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Deep tilling fields may reduce weed problems

Farmers in the upper Southeast are still dealing with thousands of acres of pock-marked and rutted fields, despite the cost and time involved in cleaning up these areas, in the long-run there may be big benefits.

The hardest hit areas by winter rains, snows and freezes generally coincide with the areas hardest hit by herbicide resistant weeds, especially Palmer pigweed. There is continuing evidence that deep tillage can help slow the spread of resistance.

University of Georgia Weed Scientist Stanley Culpepper probably said it best, speaking at last year’s Beltwide Cotton Conference, “If you have dryland production in the Southeast, Mid-South and the Mid-Atlantic states and think you can go in with 50-something-dollar herbicides and control resistant Palmer amaranth without rain, you will lose,” he said.

With ever increasing costs of production, most cotton and grain growers in the upper Southeast don’t have the margins needed to ‘lose’. When fall rains and winter freezes took away approximately 50 percent of wheat planting in the region, gone was one of few sources of cash flow in the spring/summer growing season.

Palmer pigweed has been called the biggest threat to cotton production in the Southeast since the boll weevil. Often called ‘super weed’ and much worse by growers who have to deal with it, the super villain for Southeast farmers does have one research-documented weakness: Its short-lived seed.

To be a super weed and to grow to 5-6 six feet tall and have an above ground stalk diameter akin to a sapling pine tree, Palmer amaranth has to have nutrients. To get those nutrients, it has to have a deep root system. Therein lies the silver lining for hundreds of farmers in the upper Southeast who had to go in this spring and repair fields damaged by equipment operating on wet and/or frozen ground.

There is no doubt about the many benefits of minimum or no-till cropping systems. Reduced-tillage saves farmers money in equipment, improves soil quality, improves the environment by making the soil more porous and produces better drainage. The list of benefits goes on and on.

However, one no-till practice — burndown — may be a contributing factor to the rise in weed resistance problems, especially with deep-seeded weeds like Palmer amaranth.

Soil microorganisms and insects also prey heavily on pigweed seeds. Bottom line is deep tillage and Palmer pigweed don’t dance well together.

Deep tillage also eliminates the need for another common cost-saving no-till procedure — burndown. Pigweed seed aren’t destroyed by burndown and some researchers contend it probably creates light and stimulates germination. Growers in no-till or never-till systems are reluctant to use deep tillage because of the negative impact it can have on fields than haven’t been plowed in 10 years or more. However, one-time tillage can have desired positive effects on weed management and minimal effect on the benefits of being no-till for a long time.

To minimize negative effects on no-till land, the amount of tillage is almost as important as what kind of implement is used. For example, chisel plowing and disking is an effective minimum-tillage system for erosion control. However, if two or three diskings are used, crop residue is buried and the soil is left loose and smooth and jready to wash away.

Tillage should only be enough to control weeds and provide good conditions for planting the crop. More than this simply wastes money and time and increases the risk of soil erosion.

The direction in which the tillage occurs also can have an impact on no-till land. In particular, plowing across the slope rather than up and down the slope reduces erosion and the negative impact on long-term, no-till fields.

Timing of tillage operation also is a factor on undoing some of the benefits of long-term no-till. To get better weed, insect and disease control; and to help balance work schedules, many farmers do their tillage work in the fall.

Timely fall tillage, followed by planting a cover crop has shown to significantly reduce the spread of resistant Palmer amaranth — and other herbicide resistant weeds — and cause minimal damage to fields previously in long-term, no till systems.

“We’ve seen lately a number of growers who have gone ahead and used deep tillage methods in fields that have been in long-term, no-till systems,” says Jeff Mink, a regional agronomist for Syngenta.

“I understand the benefits of no-till systems and many growers don’t have deep tillage equipment, but having to go in and repair fields damaged by fall rains and winter snows may be a blessing in disguise, if resistant weeds are a problem or even a threat,” Mink adds.

“University research indicates moldboard plowing or deep turning the soil is the most effective way of burying weed seed. Growers will need to work the land, then still need to come back with an aggressive herbicide program to manage weeds, especially pigweed,” he adds.

The benefit, Mink contends, is that instead of having hundreds of thousands of weed seed germinating in a field, the grower will have drastically fewer weeds to kill, which in terms makes herbicide treatment more effective.

In areas of North and South Carolina where herbicide resistant pigweed are already a problem, and in areas in which resistance is likely to spread, the winter 2009-2010 weather debacle may provide an ideal opportunity to deal weeds a double blow of deep tillage and intense herbicide management.

Herbicide manufacturing companies have introduced, and in many cases re-introduced a number of pre and post-emergence herbicides that can be used to manage Palmer amaranth. How these herbicides are used is a critical factor in how successful a grower will be in combining them with deep tillage.

Delaying herbicide application to allow more weeds to germinate and thus get more bang for your herbicide buck is definitely not a good thing to do.

Early season weed competition in both soybeans and cotton can result in reduced yield, though little visible impact is often seen prior to harvest.

Application of any of the post-emergence herbicides on larger weeds can result in reduced control of species that are less sensitive to either glyphosate (Roundup) or glufosinate (Ignite).

“By combining deep tillage practices and a standard herbicide program, or even using minimal herbicides that a grower would use in a no-till system, would dramatically reduce the weed population this year. And, it would help keep these numbers down in future years,” Mink says.


TAGS: Management
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