Best Management Practices for Maryland Golf Courses

To prevent the off-site movement of pesticides, site-specific characteristics and prevailing conditions should be evaluated, in addition to the selection of the appropriate pesticide. Site- specific characteristics, such as soil type, depth to the water table, geology, and proximity to surface water should all be considered before selecting and applying pesticides. For example, highly permeable materials such as gravel deposits or the sandy soils of Maryland’s eastern shore allow water and dissolved compounds to freely percolate down to groundwater. In western Maryland, karsts (limestone formations with sinks or separations in the rock) underlie the soil. These sinks can act as direct entryways to groundwater for dissolved pesticides. In addition to site characteristics, prevailing weather conditions, such as chance of precipitation, prevailing wind, humidity, etc., should be evaluated with respect to the timing of pesticide applications. For example, if rainfall is high and soils are permeable, water that carries dissolved pesticides may take only a few days to percolate downward to the groundwater.

Leaching and Runoff

Most pesticide movement in water is either by surface movement off the treated site (runoff) or by downward movement through the soil (leaching). Runoff and leaching may occur when:

• Too much pesticide is applied or spilled onto a surface. • Too much rainwater or irrigation water moves pesticide through the soil off-site or into groundwater. • Highly water-soluble or persistent pesticides are used. Weakly sorbed pesticides (compounds with small Koc values) are more likely to leach through the soil and reach groundwater. Conversely, strongly sorbed pesticides (compounds with large Koc values) are likely to remain near the soil surface, reducing the likelihood of leaching but increasing the chances of being carried to surface water via runoff or soil erosion.

Drift

Pesticide movement away from the application site by wind or air currents is called drift. Pesticides may be carried off-site in the air as spray droplets, vapors, or solid particles, even on blowing soil particles.

Air drift: Air drift is a function of droplet size. Small, fine drops with diameters of 100 microns or less tend to drift away from targeted areas.

Vapor drift: Volatile pesticides can change readily from a solid or liquid form into a gas under the right conditions (i.e., high temperatures) and cause vapor drift.

Particle drift: Particle drift is the movement of solid particles from the target area by air during or just after an application. These solid particles may include pesticides formulated as dust or soil particles to which pesticides are attached.

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