Cotton producers who plant second generation Bt cottons like Bollgard II, WideStrike and VipCot may not spray less or yield more cotton in the short term. But they should see improved control of worm pests and will have set the bar for resistance management at a very high level.
Two new, two-gene products — Bollgard II, which has been in cotton fields since 2003, and WideStrike, which has been commercially available since 2005 — have the gene that expresses the Cry1Ac protein. Bollgard II's second protein is Cry2Ab; WideStrike has Cry1f.
A third product, VipCot, the result of a cooperative effort between Syngenta and Delta Pine Land Co., is not yet commercially available.
The new technologies have improved the spectrum of worm control, according to Stewart. “There are also some subtle differences in these technologies. It's not going to show up in most environments, most years. But when you have a big bollworm year or a big fall armyworm year you might be able to tease apart the technology.”
As with Bollgard, WideStrike and Bollgard II will provide great control of tobacco budworm, according to Stewart.
“Original Bollgard was fair on bollworm and less than that on some other pests, like fall armyworm. “Bollgard II is excellent on bollworm. We think WideStrike is somewhere between the two based on all the data we've collected.
“But the big thing that the additional gene will bring, hopefully, is to prevent resistance from developing to these technologies as quickly. The idea is that if you have one gene, that's good, but resistance can develop. If you have two genes and the mode of action is different enough, it's unlikely that any one insect will be resistant to both at the same time.
“The newer technologies also have a large advantage over original Bollgard for fall armyworm and loopers. That's where you're going to really see improvement. With fall armyworm, we think WideStrike might be a bit better than Bollgard II.
“If I were to choose a Bt technology based on the pure efficacy of that product for west Tennessee, I would probably pick Bollgard II because we think it's a little better on bollworms than the WideStrike technology and that is the primary pest in this environment.
“If I were in another environment where I had a lot of fall armyworms or a mixture of fall armyworms and bollworms, it may be a tougher decision.
“The reality of the situation is that even original Bollgard is pretty good most of the time. And growers are probably going to choose technology by what variety they want to grow.”
Stewart noted that there is still a refuge requirement for the second generation of Bt cotton — planting some amount of Bt cotton and managing it according to specific guidelines. But there is a proposal to go to a so-called natural refuge for Bollgard II.
“Essentially Monsanto is trying to convince EPA that the technology is good enough and there are enough other sources of tobacco budworm and bollworm in the environment that we don't need the structured, non-Bt cotton refuge in Bollgard II. They've made a good case, so we'll see what the EPA decides.”
Walt Mullins, Monsanto's technical manager for Bollgard and Bollgard II, hopes a decision will come from EPA in late September, “but certainly enough in time for growers to know something before the 2007 season.”
Mullins said that two-gene products like Bollgard II have significantly improved inherent resistance management potential in Bt cotton, one reason why original Bollgard technology, which contains a single gene, will be available only through the 2009 season.
“In Australia, they have already outlawed the use of a single gene product because of their concern for resistance management.
“We know that it will take a while to get the Bollgard II varieties up to the performance level we need. We've made great strides and by 2009, we should be there.”
While second generation Bt cottons offer better control over original Bt technology, “This doesn't mean that there will be less spraying overall because we do have other pests, such as plant bugs and stink bugs,” Stewart said. “But you're not going to be specifically targeting the caterpillars as often.”
Stewart isn't sure that improved protection will also provide a yield increase for cotton producers. “Truth is, I don't have a lot of data in Tennessee to say that's going to happen. We have several years of data and have not seen a remarkable, consistent yield bump in Bollgard II or WideStrike versus Bollgard. But it's certainly something that could happen in the right year, if we have enough pressure.”
Stewart stressed that it will not be unusual to see worms in Bollgard II or WideStrike cotton. “I do expect the new technologies to narrow the window for worrying about worms to a seven-day to 10-day period.”
The new technologies are also going to change how cotton is scouted, according to Stewart. “We're doing a lot of work right now, evaluating stink bug and plant bug thresholds and how to sample for them.
“I'm already steering producers away from the old visual worm-checking techniques. All our scouting techniques in the past have always been based on finding worms. The bugs are going to be more important in this new system, particularly in Tennessee.”
Entomologists are evaluating sweep nets, drop cloths, visual and boll damage sampling techniques. After one year of data collection, the drop cloth is emerging as perhaps the most efficient method of sampling.
“I can do 10 drop cloths in 10 minutes. You can't look at 25 plants in 10 minutes and do a good job. We also need six or seven samples to get the kind of confidence we need.”
But more changes in scouting are ahead, according to Stewart. “I think that over the next few years, consultants are going to start developing some bug-specific samples that are going to make scouting a little easier.”