Let me start by commending producers for heeding the advice of university weed scientists by working to have a clean seed bed at planting. The battle against glyphosate-resistant weeds begins at planting with burndown and residual herbicides.
Most fields are in much better shape this growing season, in terms of managing glyphosate-resistant weeds such as Palmer amaranth and Italian ryegrass, than in the past.
Many producers have utilized paraquat, sold under the trade name Gramoxone Inteon, to control emerged weeds at planting. Paraquat has been on the market for over 40 years and is an effective tool for controlling a broad spectrum of weeds, including glyphosate-resistant Palmer amaranth.
With the current advances in technology, oftentimes a chemical manufacturer will modify a herbicide formulation to create a safer, more stable, and/or effective herbicide. This occurred recently with Gramoxone Inteon, where the formulation was changed to improve the stability and safety of this herbicide.
This new formulation can be recognized by a new green color scheme on the label as opposed to the traditional blue label. None of the active ingredients or concentrations were changed, so use rates or efficacy are similar to that in years past.
However, a new additive (whose origin is unknown at this point) was added to Gramoxone Inteon in 2011. This new carrier apparently reacts with our well water in the Mississippi Delta in an undesirable manner.
When Gramoxone Inteon is added to water, an oily, black substance begins to form in the spray tank and accumulates in strainers, screens, and on the walls of the tank (see photo).
Syngenta Crop Protection is working diligently to find the cause of this problem which, so far, seems to be unique to the Delta.
This problem can be avoided by utilizing spray grade ammonium sulfate (AMS) at 5 to 15 pounds per 100 gallons of water or a liquid AMS formulation at equivalent rates. The AMS product should be added to the spray tank before Gramoxone Inteon.
This article is in no way meant to discourage the use of Gramoxone Inteon, as this product is essential in our fight against glyphosate-resistant weeds. We do, however, want you to be aware of these potential mixing problems so that any mixing issues can be averted in the future.