Site selection, rotation, variety choices and fungicides play crucial roles in managing peanut diseases and nematodes, says an Oklahoma State University Extension plant pathologist.

John Damicone discussed problems and management options during the Oklahoma Peanut Expo, held recently at Lone Wolf.

“For nematodes and soil diseases growers need to rotate to a non-legume crop for at least two or three years,” Damicone said. “Continuous peanuts mean more and more disease pressure.”

He said growers should take soil and root samples if they suspect nematode infestations. “Growers will know if they have peanut root-knot nematode because damage is more obvious than for northern root-root knot nematode,” he said. “Roots will have big galls.

He said rotation is the best management option. “Growers can use nematicides but they are expensive.”

He said leaf spot management depends on variety selection, rotation and fungicides. “Growers want to keep defoliation to less than 50 percent by digging time,” he said.

Over a period of years, fungicide trials have shown significant yield advantages with Bravo applied full-season compared to untreated checks. “We noted better control on runner-type peanuts than with Spanish,” he said. “Runners are less susceptible to leaf spot. Virginias are more like Spanish and we typically see more leaf spot on Spanish varieties.”

He said rotation is a key and with runner varieties planted in rotated fields the risk for leaf spot damage is reduced. Growers might get by with a reduced spray program if they use the leaf spot advisory program. Preventive programs involve scheduled fungicide applications every 14 days, beginning the first of July and running through September. “The advisory program is based on weather conditions,” Damicone said. “Research shows we get more leaf spot with the advisory than with a 14-day schedule, but yields are equal.” Another reduced program involves applications in August and early September. “This program is only recommended for rotated fields planted with runner varieties.”

Fungicide options for leaf spot include Bravo, Tilt/Bravo and Stratego.

Field history is critical for managing soil borne diseases, Damicone said, and variety selection, rotation and fungicides are important factors.

Pathogens include southern blight, limb rot and pod rot. “Limb rot often causes pod rot along with Pythium,” Damicone said.

Growers have few choices for variety tolerance, but he recommends growers with field histories of the pathogens stay away from Virginia-type peanuts and FR 458. Tamspan 90 may have some tolerance to pod rot or limb rot. Fungicide options include Folicur, Provost, Abound, Headline, Evito, and Artisan.

None of those has much effect on pod rot, Damicone said. “Abound may have some effect.”

Sclerotinia blight may cause significant crop injury and is difficult and expensive to control, Damicone said. Field history, again, is a key management tool. Variety selection is also important. He said Tamspan 90 might be the best bet followed by Olin, Tamrun OL07 and Tamrun OL02.

He said determining when to spray is difficult “because fungicides are expensive. A grower can spend as much as $120 per acre. I recommend growers wait until they see disease symptoms. But don't let it get out of hand. One hit every 100 feet is too much disease pressure. Using a crop consultant may pay.”

Damicone said fungicide application shows significant advantage and preventive treatments do a better job of controlling the disease than waiting for symptoms. “But yield is about the same.”

He recommends that growers watch their crops carefully and refrain from applying unnecessary fungicides. “Don't waste money. If farmers wonder if they have disease or not, they probably don't,” he said. “Use fungicides to limit losses from disease you know you have.”

Damicone said fungicides do not cure diseases but protect non-affected plants.