Many cotton producers in the Southeast have gotten away from insect scouting in recent years, but it would be a mistake to completely let down your guard, says Ron Smith Auburn University Extension entomologist.
“The insect pests have changed, and we don't have as many pests as in the past,” says Smith. “They're not as dominant as they once were. But we all know about stink bugs and the impact they can have on fiber quality. There are still important pests out there, so someone has to look at cotton and keep insect pests to a minimum. We must know what's out there in order to know which control measures to use.”
Stink bugs continue to be an important insect pest in the Southeast, and Smith recommends a treatment threshold of 10 to 15 percent injury. “Stink bugs prefer bolls that are 10 to 12 days old. Georgia likes to use a stink bug threshold of about 20-percent damage. I'm a little more conservative,” he says.
Stink bugs have a long life cycle, he says, and at 10-percent damage, it's likely that the same number of insects still will be in the field for several weeks.
“I'd prefer to be more conservative and be ahead of the game rather than letting it go for a longer period and then trying to cut them off at the pass,” says Smith.
If the pest is a brown stink bug, growers will need to use a phosphate insecticide, he says. If the pest is a green stink bug, you have the option of using a phosphate or a pyrethroid insecticide, he adds.
“Unless stink bugs are migrating in daily from a crop such as peanuts late in the season, we should get about a two-week suppression from control measures,” says Smith.
Later in the growing season, leaf-footed plant bugs often are found in cotton with stink bugs, he says. “Their damage is identical. If we're surveying for stink bugs, we won't miss this pest if we're going by damage. The leaf-footed plant bug is a severe boll feeder, and pressure can be tremendous in southeast Alabama.
“This is a new pest that's finding its niche in our low-spray environment. In the immature stage, they come out of a clump of eggs. They'll cluster on a boll, and you'll see them on a green boll before they disperse,” says Smith.
While the primary bug species in southeast Alabama is the stink bug, there are years when growers see heavy early season pressure from plant bugs, he says. As for plant bug thresholds, the recommendation at pre-bloom is to go by pinhead square retention, with the goal being 80-plus percent square set prior to bloom.
“After bloom, the plant bugs tend to move down the plant to do their feeding,” he says. “Monitoring the pinhead squares, which is normally going to be out on a lateral branch or up the terminal, is not the best method at this point. After bloom, as you move into a field, you can look for plant bugs, both immature and adults, in white blooms. If there are many out there, you'll see them in a white bloom. Their damage is done to large squares several days prior to this time, so it shows up as dirty blooms.”
Smith recommends a treatment level of 10 to 15 percent for plant bugs. “The damage was done several days earlier. If you make a treatment, there will be a time lag before you see the white blooms cleaning up. Also, if we get into a heavy year, it's July, a foliar spray hasn't been made on the crop, and plant bugs have been out there for a month or more, you'll have adults, immatures, and eggs hatching in the plant stem. Quite often, in July, it'll take multiple applications to clean up a bad plant bug problem.”
In some years, growers also see the tarnished plant bug in their fields, says Smith, in addition to cotton flea hoppers. In 2003, he adds, clouded plant bugs did damage in growers' fields.
“Another emerging insect pest is the Southern armyworm. They're pretty much foliage feeders. About 99 percent of their feeding is done to either the flower petal or the foliage. They're black in color, somewhat like the yellow-striped armyworm. They come out of a cluster, and the cluster will look somewhat like the beet armyworm damage we saw years ago, except we don't see the corresponding brown area in one tight spot.”
Southern armyworms tend to eat the entire lower surface of a leaf, says Smith, and they normally come from a huge egg mass, with tremendous numbers on the plant. “About 1 percent of the population will go directly to the fruit, and it could be squares or bolls. They can become a boll feeder, and there are instances where this pest would need to be controlled.
“Unless there is a lot of foliage damage and a lot of egg masses, we tend to let this pest go. But it's easy to control with a pyrethroid.”
Fall armyworms also can be a problem, says Smith. “There were some pockets of fall armyworms in southeast Alabama this past year that were the worst I've seen since 1977. They literally ate up fields. We just about gave up trying to control them last year, and we lost confidence in everything we tried.
“All of the new chemistry had excellent activity on fall armyworms in research tests. However, it wasn't working last year, and timing was one of our big problems. Back in the early 1990s, when we had a real flurry of fall armyworms in some years, we had treated and untreated plots on research farms. Some were treated once per week with a pyrethroid, and we had basically no fall armyworm survivors. We had tremendous damage in untreated plots.”
From an economic standpoint, says Smith, one option for controlling fall armyworms would be two quick shots of a pyrethroid, made about five days apart.
“All pyrethroids may not be equal. But a lot of them have come onto the market since we did those evaluations in the early 1990s, so I really don't know which ones have strengths or weaknesses on this pest. The key is finding them early. If they get larger, pyrethroids may not be a good choice, and I'm not sure anything else will work. You must have pyrethroid residue out there, or you have to apply new chemistry when they're hatching. When they get in a boll, you have to wait for them to cycle out, and the boll will be totally destroyed by fall armyworms.”