The 2016 harvest season is underway across much of the Corn Belt. Getting harvest completed is top of mind, but growers should also be considering fall herbicide applications, since a good weed management program often starts in the fall.
With the increase in weed resistant problems, a spring application is often not enough to control weeds, especially marestail. A fall herbicide application can be a great way to control winter annuals that emerge after harvest, especially in no-till fields and fields with a history of marestail. Rains late in August and so far in September could end up giving us more winter annuals than normal, making an application this fall potentially more beneficial. Typically an application is best from after harvest until around Thanksgiving. An application can be successful past Thanksgiving, but once we have a hard freeze many weeds are less susceptible to herbicide.
A typical fall burndown mix that provides good control is combination of glyphosate with 2, 4-D and/or dicamba that is applied during the time listed above. This will provide good control of winter annuals and minimize the chance that these weeds will produce seed. Wet springs can prevent a timely application, so doing an application in the fall allows us to get a jump start on weed control while weeds are small and easy to control.
Many people ask if a residual in the fall is a necessary component. There are a couple of ways to look at making the decision to use a residual or not. First of all, the likelihood of a residual giving much control into the spring is somewhat slim. If we have a more mild winter with an early spring, the chances of a residual making it through is extremely slim causing you to need to spend money on a residual again in the fall. The time when a residual in the fall could last is when we have a cold harsh winter allowing the residual to persist and provide us with control into the spring. Rather than try to outguess Mother Nature, most of the time it is best to wait and spend money on a residual in the spring. However, if you have been struggling to gain control on marestail, and burndown in the fall without a residual has not worked in the past, a low cost residual component can be added.
It is easy to overthink a fall herbicide program. Often times the simple application of glyphosate and 2, 4-D and/or dicamba can become the easiest and most cost effective way to gain control. A good program is both cheap and effective. The recommendation is to spend less than 25% of your overall herbicide budget for the crop on a fall application. Most of the time this can be accomplished spending less than that.
No matter what you decide to do in terms of a fall herbicide application, keep in mind that our main goal is controlling those weeds that have already emerged.