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SUMMARY

Bay State, a new tomato for greenhouse forcing, is described and illustrated.
It was developed for resistance to Cladosporium leaf mold from crosses of Lyco-
persicon pimpinellifolium (Jusl.) Mill, and L. esculentum Mill., respectively highly
resistant and highly susceptible.

The new tomato was released for commercial trial in 1939, and approximately
one-fourth of the greenhouse tomato area in Massachusetts was planted to this
variety in the fall cropping season cf 194L

In the fall cropping season of 1940, however, the Bay State tomato growing in
a greenhoLse in Swansea , Bristol County, experienced a severe attack of leaf mrld,
caused by a new physiologic form of Cladosporium. In the fall of 1941 other
instances of the susceptibility of Bay State to the new physiologic form of the
fungus were observed. The Globelle and Vetomold varieties of tomato, likewise
developed for resistance to Cladosporium fulvnm Cke. and derived from L. pim-
pinellifolium, have shared the same experience in Massachusetts and elsewhere.

The new physiologic form of the fungus is infectious to L. pimpinellifolium ,
causing yellowish infection flecks and ultimately necrosis. On the lower leaf
surface of the necrotic areas and under moist atmospheric conditions, the fungus
grows and sporulates rather freely. This form of the fungus is considered to be
less virulent on the Bay State tomato than the normal devastating physiologic
form on Waltham Forcing; and with some degree of proper greenhouse manage-
ment should ja'eld more readily to control.

LITERATURE CITED

1. Ale.xander, L. J. Leaf mold resistance in the tomato. Ohio Agr. Expt. Sta.

Bui. 539. 1934.
2 A new tomato variety resistant to leaf mold. Phvtopath. 28:1.

1938.

3 A new strain of the tomato leaf mold fungus Cladosporium

fulvum. Ph3'topath. 30:1. 1940.

4. Bailey, D. L., and Langford, A. N. One hundred percent leaf mold infec-
tion reported on Vetomold. Canad. Plant Dis. Survey, Ann. Rpt. 20 (1940):
57. 1941.

5. Bond, T. E. T. Infection experiments with Cladosporium fulvum Cke. and
related species. Ann. Appl. Biol. 25:277-507. 1938.

6. Cuba, E. F. Control of greenhouse vegetable diseases. Mass. Agr. E.xpt.
Sta. Bui. 305 (Ann. Rpt. 1933. ):18. 1934.

7 A new red forcing tomato resistant to Cladosporium leaf mold-

[Phytopath. 29:9. 1939.

[S Control of tomato leaf mold in greenhouses. Mass. Agr. Expt-

Sta. Bui. 361. 1939.
9. Langford, A. N. The parasitism of Cladosporium fulvum Cke. and the
genetics of resistance to it. Canad. Jour. Res. (Sect. C) 15:108-128. 1937.
10. Sengbusch, R. V., and Loschakowa-Hasenbusch, N. Immunitatsziich-
tung bei Tomaten. Ziichter 4:257-264. 1932.



MASSACHUSETTS
AGRICULTURAL EXPERIMENT STATION

Bulletin No. 394 June 1942



The Control of Damping-off

of Vegetables by

Formaldehyde and Other Chemicals

By W. L. Doran, E. F. Cuba,
and C. J. Gilgut



Damping-off is one of the most serious problems of the vegetable grower, and
the results here reported should provide safer and more effective control of the
disease in hotbeds and greenhouses.



MASSACHUSETTS STATE COLLEGE
AMHERST, MASS.



THE CONTROL OF DAMPING-OFF OF VEGETABLES
BY FORMALDEHYDE AND OTHER CHEMICALS

By W. L. Doran and E. F. Guba, Research Professors, and C. J. Gilgut,
Research Assistant, in Botany



CONTENTS



Page Page

Treatments of seeds 3 Pyroligeneous acid 8

Treatments of soil 4 Oxyquinoline sulfate 8

Chlorpicrin emulsions 4 Calcium cyanamide 8

Acetic acid and vinegar 4 Ammonium hydroxide and ammonium

Copper, mercury, and zinc compounds. 6 sulfate 9

Sodium hypochlorite 7 Formaldehyde 11

Salicylic acid 7 Summary 19

Formic acid 8 Literature cited 20



The original object of this work was to determine the relative merits of certain
chemicals for the control of damping-off of vegetables in hotbeds and cold frames.
There has been a gradual change in practice, however, and most vegetable grow-
ers in Massachusetts now start plants in plant houses or greenhouses. The con-
trol of damping-off as here considered is, therefore, not limited to hotbeds and
cold frames, but conclusions are unaffected. Whether in greenhouses or under
glass elsewhere, at least 90 percent of the damping-off of vegetables in this State
is caused by Pythium spp., with Rhizoctonia important on cabbage and other
crucifers and Aphanomyces euteiches Drechsler often the pathogen in the case of
celery.

It is, of course, a common practice to treat seeds of vegetables with red cuprous
oxide, Semesan, or zinc oxide. These seed treatments give good results with
some vegetables; but with other vegetables, seed treatment is inferior to certain
soil treatments for the control of post-emergence damping-off.

Damping-off, as is well known, may also be severe in steamed soil, especially
if the soil is exposed to reinfestation by fungi before seeding.

There is need of a safe and effective chemical treatment which can be applied
to soil shortly before germination, that is, immediately after seeds are sowed and
covered with soil; and special but not exclusive attention is here given to that
phase of the problem. Some chemicals have been thus used in a limited way by a
few earlier investigators, and that work is referred to below, but such results
have not as yet had much effect on the practice of growers.

Some of the chemicals here used can be and are recommended to growers.
Others are mentioned because they are apparently good substitutes for a possibly
more effective material if or when the latter is temporarily unavailable. Still
others are discussed briefly because they show sufficient merit to warrant further
investigation.

Grouped by families, the vegetables with which most of this work was done
are as follows: Chenopodiaceae or goosefoot family — beet, spinach, and Swiss
chard; Compositae or composite family — chicory, dandelion, endive (escarole),
and lettuce; Cruciferae or mustard family — broccoli, Brussels sprouts, cabbage,
cauliflower, collards, cress, water cress, kale, and kohlrabi; Cucurbitaceae or
gourd family — cucumber, muskmelon, and summer squash; Liliaceae or lily
family — onion; Solanaceae or nightshade family — eggplant, pepper, and tomato;
Umbelliferae or parsley family — celery and celeriac; Leguminosae or pulse fam-
ily — pea.

Results are usually expressed in terms of stand or number of plants which
lived, escaping damping-off. Most of the experiments were repeated and each



CONTROL OF DAMPING-OFF 3

figure in most of the tables (e. g., Table 10) represents the average of the results
in several experiments. Such a tabulation can hardly bring out all the facts
which would be evident if each experiment were reported upon separately; but
they were thus brought together to save space, and conclusions are in each case
stated in the text.

TREATMENTS OF SEEDS

Spergon^ was used only for the treatment of the seeds of Lima bean and gave
very good results. The number of plants which lived was increased 76 percent
by it, only 21 percent by red cuprous oxide or zinc oxide, and some injury was
caused by Semesan.

Treatments of seeds of vegetables with red cuprous oxide, Semesan, and zinc
oxide were, in many experiments, compared with one another and with certain
treatments of the soil. The results, averages for each of the treatments investi-
gated, are recorded in Table 10.



'A product of the United States Rubber Company.

Table 1. — Recommended Seed Treatments for Vegetables

Beet Semesan or red cuprous oxide

Broccoli Semesan or zinc oxide

Brussels sprouts Zinc oxide or Semesan

Cabbage Semesan or zinc oxide

Carrot Red cuprous oxide or zinc oxide

Cauliflower Semesan or zinc oxide

Celery and celeriac Zinc oxide

Chicory Semesan or zinc oxide

Collards Semesan oi zinc oxide

Corn Semesan

Cress, water Red cuprous oxide

Cucumber Semesan or red cuprous oxide

Dandelion Red cuprous oxide or Semesan

Eggplant Semesan or zinc oxide

Endive Semesan or zinc oxide

Kale Semesan or zinc oxide

Kohlrabi Semesan or zinc oxide

Lettuce Red cuprous oxide or Semesan

Muskmelon Red cuprous oxide or Semesan

Onion Semesan

Parsnip Zinc oxide

Pea Semesan

Pepper Semesan or red cuprous oxide

Radish Semesan or zinc oxide

Spinach Red cuprous oxide or Semesan

Squash, summer Semesan or red cuprous oxide

Swiss chard Semesan or red cuprous oxide

Tomato Zinc oxide or red cuprous oxide

Turnip Semesan or zinc oxide



4 MASS. EXPERIMENT STATION BULLETIN 394

Table 1, based on that work and on other observations, especially as regards
safety or freedom from chemical injury, consists of a list of vegetables together
with the materials which, when used for the treatment of their seeds, resulted in
the least damping-ofif and the best stands of each. Some show a decided prefer-
ence for one chemical, e.g., celery and parsnip for zinc oxide. In the case of other
vegetables, differences between results with two chemicals were not great enough
to prove that there are preferences.

Treatments of seeds of beet, spinach, Swiss chard, tcmato, endive, lettuce,
cucumber, summer squash, and muskmelon usually gave results inferior to those
secured by formaldehyde treatment of the soil; either method satisfactorily pro-
tected pepper, celery, and chicory; and seed treatments often gave better results
than formaldehyde treatment of the soil with eggplant, onion, dandelion, and
especially crucifers.

Treatment of the seeds of such vegetables is important, especially where there
is a scarcity of seeds, where seeds are sown in the field, or where soil disinfestation
is not feasible. As far as possible, growers will do well to keep in stock all of the
chemicals^named in Table 1 and to follow the recommendations which are therein
made.

TREATMENTS OF SOILS
Chlorpicrin Emulsions

Chlorpicrin is sometimes injected into soil for the prevention of damping-off
but, because of the danger of injury to plants, such applications must be made
long before seeding. As used here, Larvacide chlorpicrin emulsion^ and Seido-
rin chlorpicrin emulsion^ were applied to soil (0.64 to 1.0 cc. in 0.8 quart water
per square foot) Immediately after seeding. Seidorin, 1 cc. per square foot, gave
good results with beet, cabbage, lettuce, pea, pepper, and spinach (see Table 2).
Damping-off of these vegetables, and of broccoli and cucumber, was also well
controlled by Larvacide chlorpicrin emulsion similarly used. Thus applied,
immediate!}' after seeding, best results were generally obtained, however, by the
use of Larvacide chlorpicrin emulsion 0.64 cc. or Seidorin chlorpicrin emulsion
0.76 cc. per square foot, greater concentrations or heavier applications being
often injurious.

When applied at the rate of 1 gallon to 30 feet of row after sowing seeds of pea
but before covering them, Larvacide chlorpicrin emulsion 1:1000 markedly im-
proved the stands (see Table 9), g'ving as good results, in fact, as did formalde-
hyde.

Used in these ways, chlorpicrin emulsions are certainly effective against damp-
ing-off. But, on grounds of convenience and practicability, they are not pre-
ferred by the writers for the control of this disease. It is difficult to secure uniform
dilutions and, hence, to make uniform applications; and the fumes of chlorpicrin
are, moreover, decidedly unpleasant.

Acetic Acid and Vinegar

Acetic acid, worked into soil before seeding, has been successfully used for the
control of damping-off (4)^.

Applied to the surface of soil after seeding, glacial acetic acid, 1.5 to 2.5 cc. in
0.8 quart water per square foot, gave good results with lettuce, pepper, spinach,
beet, chicory, dandelion, endive, cabbage, and cauliflower (see Tables 2 and 10).



-From Innis Speiden and Co. It contains 70 percent chlorpicrin.
^Frorn Japan Seed Co. It contains 45 percent chlorpicrin.
'Numbers in parentheses refer to literature cited, page 20.



CONTROL OF DAM PING-OFF 5

Table 2. — Relative Number of Plants Which Lived in Soil Treated
Immediately After Seeding



Soil Treatment'



No treatment (check) 100 100 100 100 100 100 100 100 100 ICO 100

Formaldehyde 2 cc 133 109 83 135 108 338 295 123 101 341 102

Acetic acid 2 cc Ill ... 109 106 102 136 116 124 97 214 101

Seidorin 1 cc 118 163 108 62 95 269 295 135 88 275 101

Chlorox30cc 91 103 100 90 89 227 101 50 85 145 106

Copper zeolite2 5.67 gm. .. 113 76 79 109 92 175 106 108

Vasco3 5.67 gm 110 95 100 97 103 147 106 121 101 89 82

Cuprocide 544 5.67 gm 106 86 84 91 94 220 164 123 88 93 98

Semesan 5.67 gm 55 97 44 96

Bordeaux 1.5:1.5:50 94 98 135 117 118 100 72 92

'In 0.8 quart of water per square foot.

^Containing 25 percent copper.

'A zinc compound for seed treatment, made by Virginia Smelting Co.

^A red cuprous oxide, product of Rohm and Haas.

Thus used, it often gave results which were somewhat inferior to those obtained
by formaldehyde; but, lacking the latter, acetic acid or vinegar is a good sub-
stitute.

Vinegar as commonly sold contains 4 to 5 percent acetic acid. Damping-off
was usually well controlled, and without injury to most plants with which it was
used, when vinegar (a little less than one-half pint per square foot) was worked
into soil before seeding (4).

Vinegar, 215 cc. (0.45 pint) in 1 quart water per square foot, completely pre-
vented damping-off when applied to soil immediately after seeding. Thus used,
it increased by the following percentages the number of plants which lived: beet,
427; cucumber, 112; cabbage, 56; lettuce, 24; and pepper, 106. Applied without
additional water, this quantity of vinegar interfered with the growth of cabbage
but did not affect beet and cucumber.

When applied from below, by setting pots or flats of soil in the solutions until
soil was saturated, vinegar 1.5 quarts in 1 gallon water or acetic acid 1:55 gave
good results, although net so gcod as did formaldehyde.

The soils with which vinegar was used in the experiments referred to above
had pH values of about 5.8. In one case, vinegar (215 cc. in 1 quart water per

Table 3. — Effect of Soil Reaction on Vinegar as a Soil Disinfestant



Soil Treatments



Soil pH
Values



Relative Number of
Plants Whicii Lived



Beet



Cucumber



Percentages
Whicfi Damped-off



Beet Cucumber



None (check) 5.8

Vinegar 5.8

None (check) 7.1

Vinegar 7.1



100
435

100

137



100
725

100

148




16



84



45



6 MASS. EXPERIMENT STATION BULLETIN 394

square toot) was applied, immediately before seeding, to a soil having a pH value
of 5.8 and to the same soil after its pH value had, by the earlier use of hydrated
lime, been changed to 7.L There was no injury to growth of beet or cucumber
and vinegar was effective in both soils; but, as may be seen by reference to Table
3, it was considerably more effective in improving stands in the acid soil than it
was in the soil with a high pH value.

Copper, Mercury, and Zinc Compounds

Red cuprous oxide 1 pound or yellow cuprous oxide 12 ounces in 50 gallons
water is sometimes used (13, 14) as a seedbed spray, applied first when seedlings
emerge and later at weekly intervals although, for better results, such treptment
should be supplemented by treatment of seeds. Earlier investigators (15), re-
porting good results after spraying with red cuprous oxide, obtained better con-
trol with Bordeaux mixture 2:1:50, 1 quart per square foot, two applications at
intervals of 3 days, beginning upon the first appearance of damping-off.

But Bordeaux mixture is sometimes injurious (13), seedlings of crucifers are
susceptible to injury by red cuprous oxide used in this way, and, in the work of
the writers, neither Bordeaux mixture nor a spray of red cuprous oxide controlled
damping-off as well as did seed treatments. Nor did these copper sprays, includ
ing copper zeolite, control damping-off as well as did treatment of soil with for-
maldehyde (see Table 2).

Cuprocide, 0.2 ounce in 0.8 quart water per square foot, gave good results only
with lettuce, pepper, and pea, not with the other eight vegetables with which it
was used; and stands of all of them except cauliflower were more improved or
less injured by formaldehyde.

Bordeaux mixture was also of some benefit to lettuce, pea, and pepper, but
stands were more improved by formaldehyde and even by red cuprous oxide.

When red cuprous oxide was dusted on to seedbeds, first (at the rate of 0.9
gm. per square foot) as seedlings emerged and again (at the rate ol 2.9 gm. per
square foct) a week later, cabbage was injured but stands of lettuce seedlings
were improved. In another experiment, however, stands of lettuce and celery
were more improved b> seed treatment with red cuprous oxide than they were
by that treatment supplemented by soil treatment with red cuprous oxide.

Semesan, 1 ounce in 3 gallons water (1 to 1.5 quarts for 10 square feet), has
been advocated as a supplement to seed treatment with Semesan. A much
heavier application, as used on seedbeds, was somewhat injurious and certainly
of no benefit to tomato, eggplant, radish, and spinach (see Table 2).

Dusted on to a lettuce seedbed immediately after the seeds were covered and
again a week later, Semesan, Calochlor, Corona P. D. 7, and corrosive sublimate
were injurious. Thus used, calomel (0.47 and 1.8 gm. per square foot for the
first and second applications, respectively) caused no injury and improved the
stands, but red cuprous oxide (0.85 and 2.95 gm. per square foot) gave better
results. These materials were all somewhat injurious to cabbage.

Blackleg and black rot of some crucifers have been controlled, although not
without some chemical injury, by a solution of corrosive sublimate, 1:1000, ap-
plied three times to the seedbed (2); and dilutions of 1:1280 or 1:1600, applied
directly to plants in the seedbed, have controlled Rhizoctonia wire stem (8, 9).
These results have been the basis for recommending the application of corrosive
sublimate solutions to cabbage and cauliflower seedbeds at weekly intervals be-
ginning when seedlings emerge, using 1 ounce to 10 gallons for cabbage and 1
ounce to 15 gallons for cauliflower. But this method is not widely used for the
control of damping-off. Preference is more generally given and, it seems, with



CONTROL OF DAMPING-OFF 7

good reason, to seed treatment with Semesan or zinc oxide and to soil disinfesta-
tion by other chemicals or by steam.

The use of corrosive sublimate on soil immediately after seeds of crucifers are
sown is, in any case, no guarantee of good stands. A solution, 1 :1000, sometimes
gave good results with Brussels sprouts, but the number of seedlings of coUards
and kohlrabi which lived was increased more by seed treatment with Semesan
than by soil treatment with corrosive sublimate.

Zinc oxide 0.5 ounce per square foot, applied as a dust to the surface of seed-
beds immediately after seeds are covered, has been recommended more as a
supplement to seed treatment than as a substitute for it (13). But zinc oxide so
used b}' other investigators was not very effective (15), and as used here with
lettuce was of no benefit.

In another case, zinc oxide and Vasco, a zinc compound, were twice dusted
upon seedbeds, once immediately after the seeds were covered and again a week
later. This did not improve stands of lettuce at ?11, but it did improve stands of
cabbage more than did copper-lime dust.

Zinc oxide, 0.2 ounce in 0.8 quart water per square foot of soil, improved the
stands cf lettuce and pepper less than did other treatments similarly applied
immediately after seeding; and Vasco thus used with the vegetables named in
Table 2 was not of significant benefit to any except lettuce and pepper. Zinc
oxide applied in water tends to cause the surface of the soil to cake and become
hard, and on the basis of results obtained by the writers, it is not recommended
for use in this manner.

Useful as red cuprous oxide, Semesan, and zinc oxide are for the treatment of
seeds ot seme vegetables, it does net appear that there is much to be said for
them as soil disinfestants for the control of damping-cff. Then too, when applied
in water they settle out of suspension unless continually agitated. This makes
uniformity of application difficult and probably accounts for some of the injury
on the one hand and some of the failures to control en the other.

Sodium Hypochlorite

Chlorox and Oxol, each containing 5.25 percent sodium hypochlorite, did not
in most cases give as good results as other treatments of soil or seed. That is in
line with the results of Horsfall (13) in whose work Chlorox caused some injury
and failed to control damping-off satisfactorily.

Stands of pepper seedlings were much less improved by Oxol (38cc. in 0.8 quart
water per square foot) than by formaldehyde. As may be seen by reference to
Table 2, Chlorox did not significantly improve the stands of nine out of the eleven
kinds of vegetables named. It did improve stands of lettuce and spinach but not
so much as did formaldehyde or Seidorin cr, in the case cf spinach, acetic acid.

In controlling damping-off, solutions of Chlorox thus applied to soil were no
be*^ter than standard dry treatments of seeds of pepper and endive, and decidedly
less effective than standard dry treatments of seeds of beet, chicory, cabbage,
cauliflower, eggplant, and tomato.

Salicylic Acid

Salicylic acid can be used as a soil fungicide. When worked, without water,
into soil immediately before seeding, it usually increased the number of plants
which lived and there was no injury to beet or cucumber by applications up to
10 gm. per square foot (4). Damping-off was well controlled (See Table 4) by
5 or 6 gm. salicylic acid thus applied to soil immediately before seeding. There
was some injury to cress but not to beet or pepper.



8 MASS. EXPERIMENT STATION BULLETIN 394

Table 4. — Effect of Salicylic Acid on Control of Damping-off



Salicylic Acid'



Relative Number ol Percentages Which

Plants Which Lived Damped-off



Beet Cress Pepper Beet Cress



None (check) 100 100 100 16 13

5.0 gm per square foot 410 157 136 3

6 gm. pel square foot 416 157 165 C

7.5 gm. per square f of t 521 ... ...



*In 1 quart of water.



Formic Add



Formic acid is sufficiently effective as a soil fungicide to warrant turther in-
vestigation, but it is not safe enough to be recommended to growers until more is
learned about hew to use it. When a dust containing 9 cc. formic acid (in 38 gm.
powdered charcoal) per square toot was well worked into soil immediateh' before
seeding, lettuce and beet were uninjured and the number of seedlings which lived
was increased 98 percent in the case of beet and 117 percent in the case of lettuce.
Formic acid 9 cc. (in 1 quatt water) per square foot, applied immediately before
seeding, improved the stands of lettuce but caused some injury to cabbage and
cucumber.

Pyroligneous Acid

Except for a temporarily retarding effect on early growth of cauliflower, pyro-
lignecus acid, 155 cc. per square foot, gave gccd results with several vegetables.
Worked into soil immediately before seeding, the undiluted acid improved the
stand of beets 367 percent and of lettuce 135 percent. Applied to soil (in 1 quart
water per square foot) immediately' after seeding, it improved the stand of tomato
by 149 percent, of cauliflower by 100 percent, and of lettuce by 98 percent.

Oxyquinoline Sulfate

Oxyquinoline sulfate is known to have fungicidal properties (6, 7). Applied in
solutions (1.25 quarts water per square foot) immediately alter seeding, 2 gm. per
square foot was safe with all vegetables with which it was used, except cabbage.
Damping-off was well controlled by this application and the number of plants
which lived was increased as follows: beet, 120 percent; cabbage, 62 percent;
cucumber, 107 percent; lettuce, 34 oercent; and pea, 53 percent. Beet and cu-
cumber seedlings damped-off to the extent of 43 and 21 percent in untreated soil.
In treated soil, these figures fell to 3 and 2 percent, respectively. Oxyquinoline
sulfate is, it is evident, effective as a soil fungicide.

Calcium Cyanamide

Dam.ping-off is controllable by calcium cyanamide, 10 to 12 gm. per square
foot, but it is unsafe to sow seeds until at least 2 weeks after soil treatment (4).
This is, however, a good material to use if, for any reason, soil must be tieated
long before seeding and then exposed to recontamination: tor soil treated with it
's not so promptly reinfested with damping-off fungi as is soil treated with for-
maldehyde. When calcium cyanamide, 12 gm. per square foot, was worked into soil



CONTROL OF DAMPING-OFF 9

30 days before seeding, the number of plants which lived was increased as follows:



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