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Watering the Garden to prevent chafer grub damage

The Garden’s horticultural team are today taking the exceptional step of having sprinkler irrigation on during the day around the Systematic Beds.

As part of the Garden’s commitment to sustainability, staff usually carry out as little irrigation as possible. However, today’s watering is not due to the current soaring temperatures but for the application of a biological control of nematodes to control a recent outbreak of the chafer grub, which has destroyed large parts of the Garden.

Head of Horticulture Sally Petitt explains: “The Garden has suffered widespread lawn damage on the Main Lawn and around the Systematic Beds. This has been caused by badgers who have been eating an outbreak of chafer grubs which live below the turf. We’ve tried a number of different methods to try and control their spread - from spraying citronella spray around the perimeter of the Garden to deter the badgers as they don’t like the smell, to regular mowing to eradicate the eggs. However, so far nothing has worked. We’re now going to attempt to control the chafer grub outbreak by using Terranem nematodes (Heterorhabditis bacteriophora). This is a form of biological control which is harmless to humans, but which feed on the contents of the grubs. In doing so they excrete a bacteria, and convert host tissue into products easily digestable by the nematodes, thus eradicating the grubs. We anticipate this will minimise turf damage by badgers, which travel anything up to 20 miles to feed, and we particularly want to minimise damage to the new turf we intend to lay on the Systematic Beds as part of the Monument Trust project.“

Chafer grubs, (Phyllopertha horticola and Hoplia philanthus), are soil-dwelling larvae of chafer beetles. Depending on the species of chafer, they either feed on decaying plant material or plant roots. However, several species that feed on the roots of grasses can cause problems in lawns and are very much the delicacy of the badger which has caused extensive damage to lawns as a result of feasting on the grubs. The grubs are most active from September-April and the adult beetles from May-June.

Nematodes are microscopic animals which are watered into the lawn when the ground is moist and soil temperature range is at 14 ºC. For the treatment to be effective, the soil first needs to be treated which involves three stages:

1. the application of a wetting agent/water to ensure residual moisture so that the nematodes remain active upon entering the soil
2. the application of the Terranem nematode with water
3. the thorough drenching of the site with a minimum of 5mm of water to ensure that the nematodes penetrate through to the chafer grub

Sally continues: “We’d like our visitors to be aware that this process doesn’t comply with our standard best practice irrigation policy of watering at night to maximum effect, but we are constrained by timescales and weather conditions. The areas being treated will be roped off during this process and normal service will be resumed as soon as possible.”

For more information about the Garden’s approach to practising sustainable horticulture click on the link to the left.
Publication Date
23/08/2016