Laboratory testing has found varying levels of imazapyr, an herbicide ingredient, in soil and tree samples from areas where more than 30 trees declined near the Mountain View Public Library and Pioneer Park, city officials said.
The findings confirm that imazapyr was present in the affected areas and trees, but they do not show how much the herbicide contributed to the trees’ decline or whether other factors also played a role, according to Mountain View officials.
According to the city, imazapyr was used for weed control, but Mountain View has stopped using it. Crews have removed 23 non-native sycamore trees and 10 other trees that had declined beyond recovery and posed safety risks. Two more trees in poor condition at Mercy and Franklin streets are expected to be removed soon, city officials said.
Crews are treating and monitoring the affected soil and checking the health of remaining trees. New trees will be planted once testing shows imazapyr is no longer present and city staff determine that soil and site conditions can support their long-term health, Mountain View officials said.
The investigation also has prompted the city to monitor about 150 more trees showing varying degrees of decline and symptoms similar to those found in other parts of the city. The trees are at Stevenson Park, Gateway Park, in the Castro Street roadway medians and near Castro Street and Evelyn Avenue.
Mountain View’s public tree inventory includes more than 27,500 trees, city officials said.