KTIC Radio Extension Corner: Soybean Fungicide Application

Frogeye leaf spot of soybeans

Listen to this week’s extension corner:

This is Dr. Nathan Mueller, your local agronomist with Nebraska Extension for Dodge and Washington counties. Many soybeans are growing fast and already in full bloom, or in R2 growth stage. At this point each year, agronomist and growers start thinking about fungicide applications to their soybeans.

In Nebraska, typically foliar diseases in soybean can become evident later this month of July during the beginning to full pod stage, also called the R3 to R4 growth stage. So we definitely have some time to start evaluating the need for a soybean fungicide application. Therefore, I want growers to make the following set of lists:

Create a list of the varieties planted and what field they were planted in
Now add to your list the frogeye leaf spot susceptibility rating for each variety planted. Contact your seed dealer for assistance if needed.
Create a list of soybean fields following soybeans and soybeans following numerous years of corn
Create a list of tilled and no-till fields
Lastly, create a list of which fields historically have had foliar diseases like frogeye leaf spot and brown spot. If you don’t have this list, start creating one this year for future use.

Now that these five lists are completed, create a new list that prioritizes the fields with higher risk for foliar diseases that need to be scouted first and more frequently. Higher risk fields would include those with a history of the disease, no-till, soybeans planted more frequently, and planted to a susceptible variety to the disease. For example, a no-till field rotated corn-soybeans with a higher incidence of frogeye leaf spot the past two seasons and was planted this year to a more susceptible variety based on seed company ratings is a higher risk field. This would be the first field that I would start scouting and scout more frequently. If there is not much frogeye leaf spot later this month during the R3 to early R4 growth stage in this higher risk field for frogeye leaf spot disease development, then it is likely that other fields with lower risk don’t either. Growers should scout each field, but I know this is difficult for some growers.

Use the foliar disease field risk list and scouting to drive the decision to spray a fungicide. Lastly, fungicide resistance is a growing problem. Iowa State confirmed in the 2017 growing season, that the pathogen that causes frogeye leaf spot, had resistance to the strobilurin fungicides or Group 11 Code. Growers are encouraged to use a fungicide with dual (3+11) or multiple modes (3+7+11) of action this season when spraying fungicides to control foliar diseases like frogeye leaf spot.

Additional Resources:

To listen to this radio message again and to get more information, you can visit our local website at croptechcafe.org or give me a call at 727-2775. Know your crop, know your tech, know your bottom line. This is Dr. Nathan Mueller, your local agronomist for Nebraska Extension on KTIC radio.