By Mark VanGessel, Extension Weed Specialist; mjv@udel.edu
Due to the seriousness of glyphosate-resistance, and the tendency of Palmer amaranth to develop resistance to glyphosate, UD Weed Science recommends:
1. The field should be clean at planting, using effective burndown herbicides or tillage;
2. Use a residual herbicide, applied as close to planting as possible (within 7 to 10 days);
3. Never apply glyphosate alone; an additional herbicide should be used as a tank mix partner;
a. additional mode of action must be highly effective on Palmer amaranth as well;
b. applications should be made to plants less than 3 inches tall;
4. Be sure to rotate herbicide mode of action
a. use a Group 27 herbicide in corn (Callisto, Impact, or Laudis products), avoid use of Group 14 (Valor, Sharpen, etc) herbicides in corn, except in cases of continuous corn;
b. use a Group 14 herbicide in soybeans (i.e. Valor, Reflex, or Cobra); and
5. Fields with soybeans planted two years in a row need extra precautions to avoid resistance (particularly in regards to Group 2 or ALS herbicides).
Source: Read Full Article from Weekly Crop Update
