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Forest Health

Chapter 6:  Forest Health

by Michael Rochester


Forest health has many factors that must be considered.  You should inspect the timber stands and decide if there are any issues that are affecting the health of your woodlot.  You can tell if trees are unhealthy if you know what to look for.  A couple of issues that can affect forest health are diseases and insect infestations.  In the early 1980’s, I worked on the Spruce Budworm Project that the State of Maine operated to combat these destructive pests.  The budworm fed on the new growth of balsam fir and spruce.  They greatly affected the health of the tree and killed many of the trees.  The State of Maine combated this pest by undertaking an aerial spraying program.  Anything that attacks the trees will weaken it and then it will not grow as well.  Weakened trees also become more susceptible to other diseases or insects.  It is important to remember that not all insects are bad, and most insects are beneficial to the trees .   Many insects help with pollination or act as predators and kill the bad insects.  Killing all of the insects on a tree may actually be harmful to the tree.  These pictures were taken in Quebec in the summer of 2013.  This is a spruce budworm outbreak and it is devastating to this forest.  The spruce budworm affects balsam fir more than spruce.  The fir is these pictures are dead and now a fire danger.




The budworm is still around in Maine but not in the numbers that were present in the 1970’s.  The above pictures from Quebec should start to give some concern to Maine.  Insects attack trees in different ways:


1.  They eat the foliage like the budworm or tent caterpillars that eat leaves, flowers, buds, etc.

2.  They insert their proboscis into the tree and suck out the juices and nutrients (aphids).

3.  They bore into the stem or lay eggs in the tree and the young eat the live and sometimes dead tissue (beetles and their larvae).

4.  They invade the roots and root collar area (grubs).


You should start to look for the insects in early spring and continue to look all summer long.  If you can catch the insects in early spring, you may be able to implement measures to combat them. There are many insects that attack trees in Maine and the Maine Forest Service lists 60 or more.  For a complete list that includes remedies, visit the Maine Forest Service Fact Sheet:


This list contains some of the most common insects that you may encounter and was taken from the Maine Forest Service list:


Aphids:  They infect elm, maples, willow, balsam fir, spruce, and white pine.  They pierce plant tissues and draw out the juices.  Some of the aphids are very injurious when abundant as in the case of the balsam woolly aphid.  When abundant, this aphid will kill the tree.  On elm, there are the woolly apple aphid which causes stunted twigs and rosette leaves and the leaf curl aphid curls or cups the leaves but does not rosette them. In both instances, woolly aphids are seen if the curled leaves are unrolled in early summer.  There are many species of aphids and many are tree species specific.


Balsam Gall Midge:  This is a serious pest for Christmas tree and wreath industry producers. Feeding of the young midge larvae on developing needles causes the formation of galls or swellings near the bases of the needles.  The galled needles tend to drop prematurely, thinning out the foliage on the tree.  Forest trees usually do not suffer permanent damage.


Balsam woolly adelgid (Alert):  This pest has greatly increased in numbers in the past few years in Maine.  It is very spread across southern Maine and as far north as southern Aroostook County. Entire stands of mature balsam fir as well as understory fir have been killed in many areas of the state and salvage operations are planned.  Examine your fir annually and plan salvage operations as soon as possible, if necessary.


Birch Leaf Miners:  Some of the most prevalent, and widespread causes of browning of birch leaves in Maine has been by one or the other of these European insects.  Damage is a result of feeding between the upper and lower leaf surface by the larval stages.  Though mainly responsible for aesthetic damage, the damage can weaken the trees allowing more serious pests to attack.


Hemlock Woolly Adelgid:  The hemlock woolly adelgid is a small aphid-like insect that feeds on hemlock.  This insect can be recognized by the presence of a dry, white woolly substance on the young twigs of hemlock. Injury occurs as a result of the insects sucking sap and probably injecting toxic saliva while feeding.  Damage from accumulated injuries causes the needles on infested branches to dry, turn a grayish-green color, and then drop from the tree. Buds are also killed, so little new growth is produced on infested branches.  Dieback of major limbs progresses from the bottom of the tree upwards, even though the infestation may be found throughout the tree.  Trees weakened by HWA often succumb to diseases and wood-boring insects and are readily broken and thrown by wind.  If you think you have found this insect, report the finding to the Maine Forest Service immediately.


Tent Caterpillars:  Webbings or tents in the crotches of wild cherry and apple trees in May along roadsides, hedgerows, and edges of fields indicate the presence of the eastern tent caterpillar. The caterpillars will eat the leaves off of the host tree and surrounding trees. In small trees the tents of the eastern tent caterpillars may be removed by hand and destroyed.  A forked stick or stick with a nail in it may be inserted into larger webs and by twisting it, the webs may be twisted off the branch.  This is best accomplished early in the season before the tents get large.


White Pine Weevil:  The white pine weevil kills the top of conifers and is the most serious economic insect pest of white pine.  They also like Norway spruce and can cause a lot of damage in plantations.  They kill the top leader and that causes multiple tops to grow which ruins the tree.




There are many diseases that can affect trees and it is not that important right now to know about all of them.  Diseases can be classified into two categories: those caused by infectious or living agents (diseases) and those caused by noninfectious or nonliving agents (disorders).  Examples of infectious agents include fungi, viruses, and bacteria.  Noninfectious diseases,  can be caused by such factors as nutrient deficiencies, temperature extremes, pollutants, and fluctuations in moisture.  Noninfectious disorders often produce symptoms similar to those caused by infectious diseases.  It is essential to distinguish between the two in order to give proper treatment.  What is important is to be able spot the their symptoms and then you can investigate what disease or disorder is causing them. 


One very obvious indication that something is wrong with a tree is a “conk”.  A conk is a fruiting body of a bracket fungus that grows on the side of a tree. Conks look like a part of a mushroom growing out of the tree.  They have growth rings like a tree and you tell the age of the conk by counting the rings.  They indicate that something has invaded the tree and is causing stress to the tree.  Conks are usually found on hardwood trees such as maple but can found on other species also.  Conks can weaken the structure of the tree and can allow other pests to invade the tree and further weaken it.


Some very important diseases associated with trees in Maine and their indicators are:


Beech Bark Disease:  This disease is very common in Maine and cause huge problems in stands with a lot of beech.  This disease is cause by the beech scale insect that makes a hole in the tree and then feeds on it.  A fungus then infects the tree through the tiny ruptures in the bark caused from the death and shrinkage of cells on which the scale insect feeds.  Treatments recommended that may reduce tree injury and mortality includes the following:  the removal of severely infected trees in the early stages of the outbreak, the removal of the larger trees and those on steep slopes which are said to be the most susceptible, and thinning to remove the proportion of beech and maintain stand vigor.  Future thinning activities should concentrate on increasing the dominance of maple and birch and less on beech.  Diseased beech can be cut and used for you firewood needs.  Some stands seem to have beech that remain healthy.  These trees may have some resistance and should be left. 


Shoot Blight of Red Pine:  Infection of red pines and several other species of hard pines by Sirococcus shoot blight has become increasingly common throughout Maine.  The disease is caused by the fungus Sirococcus conigenus.  The disease infects current-year needles soon after they emerge from the buds during the spring and early summer.  The fungus then has the ability to grow from the needles into the current-season shoots, and can kill the shoot tips. Branches die as terminal buds and shoots can no longer support new growth.  As the infections progress over a period of several years, usually from the lower branches to the upper branches, tree mortality can eventually occur.  Thinning stands to maximize air circulation and surface-drying of needles can help to reduce infections.  Ornamental trees can be treated with a fungicide or affected tips may be pruned and removed from the tree.


Hypoxylon Canker of Aspen:  Hypoxylon canker, caused by the fungus Hypoxylon mammatum, is one of the most important killing diseases of aspen in eastern North America.  Young cankers first appear on aspen bark as slightly sunken, yellowish-orange areas with irregular margins.  As infection progresses, the outer bark is raised in blister-like patches and sloughs off, exposing the blackened crumbling cortex.  Many trees infected on the lower bole are girdled and killed within 5 years.  An infection on the upper bole may cause only part of the crown to die, after which a lower branch may become the growing tip of the tree, but the entire tree may then die from suppression.  Some trees are so weakened by decay in the cankered zone that wind breaks the stems before girdling is complete.  There are not any known reliable control methods for this disease at this time.


White Pine Blister Rust:  White pine blister rust is the most serious disease of white pine in Maine.  You will usually notice dead and sunken areas on the trunks and branches of the trees. Small trees usually die but larger trees can live for many years.  Pine do not spread the disease to each other. The disease is spread from the Ribes family.  Currants and gooseberries are the species to be concerned with in Maine. If possible, these plants should be eradicated if they are within 1000 feet of the pine.  Control practices include physically uprooting the species or the use of herbicides (Roundup).  Pine do not spread the disease to each other.  It is also sometimes possible to prune infected areas (cankers) from trees or to excise (cut out) a canker on the stem of a high value ornamental tree, so long as the canker affects less than half the circumference of the tree.  State law prohibits the planting of currants and gooseberries in southern Maine.  European black currants and their hybrids cannot be planted anywhere within the state.


White Pine Needle Casts:  White pine needle cast diseases has been a problem in Maine for many years.  Most recent damage has been shown to be caused by the brown spot pathogen, but two other fungi are also common.  During the past several years, an increased incidence and severity of needle casts has been observed, probably as a result of the excessively wet seasons of late.  These diseases have been observed on white pine throughout the state, but have been most severe in western and southern counties.


Investigation the Problem


There is a method to identifying health related issues with your forest trees.  These are the logical steps you should follow as you try and diagnose a perceived problem.


1.     Try and identify the tree species with the problem.  Many problems, and insect related maladies, are species specific.


2.     Look at other similar trees to see if the problem is present in them or just one or two trees.


3.     Try to find out the history of the property and the surrounding properties.  Talk to neighbors to see if they are experiencing problems with their trees.  See if you can identify any environmental factors that could be causing the problem.


4.     Check the trunk and branches carefully and examine them for wounds .  Wounds and cracks provide entrances for pathogens and wood-rotting organisms.  Wounds can be caused by weather, falling trees, wood peckers, and logging.  Large defects may indicate a potentially hazardous tree that has problems and may be unstable.


5.     Note the position and appearance of affected leaves.  Dead leaves at the top of the tree are usually the result of environmental or mechanical root stress.  White birch are susceptible to sunburn after a harvest.  Opening up a stand can let in too much sun for these trees.   Acid rain has been blamed for dieback in many hardwood species.  Twisted or curled leaves may indicate viral infection or insect feeding.  The size and color of the foliage may tell a great deal about the plant’s condition.  Look for suspicious insects and collect some for further identification.


Other Factors


Winter desiccation, or drying, occurs when the foliage is exposed to cold temperatures and high winds while the ground remains frozen.  The trees can’t replace the moisture lost during the winter and they “winter burn”.  The damage is usually worse along roads where chemicals are use to treat ice and snow.  Usually, the trees recover from this damage.


Logging damage


Logging damage is one factor that can be prevented or minimized during logging operations.  Proper planning and careful operation can keep this damage to the minimum.  This list contains some of the steps that can be undertaken to limit logging damage:


·       Plan skid trails and lay out landings before harvesting operations begin.

·       Assess the stand health and tree vigor. Before the harvest.  Do not harvest all the healthy trees and leave the weak and suppressed trees.

·       Clearly identify the crop trees, and use extra caution when working near them.  This can be done in a variety of ways such as marking or "agreed on" harvest limits.  The operator has the responsibility of minimizing the damage when he is harvesting.

·       Use branches and slash in trails as a protective roadbed.  This practice also returns vital nutrients to the forest and the nutrients will be made available to the next crop.

·       Use sacrificial "bumper trees" along skid trails - designate before the harvesting begins. A good operator knows how to choose them and use them.

·       Consider what season to harvest - usually there is less damage during winter months.  Bark is easily injured from early spring through summer.

·       Use silvicultural prescriptions that concentrate harvesting activity to limited areas (i.e. small "patch cuts.")

·       The landowner, forester, logging contractor, and equipment operator all share in job performance responsibilities.

·       Agree to be more "weather sensitive" when harvesting.  Delay conditions earlier when wet conditions occur. Do not harvest after long periods of rain.

·       Extraction of larger pieces has higher potential for causing damage than that for smaller stems.  The crowns are larger and they can scrape trees along the trail, ruin regeneration, and cause unsatisfactory results.

·       Extraction of heavy loads has higher potential for causing damage than that for lighter loads.  The operator is responsible for making smaller bunches or loads.

·       Avoid harvesting “wolf” trees.  These are large trees with big crowns and will cause damage when removed.  The operator can remove some of the top and leave it in the woods. Whenever possible, leave as wildlife trees.

·       Mark skid trail locations prior to harvest.  This can help protect sensitive areas and areas you want to protect.  Sensitive areas can also be flagged off to keep access off limits.

·       Assess risk of sun scald to residual trees, especially white birch - consider trail and access and corridor orientation.


Maine Firewood Ban


The 124th Legislature instructed the Maine Forest Service to ban the importing of firewood because of the demonstrated threat the firewood poses for bringing serious non native pests into the state. Help protect Maine from invasive and alien insects.  Do not bring firewood in from neighboring states.  If you suspect someone has brought in firewood, call the Maine Forest Service.  They will confiscate it and destroy it.  Click the fact sheet for more information:  Maine Forest Service:  Firewood - Out of State Firewood Ban


Insect Alert


The Asian longhorned beetle (ALB) is a woodboring insect that attacks a wide range of hardwoods including all species of maple, birch, elm, poplar and willow (  Damage by the beetle would impact the health of forests, appearance of our neighborhoods and integrity of our infrastructure.  In addition, it would lead to losses in the forest products, maple sugaring and tourism industries and require a costly control effort.  See article on this site for complete information:  Beetle Alert

Emerald Ash Borer Alert


Origin:  Asia - Many new infestations center around campgrounds, implicating camp firewood in this insect’s spread.


Hosts:  Ash. 


Nearest Known Occurrences:  Emerald ash borer is now known to be within a half of a day's drive of Maine's border. It has been most recently found in Dalton, Berkshire Co., Massachusetts and around Prospect and Naugatuck in   New Haven Co., Connecticut; Toronto, ON Canada; Montreal Area (Montérégie Region), QC, Canada.


Description:  Metallic green beetle with wings and body tapered towards the rear.


Signs and Symptoms:  Symptoms and signs include D-shaped adult exit holes, bark splitting, serpentine frass-filled (sawdust-like waste) feeding galleries, wood pecker feeding, crown dieback, and epicormic shoots (whips growing off the trunk and branches). Many of these symptoms and signs are similar to other insects and diseases of ash. Is it EAB?


Damage:  Larval feeding under the bark girdles and kills ash trees. Since its discovery in the United States in 2002 emerald ash borer has killed millions of ash trees.

​Maine Forestry

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