Reducing Spray Drift

Bulletin 816-00

Drift Mitigation Strategies

Conscientious and experienced operators rarely get into serious trouble with drift damage because they understand drift and take steps to avoid it. Here are some management strategies to reduce spray drift for different spray application situations.

Ground Boom Sprayers

1. Use nozzles that produce large droplets whenever possible, if biological effectiveness can be maintained.
2. Keep the boom close to the spray target.
3. Use greater spray volume and use nozzles with larger orifices.
4. Use lower system pressure and check pressure gauge accuracy.
5. Use drift retardants if droplet size cannot be controlled with nozzle selection.
6. Follow label recommendations to avoid drift with highly volatile pesticides.
7. Avoid spraying on extremely hot, dry days, especially if sensitive vegetation is nearby.
8. Do not spray when conditions are favorable for an atmospheric inversion.
9. Although the distance droplets will drift is a function of many other factors such as droplet size, relative humidity, temperature and boom height, it is best not to spray when wind speeds are greater than 5 miles per hour.
10. Avoid spraying near sensitive areas located downwind. Leave a buffer strip 50 to 100 feet wide and spray this strip later when the wind shifts.
11. Be sure to keep good records (wind speed and direction, temperature, relative humidty, ect. and evaluate spray results.
12. New label requirements may use a drift model to determine the required buffer width. Travel slower (and lower boom height) and use nozzles which produce large droplets near sensitive areas. This will reduce the required buffer zone width, then, as distance from the sensitive area increases, nozzles can be changed to produce smaller droplets, if desired, and boom height raised so travel speed can be increased.
13. Select the time when drift is likely to be low for spraying the parts of the field near sensitive areas.
14. In the future, label requirements may specify nozzles that produce a certain droplet size spectrum, such as fine, medium, coarse, very coarse, etc. Carefully check the label to determine the optimum droplet size and proper nozzle size for a spray application.

Orchard and Vineyard Sprayers

Many of the same principles for reducing drift for boom sprayers apply to orchard (air blast) sprayingas well. With air blast sprayers, we have to remember that the droplet release height is where the air jet no longer controls the droplet trajectory and the wind begins to direct droplet paths. In some cases, this may be several feet above the tree canopy. Some of the practices for reducing drift are:

1. Turn off the sprayer when there are no trees present.
2. Keep the spray as close to the target as possible.
3. Minimize the small droplet fraction; however remember that the purpose of spraying is to control pests. Large droplets may not provide the control desired, without increasing the application rate.
4. Match the sprayer air jet (volume and direction) and nozzle system to the trees being sprayed.
5. Be prepared to use special techniques near sensitive areas, especially for the last few downwind rows. These may include: a) use large droplets; b) use techniques to direct spray at targets better, such as a handgun; c) spray the last few rows upwind only; d) wait and spray when the wind shifts; e) use special measures or equipment to create barriers or direct spray at the target (tunnel sprayer, etc.).

Aerial application

In most cases, experiments have shown that spraying with either airplanes or helicopters produces more drift than other application methods. This is caused by the high travel speed, the wing-tip vortices that tend to transport droplets above the wing, and the release height. There are only a few options available for reducing drift when spraying with aircraft. The single most effective strategy to reduce drift from aerial spraying is having aircraft operators who are carefully trained to make good decisions on when to spray and when to stop spraying. Here are some other recommendations:

1. Reduce spray height as much as possible without compromising safety.
2. Use a spray offset carefully; calculate how far the wind will carry the main spray swath and plan your spray paths to allow for this spray adjustment.
3. Use global positioning instruments in aircraft to assist you in making sure you are spraying the correct field and in selecting the proper spray paths. New computer software may soon be available to select optimum spray paths in real time, based in local wind and spray conditions.
4. Choose the largest droplet size that will produce the desired biological effect.
5. Point nozzles backwards (toward the tail of the aircraft) to reduce formation of the small droplets.