Dogwood Trees: Diseases and Problems

Dogwood trees, scientifically known as the Cornus florida, are great for adding color to one's garden and landscape. These trees are easy to grow and are admired for their spectacular explosion of flowers that come in red, white and pink every spring. As the dogwood trees are small even when mature, these are the perfect choice for those who love gardening, but have space problem. The flowers of the dogwood tree is also the state flower of North Carolina. Despite the ease with which they grow, there are a number of dogwood tree diseases and problems that need to be taken of.

Dogwood Tree Diseases

Flower and Leaf Diseases
Spot Anthracnose: This infection is caused by the fungus Elsinoe corni. The first parts of the tree to be affected are the flower bracts (petals). From there they spread to the leaves, young shoots and then the fruits. The initial symptoms include small, circular to elongated reddish-purple spots that appear in early spring. The centers of these spots are yellowish in color with borders that are in darker shades, generally brown to black. Infected flowers look small and distorted while those that are severely infected fall prematurely off the branches. Severely infected fruits are deformed, and 'shot hole' like formations are seen on the leaves due to infected tissue. The fungus persists through years and may cause infection to spread further throughout the tree.

Dogwood Anthracnose: One of the very common diseases of dogwood trees is the dogwood anthracnose which is caused by the fungus Discula sp.. The infection is manifested in the form of leaf spots and stem cankers. The shoots are also killed in this disease. The initial symptoms appear as medium to large purple bordered leaf spots and scorched, tan blotches. The infected areas may further increase to kill the entire leaf. The disease spreads from leaves to the twigs, down to the main stem, forming cankers on the main stem. Trunk sprouts also occur in the advanced stages of this disease.

Septoria Leafspot: In septoria leafspot, the initial infections appear as small, purple colored spots or lesions on the leaves. Although the center of these spots may become grayish, the purplish color still remains. The 'shot hole' formation that is seen in spot anthracnose rarely occur. However, it is not uncommon for septoria leafspot and spot anthracnose to infect a leaf simultaneously. This infection usually occurs in the month of July. It is caused by the fungus Septoria cornicola. In certain cases, if the berries are also infected they get discolored.

Stem Diseases
Other than the stem and branches being infected due the diseases that spread from the leaves and flowers, there are other diseases that affect these parts. Basal trunk canker is a major problem of the tree trunk caused by the fungus Phytophthora cactorum. However, for the fungus to infect the base of the trunk, there should be a prior physical injury to the area. Older trees may also be occasionally affected by mistletoe.

Root Diseases
The seedlings of this tree may suffer from root infection caused by the Pythium fungus species. It usually kills the seedlings before they reach the woody stage. Those that survive suffer from twig die-back, discoloration and scorching of the margins of the leaves. Roots of mature dogwood trees may also suffer from infection caused by the fungus Clitocybe tabescens.

Disease Control

While for some stem and root diseases physical injury is the main concern, those diseases, specially of the flower and leaves can be controlled by a regular spray of fungicides. The spread of these diseases usually depend upon the humidity conditions that is well out of our control. Hence, using fungicides is the only way of ensuring healthy growth of the trees.

Other Dogwood Tree Problems

If a dogwood tree is planted too deep into the soil, then the roots would suffocate. Always plant at the same depth as in the nursery. Over-application of fertilizers over the root area can kill the roots. It is important to carry out a soil test to determine the nutrients that the soil is deficient in. Adding too much nitrogen through fertilizers can reduce flowering of these trees.

Mechanical and chemical injuries are other common dogwood tree problems. Mechanical injuries are most commonly caused by lawn mowers or string trimmers. In case of a mechanical injury, remove the dead tissue with your fingers. Do not pull off the bark or any other intact part of the tree around the infected area. Avoid using wood paints or tools to scribe or clean the wound. Dogwood trees are very susceptible to certain common herbicides. Never spray herbicides to young sprouts or the root base with herbicides.

Dogwoods are beautiful trees that are a sight to behold when in full bloom. To ensure that these trees continue to enhance the aesthetic aspect of your garden, learn about the various dogwood tree diseases and problems and provide specific treatment for each disease.