Oak moth catepillars devour trees in Belmont 

click to enlarge Oak moth caterpillars are wreaking havoc in Belmont, commonly feeding on leaves from the Coast live oak. The trees survive the pesky attack. - MIKE KOOZMIN/THE S.F. EXAMINER
  • Mike Koozmin/The S.F. Examiner
  • Oak moth caterpillars are wreaking havoc in Belmont, commonly feeding on leaves from the Coast live oak. The trees survive the pesky attack.

Along several blocks in Belmont, trees are without leaves and appear to be dead — the result of a severe infestation of the oak moth.

Caterpillars — oak moths in the larval stage — commonly feed on leaves of the Coast live oak. But in most years, birds keep the population under control.

This year, however, is one of those that occur about every eight to 10 years in which a combination of environmental conditions — mostly weather — causes caterpillar population to erupt, said Richard Hill, an arborist with the Davey Tree Co.

Oaks infested by the caterpillars turn a tan color, and often are completely defoliated. While the trees appear dead, they aren't, according to Hill.

"The caterpillars are all over the place," Daniel Ourtiague of the Belmont Department of Parks and Recreation said. "All over mailboxes, cars, sidewalks, stuck to door handles — basically anywhere with a flat surface."

The infested oaks are clumped together in areas that resemble corridors — several blocks deep, and about a mile long — and are scattered throughout the city, said Ourtiague.

When such infestations occur, residents with infested trees on their property often scramble for solutions.

"You should see the number of calls I'm getting," Ourtiague said.

He cautioned residents that treatment options at this point are extremely limited — and people going door-to-door hawking solutions should be thoroughly vetted.

Unless the infestation repeats several years in a row, there is little risk to the trees, and no reason to remove them. Hill said that the oaks will grow a new set of leaves within three to four months.

The most effective way to eliminate the caterpillars during infestation years is through use of a biological pesticide called bacillus thuringienis that is not deadly to other living organisms, Hill said. But it must be administered when the caterpillars are very young, and it's too late to help oaks in Belmont, he said. There is an insecticide available too, but it may harm other organisms living nearby the oaks, Hill said.

"We're hoping the infestation doesn't repeat itself in 2014," Ourtiague said. "Then it could be fatal to trees that are infested two to three years in a row."

Simple steps like proper watering and fertilization can keep an infested oak healthier, Hill said.

This is the second year in a row the moths have infested trees in Belmont, though the number of trees affected last year was considerably less, he said.

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