Bill Meredith is ready to throw in the towel. As a cotton geneticist with USDA's Agricultural Research Service in Stoneville, Miss., Meredith has spent the better part of two decades educating cotton growers and industry members about the potential benefits of nectariless cotton. Unfortunately, his schooling seems to be falling on deaf ears.
It's been more than 20 years since he first published a study on nectariless cotton, and the option remains unavailable to cotton growers.
Yet, the idea seems simple enough. In order to greatly reduce the number of pests attacking your cotton crop, eliminate one of their food sources. As an added bonus, planting nectariless cotton varieties could boost your yield.
Nectar in cotton plants is a major source of food for many insects, and removing that nectar can be done with simple genetics. This nectar, which is produced by glands around the base of squares and on the underside of cotton leaves, is eliminated in nectariless cotton.
Meredith began studying nectariless cotton and its effects on lygus populations in the early 1970s. “It doesn't give immunity, but with this simple recessive gene you can take care of a major part of your problem. Removing the nectar also affects predators because you are taking away a major food supply,” he says.
A 2002 research study by Meredith compared field trials of nectaried and nectariless cotton. What he found was that the nectariless cotton actually yielded more lint, and contributed to an earlier-maturing crop.
“Producing nectariless cotton has a major, positive effect on yield,” Meredith says. “It cuts the yield loss caused by damage from insects such as the tarnished plant bug just about in half, and these numbers have been fairly consistent from year to year.”
In his study, Meredith compared field trials of nectariless cotton with stacked gene cotton varieties with treatments included for all insects including tarnished plant bugs. The nectariless cotton averaged 1,171 pounds of lint per acre to 1,029 pounds of lint per acre for the commercially available cotton variety.
A broadened study this year tested cotton yields with each variety produced under two insecticide regimes — one where six applications were made to control tarnished plant bugs and the other a check designed not to control tarnished plant bugs. The varieties with nectar lost 171 pounds of lint per acre, and the nectariless cotton lost about half that, or 84 pounds of lint per acre.
Because some industry members continue to question the yield loss attributable to tarnished plant bug damage, Meredith included Deltapine 555BR in his 2003 test due to its excellent resistance to the worm complex. The total yield for DPL 555BR with and without tarnished plant bug control was 1,840 pounds and 1,350 pounds of lint per acre, respectively, he says.
“Our results showed a significant decrease in plant bug numbers, dropping by 50 percent, and a comparable decrease in yield losses due to plant bugs. The nectariless cotton also exhibited increased earliness, which had a positive effect on yields and a slight decrease in fiber length in strength in some varieties,” Meredith says.
If nectariless cottons are so good, then why aren't nectariless varieties made commercially available to cotton growers?
The reasons, for the most part, relate to a lack of incentives to the seed companies to develop and market nectariless varieties, according to Meredith.
Prior to the advent of transgenic cotton varieties and the boll weevil eradication program, a liberal use of insecticides generally controlled plant bugs in cotton. “Before 1997, the use of insecticides to control the worm complex and the boll weevil was thought by many entomologists to also take care of the tarnished plant bug problem. However, the use of Bt cottons and the area-wide boll weevil program have greatly reduced the use of insecticides to control these pests,” Meredith says.
In addition, he says, developing and marketing these nectariless varieties requires extra work on the part of seed companies, and that's extra work they can't necessarily pass on to cotton growers. Because removing nectar from the cotton plant is done through genetics and not through biotechnology, the process can't be patented, and is available to all cotton breeders. Also, any outcrosses that could occur in nectariless cottons are readily apparent upon inspection of the affected cotton plants.
“What growers really need is the choice of the nectariless option. It certainly wouldn't hurt anything,” Meredith says. “With the control of the worm complex and the boll weevil, what will fill the void? The answer is tarnished plant bugs and stink bugs.”
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