Pheromone traps are available to monitor flights and guide in timing sprays. However, with the dramatic change in the weather, I think that particular threat is no longer a concern. I had received a report from Arkansas that levels of common rust were reaching fairly high levels even on field corn. Common rust does not overwinter in Illinois, but is carried up from the south on air currents, and usually arrives here in late June or early July. The cool wet weather we were having was ideal for rust development, and I thought that we might see some major problems with rust on sweet corn.
Infection typically takes place in the whorl, where humidity levels remain high most of the time.
Some rust pustules may develop on sweet corn in the next week if spores arrived and infection took place when it was a bit cooler. However, with daytime temperatures in the mid nineties there should not be much additional spread. Common rust is usually more of a problem on late season sweet corn, as temperatures start to drop back into the favorable range. So we probably have not avoided the rust problem altogether this season, it is just on hold for a while. With the rapid change of weather conditions from cool and moist to very warm young plants that were affected by seedling diseases and root rot problems may start to wilt in the heat of the day or show other signs of stress.