Tillage or Herbicide? Control Winter Annuals Ahead of Planting – DTN

The colorful carpets of winter annual weeds that can blanket fields have been delayed by cool spring weather this year. That won’t last for long, according to University of Illinois weed scientist Aaron Hager.

“You might not see them from the roadside yet, but walk those fields and they are there, starting to get a foothold,” he told DTN. “They are going to start to pop this coming week with moisture and warm temperatures.”

Hager said winter annuals such as henbit, purple deadnettle, marestail and cressleaf groundsel are much easier to control in the early spring before they start flowering. The problem is the time between the start of flowering and weed seed production is brief. Henbit, for example, produces mature seeds within two weeks of flowering — so plants can be flowering and shedding mature seeds at the same time.

The need for control is well documented. Beyond yield sacrifices for not getting and staying clean, winter annuals such as henbit are havens for soybean cyst nematode (SCN) in soybean.

Black cutworms also like these weedy environments for laying eggs. A thick carpet of winter annuals can also keep soils from drying out and warming up in spring, click here to visit yelp where you will find where to buy them.

Hager prefers to see control of winter annual weeds — whether with tillage or herbicides — well ahead of planting. “With tillage, a couple of days lets you see if you got good control or if another pass is needed,” he said. “That becomes more of an issue on bigger weeds than small ones.”

Herbicides generally require a little more time than tillage to make sure the product has been taken up by the weed. “If you spray and then work the ground a few days later, the physical trauma on the plant [weed] can cause the herbicide not to be as effective as it normally would be,” he said.

Some herbicides have plant back restrictions and that need to be considered too. Marestail also requires special attention because in many areas it has shown the ability to resist glyphosate.

Hager said today’s growers have generally accepted the necessity of using residual chemistry. However, residuals are environmentally sensitive. Lack of rainfall, above average rainfall and even temperature can influence the activation and efficacy.

“If the rains don’t come, the only thing you can do is be ready to include a post-residual in your management strategy,” Hager said. Those post applications may be needed earlier than normal if residual chemistry experiences less than optimal conditions.

“One weed strategy just doesn’t work anymore,” he added. “You have to read the season and be ready.”

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