Technology traits that enhance worm control while minimizing resistance potential? They’re here. And more traits are coming. For example, Syngenta has licensed its Vip3A Bt protein to be stacked with the two-gene Bt systems in Monsanto’s Bollgard II, Dow’s Widestrike and Bayer’s TwinLink varieties, forming Bollgard III, Widestrike 3, and TwinLink Plus cotton varieties, respectively. Widestrike 3 is commercially available; Bollgard III and TwinLink Plus are both in the pipeline.
Oklahoma State University cotton specialist Randy Boman is excited about the three-gene, in-plant traits that provide season-long Bt-protection against lepidopteran pests. “I’m excited to see the third Bt trait come in because it will improve our spectrum of worm control and minimize the potential for insect resistance,” he notes.
“Vip3A is a totally different source of Bt protection — it’s called the vegetative insecticidal protein from Bacillus thuringiensis (Bt). It’s a very critical enhancement to our existing double-stacked Bt trait technology. Vip3A will improve the spectrum of control on some of the caterpillar pests. And, of course, having three different Bt traits in these varieties will improve resistance management, making it more difficult for caterpillar species to develop resistance to all three proteins.
“This past season I had a test with Phytogen’s PHY 495 W3RF at Hydro, Okla. That’s the first triple stacked Bt variety that we have looked at so far in our state.”
Oklahoma cotton producers grow almost 100 percent Bt varieties, which shows they find value in the technology. Partly because of the widespread acceptance of the technology in the state and the rest of the Southwest, one of the biggest concerns of research and Extension personnel in cotton is making sure that the Bt technology does not break down, allowing insect resistance to develop.
“So there’s huge value from the standpoint of resistance management with the inclusion of VIP3A from Syngenta being stacked with two-gene Bt traits in cotton varieties,” Boman says.
With the continuing, major drought the last few years, the Southwest has seen traditional bollworm pressure diminish because of the lack of alternate hosts that keep the populations moving. “Our trapped numbers of budworm, bollworm and beet armyworm have significantly diminished to historic lows,” Boman says. “However, I’d rather have more rain and a better crop and fight the bollworm complex, especially since we have the newer three-gene protection traits in cotton coming.”
Diminished resistance potential
North Carolina State University cotton specialist Keith Edmisten is also excited about the expanded worm control and diminished resistance potential offered by triple-gene Bt traits in cotton.
“The triple-stacked insecticide trait varieties provide a built-in safeguard against worm resistance, which is important for long-term viability of the technology,” Edmisten says. “The more modes of action that we use, the less likely we are to develop resistance. Multiple modes will enable the technology to be around a lot longer and extend the efficacy.”
Edmisten is also excited about advances in technology traits that someday will control plant bugs and thrips. Plant bugs in the last two years have become more problematic for North Carolina cotton growers, especially in the northeast part of the state, which seems to be the hot spot.
“Additionally, thrips numbers have always been highest year in and year out for us and Virginia, especially during early season, slower growth when thrips damage is more severe,” Edmisten says. “North Carolina and Virginia seem to have the highest thrips pressure of all the cotton-producing states. Thrips particularly cause problems in the northeast part of the state and up into Virginia where maturity delays are even more critical. So we’ll welcome cotton varieties offering control of thrips and plant bugs.”
Additionally, cotton growers can look forward to varieties coming down the road that offer nematode resistance, according to University of Arkansas cotton specialist Bill Robertson.
“It is my understanding the nematode population actually declines with these varieties that were developed through conventional breeding,” Robertson says. “We already have some nematode-tolerant varieties that perform well under significant pressures, but they don’t lower the population. The new ones coming down the pike not only perform well in high nematode populations, they actually reduce the number of nematodes.
“Innovations like that are exciting because where we have high nematode populations, we certainly lose roots to nematodes. To compensate, we have adjusted our irrigation, and our nitrogen and potash rates; everything is geared toward the plant’s uptake ability. So nematode-resistant varieties will affect our cultural practices. For example, the protected root system will be much more effective, which will affect our nitrogen rate — we might be able to reduce our nitrogen rate and other inputs without impacting yield. We will be more efficient with our inputs, including water and fertilizer. The potential is exciting.”
Robertson says Mid-South cotton growers are also watching the advent of three-gene cotton varieties. For example, he notes PHY 495 W3RF was included in the state’s university variety trials in 2014. “Having a third Bt gene will definitely benefit the worm control efficacy,” he says.
“This past season we saw more oversprays for multiple generations of worms that got through the two-gene products. Products still control tobacco budworm, but cotton bollworm breakthroughs require overspray. With the third gene coming in, we hope it will improve our worm control in the same way that going from a single-gene to a two-gene Bt transgenic, heliothis-resistant cotton did.”