Agriculture

Update on Disease Risk in Soybean and Corn in Indiana

Darcy Telenko
July 16, 2021

Recent rains and increased humidity across Indiana have increased the risk for foliar diseases to develop in both corn and soybean. Much of the corn throughout the state has begun to tassel and soybeans are flowering. We are starting to see common diseases in the lower canopy of corn, as we were out scouting this past week. A few diseases that I have seen included gray leaf spot, tar spot, northern corn leaf blight, common rust, and northern corn leaf spot in corn.

In addition, we are tracking the activity of tar spot (map-figure 1) and southern rust (map – figure 2). On the tar spot map you can see gray areas where we have detected the tar spot in past seasons. In Indiana, we have confirmed tar spot for this season in Jasper, LaGrange, LaPorte, Noble, Porter, St. Joseph, and Vermillion. Tar spot is still at a low incidence and severity in these fields, but we suspect with the current weather conditions the disease will continue to spread (risk map figure 3). We will continuing to monitor and provide updates.

Map on the left, on the upper right corner a close up of a tar spot on a leaf and on the lower right corner a leaf with tar spots

Figure 1. July 16, 2021 map of tar spot activity in Indiana and images of tar spot on corn.

Southern rust was just confirmed in Gibson County, Indiana. It is important to continue to scout your field to determine if any of these diseases are present. Gray leaf spot, northern corn leaf blight and tar spot are the diseases that are most commonly managed by fungicides in Indiana. For gray leaf spot and northern corn leaf blight fungicides applied at VT-R1 are most effective at preventing yield loss. Scouting will help determine the level of disease pressure in a field. See link below for fungicide efficacy tables.

To the left map of southern rust and, to the right a corn leaf of southern rust — Figure 2. July 16, 20style21 Southern corn rust map. Image of southern corn rust.

Diseases in soybean is currently low, but we have found a few frogeye lesions, downy mildew, and brown spot this past week. Since the soybeans are flowering it is time to scout for frogeye leaf spot. Management practices for frogeye are aimed reducing soybean susceptibility and inoculum availability. Infected debris from previous crops is the primary source of inoculum for this disease. Any practice that helps reduced or bury the infected residue will help reduced inoculum in a field such as fall tillage or soybean- corn crop rotation. There are a number of varieties available with frogeye resistance. Fungicide spray application after growth stage R1 can reduced severity, while applications made at R3 are considered most effective for frogeye. There are number of fungicides available to use for frogeye management see links below.

To make a decision for applying a fungicide there are four things I consider – 1. Disease risk in a field – do you have a previous history of the disease; 2. Current disease activity – do you find the disease in the lower canopy while scouting; 3. Weather conditions – will there continue to be favorable weather moisture and rain for foliar diseases? And 4. Return on investment – will the yield protected by a fungicide cover the additional cost of the application?

For fungicide recommendations please see the 2021 fungicide efficacy tables developed for both corn and soybean foliar diseases can be found at the following links:

Fungicide Efficacy for Control of Corn Diseases
Fungicide Efficacy for Control of Soybean Foliar Diseases