What is a grub?
A typical lawn grub is a white, 'C' shaped larva of a beetle about a half inch in length. A grub may be the larvae of the masked chafer, European chafer (pictured), Japanese beetle or other beetle species.
How do I know if I have grubs?
Gently lift up the sod, if it easily pulls away from the ground, the root system may have been eaten by grubs. Cut into the soil and look for their presence, more than ten per square foot of lawn could indicate a problem.
The presence of beetles may be an indication that they are laying eggs in your lawn. Tan colored chafer beetles are active just after sundown and Japanese beetles can be seen flying during the day feeding on ornamentals.
Grub damage can appear two ways. First small irregular patches of lawn will appear brown, dry and wilted. Damage also occurs when racoons and crows tear up the lawn while feeding on the grubs. Both types of damage can be extensive in a severe outbreak.
How to deal with grubs.
As always an active IPM program is the best plan for dealing with any lawn pest. Periodic scouting, especially late in the summer when activity is most likely, and a healthy, resilient turf are the best defense.
If you have cut into the lawn and determined that an outbreak has occurred (more than 10/sq.ft.) an insecticide like Dylox could be used. Insecticides like Merit are often used for grub prevention, applied while the grubs are in the egg stage. Insecticides are dangerous and best handled by a licensed pesticide applicator.
Is there an organic product that can kill grubs?
The best organic control of grubs is prevention. Healthy soil and Integrated Pest Management techniques give the grass the upper-hand in grub defense.
Beetles lay their eggs in moist, irrigated soil, so a natural alternative would be to not irrigate the lawn during the mid-summer dry spells. The lawn may turn brown and go dormant but a grub problem is unlikely.
Milky spore is a naturally occurring bacterium than can be applied to the lawn to control grub populations. The soil is inoculated, the grubs inadvertently eat the spores while feeding and die, releasing millions of more spores. It can be a lengthy process but it is organic.
Another natural enemy of white grubs is a certain nematode. There are many different types of nematodes, some beneficial and others not. Hb nematodes are watered into the soil to introduce a natural predator to the grubs resulting in controlled populations.
How to repair grub damage
Because the grubs feed on the roots, grass will need to be started from scratch. Just treat the are like any other bare patch repair and be certain to keep the seed moist while germinating.