Originally Posted by Skipster
A lot of us seem to be chasing false leads or misleading ideas -- and some of these have even made their way into the RTU market. Adding PSI or PPO inhibitors changes the way the target plant works, which often cuts the legs out from underneath your glyphosate app.
A study out of Auburn was published in 2008 that looked into the glyphosate + diquat combination (like RoundUp QuickPro) and found that, although the diquat addition gave quicker injury symptoms, total weed kill was slower, more regrowth happened, and more total glyphosate was required to kill the weeds than using glyphosate alone.
Remember that glyphosate inhibits the production of aromatic amino acids via interruption of the shikimic acid pathway. When contact herbicides are used, they prevent the shikimic acid pathway from properly functioning, which inhibits glyphosate from killing the plant. After the weed recovers from the contact herbicide damage, it grows like normal.
Most glyphosate formulations already include a surfactant, so adding more just costs you more money without improving control. Sometimes you may see some phytotoxicity from the surfactant, but it is only superficial damage and not improved control. It may even reduce control.
When adding AMS, it *can* help, but not because it is helping glyphosate enter the target weed any faster. Remember, the shikimic acid pathway has to be active in order for glyphosate to kill the target weed. Fertilizing plants usually increases activity in their internal pathways, which allows glyphosate to work more efficiently. But, you're only speeding up the activity here by a day, maybe two days.
The best thing to do to maximize your glyphosate application is to mix it properly (according to the label), apply so as to get thorough coverage of the target weed, and make sure that the weed is under as little stress as possible. Then, sit back and watch the magic happen!
I would agree with this. Probably better to use something like diquat alone if you need a quick kill to impress a customer or whatever and then come back later with regular Gly.