24 MASS. EXPERIMENT STATION BULLETIN 351 



Two or three times as man^' beet and cucumber germinated and lived (see 

 Table 10) with dilutions of 1:50 to 1:30 as in the check. 



Growth of all species was injured by a dilution of 1:30 applied to soil 10 to 15 

 days before seeding, and a dilution of 1:40 was a little injurious to growth of 

 Alyssum saxatile, sweet alyssum, sweet pea, and beet, but not to Scabiosa. A 

 dilution of 1 :50 was usually harmless to these species and to Cheiranthus Allionii; 

 and this and lesser concentrations, often too weak to prevent damping-of?, im- 

 proved the growth (as compared with checks) of Salpiglossis, lupine, Canterbury 

 bells, and cucumber. 



Ammonia, as a soil fungicide for the control of damping-off, should have more 

 attention, since it is not only definitely fungicidal but also readily available and, 

 of course, a source of nitrogen. The results may not be quite the same in all 

 soils, however, for Davey and Leach (26) concluded that the fungicidal effect 

 of ammonia is influenced by soil reaction. Dilutions more concentrated than 1:50 

 will probably be injurious to many species if applied less than 10 days before 

 seeding, but this dilution or 1:60 may well be tried. Weaker solutions may, 

 of course, be used nearer to the time of seeding, but that they will protect against 

 damping-ofT has yet to be proved. 



Ammonium Thiocyanate 



Organic thiocyanates are known to be highly toxic to fungi (99), and Andes 

 (7) concluded that ammonium thiocyanate may be used for the disinfection of 

 soil. It is, however, so toxic to plants as to be a good weedicide (44), and Andes 

 found it necessary to wait six weeks before tobacco seeds could be sown safely in 

 soil treated with a 3.0 percent solution (2 quarts per square foot). 



The writer used much lighter applications. Two and 3 gm. seemed to have 

 some fertilizer value and greatly improved the growth of sweet alyssum, seeds 

 of which were sown 16 days after soil treatment, but damping-off was not pre- 

 vented by 7 gm. This amount, or even 5 gm., applied to soil 20 days before 

 seeding, was injurious to Salpiglossis, Petunia, Canterbury bells, foxglove, and 

 heliotrope. 



Ammonium thiocyanate may, therefore, be said to remain toxic to plants too 

 long to be a good soil fungicide, since the need is for treatments which may be 

 used at the time of seeding or not long before. 



Calcium Cyanamide 



Calcium cyanamide, a nitrogenous fertilizer which is known (62, 92, 65, 12) 

 to have some effect as a soil fungicide, was used in several experiments, the results 

 of which are summarized in Table 11. Applications of 6 to 18 gm. were well 

 mixed with soil, naturally infested with Pythium, 10 to 14 days before seeding. 

 Damping-off was not well controlled by 8 gm. or less, but there was good control 

 by 10 or 12 gm. or more. 



The exact quantities necessary may, on the basis of the work of Walker and 

 Larson (92) with cabbage club root, possibly be different in different soils; and 

 Boning (12) found that applications too light to prevent all infection by Pythium 

 at least delayed primary infection. 



