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In pigweed How to stop glyphosate resistance

Last week I discussed some of my experiences with Palmer pigweed through the years. I hope we can be smarter than the weeds and not come full circle to where I started with them.

We went from not being able to kill them, especially on the sandy soils in northeast Arkansas, to being able to easily kill them with Roundup or other glyphosate products to now seeing resistance problems developing with the Roundup Ready technology. If we let the resistance issue get out of hand, we will have indeed come full circle.

A lot of farmers do not know how we used to control weeds in soybeans. We grew them in rows and cultivated. Cultivation then was more than just making irrigation furrows. It was going slowly with a precisely set cultivator several times during the season to cover weeds.

The herbicide program was often a preplant or pre-emergence herbicide combination, followed by one or two over-the-top herbicides and sometimes a post-directed spray. Farmers who once controlled weeds in soybeans that way gladly forgot how when Roundup Ready came along.

Roundup Ready technology has allowed farmers to grow soybeans with about any combination of row spacing and tillage practices. Weed control has been as simple as spraying a glyphosate product an average of two times during the season.

If glyphosate becomes ineffective, many preferred cropping systems for soybeans will become ineffective. With continuous use of glyphosate-only programs for weed control in soybeans and cotton, it is not a matter of “if” but “when” these programs become ineffective.

Prevention is a much better tool for weed resistance management than trying to control the resistant weeds after you get them. With a prevention program, you maintain the usefulness of the Roundup Ready technology. If you wait until the technology does not work, you will be back to doing things “the old way.”

One of the most effective resistance management tools is crop rotation — if you are rotating to a crop that is not Roundup Ready or to one where there are good Palmer pigweed control options besides glyphosate. I do not worry as much about resistance development where soybeans are rotated with rice as long as you control the pigweeds in the rice.

Sometimes this is not as easy as it sounds. A lot of the worst pigweed problems are in northeast Arkansas on sandier soils. This makes it difficult to maintain a continuous flood, which is a good pigweed control measure. Pigweeds are always more difficult to control on the levees.

One of the most effective herbicides on bigger pigweeds in rice is 2, 4-D, and increased regulations have limited the use of this herbicide in northeast Arkansas.

However, if you get on the pigweeds early in rice, they can be controlled.

This year Arkansas farmers have increased corn and grain sorghum acreage. These crops provide the opportunity to use herbicides such as atrazine and others that are effective on pigweeds. They also can be harvested early to allow working the soil in the fall to encourage weed germination to help reduce the soil seed bank.

Everything helps and it may often mean doing some things that you would rather not have to do.

I feel strongly that we have to maintain the “easy farming” methods (compared to past methods) the Roundup Ready technology has afforded. It will require a consistent crop rotation program as well as some changes in the herbicide programs.

I will go there next week.

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