Posts Tagged ‘herbicide drift’

Off-Target Movement of Herbicides is a Concern

Friday, May 15th, 2009

Mark VanGessel, Extension Weed Specialist;

Herbicides are extremely effective products for controlling weeds and unwanted vegetation. When the herbicide lands in an area with desirable plants, it can cause discoloration, abnormal growth, or plant death. Off-target movement can have considerable consequences. Herbicides can move off target by a number of mechanisms, including: movement with water (leaching or run-off), physical drift (movement of small droplets by wind), and volatility (movement due high temperatures and moist conditions causing herbicides to vaporize after they are deposited on leaves or soil). Many herbicides can cause plant response at very low rates, particularly if the desirable plants are highly sensitive. Using application equipment and techniques to increase droplet size will reduce the likelihood of drift, but they will not overcome windy conditions. It is important to be aware of wind speed and direction. Most herbicide labels caution of increased risk when winds are in excess of 5 mph and caution not to spray when wind is greater than 10 mph. The two tables below demonstrate the potential for considerable drift with light to moderate winds.

Distance Water Droplets Will Drift While Falling 10 ft in a 3 mph Wind*

Droplet Diameter (microns) Relative Size Estimated Particle Drift (feet)
5 fog 3 miles
20 very fine spray 1,100
100 fine spray 44
240 medium spray 28
400 coarse spray 8.5

*Taken from Herbicide Spray Drift, NDSU, A-657, authored by Alan Dexter

Distance Water Droplets Will Drift While Falling 3 ft in a 5 mph Wind**

Droplet Diameter (microns) Relative Size Estimated Particle Drift (feet)
40 fog 140
100 misty rain 24
200 drizzle rain 9.5
400 light rain 4.0

**Taken from Avoiding the Potential for Drift, Monsanto Company

Be sure to use good judgment when spraying pesticides.