Simazine may be a better choice than atrazine for home lawns near surface waters

Linda Benedict, Strahan, Ronald E., Pope, Kimberly, Beasley, Jeffrey S., Kuehny, Jeff S.  |  9/12/2013 6:26:56 PM

The application of simazine instead of atrazine on lawns adjacent to lakes or ponds may reduce potential runoff. (Photo by Linda Foster Benedict.)

Figure 1. Total atrazine and simazine losses from surface runoff from a simulated lawn area.

Figure 2. Loss pattern for atrazine and simazine during the 30-minute surface runoff event.

Steve Borst, right, former graduate student, and Bret Sparks, former undergraduate student, take readings related to runoff in pesticide experiment at the LSU AgCenter Botanic Gardens at Burden. (Photo by Jeffrey Beasley.)

Jeffrey Beasley, Miao Liu, Ron Strahan, Jeff Kuehny, Kevin McCarter and Kim Pope

Pesticide runoff from lawns and other turfgrass areas is an increasing environmental concern because of its impact on surface waters used for aesthetics, fisheries, habitats, recreation, industry and consumption. Given the vast acreage of managed grass areas in Louisiana combined with precipitation levels and frequencies, the application of chemicals on turf in close proximity to water bodies increases the risk of pesticide movement into surface waters, especially as urbanization increases and management of grass areas expands.

Atrazine and simazine are commonly applied in the spring to turfgrass for the suppression and control of broadleaf and grassy weeds. In the southern United States, atrazine and simazine are routinely applied to home lawns to control broadleaf weed infestations or annual bluegrass in dormant bermudagrass as well as suppress weed competition during centipedegrass establishment.

Research conducted on atrazine and simazine application in agricultural systems has shown seasonal runoff losses of 15.9 percent for atrazine and 3.5 percent for simazine, but few studies in home lawns have been conducted for comparison. Research has shown that atrazine, a moderate to highly water-soluble pesticide, is more readily transported via surface runoff compared to simazine, which is weakly soluble and more sediment-bound. Given the results of agronomic studies and differences in solubility, the application of simazine may be preferable for turf applications where turf is adjacent to surface waters.

Unlike row-crop agricultural systems that produce food and fiber, home lawns often receive inputs to achieve a certain level of aesthetic performance. Therefore, understanding factors that involve pesticide movement, such as solubility, may allow the development of more environmentally friendly guidelines for homeowner use. The objective of this research was to compare how atrazine and simazine solubilities affect surface runoff losses from a home lawn.

Surface runoff experiments were conducted in 2010 and 2011 on turfgrass on silty loam embankments with a 10 percent slope at the LSU AgCenter Botanic Gardens at Burden in Baton Rouge. General maintenance included mowing to 3 inches weekly with clippings collected. No herbicides or nutrients were applied within six months of each simulated rainfall event. Herbicides were applied to complete turfgrass areas using a pressurized backpack sprayer. Atrazine and simazine were applied at recommended label rates. No irrigation was applied post-herbicide application.

Rainfall simulation protocols were followed. Stainless steel runoff trays were inserted into the ground to allow runoff water collection. To approximate local conditions, rainfall intensity for a two-year, one-hour precipitation event of 3 inches per hour was applied during rainfall simulations. Rainfall simulations were initiated 24 hours post-herbicide application. Initiation of surface runoff from each plot was demarked at the start of a continuous water flow into collection reservoirs. Runoff was collected for 30 minutes.

For each simulated rainfall event, total runoff volume for the 30-minute runoff event was collected. In 2011, 1-liter subsamples were collected every 5 minutes for 30 minutes and analyzed for water-soluble herbicide concentrations to characterize loss patterns. All atrazine and simazine water and soil samples were extracted and quantified.

Movement of simazine and atrazine appears to differ on complete turfgrass areas such as home lawns. Total atrazine movement accounts for 18.25 percent of atrazine applied compared to 5.69 percent of simazine applied. Atrazine dissolved in the water fraction of surface runoff accounted for 18.15 percent of applied atrazine of the 18.25 percent total atrazine lost, whereas the water fraction of simazine was 3.11 percent of applied simazine of the 5.69 percent total simazine lost (Figure 1). The remaining 2.58 percent of applied simazine lost of the 5.69 percent total simazine lost was sediment-bound simazine. Grasses have long been noted for their ability to reduce sediment movement at ground coverage above 70 percent. The greater affinity of simazine to bind with organic and soil particles appears to have affected the total amount of simazine lost during the surface runoff event compared to the more highly water-soluble atrazine.

In the second year of the study, the timing of atrazine and simazine losses was examined over the 30-minute surface runoff event. As illustrated in Figure 2, atrazine exhibited high initial losses after the onset of runoff. Within 15 minutes after the initiation of runoff, 14.43 percent of applied atrazine of the 18.25 percent atrazine lost had occurred. In comparison, simazine exhibited more of a static loss pattern, suggesting its lower water solubility affected early losses. These data suggest that although long intense precipitation events may be equated with increased atrazine and simazine movement, precipitation events that produce as little as 15 minutes of runoff have a greater effect on atrazine movement compared to simazine because of atrazine’s higher water solubility.

Based on these experiments the application of simazine to turf areas located adjacent to surface waters such as lakes, ponds, canals and bayous may reduce potential surface runoff compared to atrazine. The costs of simazine and atrazine are similar.

Jeffrey Beasley is an associate professor; Miao Liu is a graduate research assistant; and Ron Strahan is an associate professor, all in the School of Plant, Soil & Environmental Sciences. Jeff Kuehny is the resident director of the LSU AgCenter Botanic Gardens at Burden; Kevin McCarter is an associate professor in the Department of Experimental Statistics; Kim Pope is the pesticide applicator trainer with the W.A. Callegari Environmental Center.

(This article was published in the summer 2013 issue of Louisiana Agriculture magazine.)

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