Don’t Suffer Yield Loss from Frogeye Leaf Spot
April 3, 2019
Frogeye leaf spot regularly poses a risk to soybean production in the south. With an increasing prevalence of strobilurin resistance, managing this disease can be especially challenging.
Fortunately, effective disease management programs that include a variety of strategies can help growers prevent and manage resistant frogeye leaf spot in soybeans. Such strategies include planting resistant varieties and applying a fungicide with multiple of modes of action, like Stratego® YLD.
Fungicide resistance spreading throughout the South
Due to the wet conditions in the Lower Mississippi River Valley, frogeye leaf spot is an ever-present threat to soybean production in the Delta. In recent years, frogeye leaf spot is of even greater concern as strobilurin-resistant strains are increasingly prevalent in this region.
Strobilurin-resistant strains of frogeye leaf spot can cause damage during crucial early development growth stages, especially in later-planted soybeans. According to North Carolina Cooperative Extension Service, frogeye leaf spot also can cause devastating yield losses of up to 30 percent when there is extensive leaf blighting.
Fungicide resistance happens naturally due to a complex interaction between fungicide mode of action, frequency of fungicide use, application practices, cropping system and the genetic diversity of the fungus. Every time a fungicide application is made, the treatment kills the fungi with genetic makeups that are more sensitive to the mode of action. On the other hand, the less sensitive or naturally resistant individuals may survive and reproduce.
“Foliar fungicides can be extremely effective at managing frogeye leaf spot,” said Tom Allen, plant pathology professor and Extension specialist at Mississippi State University. “However, we have limited the number of active chemicals due to widespread resistance within the frogeye leaf spot fungal population to strobilurin, or Qol, fungicides. That leaves using either triazole or thiophanate-methyl fungicides as a management alternative.”
While frogeye leaf spot is a constant threat in the Lower Mississippi River Valley, it may not threaten every growing season in the Mid-Atlantic states.
“Frogeye leaf spot is something we may not see if there are several dry years in a row,” said Steve Koenning, professor emeritus of plant pathology at North Carolina State University. “But, in wet years, frogeye leaf spot tends to be widespread and causes devastating yield losses.”
Unfortunately, unpredictable weather makes it difficult to predict when frogeye leaf spot may be widespread in your area. Disease management strategies that focus on prevention will help keep your crop protected when conditions favor development of frogeye leaf spot.
Protect your soybean fields
To protect your soybean fields and prevent the spread of strobilurin-resistant frogeye leaf spot, it is essential to incorporate a variety of disease management practices. Recommendations include:
- Plant disease-resistant varieties
“One of the best alternatives for managing frogeye leaf spot is planting soybean varieties that are disease resistant,” Allen said. He recommends growers pay careful attention to unbiased university trials from multiple locations and weigh company literature about how varieties respond to frogeye leaf spot and other soybean diseases.
For maximum prevention, Koenning recommends planting varieties that have been screened specifically for resistance to frogeye leaf spot. In addition, he suggests growers plant high-quality, disease-free seeds to prevent the introduction of yield-robbing diseases, like frogeye leaf spot.
- Scout fields on a regular basis
Regularly scouting your fields for disease can help guide future disease management decisions. Remember that it is important to keep notes of disease incidence and severity to make an informed decision about how to manage disease and prevent further losses. “If there are signs of any disease symptoms, growers should take a sample and get a diagnosis from a plant disease clinic,” Koenning said. “From there, growers will likely be referred to a website that will help them determine the various fungicide options.”
- Apply a fungicide with multiple modes of action
Strobilurin-resistant frogeye leaf spot can be well-managed by fungicides with a triazole component, such as Stratego YLD. Using a fungicide that includes multiple modes of action is another good practice for more effective management. To prevent additional development of resistance, the fungicide should be tank mixed or rotated with fungicides belonging to a different group that are also labeled for frogeye leaf spot.
- Apply fungicides at the full use rate
To maximize the effectiveness of a fungicide, it is important to apply the full use rate. Not using full label rates can lead to inferior frogeye leaf spot management, as well as reduced efficacy of other diseases. Reduced application rates also can create the need for additional fungicide applications, an added expense for your operation.
- Rotate to a non-host crop
The fungus that causes frogeye leaf spot overwinters on soybean residue, making it possible for it to survive until the next growing season. If possible, Allen recommends growers rotate to corn, cotton or rice in some growing seasons to give the residue time to break down, so the pathogen can die off before soybeans are planted again.
Bayer solutions for managing frogeye leaf spot
Timely foliar fungicide applications help protect soybean plants from fungal diseases such as frogeye leaf spot. For growers, a fungicide decision is a matter of considering production needs, field history, commodity prices, proper timing and risk management.
Stratego YLD fungicide features the latest triazole technology for soybeans. With dual modes of action, it provides built-in resistance management, as well as preventive and curative activities and systemic movement for broad-spectrum, long-lasting control of tough diseases like frogeye leaf spot, among others.
Before applying any fungicide, please read the entire label for the best possible results and to confirm that the product is effective on the disease you need to control. Not every product is suitable for every situation, and correct application technique will ensure the most effective results.
©2019 Bayer Group. Always read and follow label instructions. Bayer, the Bayer Cross and Stratego are registered trademarks of Bayer Group. Stratego YLD is not registered in all states. For additional product information, call toll-free 1-866-99-BAYER (1-866-992-2937) or visit our website at www.CropScience.Bayer.us. Bayer CropScience LP, 800 North Lindbergh Blvd. St. Louis, MO 63167.
