The rapid decline in U.S. cotton acreage means one thing to Mid-South entomologists and producers — the cotton dinner table is even more crowded with sucking insects.
Speaking on a panel at the 2009 Beltwide Cotton Conferences in San Antonio, Gus Lorenz, University of Arkansas entomologist, who is responsible for integrated pest management programs in Arkansas, noted that cotton producers are learning to deal with a changing pest spectrum brought on by the use of transgenic cotton varieties resistant to lepidopteran pests and the success of the boll weevil eradication program. “We spray less for these pests, which has freed up the sucking pest complex.”
Over the past two years, “the huge reduction in cotton acreage has created more alternate hosts which are really problematic for us,” in terms of sucking pests, Lorenz said. “We're seeing extremely high numbers of pests. Cotton has always been an attractive crop for a lot of pests. We're not growing as much now, but that means there are more pests coming into (a smaller acreage) of cotton.”
Mid-South cotton acreage declined 35 percent from 2006 to 2007, and dropped 32 percent from 2007 to 2008. Arkansas acreage dropped from 1.2 million acres in 2006 to 640,000 acres in 2008.
“We have a bunch of fields around cotton now that are supplying pests, particularly plant bugs, stink bugs and spider mites. Things have changed and we have to change to meet the needs of the cotton producer.”
Lorenz noted that the cost of Lygus (plant bug) control in 2007 was about $8.65 on average across the Cotton Belt. “But Mid-South costs were $25 to $48 per acre just to control tarnished plant bug. Twenty years ago, our major pests were bollworm and tobacco budworms. With the transgenic cottons, those are not that big an issue, but we're still trying to sample the same way we did when worms were a problem. The whole plant, or modified whole plant search for worms just doesn't apply to the sucking bug complex.
“We have to use the most effective methods we can find to effectively evaluate the population out there and determine when we need to take action.”
Mid-South research entomologists including Lorenz, are evaluating sampling techniques for plant bugs and are also evaluating current thresholds.
Entomologists say that the sweep net is the most effective tool to assess plant bug populations prior to bloom, while black shake sheets are best for assessing populations after bloom. “If you monitor early square retention, that will help even more,” Lorenz said.
“We settled on an early season threshold of from nine to 12 plant bugs per 100 sweeps and three plant bugs per 5 row-feet in mid-season.”
Producers must also deal with insecticide resistance issues for plant bugs, Lorenz noted. “Certainly pyrethroids have not been effective for most of the Mid-South for the last several years. We are starting to see some problems with acephate. It's important for us to determine how to manage plant bugs without getting into resistance problems. We really need insecticides with new modes of action. The toolbox is getting pretty low for control of plant bugs.”
Lorenz said new chemistries for plant bug control such as novaluron (Diamond) and flonicamid (Carbine) “don't necessarily work with older scouting methods of spraying and then checking three days later for plant bugs. You have to look past eight to 10 days to really get a feel for how effective the products can be.”
In addition to new chemistries, Lorenz said, alternative methods to chemical control such as an area-wide management program could work for plant bugs. “We also need to maintain the insecticides that we have, particularly the organophosphates.”
Stink bugs are also emerging as a big pest of cotton, according to Lorenz. “We're beginning to learn about the damage that this pest can cause. We still have a lot of work to do on thresholds. We're not certain that the current threshold of one bug per 6 row-feet is going to work.”
On spider mites, entomologists are trying to find a correlation between mite infestation and yield decline. “The same corn-cotton interface is an issue for us there, too. We're finding that mites are coming out of corn and moving into our cotton.”
Entomologists are also seeing differences in the efficacy of miticides for early-season spider mites versus late-season mites.
On a positive note, entomologists believe that new triple-stack Bt corn hybrids will reduce the number of bollworms that emerge from corn (compared to original Bt and non-Bt hybrids).
According to panelist and Arkansas crop consultant Chuck Farr, “increases in pest pressure along with low cotton prices and high grain prices “have caused many of our cotton producers to park their cotton pickers for the 2009 growing season. Ten years ago, we faced many pest problems, including tobacco budworm and cotton bollworm. We've moved through those years to plant bugs, spider mites and other insects.”
Resistance has become a big problem in weed control as well, noted Farr. “Those in areas where weeds are resistant are struggling for control, and those who don't have resistance issues should do everything they possibly can to preserve the technology we have today.
“Roundup Ready technology gave cotton producers a great ability to increase acres with over-the-top applications of herbicide, and for the most part kept many cotton producers in the cotton business during poor economic times for agriculture. It's a great technology, but speaking from my heart and first-hand experience, it's a technology that we cannot afford to lose. We must do everything we can to preserve it.
“Resistant Palmer pigweed is part of the driving force for our cotton acres decreasing in my part of the Mid-South. Ninety percent control is not adequate anymore. Yield reductions will occur and revenues will be lost.”