The cinnamon smell that has been permeating campus since early April comes from an organic pesticide called Weed Zap, used by the custodian on the fields. This non- selective herbicide kills all plants it comes in contact with and is used to target weed growth.

Two years ago, the district replaced Round Up, a synthetic pesticide, with Weed Zap. To treat an area with a synthetic pesticide, the California Department of Pesticide Regulation requires notices to be posted for residents 72 hours before and after treatment. Weed Zap, however, is made of natural ingredients, meaning that regulations are less stringent, according to Maintenance Director Peter Auth. “We do not have to inform people that we’re treating areas because this organic herbicide is not harmful to animals or people,” he said. Concerns about Round Up’s potential to harm campus health caused the switch to Weed Zap. Round Up contains glyphosate— an ingredient that can cause eye and skin irritation, nausea, diarrhea and headaches, among other symptoms.

Gunn landscaper Miguel Ramirez said that clove and cinnamon oils, which disrupt the harmful plants’ cell membranes and comprise 90% of the Weed Zap’s volume, cause the scent on campus.

According to Auth, unchecked weed growth can affect the levelness of athletic playing fields — such as those of softball and baseball — creating the potential for injuries. Pesticides are also vital for the health of other greenery on campus. “In the natural biome, everything is competing for survival,” Auth said. “So if you’re planting a nice landscape, and weed seeds have somehow gotten into the landscape area, they’re gonna compete for water as much as your trees and your flowers will. It really comes down to a matter of keeping the plants we introduced to a landscape there.”

Weed Zap costs between $150 to $200 for a 2.5-gallon container, but is made more affordable during application by dilution water. “We mix 12 ounces of Weed Zap per gallon of water,” Ramirez said. “Sometimes we can spray 4 gallons of the solution in one day depending on the area that needs treatment. There is no schedule for the pesticide. We just spray it when the weeds are out of control.”

According to Ramirez, herbicides are typically used during the spring and summer,  since the increased amount of precipitation in spring causes an influx of weed growth. The treatment is most effective for relatively young or sprouting weeds, since larger plants have to be manually pulled out the ground. Although Weed Zap usually yields noticeable results after two to five days, many weeds become resistant to the organic pesticide as the summer progresses, making them harder to kill. To combat this issue, the conditions for pesticide application — such as changing the treatment schedule, adjusting solution concentration or varying the temperature — have to be altered throughout the season.

Although the pervasive cinnamon smell serves as a reminder of pesticide use on campus, it has received no complaints from community members. “It’s actually a very welcome smell because it indicates that Palo Alto is being proactive about our student, public and administrative populations,” Auth said.