Disease symptoms often become quite evident in corn in the dent stage, and as the plants near maturity they become more susceptible. Diseases have a lower impact on yield when they occur in the late growth stages, but losses still can occur at this stage, especially if plants die prematurely.
||Decay of stalk base caused by Fusarium.
The diseases most likely to cause premature plant death are the stalk rots. Over the last week I have seen stalk rot causing premature death in fields scattered throughout the state. Stalk rot fungi usually enter through the roots or through insect injuries. In fields I inspected, the fungi had entered through roots and were severely decaying the base of the stalk, no higher than the brace roots. Corn borer injury was not a major factor in those fields. See the last Integrated Crop Management for more information on stalk rot scouting and management.
Gray leaf spot severity has increased dramatically in some fields over the last two weeks. I have seen a number of fields with 50 percent disease severity on the ear leaf. Based on these latest observations, I think the disease may impact yield in more fields than I thought as recently as two weeks ago. Still, the overall severity is much lower than in 1994 or 1995; most fields do not have severe symptoms.
This article originally appeared on page 173 of the IC-478(22) -- September 15, 1997 issue.