October 16, 2021

Resistance issue faces soybean growers

FREEBURG, Ill. — There’s a dividing line in Illinois that has nothing to do with baseball or football. It deals with disease.

“If you drew a line from east to west across the state, right at Springfield, below that line, we have strobilurin-resistant frogeye leaf spot,” said Phil Krieg, Syngenta agronomy service representative for Southern Illinois.

While the agronomic focus has been on resistance of other types, strobilurin-resistant soybean diseases have caught the attention of agronomists and the fungicide industry.

“The resistance does not come from improper or overuse of strobilurin fungicides. It is just a naturally resistant organism that we discovered through the use of fungicides,” Krieg said.

Krieg said the resistance issue was discovered when soybean response to traditional strobilurin fungicides was less than expected.

“We were typically using a strobilurin, which prevents the disease from setting in, then we were also spraying a triazole, which stops any disease that is already present. We were not getting good control out of our strobilurins and that was isolated as strobilurin-resistant frogeye leaf spot,” Krieg said.

To tackle the issue, companies like Syngenta changed the formula to tackle the soybean disease issue from another angle and with a new set of weapons.

“We strengthened the triazole that is in our fungicides to one of the strongest triazoles available on the market today. We’ve pulled the strobilurin out and we have put in ADEPIDYN® technology. Adepidyn technology is an SDHI, which is a newer class of fungicides. It is very active on strobilurin-resistant frogeye leaf spot,” Krieg said.

Krieg said another factor that makes Miravis® Top by Syngenta stand out in the crowded fungicide field is in its general length of disease control.

“What we’ve learned with the Adepidyn molecule is it binds very well in the waxy layer of the leaf and so the plant doesn’t break it down very quickly,” Krieg said.

While control of diseases like frogeye leaf spot is a primary goal of fungicides, another benefit is maintaining plant health, particularly during stressful times.

“When we get into stress times, hot and dry, it could be cool and wet, we could be getting a lot of rainfall, all of those things can cause stress,” Krieg said.

The soybean plant reacts by producing defensive enzymes.

“If the weather gets better, it’s not like we can turn back and recoup that yield loss and that overproduction of stress enzymes,” Krieg said.

One of the keys to preserving plant health, preventing disease and tackling any disease issues that have set in is the proper timing of application.

“We want to apply at the R3 timing. That is when you have a small, three-sixteenths’ of an inch pod on one of the four uppermost nodes of the soybean plant. That is the critical timing.”

To learn more about Miravis Top, visit BoostYourBushels.com.

Product performance assumes disease presence. Performance assessments are based upon results or analysis of public information, field observations and/or internal Syngenta evaluations.

©2021 Syngenta. Important: Always read and follow label instructions. Some products may not be registered for sale or use in all states or counties. Please check with your local extension service to ensure registration status. ADEPIDYN® and Miravis® are registered trademarks of a Syngenta Group Company.

This column was contributed by Illinois AgriNews for Syngenta.

Jeannine Otto

Jeannine Otto

Field Editor