The dogwood tree is a native of the southeastern United States. It can grow to a height of 20 to 35 feet and a spread of 20 to 25 feet. It produces small yellow flowers surrounded by white bracts (modified leaves). Some varieties will have red or pink bracts, but do not do well in the warmest areas.
Leaf and flower diseases include dogwood anthracnose fungal disease and Septoria leafspot. Crown canker is a fungal disease that attacks the crown of the plant, the place where the trunk meets the roots. Clitocybe tabescens is a root rot disease that enters through the roots and can affect the whole tree.
Dogwood anthracnose appears first as light brown spots on the leaves that grow to large brown splotches that can have a purple margin. Septoria leaf spot appears as spots within the borders of the veins. They start out with an even purple color and as the disease progresses, the center will become gray.
Crown canker first appears as fewer, lighter in color and smaller leaves and the whole tree looks unhealthy. In late summer, the leaves will turn color early and drop off. The trees will also produce more flowers and fruit than normal.
Dogwood anthracnose can live in fallen debris. Rake up the area around the tree after the leaves fall to lessen the chance fo it wintering over. Plant only trees that are certified disease free. Pick a site that is not wet and gets direct sun.
Picking up debris will help prevent septoria leaf spot as well. Crown canker enters the tree though a wound usually cause by mowing the lawn. Be careful not to hit the tree.
Dogwood anthracnose has symptoms similar to other diseases. It is a good idea to get an experts opinion and follow his advice as to what if any fungicide to use. Septoria leaf spot occurs in the latter part of the season when it is normal for leaves to fall, so no treatment is recommended.
Crown canker cannot be controlled once it gets a good hold on the tree. If it is caught early enough, it is possible to halt the progression buy cutting away the canker and all of the discolored bark as well as a small amount of the healthy bark and wood. Paint the area with orange shellac and then wound paint.
Dogwood anthracnose spreads from the leaves to the twigs and then the to main branches and the trunk. When it gets this far, large cankers can develop that can kill the tree. This can happen in as little as 2 to 3 years for large trees.
Septoria leaf spot has cosmetic effects on the leave, but does not do permanent damage to the tree. Crown canker can kill the tree or make it so weak that it is more susceptible to other infections.