Improving Pesticide Efficacy and Managing Spray Drift
In pesticide application, two important factors are pesticide efficacy and spray drift management. The goal is to achieve 100% pest control with 0% spray drift. As with most situations where you can’t control all the variables, achieving this goal is a tall order.
While you can’t manage the weather variables, you can spray when the elements are not conducive to drift and manage the variables you can, including nozzle selection and orientation; sprayer calibration; sprayer speed; pesticide label requirements, and others listed below.
Researchers Note Top 3 Factors in Drift
A Mississippi State University study analyzed data from more than 100 studies involving drift from ground sprayers. Of the 16 variables considered, three were most important:
1. Wind speed. When the wind speed was doubled, there was almost a 700% increase in drift when the readings were taken 90 feet downwind from the sprayer. Hence the recommendation of spraying in 10 mph winds or less.
2. Boom height. When the boom height was increased from 18 to 36 inches, the amount of drift increased 350% at 90 feed downwind.
3. Distance downwind. If the distance downwind is doubled, the amount of drift decreases five-fold. Therefore, if the distance downwind goes from 100 to 200 feet, you have only 20% as much drift at 200 feet as at 100 feet and if the distance goes to 400 feet, you only have 4% of the drift you had at 100 feet. Check wind direction and speed when starting to spray a field.
Tips for Reducing Spray Drift and Resulting Damage
- Select the nozzle to get a large droplet size, based on pesticide and nozzle product recommendations. Use one of the new types of sprayer nozzle tips and adjust spray pressure. Higher spray pressures produce smaller droplets which are more susceptible to drift. Larger droplet sizes reduce coverage so it may be necessary to increase the carrier rate.
- Only spray the part of the field least affected when conditions (wind speed, wind direction, and distance to susceptible vegetation) are conducive to drift, and return to the rest when conditions are better.
- If using a rate controller, be careful of increased speed. Since most rate controllers increase the pressure to maintain the same gpa when the speed increases, try to maintain the speed within +10%. For example, if you’re applying 20 gpa at 8 mph at 40 psi and you increase the speed to 11 mph, the pressure will now be 75.5 psi which will produce a lot of small particles prone to drift. Also, this pressure will be above the operating range of most tips. Drift reduction agents may be helpful.
- Use new spraying technology such as the “blended pulse” to decrease the risk of drift by allowing flow rate to be controlled independently of spray pressure.
- Follow label directions. Start by thoroughly reading the label. Use the nozzle manufacturer’s guide for nozzle and pressure combinations.
- Increase nozzle size. This result in higher application volumes and less spray being deposited off-target.
- Consider using new technologies. Certain nozzles (air-induction and venture nozzles) may help reduce drift.
- Keep the nozzle close to the target. Auto height control may be limited in its effectiveness at speeds greater than 14 or 15 mph.
- Maintain appropriate travel speed. High travel speeds may result in an unstable boom, higher boom, and increased drift potential.
- Avoid applying when wind speeds are high. (See inset: Wind speed was the top factor in spray drift in this study.) As wind increases, more spray moves off-target.
- Do not spray during a temperature inversion. Temperature inversions prevent the dissipation of spray particles.
- Consider using buffer or no-spray zones near sensitive areas.
- Use a drift-control additive when needed to increases average droplet size. Do not rely on additives as your only drift-reducing technique; they cannot make up for poor spraying practices.
- Before spraying, always take into account proximity of nearby susceptible plantings, such as grape vines, horticultural crops, and specialty crops. Register with DriftWatch to receive email notification when new sensitive crops are registered in your area. DriftWatch, part of FieldWatch, is monitored by the Nebraska Department of Agriculture in the state.
For more information see Protecting Pesticide Sensitive Crops (NebGuide G2179) and Bee Aware (EC301).
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