Bollworms, resistant weeds, harvest aids, root rot and varieties all received attention during the cotton breakout session at the 25th annual Texas Plant Protection Association Conference in Bryan,Texas, last week.
Stephen Biles, Texas AgriLife Extension Service, asked the audience: “What do we do with bollworms that survive Bt cotton technology?” Also, “do a few escapes justify overspraying Bt cotton? Is yield enhanced by overspraying, even with no insect pressure?”
As for spraying escaped bollworms, Biles said cotton producers should treat them in Bt cotton the same as they do in non-Bt varieties—follow the threshold numbers. “We were unable to find any benefit to treating Bt cotton for caterpillars. Simply finding bollworms does not indicate we need to treat the field. Threshold levels to justify spraying should be the same for Bt cotton as it is for non-Bt cotton.”
That threshold should be based on larvae “larger than one-fourth inch and damage—not on egg counts or early instar.” Also, 5,000 worms per acre or eight to ten per plant is a useful trigger point.
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Paul Baumann, Extension weed specialist, said introduction of triple herbicide tolerant cotton will offer cotton farmers a new tool to battle herbicide resistant weeds, especially pigweed, but the new technology also comes with concerns.
For one thing, farmers in South Texas will have to rethink cotton stalk destruction. Now that 2, 4-D is part of the herbicide tolerant technology, it will no longer be part of the routine for killing cotton stalks after harvest. “That has been one of the most flexible options,” Baumann said. The triple tolerant package includes resistance to glufosinate, glyphosate, and dicamba.
Also of concern is spray tank contamination. Even a small amount of dicamba left in the tank could injure susceptible crops, including non-tolerant cotton. “We have seen a lot of spray drift injury,” he said. Vulnerable plants include vegetables, non-tolerant cotton and homeowner landscape plants.
“I’m not certain we have a good handle on this issue yet,” Baumann said. “When does the wind not blow in Texas?”
He added that the new technology “greatly enhances our ability to manage weed resistance. There is no question about that. But we must employ product stewardship with a new program or it will get us into another mess.”
Back to basics
Baumann offered other recommendations on effective weed control. “We can no longer wait until weeds get 12 inches to 14 inches tall before we treat. At that height, they are doing economic damage to the crop.”
He advises farmers to use multiple modes (and sites) of action and to get back to traditional weed control systems, including pre-plant and pre-emerge herbicides. “We want to mix chemistries. It can be a challenge to put three or four herbicides on the crop, including pre-plant, post-emergence and all. That’s a lot of money tied up in the crop. But have you looked at the cost—and availability—of hoe hands? Residual and knockdown activity keeps infestations in check. Properly incorporated trifluralin products are hard to beat.”
He also advised growers to be alert for signs of weed resistance. “Watch for single plants that escaped control. Look for dead plants all around it. Also, check patches of escaped weeds surrounded by dead weeds.”
Gary Schwarzlose, Bayer CropScience, said cotton harvest aid improvements through seed traits is “not likely.” He also looks for no new products specifically designed as harvest aids. “But we should test everything, spray it on cotton and pay attention. Curiosity often leads to new discoveries. Consider the past; products that were designed for something else have been used for cotton harvest aids.”
In fact, the first cotton harvest aid was discovered by accident in South Carolina back in 1938.
Schwarzlose reviewed the history of harvest aids and noted that the change from manual harvest to mechanical was the catalyst that led to widespread use. “When cotton was hand-picked, it took one person 100 hours to pick one bale of cotton,” he said. Dropping leaves was not an issue and producers would pick several times as later bolls matured.
“With mechanization, we don’t want green cotton and we want to go as fast as we can and as efficiently as possible.” That’s when defoliants and boll openers became useful tools.
One of the early desiccants was arsenic acid that was used primarily as a wood preservative. It’s no longer available.
Tom Isakeit, Extension plant pathologist, offered an update on cotton root rot control. He says 1872 marked, “the earliest reference to root rot in cotton. They thought it was a soil chemistry problem. It was not.”
For more than a century researchers looked for control measures to manage cotton root rot with virtually no success. “In 2005, we started screening new fungicide classes with a lot of grower support and an Extension-driven effort,” Isakeit said. “We screened a lot of fungicides.”
The effort finally paid off in a product initially selected to control Asian soybean rust, an anticipated catastrophe that never materialized. “In 2012 we received a Section 18 exemption for Topguard (flutriafol) and after 125 years of fighting the disease and a lot of ineffective treatments, we had a product that worked.”
Farmers treated from 150,000 to 170,000 acres of cotton with Topguard in 2013, Isakeit said, “resulting in an estimated economic benefit of $8.5 million.”
That advantage was limited to growers who had adequate moisture that would support disease development during the growing season. “Even if the fungicide was not completely effective in preventing the death of the plant, stalks tended to remain in the ground during harvest, making harvest easier and faster.”
Isakeit said continuing efforts will include fine-tuning application methods and incorporating the fungicide into an integrated pest management (IPM) program that should include crop rotation. “We still need crop rotation to help deal with other stress factors,” he said.
Current recommendation is a T-band, in-furrow spray application. “We want to protect the seed from direct contact with the fungicide.”
He also noted that farmers who irrigate should not plant dry and then irrigate the crop up. Seedling vigor could be affected.
Topguard is manufactured by Cheminova and representatives present indicated they expect full registration in 2014.
Gaylon Morgan, Texas AgriLife State Extension cotton specialist, offered a brief look at Central and South Texas variety trials.
“Variety selection is one of the most important decisions a producer will make each year,” Morgan said. That decision is made even more important, and perhaps more difficult, as new technology comes on line.
“In addition to determining yield and quality, variety selection will dictate management decisions and inputs for the entire season.”
He says previous year’s results from the Replicated Agronomic Cotton Evaluation (RACE) trials show the value of paying attention to data and making wise variety selections. “RACE trials have typically identified more than a 25 percent difference in yield between varieties (worst to best) at any given location. These yield differences will directly affect the profitability of the cotton crop.”
He recommends growers choose multiple varieties each year, based on trial data. That data will offer information on yield across a number of locations over multiple years. http://cotton.tamu.edu .