Chafer grubs are the larvae of the Chafer Beetle. There are six species in the UK: the Welsh Chafer, Summer Chafer, Brown Chafer, Cock Chafer, Garden Chafer and Rose Chafer. The most familiar being the Cock Chafer or "May bug" a large beetle that can be heard as a low droning noise on pleasant spring evenings. Though commonly the main problems on lawns are caused by just two species: the Garden Chafer and the Welsh Chafer. The grubs feed on the roots of grasses and other plants, their presence can be detected by the yellowing patches that it creates in turf. Chafer grubs can be found in the soil under the loose turf. They live within the soil for up to 3-4 years going through various "instars" as they develop. Significant damage to turf can be done by predators such as starlings, rooks, crows, jackdaws, magpies, foxes and badgers that make the most of an abundant high protein feed lying just beneath the surface.
They have stout white bodies curved in a C shape, light brown heads, with three pairs of legs and darker patches at the base of the abdomen. They are bigger than the adult beetles although their size varies according to species, 8-35mm; typically the Garden Chafer and Welsh Chafer are between 10mm and 15mm long. The head and thorax are metallic blue-green on the Garden Chafer and black on the Welsh Chafer. The grubs eat the roots and damage and eventually kill the plant. The first symptoms are yellowing patches that eventually turn brown, particularly in dry weather. These areas are then pecked at or dug up by predators. In severe infestations the turf can be pulled back to reveal as many as 100 grubs per square metre.
Methods Of Control
As with most problems the symptoms can be relieved more effectively when symptoms are first noticed. Scarify and aerate turf in the autumn. Where there is a history of infestation compress the turf by rolling it in the spring.
The nematode Heterorhabditis megidis is commonly used as a biological control within Nemasys. The nematode penetrates the grub and infects them with a bacterium which is fatal to the grub. The nematodes need to be applied to moist areas during August to early October when the soil temperatures are in excess of 12°C (54°F) and the grubs are active. The grubs are within the soil profile therefore sufficient water needs to be applied after the nematodes have been applied to bring them into contact with the grubs.
Imidacloprid is the active ingredient in Merit Turf, a systemic insecticide which acts on the central nervous system of insects with much lower toxicity to mammals. Imidacloprid works differently to other insecticides presently being marketed (i.e. carbamates, organophosphates and pyrethroids). The mode of action is based on interference of the transmission of impulses in the nerve system of insects. It has both contact and ingestion activity. The target pest"s feeding activity ceases within minutes to hours, and death occurs usually within 24 - 48 hours but can take up to 7 days depending on the mode of application. As to its performance: good reliable control, high selectivity, quick knock-down/protection and long residual activity are key features.
Domestic Insect Killer
Imidacloprid is the active ingredient in Provado Lawn Grub Killer. For optimum control it needs to be applied in May or June as this links with the egg laying period of the pests. As soon as you start seeing adult Chafer beetles, this is the best time to apply.
Apply in the early evening, and then water the product in. Mix 1 sachet (3g) with 9 litres of water in a watering can fitted with a coarse rose or a sprinkle bar and stir well. Use immediately. Apply evenly to the lawn over an area of 10 m2. Ensure the lawn is well watered to move the active ingredient through the thatch. 5 to 15 mm of rainfall is sufficient or 5 to 15 litres of water per square metre. Avoid over watering. Maximum concentration must not exceed 3g of product per 9 litres of water. Maximum use rate: 3g of product over 10 m2. Only to be used once per year.
Alternatively the professional biological control is publicly available: the nematode Heterorhabditis megidis is commonly used as a biological control within Nemasys. The nematode penetrates the grub and infects them with a bacterium which is fatal to the grub. The nematodes need to be applied to moist areas during August to early October when the soil temperatures are in excess of 12°C (54°F) and the grubs are active. The grubs are within the soil profile therefore sufficient water needs to be applied after the nematodes have been applied to bring them into contact with the grubs.