Tree Troubles In California

By Pat Gross, director, Southwest Region
May 30, 2013

 (L) The aggressive feeding of California oakworm has completely defoliated this coast live oak in northern California. Although the tree looks dead, new leaves are beginning to emerge and trees such as this typically survive without the need for insecticide treatment. (R) Limited rainfall during the winter is primarily responsible for the stress and discoloration seen on may coast redwoods.

Visits to golf courses in recent weeks have revealed some interesting problems with golf course trees, particularly with prominent California specimens such as coast live oak (Quercus agrifolia) and coast redwoods (Sequoia sempervirens). Whether it’s the limited rainfall or the temperature fluctuations this spring – nobody knows, but these species are having a tough time this spring in some locations.

California oakworm (Phryganidia californica)  

The California oakworm has been very active on coast live oak in some locations in northern California. The aggressive feeding habit of the larvae has defoliated trees, but the insect pest has a symbiotic relationship with the trees. The insects eat a lot, but need the trees to survive for future feeding and survival. No need to panic. Despite stripping the trees of leaves, the emergence of new leaves and steady recovery typically occurs from late May through July. Insecticide treatments have limited effect, so save your money and let the trees take care of themselves. Further information on this pest of oak trees is available at the University of California IPM website at UC - IPM California Oakworm    

Coast redwood stress  

Coast redwoods depend on deep, heavy water from winter rainfall for normal growth and development. During years with limited rain, such as this year, trees may show sign of stress and discoloration. Deep watering around the base of the trees may snap them out of the funk, but the real tonic is a normal year of heavy winter rains. Again don’t panic and let the trees manage through the situation.

Source: Pat Gross  (

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