CONTROL OF DAMPING-OFF 19 



SUMMARY 



There is no one best standard dry chemical treatment for the seeds oi all veg- 

 etables. Red cuprous oxide is to be preferred for some, Semesan for others, and 

 zinc oxide for still others. A list of vegetables (Table 1) together with the seed 

 treatments which most improved the stand of each is included in this bulletin. 



Applied to soil after seeding, chlorpicrin emulsions controlled damping-off 

 very well but, because of their too unpleasant fumes and the instability of the 

 emulsions, they are not preferred by the writers for this purpose. 



Damping-ofT was more effectively controlled by vinegar in an acid soil than in 

 one with a high pH value. Acetic acid and vinegar are good substitutes for 

 formaldehyde but they did not, in general, and as applied to soil after seeding, 

 give results equal to those obtained by formaldehyde. 



Spraying seedbeds and seedlings with Bordeaux mixture, red cuprous oxide, 

 or zinc oxide proved to be less effective and satisfactory in controlling damping-off 

 than soil treatments with formaldehyde or certain seed treatments. Applied to 

 soil after seeding, mercury compounds were often injurious to cruciters and, 

 even at best, results were no better than those which followed seed treatments. 



Substance? containing sodium hypochlorite gave results inferior to those se- 

 cured by formaldehyde, acetic acid, and chlorpicrin emulsions. 



Salicylic acid, pyroligneous acid, and oxyquinoline sulfate gave good results 

 with the vegetables with which they were used and they could be substituted for 

 formaldehyde in controlling damping-off of these vegetables. 



Formic acid gave results which justify its further investigation but not, for the 

 present, its recommendation. 



For the control of damping-off calcium cyanamide has its uses, more especially 

 if, for any reason, soil must be treated long before seeding. 



Ammonium hydroxide, applied before seeding to soil of an initial high pH value, 

 controlled damping-off very well, and treated soil did not become promptly re- 

 infested. Ammonium sulfate was effective in a soil with a high pH value bat it 

 had little protective effect in a too acid scil. Damping-off was prevented by 

 ammonium sulfate and hydrated lime applied together, but seeds or plants may 

 be injured unless seeding is deferred until more than 5 days after soil treatment. 



Stands of pea were much improved by formaldehyde applied in the rows at 

 the time of seeding. 



Foimaldehyde solutions, from 1 pint to about 1 quart water per square foot, 

 usually gave excellent results when applied to soil immediately after seeding. 

 Very light applications, down to about 0.6 cc. formaldehyde per square foot, were 

 fairly effective, but suggested rates of application of formaldehyde (see Table 11) 

 vary from about 1.75 cc. per square foot for more easily injured seeds such as 

 those of lettuce and other composites to 2.5 cc. per square foot for less readily 

 injured seeds such as those of beet and spinach. In practice, this means that 1 

 fluid ounce of formaldehyde is enough for 12 to 17 square feet of seedbed. A less 

 discriminating method but one effective and safe with the few vegetables, except 

 crucifers, with which it was used consists in applying a solution of formaldehyde, 

 1 teaspoonful in 1 gallon of water, immediately after seeding without determining 

 the exact rate of application of the solution. 



Repeated applications of very dilute formaldehyde, after seeding, interfered 

 with growth in some cases and gave no better results than one application 



Formaldehyde gave good results when applied to soil from below, by subirri- 

 gation, provided that the soil did not already contain too much water 



Growth of plants was usually improved by formaldehyde applied to soil not 

 previously sterilized, but this was not the case when it was applied to soil which 

 had been recently steamed. 



