Garden Advice Line
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UC Cooperative Extension
1432 Abbott Street
Salinas, CA 93901
Monterey Bay Master Gardeners is a non-profit 501(c)(3) program supporting the work of the UC Master Gardeners of Monterey and Santa Cruz Counties program.
My oak trees were infested with caterpillars from the oak worm moth. Will the trees die? How do I control them? Should I spray?
Environmental conditions and the moth's natural life cycle caused 2007 to be a "perfect storm" year for the California Oakworm (Phryganidia californica). The oak worm populations are cyclical, common in some years and virtually absent in others. A 5-10 year cycle for outbreaks is typical. There are normally two generations of moths a year, with moths first observed fluttering around the oaks in June or July. The second generation of moths will then occur around October or November.
Although the caterpillars are annoying and will denude trees by feeding on the foliage, oak worm infestation will not normally kill a tree unless the tree is already weakened by old age, stress or disease. Even if stripped of its leaves a healthy oak will recover. To remain healthy, California native oak trees require proper care, including little or no supplemental watering, well-drained soil, and careful pruning only if necessary (preferably by a certified arborist). The coast live oak, Quercus agrifolia, is the tree most often affected by the oak worm moth.
Control California oak worm with an integrated pest management (IPM) program that incorporates good cultural practices, conservation of natural enemies, and use of less-toxic pesticides, if necessary. You can clean under the tree, kill the caterpillars when they fall off, and make sure the tree is healthy. Spraying is generally not necessary, but in case of an extremely severe infestation, you can contact a certified arborist. We don't recommend attempting this yourself.
For more detailed information, see the UC Davis Pest Notes #7422.
How can I find a certified professional arborist?
The Master Gardener program does not recommend individual professionals. You can, however, locate a certified arborist in your area or verify a certification with assistance from the following web sites: the California Arborists Association (http://www.cal-arb-association.com/findarborist.html), the American Society of Consulting Arborists (ASCA) (http://www.asca-consultants.org/directory/), or the International Society of Arboriculture (ISA) (http://www.treesaregood.org).
I am concerned about the presence of the Light Brown Apple Moth (LBAM) and the proposed spraying program. Where can I get information?
According to the California Department of Food and Agriculture (CDFA), LBAM is an exotic pest that has recently been discovered in portions of the San Francisco Bay Area and Los Angeles. LBAM is a native pest to Australia that has been introduced into New Zealand, New Caledonia, Hawaii, the United Kingdom and Ireland. The presence of LBAM in the continental United States was detected for the first time in March, 2007. This moth can affect a wide variety of plants, flowers, fruits and vegetables and have an impact on agriculture due to damage or quarantines on various farm or nursery products. Information about the moth and pictures that may help you identify the moth can be found at the UC Davis Integrated Pest Management web site: http://www.ipm.ucdavis.edu/EXOTIC/lightbrownapplemoth.html. To obtain the latest information on LBAM and the eradication program, to find the toll-free LBAM hotline number, or to subscribe to updates on the LBAM aerial spraying, visit the CDFA web site at: http://www.cdfa.ca.gov/phpps/PDEP/lbam/lbam_main.html. Information on these web sites will be updated as new information becomes available.
Where can I have my soil analyzed?
In Santa Cruz, Monterey, and San Benito counties, you can take or ship soil samples to Perry Laboratory, 471 Airport Blvd., Watsonville CA 95076 (Ph. 722-7606). Perry Lab charges a fee for this service. There are no agencies available locally that provide this service for free.
Please see the following website for details regarding submission of soil samples:
When does the next Monterey Bay Master Gardener class start?
The next UC Master Gardener class will begin January 2022. Apply here.
Click here to learn more about becoming a UC Master Gardener for Monterey and Santa Cruz Counties.