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Urban forestry reports California oakworm activity concentrated in north side; treatments ongoing
Summary
City urban forestry staff say the California oakworm is defoliating primarily northern neighborhoods; crews have treated about 114 trees since July 1 and are monitoring, applying foliar sprays selectively and recommending manual removal for small infestations.
Alejandro Gonzalez, urban forest technician with the Parks and Recreation Department, updated the commission on an outbreak of California oakworm caterpillars that have been defoliating oak species in parts of the city.
“The oakworm is actually a native moth species…they come primarily and feed on oak trees throughout the city,” Gonzalez said, describing the caterpillar stage, the moth life cycle and the typical signs of infestation.
Gonzalez said staff had treated about 114 trees beginning July 1 and that the insect activity has been concentrated in the northern portion of town, with some midtown reports. He said crews are monitoring, advising residents on manual removal and, where necessary and safe, applying foliar insecticide treatments early in the morning. He added that natural predators and parasitic wasps also help control populations.
“Short term, it can be ugly to look at…Long term, actually, it’s actually pretty low impact,” Gonzalez said, noting that trees commonly recover unless they are already stressed by other conditions. He said refoliation typically begins about four to six weeks after the caterpillar generation passes through.
Commissioners and staff said the public has called frequently with nuisance complaints about frass (caterpillar droppings) and that staff have directed residents to informational material on the city website. Staff also said they are careful when scheduling foliar sprays because of possible impacts to nearby crops, flowers or standing water and therefore make treatment decisions on a site-by-site basis.
No formal policy action was taken. Staff said they will continue monitoring, continue targeted treatments as conditions require and post education materials for residents about identification, removal and expected tree recovery.
