SOIL TREATMENTS AND SEED GERMINATION 11 



An application of this or other chemical may, of course, be too light to kill 

 either fungus; but, as may be seen from Table 3, damping-off has been satis- 

 factorily prevented by as little as 7, 5, or even 3 cc. formaldehyde per square foot. 

 These are very small applications, compared with the 37 cc. per square foot which 

 results when 2 quarts of the 1 :50 dilution of formaldehyde, long a standard 

 recommendation, is applied. That method is going out of favor, principally because 

 of the 10 to 14 days' delay necessary between soil treatment and seeding. Yet 

 an application of two quarts per square foot of a slightly weaker solution, 1:75, 

 equal to about 25 cc. formaldehyde per square foot, was found by Johnson (54) 

 to be ineffective against both Pythium and Rhizoctonia after 15 days. It may be 

 that some of the smaller applications (such as the 6.37 cc. of formaldehyde in 

 1.5 ounces of a 6 percent dust) would not be effective for any longer; but they 

 are generally used with satisfactory results (100, 40). 



These new methods differ from the old, and this may be important, in that less 

 water as well as less formaldehyde is applied per square foot — as much as 1855 cc. 

 by the old method, and as little as 30 cc. or none at all by the new. The e.xplana- 

 tion is probably to be found in the conclusion of Yu (102) that the fungicidal 

 effects of formaldehyde (and of acetic acid) are greater if soil to which they are 

 applied is not very wet. It may be necessary to add more water to soil at time of 

 seeding, but the indications are that less of the fungicide is needed if not too 

 much water is applied with the treatment, especially if the chemical is mixed 

 with the soil. Then too, formaldehyde has been found to escape more rapidly 

 from a drier than from a wetter soil (100), which is one explanation of why the 

 time interval before seeding may safely be shorter. 



But the less dilute the chemical when applied to soil, the greater may be the 

 need of later watering, at time of seeding, to prevent injury. This is the common 

 recommendation when formaldehyde dust is used, and Guterman and Massey 

 (40) found it necessary to water thoroughly, after seeding, soil which had been 

 treated with formaldehyde (about 7 cc. per square foot in about 40 cc. of water) 

 24 hours previously. The writer has found their method effective against damping- 

 off and safe with the seeds used, but there was injury to cuttings of an herbaceous 

 plant, Nepeta Mussini, inserted 24 hours after this treatment of a sandy soil. 



Haensler (41) was able to control damping-off by formaldehyde 1:300, applied 

 at the rate of 0.75 quart per square foot immediately after seeding. This is a very 

 light application of formaldehyde indeed, only about 2.3 cc. per square foot; but, 

 as used by the writer, it markedly improved germination and prevented most 

 early damping-off. It was not injurious to tomato, eggplant, pepper, or lettuce. 

 It did injure cress, crucifers being more subject to injury by formaldehyde, as 

 Haensler observed, than are some other plants. Such use of fungicides, after rather 

 than before seeding, is further discussed below. 



Acetic Acid, Acetic Acid Dusts, and Vinegar 



The soil in these and the following experiments was 3 to 4 inches deep in flats 

 or earthen pans. Chemicals were applied on the basis of the number of grams or 

 cubic centimeters per square foot of soil surface.* Except as otherwise noted, 

 chemicals were worked into the soil before seeding. 



Acetic acid 1.0 to 1.2 percent (2 quarts per square foot, 1 or 2 weeks before 

 seeding) was found (28, 29) to be a safe and effective soil disinfectant. As has 

 been pointed out by Newhall, Chupp, and Guterman (70), it is less unpleasant 



^One gm. per square toot is 96 pounds per acre, and 20.8 gm. per square foot is 1 ton per acre. 



