Battle for the Belt: Season 3, Episode 18: Mid-Season Soybean Diseases

Season 3, Episode 18 of Battle for the Belt is now available: https://www.youtube.com/watch?v=tCwLdBkiXTo

In Episode 18, we discuss mid-season soybean disease management with Dr. Horacio Lopez-Nicora, the Ohio State Extension Soybean Pathologist and Nematologist.

As soybeans in Ohio enter the reproductive stages, from R1 (beginning bloom) to R6 (full seed), several key diseases begin to pose significant threats to yield. Growers should scout fields during this period, especially given the recent weather conditions, which have been favorable for disease development.

One of the most concerning diseases at this time is Frogeye leaf spot, caused by the pathogen Cercospora sojina. This disease thrives in hot and humid conditions, which have recently prevailed in many parts of Ohio. The pathogen can overwinter in crop residue if the previous winter was mild, making it a recurring issue. Frogeye leaf spot is especially damaging when it appears between the R3 (beginning pod) and R6 stages (seed fill), as it can significantly reduce yield potential. Regular scouting is recommended to detect early signs of the disease and make fungicide application decisions if necessary.

Another disease to watch for is white mold, caused by Sclerotinia sclerotiorum, which is more prevalent in northeast Ohio (Figure 1). It is favored by high humidity, moderate temperatures, and conditions such as frequent rainfall and fog presence. This pathogen infects plants during the flowering stages (R1 and R2), making that window particularly critical for crop protection. Dense canopies and prolonged leaf wetness can create ideal conditions for white mold outbreaks.

Septoria brown spot (Figure 2), caused by Septoria glycines, continues to be commonly observed in soybean fields across the state. It typically starts in the lower canopy on dead tissue and gradually spreads upward to healthy leaves. 

Sudden death syndrome (SDS), caused by Fusarium virguliforme, is another disease that tends to show up in August and September. Early symptoms include chlorosis (yellowing) between leaf veins and, in advanced stages, a bluish fungal growth on the root surface (Figure 3). SDS can lead to premature defoliation. It’s important to note that SDS can be easily confused with brown stem rot, caused by Cadophora gregata, as both diseases produce similar foliar symptoms. Accurate diagnosis is important for making the right management decisions.

Finally, red crown rot, caused by Calonectria ilicicola, is an emerging concern. Although it has not been reported in Ohio, it has been identified in neighboring states. Growers should be alert, especially in southern parts of the state, and report any suspect symptoms. This disease produces foliar symptoms like SDS, a red discoloration at the base of the stem, and can also contribute to premature plant death.

Given the range of diseases that can appear during this time of the growing season, frequent field scouting is essential. Early detection allows for more effective management decisions. Growers are encouraged to utilize the Crop Protection Network’s disease forecasting tool to support decision-making. This tool offers predictive models for soybeans and other crops, helping farmers to stay ahead of disease threats, allowing proactive management planning.

Field & Crop Progress Updates

The Western location has corn entering the milk stage (R3). At this stage the kernel is at about 80% moisture and has a yellow color on the outside but is white and translucent on the inside. The glume scar where the silk attaches to the kernel is barely visible. At this location, later planted corn entering the reproductive stages is showing gray leaf spot lesions at the second or third leaf below the ear. If you are entering silking and are in southern Ohio, scouting for severity of this disease can assist in making fungicide application decisions. The April 18^th planted soybeans are at R4 (full pod) but had some plots that reached R5 (beginning seed fill). After soybean has reached R4, the next two reproductive stages determine the size of the seed. Beginning seed (R5) occurs when one seed reaches 1/8 inches, at one of the four uppermost nodes with a fully developed trifoliate leaf node.

The Northwest and Wooster locations have the first two planting dates of corn at silking (R1). Both locations had northern corn leaf blight come in last week. Lesions were found most predominantly at the Wooster location but were found on corn between the V7 and R1 stages (Figure 4). The arrival of this disease is likely because of the high humidity the state has been experiencing and the heavy dew during morning hours. If you planted corn in late May or early June, be sure to scout your fields for severity to assist in making fungicide application decisions. If you are seeing gray leaf spot or northern corn leaf blight, please reference a previous article by Dr. Pierce Paul for fungicide application recommendations here.

At all three locations there has not been notable disease on the soybean crop.

Stay tuned to the Battle for the Belt series throughout the growing season for more insights and timely updates on crop management. You can watch the entire video playlist by visiting the Ohio State Agronomy YouTube channel: https://www.youtube.com/playlist?list=PLYlh_BdeqniI74ycivSl_yVOjWJjdjg2X