Friday, December 11, 2015

Earthworms gone wild

Nearly everyone loves earthworms. I don't remember my first childhood encounter with earthworms, but I imagine it had something to do with wet sidewalks after a rain, and rescuing "wormies" from the hot sun. As I grew older I learned to respect earthworms less for their delightful slimy "squirmy-ness" and more for their practical roles in helping gardeners and farmers, and providing food for wildlife... and other good things like fishing.

No one denies that earthworms provide hefty environmental services in the form of improved soil aeration and water penetration, and composting.  But it turns out that there are some bad guys in the earthworm community. And sometimes earthworms just show up in the wrong places at the wrong time.

Dense piles of earthworm castings, shown here, can cause
thinning of turf and excessive sponginess.  Photo by Steve
Bambara, North Carolina State University.  
Let me explain. Some types of earthworms are notorious for leaving excessive amounts of castings on the soil surface. The spongy soil and excess castings produced by these worms can make it difficult to mow, or even walk across an infested lawn. Earthworm tunneling can also disrupt grass roots and reduce turf quality. And don't talk to golf course superintendents about earthworm castings on putting greens. Besides disrupting play, earthworm activity dulls mower blades used to keep greens short and fast.

Also, it turns out that earthworms are not very welcome at airports. With the number of reported bird strikes increasing over six-fold between 1990 and 2013, airport managers are eager to look for ways to reduce bird activity around airport runways. Therefore, high earthworm populations, which attract birds, are not desirable close to airplane landing and takeoff sites.

Of course the overall benefits from earthworms on turf is great, but there are places and times where earthworms are pests.  Until now, there has been little to be done about earthworms.  A few insecticides and fungicides are known to be highly toxic to earthworms; but there are currently no pesticides (vermicides) registered for earthworm control in the U.S. And by all accounts the U.S. EPA, which regulates such things, does not appear eager to register worm-killing pesticides.

Research reported in 2010 from the University of Kentucky documented that an organic, plant-produced mixture of natural soaps called saponins could effectively be used to control earthworms for at least five weeks. The best commercial source of saponins turns out to be a byproduct of tea manufacturing called tea meal.  While the research has not resulted in anyone registering tea meal as an insecticide, a company called Ocean Organics has started importing tea meal from China and using it as a base for a new organic fertilizer.

Early-bird 3-0-1 organic fertilizer, described by some as "a fertilizer with benefits", uses a tea seed base.  Though not sold as a pesticide, it happens to be toxic to some earthworms. It is labeled for application at 6 lbs/1000 ft sq or 5 bags per acre. A 50 lb bag retails for around $55, and cost of application is around $275/Acre (it can be found at Winfield Solutions--Land O Lakes in Texas, and possibly other suppliers).

I know that any suggestions on ways to kill earthworms will be viewed with alarm by many, but there will be situations when at least short term control is desirable. On the other hand, as one researcher thoughtfully concluded, earthworms are highly adaptable creatures that are difficult to manage, and to some extent we will have to learn to take their bad along with the good.  Think about that the next time you go fishing.

1 comment:

Mike Merchant, PhD said...

Thanks to Susan Knight of Insect Interceptor, Inc. for the following link about the harmful effects of introduced earthworms in the northern US forests.

A reminder that even "good" organisms may not be good in the wrong place--and don't return your worms to the forest when you're done fishin.