Over-use of this technology is definitely a possibility in the future, because it can be used on Phytogen Widestrike cotton, and the most widely planted single cotton variety in the Southeast is Phytogen 499 with the Widestrike gene that provides similar protection as does the Liberty Link gene in some Stoneville varieties. 

In no-till cotton throughout North Carolina, the Cadillac program for managing glyphosate-resistant Palmer amaranth includes the sequential application of two PPO herbicides.

Typically, Valor SX goes out about three weeks ahead of planting in a preplant burndown application with glyphosate and 2,4-D. Then at planting, growers usually follow up with another PPO herbicide pre-emergent, Reflex. This is alarming because growers are essentially exposing pigweed to multiple applications of a PPO herbicide, which greatly increases the likelihood of resistance.

The North Carolina researchers looked at Valor SX or no residual herbicide preplant followed by Reflex, Diruon (PS II-inhibitor), or no residual herbicide at planting. 

Additionally, they looked at Diuron preplant followed by Reflex or no residual herbicide at planting. 

Gramoxone was included both preplant and at planting. This allowed the researchers to determine which PPO herbicide growers could go without.  

“Over the two-year period, and at multiple sites, we saw comparable weed control using one of the PPO herbicides in combination with Diuron at either the front or the back end of the system. 

However, in 2010 we did not receive a timely activating rainfall on our residuals at planting and systems with Valor SX preplant outperformed all others.” Cahoon says.

This past year, the researches got similar results with Valor SX preplant followed by either Diuron or Reflex at planting. In contrast to 2010, 2011 brought timely activating rainfall at planting and adequate control of pigweed with Diuron preplant followed by Reflex at planting. 

It appears taking one of the PPO herbicides out of the weed management system did not reduce control of Palmer amaranth and other weeds commonly found in North Carolina cotton fields.” Cahoon says

So we can essentially replace either PPO herbicide with Diuron if we get timely rainfall, but the safer bet is to keep Valor SX preplant.