Chafer grubs are the larvae of the Chafer Beetle. There are several species found in the UK, the most common being the Cock Chafer Melolontha melolontha, which is sometimes referred to as the May bug. This beetle can often be seen flying around during warm summer evenings as it emits a low droning sound.
Chafer grubs are not as common as leatherjackets in turf, however many of the symptoms of infestation are similar. These soil-dwelling grubs can feed on the roots of the grass and decaying plant material depending on the species. In severe cases the whole root system is destroyed and the turf can be rolled up like a carpet.
Further damage to the lawn is caused by animals and birds plucking and tearing up the turf as they search for the grubs. However it must be said the damage caused by animals and birds is generally more severe with chafer grubs than with leatherjackets.
Life-cycle of chafer grubs
The lifecycle of the chafer grub varies depending on the species of beetle and the climatic conditions. Generally adult beetles emerge from their pupal stage, as they dig their way out of the soil during May and June. They can often be seen in large numbers (where the infestation was severe) during the evenings.
They fly into nearby trees to mate until dawn, before returning back to the soil to lay their eggs. The female beetles will make several mating flights and can lay up to 20 eggs, over a 5 day period.
The eggs are laid between 150mm-200mm deep and the grubs hatch after 2-3 weeks. If the soil moisture levels are adequate, the grubs will move up through the soil to begin feeding on the grass roots.
Feeding continues through the summer, with the grubs gradually increasing in size. When they have reached full size (usually in late October), they burrow deeper into the soil as the temperatures drop, to pass the winter as hibernating larvae. If it remains mild they may actually continue feeding until it turns colder. They pupate in spring, before emerging again in early summer and the life-cycle is repeated.
However some species of chafer grub may continue feeding in the soil for up to 2-3 years before they pupate and change into chafer beetles.
Identification of chafer grubs
Be vigilant and look out for any abnormal yellowing patches on the lawn, the most severe damage is likely to occur in spring and autumn. If any patches appear, investigate further by digging into the turf to see if there are any grubs. You can also test the lawn by tugging at the grass. If the grass comes away easily then there is a good chance there is some kind of grub under the surface of the lawn.
Keep an eye out for any abnormal bird activity on the lawn. Crows, magpies, rooks and starlings all feed on the grubs. If bird activity is noticed, then it may pay to investigate further to see what the birds are after. Using a suitable implement, dig down where the birds are showing an interest to see what is attracting them to the lawn.
The grubs themselves have white bodies and brown heads, with 3 pairs of legs near the head. They are often found curled up in a ‘C’ shape, but when they are straightened they can measure up to 25mm in length.
Prevention and control of chafer grubs
Culturally there isn’t much that can be done to prevent chafer grubs. However since poorly maintained turf is more susceptible, it is important to encourage a healthy lawn with good turf care practices. Regular scarifying, aeration and applying adequate nutrition will help ensure the grass is kept in optimum condition.
Rolling during the spring time may also help, by compressing the turf.
There are products available for the control of chafer grubs, but they will prove to be more effective when they are applied before the problem gets to severe. These products are Provado Lawn Grub Killer and Nemasys Natural Chafer Grub Killer.
Provado Lawn Grub Killer
This products contains Imidacloprid which is a systemic insecticide that affects the nervous system of the grubs. Once it enters the grubs, it works quickly and death usually occurs between 24-48 hours.
For the most effective result the treatment should coincide with period the eggs are laid, which is usually late May or early June. Apply when the soil is moist and water in thoroughly after application, this will move the chemical through the thatch layer and into the root zone. 10-15 liters of water following application should be sufficient.
Nemasys Natural Chafer Grub Killer
It should be noted that this product may not be effective against all species of chafer grubs. This is a biological product containing the nematode Heterohabditis bacteriophora.
This solution is applied to the lawn at the time the eggs are being laid, the soil should be moist with soil temperatures above 12 degrees celsius. Apply during the evening and avoid applying in sunlight, as the ultra violet light from the sun will kill the nematodes (bacteria).
These biological products only work in warm soils, once the temperature drops the bacteria becomes inactive and ineffective. The turf should be thoroughly watered following the treatment, as this will wash the nematodes into the root zone where the grubs are to be found.
Keep the soil moist for the next 2 weeks. The nematodes will then penetrate the grubs and infect them with a bacteria that kills them.
When applying biological products, it is extremely important that the applicator being used (e.g. watering can, or sprayer) has been cleaned out thoroughly, especially if chemicals were used prior to this product. Chemicals such as weed killers and fungicides can be extremely harmful to nematodes and other soil bacteria.