Let’s take a look at the some of the various common tree diseases in Michigan that we treat here at Safari Tree.
Cankers are dead areas of bark that are located on the trunk, branches and/or twigs of a tree. Cankers are caused by numerous species of fungi that infect stressed or wounded trees, killing the living bark. Infected trees are characterized by discoloration, oozing sap, and sunken areas, cankers are some of the most difficult disease problems to manage. The best canker management is preventative. Keeping trees healthy and stress-free will reduce the risk of infection considerably. If a tree does have canker, the entire infected area should be removed, sterilizing the pruning tools between cuts. Pruning should not be done during wet or humid weather to minimize the spread of disease. Avoid wounding trees when doing yard work or mowing as this leaves the tree much more vulnerable to infection.
Oak Wilt Fungus
Oak wilt is a lethal disease caused by a fungus, which invades and disables the water-conducting system in white, red and other oak tree species. Different species of oaks vary in susceptibility to the disease. Red oaks typically die within 4 to 6 weeks of initial symptom development, while white oaks may survive or take 1 to 6 months to defoliate and die. Oak wilt is most often spread via root grafts between interconnected and grafted root systems. Root graft disruption and fungicidal treatments aid in preventing the spread of oak wilt.
How does oak wilt spread? Sap feeding beetles are the most common insect vector, but bark beetles have also been reported as a vector. They feed on fungal spore mats that form between the bark and the wood of the oak and carry oak wilt spores to wounds on uninfected trees. In the northern range, overland transmission takes place throughout the spring and early summer, while in the south it can occur any time of the year. Because beetle vectors (carriers) are attracted to fresh wounds it is important not to prune oaks during the season that spore mats are present. In the north, prune only during the dormant season; in the south, pruning is recommended only during December and January. Pruning paint is only necessary for wounds occurring during the growing season in the north, however, in the south, seal all wounds regardless of the season.
Pine Needle Scale and Soft Scale Diseases
Pine needle scale is a hard or armored scale – scales are aphid-like insects that produce a hard waxy shell to protect themselves from predators and environmental conditions. Pine needle scale females resemble legless bumps and damage plants with their sucking mouthparts. The smaller male scales have wings and while in the nymph stage also feed on plants. Female scale continues to feed as they produce over a hundred eggs under their shell. The mater female dies, but the eggs survive the winter under the protection of the shell.
In the spring and summer of the following year, the eggs hatch into an immature stage called the “crawler” stage. The crawlers, also called nymphs, move out from under the shell and find a new location on which to feed. As they settle, they begin to produce their hard shell. Pine needle scales feed primarily on the needles of trees. Unlike soft scales and aphids, which feed on the circulatory system of the tree, armored scales feed on the contents of individual cells. Since they destroy cells, they can cause significant dieback of infected stem tissues and in severe infestations, even the death of trees.
Symptoms of pine needle scale may include some or all of the following: thin sparse needles, white spots on needles, white waxy scale coverings, and extensive needle and branch death.
Soft scale, similar to pine needle scales, are also aphid-like creatures that feed on the sap of trees. Young scales, referred to as crawlers, feed on the foliage whereas adult scales feed directly on the branches. All soft scales feed on the sap contents of the tree, which means they are susceptible to systemic insecticides. Dormant oils and contact insecticides can also be effective, but only if they are applied to the unprotected crawler stage of the scale. Thus the timing of contact insecticide applications is critical to effective control.
Symptoms of soft scale may include some or all of the following: tip die back in branches, stunted chlorotic foliage, premature leaf drop and branch dieback, honeydew secretions on the tops of branches, and also black sooty mold growth on the honeydew.
Continuing with our common tree diseases series, one of the most common fungal diseases are anthracnose, which can infect ash, oak, maple, and sycamore trees, as well as other tree species. The fungus causes dead blotches on the leaves that disrupt photosynthesis and transpiration with can eventually lead up to spring leaf drop. As leaves mature, they become less susceptible to the pathogen. Repeat defoliation by anthracnose can directly impact the tree’s overall health and it is important to stop this disease before it begins to spread.
The life cycle of this particular fungus is noticeable to the naked eye. In the late fall and early spring months, black pimple like bumps will develop on infected leaves from the previous year. Spores are then released and blown by wind or even splashed by rain to nearby trees, causing the spread of the fungus rapidly. The primary infections produce secondary spores which affect other leaves and fruit. The secondary infections of this disease can and will continue throughout the growing season during wet periods of time.
The next more common tree disease is the Rhizosphaera Needle Cast, which is a foliage disease of spruce trees. This disease can cause significant damage to trees growing outside of their native range. Older, inner needles show symptoms first, and as the disease progresses, newer needles will begin showing symptoms as well. Infected needles first appear mottled or speckled with dull yellowish blotches, and as the disease progresses, the needles will begin to turn brown to purplish brown. The needles then drop (cast) anywhere from 3 to 15 months after the infection has occurred and also depends on the type of spruce species infected. Branches begin dying if they are defoliated in 3-4 consecutive years, though larger trees rarely die and succumb to this disease, however they may become so disfigured that they lose all of their ornamental value.
Are your trees under threat? For healthy trees, contact one of our Certified Arborists today to learn more about our preventative treatment plans.