Sclerotinia blight top yield robber It didn't come until the middle of August, too late for most Virginia-Carolina peanut growers to take advantage of this year. But, the EPA Emergency Exemption, Section 18, allowing growers to use fluazinam (Omega 500) to control Sclerotinia blight, gave growers reason to believe they can finally slow this rapidly spreading disease.
Sclerotinia blight has spread from Virginia into every peanut producing county in North Carolina. North Carolina State University plant pathologist Jack Bailey calls the disease the Number One threat to peanut production in the state. He predicts it will continue to spread across already infested farms and to new farms.
Speaking to farmers at the 48th Peanut Field Day in Lewiston-Woodville, N.C., Bailey urged growers to develop long-term plans to identify and control this destructive disease.
"There is no guarantee that we will have Omega 500 next year," Bailey says. "We will have to get another emergency exemption or a federal label before we can use the product again."
Even with an effective chemical control like Omega 500, Bailey stresses that growers must depend on cultural practices to protect peanuts from this yield robber. He showed growers how to positively identify the disease and encouraged them to mark infected areas on field maps. Go to the World Wide Web site http://www.ces.ncsu.edu/depts/pp.notes/Peanut/gallery/ to see pictures of symptoms and a complete discussion of the disease.
After vines have lapped in the row middles and peanuts have received adequate moisture, Sclerotinia symptoms begin to show up as straw colored lesions on the central portion of otherwise green stems.
"I've promoted field mapping for a number of years," Bailey says. "Scout and mark the location and severity of diseases in each field. Use these maps to focus disease management on hot spots the following year."
Bailey says cotton, corn and wheat are good rotation crops to reduce the spread of Sclerotinia.
Avoid soybeans since the fungus can survive on soybean plants.
Avoid NC 7, NC 9, NC 12C and Gregory peanut varieties in fields with a history of the disease. VA 98R, VA 93B and Perry varieties have some resistance to the blight.
Tillage tends to reduce the amount of the fungus in the soil, and Bailey says minimum-tillage or strip-till probably will not increase the disease noticeably. But, moving soil from an infested field to a disease-free field can spread the disease. Clean dirt off equipment before moving from field to field, and work from least infested fields to most infested fields when tilling and planting.
"In July, when vines are rank in wet seasons, pruning the top few inches of vine off with a sharp bushog or mower can open up the canopy and allow the vines to dry off more quickly," Bailey notes. Unnecessary applications of foliar fungicides, especially chlorothalonil, can lead to an increase in disease severity by causing the fungus to be more aggressive.
Vine damage due to unnecessary trips over the field can lead to more disease by making the tissue more vulnerable to infection."
Bailey encourages growers to listen to and follow the advice of weather based advisory services to determine when to apply leaf spot fungicides as well as when to apply a fungicide to control Sclerotinia.
The only currently labeled fungicide for Sclerotinia control is Rovral (plus Nufilm).
With the emergency exemption at the end of this season, growers were able to use fluazinam. Bailey says this material is the most effective chemical for controlling Sclerotinia blight. It is also suppressive to white mold and Rhizoctonia limb and pod rot.
It does not control leaf spot or CBR. Bailey also notes that fields with heavy infestations of southern stem rot or Rhizoctonia limb and pod rot may still benefit from the use of products like Folicur, Montero and Abound.
"Chemical controls for Sclerotinia blight generally don't pay unless greater than 10 percent of the plants are expected to become diseased," Bailey says. "This is likely to occur again in areas where this level of severity has been seen in the past, vines are close to lapping in the row middles and weather conditions are favorable, especially in rainy conditions."