This winter's record snow cover in parts of the Midwest is likely to contribute to abundant winter annual weed infestations in no-till fields, says Bob Hartzler, Iowa State University weed specialist.
In most years, winter annual infestations suffer significant mortality due to cold temperatures and freeze-thaw cycles, but the snow provided a blanket of protection. Thus, Hartzler says winter annual infestations will likely be more abundant and vigorous than in typical years.
He suggests no-tillers begin scouting fields now to determine the need for herbicide applications specifically targeting winter annuals.
"The decision to treat winter annuals prior to planting should be based both on the species present and their distribution throughout the field," Hartzler says. "Knowing what you're dealing with is essential for understanding the potential impact of the weed and selecting an appropriate treatment."
Hartzler says an identification guide focusing on winter annuals and other early season weeds is available from the University of Missouri Extension. The cost for Early Spring Weeds of No-Till Crop Production is $3.00, or it can be downloaded as a free PDF.
Fields that have a few, scattered patches of winter annuals normally do not warrant special treatment prior to planting, Hartzler says. However, the burndown program should be adjusted to ensure complete control of these weeds at planting since they can be highly competitive with the emerging crop.
"Fields with uniform infestations of winter annuals may benefit from burndown treatments made well ahead of planting," Hartzler adds. "Benefits of early applications include weeds being easier to control than at planting, and preventing the weeds from accumulating sufficient biomass to interfere with planting operations or crop establishment.
"If planting delays occur due to a wet spring, there may be large benefits achieved from controlling winter annual weeds in the next few weeks if conditions permit. As with any pest, proper identification of the winter annual weeds is critical in order to select an appropriate strategy."