TURF TIP
9/17/04

What Happens to Fertilizers and Pesticides Applied to Turf?

Now that we are entering the fertilization season for lawns, questions sometimes arise about where products go after application to lawns. Research at Purdue and many other universities has shown that fertilizers (including both nitrogen and phosphorus) and pesticides applied to turf will not move horizontally (runoff) or vertically (leaching). This is because the relatively dense vegetation on the surface allows very little product to reach the soil surface. If fertilizers and pesticides do reach the soil, they are quickly bound by the thatch or organic matter associated with turf stands. And fertilizers or pesticides that make it past the thatch are quickly broken down by the high microbial activity associated with the continuous fibrous root system of a turf stand. However, fertilizer and pesticides have been shown to move off turf under very unusual conditions. Heavy downpours on steep slopes with thin grass increase the chance of runoff, whereas thin turf over very sandy soil increases the chances of leaching. If common sense is used and the product label is closely followed, there is little or no chance for turf products to move off-target. Here are a number of ways to further minimize the chances of turf products moving off-site:

• Always follow label directions
• Avoid misapplication to sidewalks and drives and sweep off any product left on these impervious surfaces
• Always calibrate and apply the correct amount of product
• If you live near a body of water, leave an untreated "buffer strip" 10-50 feet wide around bodies of water (the greater the slope, the wider the buffer)
• Test your soil to determine if phosphorus and/or potassium is necessary and don’t apply any if not needed by the turf
• Use fertilizer products containing slow release N
• Do not apply during the threat of thunderstorms
• Water-in fertilizers with 0.25-0.5 inches of gently applied irrigation
• Do not apply to dormant turf after or before the growing season.
• Mow your lawn at 3 inches or more

Zac Reicher, Associate Professor/Turfgrass Extension Specialist

Send corrections, suggestions, and comments to biehlj@purdue.edu