2009 Michigan

Forest Health Highlights

Michigan Department of Natural Resources and Environment

Forest Management Division

www.michigan.gov/foresthealth

In this Issue:

Overview ..............................................1

Asian Longhorn Beetle ......................... 3

Forest Tent Caterpillar ...........................4

Ash Decline and Ash Yellows ................ 6

Pine Spittlebug and Diplodia Canker ....7

Drought ...............................................7

Emerald Ash Borer ................................8

Beech Bark Disease ...............................9

Gypsy Moth ........................................10

Hemlock Wolly Adelgids .....................10

Invasive Plants ....................................12

Maple Decline ....................................12

Pine Bark Beetles ................................12

Maple Tar Spot ...................................12

Oak Wilt .............................................13

Spruce Budworm ................................14

Sugar Maple Defoliation ....................14

Sirex Noctilio ......................................15
Forest Resource Overview

Michigan is a state like no other in the nation with two peninsulas 

and a large latitudinal span. From the warmer agriculture and urban 

areas in the south to the colder wooded lands in the north, the State 

offers unique ecosystems, land uses, and one of the most diverse 

forests in the United States. Nearly all of the forest land in Michigan 

was cut and/or burned during European settlement. The bulk of the 

lumber boom and most of the fires occurred in the late 1800s and early 

1900s. By 1920, the lumber boom had ended and secondary succession 

was in full swing with the recovery of the forests. Since then, these 

forests have been maturing. 

Today, Michigan has more forest land than any other state in the 

Northeast or Midwest. And, Michigan’s State Forests and a number of 

large private ownerships are certified as practicing sustainable forestry 

through the Forest Stewardship Council (FSC) and the Sustainable 

Forestry Initiative (SFI). The U.S. National Forests are managed under 

the National Forest Management Act and National Environmental 

Protection Act. There also are numerous assistance programs to help 

small forest-land owners.

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Michigan Forest Facts

• Among the 50 States, Michigan ranks 22nd 

 in land area but 10th in forest-land area.

• Forest land accounts for 19.3 million acres 

 or 53 percent of land in Michigan; 97 

 percent or 18.7 million acres is timberland.

• Sugar maple/beech/yellow birch is 

 the predominate forest type (22 percent 

 of timberland). Aspen (13 percent) is 

 the second most abundant forest type. 

 Northern white-cedar (7 percent) and red 

 pine (5 percent) are the most abundant 

 softwood forest types.

• All prominent species in Michigan have 

 moderate to high percentages of average 

 annual net growth to volume.

• Of Michigan’s forest land, 62 percent 

 or 11.9 million acres are owned by 

 families, individuals, private corporations 

 and other private groups. The remaining 

 38 percent (7.4 million acres) is managed 

 by Federal, State and local government 

 agencies.

• Sixty-five percent of the plots sampled 

 for nonnative species had at least 

 one identifiable nonnative species. Higher 

 percentages of nonnative to total species 

 were evident in the Lower Peninsula. 

 Likewise, the percentage of nonnative- 

 species ground cover to total ground cover 

 was higher in the Lower Peninsula.
Asian Longhorned Beetle Resurfaces in Massachusetts

A serious threat to North 

American hardwood forests 

has resurfaced in a big way 

in Worchester, MA. The Asian 

Longhorned Beetle (ALB) is an 

invasive insect which attacks 

sugar maple and other hardwoods such as horse 

chestnut, elms and aspen. 

The 2008 discovery of a 62 acre ALB infestation 

in Massachusetts involving thousands of maples is a 

call for all states to intensify ALB detection efforts. 

The Bug

ALB was first discovered in Brooklyn in 1996, 

entering the USA in infested wooden pallets and 

crates. To date, ALB has been detected in small 

areas of New York, Chicago, Massachusetts, New 

Jersey and Toronto, Canada. 

ALB is native to China and other areas of the 

Far East. It is a large black beetle with white spots 

on its wing covers. The beetle’s body is 1 to1.5 

inches long with very long white and black banded 

antennae. Wood boring larvae develop from eggs 

deposited in the bark. The ALB larvae tunnel deep 

into the tree’s heartwood. The following summer, 

the showy adults emerge starting the cycle all over 

by laying eggs. Emerging beetle leave a large (3/8” 

diameter), perfectly circular hole as they chew their 

way out of the tree. 

Trees Affected

ALB attacks 

11 genera of 

deciduous trees. 

Among them 

are maples, 

elm, willow, 

birch, horse 

chestnut, London 

planetree, 

aspen, ash, and 

mountain ash. 

Larval tunneling 

damages the 

vigor and 

structural 

integrity of the tree and can eventually kill trees. 

The wood of infested trees is not useable for 

dimensional lumber or hardwood veneer. Also 

impacted are maple syrup production, ornamental 

and landscaping trees, and tourism. 

Hard maple and aspen alone constitute 27% 

(7.2 billion cubic feet) of the timberland volume 

in Michigan. These two species constitute 43% 

(155 million cubic feet) of the commercial harvests 

statewide. 

Response Strategy

After discovering ALB, U.S. customs regulations 

were changed to stop introductions of ALB and 

other wood-infesting pests. These regulations require 

wooden packing materials entering the USA to be 

chemically treated or kiln dried. The current goal of 

the U.S. Department of Agriculture’s (USDA) Animal 

and Plant Health Inspection Service (APHIS) is to 

eradicate ALB wherever found in the United States. 

Michigan has been on the look out for ALB since 

it was first detected in 1996. However, the new find 

in Massachusetts re-energized early detection and 

prevention efforts. Public, Industrial, University, MSU 

Extension and private natural resource professionals, 

and State and Federal Departments of Agriculture are 

combining resources to meet this challenge. Many 

ALB detections have come from the public. Thus, 

we are continuing to educate Michigan’s citizens 

to recognize ALB. We must also educate the public 

to limit the movement of firewood. If all firewood 

would be used locally, our ability to stop the spread 

of introduced pests like ALB would be greatly 

enhanced.

2009 Survey Report

No ALB was detected in Michigan in 2009. There 

was a renewed education and outreach effort by the 

DNR, MDA and APHIS in 2009. Targeted audiences 

included natural resource professionals, forest 

recreation staff and visitors, firewood dealers and 

users and the general public. Many inquiries were 

handled including possible detections, many were 

other showy Cerambycids like the white spotted 

sawyer. 

The nature conservancy provided their member 

list for an APHIS survey for ALB in Southeastern 

Michigan. Over 5,000 of their members in the metro 

Detroit area took part in ALB detection efforts.

The DNR screened its State Park visitor database 

for visits in the last 10 years from Worcester, 

MA. We had four visits from ALB infested areas 

of Massachusetts, two in the Lower Peninsula in 

Muskegon and Berrien counties, and two in the 

Upper Peninsula in Chippewa and Luce counties. 

These sites will be intensively surveyed for ALB in the 

spring, 2010.

3
or other late season defoliators. 

Such combined stresses can 

weaken trees enough to make 

them more susceptible to attack by 

other pests. This is the first year of 

the current FTC epidemic in most 

areas, so significant impacts on 

tree growth or mortality are not 

expected.

FTC Nuisance

During outbreaks, FTC 

caterpillars can number from 1 to 

4 million per acre. They create an 

extreme nuisance to people living 

or vacationing in infested forested 

areas. Young larvae spin a thread 

and fall from the trees onto picnic 

tables, patios, and people causing 

serious annoyance. Mature larvae 

wander widely in search of food, 

often migrating in large numbers 

across roads and open areas. 

Mass flights of tent caterpillar 

moths in late-June to early-July are 

common during outbreaks. These 

flights can move millions of moths 

many miles, creating a nuisance 

where the flight ends. Mass flights 

can trigger outbreaks in new areas 

the following year. 

Life Cycle

The FTC overwinters in an egg 

mass on twigs of host trees. Eggs 

hatch in the early spring about the 

time of bud break. 

As caterpillars grow, they are 

easily identified by the white 

keyhole-shaped or footprint 

pattern along their backs. As 

the larvae grow, they consume 

increasing amounts of leaves and 

wander widely in search of food. 

Once mature, larvae spin silk 

cocoons with white to yellow 

threads on vegetation, buildings, 

and other stationary objects to 

begin pupation. This begins in mid 

to late June. Adults emerge 7 to 

10 days later. The adult moth has 

a one-to-one-and-a-half inch wing 

span, is buff colored and has a 

broad brown band across the front 

wings. They are night fliers and are 

attracted to 

lights in large 

numbers. It 

is common 

to find high 

populations in 

areas where 

nighttime 

lighting.

 

Natural Control

The FTC is a native insect 

that has evolved in the forest 

ecosystems of North America. 

Natural control mechanisms 

have also evolved which help to 

keep outbreaks from seriously 

damaging forested areas. One 

mechanism that causes population 

collapse is starvation induced by 

the caterpillars’ feeding. During 

the early stages of an outbreak, 

the trees have enough foliage to 

support the increasing number 

of caterpillars. After a year of 

two of complete defoliation, the 

large number of caterpillars need 

more foliage than is available. 

Starvation typically kills 75-95% 

of the caterpillars. Starvation also 

weakens the population, making 

it more susceptible to naturally 

occurring bacteria and virus. Cool, 

wet spring weather also plays a 

role by slowing the development 

rate of the insects while aiding 

disease transmission. These forces, 

along with building populations 

of a parasitic fly commonly known 

as the “Friendly Fly”, reduce 

populations to undetectable levels 

for many years. 

The “Friendly Fly” is a significant 

natural control occurring near 

the end of an outbreak cycle. This 

native fly, Sarcohpaga aldrichi, 

parasitizes FTC pupae in their 

cocoons. These fly populations 

often increase as FTC quickly 

disappears from the landscape. 

The result is people forget FTC and 

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Forest Tent Caterpillar

The forest tent caterpillar (FTC), 

Malacosma disstria, defoliated 

368,205 acres of hardwood forest 

in Northwestern Lower Michigan 

in 2009 (See map). Defoliation was 

very heavy in areas around Gaylord, 

Cadillac, Traverse City and Petoskey.

Widespread outbreaks of 

FTC occur at intervals of 10 to 

15 years. Historically, outbreaks 

peaked in 1922, 1937, 1952, 

1967, 1978, 1990, and 2002. 

Although statewide areas with 

high numbers of caterpillars last 

for 3 to 5 years, outbreaks in any 

one locality normally last for 2-3 

years. Outbreaks normally collapse 

quickly due to natural causes. 

FTC is a native defoliator of 

a variety of hardwood trees and 

shrubs. It feeds primarily on sugar 

maple, aspen, oaks, and birch 

and will also occasionally feed 

on other associated hardwoods. 

Historically, widespread outbreaks 

of FTC occur at intervals of 10 

to 15 years. Population buildups 

follow drought cycles, especially 

warm, dry springs. Outbreaks 

which last for 3 to 5 years 

normally collapse quickly due 

to natural causes. Defoliation 

normally begins in late-May with 

the greatest leaf loss occurring in 

the first three weeks of June. 

Damage

 Defoliation from FTC generally 

does little damage to tree health. 

Trees generally develop a second 

set of leaves after attack if more 

than 50% of the canopy is lost. 

These new leaves and leaves 

formed the year following an 

outbreak are often smaller. By the 

second year after the collapse of 

an outbreak 80% of the trees have 

normal sized leaves.

 Trees rarely die from FTC 

defoliation alone. However, 

prolonged defoliation can kill trees 

if combined with other problems 

such as drought, late spring frost, 
5

focus on this new nuisance. The 

DNRE is often accused of releasing 

this very effective biocontrol agent, 

but the credit...and blame... rests 

squarely on Mother Nature. 

Although tourism and 

homeowners would receive 

relief from the large number of 

caterpillars present in June and 

the temporary loss of leaves 

in the forest landscape, the 

costs are unacceptable. A state 

sponsored FTC spray initiative is 

not economically or ecologically 

responsible. FTC impacts are 

temporary and primarily just a 

nuisance. A spray program of this 

magnitude would unnecessarily 

impact many non-target species 

of moths and butterflies. It could 

also extend the duration of the 

outbreak by interfering with forces 

such as starvation and the buildup 

natural biocontrol agents. 

The forest tent caterpillar rarely 

causes severe damage to trees. 

The FTC is a native insect, and a 

part of a natural and balanced 

ecosystem. The DNRE generally 

restricts insecticide-spraying 

operations on state lands to the 

use of biologically sound products 

(e.g. Bt or Bacillus thuringiensis) 

and only if outbreaks pose a 

serious risk to the survival of the 

forest, or present a significant 

nuisance in areas of concentrated 

recreational use. Private 

landowners may desire and justify 

spraying to protect the leaves and 

preserve aesthetics. In making this 

decision, the landowner should 

consider goals and environmental 

concerns.
6

Ash Decline and Ash Yellows

Ahead of the advancing emerald ash borer, 

studies have been undergoing to evaluate the 

health of white ash stands across Michigan. There 

have been a number of reports in recent years that 

white ash trees were developing top dieback and 

mortality within a period of just a few years. 

The ash decline study is designed to determine 

the following:

• Distribution and severity of ash yellows, root 

 rots and butt rots

• Frequency of these diseases

• Impact of these diseases (tree ring study) 

• Risk factors, e.g., climatic, soil conditions 

 and stand management histories

Historically, ash decline periods in the eastern 

United States have been associated with drought 

stress, ash yellows, and Cytospora branch dieback. 

Ash yellows is a disease caused by bacteria that 

grow in the food-conducting tissue (phloem) of 

hardwood trees. The disease symptoms usually 

include narrower growth rings, witches’ brooms 

and epicormic sprouts, sprouts with buds that 

lack winter dormancy, cracking at the base of 

the trunk and abnormal patterns of branching. 

The bacteria are transmitted from tree to tree by 

piercing-sucking insects but no single species of 

insect has been implicated. The bacteria do not 

produce cell walls so they are too fragile to exist on 

plant surfaces or anywhere outside the interior of 

the phloem tissue. The disease spreads remarkably 

slowly in the forest. Forest health surveys of the 

incidence and frequency of ash yellows were 

completed during the 1990s in several of the North 

Central states, using chemical and immunological 

tests for diagnoses. However, there has been no 

survey of Michigan for ash yellows, although 

observations have reported the disease as being 

present in Ann Arbor street trees. The detection 

technology for diagnosing the pathogen is now 

much improved. 

The survey of ash yellows in Michigan has been 

coordinated with emerald ash borer detection 

tree surveys so that samples could be collected by 

surveyors as they examined EAB survey trees. Ash 

‘trap trees’ are created by girdling living ash trees, 

which triggers the release of chemicals attractive to 

EAB adults. Girdling also stimulates the production 

of witches’ brooms, which were collected and sent 

to the diagnostic laboratory. Over 1000 ash tree 

from around the state were sampled and tested 

for ash yellows. Based on visual symptoms, twentyseven percent of trees had ash yellows. However, 

sensitive laboratory detection of the bacterial 

pathogens diagnosed only 11% as infected. The 

distribution of the disease was wide in Michigan 

and also reached into and across the Upper 

Peninsula. Ash trees from such northern locations 

in Michigan have not been observed to show the 

typical disease symptoms, however.

Ash stands that originated on abandoned farm 

sites were found to generally exhibit from 40-50% 

ash yellows infection in the central Lower Peninsula 

(Wexford County). Similar stands in the northern 

Lower Peninsula (Emmet County) exhibited no ash 

yellows infection despite presence of positive trees 

in nearby rural settings. Occurrence of ash yellows 

in white ash forest stands was not accompanied by 

presence of sprouts, brooms, basal cracks, or ash 

yellows-type branching patterns. However, in urban 

green ash, these symptoms were associated with 

ash yellows infection. Basal cracks were associated 

with certain butt rots. Also, crown thinning and 

decline were not associated with ash yellows 

infection in the forests but were associated with 

many successive years of reduced growth prior to 

visible crown dieback. 

Average tree diameter and yearly growth rates 

were the same for ash yellows-infected and noninfected white ash trees in the Wexford County 

study area where infection was highest.

Forest white ash trees showed evidence of 

declining crown size, crown density and live 

crown ratio, and increasing crown transparency 

and crown class approximately 3-4 years before 

mortality, despite 10-25 years of insufficient 

incremental growth. Michigan white ash decline 

did not share the characteristics reported in earlier 

studies of ash decline in New York and northeastern 

North America. For example, Cytospora cankers and 

fruiting bodies were not present on branches in 

declining canopies, nor was ash yellows infection 

associated with decline. Drought stress from prior 

years did not appear to be a factor in decline since 

decline in incremental growth began ten to 25 

years prior to our studies.

Soils were similar in texture, structure and 

nutrition in the sites we studied despite large 

differences in decline and mortality. The stand 

exhibiting highest mortality and decline was the 

only stand with a history of grazing. This stand also 

exhibited an unusual top layer of root mat on the 

soil which resembled root mats typical of tropical 

forests. Further study of the origins of this soil 

problem is needed to understand its role in decline 

and mortality of white ash and other tree species.

Root and butt rots were common in stands with 

little incremental growth for more than ten years. 

Trees affected with Armillaria root rot had reduced 

crowns, rapid crown thinning and decline over 

approximately three years, and often standing 

death. Wind throw generally occurred after death 
Pine Spittlebug and Diplodia Canker

Branch flagging and tree mortality of understory 

white pine have been occurring for four years along 

the Manistee and AuSable River corridors. The 

affected area has expanded each year along both 

the corridors and has also spread 

to some inland areas in Crawford 

County. Flagging has been 

reported to occur on some bigger 

canopy white pine. Estimates 

are that this problem has caused 

70-90% mortality in the young 

white pine at the worst locations 

and has significantly reduced the 

amount of white pine in other 

sites. 

Terminal twig cankers and 

small to large cankers are 

common on individual branches 

and running cankers have been 

observed to move into trunks and 

kill young trees. This year the pine 

spittlebug has been associated 

with the origin of the cankers. 

Competition stress among the 

crowded understory white pine 

created conditions for severe 

pine spittlebug infestations. The 

nymphs, which cover themselves in frothy spittle and 

feed on the plant juices in early summer, have caused 

twig mortality in proximity to the puncture sites. 

Additionally, adult spittlebugs have been puncturing 

the bark of branches. Cankers are occurring at the 

puncture sites. Competition stress and spittlebug 

infestation has resulted in fungal pathogens entering 

the puncture sites, particularly on the branches 

where the cankers coalesce, increasing in size and 

advancing down the branches. 

Drought 

After 2-3 years of drought, rainfall returned to 

near normal levels in 2009. However, the effects 

of the drought are long-lasting. It takes years for 

trees to rebuild food reserves. The drought has 

been a major influence especially in the Western 

Upper Peninsula and areas of the Northern Lower 

Peninsula. Droughts cause visible declines in tree 

canopy vigor. Hardest hit are tree species on dry 

sites with light, sandy soils or on lowland sites with 

significant water table fluctuations. Drought-stressed 

trees are susceptible to a host of secondary pests, 

from defoliators to wood boring insects to root 

rot fungi. As a result, increases in tree mortality in 

One of the primary fungi causing the cankers 

is the pathogen DIplodia scrobiculata, known for 

its shoot blight on pines. This pathogen has been 

reported on E. white pine in Wisconsin and in 

Connecticut. Diplodia exists 

as a latent pathogen within 

a healthy host and several 

years of pine spittlebug 

infestation, competition 

stress, and possibly drought 

stress have triggered the 

pathogen. Other pathogenic 

fungi are also being isolated 

from the branch cankers and 

their role in the disease is 

being assessed. 

An unusual feature of 

the branch cankers has been 

that many originated under 

dark olive green lichens 

rather than on bare bark 

or under light green lichen 

species. Lichens are not 

plant pathogens and the 

mystery of the association 

of dark green lichens and 

cankers possibly is the result 

of spittlebug behavior. The brown adult spittlebugs 

are less noticeable on the surfaces of the dark lichens 

than at other feeding sites. 

Measures that could be taken to reduce the pine 

spittlebug infestation might include removing dead 

and dying branches and trees to reduce egg laying 

sites. Thinning the understory white pines to relieve 

competition stress should help to protect the healthy 

stands and may be useful in some of the infested 

stands. 

oak from the two-lined chestnut borer (Agrilus 

bilineatus); in paper birch from the bronze birch 

borer (Agrilus anxius); in larch from the eastern 

larch beetle (Dendroctonus simplex), and in jack 

and red pine saplings from Diplodia and Armillaria

were more common. Defoliators such as the gypsy 

moth, linden looper, fall cankerworm and spruce 

budworm were also epidemic as susceptible hosts 

became vulnerable to damage due to drought 

stresses. It will take a few years of normal or higher 

amounts of precipitation for trees to fully recover 

starch reserves and return to normal growth 

patterns. 

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8

The Emerald Ash Borer (EAB) was detected in 

two new locations in the Eastern half of Michigan’s 

Upper Peninsula in 2009. The current EAB 

Quarantine now encompasses eight of the fifteen 

Upper Peninsula Counties (See Map). For detailed 

information on the EAB quarantine, visit the 

Michigan Department of Agriculture (MDA) website 

at: 

http://www.michigan.gov/mda.

The MDA in cooperation with the United 

States Department of 

Agriculture (USDA) 

Animal and Plant Health 

Inspection Service 

(APHIS), continue to 

survey the uninfested 

counties in the Western 

Upper Peninsula. They 

deploy purple traps 

baited with an aromatic 

lure knows as Manuka 

Oil. Traps are placed 

in and adjacent to high-risk locations such as 

campgrounds, recreation areas and sawmills and 

along travel corridors. In addition, traps will 

be placed in a few Level III quarantine areas 

in the U.P. (e.g. South Houghton, Alger, and 

Chippewa counties) near remote, outlying 

single tree detections. 

A pilot project was initiated in 2008 

to test the latest research concepts for 

managing EAB outlier populations. The 

areas selected for this study include 3 outlier 

infestations in the Upper Peninsula. The 

project is called ‘SL.A.M’ to stand for Slow 

Ash Mortality. The goal is to employ and 

carefully monitor and measure the impact 

of multiple strategies to slow the rate at 

which EAB expand and impact ash trees. The 

primary goals of the project include: 

Reducing EAB population growth and 

rates of tree mortality in the core areas.

Detecting and preventing satellite populations 

from expanding and becoming core populations.

Developing and maintaining regular 

communications and consistent messages with the 

local landowners in and around the project area. 

Assisting local woodland owners and homeowners 

in making environmentally and fiscally responsible 

decisions regarding their ash trees and woodlands.

The DNRE conducts annual Firewood sweeps in 

December after closure of the firearm deer hunting 

season. All hardwood firewood left at State Forest 

Campgrounds and State Parks is burned. This 

eliminates the risk of EAB emerging from infested 

firewood the following spring. During the camping 

season, Parks and Recreation employees inspect 

all campers entering state parks. State forest 

staff conducts random inspections of state forest 

campgrounds. When found, firewood which is not in 

compliance with the EAB quarantine and the DNRE 

Director’s order is seized and burned. The Director’s 

order prohibits moving ash wood onto state lands 

unless that ash is without bark attached.

The Emerald Ash Borer (EAB)
9

Beech Bark Disease

The DNRE in cooperation 

with Michigan State University, 

the University of Michigan 

and Michigan Technological 

University continue to monitor the 

movement of beech scale and the 

progress impacts of Beech Bark Disease (BBD). The 

BBD advancing front (e.g. areas infested with scale 

before fungal infection) continues to spread east 

and west in the Upper Peninsula and to new areas 

in the North Lower Peninsula (See map). Isolated, 

satellite populations of beech scale occur well ahead 

of the advancing front in both the Western UP 

and NLP. These outliers are being studied to better 

understand scale movement to new areas, and 

colonization rates within stands after arrival. 

The USDA Forest Service Research Facility in 

Delaware, Ohio continues to collect scions from 

•

Michigan’s resistant trees to study Beech Bark Disease 

Resistance. These trees resist scale establishment. 

Without the scale, beech are not susceptible to 

infection by Nectria species which cause beech bark 

disease. Beginning in the fall of 2010, Michigan will 

establish the first seed orchard with BBD resistant 

stock. The seed from these orchards will be used 

to restore an American beech component in BBD 

impacted hardwood forests. The DNRE continues 

efforts to detect and protect BBD resistant trees. 

Michigan Technological University received an 

USDA Forest Service Evaluation Monitoring grant 

supporting a systematic survey effort to detect, mark 

and protect resistant American Beech in Michigan’s 

BBD Advancing and Killing front Areas. This effort 

will support and cooperate with the BBD Resistance 

project in Delaware, OH mentioned above.
Gypsy Moth 

Gypsy moth populations have been declining 

steadily across much of Michigan’s oak and aspen 

forests in recent years. Caterpillar numbers were high 

enough in a few areas to be noticeable and to cause 

feeding damage that could be seen from the ground. 

Defoliation must exceed 50% to be visible from the air, 

however, and no gypsy moth defoliation was detected 

during this year’s aerial survey. What has been termed 

aspen decline was again visible in many areas of the 

Upper Peninsula. Many of these areas were initially 

mapped as potential gypsy moth infestations during 

aerial surveys, but gypsy moth presence was not 

confirmed by follow-up ground evaluations.

This decline in gypsy moth activity is likely 

attributable to the insect becoming naturalized. Native 

to forests in Europe, the gypsy moth was accidentally 

introduced to Massachusetts in the late 1800’s and was 

first detected in Michigan in the 1950’s. Populations 

spread steadily in the 1970’s and, by the late 1980’s, 

hundreds of thousands of acres of trees were being 

defoliated annually. Since then, a natural enemy 

complex of native and introduced insect parasites 

and predators, as well as fungal pathogens and 

In August 2006, hemlock wooly adelgids (HWA) 

were found on landscape hemlock trees in Harbor 

Springs, Michigan. This is only the third time HWA 

have been detected in Michigan and the first 

time it has been found outside of nurseries. After 

determining that the infested hemlock came from 

Hemlock Woolly Adelgids (HWA)

10

other gypsy moth-specific organisms has become 

established across much of the state. This complex 

is responsible for causing outbreaks to collapse and 

for keeping low-level populations of gypsy moths 

from reaching defoliating levels for extended 

periods. In many Michigan forests, gypsy moths 

now behave like a native insect, with short periodic 

outbreaks followed by extended periods of low 

activity.

a nursery in West Virginia, the Michigan Department of 

Agriculture conducted trace-back surveys of hemlock 

originating from nurseries in the region to determine 

where additional infested nursery stock was outplanted in Michigan.

Elongate hemlock scales (EHS) were introduced 
monitoring HWA in eastern hemlock forests (Costa 

and Onken, 2006). Site and stand level information 

(county, ownership, TRS, GPS coordinates, habitat 

type, age, stocking) were recorded. HWA Hazard 

Zones were determined as a function of proximity 

to the 2006 infested area and by annual overwintering HWA mortality estimates (Siegert and 

McCullough, 2006). Hemlock density within the 

northern Lower Peninsula risk zones were used 

to determine plot locations, with areas of highest 

density given highest priority. The plot locations 

are shown below. A total of 82 plots were surveyed 

in 2008. The USFS Digital Aerial Sketchmapping 

System (DASM), a GPS-linked, tablet PC-based 

moving map display system, and a Trimble Nomad 

Handheld Computer were used to log the location, 

site and tree information and HWA survey data. 

Bird feeder systems designed to collect HWA 

crawlers were placed in hemlock trees at five 

sites in Emmet County, where the infestation was 

detected. These feeders and associated trees were 

monitored regularly for life stages of HWA by DNRE 

and MDA staff. 

All surveyed hemlock stands and bird feeder 

monitor trees were negative for HWA. This is the 

third season following the initial detection that no 

HWA have been found in Michigan. 

Unidentified armored scales were found on 

needles of hemlock at several sites. 

Scales will be collected in 2010 to 

determine whether they are EHS.

11

to the northeastern U.S. in the early 1900’s from 

Japan. Records of this insect exist for Michigan. EHS 

have been correlated with early stages of hemlock 

decline in conjunction with HWA. In eastern states, 

hemlock decline in some areas has been significantly 

correlated with EHS abundance but not HWA 

abundance. Also, there is evidence that damaging 

outbreaks of EHS may be enabled by HWA feeding. 

Use high-resolution digital products, including 

color infrared aerial photography and FIA-derived 

hemlock basal area surfaces, to determine where 

forest hemlock occurs in the HWA high hazard 

zones.

Conduct a stratified, standardized sampling 

survey to detect HWA and elongate hemlock scale in 

forest hemlock and in hemlock adjacent to nurseries 

that sell hemlock in the northwestern Lower 

Peninsula. 

Collect spatial, site and tree information on 

landscape and forest hemlock for use in validating 

30-meter FIA-derived hemlock basal area maps 

derived by FHTET. These maps will provide the host 

layer for the HWA component of the new regional 

and national forest risk maps.

Evaluate the use of bird feeders as a tool for 

monitoring HWA infestations.

The survey of forest hemlock is based on a 

standardized sampling method for detecting and 

Hemlock Woolly Adelgids (HWA) con’t
Invasive Plants: A Framework for Action Adopted

Maple Decline in the North Central Upper Peninsula

The Department of Natural Resources and 

Environment (DNRE) adopted Meeting the Challenge 

of Invasive Plants: A Framework for Action in 2009. 

Strategic goals set forth in this document encompass 

a central framework of prevention, early detectionrapid response, and long-term control at strategically 

prioritized sites. They also include leadership to 

set direction and empower staff, assessment and 

research to help identify winnable battles and 

education and outreach to improve and expand 

success. Four themes common to all the goals are 

presented as guiding principles. 

• Use best available science and commit to the 

 integration of new information.

• Prioritize treatments based upon values, 

 threat, distribution, and feasibility of control.

• Collaborate with colleagues and partners to 

 find optimal solutions and share resources.

• Monitor to ensure efficient and effective use 

 of resources.

Preliminary lists of priority invasive species, sorted 

into recommended action categories are presented 

for Michigan’s four major ecoregions to assist 

decision-making.

Goal one calls for the designation of a Wildlife 

Division invasive species coordinator and regional 

point staff to facilitate and coordinate action, assess 

progress, and set new priorities annually.

Maple decline in northern hardwood stands 

is being observed across the Upper Peninsula of 

Michigan. It is believed that a combination of 

edaphic, management, and drought stresses are 

contributors. Michigan Technological University has 

been awarded an USDA Forest Service Evaluation 

Monitoring grant to determine the cause(s) and 

the rate of progression of decline within effected 

stands and across the landscape. Forest management 

practices may need to be altered; short-term and 

long-term expectations may be revised on some 

habitat types/soils; and management practices during 

drought influence periods may also need to be 

modified. 

Pine Bark Beetles 

Aerial surveys detected pockets of tree mortality 

in red pine plantations in several areas of the Upper 

Peninsula. They were initially coded as porcupinecaused. Field visits found bark beetle (Ips pini) 

caused whole tree mortality associated with 

porcupine damage. The severe drought of 2006-

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2007 predisposed porcupine girdled red pine and 

adjacent pine to bark beetle attacks. Several of the 

porcupine impacted plantations in areas hard hit by 

drought were growing on productive sites. No Ips 

activity was detected in 2009.

Maple Tar Spot

Many Norway maples and varieties of Norway 

maple (e.g. Crimson King, Schwedler) shed their 

leaves in September before fall color. This is the 

second year that leaves of heavily infected trees 

were covered with tar spots caused by fungi in 

the genus Rhytisma. A late cold spring and early 

summer created ideal conditions for spore survival, 

dissemination and leaf infection. Generally, maples 

are not overly stressed by this late season loss of 

leaves.
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Oak Wilt

The USDA 

Forest Service 

continues to 

provide ak wilt 

suppression 

funds 

supporting 

a joint MSU 

Extension and 

DNRE effort to 

rid the Upper 

Peninsula of oak wilt. Oak wilt has been detected 

in two counties, Menominee and Dickinson (See 

map). The objectives of this program are to: 1) 

remove oak wilt from the UP by detecting and 

treating all infection centers; 2) educate affected 

communities to prevent the reintroduction 

of oak wilt; and 3) demonstrate an approach 

for detecting and effectively treating oak wilt 

infection centers throughout Michigan. In 2009, 

a vibratory plow was used to establish 19,723 

feet of root graft barriers to treat 32 oak wilt 

epicenters. Although much has been 

achieved, oak wilt is still active in areas 

of both counties.

The DNRE was awarded ARRA USFS 

Invasive Species funds to remove 

oak wilt from infected oak stands on 

state forest land in Grand Traverse, 

Crawford and Missaukee counties in 

Michigan’s Northern Lower Peninsula. 

This will prevent the spread of oak 

wilt to neighboring oak resources and 

prevent long distance transmission via 

the difficult to regulate movement of 

infected firewood taken from recently 

killed trees on state lands.

A new initiative to create a national 

oak wilt database has been joined by 

DNRE, Wisconsin DNR, Texas Forest 

Service and the USDA Forest Service, 

Northern Research Station, St. Paul, 

MN, and the USDA Forest Service, 

Forest Health Technology Enterprise 

Team (FHTET), Fort Collins, CO. The 

national oak wilt database will have 

a web based platform supported by 

FHTET. A draft database design has 

been agreed upon and an oak wilt 

confirmation protocol was established 

to ensure data input integrity. The 

National Risk Mapping process is also 

an integral part of the detection and 

evaluation protocol. Oak wilt risk maps 

will be used to both prioritize survey efforts and as 

the database is populated, the data will be used to 

improve oak wilt risk mapping. 

Dr. Gerry Adams, Michigan State University has 

received a USDA Forest Service Evaluation Monitoring 

grant to begin detecting, confirming and recording 

surveys data on the national database. The oak wilt 

database will serve two needs: 1) an impact analysis 

needed to project expected short and long-term 

resource losses; and, 2) operational guidance for 

prevention and suppression efforts.

Beginning in mid-summer, 2009, Dr. Adams visited 

reported oak wilt sites to confirm the presence of 

oak wilt. If sites met the confirmation standards 

established by the National Database effort, they 

were mapped and recorded. Most of the 2009 reports 

and assessments occurred in Roscommon, Crawford, 

Otsego, Grand Traverse, and Alcona Counties. 

Sixty-eight epicenters in Menominee and Dickinson 

Counties which had been assessed in previous years 

were also included in the oak wilt mapping database. 
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Two-Lined Chestnut Borer (TLCB) and 

Armillaria: Not Oak Wilt

In Crawford County in Michigan’s Northern 

Lower Peninsula there was a high incidence of 

mortality of mature northern pin oak. There 

has generated public concern in this area as the 

mortality continued to spread over the past three 

years. The cause was believed to be oak wilt until 

careful assessment was made as part of the oak wilt 

mapping project. While oak wilt was occasionally 

encountered, the past three years of advancing 

mortality was found to be caused by years of 

Oak Wilt con’t.

infestation by the two-lined chestnut borer (Agrilus 

bilineatus) and Armillaria root rot. Four successive 

years of drought on the sandy soils of this region in 

combination with the over-maturity of the resource 

predisposed this northern pin oak resource to attacks 

by these pests. Symptoms included sudden browning 

and wilting of all foliage in August. The following 

year it was common to see a single lower or midcrown branch with green leaves remaining on an 

otherwise leafless tree. The xylem of the lower trunk 

remained white and moist until attacked in the late 

summer by a final infestation of TLCB.

Spruce Budworm (Choristoneura fumiferana) is 

slowly expanding its defoliation of spruce and fir 

in several counties in Michigan’s Upper Peninsula. 

Isolated areas of mature to over mature spruce/

fir in the south central and north central Upper 

Peninsula have top kill and tree mortality caused 

by repeated defoliations. The spruce budworm 

is one of the most destructive native insects in 

the northern spruce and fir forests of the Eastern 

United States and Canada. Periodic outbreaks of 

the spruce budworm are a part of the natural cycle 

of events associated with the maturing of balsam 

fir. Balsam fir is the species most severely damaged 

by the bud-worm in the Lake States. White and 

black spruces are also hosts with some feeding on 

tamarack, pine and hemlock. Spruce mixed with 

balsam fir is more likely to suffer budworm damage 

than spruce in pure stands. 

Sugar Maple Defoliation in the Upper Peninsula – 

Cankerworms

Spruce Budworm

There were numerous reports of light to moderate 

defoliation in hardwoods dominated by sugar maple. 

Observed insects included both the Bruce spanworm, 

Operophtera bruceata, and the fall cankerworm, 

Alsophila pometaria. Defoliation localized to certain 

sections in several Upper Peninsula counties. Several 

counties reported light to abundant fall moth flights 

in 2009. No hardwood defoliation was visible via 

aerial surveys. 
Since its detection in 

New York State in 2004, the 

European wood wasp, Sirex 

noctilio, has been confirmed 

at trap sites throughout the 

eastern Great Lakes region 

of Ontario, Canada. This 

exotic wood wasp (commonly 

referred to as horntail wasp) is native to Europe, Asia 

and northern Africa and was collected in Fulton, New 

York in September 2004. The New York find marks 

15

Sirex Noctilio

the first time the insect has been documented in 

North American forests. This wood wasp is rarely 

a pest in its native areas where it confines its 

attacks to dead or dying trees. In areas where it 

has been introduced, however, it is a major pest 

of pine plantations, where it attacks living trees 

and can cause up to 80% mortality. Outbreaks 

often build up in stressed trees and then spread to 

more vigorous trees. Widespread outbreaks have 

occurred in Australia, New Zealand, South Africa 

and South America. 
For more information about Sirex, link to:

http://na.fs.fed.us/spfo/pubs/pest_al/sirex_woodwasp/sirex_woodwasp.htm 

http://www.aphis.usda.gov/plant_health/plant_pest_info/sirex/index.shtml 

http://www.treesearch.fs.fed.us/pubs/12997

To determine whether an insect that you have collected is Sirex noctilio, contact the MSU 

Plant Pest Diagnostic Clinic at 517-355-4536, or your local county MSU Extension office. 

Female Sirex are attracted to stressed trees where 

they insert their sword-like ovipositors into the outer 

sapwood, deposit their eggs and introduce a toxic 

mucus and fungus (Amylostereum areolatum). Larvae 

feed only on the fungus, which, together with the 

mucus, kills infested trees.

Symptoms of Sirex infestation include:

• Exit holes 

 approximately 

 1/8 to 3/8 inches 

 in diameter;

• Tree crowns 

 turning 

 light green 

 then yellow to 

 reddish brown in 

 the late spring 

 or early summer;

• Larval galleries 

 (tunnels) in the wood, packed with a fine 

 powdery frass (insect-produced sawdust);

• Beads of resin or streams of resin on the 

 bark, exuding from holes created during egg- 

 laying.

Pitch or resin will often weep from the tiny puncture 

wounds made by the adult females when they lay their 

eggs. The damage can be very subtle or quite obvious 

and care must be taken in using this symptom as a 

feature of fresh attacks. In Michigan, most 2- and 

3-needle pines are considered susceptible, including 

Scotch, jack, red and Austrian pines.

The Eastern Regional office of the USDA Animal 

Plant Health Inspection Service’s Plant Protection 

& Quarantine (PPQ) conducted a Sirex survey in 17 

uninfested counties in southeastern Michigan to 

continue delimiting the spread of Sirex. 

Traps were placed in Scotch, red, jack and 

Austrian pine and baited with 70% alphapinene/30% Beta-pinene blend. 

New detections of Sirex were made in 

Huron and St. Clair counties. A single female 

was caught in St. Clair County and 4 females 

were caught in Huron County at two different 

sites. All catches were made in mature Scotch 

pine and were either single trees or Scotch 

pine mixed with hardwoods. No detections 

were made in dense overstocked stands of host 

material. Positive catches were made between 

early August and mid September.

Trapping data from across the region 

indicates that Sirex populations are spreading 

naturally along the shoreline of Lake Huron to 

the north after spreading into Michigan from 

Ontario, Canada. 

MTU continues to work on a USDA Forest 

Service-funded Sirex detection survey. Sites 

were established in 2007 using groups of 3 to 5 

herbicided pine trees. The herbicides cause stress 

that increases the trees’ attractiveness to the 

wood wasp. Traps are hung from these trees and 

a subset is cut in the spring to look for larvae of 

the wood wasp. In addition, funnel traps baited 

with alpha and beta pinene are placed in the 

trees. 

To determine whether an insect that you have 

collected is Sirex noctilio, contact the MSU Plant 

Pest Diagnostic Clinic at 517-355-4536, or your 

local county MSU Extension office. 

Thanks to the following agencies for providing content for this newsletter:

Michigan State University, Michigan Technological University, Michigan Department of Agriculture, 

USFS State & Private Forestry Unit and USDA APHIS.

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