Using Ignite herbicide on Phytogen cotton that contains the Widestrike gene for insect management is becoming a popular practice for growers in Virginia and North Carolina, despite warnings that the practice may damage the crop, leaving the grower no recourse, if things go wrong.

“This is our fifth year of using Ignite on Phytogen cotton, and we’ve had little damage — none that we feel has reduced our yield,” says Windsor, Va., grower Paul Rogers.

Rogers says he fully understands the risk, but feels it’s justified as long as he keeps a watchful eye on the weather. “Some growers in our area have gotten some fairly severe burn using it, but that’s only when it is applied in the heat of the day or if they add an adjuvant to it,” Rogers adds.

In Capron, Va., Cliff Fox says he does get some burn on some of his cotton from using Ignite on Widestrike cotton. “We’re careful of how we use it and when we apply it, but still you can see some burn sometime, but not enough to damage our yields,” he says.

“I learned real quick when to ‘not’ spray it — 11 o’clock in the morning is definitely not the right time. I thought the leaves would be tough enough by that time, but after a few days you could see the burn. I sprayed a different field about 6 p.m., and I couldn’t see any burn,” Fox says.

“Waiting later does reduce the burning on the cotton plants, but I’m concerned we may not be getting quite as good weed control by waiting until late in the afternoon to spray it,” Fox adds.

Both Bayer CropScience, which sells LibertyLink cotton varieties that are tolerant of Ignite herbicide, and Dow AgriChemical, which sells Phytogen Widestrike cotton seed frown on the practice. Both claim no responsibility if growers damage their crop, but the practice is legal, as long as growers follow label restrictions on the herbicide.

Weldon, N.C., Crop Consultant Daniel Fowler says the value of using Ignite herbicide on cotton is to help growers avoid or reduce the risk of yield loss from glyphosate resistant pigweed.  “I make real sure the grower understands that the gene in the Widestrike cotton is similar to, but not the same as the gene that makes it safe to spray Ignite herbicide on LibertyLink cotton,” Fowler says.

The North Carolina crop consultant says he is seeing more and more pigweed that appears to be resistant to Roundup (glyphosate). “We’ve seen what kind of problems growers in the central and southern parts of the state have had with Roundup resistant pigweed and marestail, and we’re doing everything we can to try and stay away from those kinds of problems up here,” Fowler says.

Fowler adds that a few growers have had significant burn problems if they tank-mixed Ignite with AMS (ammonium sulfate). “And, if you have to apply it before the crop comes up, Ignite can be finicky, but when used at the right plant growth stage and applied at the right time of day, few growers have had any problems at all using Ignite on Widestrike cotton,” he says.

University of Georgia Weed Scientist Stanley Culpepper has done a number of research projects with the LibertyLink System and explains the genetic process that renders LibertyLink cotton varieties tolerant to glufosinate, the active ingredient in Ignite herbicide.

Broad-spectrum herbicide

“Glufosinate is a broad-spectrum, non-selective, foliar herbicide that effectively controls many grass and broadleaf weeds.

“Phosphinothricin, the active portion of the glufosinate molecule, inhibits the enzyme glutamine synthetase. Glutamine synthetase is the initial enzyme in the pathway that assimilates inorganic nitrogen into organic compounds. Glutamine synthetase is pivotal in nitrogen metabolism converting ammonia and glutamic acid into glutamine.

“Since plants detoxify ammonia almost exclusively through this pathway, glufosinate causes the accumulation of ammonia accompanied by cessation of photosynthesis, disruption of chloroplast structure, and vesiculation of the stroma,” Culpepper says.

The primary source of LibertyLink cotton tolerance to glufosinate is a mechanism based on metabolic inactivation of Ignite herbicide.

The glufosinate resistant BARgene of Streptomyces hygroscopicus and PATgene of Streptomyces viridochromogenes encode for phosphinothricin-acetyltransferase, an enzyme which converts L-phosphinothricin that kills plants to non-lethal N-acetyl-L-phosphinothricin.

A similar PAT gene is used in Widestrike cotton primarily to allow scientists to track the movement of the gene used to make these cotton varieties non-palatable to a wide range of insect pests that commonly feed on cotton.

Though not an exact copy, the PAT gene in Phytogen Widestrike cotton does make cotton plants tolerant of glufosinate-based herbicides, including Ignite, which is part of the LibertyLink system marketed by Bayer CropScience.

Long-time Cotton Agronomist Johnny Parker, who works for Continental Cotton Gin in Windsor, Va., says telling Virginia cotton growers not to use Ignite on Widestrike cotton is a good way to lose credibility.

“They have been using it for years, it works, it provides another good tool for managing weeds and grasses and there have been few problems with it.

Learned from neighbors to south

“I think our growers really learned from their neighbors to the south — they saw the problems growers in the Carolinas were having with herbicide resistant weeds. Palmer amaranth is the big one, but we have resistance in other weeds and grasses as well,” Parker says.

“One big tool our growers are using is Ignite. Once pigweed gets through residual herbicides, we can still manage weeds with Ignite. Without it growers would be looking at a lot of expensive hand labor to keep resistant weeds under control,” he adds.

“There is no doubt that Ignite or glufosinate helps us keep our weeds under control, especially in fields with weeds that are resistant to Roundup or glyphosate. When growers start using glufosinate on crops that are not in the LibertyLink program, then it starts getting interesting, Parker says.

“When a farmer has a weed complex that drives him to glufosinate, he must understand the risk he is taking by using Ignite or glufosinate on Widestrike cotton and weigh that against the risk he is facing by having weeds in his cotton field.

“Right now, the best option for Roundup Ready crops that have ALS resistance and possible glyphosate resistance is using Ignite. The real risk may be of over-using Ignite and getting into a similar problem we already have with glyphosate resistant weeds,” Parker stresses.

“I think the producer needs to understand the risk, he doesn’t need to be protected from the risk. It’s hard to tell cotton growers in Virginia they are messing up by using Ignite on Widestrike cotton, because they are using the combination and making 1,300-1,400 pound per acre cotton,” Parker notes.

“There are some situations in which a grower would be better off using Ignite only on LibertyLink cotton. If they know they have a problem with glyphosate resistant pigweed, and they know they will be spraying cotton the maximum amount with Ignite, they may be better off sticking with cotton varieties that have the specific gene for resistance to glufosinate,” he concludes.

In these days of high tech agriculture, with multiple genes in seed to protect crops from one thing or another, the question whether to use Ignite herbicide on Widestrike cotton comes down pretty much to common sense.

Common sense tells you that if you use the combination, you have some inherent risk. It also tells you not to spray in the middle of a hot day and to not use any kind of adjuvant to make the herbicide hotter.

Growers are not likely to get an official list of what to do and what not to do when using Ignite herbicide on Widestrike cotton. Balancing the risk involved in growing a crop is as old as farming itself, and growers are likely to make the right decision most of the time.

rroberson@farmpress.com