Of the measures required to protect endangered species, drift management is the most straightforward—follow the label. Every agricultural pesticide label includes general use restrictions to prevent or control drift, such as “Do not apply when winds are gusty or when conditions will favor movement of spray particles off the desired spray target.”
When drift could impact listed species or their habitat, the pesticide label outlines additional required measures. These often include a downwind spray drift buffer zone, also known as a setback distance or no-spray zone, between the application area and a protected area located downwind. The buffer zone distance varies by application method: aerial application can range from 0 to 320 feet; ground boom from 0 to 310 feet; and airblast sprayers from 0 to 160 feet. Liberty Ultra [link to P. 9], for example, requires the applicator to maintain a buffer of 50 feet for aerial applications and 10 feet for ground applications, along with a specified droplet size distribution.
You can reduce the buffer zone distance by using specific spray equipment such as hooded sprayers, applying a coarser droplet size, adding drift-reducing adjuvants, or maintaining windbreaks or shelterbelts. Other options include treating a smaller part of the field, lowering the application rate, or spraying under weather conditions with a relative humidity above 60%. Each of these measures decreases the buffer zone as a percentage of the maximum and is cumulative; for example, two mitigations of 50% (using an over-the-top hooded sprayer) and 30% (using a drift-reducing adjuvant and medium-sized droplets) would reduce the buffer zone by 80%. In this case, a 50-foot buffer zone would be reduced to 10 feet (50 ft. X 0.80 = 40 ft.; 50 ft. – 40 ft. = 10 ft. buffer zone). Refer to the label for the percentage reduction for each mitigation measure.
In some cases, using a single option can eliminate the need for a buffer. Again, from the Liberty Ultra label [link to P. 10], “any of the following options can reduce the ground buffer distance to 0 feet:
1. Use of an oil emulsion reducing adjuvant that makes up 2.5% of the total volume of the finished spray tank mix.
2. Application is made with an over-the-top hooded sprayer, as a layby application, or below the crop canopy using drop nozzles.
3. Use of a row-middle hooded sprayer.
4. If a windbreak or shelterbelt (such as trees or riparian hedgerows) exists between the application site and non-managed area and meets the criteria listed in the ‘Windbreak-Shelterbelt Criteria’ section of this label.
Some “managed land” areas directly adjacent to treated field edges can be included in the buffer zone footage, or the buffer zone can be eliminated, as long as the pesticide does not contact people, either directly or through drift. Examples include:
1. Agricultural fields, including untreated portions of the treated field;
2. Roads, paved or gravel surfaces, mowed grassy areas next to the field, and bare ground areas from recent plowing or grading;
3. Buildings and their perimeters, silos, or other man-made structures with walls and/or roofs;
4. Areas maintained as a mitigation measure for runoff, erosion, or drift control, such as vegetative filter strips (VFS), field borders, hedgerows, and Conservation Reserve Program (CRP) lands;
5. Managed wetlands, including constructed wetlands on the farm;
6. On-farm contained irrigation water resources not connected to neighboring water bodies, including on-farm irrigation canals and ditches, water conveyances, managed irrigation/runoff retention basins, and tailwater collection ponds.
Buffers are not necessary for application methods that are not susceptible to spray drift. Examples include in-furrow sprays, tree trunk drenches, tree injections, soil injections, or small-area applications (< 1/10 acre or < 1,000 sq. ft.) (1 acre = 43,560 sq. ft., so 1/10th of an acre equals 4,356 sq. ft.). Chemigation with overhead and impact sprinklers does not require spray drift buffers, but other protective measures might be needed.