The best treatment option for peanut disease is avoidance, says an Oklahoma State University Extension plant pathologist.
John Damicone, speaking at the Oklahoma Peanut Expo in Lone Wolf, said rotation, site selection and resistant or tolerant varieties should provide the first line of defense against peanut diseases.
“Avoid nematodes,” he said. “And avoid soil-borne diseases.” He said some fields simply may not be suitable for peanut production. “At the least, follow a two to three year rotation program with a non-legume crop.”
Damicone said the northern root-knot nematode may be the most prevalent nematode in Oklahoma with a few peanut root-knot nematodes as well.
“Take a soil sample, especially with a low yields that can’t be explained. Growers may have losses from damage they can’t see above ground, so a nematode assay is a good idea.”
Leaf spot is the No. 1 disease in the state. Management may require a three-pronged approach with variety selection, fungicide applications and rotation. “In 18 years of trials we have seen significant yield losses from leaf spot,” Damicone said. “Farmers can lose half their expected yield.”
He said risk of leaf spot infection is higher on Virginia and runner peanuts, “if growers are not rotating properly. Fungicides last about 14 days and growers may need to stay on a two-week schedule to protect plants. Fungicides protect plants like paint,” he said. “They don’t cure the disease. Be preventive.”
He recommends a full-season fungicide program for Spanish peanuts or with no rotation program. With moderate leaf spot risk with Virginia type peanuts or runners with only one year between peanut crops, a reduced calendar advisory is okay. That reduced calendar approach also works with runner peanuts and a two-year rotation program.
A full-season program would begin in mid-June and continue through September with a 14-day spray schedule. A reduced calendar approach would begin in August and run through mid-September. An advisory-based program follows Mesonet weather information to track conditions favorable for leaf spot development.
Damicone said fungicide options include Bravo, Tilt/Bravo, Absolute, Stratego and Headline.
Soil borne disease control, like nematode management, begins with field history data. He said a record of past infections, varieties planted, rotation and fungicides used previously help growers decide on a program or whether a field is suitable for peanuts. “A field history with Southern blight is critical,” he said.
He said for pod rot diseases, including Rhizoctonia or Pythium or both together, the first management option is variety selection. “Tamrun OL02 or Tamrun OL07 are good choices.” Tamspan 90 would be a good Spanish type for both pod rot and limb rot.”
He said Tamrun OL02 is a good variety selection for pod rot tolerance. Tamspan 90 is a good option with Southern blight, pod rot and limb rot. Other Spanish varieties also show tolerance to limb rot and pod rot. Virginia varieties are bad choices in fields with Southern blight and pod rot. Also, growers should avoid FR 458 in fields with pod rot history.
“Avoid Virginia type peanuts in fields with a history of pod rot,” he said. Fungicide choices include Folicur, Provost, Abound, Headline, Evito and Artisan.
Sclerotinia blight might not be the most prevalent disease in Oklahoma peanuts but it is “the worst disease you can get in peanuts,” Damicone said. In fields with a history of Sclerotinia, he recommends Tamspan 90, Olin, Tamrun OL02 and Tamrun OL07.
“Unless a grower uses Tampsan 90, we recommend fungicides, and they are expensive.”
Endura and Omega are two options for Sclerotinia control. “Apply at the first sign of disease,” Damicone said. Growers can get double duty from these two fungicides. “Endura also controls leaf spot,” Damicone said. “And Omega controls Southern blight.”
He said preventive applications of these fungicides could be too expensive. “If a grower sees a hit or two in the field, he should treat. If he sees flags all over the field, every half-acre or so, it’s too late.”
He said Sclerotinia breaks out “when it cools off.” He said Tamrun OL07 looks best in tests for Sclerotinia tolerance but ASOK-R1 “gets a yield bump, especially with a fungicide application. More improvements are coming with a big bump in value and better grades.”
Damicone said farmers should be vigilant about checking peanuts, “but most peanut disease treatments have to be preventive. However, don’t waste money and don’t use expensive fungicides you don’t need. And avoid snake oils.”