Fields that are already heavily infested with winter annual weeds like henbit, purple deadnettle, chickweed or mustards are good candidates for a fall burndown herbicide application (Figure 2).
Figure 2. Winter annual weeds, purple deadnettle on the left and henbit on the right.
Marestail (horseweed) is a winter or summer annual weed that can germinate in the fall as well as in the spring (Figure 3).
Figure 3. The common marestail (horseweed) plant is best managed when it is small in the seedling or rosette stage before bolting in the spring.
Through the fall and winter, late summer and fall-germinating plants remain in the low-growing rosette stage before bolting (or stem elongation) occurs in the spring. Marestail is more easily managed with herbicides when weeds are small and in the rosette stage. Fall-emerging plants often bolt earlier in the spring, which can make spring burndown herbicide application more difficult to control.
Dandelion is a perennial weed that spreads by seeds, which can germinate on the soil surface at low temperatures. Seedlings of dandelions quickly develop a crown and taproot. Mature dandelion plants can live for many years and become a serious problem in minimum or no-till fields (Figure 4).
Figure 4. Flowering dandelion plants.
Dandelions grow late into the fall — they are hardy plants that can tolerate frost. Palmer amaranth and common waterhemp are summer annual weeds but can still emerge after harvest and produce seed in as little as five to six weeks. Common waterhemp is a summer annual that should also be managed after harvest to prevent seed production. Other weeds that can be targeted in the fall include dandelion, common waterhemp and Palmer amaranth.
Figure 5. Young Palmer amaranth plants can grow quickly and produce seeds in the fall.
Figure 6. Common waterhemp can emerge and produce seed after harvest.
Anderson, M., Hartzler, B., and Jha, P. 2019. Fall burndown treatments for winter annual weeds. Iowa State University, Integrated Crop Management. https://crops.extension.iastate.edu.Hager, A. 2018. Fall-applied herbicides: Which weed species should be the target? University of Illinois at Urbana-Champaign, Department of Agricultural and Consumer Economics. Farmdoc daily (8): 157. https://farmdocdaily.illinois.edu.Bradley, K. 2013. Considering fall herbicide applications: It’s not just about the weeds. University of Missouri, Integrated Pest Management. https://ipm.missouri.edu.Web sources verified 10/05/2021. 8001_S2