Dogwood trees, scientifically known as the Cornus florida, are great for adding color to one’s garden and landscape. They are loved by all due to the beautiful flowers that they bear. However, they are susceptible to certain pathogens and other problems.
These trees are easy to grow and are admired for their spectacular explosion of flowers that come in red, white and pink every spring. In fall, bright red/purple leaves and fruits enhance the beauty of the tree. As the dogwood trees are small even when mature, these are the perfect choice for those who love gardening, but have space problem. The tree grows up to 20-30 feet and its spread can also be about 25-30 feet. Due to its year-round appeal and small size, dogwood tree is one of the most sought after ornamental plants in Northern America. The flower of the dogwood tree is the state flower of North Carolina. Despite the ease with which they grow, there are a number of dogwood tree diseases and troubles that need to be taken care of.
Dogwood Tree Diseases
Flower and Leaf Diseases
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.
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. This may further kill the entire leaf. It spreads from leaves to the twigs, down to the main stem, forming cankers on it. Trunk sprouts occur in the advanced stage.
Septoria Leaf Spot:
In septoria leaf spot, 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 leaf spot 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. Sooty molds (Ascomycete fungi which suck sap from their host dogwood tree) can weaken or even kill the tree if not treated promptly.
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.
The dogwood borer is a pest which in its larval or caterpillar stage eats terminal shoots or burrows beneath the bark and destroys the healthy tissues. This inhibits the flow of the sap and slows the growth of the plant. Heavy infestation can kill the plant.
Powdery mildew (a common fungal disease) may destroy the beauty (appearance) of the dogwood tree. The tree may produce less fruits when attacked by the fungus
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. ‘Root rot’ due to poor drainage can destroy the health of the tree.
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. Killing the pests that secrete the honeydew on the plant helps get rid of sooty molds because the fungi cannot grow without the honeydew. Various formulations of neem oil work great for pests. Neem oil is one of the most sought after pesticides. It is a popular and effective insecticide, fungicide and miticide too. You may control fungus diseases of dogwood tree with the help of neem oil. Dogwood tree pruning promotes reduction of certain diseases; as more air circulates within the canopy and the tree receives more sunlight.
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 provide specific treatment for each disease.