First, it’s important to make the connection that the white grubs in your lawn will hatch into Japanese Beetles and if you have Japanese Beetles they will lay eggs in your lawn that turn into white grubs.
Japanese Beetles can severely damage your roses and other plants in your landscape because they feed on the leaves and can almost completely defoliate some plants.
The white grubs ruin your lawn!
They feed on the roots of the grass near the soil surface. The damage usually shows up when it’s hot and dry because without a good root system the grasses in your lawn will start dying. Damaged areas in your lawn feel spongy when you walk on the grass because of the tunneling that’s taking place under the surface. If the damage is extensive the grass can be pulled up like carpet because the roots have been chewed off.
Skunks, Crows, Grubs and other Critters dig up your lawn to get at the grubs. In the fall when skunks are instinctively packing away the food to fatten up for the winter they can destroy a lawn in one night if it has a heavy grub infestation. Look for little holes in your flower beds. That usually means that the birds have been digging for grubs.
During the summer months when the soil is warm the grubs are usually at a depth of 2″ or less. As winter approaches they go deeper into the soil and become almost inactive. As soon as spring arrives and the soil temperatures increase they move back toward the surface and start feeding on the roots of your lawn once again.
They eat away for another 4 to 6 weeks, then emerge from the soil as adult Japanese Beetles and start feeding on your landscape. As they devour your landscape they start laying batches of eggs. Usually 20 to 60 eggs total per female beetle. And the life cycle starts all over again.
You can lift areas of sod in your lawn where you suspect you might have white grub infestation and look for the grubs. They are white in color and range in size from 1/2″ to 1″ long. If you have more that 6 grubs per square foot it’s time to think about a way to control them.
If you opt for a chemical control there are several products on the market and the best time to apply them is late August and early September. The white grubs are much easier to control when they are smaller and closer to the surface of the soil.
Biological control of white Japanese Beetle grubs can be achieved by applying the insect parasitic nematode species Heterorhabditis bacteriophora. You can purchase these nematodes under a variety of different trade names.
Another biological control is Milky Spore which is actually bacterium pacenibacillus popillae. However, this is a long term approach and can take years for the spore to spread throughout your lawn. It actually requires to ingest the spores and then as they die their carcass becomes part of the control to help spread the spores throughout your lawn.
Japanese Beetle Traps! Do they work work? Well . . . the jury is still out. Most traps use both a sex lure that attracts male beetles and sweet smelling lure that attract both sexes. Without a doubt these traps attract a lot of beetles, but some research indicates that they attract more beetles to the area of the trap than they actually trap. That means that plants in the path of the trap might suffer more damage.
If you use traps place them near the edge of the property and well away from plants that are damaged by Japanese Beetles.
Since there is some biological control that naturally takes place without your intervention it is recommend that you only consider chemical control when the infestation is severe because the chemicals disrupt the natural process of control.
I hope what I’ve given you here helps. It is confusing.