ONE of the more frequently asked questions at Harlow Carr relating to lawns and turf is that of damage caused by chafer grubs and how they can be controlled and what can be done to improve the lawn after it's had an outbreak.

The chafer grub is the larva of the chafer beetle, which feeds on the roots of grass plants. The grubs, which are about 15mm in length, creamy coloured with a light brown head and curved in a C-shape, lie dormant two to three inches deep in the soil through the winter months.

They rise closer to the surface in March/April where they feed on grass roots before pupating around May and emerging from the soil as a beetle in June. The adult beetle then lays its eggs just below the surface of the grass in July, these eggs hatching a month later into the grubs, which feed on the grass roots throughout August to November (or until soil temperatures get too low and they burrow deeper to overwinter).

From the life cycle above it can be seen that most damage to lawns occurs from egg hatch, late July/early August through to mid to late October when the young grub is feeding rapidly to increase its size before winter. Symptoms may appear on your lawn such as straw-coloured weak areas of grass where the roots have been damaged; in severe cases the lawn can be rolled up like a carpet. Sometimes more damage can be done by birds and animals digging up the lawn to feed on them than by the grubs themselves.

Proprietary insecticides have long been withdrawn as a result of the health implications from using organophosphates so nematodes are the only biological control available. The nematodes (Heterorhabditis sp) are host specific and they seek out the chafer grubs and attack the pest by entering through natural body openings. Once inside they release bacteria, preventing the chafer grub from feeding, killing the pest within a couple of weeks. The nematodes continue to feed off the dead grub and in turn reproduce, increasing their numbers, building up large populations in the soil.

Nematodes are widely available, but the guidelines for using them must be followed closely to give them the best chance of working. They should be applied between August and early October to moist soil. This is when the young chafer grubs are most active and the soil temperature is above 12 degrees Celsius. Immediately after application, water the grass well to ensure the nematodes are washed into the soil to reach the roots where the grubs will be. Keep the soil moist for at least two weeks, not allowing it to dry out. Soil moisture and temperature are key to the nematodes' survival and regeneration. Application of the treatment while the grubs are small gives you a better chance of control than once they have grown bigger, but a follow up four to six weeks later may be necessary if the infestation is severe.

Other than nematodes as a form of control, it may be worth trying some, if not all, the following suggestions:

* Pick off grubs or adult beetles by hand if you see them on the surface of the lawn or feeding on shrubs in your garden. It has been suggested that once the eggs have hatched into grubs that watering in the evening before covering with a tarpaulin will bring the grubs to the surface where they can be picked off by hand or by the ever-hungry blackbirds (July to September).

* Roll or fork over the lawn in an attempt to damage the grubs or pupae.

* Chafer pheromone traps are available which trap adult male chafer beetles. These again are widely available and are a way of giving you an early indication of how serious an attack by grubs you may get in the autumn.

With all problems faced by the desire to have the perfect lawn, be it moss, pests or diseases, the best method of control for all of these is by keeping a healthy lawn, so regular aeration, feeding (but don’t overfeed) and overseeding. Keeping a healthy, dense sward will remove those bare patches, which become havens for pests, diseases, weeds and moss ingress.


• Mow your lawn once or twice a week

• Control lawn weeds with a selective herbicide

• Fertilise your lawn

• Repair damage caused by wear and tear

• Keep weeding

• Lift and divide clumps of snowdrops and bluebells

• Keep an eye out for aphids

• Turn your compost


June/July/August: RHS Members’ Gardening Advice

RHS Members can get face-to-face gardening advice from a friendly RHS advisor every Monday and Friday from 1pm – 3pm, except Bank Holidays. Come to the advice desk in the entrance conservatory.*

8-9 June: Meet the Bonsai Experts

Immerse yourself in the fascinating Japanese art form of bonsai. With beautiful displays, the Bonsai Group will offer first-hand advice, expertise and demonstrations on these special miniature trees from 10am – 4pm. Bring your own tree along for specialist advice.*

21-23 June: RHS Garden Harlow Carr Flower Show

Celebrating seventy years of development as a garden this popular event – now in its fourth year - is a chance to browse, buy, and pick up advice from more than 50 specialist nurseries and garden trade stands. Enjoy a programme of talks and demonstrations then escape the crowds with a relaxing stroll in the stunning surroundings of the 58-acre garden. Normal garden entry and the show is open from 10am – 5pm each day. Check the website for parking restrictions at the garden and free park & ride details.

RHS Garden Harlow Carr, Crag Lane, Beckwithshaw, Harrogate HG3 1QB (use Sat Nav postcode HG3 1UE). Gardens: 01423 565418. Shop and Plant Centre: 01423 724666. Bettys Café Tea Rooms 01423 505604.