Close up of earthworm casts on golf course turf. Photo: Pete Landschoot
Burrowing creates channels in soil that improve drainage, reduce compaction, facilitate air exchange, and promote root development. Earthworms reduce thatch build-up and enrich the soil by breaking down organic matter, thereby improving nutrient availability and stimulating microbial activity.
According to Potter et al. (2011), an acre of turf can support more than a million earthworms, which can consume more than 4 tons of plant debris.
Whereas normal earthworm populations are considered beneficial, excess numbers can cause problems on golf courses and sports turf surfaces, especially in the fall. Large earthworm populations deposit thousands of casts (fecal matter mixed with soil) on the turf surface, which interfere with mowing and ball roll. They also become smeared into the turf through mowing and foot traffic, resulting in thinning of turf stands.
Earthworm casts on golf course turf. Photo: Pete Landschoot
Earthworm casts can also accumulate on mowing equipment, causing abrasion to reels and bedknives, and reducing the quality of cut.
Casts are difficult to wash from mowers and extend the time employees spend on maintaining equipment. Photo: Pete Landschoot
Build-up of earthworm casts on golf course mowing equipment. Photo: Pete Landschoot
Earthworm species inhabiting turf stands in the eastern U. S. are typically in the Apporectodea genus. These non-native earthworms (introduced from Europe) usually range from 2-3 inches and create mostly horizontal burrows in soil. Casting is most common in fall, before soils freeze. As temperatures become freezing in winter, or very warm in summer, earthworms burrow deep in soil and enter a dormant state (Potter et al., 2011).
Management of earthworms
Turf managers have attempted to manage earthworms culturally by sand topdressing of turf surfaces, converting ryegrass fairways to creeping bentgrass, acidifying soil, and other methods. Results of these programs have met with varying results, and are not always reliable in reducing the casting problem.
Chemical control of earthworms using chlorinated hydrocarbon insecticides and mercury-based fungicides is no longer an option, and no pesticide is currently labeled for earthworm control. However, thiophanate methyl fungicide and some insecticides that are routinely used for controlling pests on golf course fairways and sports fields can inhibit earthworms as a side effect. Some authors have suggested that the lethal effect of thiophanate methyl is due to the anti-cholinesterase activity of the carbamate portion of the molecule (similar to carbamate insecticides).
A recently introduced organic fertilizer product called Early Bird 3-0-1 has shown good suppression of earthworms in field trials at universities and on golf courses. This product is made with crushed tea seeds from China (a by-product of tea oil manufacture), which contain natural saponin compounds that are thought to disrupt the mucous coatings on earthworms, causing desiccation and death.
Early Bird organic fertilizer does not have information on its label for earthworm control because it has not gone through EPA's pesticide registration process. The use rate of this product is 3 to 6 lb/1000 ft2, and research at the University of Kentucky has shown early spring applications have reduced casts on low-cut bentgrass by more than 95% for at least 5 weeks when thoroughly watered-in.
In a fall trial, application of 6 lb/1000 ft2 of Early Bird reduced casts by 98% after 2 days, and 83% after 30 days (Potter et al., 2011). Treating large areas with Early Bird can be expensive, so most applications are made in small problem areas.
Potter, D.A., Redmond, C.T., and Williams, D.W. 2011. The worm turns: Earthworm cast reduction on golf courses. Golf Course Management. Sept. pp. 86-96.