Golfers throughout the upper Midwest have noticed a considerable amount of earthworm activity on fairways and approaches during the past few weeks of rainy weather. Worms are beneficial organisms that feed on various forms of soil organic matter, such as partially decomposed leaf litter. Soil-plus-organic-matter goes into one end of a worm and then soil-minus-some-of-the-organic-matter comes out the other end. They mostly feed at night, and the small dollops of worm waste, called castings, are deposited on the playing surface over the burrow
The dawn patrol of mowers and carts will smush down the soft, wet casting into quarter- to half-dollar size spots of flat, mud-smothered turf. Lately, worms have been so active on fairways that golfers have found themselves playing on surfaces that are more mud than turf. This might be the ultimate tight lie for some players, but there aren’t many golfers who feel comfortable or confident hitting a delicate shot from a slippery tabletop.
Some golfers and superintendents believe that worm populations have increased over the years, but that observation is difficult to validate without a baseline for comparison. A more plausible explanation is the fact that fairway mowing heights are significantly shorter now compared to 20 or even 10 years ago. Higher heights of cut mask earthworm activity, which is why they seem to disappear at the intermediate rough.
Mild, rainy weather keeps worms active and near the surface, while hot, droughty weather drives them deep into the soil, so playing conditions will improve as the weather heats up. However, there is relatively little that can be done to address this issue in the short term. Some superintendents elect to mow fairways during the afternoon when the turf and castings are dry, but fairways can turn into a jungle while waiting for the castings to dry during a stretch of wet weather.
There are no pesticides labeled for earthworm control, but there is a glimmer of hope for earthworm control in the future. Dr. Dan Potter has been studying the effects of tea seed pellets for earthworm control in turf at the University of Kentucky. Tea seed pellets are a byproduct of tea oil processing operations. In a nutshell, this product contains triterpene saponins, which are compounds toxic to earthworms. Water was applied to plots treated with tea seed pellets, and earthworm activity (castings) was suppressed for five weeks. Information about the tea seed pellet research can be found in the following link.
Aggressive fairway topdressing may be an effective, but expensive, long-term answer for earthworms at some golf courses, and a good topic for a future regional update.
Source: Bob Vavrek, firstname.lastname@example.org or 262-797-8743