Early fungicide application protects soybean yields

Topguard, a fungicide that provides the longest lasting disease control of any fungicide registered for soybeans, protects against Cercospora leaf blight and strobilurin-resistant frogeye leaf spot.

Growers now have a new option to control two devastating diseases that reduce soybean yield and profit potential.

Topguard, a fungicide that provides the longest lasting disease control of any fungicide registered for soybeans, protects against Cercospora leaf blight and strobilurin-resistant frogeye leaf spot. For best control, say experts, apply Topguard when it will be most effective.

Soybean growers will protect their yield potential if they make the initial application of Topguard at first flowering to control Cercospora leaf blight (Cercospora kikuchii), the No. 1 disease affecting soybeans grown in the Gulf South region.

Topguard is a broad spectrum triazole fungicide, which is highly systemic, and is stable on leaf surfaces. It is made by Cheminova. When applied early, Topguard protects late and soybeans yield more, according to university studies.

When applications of Topguard were made at very early or initial flowering, yields increased by as much as 15 percentcompared to untreated check plots in a research study conducted by the Louisiana State University Agricultural Center. Disease severity was reduced from 84 percent to less than five percent.

“Growers have been spraying at the wrong time, with less effective materials,” states researcher Ray Schneider, an LSU research plant pathologist. He began evaluating early applications of Topguard after his extensive research proved it provided more effective residual disease control than other soybean fungicides.  His research also clearly demonstrated that Louisiana growers weren’t getting effective control with products applied later in the season.

There’s a significant lag time between when the pathogen that causes Cercospora leaf blight infects the plant and when the symptoms emerge, he explains. He recommends applying Topguard at initial flowering (early R1). It will control or stop development of Cercospora leaf blight within the plant, minimize disease symptoms later in the season, and consequently, protect yield potential. 

 “Topguard is known to have very long residual activity,” he explains. “It is very effective applied at observation of first flower in soybean fields. One application provides much longer protection than other types of fungicides.”

Cercospora leaf blight is prevalent all over the state, says Boyd Padgett, LSU AgCenter Extension plant pathologist. “In some years, it is worse than others. But it is a disease that you will always be able to find.” In the most severely infected fields, if untreated, growers can lose as much as 25 percent in yield.

Padgett encourages growers to determine early which fields to treat. “If you treat when you see the symptoms of the disease, it is too late,” he stresses. “If you have a soybean that has good yield potential, you need to protect that investment.”

Howard Anderson, a crop consultant based in Wisner, La., evaluated Topguard in the field. “The key to controlling Cercospora leaf blight appears to be treating earlier, beginning at the R1 stage, with a systemic fungicide that translocates to new growth,” he notes.

“Topguard offers this type of activity. In a two-application test, soybeans treated with Topguard yielded 85 bushels per acre compared to 70 bushels for other standard treatments."

Topguard can be applied aerially or as a foliar ground-spray at 7 to 14 ounces per acre. It is most effective applied at first-flower, although a second “booster” application can be made at R3, if needed.

Topguard can be tank-mixed with other fungicides such as Headline and Quadris for a broader disease control spectrum and is also labeled to be tank-mixed with most registered soybean insecticides and herbicides.

Topguard is also highly effective as a treatment to control strobilurin-resistant frogeye leaf spot (Cercospora sojina) confirms research conducted by Melvin Newman, University of Tennessee Extension plant pathologist.

If growers aren’t getting the level of control they expect from strobilurin fungicides applied for frogeye leaf spot control, they may have resistance of the causal organism and will benefit from switching to Topguard, says Newman.

He notes that within two years, strobilurin-resistant frogeye leaf spot has spread from one field in western Tennessee to documented cases in 15 counties in five states. Growers are ahead of the problem, as most fields don’t have the resistant strain. But that advantage may not last much longer.

In 2010, a west Tennessee farmer identified the first patch of strobilurin-resistant frogeye leaf spot. Just two years later, resistant frogeye leaf spot has been found in 15 counties in at least five states, reports Newman.

“If you apply a ‘strobi’ fungicide at the right time and you see very little control, you need to change chemistry,” he advises. “We suggest switching to the triazole class of fungicides. Topguard is one of them.”

Plan to treat frogeye leaf spot on time, emphasizes Jason Hamlin, a crop consultant for North Delta Crop Consulting near Dyersburg, Tenn. He advises growers to treat fields no later than at stage R3, early pod set.

 “In an untreated field, frogeye leaf spot (resistant or not) can easily reduce soybean yields by as much as 30 percent,” he observes.

Hamlin evaluated Topguard as a foliar spray applied at R3 on strobilurin-resistant frogeye. “In the field plot, Topguard yielded two bushels per acre better than Stratego YLD, and 14 bushels per acre better than Headline alone,” he notes.

Topguard can be applied aerially or as a foliar ground-spray at 7 to 14 ounces per acre. Topguard can be tank-mixed with other fungicides such as Headline and Quadris for a broader disease control spectrum. It is also labeled to be tank-mixed with most registered soybean insecticides and herbicides.

Soybean growers should see their local dealer or go to www.cheminova-us.com for more information about Topguard.

 

 

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