At their best, tree diseases result in yield losses and poor aesthetics, and at their worst, the death of a tree. Furthermore, poor health may lead to falling limbs and branches that present a severe risk for you and your property. It’s important to recognize potential diseases and cure them to the best of your ability to avoid these risks.
Diseases are often species-specific, seasonal, and regional, so understanding the most common tree problems can help determine which ailment affects your trees.
Disease and infestation vary across the board, but several conditions are most common in yards, cityscapes, and public lands.
Most common among trees and shrubs, Anthracnose is a fungal condition that attacks fruits and flowers, leaves, twigs, and even branches. Symptoms of Anthracnose vary by the pathogen and host species but tend to impact dogwood and sycamore trees more than other varieties.
To identify Anthracnose, look for premature lead defoliation and witch’s bloom—an abnormality that causes shoots to populate a single spot densely. Applying fungicide is the easiest way to remedy this condition, but this process looks slightly different depending on the tree species.
For sycamores, apply fungicide at the bud opening or inject it systemically. For dogwoods, use fungicide near the bud break and reapply it throughout the growing season.
Diplodia tip blight is a disease that attacks numerous types of pines, such as Austrian, red, and scots pine. Typically, the condition develops at the pine base and continues upward until it kills shoots and causes half elongated needles.
Should you have trouble seeing its symptoms, look for black fruiting structures forming on the cones and between needles. To treat diplodia tip blight, apply fungicide containing thiophanate-methyl at the bud swell while using appropriate sanitation and pruning technique.
Similar to diplodia tip blight, dothistroma needle blight is a fungal disease that stunts growth in young pines and causes defoliation in mature trees. This condition affects roughly 35 pine species in North America and is known to show yellow and tan bands on needles and needle dieback.
A fungicide containing mancozeb and copper hydroxide must be applied at bud break to treat this condition effectively.
Apple scab or scab-like lesions on the leaves of a crabapple tree is a disease that causes premature defoliation. Notably, this condition only affects crabapples and usually occurs early in the season.
Apple scab is predominantly aesthetic but can lead to lengthy setbacks in a tree’s health if not managed accordingly. To treat this ailment, fungicidal agents that consist of ingredients like fenarimol should be applied at the end of the bud.
Coupled with apple scab, this condition affects crabapples and other rosaceous plants such as hawthorn and eastern redcedar. Cedar rusts affect some species more than others but are easily identifiable by the orange and rust-colored blemishes left on leaves in springtime.
Like other conditions, cedar rusts can be managed by applying fungicide on a host tree’s bud break in seven to ten-day intervals.
Transported by a tiny plant hopper insect, lethal yellow is a bacterial disease that affects Florida and Texas palm trees.
Symptoms of this condition include yellowing of a palm’s foliage, premature fruit dropping, and flower death. Instead of fungicide, lethal yellow must be treated with an antibiotic injection containing oxytetracycline hydrochloride in the trunk.
Caused by fungal pathogens, powdery mildew grows on the surface of trees while producing fungal spores and threads.
As the infection progresses, the fungus attacks young tissue and causes leaves and flowers to distort, dry up, and brown. Fungicide should be applied to treat this condition, but the easiest way to avoid powdery mildew is by planting tree varieties resistant to the pathogen.
Oak wilt is a systemic fungal disease that often results in tree death. This condition is most common throughout South Carolina, Pennsylvania, New York, Texas, and Minnesota.
This condition causes premature defoliation, leaf wilt and discoloration, and vascular discoloration. Infected trees must be injected with fungicide throughout the growing season, but red oaks cannot be treated as trees in the white oak family can.
Common among Indian hawthorn, red tip photinia, loquat, and pear cultivars, photinia leaf spot is a condition that affects tree species in the Southern US. Symptoms of photinia leaf spot include small, circular red spots on the stems, leaves, and fruit of these trees.
Spots typically expand to become considerably sized blotches with gray centers. Fungicide should be applied at bud break, but the easiest way to avoid this condition is by purchasing sanitized, disease-free plants.
Dutch elm disease only affects elm trees across the US, unlike competing fungal diseases. The disease is most often carried by US bark beetles which feed on the branches and twigs of healthy trees—thereby infecting them.
Recognizing dutch elm disease early on is tricky, so it’s important to check an elm tree’s upper branches for yellowing, wilting, and browning. Additionally, these symptoms tend to start in a condensed area then spread to nearby branches and the tree at large.
Symptoms are further hard to identify because lab tests are needed to receive accurate results. Fungicide injections should be made to prolong the life of an elm, but there is currently no cure for the disease, and most trees die within a few years after infection.
Understanding the most common tree diseases is just the first step towards recognizing symptoms and treating ailments as fast as possible but can make the difference between tree death and survival.
Treating these diseases as quickly as possible isn’t easy, but it is the best way to maintain the aesthetics of a tree while protecting others and their property from falling trees and limbs.