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 



