It's Time to Scout for Winter Annuals

March 18, 2010
ICM News

by Bob Hartzler, Department of Agronomy

In addition to wet fields and localized flooding, this winter's record snow cover is likely to contribute to abundant winter annual weed infestations in no-till fields. 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, winter annual infestations will likely be more abundant and vigorous than in typical years.

Now is the time to scout fields to determine the need for herbicide applications specifically targeting winter annuals. The criteria used to determine if winter annuals warrant treatment is 'fuzzy' at best, but without scouting fields, the likelihood of efficiently managing these weeds is low.

The decision to treat winter annuals prior to planting should be based both on the species present and their distribution throughout the field. Winter annual identification skills of many agronomists are relatively weak, but knowing what you're dealing with is essential for understanding the potential impact of the weed and selecting an appropriate treatment. An ID 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. 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. 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.


Field pennycress is a common winter annual in no-till fields.


Bob Hartzler is a professor of agronomy with extension, teaching and research responsibilities.


Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Integrated Crop Management News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on March 18, 2010. The information contained within may not be the most current and accurate depending on when it is accessed.