The South is a permanent home of the velvetbean caterpillar. And it lives in soybean fields. Instead of just saying, “there goes the neighborhood,” growers must get rid of the chewing critter. Even though its name sounds like a character on the Cartoon Network, it can wipe out new soybean leaves before moving to older ones and completely defoliating the plant.
Joey Boudreaux raises soybeans, corn, wheat and cotton with his father Ike near LeBeau, LA. They face consistent battles against stink bugs, soybean loopers and the velvetbean caterpillar.
“The red-banded stink bug is probably our biggest problem,” says Boudreaux, also working on his doctorate in agronomy at Louisiana State University (LSU). “But the loopers and velvetbean caterpillars are also on our control list.”
The caterpillar migrates northward from Central and South America into the Southeastern U.S. After overwintering in the southern tip of Florida, it heads up into soybean country.
Soybean is the main host, but the caterpillars occasionally feed on kudzu, peanut and its namesake velvetbean.
Angus Catchot, Mississippi State University Extension entomologist, says the caterpillars “are voracious feeders, usually starting at the top of the plant and feeding downward, causing complete defoliation if not controlled.
“They are primarily foliage feeders but will feed on petioles causing pods to drop to the ground after a significant loss of foliage. They generally are late-season pests of soybeans in much of the South,” he says.
When foliage is removed, they attack tender stems, buds and small bean pods. Eventually they can completely defoliate the plants. They are an annual problem June through September across much of the southern bean belt. Their damage can extend into October.
Rogers Leonard, LSU AgCenter entomologist, says these caterpillars are normally controlled when growers spray for stink bugs or other pests in soybean fields. “They're relatively easy to control, compared to other pests, but can be devastating if high infestation levels are not treated on a timely basis,” he says. “If left uncontrolled, they can defoliate a field in just a few days.”
BOUDREAUX controls them by using a pyrethroid such as Brigade at 2.1-6.4 oz. or with a bifenthrin insecticide. Catchot says other insecticides that are effective in controlling the worms include Orthene, Baythroid, Karate Z, Dimilin, Asana XL O, Prolex, Lannate, Intrepid, methyl parathion, Ambush/Pounce, Tracer, Lavin and Mustang Max/Respect. (For a more detailed breakdown of control measure and labels, go to http://msucares.com/pubs/publications/p2471.pdf.)
Catchot says that if plants are blooming and filling pods and no diseased worms are present, apply insecticide when four or more worms, ½ in. long or longer are present per foot of row, or when 20% foliage loss has occurred and worms ½ in. long or longer are present.
“If you use a shake sheet to sample for velvetbean caterpillars, the action threshold is eight caterpillars per foot of row before bloom and four caterpillars per foot of row after bloom,” he says. “If you use a sweep net, the action threshold is 75 caterpillars per 25 sweeps before bloom and 38 caterpillars per 25 sweeps after bloom.”
Leonard says the worms may emerge at any time of the season, but are usually detected during weekly field scouting. The very southern range of soybean acreage usually is infested with varying levels of this pest annually and some fields require treatment.
“About every three to five years Louisiana experiences a severe outbreak, with considerable acreage that has to be treated” he says.
Boudreaux says dry weather in early summer kept 2009 applications to a minimum. “However, late ‘wheat beans’ ran into more insect problems,” he adds. “We had to go with three applications of a pyrethroid to get them controlled.”