Michigan

Forest Health

Highlights 

2011

Michigan Department of Natural Resources
Acknowledgements

2 - Forest Health Highlights 2011

Forest Health Highlights is a summary of the condition of Michigan's 

forests during 2011 and the work done to preserve and protect them 

by Forest Management Division, Department of Natural Resources. 

www.michigan.gov/foresthealth

Written by

Michigan Department of Natural Resources

Forest Management Division staff

Photographs and design by

Michigan Department of Natural Resources

Marketing and Outreach Division staff

Forest Management Division staff

United States Department of Agriculture

Forest Service 

Michigan Department of Agriculture and Rural Development

Michigan State University

Michigan Technological University

Maps and other information provided by

Michigan Department of Agriculture and Rural Development

United States Department of Agriculture

Forest Service

Animal and Plant Health Inspection Servicer

Michigan State University Extension

The Michigan Department of Natural Resources is committed to the 

conservation, protection, management, use and enjoyment of the state’s 

natural and cultural resources for current and future generations. 

For more information, visit www.michigan.gov/dnr 

Cover photo: Balsam fir in conifer wetlands, Montmorency County.
Forest Health Highlights 2011 - 3

Forest Resource Overview. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Insects & Diseases. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

 Heterobasidion Root Disease. . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Asian Longhorned Beetle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Beech Bark Disease . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Emerald Ash Borer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

 Surveying. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

 Slowing Infestation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Forest Tent Caterpillar. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Gypsy Moth. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

Eastern Larch Beetle. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

Hemlock Wooly Adelgid. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

Oak Wilt. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

 Oak Wilt Initiatives. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

 Oak Wilt – ARRA Project. . . . . . . . . . . . . . . . . . . . . . . . . 17 

Spruce Budworm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Thousand Cankers Disease of Walnut. . . . . . . . . . . . . . . . . . . . 18

Maple Tar Spot. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Forest Decline. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Drought. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Aspen. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Hickory. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Maple. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 

White Pine. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Invasive Plant Projects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

American Recovery and Reinvestment Act. . . . . . . . . . . . . . . . 25

Table of Contents
Forest Resource Overview

From the warmer agriculture and urban areas 

in the Southern Lower Peninsula to the colder 

wooded lands to the north, Michigan offers 

unique ecosystems and one of the most diverse 

forests in the United States. Nearly all of the 

forestland 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.

Today, Michigan has more forestland than 

any other state in the Northeast or Midwest. 

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 forestland 

owners.

4 - Forest Health Highlights 2011

•	 Among the 50 states, Michigan ranks 

22nd in land area but 10th in forestland 

area.

•	 Forestland accounts for 19.3 million acres 

or 53 percent of land in Michigan; 

97 percent or 18.7 million acres is timberland. 

The Mackinac Bridge spans the Straits of Mackinac, connecting 

Michigan’s Upper and Lower peninsulas.
Forest Health Highlights 2011 - 5

•	 Sugar maple/beech/yellow birch is the 

predominant 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 forestland, 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.

•	 65 percent of the National Forest Inventory & 

Analysis plots sampled for nonnative species in 

Michigan had at least one identifiable nonnative 

species. The Lower Peninsula had higher 

percentages of nonnative species. 

Likewise, the percentage of nonnative-species 

ground cover was higher in the Lower Peninsula. 
Insects and Diseases

Healthy and productive forests are comprised of a diversity of native tree, 

shrub and herbaceous plant species, as well as an even larger number of faunal 

species for which forests provide habitat. Forested ecosystems have continuously 

adapted and evolved over thousands of years, as insect, plant, and animal 

species are naturally, intentionally or inadvertently introduced or extirpated from 

ecosystems. Prevention and mitigation of invasive plants, insects and disease 

introductions is important for the maintenance of healthy and productive forests.

 From ‘Michigan Forest Resource Assessment & Strategy’

 June 2010

6 - Forest Health Highlights 2011
Heterobasidion 

Root Disease

With the discovery of 

Heterobasidion root 

disease (HRD) in the 

Northern Lower 

Peninsula this summer, 

the DNR Forest 

Health Program has 

stepped up efforts 

to determine how 

widespread the disease 

is in Michigan. Caused 

by the fungus Heterobasidion irregulare (formerly 

Heterobasidion annosum, which was formerly Fomes 

annosum), this disease is considered among the most 

destructive fungi in North American conifer forests.

While over 200 species of conifer trees are susceptible 

to the disease, red, white and jack pine are especially 

vulnerable to attack in the Lake States.

Root rot fruiting bodies

Root rot aerial photo.

Unlike many forest insects and diseases that are 

attracted to stands that are stressed due to lack of 

management, HRD is most commonly found in 

actively managed forest stands. Fresh-cut stumps 

provide an ideal entry path for spores of HRD, which 

move through grafted roots to infect healthy trees. 

Infected trees suffer from thin crowns and reduced 

height, diameter and shoot growth. Over time, 

circular pockets of dead and dying trees mark the 

progression of the disease. Bark beetles often build up 

in trees stressed by HRD, hastening the decline and 

death of affected trees.

Once the distribution of the disease in Michigan is 

determined, guidelines will be developed to help 

minimize its introduction and spread. In Wisconsin, 

where HRD is established across much of the 

state, infected trees are burned on site to reduce 

the formation of spore-producing fruiting bodies. 

Fungicides are also applied to freshly cut stumps to 

prevent HRD from entering and moving to healthy 

trees through the root system.

Forest Health Highlights 2011 - 7
With ALB found a short 

four-hour drive from 

Michigan’s southern border, 

the Michigan DNR has 

stepped up efforts to 

detect this destructive 

forest pest to prevent its 

establishment here. In 

cooperation with the Forest Management Division, 

DNR Parks and Recreation Division surveyors 

searched for ALB in 35 state parks across Michigan 

this summer. Surveyors looked for adult beetles, as 

well as the large (3/8-inch) holes ALB make when 

they chew their way out of infested trees. No signs 

of ALB were found.

In autumn 2011, a second round of ALB surveys was 

conducted in these parks. Surveying after leaf fall aids 

in detecting emergence holes in upper branches, 

where the ALB first invades trees.

Asian Longhorned Beetle

Asian Longhorned Beetle on the 

cross section of an infested log.

Asian Longhorned Beetle on a leaf.

Asian Longhorned Beetle emergence hole.

The Asian longhorned beetle (ALB) is an invasive 

insect that most commonly attacks five genera of 

deciduous trees: maples, elm, willow, birch and 

horse chestnut. Other genera are susceptible to ALB 

but are less commonly attacked.

The 2008 discovery of a 62-acre ALB infestation in 

Massachusetts involving thousands of maple trees 

provided reason and momentum to intensify efforts 

to detect ALB in Michigan. This infestation is currently 

estimated to affect over 100 square miles of forest.

On June 17, 

2011, Ohio 

became 

the fourth 

state to 

detect Asian 

longhorned 

beetle since 

the insect 

was first discovered 

in the U.S. in 1996. ALB has also been confirmed in 

Ontario, Canada outside of Toronto.

Adult beetles were found in three ornamental maple 

trees growing in a private vineyard in Bethel, Ohio, 

30 miles southeast of Cincinnati. Ohio’s governor has 

signed an executive order restricting the movement 

of firewood, hardwood logs and host nursery stock 

out of the infested county to help prevent the spread 

of ALB.

8 - Forest Health Highlights 2011
Lake

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2009-2011 Cooperative Michigan

Asian Longhorned Beetle Surveys

MCPC volunteer survey locations

NC member survey locations

APHIS/PPQ survey locations

MI DNR 2011 survey locations

Source data: USDA/APHIS/PPQ (2009-2011)

Nature Conservany (NC) mail survey (2009)

Michigan Cooperative Pest Cadre survey (2009)

State of Michigan DNR (2011)

December 1, 2011

map author: dbopp

DISCLAIMER: The U.S. Department of Agriculture's 

Animal and Plant Health Inspection Service 

collected the data displayed for internal agency 

purposes only. This data may be used by others; 

however, they must be used for their original 

intended purposes.

Forest Health Highlights 2011 - 9
BBD-resistant Beech tree planting

BBD affected area - Luce County

Beech Bark Disease 

Since the fungus cannot invade the tree without the 

scale, researchers are focusing on trees resistant to 

the scale. The USDA Forest Service Northeastern 

Research Station in Ohio and the Michigan DNR 

Forest Management Division have been collecting 

cuttings from scale-resistant beech. Researchers at 

the Ohio research facility then graft these cuttings 

onto beech root stock. Fifteen grafts for each of the 

20 resistant trees will be used to establish an orchard 

of 300 resistant trees.

The seed orchard will be completed in autumn 

of 2012. In the meantime, 135 beech trees with 

varying degrees of beech scale resistance produced 

by this project were planted in the Upper Peninsula 

in November 2011. This planting was fenced to 

protect the trees from deer browse. The planting 

was in a heavily BBD-affected area that had many 

beech trees lost to BBD. The newly planted trees 

will be observed for many years to monitor growth 

characteristics and resistance to beech scale.

Since its discovery in Michigan in 2000, beech bark 

disease (BBD) continues to pose a serious threat to 

Michigan’s forests. This disease is initiated by a scale 

insect that attaches to the tree and feeds on sap from 

the inner bark 

layer. Damage 

from this feeding 

allows one of two 

Neonectria fungus 

species to invade 

the tree. The 

fungus inhibits the 

flow of sap, killing 

infested portions 

of the tree and 

eventually killing 

the entire tree. 

Controlling the natural spread of the disease is not 

an option because both the scale and fungus can 

be transported by the wind. Michigan Technological 

University received a USDA Forest Service grant 

in 2009 to continue surveys to detect and protect 

BBD-resistant American Beech in BBD-affected 

forests.

The area of infestation continues to spread east and 

west in the Upper Peninsula and into uninfested 

areas of the Northern Lower Peninsula. Spot 

infestations of the scale insect have been found far 

outside the primary infestation front.

According to the latest USDA Forest Service Forest 

Inventory and Analysis (FIA) data for the period 

2006-2010, there are 32.5 million American beech 

trees ≥ 5” diameter and 2.3 million standing dead

beech in the same size category. FIA estimates annual 

beech mortality in this time period of 8.6 million 

cubic feet or 103.8 million board feet per year. Much 

of this loss has been in the Eastern Upper Peninsula 

where most of the beech resource has been greatly 

affected. As BBD spreads throughout the Northern 

Lower Peninsula, the number of live beech trees will 

greatly diminish.

10 - Forest Health Highlights 2011
Beech Bark Disease in Michigan

Forest Health Highlights 2011 - 11
•	 Assisting local woodland owners and 	 	 	

homeowners in making environmentally 

and fiscally responsible decisions regarding 

their ash trees and woodlands.

Three Asian wasps that attack EAB eggs or larvae were 

released in Southern Michigan in 2007: Tetrastichus 

planipennisi, Spathius agrili and Oobius agrili. All three 

wasps were released in the Upper Peninsula in 2011 

at the Houghton County SLAM sites and an additional 

EAB site on the Garden Peninsula in the south-central 

area of the Upper Peninsula.

For more information on SLAM, visit 

www.slameab.info

Emerald Ash Borer 

The DNR is involved in many projects to survey and 

prepare Michigan’s urban and rural forests for arrival 

of the emerald ash borer (EAB).

Surveying

No new counties were added to the EAB quarantine 

in 2011. The Michigan Department of Agriculture 

and Rural Development (MDARD), in cooperation 

with the USDA Animal and Plant Health Inspection 

Service, continue to survey the uninfected counties 

in the Western Upper Peninsula. They deploy 

purple traps baited with an aromatic lure known 

as Manuka Oil. Traps are placed around high-risk 

areas such as campgrounds and sawmills and along 

travel pathways. There were no detections in the 

uninfested, nonquarantined counties of the Western 

Upper Peninsula. Traps were also placed in a few 

areas in the Upper Peninsula (Houghton, Alger 

and Chippewa counties) near remote single-tree 

infestations.

Slowing infestation

A pilot project was initiated in 2008 to test the latest 

concepts for managing EAB populations. The project 

is called SLAM, which stands for “Slow Ash Mortality.”

The areas selected for this study include two outlying 

infestations in the Upper Peninsula. These EAB 

outliers are in the St. Ignace/Moran area of Mackinac 

County, and the Laurium area of Houghton and 

Keweenaw counties.

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. 

Galleries below ash bark made by EAB larvae.

EAB adult (actual length is 1/2-inch)

12 - Forest Health Highlights 2011
The current quarantine area for the emerald ash 

borer encompasses all of the Lower Peninsula and 

eight of the 15 Upper Peninsula counties. There 

are still areas of the Lower Peninsula, especially 

the northern areas that have not yet been affected 

by EAB. So, although it is legal to move ash 

wood within the Lower Peninsula, it is advised to 

limit the movement of ash firewood within the 

Lower Peninsula as much as possible. For detailed 

information on the EAB quarantine, visit the MDARD 

website at www.michigan.gov/mdard

During the camping season, DNR Parks and 

Recreation Division employees inspect all firewood 

brought in by campers entering state parks. State 

forestry employees also conduct random inspections 

of firewood brought in by guests at state forest 

campgrounds. When found, firewood that is not 

in compliance with the EAB quarantine is seized 

and burned. In addition, the DNR conducts annual 

firewood sweeps in December. All hardwood 

firewood left at state forest campgrounds and parks 

is burned, eliminating the risk of EAB emerging from 

infested firewood the following spring.

According to the latest USDA Forest Service Forest 

Inventory and Analysis data for the period 2006-

2010, there are 162.8 million ash trees ≥ 5”

diameter, and 15.5 million standing dead ash in the 

same size category. This number does not include 

ash on nonforest lands, such as cities and urban 

environments. FIA estimates annual ash mortality in 

forested environments of 29.1 million cubic feet or 

350 million board feet per year. (This is calculated 

by comparing 2001-2005 inventory data with 2006-

2010 data.)

For more information on the emerald ash borer, visit 

www.emeraldashborer.info 

Forest Tent Caterpillar

Forest tent caterpillar (FTC) activity decreased 

dramatically across the 

Northern Lower Peninsula 

in 2011. FTC defoliation 

declined from nearly 445,000 

acres affecting 23 counties 

in 2010 to scattered, light 

defoliation in a few areas 

across the region this year. 

Starvation, parasitism by the 

‘friendly fly’ and an increase in a naturally occurring 

pathogen called nucleopolyhedrosis virus (NPV) led 

to a rapid drop in forest tent caterpillar numbers after 

two or three years of activity.

Widespread outbreaks of FTC occur at approximately 

every 10 to 15 years. In the past, outbreaks peaked 

in 1922, 1937, 1952, 1967, 1978, 1990 and 2002. 

While statewide caterpillar populations may remain 

high for up to five years, outbreaks in any one locality 

normally last for two to three years. Outbreaks 

decline quickly once parasites and other natural 

enemies become active. FTC is a native defoliator 

of a variety of hardwood trees and shrubs. It feeds 

primarily on sugar maple, aspen, oaks and birch, but 

occasionally feeds on other associated hardwoods, 

particularly during outbreaks.

As this current outbreak winds down across the 

Northern Lower Peninsula, the effect on trees 

defoliated during this period is not expected to 

be serious. Trees rarely die from FTC defoliation 

unless they have already been seriously weakened 

by drought, late 

spring frost damage 

or other stressors. 

Consecutive heavy 

defoliation can 

reduce growth for 

a period of time, 

but trees normally 

recover within a 

few years after FTC 

populations decline.

Forest tent caterpillars

Virus killed tent caterpillars

Forest Health Highlights 2011 - 13
 

Gypsy Moth

Right on schedule, gypsy moth populations crashed 

across the Northern Lower Peninsula and the 

Upper Peninsula in 2011, making it difficult to find 

a caterpillar in the forests across the region. It was 

a dramatic change from 2010, when gypsy moth 

defoliated 943,000 acres of oak and aspen trees in 

32 counties.

The gypsy 

moth feeds 

on the foliage 

of a variety 

of hardwood 

trees, 

including oak, 

aspen, willow, 

basswood, 

birch and dozens of 

other species. It is common for a population of gypsy 

moths to defoliate, or eat, most of the leaves 

off trees. When moth populations 

are high and competition for food 

Gypsy moth larva Gypsy moth-parasitic wasp.

increases, they will feed on other tree species, 

including conifers like spruce and pine. Fortunately, 

trees usually recover from defoliation as long as 

they are 

growing well 

and have 

adequate 

water and 

nutrients 

available. 

Even 

repeated 

defoliation 

rarely kills a 

tree, unless 

drought, old 

age or other stressors have 

weakened it.

Gypsy moth populations are expected to remain 

low for the next several years.

For more information about gypsy moths, visit 

www.fs.fed.us/ne/morgantown/4557/gmoth

We continue to receive occasional reports of 

Eastern larch beetle (Dendroctonus simplex) 

effects on tamarack (Larix larcinia) in the eastern 

and south-central areas of the Upper Peninsula. 

This bark beetle became epidemic as tamarack 

was stressed by the drought of 2000-2001 and 

repeated defoliations by the larch casebearer 

(Coleophora laricella), which is an introduced 

needle-mining insect. Casebearer populations 

collapsed after two years of heavy tamarack 

defoliation. We do not anticipate any building of 

ELB populations given the current condition of the 

tamarack resource in Michigan. Existing satellite 

populations of ELB should diminish unless future 

events such as drought and/or return of the larch 

casebearer cause significant stress.

Eastern Larch Beetle

14 - Forest Health Highlights 2011
Hemlock Wooly 

Adelgid

The Eastern hemlock is an important component of 

Michigan’s forests. 

Based on inventory 

data, it exists in over 

12 percent of the 

state’s timberlands. 

The hemlock wooly 

adelgid (HWA), 

Adelges tsugae, 

is a small, aphidlike insect. This insect is native to Asia and was 

transported to the United States on trees brought 

into the U.S. from that region. The HWA feeds by 

piercing small branches of hemlocks and feeding on 

the sap within. Infested needles turn brown and die. 

Infested hemlock trees often die within several years. 

Drought conditions and damage from other insects 

or diseases can increase the rate at which trees die.

HWA was found on naturally growing hemlock near 

Harbor Springs, Michigan in August 2006. This is 

the third time this pest was found in Michigan and 

the first time the insect was reported outside of 

nursery stock. It is believed the insect arrived 

with infested landscape trees that were 

shipped from outside Michigan. HWA has 

been attacking Eastern and Carolina hemlock in 

the Eastern forest since its initial discovery near 

Richmond, Virginia, in 1951.

Since 2006, the Michigan DNR and Michigan 

Department of Agriculture and Rural Development 

have cooperated in early detection surveys for the 

HWA. In 2010 surveyors found new infestations on 

ornamental hemlock trees in three counties: Emmet, 

Macomb and Ottawa. The infested hemlock trees 

were destroyed. Surveys of hemlock within one mile 

of the infested trees were conducted in 2011. No 

HWA were found. Surveys were also conducted in 

natural stands of hemlock in high-risk forests in the 

Eastern Upper Peninsula and in the Northwestern 

Lower Peninsula. No HWA were found.

The ability of HWA adults to survive in Michigan is a 

function of minimum overwintering temperatures. 

Studies indicate that HWA cannot survive 

temperatures below approximately -10 to -15 

degrees F. Because minimum winter temperatures are 

higher near Lake Michigan, HWA may survive better 

in hemlock forests in these areas.

Researchers at Michigan State University have 

developed an HWA risk map that takes into account 

average minimum winter temperatures across the 

state. Areas where minimum winter temperatures are 

highest are at highest risk and where HWA is most 

likely to survive. These high-risk areas are shown in 

red on the HWA risk map.

A second insect, the elongated hemlock scale insect 

(EHS) is believed to increase the damage caused 

by HWA. This insect arrived from Japan in the early 

1900s and has been documented in Michigan. Health 

decline in hemlocks has been documented in the 

Eastern forests where populations of EHS are high, 

but not in Michigan. Some evidence indicates that 

damaging outbreaks of EHS can occur where HWA 

feeding is heavy. EHS surveys are being conducted 

along with HWA surveys in Michigan.

Forest Health Highlights 2011 - 15
Oak Wilt

Oak wilt (Ceratocystis fagacearum) is one of the 

most serious tree diseases in the Eastern United 

States, killing thousands of oaks each year in forests, 

woodlots, and home landscapes. 

Oak wilt was first identified in 1944. 

The extent of its impact wasn’t 

realized until the 1980’s. Only in 

the last few years has oak wilt been 

reclassified as an exotic disease. 

Although oak wilt can infect many 

species of oak trees, trees in the 

Northern red oak, pin oak, black 

oak, scarlet oak, and red oak hybrids 

are most susceptible. Infected red oaks die within 

days or weeks of being infected. Members of the 

white oak group are much less susceptible and rarely 

die from the disease. Oak wilt spreads from tree to 

tree through connected root systems. Untreated, the 

fungus spreads to adjacent red oak trees, often killing 

large groups of trees within a few years eventually 

killing all nearby, root-grafted oaks. Oak wilt spores 

that can spread the disease overland are produced 

only in the year following tree mortality. Insects move 

these spores to fresh oak wounds from April through 

July. Trees, logs and firewood from killed trees 

produce these spores.

Oak wilt is established widely in the Southern Lower 

Peninsula with spotty distribution in the Northern 

Lower and Upper Peninsulas. One method of spread 

is by movement of firewood, so as 

the public moves northward into 

forested areas, the risk of spreading 

this disease grows. Cut wood is used 

on camping trips where it can be a 

source of fungus the following year.

Property values can be significantly 

reduced due to the loss of many 

trees when a single tree is infected. 

Acorns produced by oaks are a 

valuable food source of wildlife. 

More than 180 different kinds of birds and mammals 

use oak acorns, including popular species such as 

white-tailed deer, squirrels, turkey, wood ducks, 

woodpeckers and others.

Effective oak wilt management programs use a 

variety of strategies to limit the spread of oak wilt. 

•	 Avoid wounding oaks from April 15 to July 15.

•	 Do not move infected wood off-site without

debarking, chipping, or properly drying it. If 

infected wood cannot be destroyed before the 

following April, tightly cover cut logs or firewood 

with plastic tarps from April 15 to July 15. 

•	 Stop the underground spread of oak wilt by

breaking root-graft connections between likely 

diseased and healthy oaks. 

•	 Special plows used to lay underground cable are

used to break roots, stopping the underground 

spread of oak wilt. 

•	 If oak wilt is caught in the year it was newly 

introduced via overland spread from diseased 

firewood or logs to a wounded healthy red oak, 

removing the infected tree and stump removes 

oak wilt without impacting adjacent oaks.

16 - Forest Health Highlights 2011 
As part of a two-year effort, the Michigan DNR 

received American Recovery and Reinvestment 

Act (ARRA) funds to identify and treat oak wilt 

outbreaks in high-use recreation areas and in 

high-value stands of red oak in the Northern 

Lower Peninsula. As oak wilt establishes in new 

areas, spores produced by the fungus increase the 

likelihood of transmission to healthy oak trees. The 

risk of movement of oak wilt through spring and 

early summer wounds and firewood are at historic 

highs. Early detection and treatment of oak wilt 

outbreaks in urban, rural and forest landscapes can 

slow the spread of the disease and minimize the 

potential effect on Michigan’s oak trees. 

Through a combination of aerial and ground surveys, 

staff identified oak wilt on 3,026 acres of state forest 

land in Crawford, Missaukee, Benzie and Grand 

Traverse counties. Active pockets of oak wilt were 

Oak Wilt Initiatives

The DNR’s Parks and Recreation Division purchased 

a vibratory plow in autumn 2011. This unit will have 

a vibratory plow blade that can disrupt root-grafts 

to a depth of 5 feet. It will be used to treat oak wilt 

infections in state parks, state forest campgrounds 

and state forest lands. This is a much-needed boost 

to Michigan’s efforts to remove and slow the threat 

of oak wilt to Michigan’s vast oak resources.

The USDA Forest Service did not provide oak wilt 

suppression funds in 2011. Michigan State University 

Extension and the DNR had received this funding 

beginning in 2005 for the purpose of ridding the 

Upper Peninsula of oak wilt. The objectives of this 

program were to:

•	 Remove oak wilt from the Upper Peninsula by

detecting and treating oak wilt pockets. 

•	 Educate affected communities to prevent the

reintroduction of oak wilt. 

•	 Demonstrate an effective approach for 		

detecting and treating oak wilt throughout 

Michigan. 

MSU Extension evaluated past suppression efforts 

in 2011. Many treated areas in Menominee and 

Dickinson counties remain free of oak wilt. Although 

much has been achieved, untreated oak wilt pockets 

remain. These untreated areas serve as a source 

of inoculum for the continued overland spread to 

adjacent oak resources and to more distant areas via 

movement of firewood and logs.

A second grant from the USDA Forest Service will 

be used to detect, confirm and record oak wilt in a 

national database. The oak wilt database serves two 

needs: 

•	 An impact analysis needed to project 	 	 	

expected short and long-term resource 

losses.

• 	 Operational guidance for prevention and 	 	

suppression efforts. 

defined and trees showing symptoms of oak wilt 

were marked as potential spore-producing trees. 

Root graft barriers were established between 

infected trees and healthy trees using a vibratory 

plow. Over 7,200 feet of plow line was installed. 

Infected trees were cut and destroyed or sold for 

timber. Mills that purchase infected red oak trees 

process them quickly to insure the disease will not 

spread to new areas.

Because the fungus can remain in root systems for 

up to 3 years, treatment areas will be monitored 

during this period to ensure that the disease has 

been eliminated.

Oak Wilt – ARRA Project

Forest Health Highlights 2011 - 17
TCD cankers

Thousand Cankers Disease of Walnut

In May 2010, the Michigan Department of Agriculture 

and Rural Development established a quarantine 

to protect walnut (Juglans spp.) from thousand 

cankers disease (TCD). TCD is an insect-disease 

complex involving 

the walnut twig 

beetle, Pityophthorus 

juglandis and a fungus,

Geosmithia morbida.

TCD currently occurs 

in Arizona, California, Colorado, 

Idaho, Nevada, New Mexico, Oregon, 

Washington and Utah, states where the walnut twig 

beetles are native. The disease affects only eastern 

black walnut that has been transplanted in these 

western states; native walnut species appear to be 

resistant. Walnut twig beetles carry the fungus to 

black walnut trees where cankers form at the feeding 

site. Heavily attacked trees produce many cankers, 

which eventually kill the trees. It appears that the 

range of this beetle is slowly expanding eastward, 

threatening walnut trees in adjacent states. In 2011, 

Virginia and Pennsylvania were added to Tennessee 

as states east of the Mississippi with TCD.

Michigan’s quarantine restricts movement of the 

following from infected states into Michigan:

•	 All plants and plant parts of the genus Juglans, 

including but not limited to: nursery stock, 

budwood, scionwood, green lumber; other 

living, dead, cut or fallen wood, including logs, 

stumps, roots and branches; and composted and 

noncomposted chips;

•	 Hardwood firewood; and

•	Any article, product or means of transport that

risk the spread of the walnut twig beetle or 

fungus.

Articles that are not a threat and are exempt from 

the quarantine include:

•	 Nuts, nut meats and hulls;

•	 Processed lumber that is 100 percent bark-free

and kiln-dried with squared edges; and

•	 Finished wood products without bark.

Spruce Budworm

Spruce budworm outbreaks periodically cause 

extensive damage and tree mortality in spruce and 

fir forests across the Northeastern United States 

and Canada. Balsam fir is the species most severely 

damaged. Spruce mixed with balsam fir is more likely 

to suffer budworm damage than spruce in pure stands.

There was a significant decrease in the area of 

budworm defoliation in 2011. This was a welcome 

downturn following an alarming increase in the 

area defoliated by the spruce budworm in 2010. 

Repeated defoliation of mature and over-mature 

spruce and fir continues to occur in isolated areas. 

The Western Upper Peninsula has the largest area 

of budworm activity due to the abundance of overmature spruce/fir forest. Top kill and tree mortality is 

common in these stands. Periodic outbreaks are part 

of the natural cycle associated with maturing trees.

Since 1909 there have been recorded outbreaks of 

the budworm in both the Eastern United States and 

Canada. These regional budworm epidemics have 

historically occurred every 30 to 50 years. The last 

epidemic ended in Michigan in 1982. Outbreaks 

typically last 10-15 years and result in the loss of 

millions of trees. Drought cycles over the last decade 

likely contributed to the 2010 buildup. A return 

to more normal amounts of precipitation will help 

restore the vigor of Michigan’s spruce/fir resources. 

18 - Forest Health Highlights 2011
Maple Tar Spot

2011 was another banner year for maple tar spot 

(Rhytisma spp.) across much of the state. Shiny black 

raised areas on the upper leaf surface of native maple 

trees, including silver, sugar, red and box elder (yes, 

box elder is a member of the maple family), were a 

common sight this summer.

Norway maple, an exotic invasive species commonly 

found in many parts of Michigan, is also susceptible to 

tar spot and was heavily infected in many locations.

Trees infected with the tar spot fungus typically drop 

their leaves prematurely. Tar spots on infected leaves 

produce spores that will infect new leaves next spring 

if weather conditions are favorable. Maple tar spot 

infections occur most commonly in years when 

spring weather is cool and wet.

Fortunately, this leaf disease causes little damage 

to trees and no control measures are necessary. 

Interestingly, maple tar spot will not infect trees 

growing in 

areas with high 

concentrations 

of sulfur dioxide, 

an air pollutant 

produced by 

burning coal and 

oil. So, you can 

breathe a little 

easier next time 

those spots show 

up on your maple 

trees!

Forest Health Highlights 2011 - 19
Forest Decline

Forest decline refers to a gradual loss of tree growth and vigor. Declining trees 

often have some combination of off-color leaves, early leaf drop, poor growth 

and dieback of twigs and branches. This condition usually progresses slowly over 

several years. During this time trees may be susceptible to some combination of 

insect attacks, diseases and adverse weather conditions like drought and late frosts. 

These stressors can further reduce growth and may increase the likelihood that 

the tree will die.

Following is a section on the contribution of past drought years to many of 

Michigan’s forest declines, and sections describing observed declines of aspen, 

hickory, maple, oak and white pine.

20 - Forest Health Highlights 2011
Aspen Decline 

Aspen decline continues to be reported in many 

areas of the Lake States. The first reports were 

recorded in 2008.

Observations include: 

•	 Thin crowns with small leaves; and

• Increased rates of top kill and tree mortality.

These problem areas occur in pockets, likely 

corresponding to aspen clones, site conditions and/

or older clones. A similar decline in aspen was 

observed after the extreme 1976-77 drought. Other 

observed pests included Armillaria root rot, the 

bronze poplar borer (Agrilus lirgus) and Septoria leaf 

spot (Septoria musiva).

Mortality of larger aspen is often 

associated with Hypoxylon canker. 

Significant periodic defoliation by 

the forest tent caterpillar, gypsy 

moth and the large aspen tortrix in 

the last decade has also contributed 

to this decline in aspen vigor and 

overall health. The aspen leafblotch 

miner (Phyllonorycter apparella) 

and Septoria leaf spot discolored aspen 

canopies in many parts of the state in 2011.

Decline of aspen caused by some combination of disease, 

insects and environmental stresses.

Poplar borer

Drought

Following the 2006-2008 drought, rainfall returned 

to near normal levels beginning in 2009. Areas in 

the Western Upper Peninsula, however, continued 

to experience moderately dry conditions in 2011. 

Although we are in the third year of near normal 

rainfall, it takes years for trees to rebuild food reserves. 

The drought has been a major influence on tree 

health, especially in the Western Upper Peninsula and 

parts of the Northern Lower Peninsula, which saw 

consecutive years of extreme drought.

Droughts can trigger significant declines in tree canopy 

health. Hardest hit are trees that grow in light, sandy 

soils or on lowlands exposed to significant water table 

fluctuations. Drought-stressed trees are susceptible to 

a host of insect pests and diseases. Oak is affected by 

the two-lined chestnut borer (Agrilus bilineatus); paper 

birch is affected by the bronze birch borer (Agrilus 

anxius); larch is affected by the Eastern larch beetle 

(Dendroctonus simplex); and jack and red pine saplings 

are affected by Diplodia and Armillaria.

Forest Health Highlights 2011 - 21
Hickory Decline

Decline and death of bitternut hickory, Carya cordiformis, was 

reported in Michigan for the first time in 2010. Hickory decline 

has been reported in several northeastern states and Wisconsin 

for the past six years. The decline is characterized by thinning 

crowns with small, yellow leaves. This problem has historically 

been attributed to outbreaks of the hickory bark beetle, Scolytus

quadrispinosus, during extended periods of drought. Recently a 

new fungus, Ceratocystis smalleyii, associated with the bark beetle 

is causing numerous bark cankers. The cankers impair the tree’s 

ability to transport water 

and nutrients.

In 2010, decline in hickory 

was detected along the 

Menominee River in 

Southwest Menominee 

County. No new areas 

of hickory decline were 

reported in 2011.

Cankers underneath the bark of an infected hickory. Defoliation of hickory trees.

Maple Decline Increases 

in the Western Upper Peninsula

Maple dieback has been reported for the last 

few years in Michigan’s western Upper Peninsula 

and continues to be investigated by Michigan 

Technological University. On 118 monitoring 

plots established across industry, state and federal 

lands in the Upper Peninsula, northern Wisconsin 

and eastern Minnesota, the average sugar maple 

dieback level increased from just over 12 percent 

in 2010 to 16.5 percent average dieback in 2011. 

A vigorous sugar maple stand should have less than 

10 percent average dieback. Information continues 

to be processed on growth rings, climate, 

management, soil and foliage nutrients, and other 

potential factors associated with historical maple 

dieback in other regions. Initial findings from foliar 

nutrient analyses suggest imbalances in some 

nutrients compared with levels reported in the 

literature. 

Research will continue to investigate these factors 

and monitor the progress of maple dieback in the 

region, with the ultimate goal of incorporating 

findings into management plans to prevent loss 

from maple dieback in northern hardwood forests.

22 - Forest Health Highlights 2011
White Pine Decline

Dieback and mortality of understory white pine 

continues to expand in the north-central Lower 

Peninsula. First detected 

in 2006, this decline is 

associated with white pine 

growing underneath oak 

and aspen trees on sandy 

soils adjacent to the Au 

Sable and Manistee River corridors.

Branch flagging and dieback appear to be associated 

with stem cankers, often found below lichen 

attached to the affected branches. To date, two fungi 

– Diplodia and Therrya spp. – have been isolated 

from these cankers.

In addition, feeding scars caused by the pine 

spittlebug, Aphrophora parallela, are commonly found 

on trees suffering from dieback. While populations of 

pine spittlebug were noticeably lower in 2011 than 

in previous years, symptoms of white pine decline 

described above were widespread.

Further research is needed to determine the role 

of pine spittlebug damage and the fungal pathogens 

associated with this problem, and to assess whether 

drought and other stressors are predisposing white 

pine to this decline.

Canker underneath the bark of a white pine.

Pine spittlebug

The needles and branches on this white pine are dying.

Forest Health Highlights 2011 - 23
Invasive Plant Projects

The existence and health of Michigan’s natural places depends on 

controlling the introduction and spread of invasive plants. Invasive 

species are foreign to the ecosystem and are likely to cause economic, 

environmental or human harm.

24 - Forest Health Highlights 2011
American Recovery 

and Reinvestment Act

In 2010, the Michigan DNR contracted the inventory 

and removal of invasive plant species from four 

forest areas with funding provided by the American 

Recovery and Reinvestment Act (ARRA). The four 

sites were: Maxton Plains Alvar (Chippewa County), 

Shakey Lakes Oak-Pine Barrens (Menominee 

County), Van Etten Floodplain (Iosco County) and 

locations along the Au Sable River (Crawford and 

Otsego counties). Staff identified many species of 

invasive plants, including: spotted knapweed, purple 

loosestrife, common mullein, St. John’s-wort, 

Canada thistle, leafy spurge and white sweet clover.

In some locations, native species listed as rare, 

threatened or endangered were also found near the 

invasive species, requiring special care in planning 

and removing the invasive plants. Rare, threatened 

or endangered species encountered include: 

prairie dropseed, false pennyroyal, downy oatgrass, 

Cooper’s milk vetch, calypso orchid, Hill’s thistle, 

Richardson’s sedge, bulrush sedge, flattened spike 

rush, prairie avens, Alaska orchid and small skullcap. 

The surveys were completed in 2010.

The DNR completed treatment and removal of 

the most serious invasive plants at these four sites 

in the summer of 2011. Various control methods 

were used, including hand pulling and disposal, hand 

swiping with herbicides, and spot sprays targeted at 

individual plants and small groups of plants. Directed 

herbicide sprays were used to protect native, rare, 

threatened and endangered plant species. Special 

care was taken within 25 feet of rare, threatened 

and endangered species to ensure that these plants 

were not harmed. The DNR will continue to 

monitor the treated areas in the upcoming years to 

determine effectiveness of these treatments.

 Forest Health Highlights 2011 - 25