 
site (Vrocystis cepulae) which at- 
tacks only the onion and certain 
closely related speeies of plants. 
The black, powdery masses which 
are exposed upon the splitting of 
the blisters consist of myriads of 
spores, or seed bodies, which serve 
to propagate the fungus. These 
spores fall to the soil and over- 
winter there, being very resistant to 
cold. In the spring, at the time 
when the onion seeds are germinating 
and infect the young seedlings. 

Fio. 1. — Onion smut. A young bulb 
allowing unbroken blisters on scales 
and leaves. Those later split opcu 
and expose the black, powdery spore 

the smut spores also germinate 
Having established itself within the 
young plant, the fungus continues to develop, taking its nourishment 
from the onion seedling and again forming new spore blisters. 

A peculiar and important fact about smut is that the onion plant 
can be attacked by the fungus only while in the young seedling stage. 
125150°— 1!)— Bull. 1000 2 


Farmers Bulletin 1060. 

After tho plants arc about 3 inches high they become immune to 
further infection, and onion sets or onion seedlings 3 to 4 inches high 
transplanted to smiit-infeeted soil will not contract the disease. 

Smut spreads slowly in tho soil, hut an infested spot in a field will 
gradually become larger and more severely diseased each year onions 
are grown. Moreover, the spores are carried to other parts of tho 
field on the farm implements, feet of men and animals, by surface 
water, and in dust carried by tho air. It may also be carried into 
new localities on onion sets containing the disease in their outer 
scales. Purchasers of onion sets who arc not troubled with the smut 
should bo on their guard lest they contaminate their soil by planting 
smutted sets. 


Sanitary measures. — Where practicable, tho tops should be burned 
after harvest, and caro should bo taken to avoid as much as possible 

FlG. 2. — Onion seeder with a formaldehyde drip attachment for disinfecting the soil 
at tho time ot seeding, to control onion smut. The cut-off valvo Is regulated from 
tho handle. (See text for description.) 

tho returning of infected onion refuse to the soil. The spreading on 
the fields of waste from onion warehouses is a bad practice, since it 
may contain smut or other diseases which may thus be introduced 
into healthy soil. 

Use of onion sets. — Where green onions are grown for early spring 
markets or where an early crop of bulbs is desired, onion sets aro 
commonly used. Since plants grown from sets arc not attacked by 
smut, this method of propagation can be used with success on smut- 
infested soil. 

Onion Diseases and Their Control. 


Use of onion seedlings from healthy soil. — Within recent years 
northern market gardeners have to some extent practiced starting 
onion seedlings in the hotbed or greenhouse and transplanting to 
the field when 3 or 4 inches high. On southern truck farms it is tha 
general custom to sow the seed in beds in the fall and transplant 
during the winter. Where this method is profitable, onion smut can 
be avoided by growing seedlings on healthy soil until 3 or 4 inches 
high and then transplanting to the fields. 

Use of formaldehyde drip. — In the large commercial onion dis- 
tricts of the Northern States, where the use of sets or seedlings is 

Fig. 3. — Field of onions on smut-Infested soil where formaldehyde was applied. Tho 
disease has killed a large percentage of the plants in the two untreated rows In 
the center, while the remainder of the field has practically a full stand. 

impracticable, advantage is taken of the fact that onion smut can be 
controlled by the application of a solution of formaldehyde in the 
furrow with the seed. Since the young onion seedling is susceptible 
to the disease for only a short time, it is necessary to use only enough 
of tho disinfectant to keep the fungus in cheek in the soil close to 
the seed. 

Apparatus. — The apparatus for applying the formaldehyde solu- 
tion consists of a galvanized iron tank with a pipe leading down to tho 
furrow (fig. 2) . It can be made by any tinner. Such an attachment is 
offered for sale by certain manufacturers of onion seeders. The size of 
the tank will vary with the type of seeder used, but for the ordinary 


Farmers' Bulletin 1060. 

single-row seeder a 2-gallon tank is a sufficient load. It is best placed 
just behind the seed box, where the extra weight will rest mainly on 
the packing wheel. The pipe should be so arranged as to run tho 
solution directly into the center of the furrow just before the packing 
wheel closes it, and to lead it far enough down to prevent splashing 
on the shoe or the packing wheel. It is essential to have a cut-off 
valve in the pipe which can be controlled from the handle of tho 
seeder, thus enabling the operator to shut off the flow quickly at 
the end of tho row or whenever desirable. There should be about 
n five-sixteenths inch flow of liquid from the tank, in order to sccuro 

the proper quantity 
of 200 gallons per 
aero. In certain lo- 
calities the attach- 
ment has been modi- 
fied successfully for 
uso with the 8-row 
gang seeder. 

Strength and quan- 
tity of the solution.— 
Great care should bo 
used in applying this 
treatment, since too 
strong a formalde- 
hyde solution will pre- 
vent tho onion seed 
from germinating, 
while too weak a so- 
lution will not hold 
tho fungus in check. 
It is advantageous to 
increase the strength and decrease the quantity of tho liquid as much 
as possible, in order to reduce the labor of application, but this can 
he done only up to a certain limit. 

To each gallon of water use i fluid ounce of 37 to 40 per cent 
formaldehyde solution, sometimes known commercially as formalin. 1 
Apply this diluted solution at the rate of 200 gallons per acre, or 1 
gallon to about 185 feet of row. 

Whore several rows of seed arc sown close together for the pro- 
duction of onion sets, the quantity of solution applied should bo 
increased accordingly. 

Cost of application. — About 12 pounds of tho 40 per cent formal- 
dehyde solution arc required for each acre, which, when purchased 

Via. 4. — Yield of a treated and an untreated row of onions 
in the field shown In figure M. The treated rows aver- 
aged 543 bushels and the untreated ones 200 bushels per 

1 For larger quantities, 1 pint to 10 gallons gives the same dilution. 

Onion Diseases and Their Control. 


in wholesale quantities, can bo secured at about 25 cents per pound 
(1919 prices). When a single-row seeder is used, the amount of 
labor required at the time of sowing is about doubled, bringing the 
entire cost of application to 

about $5 per acre. 
3 and 4.) 

(Sec figs. 


The first symptoms of onion 
mildew, or blight, may be 
found by examining the leaves 
closely on a dewy morning, 
when a violet furry covering 
may be seen on the outer sur- 
face. Within a day or two 
the color of the leaves becomes 
pale green and finally yellow- 
ish, the furry growth becomes 
more widespread, and the dis- 
eased portions of the plant 
eventually collapse (fig. 5). 
The disease commonly starts 
in the field in spots and 
spreads to the surrounding 
areas, its development being 
greatly aided by moist 
weather. Tf the weather re- 
mains dry following an out- 
break of the disease, the plants 
send out new leaves and par- 
tially recover. However, on 
the return of damp conditions 
the fungus revives and the 
new growth becomes blighted. 
The killing of leaves in this 
manner, although it may not 
entirely kill the plants, re- 
duces growth, and the bulbs 
remain small. 

The onion mildew has been reported from most Stales where 
onions arc grown extensively. The dcstrnctivcncss of the disease, 
however, varies widely in different localities and in different years 
in the same region. As in the case of a number of other downy 

Fig. 5.— Onion mildew (blight). Note the 
fungous growth on the dying lower leaves; 
the two youngest leaves are still healthy. 
The spread of the disease to new leaves de- 
pends on the amount of moist weather pre- 
vailing. (Photographed by the Vermont 
Agricultural Experiment Station.) 


Farmers' Bulletin 1060. 

mildews, prevailing moist weather is absolutely essential for its 
development in epidemic form. Heavy losses have been reported in 
New York, Michigan, Oregon, California, and Louisiana. In the 
two States last mentioned the chief damage is to the seed crop, the 
heavy fogs which are very prevalent being especially favorable for 
the development of the mildew, which attacks the seed stalks, causing 
than to fall over before the seed is mature. 


Mildew is caused by a fungus (Peronospora schleideni) and bo- 
longs to the class of downy mildews, the most important among 
which arc late-blight of potato, grape mildew, and cucumber mildew. 
The furry masses on the affected leaves are branches of the fungus, 
which bear abundant spores. These spores arc very light and arc 
easily carried by the wind to healthy plants. However, they are 
short lived and very sensitive to drying. 

In damp weather drops of water on the plant furnish sufficient 
moisture for prompt spore germination. The resulting fungus 
growth enters the plant and absorbs food from it, thereby causing 
its leaves to shrivel and die. The fungus thus nourished produces 
more spores, which in turn are wind borne to healthy plants, whore 
under favorable conditions they again produce the disease. 

In the fall the fungus forms in the diseased loaves thick-walled 
winter spores which are resistant to drought and cold. They germi- 
nate in the spring and again start the disease in the new crop. It is 
also by moans of those winter spores that the mildew may bo spread 
from diseased fields to healthy fields in infested soils, in diseased 
onion tops, or iu sots. 


Sanitation and cultivation. — The successful control of onion mil- 
dew depends largely on attention to cultural and sanitary measures. 
Since many of the winter spores live over in dead tops, it is advisa- 
ble to rake these and burn them in the fall. Thorough cultivation is 
essential, in order to keep the crop as vigorous as possible, so that it 
may rapidly outgrow the disease when the latter is chocked by dry 

Rotation of crops. — Since the winter spores live over in the field, 
it is advisable to plant infested fields to other crops for a few years. 
It is not known how long the fungus can live in the soil, but it will 
certainly be greatly reduced in two or throe years. It is true that 
many growers prefer to grow onions for a number of years suc- 
cessively on the same soil. However, it is no doubt true that a num- 
ber of other cultivated crops yield high enough returns to bo con- 

Onion Diseases and Their Control. 


sidered in a rotation, especially when the general henefits of a three 
or four year rotation are considered. In certain seetions farmers, 
realizing the importance of this practice in the control of diseases, 
are successfully rotating onions with eabbage, potatoes, and sugar 
beets, and in some eases grain is ineluded. 

Air and soil drainage. — Inasmuch as moist conditions greatly favor 
mildew, care should bo taken to seleet fields where the air drainage 
is good, so that excessive dew and fog may be avoided. Good soil 
drainage also helps to reduce blight, since it reduces the moisture in 
the air near the surface of the soil. 

Spraying for mildew. — In the control of onion mildew, Bordeaux 
mixture applied as a spray has been used to some extent, but not 
with complete sueeess in all eases, since there is considerable difficulty 
in making the spray stick to the leaves. If spraying is to be done, 
rosin-fishoil soap should be added to the spray mixture to make it 
adhere to the leaves. The spray should be applied thoroughly be- 
fore the disease has beeome established in the field, and it may bo 
necessary to spray the field several times during the summer, espe- 
cially during the rainy season. 

In the preparation of Bordeaux mixture the ingredients should be 
xised in the following proportions : 

Where Bordeaux mixture is to be used frequently and in reason- 
ably largo quantities, it is more convenient to make up the ingredients 
in concentrated stock solutions or suspensions, since these can be kept 
on hand indefinitely if water lost by evaporation is replaced. 

Stock solution and suspensions. — Build an elevated platform to 
hold the barrels, preferably near a well or other source of water. 
Suspend 50 pounds of copper sulphate, inclosed in burlap or a loosely 
woven sack, so as just to dip into a 50-gallon barrel of water. Slake 
50 pounds of lime in another barrel and dilute to 50 gallons with 
water. Plaeo 37J pounds of rosin-fishoil soap in a barrel and slowly 
add water to make 37| gallons, stirring constantly to avoid the forma- 
tion of lumps. -These stock solutions and suspensions now eontain 1 
pound of their respective ingredients in each gallon of liquid. 

Preparation of the mixture. — Follow the directions given below 
where 100 gallons of spray mixture can be made up and used at one 
time; for smaller amounts adjust the quantities used accordingly. 


Copper sulphate- 

Uosin-fishoil soap 
Water to make—. 

4 pounds. 
4 pounds. 
3 pounds. 
CO gullons. 

1 The section on Bordeaux mixture was prepared by Mr. W. 1!. Clark. 


Formers' Bulletin 10G0. 

Provide two 50-gallon barrels with one head removed from each 
and with openings of ainplo size near the' bottom head. The flow 
from the openings can bo most easily controlled by attaching to 
them, with a pipe nipple, pieces of 1| or 2 inch rubber hose just 
long enough to hook up to the tops of the barrels while they arc be- 
ing filled and stirred. Stir the concentrated solution and suspen- 
sions thoroughly and measure into one barrel 8 gallons of eopper- 
sulphatc stock solution and into the other 8 gallons of the lime sus- 
pension. Add to each enough water to make 47 gallons, stirring 
thoroughly. Provide a trough leading under the openings of the 
two barrels and emptying into the strainer of the spray tank. 
Lower the free ends of both pieces of hose, as nearly as may be, so 
that the diluted lime suspension and copper-sulphate solution flow 
at equal rates, mixing in tho trough before entering the spray tank. 
"While the mixture is flowing into the spray tank, slowly add C gal- 
lons of the rosin-fishoil soap suspension by pouring it into the spray- 
tank strainer in a small stream, so that the C gallons will bo well dis- 
tributed throughout tho entire mixture. Do not let tho soap eomo 
into contact with either of tho other two ingredients until they havo 
mixed. This method gives a thorough mixture of all tho ingredi- 
ents without the necessity for any hand stirring. 

Do not put copper sulphate or Bordeaux mixture into tin or iron 
vessels. Use wood or copper containers. 

A copper or bronze strainer of 18 meshes per inch should bo used. 
Bordeaux mixture should bo applied as soon as made, as it is not so 
good after settling. 

Spray machines to be used. — The typo of sprayer used must bo 
decided for each individual ease. Hand or power sprayers ordi- 
narily used for potato and other vegetable spraying can be adapted 
to onions. A pressure of 100 pounds or more per square inch should 
ho maintained, and a nozzle which will give a very fine spray is 


Tn midseason or later dying back from the tips of the leaves com- 
monly occurs. "While this injury may be due in part to insufficient 
soil moisture, the trouble is often increased by a weakly parasitic 
fungus {Macros porium parasltlcum) which attacks the dying parts 
and later produces a black mold on the dead tissues. This fungus 
also commonly attacks the seed stalks, independently or following the 

Although of widespread occurrence, the actual loss due to leaf- 
mold is of minor importance, with the possible exception of tho 
injury to the seed crops of Louisiana and California. There, in eon- 

Onion Diseases and Their Control. 


junction with the mildew, it may cause 
severe damage. However, no satisfac- 
tory method of control has been per- 


A rapid dying back of the leaves 
from the tips at the time when the 
plants are approaching maturity is com- 
monly associated with the Fusarium 
rot a fleeting the bulb. (See fig. G.) 

Most of the roots eventually become 
rotted off, and in their place a mass of 
white moldy growth is produced. The 
bulbs become soft, and on cutting them 
open one finds a semi watery decay ad- 
vancing from the base of the scales up- 
ward. The rot progresses rather 
slowly, and many of the recent infec- 
tions are unnoticed at harvest time. 
The disease thus becomes a factor in 
transit and storage, where the decay 
may continue until the bulbs are en- 
tirely destroyed. 

Reports of this trouble have come 
from Ohio, Illinois, Wisconsin, and 
"Washington, and it probably occurs in 
oilier States. It is caused by one or 
more species of soil fungi (Fusarium 
spp.), which invade the base of the 
bulbs, often following maggot injury. 

Strict attention to sanitary measures 
as outlined later (see p. 10) and careful 
sorting out of diseased bulbs at harvest 
time are the chief measures to be taken 
for the control of Fusarium rot. 


In the Bermuda onion regions of 
southern Texas pink-root is the most 
serious disease confronting the grower. 
The symptoms become manifest in the 
seed bed or after transplanting by the 
roots turning pink in color, after which 
they shrivel and die. As the plant 

Fio. 0. — An onion showing Fusa- 
rium rot. Decay starting at the 
bane of the scales causes the 
leaves to die rapidly, and the 
bulb continues to rot in storage 
and in transit. 


Farmers' Bulletin 1060. 

sends out now roots they in turn eventually become diseased and f unc- 
tionless. This procedure continues throughout the growing season,' 
and although the affected plants seldom are killed by the disease, the 
reduced nourishment results in merely scallions or small bulbs being 
formed. Pink-root becomes the more destructive the longer onions 

are grown on the same 
field. It is caused by a 
soil fungus (Fusarium 
malli), which is carried 
over from year to year in 
the soil. 

The disease is being in- 
vestigated at present by 
the Texas Agricultural 
Experiment Station, and 
recommendations for its 
control must await tho 
results of these studies. 


Root-knot of onion is 
an celworm disease which 
may be recognized by tho 
spherical swellings or en- 
largements of affected 
roots, as shown in figure 
7. Tho aboveground parts 
of badly diseased plants 
are dwarfed, the leaves 
are a pale-green, sickly 
color, and the bulbs are 
reduced in size. Root- 
knot, while occurring as 
a serious trouble of many 
wild and cultivated 
plants in the southern 
portion of tho United 
States, has boon reported 
only occasionally on onions, and fortunately there is little likelihood 
that it will ever bo a major disease of this crop. It is caused by a 
minute eelworm, or nematode (Tleterodera rarficicola) , which lives in 
the soil and penetrates tho onion roots, where swellings arc produced. 
After reaching maturity in the roots, the nematode may lay hundreds 

Fig. 7. — Onion root-knot, caused by an celworm. Note 
that certain roots contain spherical swellings, from 
some of which small, dark masses (the eggs) arc 
protruding. Many active larvai of the eelworm 
escape from these egg masses Into the soil, and 
render It unfit for growing onions as well as many 
other crops. 

1 The Hoction on root-knot was prepare*! by Dr. Li. V. Iiyars. 

Onion Diseases and Their Control. 


of eggs, which hatch into active forms (larvae) and thus complete the 
life cycle. 

Soil once infested with the eelworms can he freed hy the use of live 
steam applied under considerable pressure. In large areas where 
steaming may not be practicable, the number of nematodes can be 
reduced by a proper system of crop rotation. By planting for two 
or more years on infested land crops which are not subject to nema- 
tode attack, the eelworms may be starved out to such an extent that ; 
a susceptible crop, such as the onion, will not be damaged seriously 
when planted in the soil. 

To avoid root-knot it is advisable never to plant onions on land 
that is known to be infested. 

For further details regarding the control of root-knot, see Farmers' 
Bulletin G48. 


The interval of several weeks between harvest and storage or ship- 
ment is a very critical one with relation to the development of dis- 
eases in the warehouse or in transit. The care which is taken with 
the crop at this period may mean the difference between success and 
failure in carrying it through storage or in placing it on the market 
in good condition. It should be remembered that the plant at this 
time has practically terminated its growth, and that on going into its 
dormant state it becomes more susceptible to the attack of storage- 
rot fungi and bacteria, which are continually present in the soil and 
on dead refuse. 

While going into dormancy the bulbs must be allowed to " sweat " 
or cure preparatory to storage or shipment. For this purpose they 
are ordinarily placed in crates and stacked in the field or in open 
sheds, where the sunshine and air currents aid greatly in removing 
the moisture which is given off. Thus, if the weather remains 
warm and dry during harvesting and curing, it is the common ex- 
perience of growers that the crop will go through storage with small 
losses due to decay. Prevailing rainy weather at this time, however, 
will almost invariably lead to heavy losses. The moisture is favor- 
able for the development of the fungi and bacteria, and at the same 
time it delays harvest and prevents the proper maturing of the crop. 
Under such conditions certain storage diseases, such as neck-rot (see 
p. 18) and soft-rot (see p. 20), make considerable progress before the 
bulbs are pulled. On the other hand, high humidity of the atmos- 
phere during the curing period causes the moisture given off by the 
onions to accumulate in the crates, which favors the development of 


Farmers' Bulletin 1060. 

The control of storage diseases, therefore, will consist largely of 
attention to cultural methods based on the knowledge of these gen- 
eral facts. In view of this, the following specific recommendations 
are made with regard to the handling of the onion crop. 


The organisms causing storage rots in general thrive on dead 
vegetable matter. Onion tops and diseased bulbs left on the field and 
onion refuse from the warehouse furnish excellent opportunities for 
these fungi and bacteria to multiply. The spores of certain of these 
organisms, especially those causing neck-rot (see p. 18), are readily 
carried long distances by the wind. A pile of rotting onions near 
the warehouse may thus be a means of infecting a crop a consid- 
erable distance away. All onion refuse left on the field should be 
raked and burned after harvest. Waste from the warehouse should 
he dumped in a remote place, or if spread on the fields it should be 
confined to those not to be used for the growing of onions. 


As soon as the neck of the onion bulb loses its stiffness sufficiently 
to allow the top to drop over readily the onion is ready to harvest. 
It is best to allow the tops to dry out as much as circumstances will 
permit before harvesting, since this will help to reduce the trouble 
from storage rots. If the field matures unevenly it is well to start 
pulling when most of the plants have reached this stage. An un- 
usual amount of rainy weather just previous to harvest may postpone 
the ripening and tend to cause an overproduction of "scallions" or 
" stiff necks." These should not be placed in storage, but sorted 
out and sold as soon as possible. In such event the cutting of the 
roots with a wheel hoc will tend to hasten maturity. In clipping or 
twisting the tops a neck 1 or 2 inches long should be left, to avoid 
the exposure of the succulent tissue of the fleshy scales of the bulb. 
Care should be taken to avoid bruising the bulbs and thus opening 
the way for the organisms which cause decay. The milling of bot- 
tom sets before storage causes a certain amount of bruising and 
lowers the keeping quality. 


It is essential that care be taken at harvest time to throw out all 
bulbs which show any signs of disease or insect injury. Although 
smut (sec p. 4) and mildew (sec p. 9) do not of themselves cause 
decay, bulbs which have been attacked by these fungi arc thereby 

' V'or more detailed Information relative to Horticultural methods of harvesting, eivrlng, 
nnd storing onions, see Farmers' Bulletin 35-t, "Onion Culture." 

Onion Diseases and Their Control. 


made more susceptible to the invasion of storage-rot organisms. 
Fusarimn rot (see p. 13), on the other hand, gains a start in the field 
and continues to injure the bulbs in storage. In unusually damp 
weather soft-rot and neck-rot may start in the field, and it is well 
to be on the watch for bulbs with softened necks at harvest time. 


Onions are sometimes allowed to cure in windrows in the field, 
and if the weather is clear, yellow and red varieties can be handled 
successfully in this manner. It is preferable, however, to place 
them in slatted crates soon after topping and pile in open sheds or 
in stacks in the field. In the latter case the piles should be covered 
with temporary roofs for protection from rain. Exposure of white 
varieties (see p. 18) to damp weather in the field will almost in- 
variably prove fatal, and they should be placed in a curing shed, 
where advantage can be taken of clear weather and protection can be 
given during rainy periods. 


In the Northern States onion warehouses should be built with the 
purpose in mind of keeping the temperature just above 32° F. during 
severe winter weather with as little artificial heating as possible. 
This necessitates walls consisting of a number of thicknesses of lum- 
ber and one to several air spaces. Provision is necessary for ample 
ventilation, since the bulbs are continually giving off moisture which 
must bo removed. This can bo increased materially on clear days 
by opening doors and windows for a few hours. In very cold 
weather it is necessary to heat the house during this process, in order 
to prevent the freezing of the bulbs. A steam or hot-water heating 
system or stoves placed at intervals are satisfactory. Large bulbs 
are stored in slatted bushel boxes or folding crates, while bottom 
sets should be placed 2 to 4 inches deep in shallow crates. 

Where a modern warehouse is not available, a dry cellar which can 
bo held at 32° to 35° F. can be used with good results. 


In the Northern States and on the Pacific coast, where Globe 
onions are grown most extensively, yellow and red varieties are much 
less susceptible to decay in storage and transit. White varieties, on 
the other hand, are very subject to storage diseases, especially neck- 
rot and smudge, and they require much more care during harvest and 
curing in order to be handled successfully. Tn the onion bottom set- 
growing sections the same is true of the White Portugal, as compared 


Farmers' Bulletin 1060. 

with the Red Wethersfiold, Yellow Strassburg, and Yellow Danvcrs. 
Certain white varieties, such as Queen, Pearl, and Barletta, are such 
poor keepers that they arc seldom held in storage for any length of 

In the onion regions of Texas, southern California, and Louisiana, 
the Bermuda varieties are largely disposed of soon after harvest, 
on account of their poor keeping quality and the lack of cold-storage 
facilities. In Louisiana the Creole variety is the favorite because 
it resists much more effectively than the Bermuda varieties the attacks 
of fungi and bacteria in storage and in transit. 




Neck-rot is a destructive and widespread disease of onions in stor- 
age and in transit. During certain seasons many growers have lost 
.50 per cent or more of their crop on account of this trouble. "White 
varieties are especially susceptible, but considerable loss is often sus- 
tained with red and yellow varieties. 


Usually there is little or no evidence of this disease up to or at 
the time of harvest, but after the onions are topped and have lain 
in crates for a few days the early signs appear. A softening of the 
scale starts usually at the neck, more rarely at the base or at a 

There is a definite margin between the healthy tissue and the dis- 
eased portion, which takes on a sunken, water-soaked appearance. A 
gray feltliko growth later forms on the rotting scales, which may 
bo accompanied by a gray to brownish mold, consisting of the spores 
(seeds) of the causal fungus, and by brown to black kernellike bodies 
(sclerotia) one-eighth to one-fourth inch in diameter (figs. 8 and 9). 
On red and yellow onions the pigment of the diseased portions is de- 
stroyed, while in the former the rotted tissue sometimes assumes a 
pinkish tint. The disease progresses rather slowly unless conditions 
are very moist, several months often elapsing before the entire bulb is 
destroyed. The white varieties decay most readily, while the colored 
types more often escape it and when infected show a marked resist- 
ance to its progress. 


Neck-rot is a disease caused by one or more species of fungi 
(Botrytis spp.) closely related to the common gray molds which 
attack lettuce, cabbage, and numerous other vegetables. These fungi 

Onion Diseases and Their Control. 


are not vigorous parasites and seldom seriously attack actively grow- 
ing onion plants. They do not ordinarily penetrate the dry outer 
scale of the onion, but require a wound in order to gain entrance to the 
plant tissues. Tho gray to brown moldy growth on the rotted scales 
consists chiefly of the spores of the fungi, which are especially 
adapted to dissemination by air eurrents. They are thus carried to 
tho healthy bulbs, whore they germinate and send fungous threads 
into the necks which have been wounded 
by the cutting or twisting of the tops. 
These threads then kill the tissue 
slightly in advance of their progress 
through the scale. The black, kernel- 

Fig. 8. — Onion neck-rot. The softening 
and shriveling of the scales begin at 
the neck of the bulb, with the later 
development of black, kernellike masses 
on the surface. 

Fio. *). — Onion neck-rot. Lon- 
gitudinal section of a dis- 
eased bulb, showing the outer 
scales badly rotted while the 
disease is just appearing on 
the inner scales. 

like bodies, or sclerotia, are compact masses of fungous threads, 
which, being resistant to cold and drought, serve to carry the 
organisms over winter. 


Proper care of the crop during harvest and curing is the chief 
measure of control for neck-rot (sec p. 17). Avoid exposure to damp 
weather and provide cool, dry storage. White varieties should re- 
ceive special attention, since they are very susceptible to tho disease. 
Proper sanitation (see p. 1G) is also very important and worthy of 
careful consideration in connection with this disease. 


Farmers' Ballelin 1060. 


A rapid drying out of the nock of the bulb by moans of artificial 
heat immediately after harvest is effective in the control of neck- 
rot. This is accomplished by passing a current of air heated to 100° 
to 120° F. over the onions in shallow crates until Ihe necks are thor- 
oughly dried. The threads of the causal fungus entering after the 
top of the bulb has been removed apparently require some moisture 

for their development, while 
thoroughly dried tissue offers 
a barrier to their progress. 
Experiments on a small scale 
have shown this to be a satis- 
factory method for the control 
of this disease. To apply this 
control on a commercial sealo 
it is necessary to have a special 
kiln or a special room in the 
warehouse for this purpose. 
The temperature can be raised 
to 120° F. with safety. Pro- 
vision should be made for a 
fairly rapid air circulation to 
carry off the moisture. 

Experiments are under way 
with the object of devising the 
best methods for the applica- 
tion of this principle on a com- 
mercial basis. 


Soft-rot being of bacterial 
origin differs from other stor- 
age rots in the absence of 
fungous threads and spores, 
although it is sometimes fol- 
lowed by saprophytic fungi. 
The tissue first becomes glassy or watersoaked in appearance, and 
later disintegrates into a soft, watery mass. An offensive odor often 
accompanies the rot. The organism being unable to penetrate the 
unbroken scales, infection commonly takes place through the neek, 
often before the crop is harvested. When the rot affects only one or 
two inner scales, as is often the ease (fig. 10), the only external sign 
of the disease is the lack of firmness detected on pressing the bulb 
'between the fingers. Sunburn, freezing, and external bruises due to 

Via. 10. — A section of nn onion bulb showing 
bacterial soft-rot. This Is a watery soft-rot, 
accompanied by an offensive odor, which starts 
usually at the neck and invades one or more 
scales, often leaving the outer scales Intact. 

Onion Diseases and Their Control. 


careless handling are followed very often by soft-rot, especially if the 
surfaces of the -wounds remain moist. 


Soft-rot is due to a group of bacteria 1 which cause soft rots on 
cabbage, carrot, celery, and a large number of other vegetables. As 
a class they do not attack uninjured plants, and they require a wound 
and sufficient moisture to gain a foothold. 


Crop rotation and sanitation should be thoroughly practiced to 
suppress tho causal organisms. Precautionary measures already 
recommended (sec pp. 16 and 
17) with regard to harvesting, 
curing, and storing should be 
followed carefully. Sort out 
all affected bulbs before stor- 
age or shipment. 


Because of its resemblance 
in appearance, black-mold is 
often confused with onion 
smut by growers and dealers. 
The chief distinguishing char- 
acteristic between the two is 
the fact that the blaek pow- 
dery masses of spores in the 
case of black-mold arc borne 
on the exterior of the scales 
and can be rubbed off readily 
(fig. 11). It is true that the 
disease is not confined to the 
exterior of the bulb, but as the inner scales are separated, the black 
powder will be found to exist on the exterior of the individual scales. 
Onion smut, on the other hand, as seen in storage or market, is char- 
acterized by oblong or linear brown or black lesions, most commonly 
near the base of the bulb and as deep as the third or fourth scale. 
Black-mold causes a slow shriveling of the affected scale, which 
assumes a brittle texture. Moist conditions favor the disease, while 
a cool, dry environment seems to check it. 

Black-mold occurs to some extent in northern onion sections, but 
it is of slight economic importance there. In Louisiana, Texas, and 

Fia. 1 1. — Onion Mack-mold. Compare its symp- 
toms with those of onion smut. Note the Ir- 
regular sooty masses on tho outside of or 
between the scales, accompanied by the shriv- 
eling of the scales about tho neck of the bulb, 
which gives them a brittle, papery texture. 

1 ttacilhis carotmwruH Is an example of this group. 


Farmers' Bulletin 10G0. 

California, however, it is the most important storage and transit 


Black-mold is caused by a fungus (Asperillus niger) which is a 
common organism living on almost airy dead or dying vegetable 
matter. Where it is most serious on onions, it undoubtedly grows 
and multiplies throughout the year in the soil or on dead refuse. 
It is present to a slight extent on the dead outer scales of the bulbs 
before harvest, but is not notieeable until the onions are pulled. 
Rainy weather at this critical period will result in a widespread 

infeetion, which continues to develop 
in storage or transit. 


General sanitary measures and 
protection from moisture after har- 
vest are essential. The bulbs should 
be thoroughly dry before they are 
shipped, since moisture favors the 
rapid development of the disease in 
transit. Dealers in northern mar- 
kets receiving infected lots to be held 
any considerable length of time be- 
fore consumption should transfer 
them to cold storage in order to hold 
the disease in cheek. 


Onion smudge is confined largely 
to white varieties and appears in the 
Fio. 12.— Onion smudge. Note the fi e hi j us t hefore harvest time, often 

smudgy spots made up of small black , J . . ' 

dots. The disease is confined largely continuing to develop during the 
to the outer scales of white varieties, storage period. It is characterized 
by small dark-green to black dots which appear on the outer scales. 
These small dots may be grouped together in various ways and are 
often arranged in coneentric rings, giving a smudgy, unsightly ap- 
pearance to the white bulbs (fig. 12). The fungus ordinarily attacks 
the fleshy scales only mildly and in such cases does not cause any ap- 
preciable shrinkage in storage, its chief damage being the reduction 
of the market quality of the crop. However, after rainy weather dur- 
ing harvest, when the bulbs are crated and stored without being dried 
and cured thoroughly, the disease causes considerable loss. 

Onion Diseases and Their Control. 



Smudge is caused by a fungus (Colletotrichum {Vermicularia) 
circinans), which lives over winter on onion scales in the soil or on 
bulbs in the warehouse, and consequently it increases in amount where 
onions are grown on the same fields year after year. It is widely 
distributed through the trade on white-onion sets, and by this means 
is introduced into soil new to onions. Under favorable conditions 
the fungus attacks the outer scales and forms many small black dots 
on which myriads of minute spores are produced (fig. 12). These 
spores may be carried away in drops of water to other onion scales, 
where they germinate within a few hours and renew their attack. 
The fungus passes through this whole life cycle within a few days 
when the weather is warm and moist. A little disease in the field 
before harvest will furnish spores enough to spot the bulbs very 
badly if a few days of moist weather come during harvest or while 
the crates arc stacked in the field. 


Since the development of the disease is dependent largely on 
abundant moisture, special care is needed in handling the white 
varieties. Harvest the crop without delay, avoiding any exposure to 
rain, if possible. Stack in an open shed and allow the onions to cure 
thoroughly. Place white sets in thin layers in shallow orates. 


Control onion smut by applying formaldehyde solution (1 pint to 
16 gallons at the rate of 200 gallons per acre) by means of a drip 
attachment on the seeder. 

Control blight by avoiding excessive soil moisture, by crop rota- 
tion, and by thorough cultivation. If spraying is to bo practiced it 
should bo done early and thoroughly. 

In general, storage diseases are to be controlled by the practice 
of sanitary measures, the sorting out of diseased bulbs at harvest, 
protection from rain after harvest, thorough curing, and storage in 
a dry, well-ventilated warehouse at 32° to 35° F. 



Culture nnd Uses of Okrn, (Farmers' Bulletin 232,) 
Rcnns, (Farmers' Bulletin 280.) 

Discuses of Cabbage anU Related Crops nnd their Control. (Farmers' Bulle- 
tin 488.) 

Votiito-Tuber Diseases. (Farmers' Bulletin 544.) 

Blackberry Culture. (Farnfers' Bulletin 043.) 

The Control of Hoot-Knot. (Farmers' Bulletin 048.) 

The Sniiash-Viiie Borer. (Farmers' Bulletin 008.) 

Sweot-l'otato Diseases. (Farmers' Bulletin 714.) 

The Common Cabbage Worm, (Farmers' Bulletin 7GG.) 

Watermelon Diseases. (Fanners' Bulletin 821.) 

The Asparagus Beetles ami Their Control. (Farmers' Bulletin 837.) 

Control of Diseases and Insect Enemies of the Dome Vegetable Garden. 

(Farmers' Bulletin 850.) 
How to Increase the Potato Crop by Spraying. (Farmers' Bulletin 808.) . 
Control of the Melon Aphis. (Fanners' Bulletin 014.) 
Cabbage Diseases, ( Farmers' Bulletin 025.) 
Control of tbe Onion Tlulps. (Farmers' Bulletin 1007.) 
The Sweet-Potato Weevil and Its Control, (Farmers' Bulletin 1020.) 
Fxperlments In the Control of Potato Leak. (Department Bulletin 577.) 
Celery, Storage Experiments, (Department Bulletin 570.) 
Miscellaneous Truck-Crop Insects in Louisiana, (Department Bulletin 703.) 
Anthracnose of Cucurbits, (Department Bulletin 727.) 
Potato Wart — A Dangerous New Disease. (Department Circular 32.) 
Diseases and Insects of the Home Garden, (Department Circular 35.) 
Insect Enemies and Diseases of the Tomato, (Department Circular 40.) 
A Spot Disease of Canllllowcr. (Bureau Plant Industry Bulletin 225,) 
Wart Disease of tbe Potato, (Bureau Plant Industry Circular 52.) 


Insects Injurious to Cranberry Culture. (Farmers' Bulletin 178,) Price, 
5 cents. 

Fungous Diseases of the Cranberry, (Farmers' Bulletin 221. ) Price, 5 cents. 
Spraying for Cucumber and Melon Diseases. (Farmers' Bulletin 231.) Price, 
5 cents. 

The Eggplant Tortoise Beetle, (Department Bulletin 422.) Price, 5 cents 
False Blossom of the Cultivated Cranberry, (Department Bulletin 444,) 
Price, 5 cents. 

Ithlzopus fiot of Strawberries in Transit, (Department Bulletin 531, > Price, 
5 cents. 

Further Studies of the Hots of Strawberry fruits. (Department Bulletin 080.) 
Price, 5 cents. 

Spoilage of Cranberries after Harvest, (Department Bulletin 714,) Price, 
5 cents. 

Cranberry Diseases. (Bureau Plant industry Bulletin 110.) Price, 20 cents. 
Some Fungous Diseases of Economic Importance, (Bureau Plant Industry 

Bulletin 171.) Price, 25 cents, 
A 1'lnnt-Dlsease Survey in tbe Vicinity of Sail Antonio, Texas, (Bnrenu 

Plant Industry Bulletin 220.) Price, 20 cents. 
Investigations of the Potato Fungus 1'hytophthoru Infestans, (Bureau Plant 

Industry Bulletin 245.) Price, 20 cents. 
Study of Fungous Parasites Belonging to the Genus Glomerelln, (Bureau Plant 

Industry Bulletin 252.) I'rlee, 20 cents. 
Some Insects Injurious to Truck Crops. (Entomology Bulletin 82.) Price, 

20 cents. 

Tbe Striped Cucumber Beetle. (Entomology Circular HI.) Price, 5 cents. 
A Little-Known Asparagus Pest and a Power Sprayer for Asparagus. (O. E, 
S. Document 4*}l.) Price, 0 cents.