24 Farmers' BiiUetin 1126.

tho sweet sorghums. In dry regions where the pollen ia carried for considerable distances by the wind, a Sudan grass field intended for a seed crop should he 60 to 80 rods from any sorghum. Another source of cross-pollination exists in the volunteer plants of sorghum sometimes found in fields that were planted to sorghum the previous year. To avoid such sources of trouhle, fields that have been growing other crops than sorghum should be chosen for the Sudan grass seed crop.

To make sure of pure seed, roguing the field at least once a year must be resorted to, and the rogues should bo removed before a chance has been afforded for cross-pollination. The great need of special efforts to keep Sudan grass pure is illustrated by the present condition of the sweet sorghums, very few fields of which are to bo found anywhere that are pure as to variety. They are very comimmly mixed not only with other varieties of sorgo, but also with the grain sorghums. Unless seedsmen and growers unite in an (■(Fort to keep their seed fields free from sorghum hybrids, Sudan grass will lose, much of its distinctiveness within the next 20 years.

DISEASES OF SUDAN GRASS.

RED-SPOT.

The worst disease of Sudan grass is the so-called sorghum blight,1 more appropriately designated as red-spot. This is a bacterial diseuse, characterized by the appearance of distinct reddish spots on the leaves, which gradually spread until the leaves turn brown and die. (Fig. 11.) Its effect on the plant is much the same as rust, and, like rust, it is most destructive in warm, humid regions. It is prevalen (. in the Great Plains, but does little damage there except in wet seasons. Along the South Atlantic and Gulf coasts it almost entirely prevents the profitable production of Sudan grass. (See map, fig. 3.)

No remedy or preventive of red-spot has been found other than the use of resistant varieties. Rotation with other crops not subject to the disease probably holds it in check. In localities where sorghums are regularly grown, however, they furnish a continuous source of infection.

KERNEL SMUT.

Sudan grass is subject to the kernel smut of sorghum. This disease changes the individual kernels into a mass of dark spores covered by a grayish membrane. These spore masses look like an elongated seed, fully twice as large as the healthy kernels.

i Killcniian, W. A.,and Swingle, W. T. Sorghum blight. Jn 1st Ann. Rpt., Kans. Agr. Exp. Sta., 1888, p. 281-302. 1889. Ilnrrill, T. J. A dlsoasoof broom-corn and sorghum. In Pro«. 8th Ann. Boc. Prom. Agr. 8cI.,18S7, p. 30-30. 1887. Kadals, Maximo. On tho blight of sorghum. /» Dot. Oaz. ,vol. 28 ,no. I ,p. 65-68. 1899.