Invasive Earthworms Newest Threat to Landscape and Golf Course Turf

In 2011-2012, we surveyed earthworm communities associated with casts on six Kentucky golf courses, the first such study in North America. Most of the species found in fairways were topsoil-dwellers (Aporrectodea spp.) of European origin.   As our work became known, superintendents began contacting us about problems with prolific earthworm casting on U.S. Golf Association (USGA) high-sand root zone greens in summer. That was noteworthy because casting by Aporrectodea is mainly in late autumn and early spring, and is more often a problem on fairways and pushup greens than in high-sand soils.

Figure 1. Invasive earthworms – casts on putting green

Figure 1. Invasive earthworms – casts on putting green

We sampled severely infested putting greens at several sites and found high populations of Asian earthworms (Megascolecidae Family), including Amynthas hupeiensis and Amynthas loveridgei, species not previously reported damaging golf courses.  Casts of these earthworms are larger and damage to putting greens is far greater than any we have seen from European species.  Indeed, greens may be rendered essentially unplayable, requiring golfers to knock them down to clear a path before attempting each putt.  Moreover, unlike Aporrectodea spp., which are mainly actively during cool wet periods in autumn and spring, and cast at night, Amynthas spp. are most active during the growing season (May through September), and produce surface casts both day and night, so that greens mowed in the morning are covered by new casts by that afternoon.  The worms themselves are olive to muddy-brown, foul smelling, and often curl up when disturbed.  The casts, at least on sand-based greens, typically appear more sinuous than those of other earthworms in native soils.

Amynthas  spp. are aggressive in invading new habitats. They have invaded forests of the Great Lakes region and the Great Smoky Mountains where they are upsetting soil dynamics and understory plant communities.  Amynthas spp. have become widely established around lake and river banks as a result of anglers discarding unused bait, and they have sometimes been purposely introduced to establish bait populations convenient to such areas. Amynthas spp. are sold as fish bait (known by common names such as Alabama or Georgia Jumpers, Green Stinkworm, or Green Riverworm).

How are invasive Asian earthworms being introduced onto golf courses?  Finding the answer is critical to containing the problem. Amynthas spp. are parthenogenetic, so even a single tiny cocoon or individual worm, could establish a population. The superintendent and staff of the course pictured above are adamant that the problem started within a year after the course was renovated with sand dredged from banks of the Ohio River, and sand from the same supplier was used at several other central Kentucky courses where Amynthas spp. infestations were found.

Amynthas spp. can readily be dug along Ohio River banks (http://www.catfish1.com/forums, accessed 6 June 2013), as well as smaller rivers. They are popular as catfish bait. We hypothesize that they are being introduced onto golf courses as cocoons in the river sand.  Anglers dumping bait around golf course lakes and ponds, or around reservoirs from which irrigation water is drawn, may also be a source. Report suspected infestations in Kentucky to Carl Redmond ctredm00@uky.edu

 

By Dan Potter and Carl Redmond, UK Entomology

Posted in Lawn & Turf