Can adjuvants reduce drift?
Yes, but their ability to do this is very unpredictable, which is one of the reasons why adjuvants cannot be given star ratings in the same way as nozzles. When someone makes claims about this, ask a few questions:
How did they measure drift?
If they only measured droplet size, be cautious – this doesn’t necessarily translate into the same level of reduction in drift, because drift also depends on droplet velocity and air bubbles in droplets.
What were they comparing?
If they compared spraying the adjuvant with spraying water alone, then ignore this. Adding anything to water is very likely to have a bigger effect than when it is added to a dilute product, or a more complex tank mix.
What tank mix was used? What nozzles and pressures were used?
The results will probably only apply to the tank mix, nozzles and pressures used in the tests and not to any other combination. Some adjuvants do have a significant effect with a range of nozzles and products, but make sure the results are relevant to the nozzle, pressure and tank mix that you intend to use.
Adjuvants reduce drift by making droplets bigger, and they are less effective at doing this than nozzles are. However, adjuvants might also have other benefits, like improving retention, spreading or uptake on the plant.
Some adjuvants also cause the spray fan angle to reduce, potentially changing the distribution of spray underneath the boom. We have seen some products in development that collapse the fan completely. I hope none of these make it onto the market, but for less dramatic changes, you might not realise that you are compromising the uniformity of your application.
***Bullshit alert*** You will occasionally hear claims of formulations or adjuvants that eliminate or reduce the smallest and the largest droplets, leaving only the ones in the middle that are the most efficacious and don’t drift. Many agrochemical products will do this (all EC formulations, for example) to some extent. This is a good thing, but it is quite a small effect and you might easily lose the benefit by tank mixing anyway.