Managing peanut pathogens in West Texas, despite a somewhat arid climate, poses a bigger challenge than folks might think.
“We have all the diseases peanut farmers in the Southeast and Virginia and the Carolinas have,” says Jason Woodward, Extension plant pathologist in Lubbock. “And we have a few others as well.
“The situation here has changed from ten years ago. We're no longer planting peanuts in virgin soil.”
He says disease infection does not come with the frequency that occurs in the more humid environment of the Southeast. “But disease management still presents a challenge.”
Woodward says the challenge was particularly daunting this year as farmers enjoyed better than average rainfall throughout the growing season. Leaf spot, for instance, was significantly more prevalent than usual. “We're a bit concerned about leaf spot,” Woodward says. “Even though we're basically in an arid environment, most years we can still incite leaf spot epidemics with irrigation.
It's not as common as Sclerotinia blight, but about one in five years leaf spot may be a problem.”
He says growers saw a good bit of early and late leaf spot in 2006, a dry year. “It initially showed up in August, when conditions were very dry.”
He says the wet summer of 2007 was very conducive for leaf spot. “But the potential for infection is always there. Spores are always in the soil so growers need to be mindful of the potential for infection. Leaf spot will not be as serious every year as it is in the Southeast, but we have the potential for it every year.”
Woodward says leaf spot is relatively inexpensive to control. Most fungicides used on peanuts provide some level of leaf spot suppression. Maximum efficacy is obtained when these products are used in a preventive manner. “Growers off the Caprock need to be more mindful of leaf spot, as the disease is generally more of a problem than it is on top of the Caprock.”
Pepper spot is another foliar disease that may occasionally show up in West Texas peanuts. Fortunately, management options for pepper spot are similar to those available for leaf spot.
Woodward said Sclerotinia blight may be a more damaging disease and “is on the rise in Gaines County, the number one peanut county in Texas. Growers in Gaines County must be aware of disease history within a field, and scouting is critical. As with leaf spot, maximum control of Sclerotinia is obtained when fungicides are used preventively.
Woodward is trying to develop an advisory program that would alert growers when climatic conditions favor Sclerotinia development.
He found one field with Sclerotinia in Collingsworth County, the second largest peanut county in the state. “That find was in a field with a history of the disease,” he says.
“Over the past two growing seasons Sclerotinia has flared up in the second week of July,” Woodward says. “We usually start harvest in September so we have a long time for the disease to develop. He says a better understanding of the biology of the organism will help growers time fungicide applications for best benefit.
An advisory system will provide some of that information. “We can time applications more effectively and save money in the long run,” he says. Fungicide options for Sclerotinia control are limited primarily to Omega and Endura. He says growers must use any fungicide strictly according to label directions and avoid overuse to prevent resistance.
“In Gaines County, growers should scout for Sclerotinia and apply fungicides as timely as possible. We're not following an exact preventive schedule but we do recommend applying a first fungicide prior to or as soon after disease develops as possible.”
Woodward says Botrytis blight, another fungal disease that may resemble Sclerotinia, is “an occasional problem. We would like to conduct a survey and determine the incidence of Botrytis as compared to Sclerotinia. We're not certain how severe it is, but it could become a significant problem.”
Woodward says no fungicide is currently labeled for Botrytis control in peanuts.
Verticillium wilt “is a major problem in peanuts. Most peanut farmers rotate with cotton (also a host for the Verticillium wilt pathogen). We're seeing an increase in incidence of this disease as well,” he says. “We have no chemical options for control in either cotton or peanuts. Fumigation is the only option and the cost is prohibitive.”
Rotation helps little. “The fungus can remain viable in the soil for up to 15 years without a host,” Woodward says. “Rotation will not eradicate the pathogen. It may reduce severity.”
He says peanut breeders are screening cultivars for resistance to Verticillium wilt. Cotton breeders have identified some resistant germplasm, he says. “Newer cotton varieties need to be evaluated, however.”
Verticillium has been a minor problem in peanuts. “But with a cotton and peanut rotation, the problem is becoming more severe.”
Woodward says pod rot takes the top spot as the number one disease in peanuts across Texas. “Sclerotinia is more difficult to control but pod rot affects more acres and is quite costly to control. We have a wide distribution of pod rot and it is also difficult to control. We have limited fungicides available.”
He says pod rot develops from several fungi with Rhizoctonia and Pythium being the most prevalent. “Fungicide options are limited depending on which organism is in the field. Abound is the premier fungicide for pod rot. It is a good product for Rhizoctonia and provides some suppression on Pythium.”
He says incidence of pod rot in 2007 was “intermediate but was severe in fields with a history of infestation.”
Virginia type and Valencia peanuts, “historically have more pod rot problems.”
Rotation may help but pod rot also shows up as a seedling disease in cotton, the usual peanut rotation crop.
“Preventive application is the best control strategy, where growers have a history of infection. Every field has some level of the organisms that cause pod rot but not all have economically limiting levels,” he says.
Rotating a grain crop would help and Woodward says that option may be more realistic with better grain prices. “Milo is a good option to reduce soilborne fungi,” he says. “With better prices, it's a better alternative for the grower.”
Woodward says rotation offers several positive opportunities for peanut and cotton farmers. “Disease suppression is one of them.”
He says a peanut monoculture “is never a good idea. Growers may get away with it for a year or two on virgin soil, but it will cause long-term problems. He says one year out of peanuts will help. “Two years out is even better. And, depending on the disease, a three or four year rotation is ideal.”
Woodward says tomato spotted wilt virus is rare in West Texas, “nothing like it is in South Texas and the Southeast. “It can be a real problem in South Texas,” he says.