Mitigating spray drift is a major issue today for the ag aviation industry. Proper equipment setup and application technique are essential and help greatly, but only get you so far because they do not control how common tank-mix ingredients change the properties of the spray water. Oils and surfactants in most pesticide formulations will increase the number of driftable fines. One nozzle setup can be right for one spray mixture and wrong for another. Drift mitigation adjuvants (DMAs) are essential to mitigate how chemicals change the properties of spray water and how it breaks apart exiting the nozzle.
No drop size or droplet spectrum is ideal for all applications. That ideal varies depending on the pest, pesticide, spray mixture, crop canopy, environmental conditions and the risk of drift as well as the application setup and goals. Adding an effective DMA is your best protection against the droplet size variability caused when adding some tank-mix ingredients. Figuring out the best application setup in combination with the right rate of the right DMA product for your specific situation is not difficult but it does take some effort.
Too big or too little
Every drop size has pros and cons. Deciding what is the best size is being increasingly taken out of the hands of the applicator with new pesticide labels mandating specific droplet sizes, usually coarse droplets. Sometimes labels mandate nozzle type, spray pressure and other application parameters to ensure there are no drift problems.
A general rule is that the smaller the droplet, the greater the chance of drift and loss of efficacy because of evaporation. The bigger the droplet, the faster it will fall with less drift and increased penetration into the crop canopy, but very large droplets will sometimes bounce off the leaf. Adding a polymer DMA will reduce the bounce effect, as well as droplet evaporation
In the plant or on the plant
The first question when applying pesticides should be where does the pesticide need to be, in or on the plant. Most aerially applied pesticides are systemic, meaning they move around inside the plant. The key for systemics is to get them inside the plant. Other pesticides just need to stay on the outside of the plant. If that is the case, the next question should be where on the plant; the top, middle or bottom. Most of these pesticides still need to penetrate the crop canopy to reach the pests. Large droplets penetrate into the canopy better than small droplets and are also less vulnerable to drifting away.
Deposition versus retention
The efficacy of a spray droplet depends on it getting to where it needs to be, i.e., reaching and being retained on a target, usually a crop or weed leaf. A drift mitigation adjuvant is “any material used in liquid spray mixtures to reduce spray drift.” Some drift mitigation adjuvants, particularly the polymer DMAs, reduce drift and increase retention on leaves. They also reduce evaporation allowing for longer pesticide uptake. Not surprisingly, these DMAs are referred to as deposition and retention aids.
Retention aids increase adhesion to the leaf surface, especially important on waxy and vertically oriented leaves (vertical leaves in crops like corn are particularly difficult to get water droplets to stick to). Polymer retention aids also keep the spray droplet from shattering and rebounding off the leaf surface in addition to preventing rain, wind or mechanical action from dislodging spray deposits.
Stickers are a special type of retention aid that helps spray deposits stay moist so it is not dislodged from a crop or weed leaf surface. The activity of most aerially applied pesticides is completely lost if they fall on the soil. Glues were the first stickers, but stickers also include many viscous materials such as sugars, heavy oils, fatty acids, latex, resins, film formers and DMA polymers. Humectants also help by keeping the spray deposit moist and sticky.
The bottom line is to think outside the tip – nozzles cannot do everything. The right drift mitigation adjuvant will help manage the variable properties of spray water and help get your pesticide applications deposited where they need to be. For more information on how to get the most out of your pesticide applications, contact John Garr at 765-395-3441 or firstname.lastname@example.org.