Multiple Resistance
Twenty-three counties in Southern Illinois are facing waterhemp found resistant to four modes of action-ALS-inhibitors, glyphosate, PPO-inhibitors and triazines. If resistance to a single mode of action can make weed management programs a challenge, resistance to multiple modes of action can make weed management nearly impossible. In Missouri, many growers are facing tri-resistant weeds (glyphosate, PPO-inhibitors and ALS-inhibitors). In Indiana, no-till soybean growers are facing horseweed (marestail) populations with resistance to both glyphosate and ALS-inhibitors. Other states are also being added to the list with weeds resistant to multiple modes of action.
Initially, it seemed like glyphosate-tolerant crops, like soybeans were the perfect answer to the developing resistance to ALS herbicides; decreasing soybean input costs and increasing efficiency. Unfortunately, now weeds like lambsquarters, waterhemp and ragweed are growing in resistance to glyphosate, on top of the already developed resistance to ALS herbicides, leaving growers with limited options and reducing bottom lines. Weeds don't forget they're resistant to a specific mode of action simply because it hasn't been used for a while.
One of the key resistance management recommendations from Syngenta is rotating herbicide modes of action, as well as rotating crops to help keep resistant weeds from developing.
What herbicide resistance issues are you facing? What have you done to combat this situation? How have you found success?