If you’ve noticed the sudden and rapid death of many trees across the Valley this summer, you’re not alone. We went from an extremely wet cool season to an extremely hot and dry warm season this year. Extreme weather patterns like these often cause weakened immune systems in non-native plant species, which lead to the current situation.
Recent soil tests by plant pathologist Dr. Jared Wheeler have revealed the
culprits for the most recent wave of rapid tree death: Verticillium and
Cinnamon Fungus (Phytopthora cinnamomi). Verticillium is a fungal
disease that stops vascular flow in non-native trees planted in soils with high clay content, especially on grounds that were previously farmland.
Phytophthora cinnamomi is a highly contagious “devastation mold” which
causes the rapid decay of root systems in soil with poor drainage.
Many tree and shrub species are affected, but this year, the biggest victims are Chinese Pistache, Elms, Catalpas, Olives, and Oaks. This disease is almost always fatal, and affected trees must be removed. We will soon be presenting bids for soil treatment with sulfur and/or gypsum to decrease microbial buildup in future plantings.’
While Verticilium Wilt and Phytopthora Cinnamomi are the most visible diseases affecting trees this summer, they are not the only ones found in Arizona soils.
Earlier this year, we dealt with cases of Slime Flux, especially on Elm and Ash Trees. Texas Root Rot is a common killer of trees and shrubs in soil with poor drainage. The table below, provided by Dr. Jared Wheeler, shows a list of some common microbial killers of trees in the Phoenix area.
Trees that are not native to the Sonoran Desert are generally at higher a risk of catching diseases, since they are not in their natural ecosystems and are thus are more likely to have weakened immune systems during extreme weather. We are currently removing affected trees and planning our
strategies for soil treatment and tree replacement.
For more information about Tree Diseases:
Verticillium in Pistachios (in an Agricultural Context)
Information on Cinnamon Fungus, aka. Phytopthora cinnamomi (PDF Download)
ALCA’s Presentation on Common Arizona Tree Diseases
Pinal Central Article on Verticillium Habits (written during a 2018 outbreak)