In the Running
The potential for runoff from turf to pollute our drinking water concerns many people and is a theme commonly found in newspapers and magazines throughout the country. Runoff occurs whenever rainfall or irrigation occurs faster than the ground can absorb. A small but vocal portion of the public has targeted turf as an important player in water pollution due to the perceived runoff from turf. Public opinion is important because to a large degree it drives legislation. In the past few years, new legislation has eliminated some pesticides from use on lawns and restricted the amounts of others that may be applied. As a professional, such public opinion may affect your business, but what can be done?
THE FACTS ABOUT PESTICIDES & RUNOFF
The Fungicide, Insecticide, and Rodenticide Act (FIFRA) is a federal law that requires all for-hire professional applicators to pass a state certification exam before pesticides can be applied. This requirement has lead much of the public to believe that professional applicators use different and more toxic pesticides than are available at retails stores. In reality, most of the products available to homeowners contain active ingredients similar to those used by professionals. Any differences are usually the type of formulation or the concentration of the active ingredient in the product.
|Purpose||Common name||Form||Common name||Form|
|Pre-emergent herbicide||Prodiamine||Granular with fertilizer||Pendimethalin||Granular with fertilizer|
|White grub insecticide||Imidacloprid||Liquid||Imidacloprid||Granular|
|Broadleaf herbicide||Dicamba, MCPA, triclopyr||Liquid||Dicamba, MCPP, 2,4-D||Liquid|
The likelihood for pesticides to pollute runoff water primarily depends on their water solubility and their ability to adsorb (stick) to surfaces (e.g., soil). Most pesticides have low water solubility and do not dissolve enough to significantly contaminate runoff water. The commonly used phenoxy-type broadleaf herbicides, however, do have high water solubilities. The phenoxy herbicides have relatively short half-lives, though, of approximately eight days on the foliage. In other words, half of the pesticide is degraded every eight days. Sixteen days after application only 1/4 of the pesticide remains, 24 days after application 1/8 of the pesticide remains and so on. Pesticides are degraded by many natural forces, including sunlight, plants, microbes, and naturally-occurring chemical reactions in the soil.
The amount of runoff from a site depends on a number of factors such as soil type, moisture, compaction and the amount and type of vegetation. Runoff is much less likely to occur on a dry, sandy soil that is not compacted than on a wet, compacted clay soil. Tall, thick turf is less likely to allow runoff than a bare soil.
TURF FILTERS RUNOFF POLLUTION
A number of studies conducted since the 1980s indicate that very little runoff occurs under most turf conditions. A two-year study at the Pennsylvania State University showed that runoff occurred only once from rainfall on a lawn-type turf even though the turf had a nine to fifteen percent slope and was on a clay soil. Because the researchers were interested in measuring the amount of pesticides in turf runoff, irrigation was used to cause runoff shortly after pesticides were applied. In most cases a simulated rainfall of six inches per hour was required for one to one and one-half hours before any runoff occurred. Results showed that neither chlorpyrifos or pendimethalin was found in the runoff. Less than 1 percent of the dicamba and less than 2 percent of the 2,4-D applied was in the runoff, and the majority of both occurred within the first week after application. As it turns out, turf is a tremendously good water filter. The abundant plants, thatch, and root systems act as a sponge to absorb pesticides, sediment, and other pollutants in water. Turf foliage may adsorb 30 to 60 percent of the pesticide applied. Most of the rest of the pesticide is bound to thatch or the upper soil profile where it is largely degraded by microbes and other natural forces.
AVOID APPLICATION TO IMPERVIOUS SURFACES
Despite research data much public concern exists over the potential pollution from lawn pesticides. Part of the concern stems from the lack of publicity given the data. Other concern stems from incidents of careless application or spills. Most applicators have seen others, including homeowners, carelessly apply pesticides to driveways, sidewalks, and streets. These impervious surfaces may not provide the sponge-like absorption capability of turf. It seems reasonable to expect that rainfall or irrigation could wash pesticides applied to concrete or asphalt surfaces directly into sewer systems or surface waters such as lakes or ponds. However, no one had ever tested the amount of pesticide capable of running off from such surfaces.
Good management practices and legislation should depend on sound science. The University of Wisconsin recently completed a study to determine the potential for pesticides to runoff from simulated urban landscapes. The goals were to compare retail versus professional pesticides when applied to both turf and concrete surfaces. The plots were on a 5 percent slope, and concrete was used to simulate driveways. A conventional pesticide program was used, consisting of a pre-emergence herbicide early in the spring, an insecticide for surface insect control later in the spring, an insecticide applied for white grub control in the summer and a broadleaf herbicide application in the fall (See table 1, page C4). The pre-emergence herbicides were applied as a granular formulation on fertilizer. The professional formulations of insecticides were both liquid applications, while the retail versions were both granular products. Both professional and retail broadleaf herbicides were applied as liquids. Label rates were used for all pesticides applied to both turf and concrete in order to provide a valid comparison and a worst-case scenario. Each pesticide was applied twice over a two-year period. One-half inch of water was applied to both turf and concrete plots through an irrigation system within 30 minutes after pesticide application, then again twice weekly throughout the growing season. Runoff was collected in galvanized steel troughs at the end of the plots and measured to determine total volume. Samples of runoff water were analyzed for pesticides at 0 to 1, 7, 14 and 28 days after pesticide application.
As expected, very little runoff occurred from turf, though runoff from concrete occurred over 80 percent of the time following any rainfall or irrigation. Light, gentle rain of less than ¼ inch per day did not cause runoff from concrete. Significant runoff from turf occurred only twice each year. The first occurred during snow melt and/or rainfall while the ground was still frozen at the end of winter. Runoff from turf happened a second time each year when intense rainstorms occurred over a period of several days, which caused saturated soil conditions. Small amounts of runoff (less than one cup of water from 128 square feet turf surface) from turf occasionally occurred during the year but were far less than the sometimes 25 gallons of runoff from the concrete plots.
- Pre-emergent herbicides in runoff
Only about 5 percent of the pre-emergent herbicide applied to concrete was found in runoff. Most or all of this occurred between the second and seventh day after application. No pre-emergence herbicides were found in runoff from turf.
- Post-emergent herbicides in runoff
Twenty-eight percent of the retail herbicide applied to concrete (dicamba, 2,4-D, and MCPP) was found in runoff compared to 17 percent of the professional herbicide (dicamba, triclopyr, and MCPA). About 80 percent of the total herbicide runoff occurred within one day after application, underscoring the importance of allowing liquid pesticides to dry before rainfall or irrigation. No post-emergent herbicide was found in runoff from the turf.
- Surface insecticides in runoff
Less than 1 percent of the retail surface insecticide (diazinon) was found in runoff from concrete compared to 10 percent of the professional version (chlorpyrifos). Again, most of the pesticide runoff occurred within the first several days after application. Only 0.1 percent of the diazinon applied to turf was found in runoff, and no chlorpyrifos was found in runoff from turf. Both compounds have low water solubility and are tightly bound by organic matter such as thatch. Their capacity to bind to concrete has not been researched.
- Subsurface (white grub) insecticides in runoff
Imidacloprid was used as a white grub control, though a granular formulation was used for the retail version and a liquid application was used for the professional version. Nearly 90 percent of both forms of imidacloprid applied to concrete were found in runoff water. This was startling as imidacloprid is largely viewed as a safer replacement for older pesticides such as diazinon and chlorpyrifos. Only 0.2 percent or less of imidacloprid were found in runoff from turf.
HOW YOU CAN PROTECT YOUR BUSINESS AND THE ENVIRONMENT
Follow label instructions including those regarding timing of pesticide application to avoid potential runoff due to rainfall or irrigation. Though runoff rarely occurs from turf, delay pesticide applications when the soil is already saturated with water and rain is expected. Do not apply more pesticide than is needed or allowed by the label as the extra pesticide will be more likely to runoff if it can't be absorbed by turf. Avoid accidentally applying pesticides to impervious surfaces such as concrete or asphalt. Use a drop spreader for applying granular pesticides to turf near impervious surfaces or bodies of water. If a granular product is accidentally applied to or spilled on pavement, sweep the product into the turf or place back into the spreader or container. Allow accidental applications of liquid to dry; do not wash them off the pavement with water. Liquid pesticide spills must be removed as much as possible by soaking excess product with absorbent material such as calcined clay or absorbent pads. The advantage of using calcined clay or similar material is that this can be applied to turf areas for natural degradation. Synthetic absorbent pads must be disposed of in sanitary landfills approved for pesticide disposal.
Find out the facts about pesticide runoff from turf. Join a professional organization, attend educational seminars and keep reading research-based articles in trade journals to keep current with the latest information. Adopt better chemicals and application methods to decrease the possibility for pesticide runoff to occur. Then, tell people about the facts. Use word of mouth, hold training sessions for your employees, provide “fact” sheets for your customers, and develop a relationship with the local newspapers and television personalities to inform your public. Use pesticides safely, according to the label regulations, and be prepared to speak out about the proper use and safety of pesticides based on research data.
Dr. John Stier is professor of environmental turfgrass science at the University of Wisconsin (Madison, Wis.).
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