With barley and wheat harvest in various stages, double-crop soybean planting will soon follow in some areas of the state. Weeds are generally less of a problem in double-crop soybean because of the delayed planting date. But even with fewer weeds emerging, when they are present and in combination with potential dry weather impacts on yield can be noticeable. A weed-free start is one of the most critical aspects of weed management in double-crop soybean. One of the biggest weed concerns is in managing glyphosate-resistant marestail or horseweed. Most of these populations may also be ALS-resistant. Marestail that are cut off during small grain harvest will recover, branch out, and probably be even more difficult to control. In full season soybeans, the use of 2,4-DLVE in the burndown program can provide control. However, most farmers are not willing to wait the necessary 7 days after 2,4-D application in double-crop and there is potential for drift at this time of year. So, what are the options?
- In most cases, an easy option would be to add 1 fl oz of Sharpen (or equivalent rates of Zidua Pro, Optill or Verdict) to glyphosate to control marestail stumps. Keep in mind, Sharpen at this rate helps with burndown but does not provide much residual control. For effective control, make sure to add MSO and AMS to the spray mixture when using Sharpen-containing products. Adding metribuzin improves residual control.
- Or include 1 pt per acre 2,4-DLVE in the burndown and wait 7 days to plant. If planting an Enlist E3 variety, Enlist One/Duo could be applied and then soybeans planted immediately. However, larger marestail stumps might not be completely killed. Also, be cautious of drift into sensitive areas.
- For glyphosate-susceptible marestail, apply glyphosate at 1.5 lb ae/A (40 fl oz of Roundup PowerMax3 or 64 fl oz of a 3 lb ae/gal product).
Source : psu.edu