Grubs Eating My Veggies?

Help for the Home Gardener from the Help Desk of the
UC Master Gardener Program of Contra Costa County

Client's Request: I'm finding in my raised vegetable bed what looks to me like “grubs”. A picture of one of them is enclosed. I don't know specifically that they are destructive “grubs”, but I'm concerned that they will negate all my hard work trying to grow vegetables. I'm thinking about replacing the soil although I'd rather not do that. What would you recommend that I do?

MGCC Help Desk Response:  Thank you for contacting the UC Master Gardener Program Help Desk with your questions about grubs in your vegetable bed. I enjoyed talking to you today, and the picture you sent was helpful as well.

adult masked chafer beetle

Based on your picture, the grubs infesting your vegetable bed are most likely the larval stage of masked chafer beetles. The ¾ inch adult beetles are golden brown in color, with dark brown heads and hairy undersides. The grubs are whitish in color, with brown heads and legs, dark stripes on their backs, and bristles on the undersides of their posterior abdomen. The fully grown grubs are about an inch in length, and are c-shaped. The grubs are root feeders, and are known to favor turf grasses, although they do feed on the roots of other plants as well. Based on your description of your vegetable plants, it seems the grubs did very little damage to your vegetables this year. However, I know you are eager to get rid of them!

Following is some information on masked chafer grubs. http://ipm.ucanr.edu/TOOLS/TURF/PESTS/inchaf.html 

Possible treatment options include hand-picking to remove any grubs you find in the soil, or turning the soil to expose grubs to birds and other predators. Beneficial nematodes can also be used for biological control of grubs, as described in the article at the following link. http://ipm.ucanr.edu/TOOLS/TURF/PESTS/innem.html 

If you do remove the soil to start again (as you mentioned you might), be careful with any compost you add. The adult beetles can be attracted to fresh compost or organic matter, where they will lay their eggs. The larvae (grubs) will locate and feed on roots after they hatch. Before applying compost, be sure it had been properly prepared with sufficient heat to decompose the organic material and to kill insect eggs and other organisms. Information on rapid composting can be found at this UC link: http://anrcatalog.ucanr.edu/pdf/8037.pdf  

I hope you are able to get rid of your grubs before next season. Do let us know if you have further questions.

Help Desk of the UC Master Gardener Program of Contra Costa County (TKT)

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Note: The  UC Master Gardeners Program of Contra Costa's Help Desk is available year-round to answer your gardening questions.  Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA  94523. We can also be reached via telephone:  (925)646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog  (//ucanr.edu/blogs/CCMGBlog/).