Controlling crop diseases starts with keeping accurate field records even before the seeds are planted and continuing through harvest, advises Kiersten Wise, a Purdue University Extension crop specialist.
The majority of yield-limiting diseases can be managed most effectively through good selection of seed varieties, says Wise. Producers should work with seed dealers to choose varieties that have strong resistance to previously recorded diseases.
"Good disease management starts with knowing what diseases are already present in the field," Wise says. "For example, the fungus that causes sudden death syndrome in soybeans survives in the soil and can affect the next soybean crop if conditions are favorable for disease development."
Weather conditions, planting conditions, hybrid selection and field history factor into a disease's level of damage. Farmers should check for diseases as soon as planting starts, looking at the conditions under which crops were planted and monitoring throughout harvest.
Wise recommended using the Corn and Soybean Field Guide for help in identifying diseases.
"If a producer is out in the field and sees a symptom, he or she can flip through the photographs in the guide to help narrow down what the issue might be," Wise says.
For a small fee, producers still uncertain of a disease can send a sample to the Purdue Plant and Pest Diagnostic Laboratory for diagnosis within a few days.
Action plans should depend on the type and level of disease present and potential impact on yield. There is not always a simple solution to controlling a disease once it is in the field, Wise says.
"With diseases like gray leaf spot of corn, we can reduce the risk of disease development through good hybrid selection and crop production practices," Wise says. "But if throughout the season there are weather conditions that favor disease development and gray leaf spot reaches a damaging level, fungicides are available to help manage this disease."
Producers should check for disease presence before applying fungicide because of the inconsistent economic benefit of the application.
"Keep in mind we see the most consistent economic benefit to a fungicide application when it is based on a disease threat," Wise says. "Applying fungicide in the absence of disease, or a disease threat has a less consistent yield response and a higher cost factor."
Wise says she cannot predict the major diseases for this season but we can monitor possible threats such as southern corn rust, a disease in corn that over-winters in the South and blows up on wind currents during the year.
"If it comes to Indiana at a time where we would need to manage it, we can let producers know how to best manage the disease at that time," Wise says. "Ultimately, what diseases will be problematic will depend entirely upon the weather, but keeping good records of field history and using preventative management practices based on past history will help minimize losses due to disease."