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Interesting paper just came out describing differences in volatility of Dicamba (straight), Glyphosate (straight), Dicamba + Glyphosate (mix), as well as with some drift reduction agents in the mix with the same setup.

The paper is free to view, and nice visuals to help see a bit of the variability (or consistency).


The below is just from the synopsis off the article, in case you didn't want to click the link. I'd still read through the paper. Its only 13 pages, so not too long considering how many charts there are.

Effectively, efficacy/application consistency seemed to improve significantly applying each seperately, and there was little variation in the results when both were tank mixed. Most of which were null or slightly negative.

BACKGROUND
Regulations in 2021 required the addition of a volatility reduction agent (VRA) to dicamba spray mixtures for postemergence weed control. Understanding the impact of VRAs on weed control, droplet dynamics, and spray pH is essential.

RESULTS
Adding glyphosate to dicamba decreased the solution pH by 0.63 to 1.85 units. Across locations, potassium carbonate increased the tank-mixture pH by 0.85 to 1.65 units while potassium acetate raised the pH by 0.46 to 0.53 units. Glyphosate and dicamba in tank-mixture reduced Palmer amaranth control by 14 percentage points compared to dicamba alone and decreased barnyardgrass control by 12 percentage points compared to glyphosate alone 4 weeks after application (WAA). VRAs resulted in a 5-percentage point reduction in barnyardgrass control 4 WAA. Common ragweed, common lambsquarters, and giant ragweed control were unaffected by herbicide solution 4 WAA. Dicamba alone produced a larger average droplet size and had the fewest driftable fines (% volume < 200 μm). Potassium acetate produced a larger droplet size than potassium carbonate for Dv0.1 and Dv0.5. The addition of glyphosate to dicamba decreased droplet size from the entire spray droplet spectrum (Dv0.1, Dv0.5, Dv0.9).

CONCLUSION
A reduction in spray pH, droplet size, and weed control was observed from mixing dicamba and glyphosate. It may be advisable to avoid tank-mixtures of these herbicides and instead, apply them sequentially to maximize effectiveness. VRAs differed in their impacts on spray solution pH and droplet dynamics, but resulted in a minimal negative to no impact on weed control. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

This is probably the better chart I saw to break out the variation of driftable fines changing over the tank mix partners:
Slope Rectangle Font Plot Parallel


So, the bottom is highlighting the % of the total flow that is smaller than 200µ. That is a good gauge of how much of the spray is going to be drift (whether it ends up off-target or evaporate/etc its harder to quantify).

So, the mix of driftable fines (compared to Tip Wizard info @ 141µ) might be in the realm of being 1% with straight Dicamba, and like 2% with the tank mix. Keep in mind the nozzles they used are TTI -05s, so pretty much crazy coarse. Other VC (or coarser) nozzles might be in the realm of 4-5% driftable fines, potentially doubling with the tank mix. Again, this is all relative to where straight water would have its drift baseline (% <200µ) would be.

Between the volatility reduction agents (description in the bottom of the chart), seemed to be less variation between droplet velocity. Moreso just neat to see there is very little variation:
Rectangle Slope Line Font Triangle


A bit further into the paper, it gets into some of the PH effect as far as how that might effect the volatility in vapor/volatility potential. (e.g. high PH can negatively effect herbicide efficacy, so depending on baseline water + chem as well as the VRA, it might tip the scale into subpar performance due to PH)

Anyways, figured I'd share. Good thing to start a new year by reading something new and learning a thing or two.
 
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