Japanese beetles and beetle larvae

Signs - Not specific to beetle larvae and can seem in the early stages like drought or stress. Patches of affected lawn wilt and turn yellow or brown. On investigation, the grass can be lifted easily from the soil not held down by roots to any degree. 

This can also happen with otherwise apparently healthy grass if there are enough larvae feeding actively enough. On lifting the turf and looking into the top couple of inches of soil, the soft-bodied grubs themselves are seen. Variable from 1/16" (1.5mm) long to 1 1/4" (32mm) depending on age, "C" shaped, cream colored with a darker head and three pairs of legs.

They seem to be especially keen on Kentucky bluegrass, perennial ryegrass, tall fescues and bentgrass.

Damage - dead patches of lawn, may be made worse by animals such as birds, raccoons, or moles ripping up the grass to get at the larvae. Damage usually occurs during the autumn and is more common on light sandy soils where grass growth is already poor. Rarely may affect other plants in the vicinity, but grass roots are the usual food source.

Adults feed on plant leaves and skeletonize them, they will feed on any of about 400 species, but of these 50 are preferred.

Plant Non Attractive Plants The adults do not like to feed on:

In the UK a similar beetle larva called Chafer beetles has a similar effect, here is a case study, email received by Anglian Gardener and the follow-up

Q. I have recently moved to Thetford, and my lawn has been attacked by a white caterpillar looking bug which my neighbors say are "Chafer Beetle" larvae and that they eat the grass roots. Apparently, they like the light, sandy, Breckland soil. The only suggested remedy is to lift the grass in turves and remove the larvae from the soil and roots. I did this over an area of about 4 sq m and found hundreds of larvae. This, of course, effectively destroyed the affected area of grass.

A. What you've probably got are the larvae of Chafer beetles, usually either cockchafers or garden chafers. As you have discovered, they feed on grass roots.

Damaged turf will lift away as the roots have been eaten and no longer hold the turf in the ground. Small mammals such as birds, badgers and foxes can cause further damage as they lift turf looking for the grubs to feed on. The grubs are soft bodied, cream in color with tan or brown heads.

Control used to be with Carbaryl though this is now no longer an option as this is now a restricted chemical - prescription only, used for killing head lice!

Fortunately there is a now a  biological control available to eradicate these pests. This is pet, child and environmentally friendly in a way that any chemical solution cannot be.

Go for a co-coordinated approach and apply an spring or autumn lawn feed as well to help the grass recover. The beetles emerge in the late spring to early summer and this is when they lay their eggs for next years crop of larvae. 

Don't expect a quick fix, particularly if they're endemic to the area. They may have built up in numbers for some reason over a period of time, you say you've just moved to the area - was the garden neglected? If you keep addressing the problem little and often (after the first onslaught!) then it should get under control.

Reasons to like Japanese beetles