Spraying operations can be complicated as there are many things to consider, but spray droplet size can make or break the efficacy of a spraying job!
For aerial application methods such as Drone spraying the general nozzle settings are to produce droplet sizes between coarse to very coarse or 218 to 428 microns. This specification is based on ASAE S572 nozzle standards and is commonly seen on chemical labels for foliar herbicides and insecticides.
Although the standard was developed for Tee jet nozzles, the droplet sizes are relevant for other spray systems. The older DJI AGRAS Drones use standard Tee jet nozzles but are moving into the CDA system, which XAG has been using for quite some time.
Tee jets are fixed to the one setting where you can’t vary the output in flight or calibration. If a different droplet size is required the Tee jet nozzle must be swapped. The spray width is determined by fan angle and pump pressure.
The Controlled Dosage Applicator (CDA) nozzle uses a spinning disk to determine droplet size. This is achieved by varying the speed of the spinning disk, “Faster equals smaller” and “Slower equals bigger”. The CDA’s spray width is determined by the spinning disk’s RPM, as the amount of momentum produced by centrifugal force determines how far the droplet is flung.
So, what if the Spray droplet size is too big?
- Droplets may roll off waxy leaf coating.(no absorption)
- Spray width will be reduced due to heavier droplet. (less momentum)
- Droplets may completely miss target due to less droplets per cm2
What if the droplet is too small?
- Higher risk of spray drift (smaller equals lighter)
- Higher risk of Vapour drift (drift from evaporation)
- Inversion potential because lighter droplets hang in the air longer and may float instead of land.
Wetters, Spray oils and surfactants may help with adhesion, absorption and spray drift but not all chemicals are compatible with them.
The drones Propellor system has a huge effect on droplet distribution as it will help push the product into the plant canopy, but it won’t solve the problem of incorrect droplet size!
It is essential to get the droplet size correct so the chemical will work as efficient as possible, and additives to improve performance will make it work even better!
It’s important to get it right the first time because some chemicals have soil residuals that last for several years! This means the site cannot be retreated until the residue is no longer present.
Repeated attempts on the site with the same treatment will cause chemical resistance, which makes the pest extra difficult to eradicate!
Hope you enjoyed this post and got something out of it! I find this type of thing fascinating.
If you have any questions or thoughts let me know, and if your interested in any of my drone services feel free to contact me or request a quote.
Catch you next time😉
