Driving around the county this past growing season it was not hard to find soybean fields that had some significant weed problems. I saw numerous soybean fields with major infestations of marestail. This was not a problem confined to Wayne County. Weeds were problematic in soybean fields across the state this past year and it seemed that marestail in particular made resurgence in many areas. For this reason, I want to remind soybean growers that fall herbicide treatments are a recommended practice to get control of our winter annual weeds like henbit, purple deadnettle, chickweed and especially marestail.
Marestail possesses several characteristics that make it an especially difficult weed to control beginning with the fact that it germinates over an extended time period starting in the fall of the year and also again in early spring into summer. Each mature plant can produce up to 200,000 seeds so it has a high reproductive capacity. We are also discovering that larger marestail plants are very difficult to control so targeting small plants is important. Finally, marestail has developed resistance to glyphosate, so an important chemical herbicide has been lost. An important component of a marestail weed control program has become fall herbicide application to those fields that will be going into soybeans next spring. From mid-October through November is a good time period to target emerging and young marestail plants for herbicide application. In fact, research indicates that if we have mild weather, the control period can go into December.
While marestail is the focus of these fall herbicide applications, the herbicide mix that is used should also help with control of winter annuals such as the previously mentioned henbit, chickweed and purple deadnettle, as well as providing control of some perennial weeds such as thistle and pokeweed. Therefore glyphosate is still included in the herbicide mix to help with control of some of these other weeds, but 2,4-D and dicamba should also be part of the mix. Obviously if the only targeted weed is marestail then 2,4-D by itself or 2,4-D tank mixed with dicamba is the recommended herbicide treatment. A residual herbicide like Canopy or First Rate is not needed in the herbicide mix for treatments applied after mid-October. Residual herbicide treatments should be saved for the spring application to control spring and early summer emerging marestail until crop canopy closure.
In addition to applying an herbicide treatment to the field consider also treating ditches, grass waterways and buffer areas, which can be a source of weeds and seeds that can easily be moved into the field. I know that there are some businesses in the area that are offering custom fall herbicide application at discounted rates as an incentive to take advantage of this fall period to control problem weeds now. It will pay dividends in the 2017 cropping year.
For more information about weed control and specifically marestail control in soybeans, contact the Wayne County Extension office at 330-264-8722.