Fall Herbicides – Target Horseweed a.k.a. Marestail
DR. ANTHONY OHMES
POPLAR BLUFF, MO.
The number one target weed for fall herbicides should be horseweed, also known as marestail, with all the other winter weeds controlled considered a bonus. This past spring’s wet and cold weather played havoc on burndown products providing complete control in a timely manner, especially of marestail. The attached photo is an example of some the spring burndown failures. Products containing 2,4-D or dicamba provide good control of emerged marestail in the seedling to rosette stage prior to spring bolting. These products provide more consistent control in the fall vs. spring. Scout fields for newly emerged marestail following this fall’s harvest. Marestail is considered a winter annual however it will continue to emerge well into spring, therefore the use of residual products is recommended as part of a base 2,4-D or dicamba program, especially in problem fields. However, the use of residual products does not guarantee that you will be free of weeds such as marestail at planting, so always scout in the spring ahead of planting.
Keep in mind that fall herbicide programs will not deliver control of summer annual weeds such as waterhemp and Palmer amaranth. These weeds should be managed with residuals close to planting in order to extend the residual control into early crop emergence.
There have been two articles recently written on fall herbicide programs in the MidAmerica Farmer Grower by Dr. Kevin Bradley, University of Missouri and Dr. Aaron Hager, University of Illinois. Dr. Bradley’s article looked at several aspects of fall herbicides including soil conditions such as spring soil temperatures, soil moisture, and soil nutrients available in the spring and pest interactions. Both articles addressed weed control, in particular fall herbicide programs that target horseweed.
More information on residual herbicides can be found in the Pest Management Guide, M171 at the following website: http://extension.missouri.edu/p/M171. Dr. Bradley’s and Dr. Hager’s articles can be found on the MAFG website: http://www.mafg.net/2013-Archives/. Dr. Bradley’s article is in the September 27th issue titled, “Considering Fall Herbicide Applications: It’s Not Just About the Weeds” and Dr. Hager’s article is in the October 11th issue titled, “Fall Herbicides To Control Marestail (Horseweed).”∆
DR. ANTHONY OHMES: Agronomist, University of Missouri