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Resistance is Upon Us: Weeds that are a Threat and How to Manage Them

Without proper management, weeds will eventually develop resistance to common herbicide modes of action. That’s not a threat — it’s reality. In fact, many weeds are developing resistance to so many modes of actions, they are becoming more difficult to control.
 
Here are just a few of those troublesome weeds:
 
The Culprit: Waterhemp — The Escape Artist
 
The Threat: Waterhemp can escape many pre-emergence herbicides and post-emergence applications without residuals, and this weed tends to emerge throughout the season. Its herbicide-resistance traits can transfer rapidly through pollination, which means it can infest fields easily and quickly.
 
The Resistance: Group 2 (ALS Inhibitors), Group 4 (T1R1 Auxin Receptors), Group 5 (Photosystem II Inhibitors), Group 9 (EPSP Synthase Inhibitor), Group 14 (PPO Inhibitors), Group 27 (HPPD Inhibitors)
 
The Culprit: Pigweed — The Competitor
 
The Threat: Pigweed, aka Palmer Amaranth, can experience rapid growth — up to 2.5 inches per day. Because of this, controlling pigweed with post-emergence herbicides is extremely difficult.
 
The Resistance: Group 2 (ALS Inhibitors), Group 3 (Microtubule Inhibitors), Group 5 (Photosystem II Inhibitors), Group 9 (EPSP Synthase Inhibitor), Group 27 (HPPD Inhibitors)
 
The Culprit: Marestail — The Wanderer
 
The Threat: Marestail can produce up to 200,000 seeds per weed, and about 80 percent of those seeds will germinate right off the plant. Not only that, but the lightweight seeds are easily blown across great distances by the wind — which means increased distribution.
 
The Resistance: Group 2 (ALS Inhibitors), Group 5 (Photosystem II Inhibitors), Group 7 (Photosystem II Inhibitors), Group 9 (EPSP Synthase Inhibitor), Group 22 (Photosystem I Electron Diverter)
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