Area farmers are putting out pre-emerge herbicides behind the cotton planters this week. I have recommended using a herbicide program for resistant Palmer Amaranth including the use of fomesafen (Reflex, Dawn, etc). Many farmers are including a paraquat herbicide as a tank mix to kill any existing weeds behind the planter. It has come to my attention that there have been some documented incompatibilities when mixing paraquat and fomesafen resulting in a black, tar-like substance which may clog screens, filters, etc. I was provided this guidance from Mana Crop Protection and Syngenta Ag, manufacturers of herbicide products widely used in this application.
Mana Crop Protection (manufacturer of Parazone and Dawn herbicides) provided the following mixing instructions which are clearly described in the attached document.
1. Fill tank half full, add blending agents if used; 2. Continuous agitation; 3. Add dry formulations; 4. Add all liquids EXCEPT fomesafen or paraquat product ; 5. Add paraquat; 6. Add fomesafen; 7. Add surfactant; 8. Fill tanks.
REVISED TO ADD
Dr. Wilson Faircloth from Syngenta AG shared the following comments with me after posting this information. “You should know that Mana’s mixing instructions are contrary to Syngenta’s position on Gramoxone SL2.0. We have done much work with all major manufacturers of adjuvants; I have personally done much work with many adjuvants and both branded Gramoxone and generics. One of the primary differences to point out is the mixing order. Specifically, surfactants and compatibility agents should go into the tank first and Gramoxone 2.0SL should be the LAST thing added to the tank. ”
When using Gramoxone 2.0SL.
1. Fill tank half full, add blending agents if used; 2. Continuous agitation; 3.Add surfactant. ; 4.Add dry formulations; 5. Add all liquids EXCEPT fomesafen or paraquat ; 5. Add Reflex; 6. Add Gramoxone 2.0SL; 7. Fill tanks.
The chemical manufacturers and Universities are recommending that growers perform compatibility tests before mixing significant quantities of paraquat tank mixtures. I have attached a document written by Syngenta and Drs. Stanley Culpepper and Alan York that outlines a simple “jar test” for compatibility.
This is certainly a complicated topic, due to the variation of products used among farmers and differing results obtained. If you need more guidance, please contact me.