Identification
Large, fleshy larvae of cockchafers (common and forest cockchafer), growing to 4-6 cm, cream-white and C-shaped, with a brown head, three pairs of legs and a darker, translucent tip to the abdomen. They develop in the soil for 3-4 years. Symptoms: gnawed roots, tubers and bulbs, wilting and yellowing plants that lift easily from the soil (roots chewed off), and patchy dieback of lawns and seedlings. The full cycle lasts 3-4 years: the beetles emerge during the May-June flight, the females lay their eggs in the soil, readily beneath dense turf and along field margins, and the hatched larvae pass through three developmental stages. The youngest grubs feed on fine rootlets and cause little damage, whereas larvae in their second and third year, when they are largest, gnaw thick roots, tubers and underground plant parts, causing the characteristic patchy loss of lawn and seedlings; the damaged sward can then be rolled up like a carpet because it has been stripped of roots. White grubs gather in nests, so damage appears in focal patches rather than evenly across the whole area. Cockchafer larvae are sometimes confused with the grubs of the rose chafer (Cetonia aurata) - these, however, are beneficial, breaking down dead organic matter in compost and humus, have a distinctly smaller head and fine legs and, when placed on a flat surface, move on their backs; they should not be destroyed.
Treatment
Mechanically collecting the grubs when digging over the soil and when planting, insect-pathogenic nematodes (Heterorhabditis bacteriophora) and insect-pathogenic fungi (Metarhizium) in warm, moist soil. It helps to reduce dense turf that favours egg-laying, to keep a healthy, watered sward, and to encourage natural enemies such as birds and hedgehogs. Insect-pathogenic nematodes work best in moist, warm soil (temperature above about 12 °C), in late summer and early autumn, when the larvae are young and stay close to the surface; the soil should be watered thoroughly before and after application, and the product should not be exposed to sunlight. Entomopathogenic fungi (Metarhizium) colonise the soil more durably but act more slowly and also require moisture. Cultivation practices help: careful digging and working the soil exposes the grubs, leaving them to be eaten by birds and to dry out, and new beds and lawns are best preceded by cultivation - establishing them straight onto freshly laid turf makes it easier for the flight to lay eggs. It is also worth favouring natural enemies: birds, hedgehogs, shrews and moles, which pick the larvae out of the soil. Chemical control is limited and of little effect - the larvae are protected deep in the soil, and soil insecticides against white grubs are in practice unavailable in amateur gardening (effective dressings and granules remain mainly in professional lawn care). Feeding and watering weakened plants helps them rebuild roots and survive the feeding period.
How to tell it apart from look-alikes
| Feature | White grubs (cockchafer larvae) | Wireworms (click-beetle larvae) |
|---|---|---|
| Larva appearance | Thick, soft, fleshy, cream-white, curved into a C shape | Thin, hard, cylindrical, yellow-brown - a chitinous 'little wire' hard to crush |
| Damage to roots and tubers | Large, irregular cavities gnawed in thick roots, tubers and bulbs | Narrow, round tunnels bored deep into tubers, seeds and roots |
| Life cycle and adult insect | Development 3-4 years; the adult is a cockchafer - a large beetle flying during the May flight | Development 3-5 years; the adult is a click beetle (Elateridae), springing away with a click when laid on its back |
| Behaviour after removal from the soil | Curls into a C shape, is clumsy and limp | Stays straight, stiff and springy |
Control — organic and chemical methods
Organic and biological methods
| Method | How it works | When to use |
|---|---|---|
| Mechanical collection of larvae | When digging over, cultivating the soil and planting, the grubs are picked out by hand; genuinely effective in small gardens and on newly established beds. | Spring and autumn during soil cultivation |
| Insect-pathogenic nematodes (Heterorhabditis bacteriophora) | The nematodes penetrate the larva and infect it with symbiotic bacteria; they work in moist soil at a temperature above about 12 °C, most effectively on young grubs close to the surface. | Late summer and early autumn |
| Entomopathogenic fungi (Metarhizium) | The spores germinate on the larva's body and grow through it with mycelium; they act more slowly than nematodes but colonise the soil more durably. They require moisture - this is a population-reducing method, not an immediate one. | Warm, moist soil |
| Cultivation practices and supporting natural enemies | Digging exposes the larvae to birds and to drying out; birds, hedgehogs, shrews and moles reduce the population. Reducing dense turf and cultivating the soil before establishing a lawn make it harder for the flight to lay eggs. | Whole season; especially before the flight |
Chemical methods
| Method | How it works | When to use |
|---|---|---|
| Soil insecticide acting mainly through ingestion (ryanoid) | Soil products (including anthranilic diamides such as chlorantraniliprole) act mainly through ingestion after being eaten and kill the larvae above all in professional lawn care; in amateur gardening, registered products against white grubs are in practice unavailable, and effectiveness is limited by the larvae being hidden deep in the soil. | Limited, mainly professional lawns |
We give active-ingredient groups and modes of action, not brand names — specific products and their approval vary by country and are sometimes withdrawn. Always check and follow the current label.
Sources
- Atlas of plant pests
- Institute of Plant Protection – NRI (Poland)
