Keeping the California oak moth under control

Julie Day, a horticulturalist for Stanford University, was walking along a road on campus with her lunch in hand when she noticed that something was not quite right about the foliage.

“I was walking past a group of trees, and I went, ‘Oh my god,’” Day said. “I ran to the office, grabbed the camera, took photographs, sent emails and made phone calls. It was high alert.”

Day’s reaction was in response to the first outbreak of the California oak moth, an insect native to coastal California that feeds voraciously on the California oak and other deciduous trees.

According to grounds supervisor Max Pinedo, the outbreak took place not only at Stanford, but also in many parts of California.

So far this year, there have been two spikes in the moth population, one in April and May and then another in September. Each spike represents a new generation of moth. The previous generation mates and lays eggs, leading to a new batch of caterpillars that eventually turn into moths themselves and continue the cycle.

“[Currently] we are entering the third generation for the year,” Day said. “It is not as heavy as the first and the second were because we’ve already done some control.”

According to Day, measures such as daily monitoring will be taken to keep the moth population in check.

With vigilance and a little luck, Day hopes there will not be a fourth outbreak.

According to human biology professor Carol Boggs, predicting whether an outbreak will happen can be very difficult, especially since there are so many factors at play.

“For moths and butterflies in general, weather conditions are very influential,” Boggs said. “You can’t say we are going to have an explosion this year because it’s been five years since we’ve had an explosion.”

A decrease in the number of natural enemies could cause an outbreak in population size, Boggs said.

In response to these outbreaks, the University uses an integrated pest management system– a variety of methods that track and combat the pest populations in a way that is designed to do minimal harm to the environment.

Stanford tracks the populations before outbreaks because timing is crucial in controlling the moth populations. When the California oak moth is a pupa, it has a hard shell that is not easy to penetrate. During the moth stage, the chemicals would have to be sprayed into the air. Therefore the abatement must be done in the short window of time during the caterpillar stage.

The University uses several different control methods. Over the last few years, staff have power-washed trees, introduced natural predators and used insecticides.

Last summer, the University used an insecticide named Conserve, a “turf and ornamental insect control, a low toxicity type of chemical derived from natural sources,” wrote Pinedo in an email to The Daily.

The insecticide is diluted to six ounces per 100 gallons of water before it is used, he added.

Pinedo noted that all aspects of the abatement program are targeted around campus spots with high levels of walking traffic. The California oak moth does not normally kill the tree, but problems arise when the tree is placed in an urban environment.

“If the plants are stressed for other reasons, like they are surrounded by asphalt or people are biking over their roots, then defoliation can be more serious,” Boggs said.

Yet, the decision to control the population is not always solely based on the oak trees’ ability to survive.

According to Day, decisions regarding abatement are made with the public’s comfort in mind, particularly in high profile areas.

“[We want] to make sure that everyone is comfortable on campus,” Day said.

In addition, the abatement programs are used not only to protect the trees, but to protect the campus’s overall aesthetic look, particularly for visitors and prospective students.

“Sometimes people will be concerned about aesthetics,” Boggs said. “Stanford doesn’t necessarily want its oaks to look like something has been tearing it to shreds. They don’t really want Tussock Moths–a moth that experienced a similar rise in population in 2007–to be dropping out of trees on top of ProFros.”