The Relationship between Sand Topdressing and Earthworm Casting in Warm-Season Turfgrass.

As earthworms feed, they can egest soil and nutrient-rich aggregates (casts) on the soil surface. In low-cut turfgrass systems, such as golf course greens, tees, and fairways, surface casting can result in a muddy playing surface, ball roll issues, water retention in the canopy, weed and pest invasion, reduced aesthetics, surface softening, and reduced photosynthesis. As the use of pesticides for earthworm control is illegal in the United States, earthworms must be managed through cultural practices. Sand topdressing is one method of earthworm control studied for use on golf courses, with the assumption being that the abrasive sand particles will deter the soft-bodied earthworms from remaining in the system; however, effects have been varied.

The purpose of this study was to test the effect of heavy (2.54 cm yr⁻¹) or light (0.64 cm yr⁻¹) sand topdressing treatments on casting activity of earthworms in ‘Patriot’ bermudagrass (Cynodon spp.) in both native soil (Captina silt loam; fine-silty, siliceous, active, mesic Typic Fragiudults) and sand-capped rootzones (12.5 cm of medium-coarse sand that meets USGA particle size specifications for putting green construction).

Results indicate that casting activity peaks in spring and fall and casting rates are higher in sand rootzones, regardless of topdressing treatment. Additionally, within the soil rootzone, heavy topdressing resulted in higher casting rates, while in the sand rootzone, casting rates were similar, regardless of topdressing treatment. These results are counter to expectations, and soil properties and earthworm species are being investigated to gain insight into why there is greater casting in sand rootzones and heavy sand-topdressed soil plots.