Vigilance for peanut insect pests recommended

Insect pests have not established themselves as a reason for significant investment in West Texas peanuts so far, says a Texas A&M entomologist, but farmers should exercise caution to make certain they don't sneak in and damage profit potential.

Scott Russell says West Texas remains a relatively new peanut area, with about 20 years production history, so insects are more sporadic pests than annual problems. He offered suggestions for managing pests throughout the peanut growing season during a recent production seminar in Brownfield.

He starts with potential at-planting pests.

“Scout for white grubs,” he says. “Those are the larval stage of the May and June beetles and can be a sporadic problem in peanuts. White grubs can reduce stands and are more likely to show up following infestation in a grain crop.”

He says distribution through the field will be “clumped. So there is no need to treat the whole field. Scout and isolate the problem areas before treating.”

He says in some cases growers may need to replant and use an at-planting inoculant.

He also considers wireworms, larvae of click beetles, sporadic pests and most troublesome following a grass or grain crop. They also may reduce stand, but may be more troublesome when they feed on pegs.

Wild hogs

He turned to another, larger, pest that appears to be increasingly difficult to manage. “Wild hogs are attracted to carbon dioxide given off by newly planted seed,” Russell says. “Hogs also cause trouble at harvesttime.”

Cracking-time pests include wireworms, southern corn rootworms and thrips.

“Southern corn rootworms are very small, light colored caterpillars. They like high organic matter soils and moisture. Farmers in the Southeast often apply a preventive treatment for Southern corn rootworm but we recommend scouting and monitoring larval activity. We don't suggest making treatment decisions based on adult populations.”

He says tobacco, Western flower and onion thrips may infest peanuts. Western is the most abundant. “All three can infect peanut with tomato spotted wilt virus,” Russell says. ‘In some areas, that's reason to control but we have seen no economic incentive to treat on the Plains. We don't have significant numbers of TSWV infestations, not even on weed hosts.”

He says thrips may stunt plants, “but we have no documented returns in yield or maturity by controlling them. We also see no grade advantage.”

Foliage feeders

Foliage feeding pests include corn earworms, armyworms, cutworms, and clover worms. “Some years infestations are heavy enough to justify pesticides,” Russell says.

Again, the key is to scout thoroughly and determine if pest populations warrant the investment. He says a black cloth, 40 inches wide, offers the best scouting tool. “With the black cloth, even the smallest pests show up.”

He says growers should count the number of worms per foot of row in several locations. “(Foliage feeding) pests tend to be disbursed across a field fairly uniformly.”

Still, he says peanuts can take significant defoliation without adverse effects on yield. He says tests have shown peanuts taking up to 60 percent foliage loss and still making a good crop. Economic threshold, he says, is six to eight worms per foot of row. “A number of products are effective and with limited effect on beneficials.”

Russell says grasshoppers occasionally build populations that require treatment. “We don't have a specific economic threshold, but we need to watch the numbers of nymphs. (Nymphs can't fly.)”

He says canopy size and general plant health also figure in treatment decisions. Wet conditions may kill some off. “But if we see a lot of nymphs and significant damage, we may need to treat.”

Near harvest

Caterpillars, grasshoppers and spider mites may cause problems near harvest. Spider mites like hot, dry conditions and may come in after beneficials are removed. They can cause significant damage by sucking juices from the plants. “As numbers of spider mites increase, farmers may see webbing.”

He says a number of pests may damage roots and pods. “Lesser cornstalk borers can show up at any time during the season. These are soil-dwelling pests found on plant stalks just below the soil surface, especially on peanut pods and pegs. They may open pods up for aflatoxin.”

Russell says economic damage may occur when 10 percent to 15 percent of plants are infested.

“Look for silken tubes. Lesser cornstalk borers also like dry soil, so scout regularly in hot, dry weather.”

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