In controlling weeds in a cotton crop, Missouri Extension researchers have been studying systems to find out if it's possible to make only two passes through a field and still maintain weed control. Of special interest is utilizing a Roundup Ready system with residual herbicides that will carry a crop through the year.

The ability to obtain adequate weed control from fewer field passes would impact producers' bottom lines through using less diesel, labor and herbicides.

“We're checking several application timings: pre-emergence, cotyledon, over-the-top at three- to five-leaf, and directed sprayings at eight- to 10-leaf. Out of those growing stages, we're picking combinations of two to find out what works best,” says Robert Cobill, a research associate of Missouri Extension weed specialist Andy Kendig.

Cobill and others have been developing a two-pass system based on tank mixes of residual herbicides with glyphosate.

He says the “key” to the research has been a three-way mix of Roundup/Dual II Magnum/MiloPro. Roundup kills the early weeds, Dual is a residual grass herbicide, and MiloPro works as a residual broadleaf herbicide.

Other herbicides being studied are Prowl/Cotoran as a pre-emergence; Roundup Ultramax at any of the stages; Dual II Magnum/MiloPro at cotyledon and over-the-top at three- to five-leaf; and Cotoran/MSMA at eight- to 10-leaf.

Weeds looked at in the study are Palmer pigweed, common cocklebur and goosegrass. So far, “control has been good with almost every treatment — anywhere from 86 to 95 percent in holding the three weeds in check.”

For comparison, “we put out some three-pass programs, and control was comparable to findings for two-pass. What we've found is by going with this particular two-pass program, we're getting similar results to a three-pass. It shows the versatility of the program in that you can use it in a variety of stages,” says Cobill, who spoke at the Delta Center field day at Portageville, Mo., on Aug. 30.

Why use MiloPro? “We've worked with this product in some past studies and saw that it had some potential. We brought it into this study, and it's worked very well. Right now, I'm not sure if it's even available for purchase.

“It isn't labeled for cotton. We're now checking to see if it has any effect on crop-to-crop injury, although that hasn't been seen yet.”

MiloPro was typically used in Texas on milo crops. Cobill is unsure how much it's used there now.

“We've talked to the manufacturer — Griffin — about a label for cotton and they expressed interest. Where that stands, I'm not sure.”

Envoke is another product Cobill has been studying for several years. An ALS compound with a low use-rate, Envoke is a new product similar to Staple. Envoke should be available to producers in 2003 or 2004.

“We've been using it at two-tenths of an ounce per acre, and it's been very strong on cocklebur and morningglory species. However, it's a bit weak on prickly sida and pigweed.”

Another product researchers are checking is a pre-mix of Envoke and Caparol called Suprend. “We put it out at a high rate of just over a pound and a low of eighteenths of active ingredient per acre. It was placed on fields alone and in combination with other herbicides. It was direct-sprayed at both six- to nine-leaf and layby. Typically, we found better control for Suprend at the six- to nine-leaf stage. Both Envoke and Suprend give really good control.”

Envoke/glyphosate mixtures have also been looked at. Cobill says while weed control was good, the Envoke did cause “significant” yellowing and stunting.

A system much like Roundup Ready, Liberty Link cotton is also on Cobill's radar screen. So far, he's seen no adverse crop response to Liberty (a nonselective herbicide) applications.

“The weed control was excellent. Control of pigweed and grasses was enhanced with a pre-emerge.”