Drift Management to Avoid Herbicide Damage
Written by Kurt Hembree (UCCE Fresno County)
Reducing spray drift is necessary to prevent crop injury, both within the field being treated and off-site. Environmental conditions (air temperature inversions, wind velocity, etc.), applicator awareness, type of spray equipment, nozzle selection, spray boom operating pressure, water volume discharge, and other factors affect the degree of drift that may occur during any application. While spray shields do not guarantee drift will not occur, they can greatly minimize the risk of drift, especially in open fields or where young vineyard and orchard plantings are being treated.
The following steps should be taken to minimize the risk of drift from ground sprayer equipment:
1. Don’t spray when it’s windy: Do not spray in winds above 6 - 10 mph.
2. Be cautious on calm days: Do not spray under dead calm conditions in early morning, evening, or the night. Calm conditions are often associated with temperature inversions which can result in long-distance spray drift (1 mile or more). Burning brush on calm days can give an indication on the presence of temperature inversions (refer to local regulations on restrictions for obtaining a burning permit).
3. Check the buffer zones: Refer to the product label to determine adequate buffer zones outside of the field treated. Do not spray if the wind is blowing towards a nearby sensitive crop, garden, waterway, or other sensitive area.
4. Use a shield: Consider equipping your sprayer with a protective shield. A number of designs are available that can reduce drift between 35 and 75%. Avoid spraying trunk-to-trunk with unshielded spray booms.
5. Use a spray drift retardant: Spray drift retardants are available that can be added to many products to help reduce off-target drift.
6. Check the formulation: Use amine formulations of 2,4-D when possible. Use special care when using ester or other volatile herbicides. Avoid spraying these products on or immediately before hot days.
7. Sprayer type: Sprayers designed to apply herbicides at low volumes (<10 gpa), such as controlled droplet applicators, produce extremely fine droplets which can drift long distances. Advances in sprayer technology allow for certain postemergence herbicides (like glyphosate) to be applied through low volume, shielded equipment or in low doses based on weed populations present at the time of treatment.
8. Watch the nozzle pressure: Avoid nozzle pressures above 45 psi for conventional flat fan tips. Excessive pressure can create fine droplets that are prone to drift. Use a minimum of 10 gal/acre, unless otherwise specified on the label.
9. Nozzle height: Operate nozzles at their lowest recommended height. For 80° tips, this is 18”, and for 110° tips, this is 12”. Orienting nozzles forward also allows for further height reductions.
10. Nozzle selection: Special nozzles are available by various manufacturers, that create coarse, low-drift sprays. These nozzles can reduce drift by 50 to 95%.