Strategies to Control Marestail
This is easily one of the worst marestail years I have seen. Marestail is a weed that can follow a winter or summer annual life cycle. Marestail plants start out as a rosette, generally bolt in April/May, flower in July, and set and disperse seed from August to October. Each plant can produce up to 200,000 seeds that travel via the wind.
For those of us who deal with marestail, we know that post-emergence control of many marestail populations is close to impossible. As such, the goal of a marestail management program is to ensure that the combination of fall and spring burndown and residual herbicides results in a weed-free seedbed at the time of soybean emergence, and little to no emergence of marestail between soybean emergence and crop canopy closure. But keep in mind that even the most effective marestail management programs can fail to completely achieve this, but they often keep the populations low enough in the soybeans that they are not problematic.
For marestail control suggestions, OSU Extension Weed Specialist Dr. Mark Loux suggests the following as one possible approach:
Apply a combination of glyphosate and 2,4-D in the fall, followed by application of residual herbicide in the spring prior to soybean emergence. At the time of soybean planting, the field is likely to be infested with marestail that emerged earlier in spring, so include effective burndown herbicides to control emerged plants. Keep in mind these plants can be very small and not noticeable.
The idea here is to apply an herbicide treatment in the fall that adequately controls emerged marestail, but does not break the bank and allows use of residual herbicide in the spring. Canopy herbicide can also be used in the fall, but use of metribuzin in the fall preserves the option to plant corn the following spring. Follow the OSU Extension CORN newsletter for the latest updates at corn.osu.edu