Earthworms are found in just about every soil environment, including on golf courses. Their presence usually goes undetected by golfers, but occasionally they will cause annoying disruptions to the playing surface. Earthworms produce small soil mounds, called casts or castings, that can impede ball roll and present a tricky lie for anyone unlucky enough to have their golf ball come to rest next to them or on top of one that has been flattened by mowing.

The casts are basically finely processed soil that has passed through a worm’s stomach. Earthworms feed on soil – specifically decaying animal and plant matter – and they play an important role within the soil community. However, those worms that spend their lives at or near the soil surface can make quite a mess on a golf course.

Worm cast issues occur at different points throughout the year but they are usually most problematic during the spring and fall. Earthworms prefer moderate soil temperatures, so they are more active near the surface during mild weather. When things are too hot or too cold, they will move deeper into the soil. Once conditions change, they will rise again and feast on the organic matter close to the surface, leaving casts behind.

The amount of moisture present at the surface contributes to how big a mess earthworm casts can make. Periods of wet weather will cause casts to stick to golf cart tires, mowing equipment, golf clubs and the bottom of your shoes. High populations of worms can literally move tons of soil, making a fairway look like it was just core aerated. Things can get even messier if the maintenance team needs to mow areas that are covered with moist casts. The casts squish down like little pancakes and it can look like there are thousands of bare spots in a fairway.

Unfortunately, there is little that can be done to eliminate worm casts. There are no pesticides that are explicitly labeled for combating earthworms on golf courses in the United States. Products used to control other pests that also happen to reduce earthworm activity near the turf surface are becoming increasingly rare. It’s also important to remember that apart from the casts, earthworms are a desirable part of the soil environment and they help to create better growing conditions for the grass on a golf course.

Many golf course superintendents simply try to wait until the casts have dried, and then drag them back into the turf canopy where the soil quickly disappears. Sandy soils, which tend to dry faster, are usually easier to disperse. Unfortunately, maintenance teams don’t always have the luxury of waiting to mow certain areas until worm casts have dried and can be broken up, especially in shady, moist environments where the casts take a long time to dry. Play will also start early in the morning regardless and golf carts can make a mess of the casts before they are dry enough to disperse.

Worm casts can be an annoying and unsightly disruption to course conditions, but the unfortunate reality is that there isn’t much superintendents can do about them in many situations. If you notice worm casts at certain times of the year where you play golf, please try to be patient and know that the maintenance team isn’t happy about them either.