Fall Herbicide Applications – an Integral Part of Marestail Management

Horseweed or marestail is probably the weed I heard more about this summer than any other weed. By Ag Progress Days 2012, it was quite clear that it has developed and/or moved into the western part of PA as well as being a common site in the southeast and south central parts of the state. The increasing acreage of no-till soybean is likely helping to drive this problem weed. We do not have an extensive database to turn to with regard to management of marestail in PA. Our neighbors to the West at Ohio State University (as well as to the south in Delaware and Maryland) have been battling glyphosate (and ALS-resistant) marestail for several years and have been very involved in researching its control and making recommendations. Fall herbicide application is one option. The following article comes compliments of Dr. Mark Loux at OSU.  It was published on September 4, 2012 in the C.O.R.N. Newsletter. Thanks Mark.

Fall herbicide treatments are an important component of marestail management programs. The primary role of the fall treatment is to remove the marestail plants that emerge in late summer and fall, so that the spring herbicide treatments do not have to control plants that have overwintered. Failure to do so results in a population of plants in spring that is tougher to control and needs to be treated earlier, which introduces variability in burndown effectiveness and means that residual herbicides may be applied earlier than is optimal. Conversely, an effective fall treatment results in a weed free seedbed in early spring, and more flexibility in the spring burndown/residual treatment timing. The treatments recommended in the aforementioned articles will provide effective control of emerged marestail. Marestail plants are small in the fall, and easily controlled with 2,4-D.

The major errors with fall treatments where marestail is a target are:
1) using glyphosate or ALS inhibitors alone; and
2) spending money on residual herbicides that is better spent in the spring.
The application of Canopy/Cloak products in fall can provide substantial residual control into the following spring of marestail that are not yet ALS-resistant, and other weeds as well. However, many marestail populations are ALS-resistant, and it’s important to save most of the residual herbicide for the spring application. Our research has consistently shown that other residual herbicides – including Valor, Authority, and metribuzin – provide little residual in the spring when applied in fall. The utility of these herbicides comes from spring application.

The basic information on fall herbicide treatments can be found in a number of C.O.R.N. articles from previous years, including the following:

“Fall herbicide treatments”

“The ABC’s of fall herbicide treatments”

“Should residual soybean herbicides be applied in the fall?”

“Fall herbicide treatments – focus on marestail management”