Products, Vendors, CAD Files, Spec Sheets and More...
Sign up for LAWeekly newsletter
Fungi are everywhere in the natural and urban forest. They are tiny, filamentous, plant-like organisms that can parasitize plants and trees. While many are beneficial or essential to tree health, others are a cause of disease. Among the most universal fungal problems for common tree species across the United States are phytophthora, stem cankers and anthracnose.
Phytophthora, commonly referred to as root rot or collar rot, is a genus of oomycetes which are organisms similar to fungi. There are 59 species of phytophthora and each of them cause disease in plants. Common hosts include, but are not limited to, dogwood, maple, hemlock, fir, cedar, and white pine. One particular species, Phytophthora ramorum, is the pathogen causing the disease ?EUR??,,????'??sudden oak death?EUR??,,????'?? in California?EUR??,,????'???s native oaks. Many other nursery and landscape plants, like rhododendron, carry the disease. Though the Phytophthora ramorum does not kill some of the plants which carry the disease, it is usually fatal in susceptible oaks like tanoak. The disease has not spread beyond California and Oregon.
Depending upon the degree of infection, phytophthora can be difficult or impossible to cure. For an established landscape tree, the tree can be treated with fungicides like Phospho-jet, an Arborjet product.
Control: Tree removal, spray or injection with potassium phosphite.
Cankers are lesions in the trunk or branch caused by various fungal and bacterial pathogens. Canker causing pathogens are usually specific to a particular host plant but virtually any type of tree can be affected by cankers. As previously mentioned, there are various species of phytophthora that cause trunk cankers. Cankers can also be the result of mechanical injury to the trunk or stem. A common form of mechanical trunk injury which can lead to the formation of cankers. A lawnmower or string trimmer can injure tree bark and lead to a canker.
As with phytophthora, certain cankers can be treated with fungicides, however, while the spread and growth of the infection may be slowed or stopped, the distorted trunk or stem growth of the canker will remain unless physically removed or until it is entirely grown over.
Control: Pruning, tree removal, fungicides, including Debacarb.
Anthracnose, or leaf blight, is a fungal disease that includes many species of fungi and affects many species of trees. Tree species most commonly affected by anthracnose are dogwood, sycamore, white oak and black walnut, but the disease is also found on ash, birch, elm, hickory, linden, maple and poplar. The various species of anthracnose causing fungi tend to be uniquely specific to their host plant.
Visible symptoms of the disease vary with species and host but most commonly, infected leaves develop tan to reddish brown lesions that extend along the veins of the leaf. defoliation, sometimes with complete leaf loss, occurs on many trees by late spring in cool wet years. Sycamores are particularly susceptible to repeated defoliations by anthracnose.
Control: Allieviate soil compaction, limit watering, fungicides, including chlorothalonil or thiophanate-methyl effective with Modesto ash only.
Sean Facey is a representative with Arborjet in Woburn, Mass.
10: Feet. When using hand compression sprayers to apply fungicides, note that these models of sprayers are not suitable for spraying trees more than 10 feet in height. Source: University of Minnesota Extension
85 to 90: Degrees. If using sulfur as a fungicide and the temperature is over 85 to 90 degrees Fahrenheit at the time of application, some foliage may burn. At low temperatures, no fungicidal activity will occur. Source: Oregon State University Extension
Francisco Uviña, University of New Mexico
Hardscape Oasis in Litchfield Park
Ash Nochian, Ph.D. Landscape Architect
November 12th, 2025
Sign up to receive Landscape Architect and Specifier News Magazine, LA Weekly and More...
Invalid Verification Code
Please enter the Verification Code below
You are now subcribed to LASN. You can also search and download CAD files and spec sheets from LADetails.