Successfully controlling yield-limiting crop diseases comes down to analyzing field history and making the right management decisions for individual fields, says a Purdue Extension plant pathologist.
Once soil-borne crop diseases are present in a field, they rarely disappear. When the right weather conditions present themselves, diseases such as sudden death syndrome, root rot, white mold and seedling blight can substantially decrease crop yields.
"Managing diseases starts with knowing what is present in the fields," Kiersten Wise said. "Growers need to know what diseases have shown up in their fields in the past, and they need to plan for those diseases even if they haven't seen them in a few years."
Disease development is mostly dictated by environment, planting date and seed variety. Wise said there could be more problems after a very warm, wet winter because soil-borne diseases are there and waiting for the right conditions to flourish.
"Soil diseases don't go away, so growers need to plan to manage them," she said. "Knowing the field history can help growers choose varieties that are resistant to previous disease pressures."
With soybeans, growers have a few more seed treatment options. But with no treatments to effectively fight sudden death syndrome, Wise said variety selection and planting date are extremely important in fields with a history of this disease.
Fields with disease history should be planted as late in the season as possible.
Corn growers also have a variety of disease management choices, including hybrid selection and fungicide applications.
"Foliar disease organisms won't be as affected by the mild winter. Instead, they will depend more on the weather during the reproductive stages, probably in July," Wise said. "At that point, if growers are seeing foliar diseases, they can consider fungicide treatments."
Many fungicide purchases have rebates if the orders are placed before the crop is planted. Wise said corn producers should consider a few factors in deciding whether they might need to consider fungicide application.
"If farmers are planting into fields with a lot of residue, if they're planting susceptible varieties and if their fields are continuous corn, they could possibly benefit from a fungicide later in the season if the environment is favorable for disease development," she said.
Purdue Extension's Corn and Soybean Field Guide offers more information and helps producers identify crop diseases throughout the growing season. It's available for $7 in Purdue Extension's The Education Store at https://mdc.itap.purdue.edu/item.asp?itemID=20394 
Growers who are uncertain about the identification of a disease also can send samples to the Purdue Plant and Pest Diagnostic Laboratory for diagnosis within a few days. More information is available at http://www.ppdl.purdue.edu/PPDL/