Earthworms—Friend or Foe?

Compared to the long-term average, September was relatively dry, with only 1.70" of rain.  However, from October 15-23, the golf course received over 2.20" of precipitation.  These soaking rains were welcomed, however along with the saturated soils came the appearance of worm castings on the tees and fairways.

Earthworms act as nature’s aerifiers, providing a service by creating pore space for air, water, and plant roots, as well as increasing the microbial population in the soil they process. How important are earthworms to healthy soil? To quote Charles Darwin: "...it may be doubted if there are any other animals which have played such an important part in the history of the world as these lowly organized creatures."

So why wouldn’t we be happy with the help in creating pore space in the soil?  Well, the work they do below ground is fine, but the downside to having earthworms on a golf course is that when they expel soil on the surface, it leaves little hills, like miniature volcanoes.  At best, these piles can be dragged or broomed off when thoroughly dry.  However, when we have moisture in the air, these piles stay wet.  Dragging them turns them to mud.  Left alone, the piles get squished by carts and mowers leaving mud spots about the size of a quarter.

Earthworm castings on #16 tee.

At some golf courses, especially in the UK, this is an ongoing problem.  Numerous strategies have been employed where worms have created such a problem. As there are no products labeled for the control of earthworms, some people have tried spraying mild soap solutions in hopes of irritating the worms and discouraging their surface activities.  Others have used an aggressive topdressing program of straight sand to create a surface that, like the greens, is abrasive and uncomfortable for the worms. Fortunately for us, it is only during unusually wet periods that we have to deal with the mud piles.  

There is some debate over why the worms come to the surface when conditions are wet.  One theory is that there is a lack of oxygen in the soil, and the worms need to come up for air.  A second possibility is that the worms can obviously move from one location to another more easily above ground than underneath, and that when conditions are wet, they can retain their moisture and safely move across the surface.

 

A final thought about the earthworm population to contemplate: Some scientists calculate that in the soil of a dairy farm, per acre, the total weight of all of the earthworms that live underground exceeds the weight of the cattle grazing above ground—it’s a wonder we don’t feel the earth moving beneath our feet.