Dealing With Insect Lawn Damage
Dealing with Lawn Bugs
In order to control pesky insects in the lawn, including Cotinis nitida (the June bug) and the Masked Chafer, you need to understand their life cycles, their body types, and what they like to eat.
Cotinis nitida, the June Bug
The June Bug does the most damage to the lawn in its larval form. (That's the immature form that looks like a worm or caterpillar.) Adult June Beetles lay eggs in the soil in the summer. The larvae live in the soil under the lawn eating soil, humus, and lawn grass roots. In the spring, they pupate in the soil and emerge as adults (green flying beetles). The adults eat the fruits of peach trees.
These pests are really not a threat to lawns. They're more of a problem if you want to grow fruit trees, than anything. Don't worry about controlling them in the lawn.
Masked chafers are not so innocuous, though. This pest primarily attacks Kentucky Bluegrass and tall fescues. It can also attack bermudagrass in the warmest areas of the country. Larvae masked chafers are the most damaging in the pest's life cycle. The larvae are grubs, and are particularly damaging in areas where Japanese beetles are under control. (In a sense, the masked chafer takes the place of the beetles.)
The larvae are close to the surface of the soil, eating plant roots, in the mid to late spring (April and May) and again in the fall (September-October). That is when damage will show up. Lawn grass affected by masked chafers will not recover from drought and will die in uneven patches.
You can use traps to catch the adults during the mid summer. Keep irrigation to a minimum during the summer, as water encourages the survival of the insects. Milky spore is not effective in controlling masked chafers, unfortunately. There are some insecticides (grub treatments) that are affective. You have to select treatments that will work on masked chafers, not just Japanese beetle grubs. The grub control must be applied when the grubs are actively feeding at the top of the soil.
Remember-the key to good lawn insect control is timing the control so that you're targeting the right best at the right time for the chemical.