Earthworms make those little mounds

It seems fall has finally arrived. The cooler temperatures have been nice. They have also have helped retain some of the moisture from the rain we received.

//

This moisture is a big help to plants that have struggled all summer. However, with the softer soil I have received numerous calls and questions about moles and about little mounds of soil on the top of the grass. Many times, moles and the little mounds are in the same area.

There is a reason for this. These mounds are made by earthworms. Earthworms are one of the favorite foods of moles. So when high numbers of earthworms are present, moles will be close by.

The little mounds are actually earthworm castings, which are most frequently found during cool, moist weather, when earthworm activity is at its highest.

At a glance, many people believe these small mounds indicate insect damage. Mole crickets, which are a major pest of turfgrass, can make mounds that look like those created by earthworms. A solution of one to two tablespoons of dishwashing liquid mixed in 3 to 5 gallons of water can be poured over the mounds and will bring the creatures to the surface.

The good news is that earthworms are primarily beneficial organisms that do not harm or feed on the turf. Instead, they burrow through the soil, feeding on microorganisms and partially decomposed organic matter. This activity helps improve aeration and the movement of water and fertilizer through the soil.

After earthworms feed, they move to the soil surface to deposit the castings. The castings are beneficial for the turf because they add organic matter and nutrients to the soil and improve soil structure.

However, when earthworm populations explode, they are capable of producing an overwhelming number of castings in the lawn. These castings can be unsightly and over time can create a lumpy surface.

A number of steps can be used to reduce the number of mounds. First, smooth the soil surface by raking the castings. Next, irrigate lawns with an inch of water once a week to encourage deep root development. Deeper roots allow turf to go longer between watering, which permits the soil surface to dry before the next watering. Earthworms are less likely to come to the surface when it is dry.

Third, mow the grass at the highest recommended height to help hide castings. For Bermuda, zoysia and centipede, the recommended mowing height is 11/2 inches. St. Augustine's mowing height is 21/2 inches in full sun to 4 inches in shade.

Besides moles, there are other natural enemies of earthworms that can aid in the control of earthworm populations. These include ants, centipedes, birds, snakes, toads, carabid beetles and nematodes. These predators don't cause problems in the lawn as moles do.

Some people would like to control earthworms with pesticides; however, there are no registered pesticides for earthworm control. Remember that the castings will go away and that earthworms are beneficial organisms.

If the results of the soil drench are mole crickets, then these insects need to be controlled before they damage the turf. Mole crickets were introduced into this country from South America about 1918. Two main species affect turfgrass -- the Southern mole cricket and the tawny mole cricket.

Mole crickets damage turf by tunneling through the sod, and the Southern mole cricket eats the roots. The tawny mole cricket is a predator and eats other insects, but does a great deal of damage by tunneling.

There are two options for control. First, treat with a fast-acting product. These products need to be applied as late in day as possible.

Mole crickets move around on top of the grass at night. If applied as close to dark as possible, the insecticide will be at full strength.

The product that can be used for this is bifenthrin (Ortho Max Bug-B-Gon).

The other option is to treat with a longer-lasting insecticide such as imidacloprid or fipronil. The imidacloprid (Bayer Advance Lawn Product) will give control for up to three months. Fipronil (Chipco Choice or Top Choice) will give season-long control. Fipronil can be found where commercial lawn care professionals purchase pesticides.

Any pesticides used on mole crickets will give better results when they are applied to young insects. When they reach the adult stage, they are harder to control.

Charles Phillips is a retired Columbia County Extension Service agent and operates Hort Consulting. He can be reached at cphillipshort@comcast.net.