Disease pathogens are always lurking about, searching for a vulnerable entry point into a tree or shrub.
That is why excellent health is a plant’s first, strongest line of defense against attack from a disease. It limits the plant's vulnerabilities. The perfect analogy is a strong human immune system versus a weak immune system. You will be less susceptible to sickness with a strong immune system.
Most tree diseases are caused by fungi, though there are some caused by a virus or bacteria.
If you know your tree or shrub has a disease, we recommend the following approach:
- Identify the disease. Are there options to fix/suppress the disease? Or will the plant have to be removed?
- Determine why the disease occurred. What are the underlying health issues that led to this problem?
- Fix the underlying issues since this is probably why the disease occurred in the first place. Even if you have to remove the plant, this may save others from a similar fate.
- If it is possible to fix/suppress the disease, are there organic options you can use to do so? There are plenty of knock-down, drag-out chemicals that will nuke the landscape. Why cause harm when there are environmentally-responsible solutions available on the market?
- Continue practices that maintain and increase the health of your trees and shrubs, once the disease has been controlled or suppressed.
This approach to treating disease may be more difficult, but in the long run it is the better option because it creates longer-lasting solutions that have less negative impact on our planet.
In case you are interested, here is some information on the common diseases in this area:
Anthracnose:(Oak Anthracnose, Dogwood Spot Anthracnose, etc.) Anthracnose is a common term used to describe a fungal pathogen that affects various hardwood trees and ornamental plants. Anthracnose causes leaf, fruit, and twig lesions, as well as irregular dead areas on leaf margins and between leaf veins. Oak, sycamore, ash, elm, maple, and dogwood are all susceptible to anthracnose.
Tip Blights:(Kabatina Tip Blight, Phomopsis Tip Blight, Sclerophoma Tip Blight, Diplodia Tip Blight) These fungal diseases affect a wide variety of coniferous evergreens. Moist conditions and shady sites make the ideal setting for tip blight to establish itself then spread. As the tip blight spreads, the tips of the plant begin to fade from green to yellow and then eventually become brown. Infection will then spread and eventually kill the infected individual branch or stem. The entire plant may die depending on size of the plant, site conditions, and existing health of the plant.
Leaf Spots:(Cherry Leaf Spot, Entomosporium Leaf Spot, Septoria Leaf Spot, Guignardia Leaf Spot, Algal Leaf Spot, Black Spot) Leaf spots are fungal diseases that primarily affect the foliage on the plant. The various types of leaf spots are host-specific and generally only affect certain plants located within related plant families, genus, or species. This fungus creates leaf spots on the leaf that are usually uniform in shape. Leaf spots impede vital leaf functions and cause premature leaf drop. This can weaken the plant, which usually predisposes the plant to other ailments or attack by insects.
Rusts:(Cedar-Quince Rust, Cedar-Apple Rust, Cedar-Hawthorn Rust) Rust is a fungus that attacks many portions of a plant. Several consecutive years of rust infection will cause plant deformations. Rust spores are visible as an orange powder on plant surfaces. Wet, moist conditions are ideal for rust infections.
Slime Flux:This is a condition that is also known as Wetwood or Bacterial Wetwood. It is caused by a bacterium that enters the bark or root system through a wound. The fluxing, or weeping, is the tree protecting itself from the damaging decay bacterium. If this fluxing does not occur, the bacteria will grow, create cavities, and kill the cells that create bark growth. This weakens, stresses, and eventually kills the tree.
Seiridium Canker:Seiridium Canker is a very aggressive and damaging fungal disease pathogen that is found throughout the world. Seiridium Canker affects plants within the cypress family. This disease is commonly called Cypress Canker. It often attacks Leyland cypress in the Southeast. Arborvitae, italian cypress, and juniper are also susceptible to Seiridium Canker.
Passalora Needle Blight:This is a serious disease that affects a wide range of coniferous plants. The name of this needle blight has changed several times since its discovery. It used to be called Cercospora, Cercosporidium, and Asperisporium. Passalora Needle Blight begins on the foliage located within the interior of the plant eventually spreads throughout the entire canopy. Juniper, leyland cypress, arizona cypress, bald cypress, cedar, arborvitae, and cryptomeria are all vulnerable to Passalora Needle Blight.
Powdery Mildew:Powdery Mildew is a category of fungi. It is one of the most common and recognizable diseases of ornamental plants in the Southeast. It looks like a white, powdery substance on the foliage of the plant. There are many different types of Powdery Mildew that affect specific species, such as dogwood and lilac. This disease is not usually fatal but will cause plant damage if left untreated.
Phytopthora:Phytopthora is derived from a Greek word meaning “plant destroyer.” It is a very harmful pathogen that causes numerous blights, root rots, crown rots, and stem rots on woody plants and trees. Phytopthora thrives in poor soil conditions that are uninhabitable for beneficial soil microbes, especially where there is too much water saturation. When these conditions exist, the plant is likely already stressed, which is an ideal time for Phytopthora to move in and cause damage.
Bleeding Canker:There are many different species of Phytopthora that cause harm to plants. There is one in particular that is responsible for Bleeding Canker on trees. This species of Phytopthora is P. cactorum. It is a soil-borne fungus that enters plants through wounds, injuries, or weakened areas. It is easy to spot Phytopthora Bleeding Canker on the trunk of the host tree. The infection site will have lesions that will ooze or “bleed” a black liquid. The wood behind the infection site may be stained and reddish-brown in color.
Bacterial Fire Blight:This is a bacterial disease that is thought to have originated in North America. It is one of the oldest known diseases in the world. The infection makes the infected parts look blackened, shriveled, and cracked as though damaged by fire. There are a number of species that are susceptible to Bacterial Fire Blight, but the rose family is most susceptible.
Bacterial Leaf Scorch:As the name suggests, bacteria cause this chronic disease known as Bacterial Leaf Scorch. The bacteria are introduced into the plant by xylem-feeding insects, such as leafhoppers. The bacteria colonize within the xylem and clog water-conducting plant tissue. This causes a decline in health and ultimately death. Sycamore, elm, maple, and a number of other species are susceptible to Bacterial Leaf Scorch.
Dutch Elm Disease:Dutch Elm Disease is a fungus that primarily affects elm trees. Dutch Elm Disease first appeared in North America in the early 20th century and virtually destroyed the majority of America’s elms. This disease enters the tree via bark beetles. In an attempt to keep the fungus from spreading, the tree responds by plugging its own xylem tissue. Water and nutrients cannot move within the tree and it eventually dies. In short, the disease causes the tree to kill itself.