ANNUAL REPORT, 1940 31 



efifect of ammonia, the odor of which is sometimes strong when the salt 

 is applied to limed soil. 



With the object of determining the length of time that a soil-disinfesting 

 effect persists, or how soon soils variously disinfested become badly re- 

 infested, seeds were sowed at various intervals of time after treatment of 

 soil in open flats in a greenhouse. Applied immediately before seeding, 

 formaldehyde, calcium cyanamide, formic acid, salicylic acid, oxyquinoline 

 sulfate, acetic acid, and vinegar were about equally effective although they 

 were not equally safe; calcium cyanamide, especially, being harmful. 



Formaldehyde gave good protection against damping-oflf for one week, 

 fair protection for two weeks, very slight protection for three weeks, and 

 none whatever when seeds were sowed four weeks after soil treatment. 

 There was partial control by the other chemicals when seeds were sowed 

 as late as four weeks after soil treatment. When thej^ were sowed six 

 weeks after soil treatment, the only chemical which still showed any pro- 

 tective effect was calcium cyanamide. 



Chemical Soil Surface Treatments in Hotbeds for Controlling Damping- 

 off of Early Forcing Vegetables. (W. L. Doran, E. F. Guba, and C. J. 

 Gilgut.) In a continuation of the work of determining the least quantity 

 of formaldehyde which is or may be effective and the search for more 

 convenient ways to apply it, soil was watered, immediately after seeding, 

 not with water alone but with dilute solutions of formaldehyde. They 

 were so applied that each square foot of soil surface received 0.2 to 3.0 cc. 

 formaldehyde in 1 quart of water. 



There was poor or no control by 0.2 cc, but beet, cress, cucumber, and 

 lettuce, the seeds of which germinate relatively rapidly, were well pro- 

 tected by as little as 0.6 cc. and nearly as well by 0.4 cc. per square foot. 

 A little more may be needed when more slowly germinating seeds are 

 involved, for seedlings of eggplant damped-off with 0.6 cc. But damping- 

 oflf of all these species was as well controlled by 1.0 cc. per square foot 

 as by heavier applications. 



Such an application, 1 cc, leaves a considerable margin of safety, for 

 2 cc. per square foot did not injure the growth of seedlings of any species 

 and injury to growth caused by 3 cc, slight to begin with, was soon out- 

 grown. There is, however, more formaldehj^de in recently treated soil 

 during the germination of seeds than during the subsequent growth of 

 seedlings, and it was several times observed that germination may be 

 injured by applications which do not affect growth. Germination of the 

 other species was not injured by 3 cc, but germination of cress was some- 

 what retarded by 2 cc, not by 1.6 cc, per square foot. Crucifers are 

 especially susceptible to injury by formaldehyde and, for them, about 

 1.5 cc. formaldehyde per square foot, applied as above, is probably the 

 limit of safety. 



Dusting of seeds of crucifers with zinc oxide or, in some cases, with 

 Semesan resulted in better stands of seedlings than did the application of 

 formaldehyde to soil after seeding. Both zinc oxide and Semesan dust, 

 as seed treatments, gave better results with crucifers than did red copper 

 oxide. 



Formaldehyde 1.9 cc. (in 0.8 quart water) per square foot gave good 

 control of damping-off of spinach, lettuce, pepper, cucumber, beet, and 

 tomato, but about 2.5 cc. gave better control with celery and Swiss chard. 

 That quantity of water per square foot is not too much if soil is not too 



