Turf Talk >>>
EARTHWORMS IN TURFGRASS: Friend and Foe
By Steve Hong, Ph.D.; David W. Held, Ph.D.; and R. Chris Williamson, Ph.D.
Alabama Turf Times >>> Wi n t e r 2011
E
arthworms are soil-dwelling organisms and play major roles in soil formation, aeration and drainage, breakdown into rich humus and incorporation of organic matters, and enhancement of microbial activity in soil. Overall, earthworm activity in soil improves soil fertility by depositing minerals and plant nutrients in an accessible form. Thus, there is no question that earthworms are beneficial organisms. Alabama has 28 species of earthworms. The species present statewide are influenced by soil type, with more species exclusively in the sandy loam soils of the coastal plain. Despite the benefits, earthworms can be highly problematic in close-mown golf courses, particularly on native soils. In this case, the worms don’t consume the grass but instead leave casting material (feces) on the surface (Photo 1). Casts get smoothed by rollers, smother the grass and can increase maintenance of equipment. Earthworms can also cast so heavily that they smother and kill sections of St. Augustinegrass lawns along the coast. No pesticides are legal for control of earthworms in the United States; however, there are alternative, non-pesticide management options for suppressing earthworm castings.
18
Soil amendments Because of the sensitivity of earthworm skin (cuticle), the use of angular, abrasive soil aggregates, as topdressing amendments, may provide a viable management option for golf course superintendents. Black Jack (Photo 2, a byproduct of the coal industry), Amber Jack (a byproduct of the paper-mill industry) and Best Sand (a more-angular topdressing sand) have been tested for efficacy against earthworms. Topdressing with these products in spring, or in both spring and fall, can reduce earthworm casts by 30% to 40%, relative to untreated control plots. The magnitude of reduction isn’t outstanding,
but just simply substituting another product during topdressing can be a simple way to reduce earthworm casting problems.
Expellants Expellants do just that; they cause worms to surface, usually in just a few minutes after being irrigated into the turf. Most will die on the surface or burrow back into the soil and die. Regardless, you should anticipate a cleanup if any expellant is used. Tea-seed pellets (from camellias), dishwashing liquid and mustard-seed powder are examples of earthworm expellants. Dishwashing soap and
Quick Facts about
EARTHWORMS • Earthworms are beneficial organisms that improve soil properties. • Problems result from castings deposited on the turf surface typically in spring and fall. • No pesticide can be legally used to control earthworms.
• Soil amendments such as byproducts of coals and papers reduce cast density on the surfaces. • Expellants cause earthworms to evacuate the soil, reducing castings but requiring extensive cleanup.