Cotton farmers are about to move to the next level of transgenic, insect-tolerant technologies — products that promise to provide improved control of caterpillar insects such as bollworms and, until now, largely uncontrolled foliar feeding pests.
But what can growers expect from those new products — Monsanto's Bollgard II, Dow AgroSciences' WideStrike and Syngenta's new VipCot — and how can they determine which of the new transgenics they should plant on their farm and how to properly manage them?
“All of these technologies will have a fit for us in the Mid-South,” says B. Rogers Leonard, professor of entomology at Louisiana State University's Macon Ridge Branch Research Station near Winnsboro.
“What they really bring to the market is the opportunity to improve control of heliothine pests and increase the spectrum of control. The bottom line is that the variety they are put in will dictate where they fit because it will be difficult to ascertain any differences when you're looking at them in the field unless specific species of insects are present.”
Leonard discussed what research is showing about the next generation of transgenic cottons at the Cotton Incorporated 2004 Crop Management Seminar in Robinsonville, Miss. The Seminar drew about 250 persons.
Although it may be difficult to detect differences from the turn-row, Leonard and his fellow researchers say farmers may have to treat the new cotton products differently when it comes to scouting for insect pests.
“I believe that each of these technologies are different enough they are likely to require slightly different scouting protocols. That's because the activity of the insects is a little bit different so recordkeeping may become more important as we grow more of these varieties.”
Each of the new technologies appears to offer significantly improved control of bollworms, a pest that also required cotton entomologists to alter scouting methods after Bollgard cotton first arrived on the scene in 1996.
“The problems we've had with Bollgard and bollworms are likely to go away,” Leonard noted.
They will also provide an improved spectrum of control. “Many of these other caterpillar pests, such as armyworms and loopers, that we see in late season may no longer require insecticide applications.”
And they should also provide growers with better resistance management tools because of the presence of two proteins that will “elevate the overall dose of Bt in those plants,” he said. “It may offer some opportunities for using the various technologies in a spatial pattern to reduce the need for refuge.”
The VipCot lines express a vegetative protein from Bacillus thuringiensis that is different in structure and mode of action than other transgenic cottons, he noted. Syngenta expects to receive registration for VipCot in 2004 or 2005 and to begin commercialization of the product in 2006. (Bollgard 2 and Widestrike have received registration from EPA.)
Leonard says he believes the new transgenics could allow Mid-South farmers to reduce insecticide sprays for caterpillar insects by about 50 percent. “There will be some instances where no caterpillar sprays will be needed. I hope we have a lot of those, but I'm not confident enough to say that at this time.”
Tests in Louisiana over the past four seasons indicate that Bollgard 2 cotton had the lowest number of tobacco budworm/bollworm-infested fruiting forms and associated damage compared to conventional and Bollgard cotton varieties.
Bollgard 2 plots not treated with insecticides averaged 0.1 percent larvae and 0.9 percent damage compared to 1.1 percent larvae and 3.8 percent damage for untreated Bollgard cotton; 2.2 percent larvae and 8.1 percent damage for conventional cotton sprayed with four to six applications of insecticides; and 5.4 percent larvae and 16.3 percent damage for untreated conventional cotton.
“We were never able to completely zero out the pest damage with these new technologies, but we can limit the damage to less than economic levels,” he said.
Bollgard 2 also demonstrated satisfactory control (greater than 95 percent) of foliage feeding insects compared to conventional non-transgenic and Bollgard cottons. “Studies by other entomologists show that Bollgard 2 cotton provided significantly better control of bollworms, soybean loopers and beet armyworm,” according to Leonard.
Louisiana trials with Dow's WideStrike also indicated substantial reductions in the number of tobacco budworm/bollworm larvae and damaged fruiting forms in the tests conducted from 2001 to 2004.
WideStrike plots not treated with insecticides averaged 0.4 percent larvae and 1.1 percent damage compared to 2.5 percent larvae and 6.5 percent damage for conventional varieties sprayed with four to six applications of insecticides and 4.7 percent larvae and 16.1 percent damaged for conventional cotton not treated with insecticides.
“Syngenta is still selecting the event it will use for its final VipCot transgenic lines,” said Leonard, “so we don't have as much information on VipCot's efficacy as we do the other new transgenics. However, all current results suggest that VipCot will provide satisfactory control of heliothines, armyworms and loopers.”
Taken together, Bollgard 2, Widestrike and VipCot will probably reduce the need for foliar sprays against caterpillar insects, according to Leonard. But he does not believe the reduction will translate into fewer insecticide sprays in general.
“Previous speakers today have talked problems with plant bugs and stink bugs,” he noted. “It's likely that many of these caterpillar sprays suppress — if not control — these bug populations so additional sprays may have to be added for bugs.”
Leonard says the refuge requirements for Bollgard cotton will remain in effect for the new technologies that have been approved — Bollgard 2 and Widestrike.
“The same recommended agronomic and integrated pest management practices are necessary,” he noted. “They are considered high dose under the definition of EPA and the refuge requirements will be exactly the same as they are for Bollgard cotton.”
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