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Resistant pigweed and thrips -- a connection?

Is there a connection between increased use of pre-plant and pre-emerge herbicides slowing down cotton, making it more susceptible to thrips pressure and disease? This issue will be addressed at the Cotton Consultants Conference, during the 2014 Beltwide Cotton Conferences, Jan. 6-8, in New Orleans.

An indirect consequence of managing glyphosate-resistant weeds like Palmer amaranth appears to be an increase in foliar sprays for thrips in cotton, according to Mid-South Extension entomologist Gus Lorenz. This effect, which has to do with changes in weed control that limit the plant’s ability to “outrun” thrips pressure, will be a topic of discussion at the Cotton Consultants Conference, during the 2014 Beltwide Cotton Conferences, Jan. 6-8,  in New Orleans.

The National Cotton Council-coordinated consultants forum, will begin at noon on Jan. 6 with a half-day session that will focus on new developments from industry, including discussions of new varieties, chemistries and emerging technologies.

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The forum will continue on Jan. 7, when selected technical conferences join  the consultants conference at specific times to discuss key issues in those disciplines, including current research. The technical conferences will conclude their meetings at noon on Jan. 8.

“We believe that having some of the technical conferences meet with the Cotton Consultants Conference will foster a lively exchange of ideas and shared experiences among researchers and others who assist producers with making key decisions,” said Bill Robertson, the NCC’s manager, agronomy, soils and physiology, who coordinates the conferences.

Are herbicides slowing down cotton growth?

Tuesday morning, the technical conference will present a program on resistant weeds, thrips control and the advent of new weed control technology. Lorenz connected the dots between the issues.

“With resistant weeds, we’ve begun to use a lot more pre-emerge herbicides the last few years and obviously the ones of us with enough gray in our hair can remember what it was like before Roundup Ready technology, when we were having to use some harsh pre-emerges and pre-plant incorporated materials to keep weeds down,” said Lorenz.

These materials, along with cool, wet environmental conditions over the last two years “haven’t been conducive to good, early growth,” Lorenz said. “The impact that pre-emerges are having on cotton, and the fact that we are having to come over the top of cotton with herbicides that slow cotton down, is giving us some issues with thrips control. A lot of times, we can outrun thrips if we get good growth early on.”

It’s also created issues with nematodes and disease, according to Lorenz.

Can dicamba, 2,4-D crops help?

 “You can visually see the difference in fields that have don’t have those products down and where they do. The growth is so much better. The plant pathologists may tell you we’ve had more seedling disease as well.”

It adds up to more costs in cotton, noted Lorenz. “When you spend the money for a seed treatment, and then you have to make one or two foliar applications, we end up spending way too much money for thrips control in cotton. The problems that we’ve had with thrips have pretty much coincided with the onset of pigweed resistance.”

While dicamba- and 2,4-D weed technologies won’t mean a return to a total post system of weed control, “I do think the new technologies will help.” Lorenz said. “What we’re looking for is something that is going to get us past the harsher pre-emerges that are slowing down cotton growth.”

Over the past few years, cotton producers have grown accustomed to both the ease and the efficacy of seed treatments, and many have told Lorenz that they don’t want to go back to in-furrow treatments of insecticide or fungicide.

Herbicide drift is a concern

The Cotton Consultants Conference will address this issue, as well as recent concerns about thrips resistance to thiamethoxam, a second generation neonicotinoid insecticide and the active ingredient in several cotton seed treatments.

Robertson noted that Mississippi Extension cotton specialist Darrin Dodds and others will present research on “simulated drift with low levels of 2,4-D and the impact it has on non-tolerant cotton. They’re going to tell us what to expect and how to prevent problems with some of the new technologies that are coming up.”

Clemson Extension weed specialist, Mike Marshall, said weed scientists will present several talks on dicamba and 2,4-D technologies, including particle drift in cotton and other crops.

“We want to give consultants an idea of what’s coming and what kind of phone calls they should expect from growers.”

Marshall will also discuss research on new herbicide technologies. “In my plot work, the results have been good. The combinations of dicamba, 2,4-D, glyphosate and Liberty look pretty promising on Palmer amaranth and other weeds.”

Marshall noted that there is one combination in the plots that looked best and he’ll discuss this option at the consultants conference.

Robertson said other key topics at the joint session of consultants and researchers include, target leaf spot, which has emerged as a problem in the Southeast and Mid-South; nematode control; on-farm variety testing; irrigation and plant growth regulator interaction; irrigation instrumentation/data collection for help in scheduling; alternative nitrogen products; and how cotton production is being affected by today’s various crop rotation scenarios.

The Beltwide will continue to offer continuing education units or “CEUs” and serve as the venue for the following recognition events:  The Cotton Foundation/Farm Press Publications’ High Cotton Awards, Cotton Grower magazine’s Cotton Achievement Award and Cotton Farming magazine’s Consultant of the Year. The National Cotton Ginners Association will continue to conduct meetings in conjunction with the Beltwide Cotton Conferences, including participation in the technical conferences for cotton ginning and cotton engineering-systems.

For the 2014 Beltwide Cotton Conferences, self-registration will be available 24 hours a day beginning the evening of Jan. 5 while the same can be done at a staffed registration desk that will open on the morning of Jan. 6. Housing/registration instructions, a schedule of events and general information are at

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