1902.] DISEASES AND INSECTS, ETC. 1 39 



There are other diseases which may be prevented by either 

 disinfecting the seed, or the soil in which the seed is planted. 

 To this class belong onion smut (Ustilago cepulse, Frost); 

 barley smut (U. hordii. P., Kell. & Sw., and U. nuda, Jens.) ; rye 

 smut (Urocystis occulta, Wallr.. Rabh.); oat smuts (Ustilago 

 aveuc-e, P. Jens., and U. levis, Kell. & Sw. Magn.); wheat smuts 

 (Tilletia fcetens, B. & C, Schrt.; T. tritici, Bjerk., Wint., and 

 Ustilago tritici, P., Jens.) ; and potato scab (Oospora scabies, 

 Thax.). 



The potato scab may be prevented by soaking the seed 

 potatoes either in corrosive sublimate or in formalin. This 

 destroys any of the scab fungus which may be attached to them. 

 In the cases of the various smuts just mentioned, it has been 

 found that the smut fungus gains entrance only when the host 

 plant is very young. This peculiar habit in the life history of 

 these fungi is taken advantage of in preventing their attacks. 

 Two successful methods in combating the onion smut are in 

 use. The first is by starting the seedlings in soil free from 

 smut germs, and then transplanting them when they are large 

 enough to resist the entrance of the smut fungus, which is 

 when they are about the size of an ordinary lead pencil. The 

 second is by drilling a mixture of lime and sulphur into the 

 furrow when planting the seed. No successful treatment for 

 the smut of corn (maize) has been found. The corn smut 

 fungus gains entrance only when the host plant is very young 

 and tender, as do the other smuts just named, but also after the 

 corn plant is large. For this reason the treatment which is 

 effective in preventing the other smuts referred to fails to 

 prevent corn smut. Oat smuts and the other grain smuts, 

 which have been mentioned, are successfully treated by soak- 

 ing the seed either in hot water or in formalin. The latter is 

 gaining favor among farmers because it appears easier to 

 manipulate. 



Against some diseases the best known methods of warfare 

 are the saw, pruning knife, and fire. In this class is the 

 black knot of plum and cherry. The knots should all be cut 

 out and burned early in the winter, and when the summer knots 

 begin to appear they must be treated in the same way. Spray- 

 ing with fungicides may sensibly decrease the depredations of 

 the fungus, but cannot be depended on to keep it under control. 

 Peach yellows is combated in a similar way, except that the 



