Weeds can become a major problem in crop production when not controlled prior to planting. This is especially important in no-till systems. Weeds emerging in late summer through fall can overwinter and flower to set seed in the spring and early summer. Identifying weeds before planting corn can be difficult, especially if plants are in the rosette state of development.
Scouting fields before planting can identify what weeds are present, their population, and their growth stage.1 This information helps to determine what management practices and herbicides would be most effective for protecting the upcoming crop prior to planting and after establishment. For more information, read the Q&A article, Making Decisions Based on Weed Scouting in Corn.
Good weed control during the first four to six weeks after planting is critical for maintaining yield potential. A clean start helps to conserve moisture for the crop, promote good seed-to-soil contact, and helps prevent weeds from binding up planters. For more information on early and late burndown herbicide applications, read Benefits and Limitations of Early Burndown Applications or Benefits and Limitations of Late Burndown Applications.
Considerations for No-Till Systems
Winter annual weeds have become a larger problem in no-till fields due to the limited use of soil residual herbicides and the reliance on postemergence weed control associated with planting herbicide-resistant crops. Marestail has become a difficult to control weed for no-till fields because there are many populations that are glyphosate-resistant.2 It is important to control marestail when it is small, which can require control as soon as equipment can enter the field.3
Plant debris in no-till fields can provide overwinter protection for germinated weeds, increasing weed populations.4 Fields that have been in no-till production for a few years may have a few scattered patches of weeds, which may not seem economically important to control. However, these patches may have enough time to seed out before a burndown application is made, creating problems in subsequent years.3
Identification of Common Early Annual and Perennial Weeds
Common weeds that may be present in fields prior to planting corn in the South include marestail, henbit, Italian ryegrass, wild mustard, red sorrel, Carolina geranium, smartweed, lambsquarters, and pigweed. CLICK BELOW FOR IMAGES AND MORE INFORMATION.
For more information about managing winter annual weeds, read the Spotlight: Tillage Effects on Weed Management .
1 Pittman, K., Flessner, M., and Ackroyd, V. Start the season out right: plant into weed-free fields. https://integratedweedmanagement.org/index.php/iwm-toolbox/cultural-practices/plant-into-weed-free-soil/
2 Werle, R. and Sandell, L. 2013. Managing winter annual weeds starts this fall. University of Nebraska. https://cropwatch.unl.edu/managing-winter-annual-weeds-starts-fall.
3 Hartzler, B. 2009. Managing winter annual weeds in no-till fields. Iowa State University. https://crops.extension.iastate.edu/cropnews/2009/04/managing-winter-annual-weeds-no-till-fields.
4 Clay, S.A. 2016. Selected broadleaf weeds in South Dakota corn fields. South Dakota State University. iGrow Corn: Best Management Practices. https://extension.sdstate.edu/sites/default/files/2019-09/S-0003-39-Corn.pdf.
5 Barber, T. 2020. Winter weed questions already?. University of Arkansas. http://www.arkansas-crops.com/2020/01/09/winter-questions-already/.
6 Fishel, F., Johnson, B., Peterson, D., Loux, M., and Sprague, C. 2000. University of Missouri Extension. NCR 614. http://weeds.cropsci.illinois.edu/extension/Other/NCR614.pdf.
7 Rumex acetosella. NC State Extension. https://plants.ces.ncsu.edu/plants/rumex-acetosella/.
8 Steckel, L. Pigweed description, history and management. The University of Tennessee. http://www.utcrops.com/weeds/pigweed.htm.