Root rot on boxwood trees may cause devastation to the trees with severe cosmetic damage and decline. For a vigorous landscape with healthy plants, become accustomed with ways to recognize these fungal infections of boxwoods and employ the most effective management methods for prevention and control.
Well-maintained, strong boxwood trees are healthy and ready to avoid and fight off attack by fungal pathogens whereas poorly cared for trees are not. Grow boxwood trees in partial shade when possible, though these trees will still grow successfully in full sun exposure, according to the NC State University Cooperative Extension Service. Boxwoods thrive in well-drained soil with a pH of 6.5 to 7.0.
The main fungal pathogens responsible for root rot on boxwood are Phytophthora nicotianae, Phytophthora cinnamomi and Phytophthora parasitica. Fungi thrive in waterlogged soil and areas with high moisture content and warm temperatures, according to the Clemson University Extension. The soil-borne fungi invade feeder roots and progress further into the root system.
Root rot infections of boxwood trees begin with darkening of roots as they begin to decay followed by signs above ground with the curling and fading of leaves to a light yellow-tan hue. Bark dies and pulls away from the boxwood tree near the crown and the entire crown of the tree often yellows under severe infection. Visible, above-ground symptoms generally occur once the roots are in an advanced state of rot, leading to decline and tree death.
For natural control of root rot on boxwood trees, plant healthy trees and do not replant boxwoods where an infected boxwood was removed as soil-borne fungi will infect the new tree, according to the NC State University Cooperative Extension Service. If your planting site has drainage problems, consider planting your boxwood in a raised bed to improve the problem. For severely infected boxwoods, remove your tree entirely.
For chemical control of root rot problems on boxwood trees, realize that the effectiveness is low and not a cure for an existing problem. When used in conjunction with natural control methods, results are more successful. Existing fungi are not killed, but chemicals control the continued spread and infection due to pathogens present in soil. Use a soil drench for uninfected or mildly infected boxwoods; choose a fungicide with the active ingredient mefenoxam or metalaxyl, according to the Virginia Cooperative Extension. Contact a licensed professional or your local county extension agent for control assistance for your particular region.