How to tackle Earthworm Casting


Ed Pettit is Managing Director of the Maintenance Division at Carr Golf, providers of agronomy and course maintenance solutions to 17 golf courses throughout Ireland. Here he discusses a common problem for golf clubs across Ireland – earthworm casting – and how we can best tackle the issue.

Living with the enemy

Earthworm casting is fast becoming one of the most challenging aspects of golf course maintenance, with the sports turf research institute recently rating earthworm casting as the main problem about which they receive queries. Greenkeepers throughout the world are trying find a solution amid growing pressure from club golfers and committees.

Firstly, what is Earthworm Casting?

Earthworms ingest soil and organic matter for nutrients, and they then deposit the resulting faecal matter as mounds on the soil surface. These mounds or “casts” adversely affect playability and surface firmness. When maintenance equipment rolls over the casts during mowing, the smearing of soil causes a loss of density and thinning of turf in heavily affected areas.

Why has this problem become more widespread in recent years?

Historically the pesticides used to kill earthworms would reduce the population to such an insignificant level, that it would take several years before the problem would reoccur. The residues of these strong chemicals are finally dissipating from soils and the result is a dramatic increase in population. In more recent years the use of the fungicide Carbendazim provided some relief as an unintended side effect was to deter casting earthworms from surface activity. Carbendazim was deregistered in the Republic of Ireland a number of years ago and the UK has followed suit recently.


Carr Golf’s Top Tips to Manage Earthworm Castings

  1. Collect your grass clippings

Reducing the availability of food influences the population of earthworms. Returning grass clippings during mowing creates a limitless supply of organic matter for earthworms to feed on. Collecting or boxing off clippings on fine surfaces may be one strategy to reduce the problem of casting. This tactic has worked very well for us in clubs such as Royal Curragh, Foxrock and Charlesland – it’s simple, but effective.

  1. Undertake a fairway topdressing program

Earthworm populations are highest in light and medium textured loam soils, common place throughout Ireland. Smaller populations exist in coarse, abrasive, sandy soils, such as those found on golf course greens. The abrasiveness of sand particles and the susceptibility of such soils to drought can influence the species composition and population. Our fairway topdressing program at Castleknock Golf Club over the last number of years has all but eliminated the problem.

  1. Trialling tea seed oil

In recent years, we have trialed tea seed oil with some positive results. This can be an effective approach to managing the casting problem though the efficacy is dependent on the organic matter content of the soil and environmental factors during the time of application. The resulting accumulation of dead earthworms on the surface should be removed promptly for the benefit of golfers!

  1. Use ammonium sulphate fertilisers

Research in the US has reported declines in the earthworm populations directly related to declining soil pH or increasing acidity. From our experience, this is evident in Ireland where earthworm populations on the acidic, peaty soils found in bogs is typically low. Therefore, using sulphate based fertilisers is beneficial by increasing acidity at the soil surface. We are trialling a sulphur based product at the moment with a similar intention at a number of our golf courses.

It’s not all bad news though……

There are over 200 species of earthworms in the soil and the vast majority of these do not create casts. In fact, the benefits of a healthy earthworm population on your golf course are several. Earthworm’s tunnels relieve soil compaction and create passageways through which air and water can percolate. They help to breakdown the thatch and accelerate nutrient recycling, all of which improves the functional and visual quality of surfaces.

The fact is that Earthworms provide more benefits than harm to our golf courses so we need to learn to live with our little friends. The more we understand this issue the better we can manage it. The best solution is likely to involve a combination of the aforementioned approaches, depending on the financial means of a golf club.