How to identify and deal with White grubs

White grubs

Scarabaeidae larvae — Popillia, Cyclocephala, Phyllophaga

also called Chafer grubs, Lawn grubs

Fat C-shaped larvae of Japanese beetle, June beetle and chafers that eat grass roots until the turf lifts like a carpet. Nematodes in late summer, while the grubs are small.

Insect Root feeder Serious SpringAutumn

How to know it

A soft white grub 15–40 mm long, lying in a C with a tan head and three pairs of true legs at the front, found in the top 5 cm of soil under damaged turf. Which beetle it will become is read from the pattern of tiny hairs on the underside of the last segment, but for garden purposes the treatment is the same.

What you'll see

Irregular brown patches in the lawn from late summer that stay brown however much you water them.
Turf that peels back like a carpet because there are no roots holding it — the diagnostic test.
Skunks, raccoons, crows and moles tearing the lawn up at night to get at them.
Wilting in a hot spell on turf that should not be short of water.
Grubs turned up whenever you dig a hole in the lawn edge or lift a border plant.

Where it comes from

One beetle, two problems: the adults feed on leaves and flowers above ground in midsummer and lay in moist, short turf, and it is their larvae that ruin the lawn. Grubs hatch in late summer and feed near the surface through autumn, move deep to overwinter, come back up to finish in spring and pupate. June beetles take two or three years to complete the cycle.

Irrigated, closely mown lawns in full sun are the preferred nursery, because that is where the beetles choose to lay. Dry midsummer turf is largely passed over. Damage shows in September and again the following April.

Dealing with it

Water in parasitic nematodes (Heterorhabditis bacteriophora) in late summer while grubs are small and near the surface, onto damp ground in the evening.
Peel back the turf and pick the grubs out by hand where the patch is small.
Water and feed the damaged lawn to push regrowth once the grubs have gone; grass recovers well if the crowns survive.
Reseed bare patches in early autumn rather than waiting for them to fill in.
Take the animals digging your lawn as the symptom, not the cause — fencing them out just moves the damage.

Keeping it out

Let the lawn go dry and dormant through the beetle flight in midsummer; they will lay somewhere greener.
Mow higher and encourage deep rooting so the turf can carry a few grubs without showing it.
Overseed with tall fescue or a ryegrass carrying endophytes, which grubs and their beetles find much less inviting.
Deal with the adult Japanese beetles on the roses, and do not hang a pheromone trap that invites more in to lay.
Check the count before treating — up to five grubs per square foot in a healthy lawn is not worth acting on.

What it goes for

Roots & tubersSeedlings

Lawns above all, then strawberries, potatoes, sweetcorn, roses and the roots of newly planted stock.

Who hunts it for you

Beneficial nematodesSteinernema & Heterorhabditis spp. Microscopic worms watered onto damp soil that hunt down soil-dwelling grubs and release a bacterium that kills them within days. Timing is the whole thing: warm, damp soil and a small target grub, which means late summer for most of what they are used against.
Garden birdsPasseriformes Both things are true: birds strip your currants and a brood of blue tits takes several thousand caterpillars out of one fruit tree in a fortnight. Net what you must and welcome them everywhere else — a nest box near the apples is worth more than a spray. Grow to recruit it: Echinacea,Elderberry,English holly,Goldenrod,Rudbeckia,Sunflower