. Diseases of small grain crops in Illinois. Grain. 64 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 85 season advances, these spots enlarge, reaching sometimes an inch in length, and the tissue in the center dies. The clear, trans- lucent tissue around the dead center resembles a halo and gives the disease its name, fig. 21. Spots may be prolonged into points at one end and sometimes a faint trace of several halos may be seen in larger spots. Or the halo may be extensive and run as a streak nearly the length of the leaf. When spots occur close together and join each other, all of the leaf beyond t
. Diseases of small grain crops in Illinois. Grain. 64 ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 85 season advances, these spots enlarge, reaching sometimes an inch in length, and the tissue in the center dies. The clear, trans- lucent tissue around the dead center resembles a halo and gives the disease its name, fig. 21. Spots may be prolonged into points at one end and sometimes a faint trace of several halos may be seen in larger spots. Or the halo may be extensive and run as a streak nearly the length of the leaf. When spots occur close together and join each other, all of the leaf beyond these spots dies. In severe infections the entire leaf dries up and turns brown, but the halo usually is distinguishable even on the dead leaf. On the chaff, each minute spot of infection is surrounded by a light green to yellowish-green halo; if the entire chaff is infected, the tissue between the veins turns yellow and becomes translucent. Life History.—Tests have shown that halo blight bacteria live over winter on the oats seed and cause primary infection in the spring on the first leaves. On seed these bacteria are able to remain alive for at least two years, and it seems quite possible that they may live over in the soil and on diseased plant refuse for an equal period. Infection in oats fields shows an increase after rainy periods, indicating that moisture favors development of the disease. Both rain and wind easily may spread the bacterium from plant to plant as well as to different parts of the same plant. Importance.—Halo blight is important chiefly because of its destruction of leaf tissue. In Illinois oats fields it behaves as an. Fig. 21.—Halo blight of oats. Bacterial infection of oats leaves results in the appearance of yellow-green, oval spots surrounded by clear, translucent Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may
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