Identifying and dealing with Chafer Grubs
Identification, types and life cycles
Chafer Grubs are the larvae of the Chafer Beetle of which there are 6 species in the U.K. Chafer Grubs feed on the roots of turf grasses in the top 50-150mm of the soil.
Adult Beetles will emerge and mate in May and lay eggs in June. The larvae usually hatch in late June when the grubs will begin to grow in the rootzone feeding on roots and move deeper into the soil profile over the winter months raising through the profile in the spring and the life cycle begins again.
When are they a problem?
Damage to turf becomes most apparent when they feed on the roots during the Autumn and Winter indicated by a yellowing of the turf due to the damaged root structure.
The problem is often particularly evident when wildlife damage causes tearing or lifting of the turf in search for the grubs. This can be from birds, badgers and foxes. Unfortunately, they are particularly prevalent in sandy loam soils and tree or shrub lined fields form a perfect habitat for Chafer Beetles prior to laying their eggs.
What can we do to prevent/reduce their impact?
For operations to be most effective, they must be done based on the life cycle of the pest.
When you are certain that you have a Chafer Grub infestation after digging trial holes and identifying the pest or seeing the damage caused by feeding wildlife you can;
Do scarification operations and regular rotary mowing (with collection) on the affected areas in late May and June to disrupt the adult mating and egg laying process and help control the adult population. Chafer beetles/grubs will tend to attack the same areas year on year especially favouring turf near wooded areas and shrub beds.
Low thatch levels are associated with lower impact infestations of chafer grubs so keeping thatch to a minimum in general will help in keeping control of populations.
Chafer Beetle pheromone traps offer some protection, supplied with a pheromone lure they attract the beetles and trap them inside, so they are unable to escape preventing them from laying their eggs in the turf. One trap will typically cover 2000m2 and used between May and June may offer some benefit. Please follow trap specific instructions as to where to locate the trap.
How can we deal with Chafer Larvae?
Chemical pesticide options for Chafer Larvae control are limited, especially with increasing regulations on pesticides for environmental and safety reasons. Some professionals may have access to restricted-use insecticides that target soil-dwelling larvae; however, these are not available for general public use.
Biological control such as the use of nematodes is available however has mixed success as soil conditions have to be suitable for a 2-week period for nematodes to be effective. The nematode penetrates the grub and kills it. The nematodes need to be applied to moist areas during August to early October when the soil temperatures are above 12 degrees and the grubs are active. Sufficient water needs to be applied after the nematodes have been introduced to bring them into contact with the grubs. Specialist advice should be sought if taking this approach.
Mechanical control can be achieved by the use of shallow aeration techniques such as sarel rolling or from a star shaped slitter such as those found on a multi-groom tractor attachment. This needs to be done in the early autumn or spring when the grubs are active and near the surface. Several passes may be needed to have sufficient control.
How best to repair affected areas?
Before any remedial work is undertaken, good cultural practices will increase the turf’s ability to overcome damage from root loss. A strong, healthy plant is able to recover more quickly and develop new rooting structures to compensate for any damage caused during the feeding.
Depending on indigenous soil a 60/40 or 70/30 rootzone screened for stones to between 3-5mm is ideal topdressing material to repair areas. When dressing areas it should be done with a pan shovel and lightly dusted little and often.
A popular method is to put an adequate amount of dressing in a wheelbarrow or trailer and thoroughly mix Perennial Ryegrass seed in with the dressing. The critical thing with these repairs is little and often so the grass below is not being smothered and so the new material binds with the indigenous soil, hand forking the area beforehand can help with this, and the material should be raked in using a plastic landscaping rake. Doing this once per week until the area is returned to a level. (You may need to allow a few weeks for seed to establish before adding more dressing) Consider covering the areas with germination sheeting to speed up establishment of new seed and to protect from pests.
If chafer damage is deeper than 5 cms then re-turfing may be the only option to facilitate continued use.
These repairs are of a similar nature to goalmouth repairs so please refer to our learning resource on goal mouth repair within our pitch maintenance tasks section.
