Wallaces Farmer

Be ready to combat this foliar soybean disease early to protect yield.

June 17, 2020

3 Min Read
Frogeye leaf spot on soybean plants.
SYMPTOMS: Frogeye leaf spot begins as circular to angular dark, water-soaked spots on soybean leaves and develops into brown spots.Courtesy of Syngenta

With warm weather, now is the time to plan for any soybean diseases that may crop up. Wet spring weather left behind moisture in the soil, and the rising warm temperatures provide a conducive environment for foliar diseases to thrive and infect soybean plants. University researchers have identified frogeye leaf spot as one of the top soybean diseases observed in 2019.  

Many growers are familiar with this disease and its ability to overwinter in crop residue. However, less familiar in Iowa is frogeye leafspot that is resistance to strobilurin, the active ingredient in several foliar fungicide products. 

James Hadden, technical fungicide lead for Syngenta explains, “Strobilurin-resistant frogeye leaf spot is common in the southern U.S. However, the disease is spreading, and we’re seeing more cases in Iowa every year.” 

Watch for early symptoms  

Symptoms are not always visible in its early stages, and it is often too late to effectively manage the disease when symptoms become widespread. If fields have a history of frogeye leafspot or there were cases of it in neighboring counties, Hadden encourages growers to take preventive measures to protect soybeans from infection. To prepare for potential infection of soybeans by this disease, consider the following: 

Warm temps. Frogeye leaf spot thrives in warm temperatures (77 degrees to 86 degrees F) and humid conditions (greater than 90% relative humidity). Frequent rain can also increase the geographic range of the disease. 

Dark spots. When scouting for frogeye, look for small dark spots on the leaves. Center lesions become gray to brown and have a reddish-purple margin. Another symptom is irregular patterns of blighting on the leaf. 

“Strobilurin-resistant frogeye leaf spot can be especially devastating because it’s harder to treat with older fungicides,” Hadden says. 

Conditions, timing

If frogeye infection is likely, scouting soybeans often and applying a fungicide at the R3-R4 growth stages can help save yield and improve your return on investment. Hadden recommends Miravis Neo fungicide for soybeans. 

“Miravis Neo helps growers reap more bushels more often through its disease control from three active ingredients: azoxystrobin, propiconazole and Adepidyn technology,” he says. “In addition to plant-health benefits from two of the three active ingredients, Miravis Neo is extremely broad spectrum. When applied at the optimal timing, growers can depend on this fungicide product to clean up both susceptible and strobilurin-resistant frogeye leaf spot, as well as other key soybean diseases like brown spot, aerial web blight and more.” 

If the risk of disease rises, growers have the time and tools to protect their crops and profit potential this year, he adds. The disease may cause severe defoliation during warm, humid weather. Frogeye leaf spot can be distinguished from other soybean foliar diseases by the reddish-brown or purple ring surrounding the round leaf spots. 

Frogeye can occur at any time during the growing season but seems to typically show up after soybean flowering. Young leaves on the tops of the plants tend to be most susceptible. Infection and disease development are favored by warm, humid weather. 

Source: Syngenta, which is solely responsible for the information provided and is wholly owned by the source. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset. 

 

 

 

Subscribe to receive top agriculture news
Be informed daily with these free e-newsletters

You May Also Like