Earthworms In Golf and Athletic Field Turf: Making A Mess In Fall

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 can also accumulate on mowing equipment, causing abrasion to reels and bedknives, and reducing the quality of cut.

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 the 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 cast problem.

Chemical control of earthworms using chlorinated hydrocarbon insecticides and mercury-based fungicides are no longer options, 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).

Organic fertilizer products containing crushed tea seeds (a by-product of tea oil manufacture) have shown good suppression of earthworms in field trials at universities and on golf courses. Such products contain natural saponin compounds that are thought to disrupt the mucous coatings on earthworms, causing desiccation and death.  Availability of products containing saponin compounds is currently limited and do not have information on labels for earthworm control because they are not registered through the U.S. Environmental Protection Agency as pesticides.

Reference

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.