If you’ve got herbicide resistant marestail, one of these burndown options may be your best bet.
During this past winter, we distributed a new Factsheet from Mark Loux at Ohio State University and Bill Johnson from Purdue titled “Control of Marestail in No-till Soybeans”. It is available as a pdf on-line. We also still have copies available if anyone would like some. This is a nice two page summary for marestail or horseweed management in soybean. With the warm weather kicking, you can expect the marestail to quickly increase in size and decrease in susceptibility to control with herbicides. Pay particular attention to selecting “effective burndown herbicides”. Here is a summary of this section compliments of Loux and Johnson.
Apply effective burndown herbicides in spring. Do not plant soybean into existing stands of marestail. Start weed-free at the time of planting by using one of the following preplant herbicide treatments, applied when the marestail plants are less than 4 inches tall.
- 2,4-D ester plus glyphosate (1.5 lb ae/A).
- 2,4-D ester plus Gramoxone 2.0 (3 to 4 pts/A) plus metribuzin-containing herbicide.
- Liberty (29 to 36 fl oz/A) or Liberty plus a metribuzin-containing herbicide
- Saflufenacil product (Sharpen or Verdict) plus MSO (1% v/v) plus either glyphosate or Liberty
- A 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 (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 lb/A should be applied at least 30 days before planting, with 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 an herbicide that contains chlorimuron (Canopy, Cloak, Fallout, Valor XLT, Envive, Authority XL) or cloransulam (Gangster, Sonic, Authority First). The addition of metribuzin to any burndown treatment can also improve control of emerged marestail. A number of additional residual herbicides can be added to the burndown for control of later emerging seedlings.
Source : psu.edu