In Arkansas Bollworms descend on soybeans
Aug 18, 2006 12:00 PM, By David Bennett Farm Press Editorial Staff dbennett@farmpress.com
Alarming numbers of bollworms are moving through Arkansas soybeans. A “super heavy” bollworm flight — upwards of four and five times threshold levels — is currently in the central portion of the state and moving north, says Gus Lorenz.
“They're moving fast,” says the Extension entomologist. “Trap counts are already high in the northeast. Certain fields are being, or have been, hammered.”
Hot spots include any late-planted, double-cropped soybeans that are beginning to bloom, especially if plants haven't lapped the middles. The pest is also plentiful in fields with thin stands or with thin spots.
“North Arkansas farmers need to be especially vigilant. For the most part, the worms may have already rolled through the south.”
Bill Robertson says thus far cotton hasn't been badly hit by the worms. But the Arkansas Extension cotton specialist has gotten news of soybeans “where almost every pod in an entire field has been taken out. Even though they're on soybeans now, cotton growers need to know the bollworm numbers are extremely high.”
Farmers growing multiple crops typically watch cotton closely and leave soybeans to scout last. “Sometimes, by the time they notice there's a problem, there may be no pods to harvest,” says Lorenz. “I'd check every bean field but I'd really be thorough in late-planted fields.”
Stink bugs are often cited as the number one pest in soybeans. But bollworms can be the most devastating insect for the crop.
“They have the potential to wipe out a field's yield. Unfortunately, we've seen that in some cases. A county agent in central Arkansas just told me he'd been in a field and could hardly find a pod. The worms had chewed through it.”
Without pods to make the plant mature such hard-hit fields will stay green until frost.
Bollworms can be cannibalistic. Even so, with crops to eat, their numbers can reach as high as one per plant. They normally work their way up and down the plant, stripping pods as they go.
“They love eating the blooms as much as the small, developing pods. They'll also feed on the bigger pods — they're just gluttons. These worms can take out a whole field in two or three days.”
Exacerbated
This season's drought has exacerbated the bollworm problem. But it isn't just bollworms. Lorenz is seeing an upsurge in activity for all Lepidopterous pests — saltmarsh caterpillars, beet armyworms, and fall armyworms are also about.
“All of those really enjoy hot, dry weather. And the hotter and drier, the better time they have. Obviously, they are really having a party, right now.”
On the back of such a dry season, having bollworm problems break out didn't surprised entomologists at all.
“When the drought started and then continued, the thought had been, ‘if this keeps up, they're coming.’ It was just a question of how bad a problem they'd be.”
Spider mites, another hot, dry weather pest, are currently tormenting southern Arkansas. In some areas, says Lorenz, “mites are exploding. Growers down there are battling spider mites like they've never had to before, if ever.”
In the race to the cotton crop finish line, growers' money is already tight. Much has already been spent on diesel to keep irrigation going.
“It's difficult to convince many farmers of the magnitude of the damage these pests can cause. Bollworms in soybeans and spider mites in cotton are nothing to play with. But they're loath to spray because, frankly, they're teetering on being broke. Or they're already broke. Knowing that, I feel so bad telling them they need to spray.”
If there's any good news it's that bollworms in soybeans are easily controlled. There are a multitude of options Lorenz recommends. Among them: pyrethroids and several new products like Steward and Tracer.
“Those are all very effective, even more so on worms in beans because they're more exposed and easier to kill. Because of that, the rates differ between soybeans and cotton.”
Producers who find a bunch of big worms in their soybeans often say, “‘These worms are already too big and I don't think they can be knocked out. And even if I could, they're going to cycle out soon.’
“In soybeans, that's the wrong path to take. Fact is, when bollworms get into the last couple of instars the problem ratchets up. That's when they eat 90 percent of what they'll consume in their larval stage. You don't want to let them pupate.”
As for the spider mites, there are several products available for control.
“Some of the best we're seeing are the bifenthrin products. Those are cheap, although they don't give long-lasting control. But at this stage in the game, all you're trying to do is buy a little time to get the crop finished. I'd look at the cheaper controls and go that route.”
