DISEASES OF MAIZE 245 



agreed that the principal and perhaps the only source of infection is from the flying 

 conidia produced by the germination on the ground of the mynad spores of the smut 

 boil. Warmth, moisture and soluble food material are very essential to the germina- 

 tion of the spores and the spread of the disease. Naturally, therefore, as the season 

 of active gro^^•th progresses the conditions favorable to spore germination increase 

 and the number of pustules is increased as the foliage, tassels and silk increase to 

 afford a suitable matrix for the conidia. The abundance of silk and the great 

 amount of nourishment in the grains explain the enormous development of the 

 smut boils, which often attain the size of a man's head. The infection is purely 

 local; the disease does not spread, as is shown by the appearance of the smut 

 boils at the point of infection two to three weeks after the conidia have made their 

 entrance into the host. Thus, it is seen that infec- 

 tion may take place at any time in the gro-ning 

 season, and the longer the season of growth, the 

 greater the infection is likely to be. It is reported 

 that sweet maize is more susceptible to the disease 

 than the ordinary field maize ; estimates on the per- 

 centage of infection of the latter have been variously 

 stated at from five-tenths to twenty-six per cent. It 

 therefore follows that the extent of infection depends 

 considerably upon five factors: (i) seasonal condi- 

 tions, a rainy season tending to keep much of the 

 conidia washed out of the air, while much dry 

 \.-eather is fatal to the germinative po\Aers ; (2) the 

 tiickness of planting, the moisture held by the plants 

 being increased as the foliage is multipHed; (3) the ^^.^^ ^^^^ j^^.,^ 



presence of decayed vegetable matter; (4) manure, 



which may be infested with spores; (5) the degree of maturity of the dififerent 

 parts of the plant. The only practical method of prevention, so far as known, is 

 to gather all smut pustules as they appear, care being taken to prevent scattering 

 the black powder (spores), two or three times in the growing season and destroy 

 them by burning or placing in boiling water. Great care should be taken, also, in 

 seemg that, as tar as possible, the manure for the maize field is free from spores. 

 Experiments have sho\\-n that the hot water treatment used for smut of oats and 

 wheat is of no avail in combating maize smut ; this is explained by the fact that 

 inoculation of the host comes not from the seed but from the flying conidia which 

 alight upon the gTo\\"ing plant. Maize smut has been fed to cattle in numerous 

 instances in large quantities for a considerable j)eriod of time without apparent 

 injury. 1 



323. Bacterial Disease. — There has been observed in Illinois and other 

 North Central States a bacterial disease of maize, which not only does consider- 

 able damage to maize in some localities, but it is supposed that the germ which 

 causes the disease in maize is able to cause a sudden and fatal disease in cattle. 



IFor detailed study of maize smut, see Ind. Rpt. 1899 (12), pp. 84-135; also 

 Farmers' Bui. 69; Kan. BuL 62 ; Ohio Bui. 78. 



