If the field were a disease magnet, then the peanut would be the steel. It's not just one, but many diseases that come at the farmer when they plant the crop.
It has led researchers to devise indexes to help reduce risk and account for variables in production and cultural practices, and pushed breeders to come up with “multiple-disease resistance.”
“Wise management of diseases is an essential part of profitable peanut production,” says Barbara Shew, North Carolina State University Extension plant pathologist.
The basic elements of management include long rotations, cultural practices, use of resistant cultivars, early disease detection, weather-based disease prediction and proper pesticide selection.
Cultural and chemical controls are usually used in combination for maximum benefit.
Breaking the magnet, steel effect is one-part prevention and another part cure.
In the list of general recommendations for the prevention of peanut diseases, rotation ranks at the top for a specific reason.
“The big question about rotation has to do with soybeans,” Shew says. “We really want to stay away from soybeans. Be out of soybeans for three years.”
Continuous peanuts set up nurseries for pathogens. Breaking the cycle with cotton or a grass crop interrupts the disease cycle. Stay away from soybeans.
Two- or three-year rotations are recommended. The idea is, the longer the rotation, the better. Rotations help reduce disease incidence. That's why Extension specialists continue to preach rotation, rotation, rotation.
Research has also shown that conservation-tillage reduces leafspot and other diseases in peanuts. North Carolina State University Extension specialists have developed a Risk Index that can help farmers determine if it's worth making the transition from conventional to conservation-tillage.
The word early in some cases means before planting; in other cases, preventative. “Some early detection begins before the season starts,” Shew says. That would include nematode problems in fields. A sample should be taken early. In most cases, a combination nematicide-insecticide application should be made before planting.
In the case of Cyldrocladium black rot or CBR, it's based on history, but you have to do it before the season starts. “Use resistant cultivars and then think about fumigating,” Shew says. “If the percentage of CBR is less than 10 percent, plant a resistant variety, assuming a good rotation,” Shew says. “If it's more than 10 percent, treat with Vapam or metam sodium, the recommended fumigant for CBR.”
For the most part, treatment for leafspot is a pre-emptive strike. If you wait until you see leafspot, it's too late. That's because it takes about two weeks for the disease to be visible after the infection has occurred. “If we wait, we're too late,” Shew says.
She recommends using weather-based advisories to determine when to spray. These advisories take into account the amount of rainfall and predicted rainfall and recommend the timing for sprays. Although the savings vary from site to site and within years, the weather-based advisories have been shown to save farmers one to two sprays over the course of the season. Fungicides include Headline, Bravo, Folicur, Abound, Stratego, Tilt-Bravo and a new one, Endura.
For stem rot or white mold, Shew recommends following the leafspot advisories. “That seems to work very well.”
In treating peanut diseases with fungicides, it's important to rotate materials. “Resistance management is something we've been preaching for a while now, especially with the newer fungicides that have the potential for resistance,” Shew says.
Because the newer fungicides have specific modes of action, they pose the potential for pathogens to develop resistance if not rotated with different modes of action, Shew says. “We have a lot of choice and different fungicides have different strengths and we want to be able to have those around for a long time to come,” Shew says.