SOIL TREATMENTS AND SEED GERMINATION 



23 



protect cotton against root rot and by Davey and Leach (26, 58) to reduce the 

 extent of infection of sugar beets by Sclerotium. It does not necessarily follow 

 that it would be useful against damping-off, for Neal and Gilbert (67) state that a 

 4 percent solution should be applied to soil at least six months before planting, 

 and that is certainly too long to wait if only damping-off is being combated. 



Ammonium hydroxide (sp. gr. 0.9, a minimum of 27 percent NHg) diluted 

 with water in the proportions of 1:30 to 1:80 was applied to soil (2 quarts per 

 square foot) 8 to 15 days before seeding. Results with beet and cucumber, means 

 for five experiments with each species, are recorded in Table 10. 



Table 10. — Effect of Ammonium Hydroxide on Damping-off, Final 

 Stands, and Growth of Seedlings 



There was practically no damping-off of these or other species with a dilution 

 of 1:30; very little with 1:40; more, although usually not much more, with 1:50; 

 too much, although less than in the check, with 1:60; and no control with lesser 

 concentrations. For the prevention of damping-off caused by species of Pythium 

 and Rhizoctonia, both of which were isolated from damped-off plants, it was 

 necessary to use dilutions of 1:40 to 1:50, which means not less than 9 gm. NH^ 

 per square foot. 



The following treatments, by preventing pre-emergence damping-off, also 

 improved germination unless, because of too great a concentration, there was 

 chemical injury to some species. 



