DRAFT - DO NOT CITE!

Revised, Sept. 24, 1999
by Richard C. Derksen, USDA-ARS, ATRU, Wooster, Ohio (e-mail: derksen.2@osu.edu)
Original draft provided by Skee Jones, EPA

Best Management Practices for Airblast/Air-assist

treatment of tree/vine/bush crops

GENERAL RECOMMENDATION

It is the operator's responsibility to ensure that the best management practices available are being implemented during each application to avoid drift problems. Each block has the potential to be optimized for delivery strategies because of tree size, orientation, cultivar vulnerability, etc. Identification of high risk border sites (neighboring houses, water, roads, crops, etc.) near each block will insure minimal off-site movement problems if a strategy for minimizing drift for that area is planned in advance. Treating each block as needed also aids the planning and implementation of IPM (Integrated Pest Management) tactics wherein sites and cultivar combinations tend to differentiate pest problems. Operating procedures must be customized for each site as well as for the application needs. Consult equipment manufacturer's and formulator's product information, research publications, and other guidance for recommendations concerning pesticide application methods that will improve application efficiency and reduce spray drift potential. Your local extension service may be a good source of this information.

SPRAY DIRECTION

Drift potential is much greater from applications made to the outside rows of a treatment area. If the rows of trees, vines, etc. are parallel to the field edge, spray the last row of smaller trees, vines, or bushes using nozzles on one side only, with spray directed into the treatment area. Larger crops that must be treated from both sides should be treated with the air and spray delivery system orientated to try to eliminate spray movement over the top of, under, through the crop. Shut off nozzles on the side away from the orchard when spraying outside rows. Shut off spray delivery before exiting the orchard when turning at ends of rows and when passing gaps within rows. Vertical towers or masts on sprayers can aid in directing spray into the crop canopy while minimizing spray losses over the top and under the crop. Use of tree canopy sensors for nozzle shut-off should be considered for sparse plantings in particular.

AIR DELIVERY

The most effective drift mitigation tool for orchard sprays is to not direct spray over the canopy or to spray between gaps in plantings. The use of tower, cross-flow, or wrap-around sprayers have all shown drift reduction potential and possible efficacy improvements. Use the lowest necessary air speed to minimize movement through and over a canopy. High air volumes more spray material more efficiently than high air speeds. Enough air should be supplied to transfer spray to the canopy and to keep the spray material within the canopy. Reducing travel speed decreases the air speed necessary to delivery the spray into the canopy. Slowing travel speed increases the efficiency of the delivery of spray to the target canopy and provides better control of the fate of the spray. Use air guides and directional control of nozzles to direct the spray into the canopy.

DROPLET SIZE

A major way to reduce drift potential is to properly manage droplet size through a combination of nozzle selection and operating pressure. The best drift management strategy is to apply the largest droplets that provide sufficient coverage and control. Applying larger droplets reduces drift potential but will not prevent drift if applications are made improperly, or under unfavorable environmental conditions (See Wind, Temperature and Humidity, and Temperature Inversions). Large droplets could also create excess spray runoff. Drift potential is much greater from applications made to the outside rows of a treatment area. It is important to manage operating parameters such as droplet size when treating the outside rows of canopies that are higher off the ground.

WIND

Avoid application when winds are calm and when greater than 15 mph. However, many factors, including droplet size and equipment type determine drift potential at any given wind speed. Applications should be avoided when winds are calm because the direction of spray movement may be variable and a temperature inversion may exist. Operators should be aware of how local terrain can influence wind patterns. Cold air drainage on slopes can cause airborne spray particles to move down a slope, away from a treatment area. Wind direction directly down drive rows (parallel with the sprayer) should be avoided or spray delivery should be shut off prior to the last of the crop in the row. Wind speed and direction should be continuously monitored at the site at the time of application.

SENSITIVE AREAS

The pesticide should only be applied when the potential for drift to adjacent sensitive areas (e.g. residential areas, bodies of water, known habitat for threatened or endangered species, etc.) is minimal (e.g. when wind is blowing away from the sensitive areas). Do not make applications when the wind is blowing toward a nearby sensitive area unless adequate buffer distances are used. Check labels for recommended minimum buffers. Land owners and applicators are responsible for knowing and taking into account the location of all sensitive areas including endangered species, organic farms, and public use areas including school bus stops, etc.

TEMPERATURE AND HUMIDITY

Low humidity and high temperature increase the evaporation rate of droplets and therefore increase spray drift potential. Avoid spraying during conditions of low humidity and/or high temperature. When making applications in low relative humidity, set equipment to produce larger droplets to compensate for evaporation. If applications are necessary when conditions that promote high rates of evaporation exist, spray equipment should be modified to produce larger, less drift-prone, droplets. Spray applications made in foggy conditions should be avoided as they can increase drift potential.

TEMPERATURE INVERSIONS

Avoid applications that allow sprays to reach a temperature inversion layer above the treatment area. Temperature inversions restrict vertical air mixing, which causes small, suspended droplets to remain in a concentrated cloud. This cloud can move in unpredictable directions due to the light variable winds common during inversions. Temperature inversions are characterized by increasing temperatures with altitude and are common on clear nights or with very limited cloud cover and light to no wind. They may begin to form as the sun sets and often continue well into the morning. Their presence can be indicated by ground fog; however, if fog is not present, inversions can also be identified by the movement of smoke or dust from a ground source or smoke generator. Smoke that layers and moves laterally in a concentrated cloud (under low wind conditions) indicates an inversion, while smoke that moves upward and rapidly dissipates indicates good vertical air mixing. Local sources of weather information may help identify the presence of temperature inversions. Do not spray the outside two rows in all directionsif inversion or fog potential is significant.

BUFFER ZONES

Vegetative buffers combined with windbreaks at the edge of plantings can also significantly reduce the amount of pesticide drifting out from treated crop areas to neighboring sites. NRCS agents within each state can aid the planning of such buffer/windbreak areas.

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