Weed, insect resistance in cotton
Feb 9, 2010 9:54 AM, By Roy Roberson, Farm Press Editorial Staff
Managing resistant insects and weeds goes well beyond important say Roger Leonard and Stanley Culpepper — it is essential from both economic and production standpoints to continue growing cotton in the South.
Leonard, an entomologist at LSU’s Ag Center, says one of the first glimpses of insect resistance seen by farmers in the Southeast was pyrethroid resistant budworm and bollworm. This was far from an unmanageable problem, but opened the eyes of entomologists as to future problems with advanced insecticide technology back in the 1970s.
“We didn’t know exactly what to make of the problem back then, but all of us in the cotton pest management business saw fields where pyrethroids didn’t work,” Leonard said, speaking at the recent Beltwide Cotton Conference in New Orleans.
When Bollgard came onto the market, the problem of pyrethroid-resistant insects highlighted the efficiency of these new products.
Before Bt cotton, growers in the Mid-South routinely sprayed an average of four to six times and up to 10 times for the tobacco budworm-bollworm complex. The early Bt products cut sprays by 50 percent. The new generation of Bollgard and WideStrike products will likely cut another 50 percent of insecticide use. This technology still won’t eliminate the need for insecticides in some fields, but it will significantly reduce the amount of conventional materials used by cotton farmers, Leonard says.
“Despite the success of these products in managing the bollworm-budworm complex, they do not make cotton insect-free. In fact, these materials accentuate the need for a well-trained professional to scout for secondary insects not controlled by Bt technology.”
Rotating insecticides is critical, Leonard stresses, to maintain a high level of efficacy and a relatively low cost.
Culpepper, a weed scientist at the University of Georgia, also speaking at the Beltwide meeting, says the reason for the dramatic increase in use of glyphosate-based weed management programs throughout the South is primarily simplicity of using these products, combined with there high level of efficacy in controlling a wide spectrum of weeds.
From 1997 to 2001 Roundup Ready cotton went from zero to 67 percent in the South. By 2006, at least 97 percent of the cotton in the Southeast was planted to Roundup Ready varieties.
In 2000, the first case of glyphosate resistant horseweed was confirmed, and this was further confirmed in cotton in 2001. Horseweed has not been a severe problem in cotton for the most part, but it did open the eyes of weed scientists across the country that there were changes occurring in weed management from glyphosate-based systems.
“Despite the growing evidence we would likely have future problems with glyphosate-resistant weeds, use of the technology continued to spread rapidly. Cotton acreage in the Mid-South and Southeast continued to increase well into the 2000s.
“In 2004, the first case of glyphosate resistance was documented in Palmer amaranth pigweed in Georgia. Growers who have faced this problem can attest that all weeds are not created equal, Culpepper says.
“By 2006, resistance was confirmed in five states and by 2009 glyphosate resistant pigweed was confirmed in 120 counties in eight states, and I’m soon to add another 10 to 12 counties in Georgia,” the weed scientist adds.
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