Marestail
Marestail
This year may be an ideal year for farmers to invest in fall herbicide programs. Mark Loux, Ohio State University’s Weed Specialist, provides some great information for farmers regarding weed control this fall. Additional details and recommendations can be found in this week’s C.O.R.N. newsletter at http://agcrops.osu.edu.

Why apply fall herbicides this year? Applying herbicides this fall can compensate for increased weed populations and make life easier in the spring. Due to the wet weather conditions earlier this year that prevented planting and some herbicide treatments, there are more weeds in our fields this time of year than we normally see.

Both winter annual and summer annual weeds have added a substantial number of weed seeds to the soil seedbank. Winter annuals and marestail weed seed lacks dormancy and will emerge this fall. Fall herbicide applications prevent dense mats of winter these weeds from forming in the spring that slow the soil from drying out and warming up, interfere with fieldwork, and harbor insects and soybean cyst nematode.

Loux provides a few reminders to follow:

Applications can be made now through Thanksgiving, and possibly later. Once hard freezes occur, certain weeds like dandelion and thistle become less sensitive to herbicides. Applications during periods of very cold weather or when the ground is snow-covered are discouraged. Recent rain will lead to germination and emergence of the weeds that have been missing until now.

Will crop residue after harvest cause problems? In Loux’s experience, the herbicides seem to work regardless of whether residue is present. Farmers can wait after harvest to let the residue settle and weeds to poke through before applying herbicides. Dense crop residue usually prevents marestail from emerging as well.

Will applications be complicated or pricey? The primary goal is to control weeds that have already emerged with relatively low-cost two-way mixtures. Loux’s philosophy has been to start with 2,4-D, and then add another herbicide to provide more comprehensive control. Based on his research, herbicides that make the most sense to add to 2,4-D include glyphosate, dicamba, metribuzin, simazine, Basis (and generic equivalents), Express (and generic equivalents), or Canopy/Cloak DF or EX. These allow either corn or soybeans to be planted the following year with these exceptions: simazine - corn next year; Canopy/Cloak - soybeans next year; Basis - possibly restricted to corn based on rate and geography. Loux does not see a need for three-way mixtures, unless a low rate of glyphosate is added to a two-way mix to control grass or improve activity on perennials.

Is there an advantage to including residual herbicides? No, because nearly all dissipate over the winter and fail to control spring-emerging weeds. The primary exception to this is chlorimuron (Canopy/Cloak), which does persist at high enough concentrations to provide some control in spring. Loux’s research has shown that applying other residual herbicides in the fall for spring control is a waste of money. The good news is that any effective fall herbicide treatment with or without residual will result in a weed-free seedbed usually into April, so that spring-applied burndown/residual treatment just has to control small weeds that emerge in the few weeks prior to planting.

For additional information, please visit https://agcrops.osu.edu or contact the Putnam County Extension office at 419-523-6294, by email at Scheckelhoff.11@osu.edu or stop in at 1206 East Second Street in Ottawa. You can also find us on Facebook by searching for OSU Extension Putnam County.