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With fewer weevils, bollworms: Plant bugs find room in cotton

Nobody will ever write a song about plant bugs or erect a statue of one. The insects are simply not capable of causing as much damage to cotton as boll weevils and tobacco bud-worms have caused.

But cotton producers shouldn't underestimate them either. The critters can knock 100 pounds to 200 pounds off cotton yield potential and/or significantly delay crop maturity, according to entomologists.

And plant bugs are rising up the list of top cotton insect pests, beneficiaries of a low spray environment created by boll weevil eradication and Bt cotton.

So it's little wonder that cotton producers, consultants and entomologists are wanting to get to know the plant bug a little better. Here's a few characteristics:

  • It's hardy. According to Scott Stewart, cotton insect specialist at University of Tennessee's West Tennessee Experiment Station in Jackson, Tenn., plant bugs overwinter as far north as Canada, so surviving until spring in the Delta is no challenge.

  • It's resistant to some insecticides. “Depending on location, there is documented resistance by plant bugs to Bidrin, pyrethroids and methyl parathion,” Stewart said.

  • It's mobile. Adults can be in a cotton field in the morning, but could be gone by that afternoon. “It's hard to find a habitat they don't live in, and it's easier to list what they don't eat than what they do,” Stewart said. “It's difficult to try to reduce populations of this insect by managing things outside the field. And now they've been elevated to much more of a major pest status.”

The first step in a good plant bug management program is finding the insects, notes Stewart — a skill that requires growers to change tactics as the season goes on.

“Early in the season, a sweep net is an effective tool — we have adult populations and small plants. Later in the season, you need a drop cloth and visual examinations. You're looking for nymphs in the mid-canopy, inside squares, behind bracts.”

Nothing substitutes for footprints in the fields, according to Somerville, Tenn., crop consultant Len Doyle. “The key to scouting, no matter what the pest, is to get in the fields two to three times a week and watch for changing patterns.”

Doyle and his son, Clint, consult for cotton producer Willie German on about 3,600 acres. “We start scouting during the first two weeks of squaring, going with a threshold of 7.5 plant bugs per 100 sweeps of the net,” Len said.

Between the third week of squaring and first bloom, they employ a two-stage scouting program. First, they sweep for adults, adhering to a treatment threshold of 15 bugs per 100 sweeps. They also begin using a drop cloth to count larvae and nymphs, watching for a threshold of two bugs per 6 feet of row.

Plant bugs don't always cause damage when present in the field, so the Doyles augment captures with visual inspections of fields and individual plants.

“We don't let our square retention drop below 80. We don't let it happen,” Len said. “If we see a pattern developing over two to three days, and the retention is dropping, we're going to spray.”

Stewart added that plant bug scouting often becomes more difficult later in the season. “Then you have adult and nymph populations, visual scouting is difficult, sweep nets are only good at collecting adults and square retention isn't as reliable anymore, but the plant is naturally senescing fruit.”

Stewart suggests looking for dirty blooms, which indicate that squares have been fed upon. “If you see those types of things more frequently, you know you need to start looking for plant bugs. The good thing is the plant can tolerate a few more plant bugs as the season progresses.”

The Doyles point out that if a plant bug has been feeding on a square, “you can squeeze it and get a milky secretion,” Len said. “If it's a natural shed, it's dry and crunchy.”

Stewart recommends Orthene, Centric and Trimax for control of plant bugs. “All things being equal, I lean toward Centric because it shows a little better activity on plant bugs than the other neonicitinoids (a new class of chemistry).”

Three neonicitinoids are on the market — Centric, Trimax and Intruder, Stewart noted. “Centric is pretty good plant bug material and a good aphid material. Intruder, which used to be called Assail, is probably the best for aphid control, but tends to be weak on plant bugs. Trimax is kind of in-between.

“Orthene is still a good material and Bidrin is still a good material in most areas, but there is some resistance in some areas.”

While neonicitinoids are easier on beneficial insects than other products used for plant bug control, “they're not exactly what I would call soft,” Stewart said.

“But they definitely are safer to handle than some of the other compounds. The downside is that they are little more expensive when you compare the best rates of Orthene and Bidrin to the best rates of the neonicitinoids.”

The presence of other pests can also affect the choice of products, according to Stewart. “Early in the season, your material choice is going to be influenced by aphids. If you have a lot of aphids, you would be less inclined to use something like Orthene and more inclined to use Bidrin or one of the new neonicitinoids.

“When you get into mid-season, you're dealing with Bt cotton and potentially bollworms that have escaped Bt cotton or stinkbugs. The pyrethroids, especially in west Tennessee, have good activity on all three.” (plant bugs, stinkbugs and bollworms).

The mobility of adult plant bugs can cause some consternation for cotton producers. “Sometimes, the plant bugs may not be feeding,” Len said. “They could be breeding. So they may be there in the morning, but not be there the next day.”

In 2002, that characteristic pushed the Doyles toward Centric, which has good residual activity on the pest. “We got control up to 10 days on plant bugs and 14 days on aphids,” Len said. “So that gives us a bigger window for control. So whether they're feeding or breeding, we're going to get them.”

“I liked the residual,” Clint added. “You still have to get in the field to scout. But you have the confidence that it's working.”

“Our first time around, we used Centric at a rate of an ounce and a quarter,” Len said. We used it one more time at an ounce and a half about 15 days later when we also had some stinkbugs and averaged 909 pounds over 3,600 acres of cotton. That's not too shabby on non-irrigated, hill ground.”

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