WEST LAFAYETTE — 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 pre-emergence 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: