Control annual weeds with fall-applied herbicides ahead of corn and sorghum
With row crop harvest well underway, it is time to start planning fall herbicide applications. Herbicide applications in late October through November can improve control of difficult winter annual weeds. Fall weed control is associated with warmer soils and easier planting in the spring, however, it is important to remember that fall-applied herbicides may limit your crop options in the spring. Also remember that herbicides should not be applied to frozen ground.
Some of the key herbicides to consider for fall herbicide applications include Autumn Super, Canopy, Spartan or Authority, and Valor for residual activity. For burndown activity, glyphosate, 2,4-D or dicamba are good options to consider. One thing to keep in mind about residual activity from fall herbicide applications is that weather conditions will influence the length of residual control and the weed emergence patterns. So, even though they provide some residual activity, additional spring application pre-emergence herbicides will likely be needed for season-long weed control.
Some of the key weeds to target with fall herbicide applications are marestail, henbit, dandelion, prickly lettuce, pepperweed, field pansy, evening primrose, and recently-emerged cool-season grasses. When higher rates of herbicides are used, some control of early spring-germinating summer annual broadleaf weeds such as kochia, common lambsquarters, wild buckwheat, and Pennsylvania smartweed can be achieved.
Marestail is a problem that merits special attention. Marestail is much easier to control in fall or early spring while it is still in the rosette growth stage (Figure 2). 2,4-D or dicamba can effectively control fall-emerging marestail plants. Sharpen can also be very good on marestail and may provide residual control through spring, but should be tank-mixed with 2,4-D, dicamba, or glyphosate to prevent regrowth. Valor is another product that may provide residual control of marestail. Because many marestail populations are resistant to Group 2 herbicides, ALS-inhibitors like Autumn Super and Canopy may not provide control if applied alone.
The use of trade names is for clarity to readers and does not imply endorsement of a particular product, nor does exclusion imply non-approval. Always consult the herbicide label for the most current use requirements.
Every year K-State Research & Extension has available on-line or printed books that you can picked up at your local or district Extension Offices. 2020 Chemical Weed Control for Field Crops, Pastures, Rangeland, and Noncropland, K-State publication SRP-1148.
Information provided by Sarah Lancaster and Vipan Kumar, K-State Research & Extension Weed Science Specialist.
Stacy Campbell is an Agriculture and Natural Resources agent in the Cottonwood District (which includes Barton and Ellis counties) for K-State Research and Extension. You can contact him by e-mail at firstname.lastname@example.org or calling 785-628-9430.