Alabama cotton insects scouting

AUBURN UNIVERSITY EXTENSION Entomologist Ron Smith discusses cotton insect pests with a participant at the recent Cotton & Soybean Scout School held in Autaugaville, Ala.

Cotton insect pests taking backseat to weed, disease problems

Insect problems in Alabama cotton are taking a backseat to weed and disease issues. Stink bugs still could pose a threat under certain conditions. Determining an accurate threshold is important in stink bug management.

From an insect pest standpoint, these could be viewed as the best of times for Alabama cotton producers, says Ron Smith, Auburn University Extension entomologist.

“We need to just admit up front that cotton insects in our state are not the problem they once were,” said Smith at the recent Cotton & Soybean Scouting Short Course held in Autaugaville, Ala.

“Insects are taking a backseat now to weed problems like resistant Palmer amaranth and to some extent, disease problems.”

It used to be that cotton varieties had the potential to yield 750 pounds per acre in a good year, he says. Now, they have 1,500-pound-per-acre potential.

“Even though insect problems are not as significant as they used to be, we still need to fine-tune our control programs,” says Smith. “There’s still a place for fine-tuning cotton insect control rather than fighting for our lives. We can focus on growing cotton for yields.”

Alabama cotton producers have about a $75-per-acre advantage when it comes to insect control over their counterparts in Mississippi.

“We don’t want to go down the same road they’re going down. They’re spending a lot of money for insect control that we’re not spending,” he says.

Even though Alabama cotton producers have learned that worms are of little to no consequence, it’s helpful to be able to recognize the different species of caterpillars when they occur, says Smith.

On the other hand, stink bugs have the potential of being by far the most damaging insect pest from central to southeast Alabama in the Coastal Plain region, he adds.

“There are a number of different insects that damage cotton, but there are certain pests we focus on only during certain times of the season,” says Smith.

The cotton bollworm and the tobacco budworm used to be common caterpillars, he continues.

“At some point in the season, rather than looking at a lot of terminals and not much else, you want to switch and look at fewer terminals and fewer plants because you’ll have to spend more time per plant.

“You’ll have to open a number of squares and examine white blooms and red blooms for worms that have hatched and are starting to mature.”

Time of boll damage

The life cyle of these pests is about 15 days, so they’ve got a lot of feeding to do when they go to bolls, and that’s when they do the real damage, he says.

“There are other caterpillars besides the budworm and bollworm, but we haven’t had any of these on cotton in a number of years.

“One of these is the fall armyworm. We’ve had a lot of armyworms on grasses, peanuts and soybeans in recent years. But it’s a different species of armyworm from what we see on cotton.”

Even though there’s an abundance of grass or rye armyworms on cotton, it doesn’t mean anything because it’s a different strain, says Smith.

“There are currently a lot of armyworms in Florida feeding on corn, and we’re not sure what this means, but they don’t like cotton at all,” said Smith in late June. “And they’re easier to kill on these other crops.”

Armyworms do not lay eggs individually but in masses, and the masses normally are underneath the leaves, he says.

“If I was a cotton scout, I’d stay informed of the ‘big picture,’ but I wouldn’t spend a lot of time looking for armyworms on cotton unless I had heard they were somewhere nearby on cotton.

As they get larger, they’ll go to white blooms, or they’ll be underneath red blooms. If I heard we were having armyworms this year, I’d look for etching on boll bracts. Then I’d look inside there to find the small fall armyworms. We haven’t seen them in a number of years now.

Initially, they’re very green when they’re feeding on this boll bract, but later, they’ll develop some color.”

Alabama growers haven’t seen beet armyworms since 1994 or 1995, says Smith.

“It takes several things to get a huge population of beet armyworms going, and we don’t expect to have those conditions anymore.

“They’re a dry weather pest, but you’ve almost got to be making area-wide applications and suppressing parasitic wasps to get an outbreak.

“On field-by-field applications, you don’t get that total suppression of the parasites that control the beet armyworm. When we had the boll weevil eradication program, we were making applications that were taking out the parasites. Beet armyworms also are more foliage feeders than fall armyworms.”

Another sporadic cotton insect pest is the yellow-striped armyworm, says Smith.

“We see very few of these thanks to Bollgard II cotton, and they’re seldom an economic pest. The Southern armyworm also has been taken out of the picture by new hybrid technology.

The cabbage looper or the soybean looper hasn’t been a problem either since the advent of two-gene cotton. But they were statewide on soybeans this past year.”

Stink bugs

The green and the Southern green stink bug can be found in Alabama cotton, says Smith.

“I found a lot of green stink bugs last year in central Alabama, and their habits are different from those of the Southern green stink bug, which we mostly see in the summer months.”

Stink bugs, he says, normally feed on cotton bolls that are about 10 days old, are about the size of a quarter in diameter, and are still soft.

“We had a lot of stink bugs on wheat this year, though some of those were the rye stink bug. We had a third consecutive mild winter, and a lot of these should have overwintered.

“In the past two years, the heat and drought in June suppressed their numbers. But a lot of them are building on corn right now. We could be set up to eventually have a bad stink bug year. They have the potential to be the most damaging insect in cotton in the Southeast.”

If they do come into cotton fields prior to about the third week of bloom, when the first soft bolls are on the plant, they will go to younger fruit, says Smith.

“I guess it’s debatable whether they will go to squares, but there’s not much evidence that stink bugs will feed on squares.

“We don’t have to be many weeks into bloom to have small thumb-sized bolls, and I can assure you a stink bug can find each one of those. If those are the oldest vegetation out there, they’ll make mush out of them.

“This year, we could have stink bugs before we have 10 to 12-day-old bolls. If so, you won’t have 10 to 12-day-old bolls because the stink bugs will get them all.”

The classic sign of stink bug damage is an indention on the boll, says Smith.

 “And when we normally see that, we look internally to see if there is any deteriorating tissue where the stink bug is trying to feed through to the seed to get to protein. Boll rot organisms are introduced as it is feeding, and you’ll eventually get boll deterioration from the inside.”

If weather conditions are wet in August and there is a lot of stink bug feeding, you’ll see yellow-stained lint where moisture gets into the boll, says Smith.

“We had that several years ago when we first starting planting Bollgard cotton and didn’t quite know what it was. But you’ll need a really wet year for these conditions to form.”

One other insect that does damage very similar to that of the stink bug is the leaf-footed bug, normally found farther south, says Smith.

Big numbers

“These can be seen in tremendous numbers, and their damage is indistinguishable from that of the stink bug. The immatures are orange in color and they come out of an egg mass. You can find them in an old garden with old tomato plants.”

Stink bugs sometime damage the entire boll, says Smith, but more than likely, they’ll get one or two locks out of a boll. Anything from a normal boll to a partially damaged boll is possible with this insect pest.

“We do change the threshold level as we move through the summer. We want to pull 25 bolls that are about the size of a quarter and soft to the touch. We then get a percentage of the damaged bolls.”

First of all, crush only the bolls that have external damage, advises Smith.

“If you reach the threshold, then you don’t even have to crush the remainder of the bolls. It’s a faster way of doing it.

“If you don’t get a threshold by just crushing the ones with external damage, go ahead and crush the rest of the bolls.

“A lot of times, if we get real stink bug problems in the summer, you’ll reach a threshold by crushing just the bolls with external damage. It’s slow crushing those bolls, especially if you’re in the commercial scouting business.”

Internal damage is most important, he says.

“At week 1 and 2 of bloom, we can let 30 to 50 percent damage go before you call it a threshold. Weeks 3, 4, 5 and 6 are the critical weeks for stink bug injury in cotton.

“That’s also the month when you make the most bolls. As cotton is maturing out, and you find fewer and fewer bolls that are soft to the touch and are 10 to 12 days old, then you rate your threshold.”

Research has not shown any yield increase by spraying 10 percent early or 10 percent late, he says.

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