Rain, heat and humidity are a recipe for disease in the field. Edward Sikora, an Alabama Cooperative Extension System plant pathologist, said foliar diseases have become more prevalent on soybeans during the last several weeks.

“We have a number of soybean sentinel plots at different research stations to monitor for soybean rust,” Sikora said. “However, I also use those plots to track other diseases that might pop up during the season.”

Unusual Weather

Sikora said the weather is mostly responsible for the higher levels of foliar disease pressure.

“In a general plant pathology course, on the first day they show you the disease triangle,” he said. “One corner will be the host. Another corner will be the pathogen. The other corner is weather.”

He said approximately 80 percent of all plant diseases are caused by fungi. Approximately 99 percent of the common fungal diseases thrive in warm, wet weather.

“Unless we run into a dry patch in late August or September, these diseases will keep going,” Sikora said.

Soybean diseases to watch are:

“In years like this, where field soil is saturated, it will only kill plants in small patches in a field” Sikora said. “But it is usually a good sign for the grower in our state because it means there is a lot of moisture in the soil, which is typically good for the crop.”

As far as root and stem diseases are concerned, Sikora said there is not much producers can do at this time.

"Realize you have the problem and avoid the areas if you can," he said. "Consider rotating to a non-host crop like corn, if possible."

Sikora said with soybeans, frogeye leaf spot and target spot are going to be diseases to focus on this August—and possibly soybean rust later in the season. Producers can usually control these foliar diseases with a single, well-timed fungicide application at the R3 or R4 growth stage.

“Try to get that fungicide application out before the disease shows up. That should give you approximately three weeks of protection,” Sikora said. “Go with a mixture of active ingredients because we have detected frogeye leaf spot populations resistant to strobilurin-type fungicides in Alabama.”

He said this is a good year for producers to protect their crop and their yields because of the high prices for most commodities.

Corn Disease

Southern corn rust appears to be statewide.  For the most part, the corn crop is maturing and is beyond the point where a fungicide application would be beneficial. However, in fields that are in the reproductive growth stages, producers should take care to scout their fields for the disease. If present, producers should make a fungicide application if they have not applied a product previously.

“If Southern rust gets going in a field early, it can really knock down yields,” Sikora said. “Depending on how widespread it is in a given field, producers may want to consider a mixed compound-type fungicide to protect those yields as well.”

Much more information on soybean and corn disease control is available in Episode 21 of the Alabama Crops Report Podcast.

Source: Alabama Cooperative Extension System, which is solely responsible for the information provided and is wholly owned by the source. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.