Be On the Lookout for Field Crop Diseases

Scouting a field can be very valuable in helping identify a problem early and allow for treatment to occur. One disease to be on the lookout for this year is tar spot. The most recent edition of the Pest & Crop Newsletter from Purdue University stated that tar spot has been documented across the state including in Putnam County. 

Tar spot produces raised, black fungal structures on leaves, stem, and husk of affected corn plants. These spots can be surrounded by a narrow tan halo. The spots will not rub of when you touch them. Tar spot can be difficult to distinguish from other diseases; thus, it is usually confirmed via laboratory testing. For more information about what tar spot is, how it spreads, and management options, please view the Diseases of Corn – Tar Spot publication from Purdue University Botany and Plant Pathology.

With the amount of tar spot being confirmed in Indiana, many producers have asked Darcy Telenko, Purdue University Associate Professor of Plant Pathology, if they should apply a late season fungicide or do a second fungicide application this year.  Darcy’s comments include:

1. What growth stage is the corn? If at dent (R5) or beyond she would not recommend an application.
2. What has been the history of tar spot in your field? How much disease do you see currently? Where is the disease in the canopy? Just lower leaves or has it moved up to the ear leaf?
3. When was a fungicide applied? If more than 3 weeks, then the effective period for many fungicides has run out.
4. Has the environment been favorable for tar spot development? Utilize Tarspotter, the Corn Tar Spot Disease Forecaster app from University of Wisconsin to check your field’s risk. 
5. If you do decide to make a fungicide application at this point in the season, leave check strips to determine if the fungicide gave you a return on your investment.

In the case of soybeans, one of the issues to be on the lookout for is Sudden Death Syndrome (SDS). SDS is a soil borne fungus that survives in plant residue that causes yellow, interveinal chlorosis and necrosis of the leaf tissue. The veins in the leaves will remain green. Eventually, the leaves die and prematurely fall from the plant, while petioles remain attached to the stem. Cool, wet weather during early vegetative stages promotes this problem. Therefore, delayed planting to avoid the cool, wet weather can help with this issue. You can also select varieties that are less susceptible to it.

Scouting your field can help you identify issues as they begin to arise. Additionally, individuals are welcome to view the Indiana Field Crop Pathology Blog to learn more about different issues throughout the state as they are identified.  One of the more recent articles was about red crown rot in soybeans and what to do if you suspect it. Red crown rot is a new concern for Indiana producers. It has been confirmed in four counties in 2024.