2019 harvest continues to progress across the Corn Belt and weed control issues are visible from the combine cab. Fall applications of herbicides may give growers an option to control winter annuals, biennials and perennials. Factors that need to be taken into consideration are targeted weeds, next year’s planned crop and, of course, Mother Nature.

Controlling winter annuals with a fall herbicide application can be more effective than spring burndowns. Winter annuals such as marestail generally stay in the rosette stage in the fall, making burndowns more effective. 2,4-D and/or Banvel® offer a great option for a burndown, and off target movement is greatly reduced as well in the fall. Higher application rates may be necessary for fall applications but can be more effective than lower rates used the following spring.

Fall applications of soil residual herbicides are effective when soil temps fall to 50°F or less (but not frozen). The colder soil temps can increase the herbicide persistence, with more activity next spring when weeds break dormancy which can increase control. Next year’s crop must be taken into consideration when selecting active ingredients. For example, atrazine eliminates soybeans as an option for the following spring, while Valor® and Fierce® give the grower the option for either corn or soybeans.

Control of the waterhemp complex (Palmer Amaranth included) is generally sporadic with fall applied soil residuals due to their emergence patterns in the late spring and summer.

Mother Nature still has the final say in how effective fall applications of herbicides will work. A warm mild winter increases degradation of soil residual products. Delayed harvests can also shrink the window of application.

Fall applied herbicides can improve control of troublesome weeds as well as reduce spring workloads. As always, please read and follow the label for any pesticide application.

Additional Information:

1. https://agcrops.osu.edu/newsletter/corn-newsletter/2015-31/fall-herbicide-applications-and-new-technology
2. https://farmdocdaily.illinois.edu/2018/08/fall-applied-herbicides-which-weed-species-should-be-the-target.html