Marestail can be one of the most challenging weeds to control prior to planting no-till soybean. Already this season some have reported poor marestail control following applications of glyphosate plus 2,4-D. Poor control can be caused by several factors, including large plant size and resistance to glyphosate. If a marestail population is resistant to glyphosate, a pint of 2,4-D in the spring is generally inconsistent/ineffective when it’s the only product in a tankmix active on the resistant population.
Adding Sharpen or metribuzin to glyphosate plus 2,4-D can improve marestail control. Include MSO with Sharpen and be sure to adhere to planting intervals in treated fields where another soil-applied PPO inhibitor will be used. Glufosinate (Liberty, Interline, etc.) or Gramoxone SL are other options to control marestail before planting. Control is often improved when these products are tankmixed with metribuzin and 2,4-D. Both glufosinate and Gramoxone are contact herbicides, so be sure to adjust application equipment (nozzles, spray volume, etc.) to ensure thorough spray coverage.
Tillage is another option to control emerged marestail. Delay tillage until field conditions are suitable and be sure to till deep enough to completely uproot all existing vegetation.