In September the high-school and middle-school quads were covered with sticky sap that rained down from the trees and had a horrible smell.

Jay Holman, director of the physical plant and head of maintenance, decided to investigate.

"At first we thought an animal had gotten behind the middle-school lockers and died. We never would have imagined that the smell came from the trees," Holman said.

The trees near rooms 5 and 6 and in the middle-school quad are Chinese Hackberry trees, according to arborists from Fallen Leaf Tree Service, the school’s tree service.

This year the Hackberries produced an excessive amount of sticky sap.

“It smell[ed] like [someone’s] armpits when they haven’t taken a shower in three weeks,” said sophomore Gordon Ho.

According to Holman, Fallen Leaf Tree Service said the Hackberry trees were infested with Woolly Hackberry aphids, which attack and eat the trees.

According to the Statewide Integrated Pest Management Program (SIPMP), an organization founded by the University of California system to educate the public about pests and their control, the aphids create honeydew, which rains down from the trees.

After landing on leaves, honeydew creates a viable environment for mold and fungi growth, which produced the unpleasant odor, according to the SIPMP Website.

Tree specialist of American Arbor Matthew Moore wasn’t surprised that the honeydew smells bad.

“I imagine [the honeydew] would smell [bad]; it’s [aphid] urine,” Said Moore.

The aphids attack only in early fall and late spring, Holman said. To get rid of the insects the trees must be injected every three years in mid-winter with an insecticide.

The trees on campus have not been treated since they were planted— around the same time the school was built— because there was no need for it, said Holman.

According to Down Garden Services, another gardening service that offered information on treating the trees, the safest insecticide for treating aphids is pyrethroid, a synthetic compound similar to a pesticide found naturally in chrysanthemums.

The school’s current and previous tree services, Fallen Leaf Tree Service and Tree Care Incorporated, both said that they were unaware of an aphid infestation, and therefore did not treat the problem.

As a temporary treatment, maintenance sprayed the trees and pressure washed the sidewalks with water.

If the trees cannot be treated because the chemicals used could possibly be harmful to students, faculty, or the environment, they will be removed and replaced, since diseased trees are more prone to limb breakage, said Holman.