White grubs are the larvae of several species of scarab beetles. They are weird, kind of alien-looking little creatures that curl up into a C-shape when disturbed. They tend to grow to around 1-inch long, but some species can get much larger.
I have three raised beds in my garden area and replant them every spring and fall.
For the last couple of years, I have found an unusually large population of what I believe is a kind of grub called Cyclocphala, or masked chafers. The larvae have brown heads and legs and have dark stripes across their backs. The adults (beetles) are golden-brown and have an almost armor-like, shiny coating on them.
“It is not possible to identify these grubs without looking closely at features such as mouthparts and small hairs (called setae) located on their bodies,” said Karey Windbiel-Rojas, with the University of California Statewide Integrated Pest Management Program.
“However, they are the larvae of scarab beetles, and based on where you found them, they could be masked chafers, green fruit beetles, or something similar. What they are very likely NOT are Japanese beetle larvae, since those are more or less non-existent in California.”
Handpicking grubs from raised beds (as I do) and containers can be all the control needed. I have had no noticeable plant damage in my beds.
If you or a neighbor have chickens, they absolutely love grubs and will be overjoyed to help you cut down the population.
Grubs can, however, do major damage to turfgrass. Most damage occurs during late summer or early fall. You will see patches of brown, drying lawn in the infested areas.
Additional damage is often done by moles, voles, birds or skunks that are digging in the grass to feed on the grubs.
Before taking any control measures, dig around the root level of the grass to confirm that in fact the damage is caused by grubs. If you find more than six grubs per square foot, you may want to take action.
Since grubs feed close to the surface, aerating the soil can kill significant numbers of them.
Nematodes (tiny, microscopic roundworms) can also be applied to control grubs. They should be applied when the grubs are young and not overpopulated.
It is best to do so in late summer or early fall. A second application is highly recommended. Be sure to do your research about the proper way to prepare and apply nematodes for grub control.
If these natural measures don't work, it is important to know what kind of grub (or any other kind of pest) you have before deciding to use chemical control.
Get advice about the right chemical to use and the right amount necessary to get the job done. A wrong decision can mean wiping out other species.
You can take a grub (or another pest) specimen into your local Master Gardener office to get information about what to do.
by UC Master Gardener Rebecca Jepsen
This article first appeared in the May 19, 2019 issue of the San Jose Mercury News.