PHC Update - Southwest Michigan 2024
Beaudry Arbor Care, LLC
Below you will find information on some of the most pressing challenges that professionals in the tree care community are actively working to meet in 2024. Experts at MSU and the MDNR are working with local Arborists to ensure the latest research, and treatment information is passed on to a wider audience. We created this page on our website to help share this information, and to educate our clients on how it impacts their landscape trees and shrubs. Please feel free to reach out to us with any questions or concerns you may have.
Oak Wilt (B. fagacearum): Oak wilt refers to a fungus called Bretziella fagacearum that affects the Fagaceae family of trees which includes beeches, chestnuts and oaks. This fungus causes mortality in members of the red oak family (Red, Black, Pin,) within a matter of weeks after infection. White oaks can also be killed from this disease, though it is less common due to a difference in their vascular system that allows them to better contain the spread of the fungus. Oak wilt spreads by two main pathways. The fungus can infect an oak tree via root grafts from other neighboring infected trees, or by an insect vector known as a picnic beetle. In the spring, and early summer the fungus produces a sweet smelling fungal mat on previously infected trees. The beetles are attracted to the sweet smell of the fungal mat. Once the beetles come in contact with the mat, they travel to other oak trees - carrying the fungal spores on their bodies. If a tree nearby has open wounds caused from improper pruning, or storm damage - the beetle will land to feed on the wound, depositing the oak wilt spores as they feed. The spores will enter the wound, and infect the tree. The disease affects the vascular system of the tree, plugging the water conducting vessels in the sapwood, restricting or eliminating the tree’s ability to transport water to the canopy.This causes the leaves to turn brown along the margins, curl, and fall to the ground.
Once infected, the fungus can travel through the root system into neighboring, healthy oaks. If left untreated the disease can travel through entire stands of red oaks because their roots graft, or grow together over time - which facilitates the spread. Infected trees cannot be treated, and specific methods should be followed when removing trees that died from oak wilt. Surrounding trees can be treated, or root grafts can be severed to eliminate the ability for the fungus to spread.
Please reach out to Beaudry Arbor Care if you or someone you know sees the leaves of their oak tree turning, and falling in the summer. Also, please help us by spreading this information to friends and family to ensure that no one is having their oak trees pruned from the end of March through October. Open wounds attract picnic beetles that could be carrying fungal spores.
*Oak wilt symptoms *Oak wilt spore mats *Oak wilt infection
Apple Scab: Does your Apple or Crabapple tree lose its leaves mid-summer? Do your Apples have black spots? It is possible that your tree is suffering from Apple scab, the most common disease found in apple, crabapple and pear trees. The intensity, and spread of the fungus depends largely on the weather in the spring. The fungus overwinters on fallen diseased leaves, and releases spores in the spring. Those spores are carried by wind, splashing rain, and irrigation. Once they are on the leaves, they need moisture to survive and continue to spread; which is why wet springs tend to cause an uptick in the severity of apple scab. This fungus is preventable in most cases, and it can be very helpful for homeowners to remove the leaves after they fall to eliminate those infected leaves.
*Apple Scab fungus on fruit *Apple Scab fungus on leaves
White Pine Weevil: This insect is considered the most destructive pest of the Eastern White Pine in North America by the MDNR. This insect causes damage by killing the primary leader of the Eastern White Pine, Colorado Blue Spruce, Norway Spruce, and Serbian Spruces. Scots, Red, Jack, and Austrian Pines can also be damaged by this insect. This pest is attracted to these trees when they are young, and less than 20 feet in height. They overwinter in the leaf litter near host trees, and travel up the tree in March-April where they feed on the terminal leader and lay their eggs. Once the eggs hatch, the larvae feed on the nutrient rich leader, eventually girdling and killing it. Once the damage is done, the leader turns brown and curls in a distinctive shepherd's crook shape. With the terminal leader dead, multiple other branches will grow up in its place, which creates a multi-stemmed, bush-like structure that stunts the tree’s growth, and leads to future structural issues. If you have new spruce or pine plantings in your yard that are less than 20 ft high, and want to ensure their overall health and longevity please feel free to reach out.
*Adult White Pine Weevil *Weevil damage to Norway Spruce
Spongy Moth: You may be familiar with this insect, or know someone who has struggled with it in the past. The Spongy Moth is an invasive insect that is native to Europe. This insect is most destructive in their larval stage (caterpillars) as they feed on the crown foliage of many different hardwood trees; their favored host being all varieties of oak trees. In Michigan the eggs hatch from brown fuzzy egg masses on the trunk of the tree (remove them if you see them!) in early to mid-May and feed on the foliage of their host tree for 6-8 weeks. The young larvae feed during the day. As they grow they begin to feed at night, and move down the trunk during the day to hide from predators in the bark furrows. The larvae can defoliate 60-90% of their host tree’s foliage depending on their concentration. The loss of foliage in the spring will weaken a healthy tree, and at times can cause mortality in unhealthy host trees. Once defoliated, the tree must spend precious energy to re-leaf - in order to make and store enough photosynthate for the following spring. Not only do they defoliate trees, but they also can make a mess of decks, roofs, hot tubs, and other outdoor areas because of the frass that they excrete while feeding in the tree. This can be a major problem for some, and it is cases like this where treatment may be recommended. Outbreaks of this pest usually last 2-3 seasons as they are naturally killed by a bacteria (Bacillus thuringiensis) that spreads through the population in areas of high concentration. Please feel free to reach out if this insect is causing issues around your home.
*Spongy Moth Female Adults w/ Egg Masses *Spongy Moth Larvae
Box Tree Moth: This insect is an invasive landscape pest that has now been found in 12 different counties in Southwest Michigan since 2021. It is native to China, Korea and other parts of Asia and their primary host plant is the boxwood shrub. Beloved for its year round color, boxwoods are an extremely common landscape shrub. Experts at MSU, MDARD, and the MDNR are working to develop quarantines for this insect, as well as the Spotted Lanternfly which has also now been found in Michigan. Like the Spongy Moth, this insect does the majority of its damage in the larval stage, feeding on the foliage of boxwoods. Once defoliated, the larvae continue on to consume the bark which girdles and kills branches, eventually the shrub itself. As the larvae feed they spin silken webs to hold leaves together in order to create protected areas. This insect produces multiple generations per year. Pupation and reproduction take place throughout the spring and summer. Please be on the lookout, and keen an eye on your boxwood shrubs throughout the year. Early detection is vital to ensure this pest does not spread throughout the Great Lakes region and beyond. Please reach out to us, or call the Michigan Department of Natural Resources at 1-800-292-7800 if you see this invasive insect.
*Box Tree Moth Larvae on boxwood *Adult Box Tree Moth
Phytophthora Root Rot: A pathogen that is found in most soils, phytophthora favors wet conditions for reproduction and sustainability. There has been a noticeable uptick in root rot cases found in landscape trees and shrubs here in Southwest Michigan. Experts attribute this rise to prolonged periods of rain due to climate change, as well as improper irrigation, and planting techniques. Symptoms of Phytophthora, and other root rot pathogens can be mistaken for plants that are suffering from drought stress. This leads homeowners to think their tree/shrub needs more water when in fact more water only hastens the tree/plant’s decline. Leaves will turn dull green, yellow, or in some cases red or purple. Trees and shrubs may decline over a period of years, or may be killed in a single season. Established trees are still very much affected by this pathogen; it is believed to be one of the major contributors to the increase of Oak Decline here in Michigan. If you are worried your trees or shrubs may be experiencing a form of root rot, take a soil knife or garden shovel and dig up a small portion of the roots. If the roots are brown instead of a healthy white color, and the outer epidermis of the root peels off easily, there is a possibility that root rot could be present.
*Healthy roots vs damaged roots (root rot)
*Phytopththora in Rhododendron
Pine Bark Beetle (PBB): Another pest troubling our region, the pine bark beetle is causing issues for homeowners, municipalities, and Michigan foresters.The name refers to several different species of bark beetle, many of which are found here in Southwest Michigan. These pests, like many others, are considered secondary pests; meaning they are not normally the primary cause for the decline of a tree. These insects are opportunistic, and are attracted to the pheromones released by stressed trees. Symptoms of PBB infestation commonly manifest as thinning canopy coverage, needle loss, and crown dieback. Nearly all species of pine are susceptible to PBB attacks. The adults lay eggs in clusters on the bark of host trees, and as the larvae hatch, they burrow into the tree and feed on the nutrient rich phloem and cambium inside. The act of burrowing into the tree leaves BB sized holes in the bark, and the holes will have a distinct pitch tube just around the entrance - a defense reaction from the tree. As the larvae feed, they create distinct galleries under the bark, and can be seen in the photo below. Once mature, they pupate and exit the tree in search of another suitable host. The expansive feeding of the larvae girdles, and eventually kills the host tree. This is a difficult pest to manage as infected trees must be removed and their brush destroyed; then the bark of remaining healthy trees should be treated to prevent further infestation.
*PBB entrance holes *PBB galleries
Spotted Lanternfly (SLF): An invasive sap-feeding plant hopper, native to China, India and Vietnam, the Spotted Lanternfly has experts on high alert in the eastern United States, and Great Lakes region. Dead adults were found in two areas of southern Michigan in 2020, and a colony of live SLF were found in Oakland County in 2022. SLF is a species of sap sucking insect, able to pierce the bark and feed on the sap of over 70 different species of trees, shrubs, and vines. This insect can feed on a variety of hardwood trees including black walnut, maples, willows, and poplars which is cause for concern here in our region. Fortunately, SLF is not a pest that is likely to kill a host tree, though it can severely weaken younger vulnerable trees and shrubs. If you observe this pest anywhere, in your travels, or at home please immediately contact the Michigan Department of Natural Resources, call or text 1-800-292-7800.
*SLF adults *SLF larva
Beech Leaf Disease (BLD): In 2022 beech leaf disease was found in Michigan for the first time in St. Clair County, and shortly after was discovered in Oakland and Wayne counties. This disease is not caused by an insect, fungi, or bacterium; BLD is actually caused by a nematode - a microscopic worm-like organism that is found in virtually all soil. Many nematodes are beneficial, however some can cause diseases. This nematode attacks the buds of beech trees, infecting them before the tree produces leaves. The nematodes then feed on the inside of the leaf surface, causing the unique dark banding shown in the picture below. In addition to the dark bands, leaves will appear to thicken, curl, and prematurely fall. Nematodes have no means of traveling great distances on their own, and it is hypothesized that large wind events are causing this nematode to spread. Foresters and researchers with MSU and the DNR are very concerned about this nematode spreading to our Beech forests in northern and western Michigan. This nematode also affects the European and Tri-Color Beeches, common and prized landscape trees. There are some BLD look-alikes that cause similar symptoms like the Beech leaf curl aphid; however, the dark banding between leaf veins is a dead BLD giveaway. Please contact us if you think you may have a Beech tree that is suffering from BLD.
*Cupping & curling of leaves caused by BLD
*Interveinal banding
Source Material:
Deborah McCullough - Professor, Department of Entomology, Michigan State University
fs.usda.gov/managing-land/invasive-species
ISA Michigan - Arborcon 2024
www.beaudryarborcare.com - Zachary Beaudry
https://ipm.ucanr.edu/PMG/PESTNOTES/pn7421.html
Diseases of Trees and Shrubs, Second Edition: Wayne A. Sinclair and Howard H. Lyon
Arborist News Volume 23 Number 3 June 2023: Planning for Climate-Ready Tree Species: Daniel C. Staley
