Phytophthora is a genus of oomycetes that are similar to fungi. There are 59 species of Phytophthora , all of which cause disease in plants. Phytophthora ramorum is the species responsible for Sudden Oak Death. Phytophthora are natural and universally occurring soil organisms which attack roots in poorly drained or anaerobic soils. As infected roots discolor and decay, the result is wilt, canopy dieback, cankers on the trunk, general decline and death. Phytophthora species are host specific attacking many types of trees including ash, cherry, pine, spruce, hemlock, fir, pear and dogwood.
Leaves will appear drought-stressed, sometimes turning dull green, yellow, red, or purple as they wilt. Infected bark is water-soaked, with red-brown discoloration and has a disagreeable odor. Bleeding cankers form at the base of the trunk and eventually lead to death. Phytophthora root rot infection is often followed by beetle infestation and/or an alternate pathogen infection.
Photo A taken by William M. Brown, Bugwood.org
Photo B taken by Joseph Obrien, USDA Forest Service, Bugwood.org
Arborjet recommends the use of PHOSPHO-jet, a systemic fungicide for treatment of Sudden Oak Death. Arborjet recommends a two pronged approach.
1. Micro-injection of PHOSPHO-jet into susceptible host trees
2. Amend the soil around the tree with humates (high quality organic matter). Phytophthora thrives in poorly drained and anaerobic soils. The addition of humates will help to increase soil aeration and make the root environment less conducive to disease development. Arborjet recommends a product such as Biostarter which includes beneficial bacteria that will create a less hospitable environment for Phytophthora. Humates are available from Boston Tree Preservation.
When to Treat
Generally, the best seasons for injection are fall and spring, as uptake occurs when trees are transpiring. The environmental conditions that favor uptake are adequate soil moisture and relatively high humidity. Soil temperature should be above 40 degrees F for trunk injection. Hot weather or dry soil conditions will result in a reduced rate of uptake, so trees should be watered if applications are made when soil is extremely dry. If treating trees in the summer, inject in the morning for the quickest uptake. Tree health will affect treatment efficacy, so assess tree health prior to treating. For example, a declining tree (>50% canopy dieback) is a poor candidate for treatment.
What to Expect After Treatment
Tree recovery will be dependent upon the severity of the Phytophthora infection at the time of trunk injection. PHOSPHO-jet acts as a fungicide and as an added benefit, stimulates new root growth. The addition of humates will create a soil environment that favors root growth over disease development