Farmers need to start scouting their fields for winter annual weeds and making decisions about spring burndown herbicide applications, a Purdue Extension weed scientist says.

Nearly all fields will require some form of spring herbicide treatment, but the earliest attention will need to be given to fields that didn’t receive one last fall.

“The jury is still out on how the past winter affected winter annual weeds that emerged last fall and were not controlled with a fall herbicide application,” Travis Legleiter said. “Either way, it’s likely that spring burndowns will need to be made to control some winter annual weeds – in particular, marestail.”

Many winter annual weeds will start to grow rapidly as the weather consistently warms.

The key to controlling rapidly growing weeds is to properly time spring burndown treatments while considering weed sizes and air temperatures.

“Applications need to be made when weeds are actively growing but when plants are still small, or prior to bolting for marestail,” he said. “To ensure that plants are actively growing, make applications when nightly temperatures have maintained above 45 degrees Fahrenheit for four to five days.”

For longer-term weed control, Legleiter said it’s best to apply a spring burndown herbicide, then come back before crops emerge and apply a preemergence residual herbicide – especially in no-till soybean fields where marestail and pigweed species are growing.

“If planning on using residuals, maximize the residual control into the cropping season by applying the products preemerge rather than tank mixing it with early spring burndown,” he said.

In cases of no-till soybean fields with a lot of marestail, farmers might need to apply multiple spring burndown treatments in addition to residual herbicides.

More information about spring burndown applications can be found in the following free, online articles:

Weeds in winter wheat fields also might need some attention as wheat continues to green up. Some fields have winter annual weeds that will require a spring herbicide application – in part because of how wheat fared in the bitterly cold winter months.

“In typical years, winter annual pressure in wheat is less of a concern, but with potentially weakened wheat stands, the pressure from winter annuals will be more of a concern,” Legleiter said.

Some of the most important considerations for wheat growers developing a weed-control plan include the wheat growth stage and soybean plant back restrictions for fields that will be double-cropped.

One option, Legleiter said, is to combine spring herbicide applications with topdressed nitrogen. Growers who go this route need to be sure to read herbicide labels.

“Many of the herbicide labels do allow for liquid nitrogen to be used as a carrier but might have differing adjuvant requirements and growth stage restrictions as compared to applying with a water carrier,” he said.

Legleiter also said the use of liquid nitrogen as a herbicide carrier also can mean increased risk of crop injury.

More information about spring herbicides and wheat can be found in a free, online article titled Spring Herbicide Applications on Winter Wheat. The article, written by Legleiter and Johnson, covers a number of herbicides, application timing, plant back restrictions and more.