The entomologists have been telling us all spring that insects are active far earlier than normal this year. As you might guess, that has been the case with a few diseases as well. An example of an early disease occurrence is corn rust. Unlike cedar-apple rust, which overwinters in Illinois, the corn rust fungus must move in from the south each year. It literally blows here on the wind. In most years (the past 15) rust occurs on sweet corn in mid-June. The literature from the 1970s reports rust spores arriving from the South in early July.

If you know something about plant pathology, you may recall that plant diseases have a latent period. This is the time from infection to symptom development. The latent period for corn rust is 7 days. We saw uredinia rust spores on sweet corn plants in Champaign County on May 30. This indicates that spores were here to cause infection on May 23. Certainly this is much earlier than occurs in most years.

Why is rust moving into our area so early? In the case of corn rust, it is in part due to the warmer weather in the South. Corn is planted earlier in the South, and the rust fungus can build spore populations earlier. A few good rain storms with high winds transport these spores to us in Illinois.