18 MASS. EXPERIMENT STATION BULLETIN 394 



good protection, it failed in this experiment as in earlier ones, to increase stands 

 as much as did 1 teaspoonful formaldehyde per gallon similarly applied. 



It is sometimes desirable to water soil from below as, for example, after sowing 

 small seeds which might be buried or washed out if soil were watered from above 

 in the usual way. If soil does not already contain too much water, formaldehyde 

 may be effectively applied at the same time and from below. 



Immediately after seeding, formaldehyde was applied by subirrigation to a 

 relatively dry and sandy soil (abcut 4 inches deep) in flats and pots, by setting 

 them into shallow pans of the solution until the soil was saturated. Damping-off 

 in soil which received only water killed 50 percent of the beet, 28 percent of the 

 lettuce, and 37 percent of the cucumber seedlings. There was no chemical injury 

 to these vegetables and all damping-off was prevented by formaldehyde, 3 tea- 

 spoonfuls per gallon of water. This treatment increased the number of plants 

 which lived by 176 percent in the case of beet, 100 percent in the case oi lettuce, 

 and more than 400 percent in the case o' cucumber. Formaldehyde 2 teaspoon- 

 tuls per gallon may be enough, for, thus used only with beet, it greatly reduced 

 the severity ol damping-off and increased by 225 percent the numbers of seedlings 

 which lived. 



In the experiments represented in Table 18, a dry soil was brought to several 

 different percentages of saturation with water before treatment with formaldehyde 

 (3 teaspoonfuls per gallon), applied from below after sowing seeds of beet. This 

 treatment was effective if soil before treatment was no more than 25 percent 

 saturated, but it was ineffective if soil before treatment was already 50 percent 

 saturated. 



Table 18. — Effect of Soil Moisture on Control of Damping-off of Beet 

 BY Formaldehyde Applied From Below 



Soil Moisture Relative Number Percentages 



Before Treatment of Plants Which 



Treatment Which Lived Damped-off 



Water only(check) 100 54 



Saturated Formaldehyde^ 500 50 



50% Saturated. . Formaldehydei 840 31 



25 % Saturated . . Formaldehydei 1233 



Air Dry Formaldehyde^ 1075 



' 3 teaspoonfuls per gallon of water. 



Formaldehyde solutions were, immediately after seeding, also applied by sub- 

 irrigation to relatively dry soil in metal flats^ so made, with double bottoms, that 

 soil can be watered from below. The volume of soil was small, only about 2 

 inches deep, and the application of the solution, equal to more than 1.5 quarts 

 per square foot of soil surface, was heavy. Under these conditions, 1 teaspoonful 

 formaldehyde per gallon gave good and best results, increasing the number of 

 plants which lived by 31 percent in the case of lettuce, 130 percent with cabbage, 

 and 85 percent with tomato. More than 1 teaspoonful formaldehyde per gallon 

 injured cabbage and lettuce but not tomato. 



It should be noted that in all the experiments mentioned in this bulletin, soil 

 after treatment was watered from above, not below. In the few experiments in 

 which the comparison was made, formaldehyde, acetic acid, vinegar, and salicylic 

 acid were less safe if, after fungicidal treatment, soil was watered from below. 



'Waterite seed flats. 



