What is in this article?:
Pigweeds can grow extremely fast when resources are available so thorough and timely scouting has been key in order to stay on top of the issue.
Resistant pigweed calls for a more diversified weed control strategy.
No silver bullet
Producers who have pigweeds that have escaped numerous glyphosate applications have no simple, economical solutions. Removing existing weeds and preventing additional flushes are necessary. A pigweed that has reached waist high after several glyphosate applications is not going to be easily controlled with chemicals.
A grower’s typical first response is the consideration of alternative over-the-top broadcast herbicides. Few herbicides provide burndown control of broadleaf weeds. Since Staple LX herbicide can be tank-mixed with glyphosate and adds additional burndown as well as residual weed control (note crop rotation restrictions on label) some consider this route. If considering Staple LX, pay close attention to the label in regards to weed size, rates and application requirements. The effectiveness of this product depends heavily on these factors. It should be noted that with waist-high GRP escapes, the highest labeled rate of Staple LX over the top will not solve your dilemma.
Another possibility is applying Liberty herbicide over-the-top—if you have the Liberty Link trait. Typically, we (in the Southwest) have challenges getting Liberty to control pigweeds effectively with our low humidity and high temperatures. As is the case with Staple LX, following label instructions makes a tremendous difference in the outcome of a typical Liberty application. However, it is not realistic to expect the highest labeled rate of Liberty to control waist-high GRP escapes either.
Some growers also ask about Envoke. Generally speaking, Envoke performs similarly to Staple LX (and crop rotation restrictions should be considered). It should be noted that Envoke does not list Palmer pigweed on the cotton section of the label and Palmer is the most prevalent species of GRP. For those considering its use for over-the-top applications to GRP escapes I would classify my expectations to be similar to the previous comments about Staple LX, do not count on it to clean up your GRP escapes.
While all of these products have benefits in certain situations, none of these options will effectively control GRP escapes, and that leaves us with the previously mentioned options for removal—tillage and/or hand hoeing. In most cases tillage needs to be part of the salvage operation.
Although many have committed to no-till production, GRP is a game changer. I haven’t seen a pigweed that can survive a cultivator. However, cultivating (or any stirring of the soil) will likely lead to an additional flush of pigweeds. Therefore, a residual herbicide application following the salvage operation (tillage/hand hoeing) is highly recommended. The challenges with the current crop stage (early bloom) are getting the residual herbicide in contact with the soil and getting it activated.