Golf Greens Pests

Earthworm casts, when present in relatively large number, can be a major maintenance and cosmetic problem. Damp casts will stick to the front and rear rollers of cylinder mowers, potentially increasing the cut height slightly if not regularly cleaned off. Casts will smear when brushed whilst moist causing potential problems of smothering the grass especially if they are not brushed again or switched once the sward and casts have dried in the day. In addition, the negative impact casts can have on ball roll and direction of putt can be considerable.

For much of the year, when the weather is (usually) relatively dry, earthworm activity is primarily within the rootzone region below the surface of the green. Damp, cool weather will bring certain earthworm species to the surface.

The use of pesticides to kill earthworms in the past has contributed to the build-up of thatch on many greens. Currently (2023) there are no synthetic pesticides available to kill earthworms, unlike in the past, yet the drive to control them continues unabated. Some products, which are sold as ‘soil conditioners’, have a side effect of killing and especially inhibiting earthworms and arguably this is the main purpose for using these particular products as their credentials for being a genuine soil conditioner are spurious at best. High densities of earthworms are a problem at certain times of the year when surface casting occurs, and these do reduce the quality of a playing surface.
The application of earthworm suppressants, often with sulphur constituents (for example Clear Cast Green), might also be considered to try and reduce surface casting activities. Regular, but controlled and not excessive, applications of sulphate of ammonium and sulphate of iron can help to maintain an acidic surface which is relatively earthworm free.

Earthworm activity can be significantly reduced in acidic soils, especially at or below pH 5.5. Aiming to acidify a surface layer can be considered appropriate to help reduce earthworm surface activity, although care will be needed not to over acidify which would lead to a thinning of the sward. A soil pH of 5.0-5.5 can usually be considered quite suitable for a healthy fine fescue and browntop bentgrass sward and this would often be an ideal pH at which to maintain such a surface. If dwarf perennial ryegrass had been over sown onto a green, then the ability to create a suitably acidic surface will be significantly reduced because perennial ryegrass will not produce a viable surface at this low pH.

The need to control earthworms at low densities is questionable and probably unnecessary. The beneficial effects outweigh any negative impact at such levels. Their contribution to a healthier and more diverse soil biology, with an increase in beneficial micro-organisms which are antagonistic to undesirable turfgrass diseases, can be considerable. This can also reduce the impact and extent of disease attack and build-up greater resilience in the turf.

Grubs (chafers and leatherjackets) can be a problem, ranging from being a mild nuisance, especially from bird pecking activity to causing serious issues of sward defoliation where very high concentrations of grubs are present. Small quantities of grubs should not be a cause for concern for most clubs, especially if a well-established and well-rooted sward has been produced.

Where effective chemical pesticides are not available there will be a greater reliance on good cultural and physical practices, as well as selective biological control for insect grubs.

Leatherjacket and Chafer grubs might be able to be reduced through the use of applied nematodes as a form of biological control. There are limitations to this practice as the life cycle of the nematode is restricted to when it can be applied. In addition, environmental conditions also impact on the effectiveness of this form of biological control of grubs.

Other pests which can cause localised damage include rabbits, which can be a problem on some courses, especially those on sandy soils or where courses are located next to agricultural crops. The majority of rabbit scrapes will typically be adjacent to bunkers, on fairways or rough areas, much less so on golf greens or tees.

Badgers can in some cases cause severe tearing up turf and excavation of ground, especially where there is a significant presence of earthworms, leatherjackets or chafer grubs. However, in practice it is a rarity for this to occur on a golf green.

Fox damage can result in holes which they dig for food sources within the soil and these need to be constantly filled in. The fox will naturally move on, possibly moving to find another food source, although this might take several weeks.

Mole activity is quite visible due to the often-large mounds of soil which are excavated, however, the mole activity would typically be focused on fairways, surrounds and occasionally encroaching onto tees.

Nematodes can be a particular problem on high sand-based greens which are intensively maintained. This puts the grass plant under considerable stress and whilst nematodes are present in soils and sands, the intensity of maintenance practices help contribute to creating a situation whereby the effects of the undesirable nematodes become noticeable and negatively impact on the quality of the sward. The encouragement of an increased soil micro-biology can help to control and counter the effects nematode activity.