Already a hotspot for herbicide-resistant weeds, Arkansas experienced even more weed troubles this summer. Flooding this spring scattered seeds from resistant weeds all across the cropland. These seeds took root and created a carpet of resistant weeds in fields that used to be clean.

On a trip sponsored by Dow AgroSciences, members of the media visited the area along the White River in north-central Arkansas. Here flood water covered 100,000 acres of farmland. As the water receded, growers hurried into the fields to replant. Often, timely applications of herbicides were delayed. Now those fields are tangled with difficult-to-treat, resistant weeds.

Malcolm Haigwood, grower and custom applicator at Newport, AR, took the group to two soybean fields sitting across the road from each other. One field was completely clean with no weeds in sight. In the other field, soybean plants were barely visible among the giant Palmer pigweed stands.

What happened? Haigwood said it was a combination of poor timing and incorrect herbicides applied after both fields were flooded and then replanted.

“Both fields were (re)planted the same day,” he explained. “The difference in the fields is one had a preplant herbicide put down in a timely fashion so it was activated and then followed by timely postemerge applications. Three applications of glyphosate combined with another chemistry with a different mode of action were applied. The other (weedy) field had only two applications of glyphosate.”

The cost of treating these resistant weeds is high, Haigwood says, considering he used to only need one application of glyphosate a year, which cost just $12 to $15/acre. The four applications of herbicides total $80/acre.

In addition, the field is treated four times versus just one. Haigwood does some custom application and now he needs three sprayers to handle his application jobs versus only one sprayer a few years ago.

Glyphosate is still a good product, Haigwood added, but it can’t handle resistant pigweed alone, and certainly not after pigweed grows beyond 4 in. He said growers also need to follow recommended rates for herbicides. Under-applying a herbicide to save money only gives weeds more room to develop resistance.