Pests and Diseases - Irrigation, Landscape Lighting, Tree Services
tar stain disease - plant disease and pest image - cropped

Identifying Pests and Diseases

The following pathogens are a few of the most common that we see and actively look for. The key to positive plant outcomes is early detection, which is why our plant health care services include regular inspections. Sometimes early detection is complicated by secondary infections, environmental stresses, or overlapping symptoms.

Click on each pest or disease to learn more about it. If you have specific concerns or need help identifying the source of your plant’s symptoms contact us today.

beech bark disease
Image credit: Angile (Own work) [CC0], via Wikimedia Commons
Status: Established in Michigan - particularly eastern U.P., and northern lower.

At risk: Beech species

Beech bark disease is a fungal infection spread by a scale insect. At least two fungal species cause Beech Bark Disease. Introduced via European nursery stock in the late 1800s. It was first detected in Michigan in the year 2000, and the condition is indicated by a fuzzy white coating on the tree's bark and branches.

Secondary infections result because the blight attracts aphids that excrete a honeydew. This honeydew attracts a sooty mold fungus - which does not harm the tree.

Beech Bark Disease can be treated with injections in the late summer with good prognosis.

For additional information on Beech Bark Disease, consult resources at the Michigan State University Extension.

Image credit: USDA-APHIS [Public domain], via Wikimedia Commons

Status: Established in Michigan's Lower Peninsula

At risk: Ash trees

Discovered in Michigan in May 2002, this devastating insect likely arrived half a decade prior.

Initial symptoms include yellowing and thinning of leaves. As is common with other borers, branches at the top begin to dieback first, progressing downward. D-shaped holes about 1/8" in diameter are another sign.

The most destructive part of this insects life-cycle is when the larvae hatch and burrow back and forth under the bark. Ash trees may die within two to three years after they become infested

We can treat this threat anytime throughout the growing season with trunk injections over a two-year course. The canopy of the affected tree needs to be two-thirds foliated or better for the injections to work

For more information, consult the Tree Doctor's resources at the MSU Extension.

Hemlock Woolly Adelgid
Image Credit: Chris Evans, University of Illinois,
Status: Watch List - Detected in Michigan

At risk: Hemlocks

First reported in the eastern US in 1951, this devastating insect has been located along the Lake Michigan shoreline. Native to Asia, these small aphid-like insects decimate the popular and vital hemlock species. These insects feed by sucking sap from the twigs at the base of a hemlock's needles. Since every HWA is a female with asexual reproduction, populations can grow very quickly.

Trees can survive four or five years infestation before mortality, but left untreated results in a mortality of 95% of hemlock populations.

Identification is key to this pest. First, some observers mistake a fir, pine, or spruce as a hemlock. Second, Elongated Hemlock Scale is sometimes mistaken for HWA though it can be differentiated by the fact that HWA is located at the base of the needles while scale feeds on the needle surface itself.

As always, the MSU Extension offers more resources on hemlock woolly adelgid and other pests too.
Oak Wilt leaf
Oak Wilt
Image Credit: Paul A. Mistretta [USDA Forest Service,]
Status: Established in Michigan

At risk: Primarily red oaks (northern red, black oak, and pin oak). Red oaks often die within a few weeks - white oaks are more resistant.

Like Dutch Elm Disease, Oak Wilt is caused by a vascular wilt fungus that is transmitted by insects and root grafts to nearby trees. Death is typical within several months. Symptoms first appear at the leaf tips, moving toward the base of the leaves. Leaves may appear wilted or discolored, and symptoms are often misdiagnosed as other conditions.

Pruning or otherwise injuring oaks from April 15 to Nov 15 (varys depending on the weather) makes healthy oaks susceptible to infection from diseased trees. Don't prune oaks if the temperatures are going to be above 45 degrees no matter what time of year.

Among the many reasons we don't use climbing spikes, the spread of oak wilt is among them. Once a tree is infected, it becomes systemic for the whole tree - hence the spread via root grafts to nearby trees.

Read more at's 2017 press release or the MSU Extension's Tree Doctor.
Needlecast [Insert - Fruiting bodies]
Image credits: Main photo: Bruce Watt, University of Main, Insert: Michael Kangas, NDSU - North Dakota Forest Service |
Status: Established in Michigan

At risk: Conifers, primarily spruce; Colorado blue spruce is most susceptible as are similar species such as Black Hills.

Needlecast is caused by a fungal infection that can occur from April through October, though generally most common in the early spring. It can be confused with natural needle drop, certain mite or scale damages, and various environmental causes including "winter burn."

Spring infection usually affects last year's needles, not the new growth. Further complicating diagnosis is a predisposition to secondary infections. Needles on lower branches are most commonly affected because they remain damp the longest. Both the lack of evaporating sun and adequate airflow can increase the risk of fungal infection.

Needles will become yellow, and then purplish-brown before casting (falling off). The infected needles are identified by fruiting bodies of the fungus protruding from the stomata of the needles (the holes in the needle designed for gas exchange).

Learn More about Rhizosphaera needlecast with The Plant Doctor

Pine root collar weevil and damaged trees
Adult Weevil
Image credit: [insert] and infested trees. Image Credit: Jennifer C. Giron Duque, University of Puerto Rico [insert], Steven Katovich, USDA Forest Service,[]
Status: Established in Michigan

At risk: Pines - especially Scots, red, jack, Austrian, and eastern white

Weevils have a two-year lifecycle to reach adulthood. As adults, they continue to feed and reproduce for an additional two years - sometimes resulting in three generations of weevils attacking the same tree.

Damage is caused primarily by larvae feeding below ground-level, secondarily by adults - which feed on the bark of live trees. Among the more notable symptoms: fully-girdled trees will fade entirely from green to yellow to red.

Additional recommended reading on the Pine Root Collar Weevil is available from the MSU Extension.

Pine wilt victim with nematode insert photo
Image credit: Nematode insert - Natural Resources Canada; Tree Mateinsixtynine [GFDL or CC BY-SA 3.0], via Wikimedia Commons
Status: Established in Michigan

At risk: Primarily Scotch (Scots) Pine, additionally Austrian, Mugo, Jack, and occasionally white pine

Pine wilt starts in individual twigs and branches, turning needles grayish-green, then brown. Caused by Pine Wilt Nematode (Bursaphelenchus xylophilus), this microscopic worm-like organism is transferred by the Pine Sawyer Beetle. When concentrations of the nematode increase, the vascular system of the tree becomes clogged, causing the host to wilt and often die within just a few weeks.

As the wilt progresses, secondary attacks and infections often include bark beetles and blue strain fungus. Symptoms can mimic other blight, weevil, and beetle conditions.

Because of the popularity of Scots pine in northern Michigan landscapes and a tendency to plant in monoculture stands this infection has disastrous potential.

More information on Pine Wilt is available from the Tree Doctor.

Adult twolined chestnut borer
Adult Beetle
Image Credit: Robert A. Haack, [USDA Forest Service,]
Status: Established in Michigan

At risk: Chestnuts, Oaks, Beech

Native to North America, these flat-headed beetles bore D-shaped holes that typically appear first in the upper branches of stressed trees.

This pest bears many similarities to the Emerald Ash Borer (EAB). Adults emerge and feed in May and June, breeding afterward. The larva emerges and feeds June through August. Starting in mid-July, the upper branches become discolored, stunted, and even die back.

Armillaria root rot has been associated in conjunction with TLCB. Two-Lined Chestnut Borers are also confused with oak wilt and other stress/decline conditions.

Treating Pests and Diseases

Commonly recommended (and outdated) pest and disease control measures often include soil drenches. Soil drenches waste a lot of product while killing beneficial fungi (mycelia), microbes, and insects in the soil.

We don’t spray trees unless we absolutely have to. Spraying can be one of the most wasteful delivery methods, which also increases environmental impact. Soil drenches are likewise not a preferred method unless the tree is too small for direct injection.

When it comes to treating pests and diseases within your landscape the right way, our plant health care services use the very best techniques, like the Arbor-Jet system. We use these techniques to make sure we’re only using the smallest dosages possible, never wasting any.

Before treating any trees, it’s essential to get to the root cause. Plants become susceptible to infection when they’re not healthy or are environmentally stressed. Let’s treat the problem (which often is in the roots and soil), not just the pest symptom. Creating a healthy environment (sometimes utilizing our Air Spade) reduces the chances we even need to administer medicines.