With December corn futures approaching $8/bu., many producers are considering making foliar fungicide applications to minimize yield loss caused by diseases, said a University of Nebraska–Lincoln (UNL) specialist.

Producers should consider several disease risk factors in deciding to use a fungicide to insure they get the maximum benefit, said UNL Plant Pathologist Tamra Jackson.

First is crop susceptibility. Gray leaf spot is the most common foliar disease of corn in the Midwest, and producers are more likely to get the greatest benefit from fungicides when treating susceptible hybrids.

Second, continuous corn tends to have more of the diseases that overwinter here in Nebraska, such as gray leaf spot, Jackson said.

Third, tillage practices affect the presence of fungal diseases because fungi overwinter in crop residue.

Fourth, overhead sprinkler irrigation and especially the wet weather conditions that much of Nebraska has experienced recently promotes most fungal diseases because these organisms need moisture, or at least high humidity, in the canopy to infect the plants.

Fifth, the later planting dates this spring can contribute to worse foliar diseases later this summer, especially for southern rust if it develops. All diseases have a greater impact on yield when they are active in the plant during grain fill. The potential for disease later in the season is greater this year and might make fungicides more profitable then. Fungicides provide protection for 14-21 days, making timely applications critical.

Several products from two classes of systemic fungicides are available for treating corn, Jackson said. The strobilurins provide protection and can be applied before the disease develops or early in the disease process. Triazoles are more curative than preventive and can be applied after the disease develops, as long as the producer doesn’t wait too long. Products are combinations of the two classes and have characteristics of both. Be sure to read the label carefully before making a fungicide application because there are some differences among the products. Those differences include:

  • Harvest interval. Most strobilurins can be applied up to seven days before harvest. Triazoles are much more restrictive. Harvest interval can be as little as 30 days. In some cases, application can’t be made after brown silk stage. Unfortunately, some foliar diseases don’t develop until after brown silk stage.
  • Reentry interval. Most of the fungicides used on corn are not acutely toxic to humans as some other pesticides. Most do have specific safety precautions that need to be observed, though. Some have ingredients that cause substantial but temporary eye injury so producers want to make sure they’re wearing all the appropriate safety gear listed on the product label.
  • Ecological hazards. Some products are toxic to aquatic invertebrates and fish. These products should never be applied over surface water or where they may run off into lakes or streams.
  • Adjuvants and tank mixtures. Company recommendations have changed within recent months for some products regarding their use with adjuvants and tank mixtures particularly when applying them before tasseling. Make sure that you’re familiar with the latest recommendations to avoid the potential for plant injury when using fungicides.

For more information about specific products, contact the company that makes the product. UNL county extension offices will have more information as will the pesticide education office in Lincoln and any specialist on the UNL extension plant pathology team.