- Author: Help Desk Team
It's Spring, and many gardeners are turning with anticipation to their vegetable gardening beds and thinking about summertime harvesting and feasting. If you're one of them, you may find an unexpected surprise of white grubs just below the surface when you start to prepare your soil for planting.
Although we typically think of grubs as being specific to lawns, where their root feeding can cause brown patches, they also show up in vegetable beds. Most of what we call grubs are the larvae of the Masked Chafer beetle. They are whitish with brown heads and legs, and when fully grown are about 3/4” long and c-shaped. This time of year they are just starting to migrate upward in the soil from about 8” deep where they have overwintered.
Unless there is a significant infestation, the best control for grubs is to handpick them from the bed as soon as you see them and leave them for the birds to find. If there are too many for hand-picking, another option is to apply beneficial nematodes (Heterorhabditis bacteriophora), which are tiny parasitic roundworms that enter the grub's body and kill it within a few days. Beneficial nematodes are often available at local nurseries.
Beneficial nematodes should be applied in the summer and early fall when the grubs are young, and are most effective when applied to soil that is over 60°F. The nematodes move through moist (not soggy) soil, so it's important to irrigate both before and after application. A second application about two weeks after the first will help with successful control. Keep in mind that beneficial nematodes are killed by light and heat, so it can be a good idea to apply them in the cooler, evening hours.
For more information on beneficial nematodes and how to apply them in your vegetable beds, please see our Pest Note at https://ipm.ucanr.edu/TOOLS/TURF/PESTS/innem.html
Help Desk of the UC Master Gardeners of Contra Costa County (RDH)
- Author: Lauren Fordyce
While preparing your garden for planting this spring, you may have found white grubs in the soil. Discovering these fairly large, white grubs can be alarming, but they usually won't cause significant plant damage.
Grubs are the soil-dwelling larvae of beetles in the Scarabaeidae family, also simply called scarabs. They are generally curled in a C-shape with whitish bodies and 6 legs. Grubs of some species may be less than 0.5 inch long, while other species may be up to 2 inches. Some grubs feed on living plant material while others do not.
Masked chafer beetle grubs are often what people find in garden beds in California. If you find large grubs in compost, those are likely the larvae of the green fruit beetle (also commonly called figeater beetle and green fig beetle). Japanese beetles are not usually present in California, but there are a few small hot spots under eradication efforts by the California Department of Food and Agriculture.
In most cases, the presence of grubs does not require pesticide treatment and populations of 6 or less per square foot won't cause significant damage. If you notice them in your garden beds, they can be hand-picked and killed. Some may choose to feed them to their backyard chickens or leave them out for wild birds. Beneficial nematodes can be applied to control grub infestations.
To learn more about common white grubs, visit https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=56797
- Author: Lauren Fordyce
You may be noticing white grubs in your compost piles, lawns, or garden beds. These white, c-shaped critters can be 1/4 inch long or 2 inches long, depending on the species. White grubs are the larvae of some scarab beetles, and though many of them can cause damage to our landscapes, not all of them do.
There are three species that feed on the roots of grasses, making them a potential pest to lawns when in high numbers. These species may also be found in landscape or garden beds that are near grassy areas or were recently converted from grassy areas. Compare the size of white grubs you may find, as some species are much larger or smaller than others and can help you determine which is present.
- The larvae of masked chafer beetles are 1 inch long with dark heads and six legs. Adult beetles are golden brown and can be seen flying around in the evening hours.
- Billbug larvae are 3/8 inch long, also with dark heads andwhitebodies, but these grubs lack legs. Adults are brown weevils.
- Black turfgrass ataeniusls larvae are 1/4 inch long– much smaller than masked chafer grubs. Adult beetles are black and shiny.
One of the largest species of white grubs you might find in California are of the green fruit beetles, also known as figeater beetles or June beetles. The grubs of these beetles can be up to 2 inches long and are commonly found in compost piles, or near ripe and rotting fruits– which they feed on. These grubs, however, won't usually damage your landscape or garden plants. The adults are very large, metallic green beetles that are often mistaken for the invasive Japanese beetle, which is much smaller and, for the most part, is not found in California.
In most cases, the presence of white grubs does not require treatment and populations of 6 or less per square foot can be tolerated. If you notice them in your garden beds, they can be hand-picked and killed. Some may choose to feed them to their backyard chickens or leave them out for the birds. When infestations of grass-feeding white grubs occur, the lawn may feel soft and spongy, sometimes able to be rolled back like carpet. You may also notice animals like raccoons and moles digging in your yard, looking to snack on some white grubs.
To learn more about identifying and managing white grubs, see Pest Notes: Lawn Insects.
- Author: Elaine Lander
We've had many reports in the last two weeks from people asking what those big green, buzzing, beetles are. Green fruit beetles (Cotinis mutabilis) are members of the scarab beetle family and are sometimes known as fig beetles or figeater beetles. They are related to green June beetles (C. nitida) which are more commonly found in the South Eastern United States.
Green fruit beetles have a metallic green color and can be up to 1 1/3 inches long with prominent legs and antennae. The adults eat maturing soft fruit like figs and stone fruits, while the larvae (grubs) are found in compost or other decomposing matter. More on these occasional pests can be found on our website.
Advice for the Home Gardener from the
Help Desk of the UC Master Gardener Program
of Contra Costa County
Home Gardener's Request: Thank you for calling the UC Master Gardener Program Help Desk concerning moles in your lawn. I'm sending links (below) for the information that we promised.
Master Gardener Help Desk Response:
For Moles: http://ipm.ucanr.edu/PMG/PESTNOTES/pn74115.html.
You mentioned that you have had grubs previously, and it may be that moles are still present because grubs are a food source for them. If you can eliminate the grubs, the moles may move on. The above 'pest note' link (above) suggests that trapping is the most dependable control method for moles, and it gives detailed information should you decide this is necessary.
For Grubs: The links following also provide some information on lawn grubs: http://ipm.ucanr.edu/TOOLS/TURF/PESTS/inchaf.html
This link gives more details about treatment: http://ipm.ucanr.edu/PMG/PESTNOTES/pn7476.html
Turf Management: Finally, UC has an extensive website on general lawn management at:
http://ipm.ucanr.edu/TOOLS/TURF/
Most control methods for grubs are only effective while they are actively feeding and as we move into the colder part of the year, grubs are not so active. You can check your lawn by rolling back a bit of turf to see if grubs are present. If the mole damage is not too great, you might want to wait until spring to reassess the situation. Meanwhile, plan on giving your lawn the best care, with adequate irrigation and care and not to over-fertilize. This will give it the lawn its best chance to withstand pest damage.
If you have further questions, please do not hesitate to contact the Help Desk again.
Good luck with your lawn!
Help Desk of the UC Master Gardener Program of Contra Costa County (SMW)
Notes: Contra Costa MG's Help Desk is available almost year-round to answer your gardening questions. Except for a few holidays (e.g., last 2 weeks December), we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 2380 Bisso Lane, Concord, CA 94520. We can also be reached via telephone: (925) 608-6683, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/. MGCC Blogs can be found at http://ccmg.edu/HortCoCo/ You can also subscribe to the Biog.
