High than usual amounts of common rust on corn in 2008

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

This year, there have been higher than usual amounts of common corn rust showing up, as weather conditions were conducive for the disease early on. The fungus spreads by airborne spores traveling on wind currents and storms from the South, and does not overwinter in Michigan. Common rust rarely causes economical loss in field corn, as most hybrids have adequate resistance. Unless there are other foliar diseases present, such as gray leaf spot or northern corn leaf blight, it isn’t usually an economic proposition to apply a foliar fungicide. Seed corn inbreds may be much more susceptible to rust and are commonly treated with a fungicide to control rust and other foliar right around tasselling. If a fungicide is to be used, it’s important to make the application early before the disease has a chance to become established. Once the pustules begin to produce the reddish-orange spores (called uredospores), repeating cycles of infection can take place, spreading the disease. New infections can occur about every seven to 14 days. A single application of fungicide is best made at tasselling, which has passed except for a few of the seed corn inbreds. Most corn is now in the grain fill period, which is beyond the optimum time for fungicide application.

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