Avoid denial

Published on: 14:01PM Dec 03, 2010

Chuck Foresman

We continue to hear more university experts throughout the Midwest and South say that growers shouldn’t wait to find out if weeds are confirmed resistant to glyphosate. If you’ve noticed problems controlling weeds, treat them as if they are indeed resistant to keep them under control. 
Recently this message was reinforced at an Arkansas symposium, which they called a “pigposium,” focused on Palmer pigweed control. However, the keys shared by those researchers can be applied to any potential resistance, including closely related waterhemp.
In some areas, growers have seen weed resistance explode from a noticeable patch to a disaster in just a few years. But these weeds can be managed, and disaster can be averted. Here are a few tips to embrace now, before resistance takes over fields.
  • Use a pre-emerge herbicide. 
  • Follow rate recommendations on the label. They are there for a reason. Cutting rates is a good way to develop resistance. Surviving weeds pass their tolerant genes on to the next generation, and the weeds get stronger year by year.
  • Prevent weed seed production, since tough weeds can produce thousands of seeds, which can remain viable in the soil for 3 to 6 years.
  • The difference between weed control and failure can be just a couple days. Some weeds, including pigweed species, can grow as much as 1 or 2 inches a day. Smaller weeds are more susceptible to herbicides.
  • Protect the chemistry we have. Overusing any herbicide, including glufosinate, HPPD inhibitors and PPO inhibitors, can cause resistance, so herbicides must be rotated and used wisely.
  • Control weeds in field perimeters, ditches, waterways, levees, etc. Weeds left there produce seed and can create problems for future years.
  • Understand weed germination timing. If weeds germinate throughout the growing season, overlapping residual herbicides may be needed until crops canopy.
  • Don’t forget about fields after harvest. Depending on the weather and geography, problem weeds and/or winter annuals can germinate and go to seed after harvest, so be watching for potential problems and plan burndown applications as needed.
  • Rotate crops and chemistries. Different brand names don’t necessarily mean different chemistries, so make sure you know how herbicides are working.