The irony of cotton insect control is that you can learn a lot more in a bad year than in a good year, says Ron Smith, Auburn University Extension entomologist.
“We haven’t learned much in recent years,” said Smith, speaking at the East-Central Alabama Cotton/Peanut Tour.
Early this season, grasshoppers were very abundant in Alabama cotton, and they posed a potential problem until cotton reached about the fifth true-leaf stage, he says. “Thrips were not as bad as they have been in some years. Some of this was due to the fact that there were some rainstorm events during that window. It has been my experience that rain will drown immature thrips and that a good, hard-driving rain is about as good as a foliar spray,” says Smith.
All of the thrips control growers have available to them at planting are somewhat equal in performance, he says.
“Some look better at times than others. But under heavy pressure, all of them would benefit from supplemental foliar controls,” says Smith.
Growers saw plenty of adult tarnished plant bugs in June, says the entomologist. “But in my opinion, the square loss did not correlate with the number of adult plant bugs we saw, and even though they were in the field, a lot of the fields remained what I would call above the threshold level as far as pinhead square set,” he says.
Aphids are another insect pest in that same window, says Smith. They built slowly, and they were slow to die off from the naturally occurring fungus, he adds.
July, he says, turned out to be troublesome for Alabama cotton producers. “We had a major tobacco budworm flight and the worms from that flight for about the first two weeks of the month. Beginning on about July 18 or July 20, we had a major bollworm flight, but the larvae didn’t cycle out until about the first week in August.
“We don’t know where these tobacco budworms came from, but there was a generation that caused heavy foliage loss to peanuts in Alabama and Georgia during the month of June. We weren’t smart enough to know it was going to translate into heavy pressure on cotton. It could be that we’re influencing these worms to some degree as we rotate or shift these crops around from cotton to corn to soybeans and other things. I’m not sure this is the answer. I’ve talked with other entomologists in the Southeast, and none of us has a clue where these tobacco budworms came from,” he says.
Smith says he works on five different experiment stations in Alabama, with one being in southeast Alabama’s Wiregrass region. “On July 3, in the Wiregrass, we stepped out of our vehicles and we saw tobacco budworm moths in cotton like we hadn’t seen in several years. We went back the next week and saw one and two-day worms everywhere, so we immediately started our own tests,” he says.
Research documented a few days later showed that pyrethroids applied to these tobacco budworms was “about like spraying water into a high level of resistance,” says Smith. “That left us with Tracer — which was in short supply — and Spirit — which is about $15 per acre. In general, conventional varieties in my plots and in a lot of other places took heavy damage.”
On about July 20, he says, the pressure seemed to slack off, but that was because the bollworm moths that were depositing their eggs did it down in and on the white bloom.
“Those worms were — in a lot of cases — five to seven days old when we detected them, and this means even the pyrethroids didn’t do a very good job of cleaning them up. I along with the people with whom I work miss this generation every year. I’m convinced that no one can accurately scout for that July 20 bollworm generation that comes off of corn and into cotton.”
The only way to handle that population, he advises, is to make an automatic spray of a pyrethroid on about July 20, and this would hold true for conventional cotton as well as some of the genetically altered varieties.
“You could move that July 20 date forward or backward a day or two depending on the weekend. But every year, we’re usually too late. Another big factor in this damage that we got from this generation of bollworms was that where sprays had been made in recent weeks for aphids, tarnished plant bugs or whatever we were spraying for, the beneficial were not found and the worm damage was about four to five times as heavy as in fields where beneficial were present.
“I would suggest in future years, that if we’re planting conventional cotton, and we have any reason to suspect we might have a bad worm year coming, that we’re just going to have to overlook all bug damage prior to about July 20, and keep all beneficials present until that date.”
This also applies to single-gene cotton like Bollgard and the double-gene cotton like WideStrike and Bollgard II, he says. Measurable damage was seen where those varieties were planted, he added.
You could visibly see worm damage in just about everything this year, says Smith. “We estimate that varieties like DPL 555 give about 60 percent bollworm control. Beneficials give us another 20 to 30 percent control if they’re present. This leaves about 10 percent escapes, and that’s what we had. When there are no beneficial present, we get about 40 percent of the worms emerging on the single-gene Bollgard cotton like 555. Beneficials make a big different even in varieties that have the worm technology.”
Alabama cotton growers also saw more stink bugs this year, says Smith, more since about 2005. And researchers are still learning about the pest, he says.
“But a few things seem real clear. First, a lot of growers are still not tuned into stink bug damage, and they’re allowing too much damage as a whole before they treat. Stink bugs are difficult to scout for. We’re refining it a little more every year. By the time you find them in your field, as far as being visible, the damage is somewhere between 10 and 20 percent of the susceptible bolls that normally have internal injury, and that will cause hardlock or rotten bolls when the cotton opens.”
Another point that is often forgotten is that stink bugs have a long life cycle — longer than any of the other cotton insect pests, says Smith. This life cycle can last up to 70 days.
“If you have a stink bug on July 4, that same stink bug likely will still be in the field when your cotton is maturing.”
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