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Tree & Plant Fungal Diseases Common to Portland

This post features some common tree and plant fungal diseases often found in the Portland and SW Washington areas. Why? Because we know many Portland homeowners like to be proactive when it comes to potential problems in their landscaping. 

Photinia Leaf Spot

Photinia is a popular shrub used for hedges in many Portland yards, which is why we want to tell homeowners about this very real threat. Photinias are very susceptible to the fungus leaf spot called Entomosporium, which can defoliate photinia plants.

It affects several species of photinia including Photinia x fraseri and red-tipped photinia (two of the most common) though it also attacks other ornamentals, such as serviceberry, flowering quince and mountain ash.

Signs of the blight

New infections appear as small circular leaf spots that are darker red than the surrounding area.  Older necrotic (dead tissue) spots have ash-gray centers surrounded by a darker red halo.  If the plant is heavily infected, the individual spots may run together to form one larger area.

Infection will spread to twigs where it forms cankers on the branches. In addition, heavy infections may cause premature leaf drop causing ‘easy to spot’ bare areas.  

Photinia leaf spot is often confused with physiological leaf spot so look for sunken gray centers as they are characteristic of fungal leaf spot and not physiological leaf spot.  

Verticillium Wilt is destructive

A wide-spreading fungal disease that lives in the soil, Verticillium Wilt attacks susceptible plants through their roots and spreads through the plant’s vascular system.  It affects maples, redbud (Cercis), ash euonymus, tomatoes, and strawberries.

A plant or tree may have the disease if its leaves are curled, wilted, discolored, or dying.  Symptoms usually appear in spring or fall when temperatures are mild.  The fungus plugs up the water conducting vessels in the roots and stems of the plants.  Resilient, it can survive in the soil for years making it a long-term threat.

The good news? It’s treatable. 

The first step is to confirm the symptoms are caused by verticillium wilt and not something else as other diseases have similar indicators.  This is best done by a plant health care expert (of which General Tree has many) who will do a thorough inspection.

Treatment usually focuses on giving the plant the best care possible so that it builds up its natural resistance.  This includes regular watering and providing afternoon shade (if possible).  Managing trees infected with verticillium wilt takes time and knowledge.

Seiridium Canker

Plants affected by Seiridium Canker are incense cedar, leyland cypress and juniper. Signs are easy to spot as the foliage yellows on affected branches and turns brown in the spring with smaller branches usually infected first and eventually, moving to larger branches.

Upon inspection, you’ll see a sunken canker on the branch below the infected foliage.  The bark turns brown and small fruiting bodies form in the cankered area.  You may also see drops of resin in and around the sides of the canker.  Larger trees often slowly decline from the cumulative effects of many cankers.

If you see signs of plant fungal diseases in your yard, contact General Tree.  One of our Plant Health Care technicians will do a thorough assessment and offer treatment options.