Abundant earthworm castings and high-quality turf conditions are mutually exclusive. Castings interfere with ball roll and mowing. When smashed by foot, cart or mower traffic, the casts smear and cause turf thinning. While earthworms are desirable in many horticultural situations, having an abundance of them in closely mown areas on a golf course causes problems.
In most parts of the country, there is typically heavy earthworm casting activity for one to two months each spring and fall. In winter and summer, when soil temperatures are too cold or too hot – i.e., below 50 degrees F or above 68 degrees F – earthworms move deeper into the soil profile and rarely come to the surface to feed. Based on observations during recent USGA Course Consulting Service visits in the Pacific Northwest, we have hit the seasonal sweet spot for earthworm surface feeding.
For decades, superintendents all over the world have been looking for the magic bullet to control earthworm castings. Over the years, many people have thought that sand topdressing would discourage earthworms from feeding at the surface and subsequently leaving a casting when they were done, but some researchers have found this not to be the case (Boyle, et al., 2019).
Chemical control products that worked well many years ago are no longer available or allowed. Currently, there are no pesticides labeled for use on earthworms. However, fungicides containing thiophanate-methyl, some insecticides and saponin-based fertilizers have secondary effects that can help reduce the number of earthworms feeding at the surface. Controlling pest pressure and promoting turf growth with these types of products during peak earthworm casting periods can be an effective strategy. It’s worth noting that if saponin-based fertilizers are used, be ready for a rapid cleanup since some golfers may find worms on the turf surface objectionable.
If these products are not part of your turf care program, waiting until castings are dry to mow or blow them off playing surfaces will make cleanup much easier and less damaging to the turf and mowers. For more information, check out our article “Managing Earthworm Casts on Golf Courses” or reach out to me.
Reference:
Boyle, P.E., Richardson, M.D., Savin, M.C., Karcher, D.E., & Potter, D.A. (2019). Ecology and management of earthworm casting on sports turf. Pest Management Science, 75, 2071-2078.
West Region Agronomists:
Brian Whitlark, regional director – bwhitlark@usga.org
Cory Isom, agronomist – cisom@usga.org