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Forest & Shade Tree - Insect & Disease Conditions for Maine
July 14, 2007

We are pleased to announce a new addition to our staff at the MFS Entomology Lab. Colleen Teerling, who comes to us from New Brunswick, joined us in mid-June.  Colleen received her M.S. degree in Entomology from Simon Fraser University and will be conducting work with the hemlock woolly adelgid, the browntail moth, and with many other projects.  She comes to us with 15 years of entomology field and lab experience.  Please join us in welcoming Colleen to our unit!

While the weather this year has been near normal in terms of rainfall, the effects of the previous two years’ of wet weather is still having an impact on tree appearance and health.  Needle diseases on many of the conifers are still quite apparent, even though most infections are on older needles, and occurred in previous seasons. The effects of spruce needle cast continue to be severe and widespread. Diplodia tip blight, Sirococcus needle blight, and Lophodermium needle cast of hard pines (primarily red and pitch pine) likewise have all been visible and damaging over a wide area. And now a needle cast of white pine is causing concern as it affects a larger geographical area than has ever been previously recognized (described under the Diseases and Injuries section of this newsletter).   By contrast, there have been very few samples seen or sent in of hardwood leaf diseases, indicating that infection levels for current-year conifer foliage, as well as for the hardwoods, will be lower.

Tree diseases are in the forefront this year with the insect problems to date being relatively minor in scope (Knock on wood! We do still have late season defoliators to contend with).  Keep an eye out for fall webworm nests and remove them before they get large and unsightly.  Saddled prominent defoliation is expected in western Maine and the Falmouth area and larvae are starting to feed in those areas.

We are very concerned about an exotic insect that has been devastating the ash trees in the central states and has recently been found in Pennsylvania.  The emerald ash borer (Agrilus planipennis) was found in Michigan in 2002 and has since spread to Ohio, Indiana, Illinois and now Pennsylvania (maps).  This insect attacks all species of ash in North America and kills them, no exceptions.  It has already killed millions of trees in the affected states. All forms of ash in the infested area are quarantined - no movement of any ash nursery stock, logs, chips, or any type of hardwood firewood is allowed out of those states.  One of the primary pathways for spreading the emerald ash borer is movement of infested firewood.  People take firewood everywhere.  Just last week during a 4 hour firewood survey at a Maine rest area revealed a  person from Ohio bringing firewood in to Maine despite the fact that he KNEW it was quarantined!

The infestation in Pennsylvania has just been discovered and people may inadvertently move emerald ash borer as they move firewood to camp.  Please help spread the word to “Buy it Where you Burn it” and not move wood long distances.

The weekend of July 20-22 is the fifth in a series of Insect Blitzes held at Acadia National Park.  This year the focus is Spiders, I know, spiders are not insects but somebody has to study them.  The goal of the Blitzes is to help the Park learn what lives in the Park so that they can do a better job of protecting everything that is a part of the ecosystem.  To date ants, moths & butterflies, beetles and flies have been targeted.  Each year new species for Maine have been added to those already known to exist here. 

The Maine Forest Service, Maine Entomological Society, University of Maine, and the College of the Atlantic all work to support the Blitzes. Experts and amateurs join together to collect as many different species as can be found in 24 hours and then pin, label and identify each specimen.  The Blitzes attract taxonomists from all over North America and have gained high acclaim. The Moth & Butterfly Blitz was highlighted on a Maine Public Television Quest show (Summer - Getting the Bugs Out) in 2005, and last year's Fly Blitz was written up in the July 2007 edition of Audubon magazine.


Arborvitae leafminer (4 species) - It is getting late to control the adult leafminers in most of the State. Control may need to take place in August when the larvae hatch and begin mining the foliage.  See issue 3 for control recommendations.

*Forest Tent Caterpillars (Malacosoma disstria) - We finally found small populations of forest tent caterpillar in northern most Maine. The towns of Presque Isle, Fort Kent and Fort Fairfield each had 1-10 acres of trees stripped by the caterpillars but aerial survey showed it was very localized.  The populations may build next year though.

*Fall Webworm (Hyphantria cunea) - The population of fall webworm is expected to be high again this year.  Look for loose tents containing tiny, grayish, fuzzy caterpillars on alder, apple, ash, beech, birch, cherry, elm and oak.  Clip and destroy these small developing tents to help reduce the problem locally.  Carbaryl (Sevin), Diazinon, acephate (Orthene) and Bt are registered for use against this pest.

*Gypsy Moth (Lymantria dispar) - Populations of gypsy moth are generally low and many caterpillars were infected with a fungus spread by wet weather.  This situation is in sharp contrast to reports we have received from our counterparts in the Mid Atlantic states who have been dealing with building populations and significant defoliation.  Anticipate low levels of gypsy moth again next year. 

Mountain Ash Sawfly (Pristiphora geniculata) - The larvae of the mountain ash sawfly are feeding now and damage is apparent on trees infested with this pest.  If numbers do not appear to be that great, wait until next year and either clip off the infested branches or treat when the larvae have just hatched in late June.

Saddled prominent (Heterocampa guttivitta) - Larvae of the saddled prominent and other leaf feeders have been found in the Falmouth area.  Western Maine will be checked next week for larvae feeding on hardwoods.  Now is the time to control these voracious pests before they strip all the leaves from the trees.  Bacillus thuringiensis (Bt), carbaryl and cyfluthrin are registered for the control of the saddled prominent.

Twig Borers on white pine (Pityophthorus sp.) - Flagging of small branches has been very noticeable on white pine in the southern half of the State.   This is caused by a very small beetle boring down the twig.  The damage started last year and became obvious this spring.  This beetle does not harm the tree but it has generated questions. 

*White Pine Weevil (Pissodes strobi) - It’s not too late to correctively prune infested white pine leaders.  Although larvae have dropped out of the leaders in southern and central Maine, pruning will still help trees to retain their upright stature.  Prune back to the first healthy whorl of branches and remove and destroy infested branches (the larvae may still be in the leaders in northern Maine and destroying them will help reduce the population.)  Then select the best lateral of this top whorl and prune off all remaining laterals leaving the single best lateral to form a new leader.

*Yellowheaded Spruce Sawfly (Pikonema alaskensis) - Larvae are gaining size now and defoliation is becoming obvious on roadside spruces.  Control now with Spinosad or carbaryl to limit damage.  The population appears low overall.

Diseases and Injuries

White Pine Needle Cast (Canavirgella banfieldii) – This needle cast  disease, first recognized and named in Pennsylvania in 1996, has caused widespread needle loss to both young and old white pine in western, central, and southern Maine (image).  The fungus infects only current-year needles during June and July, and causes tan spots to appear on the elongating needles.  The browning continues towards the needle tips.  The base of infected needles usually remains green.  A peculiar symptom of the disease is that usually not all needles in a fascicle become infected – two or three in each fascicle remain green and healthy. During the summer and fall, the affected needle parts will turn a reddish brown.  The year following infection, needles are shed.  The needle loss observed this year during mid-June was comprised of needles that were infected last year.  We are monitoring disease progress to see if a high level of infection has occurred this year.

The fungus produces two spore types, asexual spores in pycnidia, and sexual spores in hysterothecia.  In Maine, pycnidia have been identified from one-year old needles collected when still attached to the tree.  Hysterothecia have been found on older needles that have been shed and were collected on the ground.  The crowns of larger trees appeared rusty and off-color before the infected needles dropped.  Now that most infected needles have fallen, crowns appear thin.  There are no controls known or recommended at this time.  However, an alert forester has made the observation that regeneration which had been precommercially thinned was much greener (less infected) that those in areas left unthinned.  Improvement of air circulation, which permits more rapid drying of foliage, may account for this.

The disease has been reported in western Maine from Waterford, Lovell, Bethel, Rangeley, and Farmington.  It has also been observed in Belfast and Searsport.  Reports have also indicted noticeable levels in northern New Hampshire and Vermont.  In Maine, heaviest infections appeared to have been in the western mountain region, but we suspect that the disease occurs, perhaps at less intense levels, throughout most of the central and southern Maine pine growing region. 

Damage from white pine needle cast is expected to be minimal, especially for older (larger) trees.  While regeneration and sapling-size trees may experience a loss in growth, there are no known reports of white pine mortality occurring as a result of this disease.  The high occurrence of this is likely the result, once again, of the extended and abnormally wet weather in the spring and summer of 2005 and 2006.  

Northern White Cedar Survey - Personnel from the USDA Forest Service have been conducting a survey of the condition of northern white cedar in Maine and in Michigan.    Inventory data has indicated an abnormally high level of dieback and decline in many areas, and the survey is attempting to substantiate the trend and determine causal factors.  Assistance with the Maine portion of the survey was provided by several individuals of the Maine Forest Service, Forest Health and Monitoring Division. Several stands of northern white cedar were surveyed in northern Maine in the Ashland area, and across central Maine, from Madison to Penobscot.  Insect and disease conditions observed included scattered, light damage from arborvitae needle miner, needle blight (tentatively identified as Phomopsis, Macrophoma, or both), several internal decays of both brown and white rotting fungi (likely including Armillaria mellea and Poria subacida among others) and mechanical injuries from both natural and timber harvesting-related causes.  Survey results and recommendations will be summarized when the project is completed later this year.

Needle Cast of White Spruce (Rhizosphaera kalkhoffii) – Earlier this season we reported on the substantial damage that ornamental Colorado blue spruce and white spruce were showing as a result of the needle disease caused by the fungus Rhizosphaera kalkhoffii.  Observations in two separate stands in the Aroostook River valley near Fort Fairfield have shown that the disease has also caused substantial needle loss and tree decline on native, naturally occurring white spruce in forest stands. Complicating this condition of stand health is the presence of the spruce beetle (Dendroctonus rufipennis), a native insect that favors the older, largest trees for breeding.  Tree mortality attributed to the spruce beetle is occurring in these stands, and is reported to be fairly common throughout the Aroostook region.   The extent to which the needle cast may predispose these trees to beetle infestation is not known, but is undoubtedly another significant stress with which the affected trees must deal.  In any case, this appears to be the first documentation of significant damage to natural stands of white spruce by Rhizosphaera kalkhoffii in Maine.

Balsam Fir Tip Dieback – Numerous reports and samples have been received over the past several weeks concerning a tip dieback on balsam fir.  On an individual affected tree usually a few, but sometimes many branch tips are dying or dead, and hold needles that are bright reddish-brown in color.  Needles remain attached to the twigs: needle cast diseases have not been found on samples examined.  In most instances, the branch is killed approximately six to eight inches back from the tip.  There are several reported causes of this kind of symptom development, but the one that seems to fit samples we have observed appears to be the result of a minor canker-causing fungus, Fusicoccum abietinum.  This disease has been referred to as “balsam fir red flag.” It appears in late spring and early summer as a very slight constriction between the living portion of the twig and the dead portion.  This is generally considered unimportant except in landscape and Christmas tree plantings.  Tree aesthetics can be improved simply by clipping and removing the dead tips. 

Occasionally, very small mechanical injuries have been found associated with the tip dieback syndrome.  In these cases, damage may have occurred from hail, or possibly by feeding from adult Monochamus  spp. (pine sawyer and related) beetles.  Some trees may have damage from one or the all causes indicated here.  In any case, damage is expected to be minor and easily corrected by pruning.

Sudden Oak Death (Phytophthora ramorum) – Phytophthora ramorum has not been found in Maine, but a survey is being conducted this summer here and in several other northeastern states to monitor for this disease.  Currently, the disease is known to occur in natural forest stands only in California, Oregon, and Washington.  Because of its wide host range, and because many susceptible species are important to the nursery and landscape trades, the potential exists that the pathogen may be moved from infested to non-infested areas, even though strict quarantine regulations are in place. Last year for example, the pathogen was found on infected nursery stock shipped into Farmingdale, and was eradicated. In Maine, four watersheds are being monitored this summer to screen for the presence of P. ramorum.  The four watersheds are located in Gardiner, Brunswick, Wells, and Fryeburg.  These watersheds will be sampled a total of five times during the growing season.  Two sample periods have already been analyzed.  While no P. ramorum has yet been found, all four locations have shown the presence of other Phytophthora species.  Survey results will be available when all sampling has been completed.


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, 50 Hospital Street, Augusta, Maine 04330-6514, Phone (207) 287-2431, Fax (207) 287-2432.

04/07 Forest Health & Monitoring Division                                                                      Augusta, Maine