Tree of Heaven Removal at South County Maintenance Yard

The invasive tree of heaven is a growing management issue at the South County Yard. Left unmanaged, tree of heaven will damage the hardscape and buildings, so treatment is necessary before tree of heaven spreads throughout the facility, damages infrastructure, and spreads beyond Valley Water-owned lands. Several large trees grow along the southern fenceline, one large tree is in the middle of the parking area, and several suckers and saplings are scattered throughout the facility, growing in cracks in concrete and near buildings. Two herbicide-based approaches are proposed to remove these trees. Trees under about 6” DBH (diameter at breast height) would be treated with basal bark triclopyr. This is a treatment in which herbicide is painted or sprayed onto the lower 12-15” of the bark including the root crown using an oil-based herbicide. Trees greater than 6” DBH would be treated with hack-and-squirt treatment with concentrated imazapyr. This treatment involves using a small hatchet to make shallow cuts into the cambium around the trunk while leaving intact strips of bark so that conductive tissues can continue to push herbicide down into the root system. Removal efforts would start in August or September. A crew of 3-4 applicators would finish the initial treatment in half a day. Tree of heaven requires multiple years of sustained management efforts. About 30 days after the initial treatment, an inspection would determine whether follow-up treatment is needed that season. Two treatments per season for the first three years is typical, though stubborn trees may require additional treatments. Dead biomass (peeling bark, fungi, no nearby suckers) may be removed after a year of showing no signs of life.