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Forest & Shade Tree - Insect & Disease Conditions for Maine

April 24, 2007

Welcome readers to the 2007 season of the Insect and Disease Conditions reports.  After undergoing several personnel changes in the Forest Health and Monitoring Division of the Maine Forest Service during 2006, and a brief hiatus in this newsletter, we are back in our efforts to keep foresters, landowners, growers, and others informed of upcoming forest and tree pest issues.  Our aim is always to protect and improve the forest resources of the state, and we appreciate your efforts and interest in this endeavor.

Two major changes in personnel have occurred since this newsletter was last produced.  Don Ouellette, a Forest Entomologist with the Division for 37 years, retired this past September.  Don was critical to the oversight and management of the forestry quarantine program. His professional competence and manner served the public to the highest standards.  While we will miss Don’s long experience and expertise in Entomology, we wish him well as he follows what we hope will be a very enjoyable retirement.  And as many of you are aware, Clark Granger retired last spring after a long and distinguished career as Forest Pathologist here with the Maine Forest Service.   An expert field diagnostician, Clark was always willing to help forest and shade tree clients with a reassuring smile and with helpful and practical information.   We will miss greatly his expertise, and wish him the very best as he enjoys a very active retirement.

As always, we anticipate an extraordinarily busy season.  To accomplish all that we must, we invite you, our loyal stakeholders, to assist us with our mission. We recognize that many of our readers are capable of competently identifying a variety of forest and nursery insects, and are good plant disease diagnosticians as well. We ask you to be vigilant, to make timely observations and to forward them to us. So if you're willing to contribute, please send an email to Bill Ostrofsky indicating the sorts of problems you're willing to report (forest, Christmas tree, nursery, shade tree etc.), and I'll respond with requests for observations during the course of the season.

While all of our staff are anxious to assist in any way possible, we have specialists to help with certain types of problems. Our State Entomologist, Dave Struble, makes policy for the division. Allison Kanoti, who joined the Entomology Laboratory crew last summer, manages insect quarantine activity for the division, particularly hemlock woolly adelgid and pine shoot beetle, and performs insect identifications. Charlene Donahue oversees most of the forest insect survey work, curates the insect collection, and also performs insect identification work. Wayne Searles, Grayln Smith, and Mike Skinner serve as field technicians. Bill Urquhart works both in the lab and field.  Jean Maheux serves as our secretary/receptionist. Bill Ostrofsky, hired last fall, manages diagnoses of forest and shade tree diseases, oversees disease quarantines, responds to Christmas tree problems, and assists in compiling this newsletter.

We have attached the following items to this report for your use:

* Advice and technical assistance sheet (pdf) (rtf).

* Insect Report Form for reporting insect problems (pdf) (rtf).

* Disease Report Form for reporting diseases and unidentified problems (pdf) (rtf).

Have a Great Season!

IMPORTANT: Attached please find a mailing list sign up and renewal form (pdf, rtf). We are required to update mailing lists annually. Please complete and return this mailing list at your earliest convenience.

Laboratory Hours

Our business hours for 2007 will be 7:30 a.m. to 4:00 p.m. Monday through Friday, except for holidays.  However, we may not be able to staff the I&DM Lab at all times. So if you call and receive no answer, please call back another time. And if you plan to visit the Lab, you may wish to call ahead just to make sure someone will be present to meet with you.

Arbor Week This Year is May 21-26

Arbor Day in many states is celebrated on various dates in April with the last Friday in April (April 27th this season) being designated as National Arbor Day. As our season for tree planting is somewhat later than most other states, Maine has chosen to celebrate Arbor Week during the third full week in May which has proven to be better overall for tree planting and other outside activities.

To demonstrate the economic and ecological benefits of urban and community forestry to Maine communities, Project Canopy will host a state wide Arbor Day ceremony on May 21st from noon-3:00 pm at the Augusta State Capitol. There will also be Maine Tree City USA Awards as well as tree seedling distribution during the ceremony. Interested individuals are encouraged to contact Project Canopy regarding specific opportunities such as discussing the benefits of urban and community trees with elected officials, event set-up, handing out seedlings and coordinating local celebrations throughout Maine.

Quarantine News

Maine has five forestry-related quarantines.  These include a quarantine on (1) Ribes spp. (currants and gooseberries), (2) gypsy moth, (3) European larch canker, (4) hemlock woolly adelgid and (5) pine shoot beetle.  The quarantine on Ribes prohibits planting, possessing or propagating plants in the genus Ribes in some parts of the State and the species Ribes nigrum and its cultivars throughout the State.  The four other forestry-related quarantines restrict the movement of certain forest products that have the potential to spread specific tree pests or diseases.   Regulated material may move freely within their respective quarantine zones, but must go to facilities with compliance agreements if they are moved outside of the quarantine zone.  The compliance agreements require certain practices of the receivers to help reduce the risk of spread of the target insect or disease organism.

Over the winter changes were made to the gypsy moth and pine shoot beetle quarantine areas.  The gypsy moth quarantine zone was expanded to include the following towns:

  • In Aroostook Co.:  Glenwood Plantation, Houlton, New Limerick and Orient
  • In Piscataquis Co.:  Shirley, Elliotsville Township, Katahdin Iron Works Township, T1 R10 WELS, T1 R11 WELS, T2 R10 WELS, T7 R9 NWP, TA R10 WELS, TB R10 WELS, TB R11 WELS, and Veazie Gore,
  • In Somerset Co.:  East Moxie Township.

An additional expansion of the quarantined area for gypsy moth is anticipated in the coming months. 

The pine shoot beetle quarantine was also enlarged. The regulated area now includes all counties except Aroostook and Washington.  Regulated material may move freely within this area.  Pine moving from the quarantine zone to Aroostook or Washington County needs to go to a facility with a compliance agreement.

Early Season Guide to Pest Management

The following table should assist you in the early season planning process.  Remember that this is just a guide and that conditions will vary.  Information on any entry preceded by an * may be available on our website or can be requested by calling or writing to the Insect and Disease Laboratory, 48 Hospital Street, Augusta, Maine 04330-6514, Phone (207) 287-2431, Fax (207) 287-2432.

Insect or Disease

Cultural Controls

Chemical Controls

Apple Scab

Remove any fallen leaves not raked last autumn; plant resistant crabapples such as ‘Adams’, ‘Baskatong’, ‘Beverly’, ‘Bob White’, ‘David’, ‘Dolgo’, ‘Donald Wyman’, ‘Liset’, ‘Red Jewel’ and ‘Sugartyme’.

Propiconazole (Banner) or Thiophanate methyl (Cleary’s 3336) or Chlorothalonil (Daconil, Ortho multi purpose fungicide) or Mancozeb (Dithane, Fore, Protect, Zyban) every ten days during wet weather.

*Balsam Gall Midge


Diazinon or chlorpyrifos (Lorsban) late May to early June.

*Balsam Shootboring Sawfly


Lorsban 4E or Diazinon AG500 3 times at 5 day intervals during the 2 weeks following the observation of activity of adults (mid-late April) or in the two weeks prior to normal balsam twig aphid spray dates.

*Balsam Twig Aphid


Diazinon or chlorpyrifos (Lorsban) at bud break.

*Birch Casebearer


Malathion or carbaryl (Sevin) applied after most or all of the cases have moved to opening buds.

Black Knot of peach, plum, and cherry (UMO Fact Sheet)

Prune and destroy knotted twigs and branches.

Thiophanate methyl (Cleary’s 3336 or Fungo Flo) when dormant and twice again at three week intervals.

*Browntail Moth

Clipping of overwintering webs is only effective prior to the time larvae beginning actively feeding on emerging foliage (mid to late April).

The use of pesticides is a complex issue requiring professional assistance.  Call for more information.  New regulations in 2006.

*Bruce Spanworm


Emerges early as buds begin to swell on northern hardwoods, especially beech. Larvae bore into buds. Controls not usually recommended.

Cyclaneusma Needle Cast of Scotch pine

Use disease free planting stock; remove non crop Scotch pines from area.

Chlorothalonil (Bravo) prior to bud break and during wet periods throughout growing season.

Dogwood Anthracnose (USDA How-To)

Remove any fallen leaves not raked last autumn; fertilize trees; prune out dead twigs and suckers; plant Chinese or Japanese dogwood instead of native flowering dogwood.

Chlorothalonil (Daconil 2787), or Thiophanate methyl (Cleary's 3336, Fungo Flo, Zyban) or Propiconazole (Banner) or Mancozeb (Dithane, Fore, Protect) at bud break and again three times at three week intervals.

Dutch Elm Disease

Plant disease resistant elms; eliminate all potential beetle breeding elm material within 700 feet of trees to be protected.

Dormant applications of methoxychlor or chlorpyrifos for beetle vector control if treatment appears on product label.

*Eastern Tent Caterpillar (USDA Pest Alert)

Prune out egg masses on twigs prior to hatch; remove and destroy small tents as they develop (late April-early May)

Acephate, carbaryl (Sevin), cyfluthrin or Bt on warm days when larvae leave tents to feed.

*Fall Cankerworm


Acephate (Orthene), Bt., carbaryl (Sevin), cyfluthrin applied while larvae are small (late May-early June on boxelder in Aroostook County).  Early to mid May on elm and oak in southern Maine.

*Gypsy Moth

Scrape egg clusters from tree boles and larger branches into a container and destroy them.  Complete before egg hatch (late April).

Acephate (Orthene), Bt, carbaryl (Sevin), cyfluthrin, or diflubenzuron (Dimilin) when larvae are actively feeding (early June).

Hawthorn Leaf Spot, Mt. Ash Leaf Spot

Remove any fallen leaves not raked last autumn; plant resistant sorts such as Crataegus crus-galli.

Thiophanate methyl (Cleary's 3336, Fungo Flo) or Chlorothalonil (Daconil) or Mancozeb (Dithane, Fore) as leaves unfold at two week intervals until dry weather.

*Hemlock Woolly Adelgid (USDA Pest Alert)

Watch for signs of infestation and report immediately.

Call for information.

Horse Chestnut Leaf Blotch (UMO Fact Sheet)

Remove any fallen leaves not raked last autumn.

Thiophanate methyl (Cleary's 3336, Fungo Flo) or Chlorothalonil (Daconil 2787) at bud break and twice more at 14 day intervals.

*Larch Casebearer (USDA FIDL)


Carbaryl (Sevin), or cyfluthrin (Tempo) applied after most cases have moved to the expanding needle clusters (late April to early May).

Maple Anthracnose (USDA FIDL)

Remove any fallen leaves not raked last autumn.

Thiophanate methyl (Cleary's 3336 or Fungo Flo) at bud break and twice again at 10-14 day intervals.

Peach Leaf Curl (UMO Fact Sheet)


Chlorothalonil (Bravo) or Ferbam (Carbamate) or Ziram applied as full coverage spray when trees are dormant.

*Pear Thrips (USDA Pest Alert)


Controls and timing not well understood.  Thrips are active on expanding maple buds at which point much of the damage is done.

Pine-Pine Gall Rust of jack and Scotch pine

Prune rust galls from lightly infected trees; rogue heavily infected trees from plantations before May 1.  Use disease free planting stock.

None at this time.

Rhabdocline Needle Cast

Swiss Needle Cast of Douglas Fir

Rogue severely infected trees from plantations before May 1.

None at this time.

*Satin Moth


Tiny overwintering larvae move to expanding buds/foliage to feed by mid to late May.  Treatment of infested poplars and willow should begin early with Bt, carbaryl (Sevin) or cyfluthrin.

Sphaeropsis Shoot Blight of two and three needle pines

Use disease free planting stock; remove non crop tree hard pines from area.

Chlorothalonil (Bravo) at bud break and when shoots are half grown.

*Spruce Gall Adelgids (eastern, Cooley)

Prune off and destroy new developing galls in mid to late June.

Treat infested trees just prior to bud break with carbaryl (Sevin) chlorpyrifos (Lorsban) or imidacloprid (Merit).


Watch for ticks throughout the field season (April-November).  Avoid high risk areas if possible, inspect yourself daily and remove ticks and use repellents as directed.

Compounds containing DEET can be used as repellents.  Those containing the toxicant permethrin can be used on clothing as directed.

*Viburnum Leaf Beetle (Cornell Site)

Where possible, prune off any twigs with scabby, egg-filled holes prior to  May 1st.

Watch early (mid to late May) for developing larvae and treat with acephate (Orthene), carbaryl (Sevin), or chlorpyrifos (Lorsban).

*White Pine Blister Rust

Prune cankered lateral branches from trees and excise stem cankers by removing bark at least four inches above and below and two inches either side of discolored bark.

None at this time.

*White Pine Weevil

Refrain from planting white pine or spruce for reforestation in open areas, on heavy clay soils, or on heavily sodded fields. Correctively prune damaged trees to establish new leaders.

Commercial Forest and Christmas Tree Plantations:  Dimilin before weevil activity commences.  Licensed applicators who have stocks of Lindane on hand may apply for a limited use permit from the Board of Pesticide Control (287-2731).

*NOTE: These recommendations are not a substitute for pesticide labeling. Read the label before applying any pesticide. Pesticide recommendations are contingent on continued EPA and Maine Board of Pesticides Control registration and are subject to change.

Caution : For your own protection and that of the environment, apply the pesticide only in strict accordance with label directions and precautions.

Restricted-use pesticide may be purchased and used only by certified applicators.


*Balsam Gall Midge (Paradiplosis tumifex) - Balsam gall midge populations are still light but Christmas tree growers should still be on the lookout for it. In mid to late May watch for small orange midges, they are often easiest to see in the early evening when the breezes die down.  Treatment is applied approximately two weeks after adults have been seen in large number (late May to early June) as the new needles flare and begin to flatten. 

*Balsam Shootboring Sawfly (Pleroneura brunneicornis) - This sawfly is usually less abundant in odd numbered years and we have not had any reports of outbreaks.  Adults are active at the end of April flying around the fir trees..

*Balsam Twig Aphid(Mindarus abietinus) - Twig aphid tends to be a perennial problem for Christmas tree growers.  Check for aphids in May before budbreak, if trees were damaged last year they may need to be treated this year as the population will build up.

*Browntail Moth (Euproctis chrysorrhoea)  -  The population of browntail moth has decreased dramatically in the past two years.  The “hot spots” are in parts of Brunswick, Topsham, West Bath and Freeport.  In some locations the webs are now found primarily in lower shrubs and trees.  Pruning out the webs and destroying them (drop them in soapy water) may eliminate the problem. Clipping should be completed by the end of April and insecticide applications (if warranted) should be made during the month of May.  There are new restrictions on controlling browntail moth near water so please check before spraying.

*Eastern Tent Caterpillar (Malacosoma americanum) - (USDA Pest Alert) It is still early but it is hard to find an egg mass or tent from these early season defoliators.  Populations will be down again this year, but check your crabapple and cherry trees for the webs in the branch crotches and remove before they get too big. 

*Fall Cankerworm (Alsophila pometaria) - Localized populations of fall cankerworm defoliated trees in York county last spring and adults were active again in the fall.  Look for tiny caterpillars feeding on emerging foliage in late April to early May. Cankerworms feed on a variety of hardwoods, especially oak, elm and apple. Control applied early is more effective then waiting until most of the foliage has been eaten.

*Forest Tent Caterpillar (Malacosoma disstria ) - (USDA Pest Alert) States west of us have been dealing with an outbreak of forest tent caterpillars that has necessitated control programs in Vermont and New York.  Maine has been fortunate to have missed the problem this time around and the population is still very low.  Let’s hope it stays that way!

*Hemlock Looper ( Lambdina fiscellaria ) - There were small pockets of hemlock looper damage reported last year but no reports of large hemlock moth flights so damage should be minimal.  If you had a problem with looper last year, you will want to be on the lookout for it in June this year.

*Hemlock Woolly Adelgid (Adelges tsugae) - (USDA Pest Alert) Hemlock woolly adelgid (HWA) was first detected in Maine forests on Gerrish Island in Kittery in 2003. It has now been found in  five towns in southernmost York County.  These infestations are considered to be the northern edge of the general infestation in eastern North America.  While we have also found HWA-infested landscape hemlocks as far north as Bangor, in all of these cases the hemlocks appear to have been infested when out-planted.  (And these introductions have been eradicated). 

The mild winter of 2005-2006 led to low overwintering mortality of the adelgid, and subsequent population buildups in the infested areas.  Some spot infestations coalesced, new infestations were discovered and populations at known sites increased.  Conversely, assessment conducted this spring showed an average of about 70 percent overwintering mortality after this winter’s weather – and no infestations were found outside the currently infested towns.  Neighboring New Hampshire populations averaged about 55 percent mortality over the winter.  Even though these numbers seem significant, the reproductive potential of the adelgid can offset this level of mortality (2 generations a year, up to 100 eggs to 300 eggs per adult). 

We continue to monitor sites where trees from uncertified shipments were outplanted and where infested landscape trees were detected and destroyed in the past.  In 2006 an additional site with infested landscape trees was reported and treated.  Stay vigilant in inspecting your forest and ornamental hemlocks for the presence of this serious insect pest.  If you would like to learn more about how to look for hemlock woolly adelgid please contact us.

Maine’s present HWA quarantine restricts the importation of nursery stock and logs from infested areas of other states into Maine (interstate movement).  The Maine Department of Agriculture and Forest Service are currently working on a HWA quarantine on movement of hemlock products within the state.  Infested towns that will be under quarantine include Eliot, Kittery, Ogunquit, South Berwick, York, and Wells. This new, expanded quarantine would regulate the intrastate movement of nursery stock and logs from the infested towns.

*White Pine Weevil (Pissodes strobi) - Control of white pine should be under way by the time you receive this publication.  The adults lay eggs and feed on the terminal leader of pine and spruce in early spring.  On ornamentals covering the leader with a nylon stocking secured with a twist tie can block the female from laying eggs. Remove the covering before the leader begins to elongate. This of course is not practical on a large scale and chemical control may be warranted for Christmas tree or timber plantations.

Diseases and Injuries

Weather/Unusually High Precipitation -  The weather exerts considerable control in determining the outcome of many tree pest problems.  The excessive moisture conditions that have persisted over the past two years have been unusual, and it appears this trend will continue on into the coming spring, as well. 

Localized damage to several Christmas tree plantations was reported last year.  Damage occurred where soils were either shallow and overlying an impermeable layer such as bedrock, or where trees were planted on heavier, marine-derived clay soils.  High moisture levels are believed to have resulted in localized pockets of flooding in these soils, with the tree roots suffocating and dying.  Remedies for this situation are difficult and expensive, since this means changing site characteristics, either by surface or sub-surface draining.  Planting trees on sites less prone to flooding is also an obvious recommendation but one option not all growers have.

An increase in leaf and needle diseases is also a consequence of excessive moisture.  This is particularly the case when the rains occur during the spring of the year, when needle elongation and new leaf development occurs.  Conifer needle casts and hardwood anthracnoses (see below) may be severe again this year.

On the brighter side, cool, wet springs also favor development of pathogens of some of our most serious insects, including gypsy moth, forest tent caterpillar, Eastern tent caterpillar, and browntail moth.  These pests have been kept in check over the past  two years, largely as a result of the wet, cool springs.

Another positive effect of the wet weather is on overall tree vigor.  While it is true that some growers have seen some tree mortality from flooding, the great majority of the forests and woodlands in Maine thrive with abundant soil moisture.  Considering the alternatives of too much or too little moisture, drought will damage more trees over a wider area, and across a wider array of site conditions, than will high moisture levels.   We should consider ourselves fortunate that we are not experiencing droughts similar to those of the mid-1990s and early 2000s.

Anthracnose Diseases - (USDA FIDL)Unusually wet weather conditions that persisted throughout the spring, summer, and fall of 2005 and 2006, resulted in a number of widespread foliar fungal diseases of hardwood trees.  Oaks, ashes, maples, and birches were all affected to some degree statewide.  Most notable were Mycosphaerella fraxinicola on ashes in central and mid-coastal regions of Maine, and Septoria betulae on paper and yellow birches in the western regions of the state.  Maples were also similarly affected with other leaf-disease fungi.  Because the trend in wet weather appears to be continuing on into the spring of 2007, careful consideration should be given to providing protection from these leaf pathogens, particularly in ornamental settings, with the use of fungicides.  Should substantial defoliation occur this year to trees already largely or partially defoliated during the previous two years, tree growth will suffer, and overall tree vigor will be lower. 

Rhizosphaera Needle Cast (caused by the fungus Rhizosphaera kalkhoffii) – (UMO Fact Sheet) Very wet spring seasons also seem to have provided ideal conditions for buildup of Rhizosphaera needlecast infection on spruce, especially in landscape situations. We have received calls from many homeowners who report thinning of the lower crowns of their spruce trees, particularly Colorado blue spruce and white spruce. Most frequently affected are border plantings of larger blue spruce, where trees provide a screen between abutting properties, but solitary trees may be affected as well. The thinning lower crowns on the border trees have the potential to compromise their function of providing privacy screens.

While it is possible to spray for control of this disease in the landscape, it is not often done. For effective control, at least two sprays are required (at half needle elongation and again when needles are fully elongated), and affected trees are often so large and numerous that chemical control efforts are discouraged.

Rather than spray, many homeowners will opt for resistant varieties (Norway spruce is among those exhibiting resistance) or the screening effect of a thinning blue spruce border planting may be reinforced by planting another evergreen hedge (not spruce) in front of the infected border trees.

For those who do wish to spray, chlorothalonil alone, or in combination with other fungicides, is effective.

Salt Damage (caused by movement of deicing salts from road surfaces to susceptible plant species) - Symptoms of salt damage to roadside vegetation were not more prevalent than usual during the past winter season. Heavy snows this year occurred relatively late in the season, from mid-February on.  Temperatures after most storms became reasonably warm, likely resulting in less use of salt.  Likewise, there was little need for use of salt for deicing in the late fall and early winter of 2006

Salt damage, when it does occur, is of two types: (1) foliage browning, especially of white pine growing very closely to traveled road surfaces, the result of direct salt deposition on foliage due to the action of passing traffic and (2) foliage browning of fir, hemlock and white pine, growing at greater distances from traveled road surfaces, but sited where root systems could take up pooled, salty water.

Most but not all affected trees will recover as the season progresses, with new green growth masking the presently brown needles, many of which will fall prematurely as the season progresses.

Winter Injury - Every winter season brings damage to nursery and landscape trees through snow and ice breakage, cold temperatures, and winter dessication. Often these effects are immediately apparent as winter browning and broken stems, but often damage doesn't become conspicuous until flower buds don't break into bloom or worse, no buds break at all because a plant has died over winter.  The last two April snowstorms of the season resulted in substantial branch breakage, especially of white pines.  Milder temperatures allowed the heavy, wet snows to build on the branches, resulting in branch failure.  We expect reports of instances of winter injury to increase as the spring season unfolds, and damage becomes more apparent.

If you have recently planted tender landscape stock, especially exotic sorts, and have noted some winter damage, take heart. For many species, hardiness increases with age, and winter injury may diminish over the years as your plants mature.

04/07 Forest Health & Monitoring Division