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Rust on sweet corn

Rust on sweet corn

This fungal disease occurs commonly on Long Island during fall, as well as elsewhere in the northeast.  It has the greatest impact when it affects husks because symptoms impart an unsightly look to the ears which can affect sales.  Rust is not observed every year in every crop, thus it is important to scout crops to determine if either disease is present and fungicides are warranted.

Symptoms of common rust are small round spots with dusty orange spores.

Fungicides are recommended in early whorl stage plantings that are showing symptoms. Economic impact is unlikely when symptoms start on older plants, especially after ears have started to develop. Applying fungicides starting early in disease development, when very few symptoms are present, is critical to successful control of most fungal diseases.  Using a spray boom with drop nozzles will increase spray coverage on leaves low in the canopy.  There are 2 groups of targeted fungicides effective for rust and also Northern corn leaf blight, another important disease: FRAC Group 11 (which includes Quadris and Headline) and Group 3 (Bumper, Fitness, Proline, Propimax, AmTide Propiconazole, and Tilt).  Headline AMP, Stratego and Quilt contain both types of fungicides and are good choices when few applications will be made.  Targeted fungicides are more rain-fast than protectants (Bravo or Dithane) and have a longer period of activity.  Alternate among these groups and tank mix with a protectant fungicide to manage resistance developing in these pathogens.

Please Note: The specific directions on pesticide labels must be adhered to — they supersede these recommendations, if there is a conflict. Any reference to commercial products, trade or brand names is for information only; no endorsement is intended. For up-to-date information on labeled fungicides see Cornell Integrated Crop and Pest Management Guidelines for Commercial Vegetable Production

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