Late-Season Decisions

Fungicide applications at this point often involve levels of disease and projected digging date.

⋅ By Amanda Huber ⋅

Late peanut season may seem like a race to the finish. Unfortunately, it is often a race between diseases, such as leaf spot, and the crop reaching optimum maturity. The dilemma is whether to apply another fungicide treatment to keep leaf spot from defoliating the crop, while also reducing the bottom line, or let the crop finish out with no added protection, saving that input cost.

Fortunately, Extension specialists offer guidance with the late-season disease and insect problems.

Premature defoliation due to leaf spot diseases is shown in the non-treated control at left. Chlorothalonil was used on the peanuts at right in a fungicide trial at the Brewton, Alabama, Agricultural Research Unit.

If, Then Leaf Spot Scenarios

University of Georgia Extension plant pathologist Bob Kemerait offers a series of “if, then” questions and answers for producers on a progression of leaf spot and spraying or digging. 

If you are a few weeks out from digging, he says, continue to assess your field for disease.

“If leaf spot is not a problem, nor white mold, then you may not need the sprayer in the field again. If leaf spot is in the field and not too severe, you might consider one last application,” Kemerait says.

“If you have lost 25% of peanut leaves, anticipate digging within two weeks, regardless of maturity. If you have lost 50%, you have a week to 10 days max.”

Finally, he says, if you have lost 75% or more – dig immediately, as the pods are likely dropping off now.

Factor In Tropical Weather Threats

Alabama Extension plant pathologist and Auburn University assistant professor Amanda Strayer-Scherer offers similar end-of-season suggestions for peanut producers as they begin to plan for digging. 

“Leaf spot diseases can severely defoliate peanuts if not controlled. At this point in the season, you may be questioning whether you need to apply fungicides to manage these diseases.Producers that are close to digging may not need a fungicide application or may need a final application.

“If you have three weeks to go until you are projected to dig, and there is little-to-no disease in the field, then you will not need to put out additional fungicides unless there is a threat of a tropical storm or hurricane,” she says. 

The more complex decisions come when there is a measure of disease in the field. 

Strayer-Scherer says if you are more than two to three weeks away from your projected dig and are seeing some leaf spot beginning to develop, but less than 25% defoliated, then consider applying chlorothalonil at 1 to 1.5 pints per acre tank-mixed with tebuconazole at 7.2 ounces per acre, Alto at 5.5 ounces per acre or Topsin at 10 ounces per acre.

“If you are on your last spray and very little leaf spot is present, then 1.5 pints per acre of chlorothalonil may be all that you need.”

For peanuts that are 50% or more defoliated from leaf spot, another fungicide application will not be beneficial, she says. “Instead focus on selecting a dig date sooner rather than later.”

Look For Soilborne Disease

A white mold fungicide can be added to the last leaf spot application if soilborne disease is a concern and some late-season insurance is needed. 

“If white mold is confined to individual plants scattered across the field, then consider adding tebuconazole. However, if the disease is more severe, consider using a more effective white mold product such as Convoy or Excalia,” she says. 

In an added caution, Strayer-Scherer says to check the pre-harvest intervals for any products used late in the season. Some products such as Alto, Convoy or Excalia have a 30- or 40-day PHI.

Don’t Forget Fertility Applications 

North Carolina State University Extension peanut specialist David Jordan offers these tips for approaching mid-season fertility and late-season disease problems. 

On the subject of disease management, Jordan says producers should start and end with chlorothalonil with three or four sprays in between for a good approach to leaf spot/stem rot control.

“We recommend starting at the R3 growth stage of peanut, but no later than July 10, regardless of growth stage. The year started on the dry side, like 2021, but we might also get in a rhythm of rain in July/August like last year, which was adequate in many places for an outstanding crop.”

For elements such as manganese and boron, Jordan’s suggestion requires keeping a watch on the crop for problems.

“For manganese, if you see an issue, jump on it quickly even if it is before fungicide sprays,” he says. “If applying ‘just in case,’ I suggest the manganese going out with the first or second fungicide spray, and boron going with the second or third fungicide spray.” 

Jordan says that liquid products do not always deliver what dry products do unless one commits to multiple applications, and in some cases, boron and manganese can be compatible in the tank but not always. PG

MyIPM For Row Crops App

From Clemson University, producers have a new tool to help identify and defeat diseases and pests. MyIPM for Row Crops app was developed at Clemson University in collaboration with specialists from a number of land-grant universities and the Southern IPM Center.

The free app is available for Android smartphones in the Google Play Store and for iPhones in the Apple Store. It includes descriptions and photos of key pests and diseases of row crops, as well as information on integrated pest management strategies, including registered pesticides for each pest.

“The app currently includes sections on insects in corn, cotton, grain sorghum, peanut and soybean,” says Tim Bryant, assistant coordinator for the Clemson Integrated Pest Management Program. “It also includes information about diseases in peanut.” 

Help In The Field

The MyIPM app was originally developed in 2012 by Clemson professor Guido Schnabel. The new app was developed using the same structure.

Francis Reay-Jones, Clemson IPM coordinator at the Pee Dee Research and Education Center, says, “The app content is maintained by Clemson researchers in collaboration with Cooperative Extension Service scientists at eight universities across the Mid-Atlantic, Southeast and Southern United States.

“The app is a complement to our Extension production guides and pest management handbook,” Reay-Jones says. “Because the app is entirely downloaded, contents can be accessed from anywhere, including in fields where cell phone networks may be limited.”

The home screen lets users choose the crop and pest or disease. Pest-specific information includes an overview about each pest and its management. The image gallery features a number of insect or disease pictures and symptoms as well as pictures illustrating management solutions. Users can zoom in on each picture. 

Under the feature picture of every pest-specific page, users can choose to list active ingredients and trade names registered in the United States. Active ingredients are color coded according to Fungicide Resistance Action Committee code or Insecticide Resistance Action Committee code. 

On the insect or disease page, tapping trade names displays many available pesticides for the specific insect or disease including active ingredients, efficacy rating, preharvest interval and reentry interval values. To quickly look up active ingredients and trade names for a specific pest, users can tap the insect or disease on the top and choose another pest on the drop-down menu. PG

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