May 20, 2007 

About this newsletter... 

The Forest Health Protection unit of the Forest Service located in St. Paul, Minnesota 

produces this newsletter. Our intent is to keep Federal land managers in the Upper Great 

Lakes region abreast of forest health related issues such as insect and pathogen outbreaks. 

What to expect in 2007... 

So, what does our crystal ball see for this coming summer? 

Drought impacts - much of northern Minnesota, northern Wisconsin, and the U.P. have 

lingering drought concerns. Drought is a major contributor to a variety of forest health 

issues. Drought can initiate declines in many tree species including black ash, sugar 

maple, paper birch, white spruce and yellow birch. Wood borers and bark beetles thrive 

in drought stressed trees. Be aware of insects such as the pine engraver, Ips pini, 

attacking red and jack pine; hemlock borer, Melanophila fulvogutatta, attacking hemlock; 

two-lined chestnut borer killing oaks; and bronze birch borer infesting birch trees. 

Armillaria root disease is likely to be more prevalent during dry periods. Armillaria 

fungi are present in many forest soils, just waiting for weakened trees to provide a food 

source that they can invade. Also, many caterpillar outbreaks coincide with drought 

periods. Watch for increasing gypsy moth activity, especially in Wisconsin. Another big 

concern will be Diplodia shot blight and canker on red pine. Watch for seedling red pine 

mortality caused by Diplodia. 

Palmer Drought Index 

U.S. Drought Monitor 

http://www.drought.unl.edu/dm/DM_ 

midwest.htm 

Lake States 

Forest Health Watch Northeastern Area 
Sugar maple decline – Last spring we received many reports of sugar maple defoliation 

in far northern Wisconsin and adjacent areas in the U.P. Most of the damage was high in 

the upper crowns of trees. It appeared that frost may have played a key role along with 

some insect defoliators. Whatever the cause, the impact may still be observed this spring. 

Crown decline (dead twigs and branches, small leaves, thin crowns) is often observed for 

a year or two after a stress event. Trees generally recover if growing conditions are 

favorable. But, if other stress events follow, such as a drought, then further decline may 

occur. Please send us any reports of crown decline in sugar maple or in yellow birch. 

Spruce budworm –This early 

season defoliator of white spruce 

and balsam fir remains locally 

active in the region. White spruce 

plantations and older balsam fir are 

the most likely places to observe 

spruce budworm. In late may look 

for caterpillars tunneling in 

expanding buds and new foliage on 

spruce and fir. Budworm 

caterpillars use silk to tie needles so 

infested shoots are often webbed 

together. Carefully pull these apart 

to locate the caterpillar wrapped up inside. 

Jack pine budworm – The past three years have seen some extensive areas of jack pine 

budworm defoliation in Minnesota, Wisconsin and in Michigan. Normally, budworm 

outbreaks are regional in extent and last 2-3 years. After a couple of years most 

outbreaks terminate. This current outbreak has been more a series of localized outbreaks 

with intense defoliation being concentrated in the central and eastern U.P., and northwest 

Minnesota. Last year, defoliation expanded into eastern Minnesota and northern Lower 

Michigan. What this year holds is still unclear, we would normally predict a population 

collapse but there are jack pine areas where the budworm populations appear to be rising 

rather than dropping, such as the western U.P. 

We have had reports of jack pine 

budworm feeding extensively in red 

pine in west central Wisconsin and in 

portions of central and northwest 

Minnesota. This is not a common 

occurrence. Red pine with budworm 

feeding damage will have a very thin 

upper crown and top-kill can occur. 

Close inspection should reveal pupal 

cases and clipped needles tied loosely 

with silk webbing. Please report any 

defoliation in red pine that looks like 

the adjacent photograph. 

Red pine damaged by jack pine budworm, 

photo courtesy of Todd Lanigan, WI DNR. 
Early Spring Insects and Diseases... 

The following are some of our more commonly reported tree problems in early spring. 

Anthracnose diseases of hardwood leaves are widespread in eastern North America. 

The most common symptom of this disease is dead areas or blotches on infected leaves. 

However, classic symptoms are not always seen, especially on ash trees. Anthrachnose 

on ash often causes leaf drop to occur with few or no spots on the fallen leaves. In most 

cases, anthracnose is simply an aesthetic concern and not a serious health problem for 

trees. In general, we have more anthracnose observed during wet springs. For more 

information see: http://www.na.fs.fed.us/spfo/pubs/fidls/anthracnose_east/fidl-ae.htm 

European pine sawfly, Neodiprion 

sertifer, is a very common early season 

defoliator on Austrian, Scots, red and 

jack pines. Landscape mugho pines are 

often infested. This is an exotic species 

to North America. It is much more 

common in the southern portions of the 

Great Lakes region than further north. 

There is a native sawfly, the red pine 

sawfly, Neodiprion nanulus nanulus, 

that looks very similar and is often 

found feeding on red and jack pine at 

the same time of year. Telling the two 

species apart by larval appearance is difficult. The red pine sawfly has a habit of eating 

only the outer two-thirds of needles, leaving a distinctive pattern with the basal one-third 

remaining. 

Larch casebearer -- Larch 

casebearer is a very small 

caterpillar that feeds on larch 

needles. Half-eaten needles make 

infested trees appear burnt from a 

distance. Close inspection 

reveals tiny cases made of 

hollowed needles. The 

caterpillars live inside these 

cases. Casebearer activity has 

been reported for the last several 

years, especially in the central 

portions of the U.P. and in parts of northern Minnesota. 

European pine sawfly 

Larch casebearer case on a tamarack needle. 
Eastern tent caterpillar – This is one of our 

earliest and most common leaf feeders in the 

upper Midwest. Eastern tent caterpillar forms a 

characteristic silk tent on cherry, apple and plum. 

Other tent-making caterpillars, such as the fall 

webworm, uglynest caterpillar or cherry scallop 

shell moth, appear later in the summer and their 

tents enclose foliage. The eastern tent caterpillar 

tent is very neat in comparison and does not 

enclose leaves. 

Tents formed on cherry by 

eastern tent caterpillar 

Balsam twig aphid – Feeding damage causes 

the new needles to curl and distort (see photo). 

Pulling the needles apart should reveal small 

aphids coated with a white dusting. The 

damage is cosmetic and not a tree health 

concern. Christmas tree growers become 

concerned since the curled needles persist. 

Several predators including lady beetles attack 

the aphids and generally keep the aphid 

populations well in check. 

Venturia shoot blight – caused by the fungus Venturia 

macularis, is common in many young aspen stands. This 

shoot blight (fungi) can have a profound effect on height 

growth and crown position of individual stems. Young 

aspen trees that lose their dominant or co-dominant crown 

status in dense young aspen sucker stands, tend to be 

eliminated. This is part of the natural thinning process that 

occurs frequently in these developing stands. 
Introduced basswood 

thrips – Thrips are tiny 

insects that scrape and 

damage newly developing 

leaves when they are still in 

the bud stage. Thrips 

feeding causes very early 

season defoliation on 

basswood. Under close 

inspection you should see 

aborted buds and shredded 

leaves. Trees appear to 

have a “ragged” appearance 

(see photo). The timing 

between thrips emergence from overwintering in the soil and bud development seems to 

be the key for determining the amount of damage in any given spring. Damage is 

intensified if the thrips get to the buds before the leaves expand. For more information 

see: 

http://www.na.fs.fed.us/spfo/pubs/howtos/ht_bassthrips/ht_bassthrips.htm 

Basswood thrips defoliation 

Birch leafminer – Birch leafminer is a sawfly. The 

adults are small, black, fly-like insects. In May, 

adult sawflies can been seen landing on birch leaves 

where they lay eggs. The larval sawflies tunnel and 

feed inside of the birch leaf tissue forming a blister 

or leaf mine. The leaf in the photograph shows 

several leaf mines on a birch leaf. These mines 

expand and the leaves begin to brown in June and 

early July. There are several birch leafminer species 

in the Great Lakes region, all of them are exotic. 

White barked birches are more often attacked than 

are yellow or river birch. High populations can 

make landscape trees very unsightly. Birch 

leafminer populations have been relatively low the 

last year or two. For more information see: 

http://www.na.fs.fed.us/spfo/pubs/howtos/ht_birch/ht_birch.htm 
Updates on exotic pests... 

Exotic invasives are a significant concern for our Great Lakes forests. We have several 

invasives that literally threaten to alter forest ecosystems by killing or deforming key 

forest tree species. Michigan is taking the brunt of the initial impact. Beech bark disease 

is reaching epidemic levels, the loss of much of our American beech resource will have 

major impacts on parts of the Hiawatha and Manistee National Forests as well as Pictured 

Rocks National Lakeshore. Emerald ash borer is building populations across Lower 

Michigan threatening native green, black and white ash trees. Sirex wood wasp appears 

to have a firm foothold east of Michigan and could enter the western Great Lakes region 

soon. This would threaten our pine resource. We also have a confirmed infestation of 

hemlock woolly adelgid in Michigan. Those are just four major threats, we still have 

gypsy moth moving into northwest Wisconsin and northeast Minnesota and several 

exotics plants invading our forests. Updates follow on emerald ash borer and beech 

bark disease. 

Emerald ash borer (EAB)... 

The map below shows location data where EAB has been found to date. A few outlier 

populations have received eradication treatments including Brimley State Park in the 

eastern Upper Peninsula of Michigan. Hopefully that site no longer has an established 

EAB population. Unfortunately, outlier populations in the Chicago area and in Maryland 

have proven to be more extensive then initially thought and local eradication appears 

unlikely. Major survey efforts continue in many states. Research activities on emerald 

ash borer are underway with a major emphasis on refining survey tools, insecticide 

efficacy, and biological controls. The 2006 research review for emerald ash borer can be 

viewed at the following web site: 

http://www.fs.fed.us/foresthealth/technology/pub_titles.shtml#E 
Beech bark disease (BBD)... 

This update was taken from the 2006 Michigan Forest Health Highlights, it was prepared 

by the Michigan DNR, Forest, Mineral & Fire Management Division. 

Beech scale populations in the Upper Peninsula moved westward to Munising in 2006. 

Scale populations are building rapidly as the advancing and killing fronts expand in the 

Upper Peninsula. In killing front areas, forest resource professionals are facing the 

challenges of salvaging stands before trees die or snap. Hardwood stands with high 

numbers of beech which historically regenerated naturally after selection harvests now 

often require tree planting programs to ensure a future, fully stocked, sustainable forest 

resource. A minor beech component is left in many stands to provide wildlife food and 

habitat as stands transition to other tree species mixes. Hazard tree management due to 

the threat of beech snap and tree mortality is now a fact of life in parks, campgrounds and 

cities in the eastern Upper Peninsula. 

Since the discovery of beech bark disease (BBD) in Ludington State Park in 2000, the 

BBD killing front has expanded very slowly in the west-central Lower Peninsula. Based 

on data from the Michigan Beech Bark Disease Monitoring and Impact Analysis System 

(BBDMIAS), a cooperative network of statewide BBD monitoring plots, only Mason, 

Oceana and Muskegon counties have suffered beech mortality as a result of infection 

from Neonectria fungi, the pathogens responsible for the wood decay and ‘beech snap’ 

that occurs in BBD-infected trees. 
Any idea what’s going on here??? 

The photo to the left is of a young jack pine. The photo 

was taken in early August. The terminal is dead and 

curled into a “Shepherds crook”. Any idea of the cause? 

The terminal was killed by white pine weevil, Pissodes 

strobi. The larval stages of this weevil feed inside the 

previous years terminal, eventually causing enough 

damage to girdle the shoot and kill the newly expanding 

terminal growth at the very top of the tree. 

Though the common name is “white pine weevil”, the 

insect infests the terminals of many conifers including 

white, blue and Norway spruce, jack and Scots pine, and 

on occasion red pine. 

White pine weevils are not tree killers, rather they cause 

trees to become deformed, crooked, and multi-stemmed. 

This becomes an issue if trees are grown for high quality 

wood products. 

Quiz... 

Test your knowledge. The photographs below are of a common woodland butterfly often 

observed in early spring and a small green weevil that can be very abundant on the leaves of 

many of are hardwood trees and shrubs. The answers are on the next page. 
Quiz answers... 

The butterfly is a mourning cloak, one of only a few species that can be found flying in the very 

early springtime. The adults over-winter in protected places such as under bark flaps, inside 

hollow trees or in a sheds or garages. As soon as the weather warms in the spring the adults can 

be observed. The caterpillar stage of this butterfly is called the spiny elm caterpillar, it has 

abundant large spines and is black in color with red dots on its back. The caterpillars can be 

found feeding on elms and willows in late May and June. The small weevil is a Polydrusus

weevil. It is an exotic (non-native) species to North America. Adults can be very numerous 

feeding on hardwood leaves. The larval stage (grub) feeds on the roots of hardwood trees and 

shrubs. This weevil has been a pest in some nursery situations. Because it is green and rather 

fluorescent in appearance it may be mistaken by some for emerald ash borer. But, it has a classic 

weevil body shape with an extended snout. Emerald ash borer adults would be more flattened 

and bullet shaped. 

What About Exotic Weeds... 

Early spring can be a great time to locate infestations of garlic 

mustard. This invasive plant is green and growing very early in 

the spring. In fact, the plants stay green during the winter. The 

white flowers are present in May. In areas where this weed is still 

not common, pulling or herbiciding small patches of garlic 

mustard can prevent local spread of the weed. Control work 

should be done before seed set and dispersal in early to midsummer. Garlic mustard is often found along woods edges and 

trails. It prefers sites with nutrient rich soils and a good moisture 

supply. 

Mammal damage... 

Insects and pathogens are obviously not the only causes of damage 

to trees. In the Great Lakes region mammal caused damage can be 

common. One could argue that in some areas deer browse is the 

most significant damaging agent on the landscape, especially for 

certain tree species. White cedar, hemlock, and white pine are three 

conifers that are often browsed heavily by deer. Regenerating these 

species can be difficult in many areas because of repeated browse 

damage. Snowshoe hares and rabbits can also cause extensive 

injury on seedlings and small trees. Mice and voles can girdle 

stems, especially when young trees are growing in heavy grass. 

Beavers obviously are a damaging agent in some situations, not 

only by chewing stems but also by building dams that alter water 

flow patterns or flood areas. Porcupines can be destructive. They 

often chew off large patches of bark on a variety of trees, this can 

cause branch death or top-kill. Squirrels clip twigs and chew bark 

and can cause branch or twig death when they remove cones in the 

late summer and fall. 

Porcupine injury (J. O’Brien) 

Garlic mustard 
We have another mammal that causes a great deal of damage, 

especially in urban landscapes. Human caused injury can be 

a major problem for many trees. Lawn mower injury, weed 

whackers, ropes and wires, construction activity and other 

human caused abuse kills and damages many trees. We also 

have to consider poor planting practices and improper pruning 

techniques as human caused. Campsites are a great place to 

view some of the abuses people heap on trees, everything 

from hatchet injuries to burns caused by lanterns. Injured 

trees or poorly planted trees are much more prone to insect 

attack or invasion by pathogens. 

Rope and lawnmower injury 

Beaver activity 

“Lantern injury” 

Photo J. O’Brien 

Rabbit damage 
Get to know your fungi... Information and photos provided by Dr. Joseph O’Brien. 

Common name: Red tree brain 

Scientific name: Peniophora rufa 

Description: Orange, highly wrinkled, small 

sporocarps occur on poplars and willows, usually 

on decaying trees and branches on the ground. 

Habitat/host: Populus, Salix 

Relevance: Decays only wood that is already 

dead. Common and widespread. 

Common name: Violet-toothed polypore 

Scientific name: Trichaptum biforme 

Description: Brackets with boring whitish upper 

surface, and a beautiful lilac, pored undersurface. 

Habitat/host: Occurs across the country in every 

state on hardwoods. 

Relevance: Causes a yellowish sapwood rot in 

standing trees, and is a major decomposer of 

hardwood slash. 

Common name: Rusty-gilled polypore 

Scientific name: Gloeophyllum sepiarium 

Description: Brown, concentrically zoned 

brackets with a whitish margin, maze-like pores 

underneath. 

Habitat/host: Conifers 

Relevance: This fungus causes a brown rot in 

conifers, usually seen on downed branches and 

stems. 
State forest health highlights... 

Our state cooperators in Michigan, Minnesota and Wisconsin annually put together a report 

called Forest Health Highlights. These reports are an excellent record of the major insect and 

disease activity within each state. Much of the information is directly relevant to federal lands in 

the Lake States. They are developed in cooperation with the Forest Service, Forest Health 

Monitoring (FHM) program, and can be accessed at the FHM web site: 

http://fhm.fs.fed.us/fhh/ncregion.shtm 

Upcoming forest health workshops... 

The 56th North Central Forest Pest Workshop will be held September 24-27 in Shoreview 

Minnesota. That is a north metro suburb of Minneapolis/St. Paul. The workshop is an annual 

gathering of persons interested in forest health in the north central portion of North America. It is 

usually attended by plant pathologists, entomologists, foresters, and other scientists and students. 

For more information visit: 

http://www.na.fs.fed.us/fhp/regional/ncfpw/index.htm 

Publications and resources... 

Almost all of our publications are available via our home page 

found on the World Wide Web. This can be accessed at: For More Information 

Forest Health Protection 

USDA Forest Service 

http://na.fs.fed.us/fhp/index.shtm 1992 Folwell Avenue 

St. Paul, MN 55108 

(651) 649-5262 

Copies can be obtained by contacting our office at the address skatovich@fs.fed.us 

or phone number listed to the right.