Don't neglect foliar, soil borne diseases in peanuts

Whether they’ve been at it awhile or whether they’re new to the crop, all peanut growers have this in common: They’ll face disease pressure.

The changes in the peanut program didn’t take away the need for “a substantial level of protection,” particularly with respect to soil borne diseases, says Jay Chapin, Clemson University Extension peanut specialist.

Varieties bred to grow under Virginia and northern North Carolina conditions are increasingly grown further south. A full two-thirds of the projected 50,000-plus peanut acres in South Carolina will be in Virginia-type varieties.

“We’re taking varieties that were developed under North Carolina and Virginia conditions and dragging them down south into a different disease situation than they were bred for,” Chapin says. “Most Virginia-type varieties weren’t bred to have a high tolerance for white mold like some of the runner varieties are. We’re also growing Virginia varieties under more intense leafspot pressure.

“Our experience has been that with both leafspot and soil borne diseases, particularly white mold, we need a substantial level of protection,” Chapin says.

Chapin places South Carolina peanut growers in four categories: traditional growers; growers with two years of experience; growers with one year of production; and new growers.

“But what it comes down to is that over 80 percent of our acreage this year will be on new peanut land,” Chapin says.

As for the control and protection needed on peanuts, Chapin categorizes that as well in levels.

Level one is a basic five-spray chlorothalonil or Tilt/Bravo program for leaf spot control only. This is an option for dryland production with no peanut history and no soybean history in the last five years. The grower makes the assumption that there is essentially no soil borne disease pressure.

“Although we can make some very high yields on new land with these minimal programs, some additional soil disease treatment usually pays off,” Chapin says. All treatment programs begin with Bravo or Tilt/Bravo treatment no later than 45 days after planting. For leafspot-susceptible varieties under irrigation, tank-mixing Bravo with the 30-35 day after planting Cadre application is also recommended. These are about $35 per acre programs.

Level two substitutes products with soil disease efficacy at the 60 and 75 days after planting treatments. “This is the minimum level of soil disease control that I prefer even on new land without a soybean history,” Chapin says. “These are about $55-$60 per acre programs and the extra investment usually pays off. Typically, we alternate a non-strobilurin like Folicur or Artisan with one of the strobilurins (Abound or Headline).”

Level three is the normal level of soil disease protection on rotated peanut land. “This is what you need if there is a recent — five-year — soybean history,” Chapin says. “In such a rotation, you can expect significant white mold pressure.”

In a level three program, “we typically apply four soil disease treatments at about 60, 75, 90 and 105 days after planting, with no more than two total strobilurin treatments.” The cost is in the $75 to $80 range. Under irrigation, two high rate (18 ounce) applications of Abound at 60 and 90 days after planting have also performed well. “In soybean rotations, we are concerned about Cylindrocladium black rot (CBR),” Chapin says. “Tim Brenneman’s research at Tifton has shown that at least we can get some suppression of CBR when we have Abound, Headline or Folicur in the program.”

Level four treatment only applies to rotated peanut fields with a proven history of severe white mold loss under level three treatment programs. “Here we use higher rates of Moncut or Artisan for white mold as well as at least one strobilurin application,” Chapin says. “Cost can be $100 per acre and profitability becomes questionable under dryland production.

“White mold is our major soil disease concern,” Chapin says. “We also have significant problems with both Rhizoctonia limb rot and CBR, but white mold is the most consistent threat.

“We try to design treatment options that cover most of the bases and minimize the risk of resistance within each level of protection, yet still give growers some flexibility in materials choices,” Chapin says.

“We know that leafspot is a concern for new growers just as it is for growers with a history of peanut production. If they don’t follow a good leafspot control program, they’re going to have serious defoliation.

“If they give up and don’t use an additional application when we have tropical storms delaying harvest, it can be a costly loss,” Chapin says.

Most new growers quickly take diseases seriously and discover that fungicides pay. “The only way to make money with peanuts is to make high yields,” Chapin says. “And the only way to have high yields is to prevent disease. Our experiment station and on-farm tests have documented yield increases and profitability of soil disease control.”

The bottom line is, soil disease and leafspot disease control pays. White mold is often the most severe under drought conditions. “We do modify our application intervals to account for weather conditions,” Chapin says. “With the level of soil disease pressure we have, our growers have to use the weather forecast as best they can to try to get preventative treatment washed into the soil under dryland conditions.”

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