Bacterial Cankers And Anthracnose

Minnesota has had a wet spring. The Twin Cities have experienced a winter that seemed to drag on for longer than expected, and only reluctantly given way to a wet spring. Many people assume that an abundance of water is healthy for trees. In many cases, that assumption is true: but not always. 

Sometimes an excess of water can cause bacterial and fungal tree infections to spread more. To help homeowners ensure their trees are healthy this spring, Birch Tree Care discusses two diseases that are hampered by wet springs.

Bacterial Cankers 

The bacterium that causes canker, Pseudomonas syringae, penetrates trees through damaged bark or an existing wound, such as a pruning cut.  Bacterial canker is found commonly on Cherries, Crabapples, and Plums. Bacterial canker infections happen during Autumn, Winter and early Spring - during cool, wet weather. The infection spreads by rain, water, and pruning tools not disinfected. 

Cankers begin to form in mid-spring, and soon afterwards shoots may die back. Small holes appear on foliage from early summer.

This bacterial infection is relatively easy to spot -  "gummy" lesions characteristically form on branches or trucks. In spring, when trees begin active growth,  a sour-smelling sap may ooze from these troubled areas. The bacterial cankers become darker than the surrounding healthy bark, and the underlying tissue is moist and reddish-brown to black.

If the infected area circles the branch or trunk, the leaves above the diseased area turn yellow. When this happens, the growth of the branch or tree stops entirely, and the tree or branch dies.

Birch Tree Care has over 30+ years of professional experience in tree related diagnostics. This wealth of experience allows us to share some valuable insight with you in accurately identifying and treating a bacterial canker.

Symptoms of bacterial cancers are not only present in branches and trunks but also shoots and leaves. Other signs like wilting leaves, shoot dieback and more only make bacterial cancers easier to spot. 

Bacterial cankers may cause small brown spots to appear on leaves. These brown spots are usually round and fall out later,  leaving leaf holes. Overall, this produces an appearance that looks as if the leaves have been hit by shotgun pellets.


  1. Prune flowering trees during blooming (July and August) when wounds heal fastest.

  2. Remove wilted or dead limbs well below infected areas. Burn these branches, or take them to a landfill. 

  3. Paint the freshly cut area with wound paint to protect the tree against re-infection.

Birch Tree Care offers free quotes to customers. If you would like to have your ornamental trees expertly treated, reach out to our certified experts today.


Fungi in the genus Colletotrichum cause anthracnose. Colletotrichum is a  group of plant pathogens responsible for diseases on many plant species. Spores overwinter in infected twigs, branches or fallen leaves and spread through wind and rain the subsequent season.  

Infected plants develop dark, water-soaked lesions on stems, leaves or fruit. The centers of these lesions frequently become covered with pink, viscous masses of spores, especially during moist, warm weather. 

Common hosts include ash and oak. In ash trees, infection usually occurs in the foliage or twigs. In oak, however, the infection can happen in the twigs, shoots, leaves or buds. The optimal temperature for anthracnose to develop in ash is15-20°C and the fungus grows more rapidly with wet weather.  Oak anthracnose develops most quickly when temperatures around 10 °C.

Ash leaves infected during spring become misshapen. In early infection, leaves develop brown and yellow blotches while the edges of the foliage curl and eventually fall off.

In early infection, leaves develop blotches of necrosis, while later infections produce necrotic leaf spots with a chlorotic ring. Severe infections can cause significant defoliation: eventually, larger branches may be cankered and killed. Several seasons of infection can cause trees to decline or become susceptible to other pests. 

In oak, there are generally three phases of the disease; twig blight, where young branches are encircled and killed, shoot blight, where new shoots are killed during expansion, and leaf blight, where leaves become distorted and necrotic at the tips or along veins. Repeated infections of established trees rarely cause permanent damage, but younger trees may need protection.


  1. Remove cankered branches and prune trees. Pruning the tree increases air circulation and helps prevent moisture. 

  2. Rake and destroy fallen leaves where the fungus can overwinter. 

  3. Apply a fungicide containing Chlorothalonil.

Fungicides are toxic carcinogens and must be applied correctly. Reach out to Birch Tree Care to book tree care and expert service.