Control of marestail in no-till soybeans
Steps for effective management of marestail
1. Use fall herbicide treatments in fields with a history of problems or where marestail seedlings are observed in the fall. The primary goal of a fall treatment is control of emerged plants, and it is not a substitute for a spring preplant herbicide treatment. An application of burndown and residual herbicides is still required in the spring in fields that were treated in the fall. Products containing chlorimuron can provide residual control into the spring if the marestail population is not ALS-resistant, but do not expect a fall herbicide treatment to adequately control marestail that emerges in May or June. Authority, Valor, and metribuzin products and mixtures should be applied in the spring, not in the fall. Where a fall application is necessary, we suggest minimizing costs by applying one of the following:
glyphosate + 2,4-D; or dicamba + 2,4-D; or 2,4-D + a low rate of Canopy/Cloak EX or DF
2. Apply effective burndown herbicides in spring. Do not plant into existing stands of marestail. Start weedfree at the time of planting by using one of the following preplant herbicide treatments, applied when marestail plants are less than 4 inches tall. Note - tillage also effectively removes marestail.
- 2,4-D ester plus glyphosate (1.5 lb ae/A)
- 2,4-D ester plus Gramoxone (3 to 4 pts/A) plus a metribuzin-containing herbicide
- Liberty (29 to 36 oz/A) or Liberty plus a metribuzin-containing herbicide
- Saflufenacil product (Sharpen, Optill, or Verdict) plus MSO (1% v/v) plus either glyphosate or Ignite
The mixture of glyphosate and 2,4-D ester has become more variable for control of marestail over time in some fields. Plants should be in the rosette stage at the time of application for best results. In fields where this mixture has previously failed to provide effective control, use one of the other burndown treatments listed above (2,4-D ester can be added to any of these).
Use the highest rate of a 2,4-D ester product that is allowed, based on the interval between application and soybean planting. For all 2,4-D ester products, rates up to 0.5 lb active ingredient/A must be applied at least 7 days before planting. Rates between 0.5 and 1.0 lb/A should be applied at least 30 days before planting, with the the exception of several products (E-99, Salvo, and Weedone 650) that allow 1 lb/A to be applied 15 days before planting.
In ALS-sensitive populations, the activity of any of the above can be improved with the addition of a herbicide that contains chlorimuron (Canopy/Cloak/Fallout, Valor XLT, Envive, Authority XL) or cloransulam (Gangster, Sonic, Authority First).