Alder Flea Beetle (Altica ambiens) ­­– Populations of alder flea beetle seem to be enjoying a boom.  Field technicians in our inventory unit noted that they needed to close truck windows to avoid larval intrusions to the passenger cab when travelling roads overarched by alders and several have noticed and reported the stretches of alder with lacy brown leaves along roadsides in their travels through Maine.  In his documentation of the biology of the alder flea beetle (MAES Bull. 265, 1917) William C. Woods describes the scene of an outbreak of this species well: “…By the middle of August practically all of the leaves of every alder bush…had been skeletonized by the larvae, and the trees looked brown and bare as though they had been swept by a fire.”  Although infestations have not uniformly reached that level, copses of alder can be found that fit that description.  This is not an economic pest in Maine, as alder are of little economic significance. 

Photo: Alder flea beetle adult on damaged alder leaf. (MFS Photo)

Outbreaks are reported to last two to three years.  Woods noted that the flea beetle prefers to oviposit within the leaf-rolls created by alder tubemaker moths (Acrobasis rubrifasciella), and noted that a drop in numbers of the moth coincided with the collapse of the 1912-1915 outbreak of alder flea beetle.  A quick lunch-time search of alder around the Old Town office revealed some sign of the tubemaker (one frass tube) and ample evidence of alder flea beetle including damage to foliage and feeding adults (along with two species of sawfly, woolly alder aphids and two Calligrapha spp. beetle).  

Asian Longhorned Beetle (Anoplophora glabripennis)– August has been designated “tree check month” by the USDA APHIS, in part because of the August 2008 detection of Asian longhorned beetle in Worcester, MA.  We are in the period now where we would expect peak emergence of adult Asian longhorned beetles in Maine if it were here. Asian longhorned beetle has not been confirmed in Maine.  Please take some time to become familiar with its appearance and the damage it causes so if it is in Maine we find it early and respond quickly.  If you need informational material to distribute to friends or clients please let us know.  You’ll find more information at www.maine.gov/alb. 

Photo: The invasive Asian longhorned beetle (left) and native look-alike (right) (Photo PA DCNR)

Balsam Woolly Adelgid (Adelges piceae) – Observations have come in from many corners of balsam woolly adelgid (BWA) populations rebounding.  High density trunk phase populations (those found on the stems of the tree) have been observed in New Sharon (Franklin County), Rome (Kennebec County) Bangor (Penobscot County) and Washington County.  Populations of moderate density have been observed in Lincolnville (Waldo County) and Calais (Washington County).  Combine current populations with a history of chronic infestation and the stress of an abnormally dry growing season and you have a formula for increased fir mortality in Maine’s coastal and interior regions (http://digitalcommons.colby.edu/cgi/viewcontent.cgi?
article=1002&context=atlas_docs).

Photo: Three wool-covered balsam woolly adelgid (in crevice above finger) and a predatory green lacewing larva (Chrysopidae) covered with BWA corpses and other debris (right of BW). (MFS Photo)

Browntail Moth (Euproctis chrysorrhoea) – Browntail moth larvae have hatched and are skeletonizing the leaves of oak and apple trees in the Midcoast region. The infestation will again be severe in Sagadahoc County and spreading into Freeport, Yarmouth and Falmouth (Cumberland County). Reports of moths and/or damage have come in from Eliot to Rouque Bluffs indicating spot infestations may be found anywhere along the coast and inland as far as Turner (Androscoggin County) and Waterville (Kennebec County).

Photo: Developing overwintering web of browntail moth caterpillars.  Note the characteristic binding of the leaf stems to the twig with tight "ropes" of silk (top of photo). This will keep webs fastened to the tree through tough winter storms, allowing the caterpillars to be right next to their food source when the buds just start to swell. (MFS Photo)

Look for brown leaves at the tops of oak and apple right now and leaves wrapped tightly together at the very tips of oaks and apples once the rest of the leaves have fallen. Consider what your strategy for next year will be.

Dogwood Sawfly (Macremphytus spp.) – Dogwood bling?  That is how this insect is described by one University of Illinois extension specialist, http://web.extension.illinois.edu/cfiv/eb294/entry_9063/.  Unless you catch these guys early, it is probably the best way to think of them.  Dogwood flowers bring swarms of beneficial insects including adult parasitoids and pollinators, so avoiding broad-spectrum chemical insecticides on this pest is a sensible practice.  If you catch the sawflies early, hand picking and application of horticultural oils or soaps are effective ways to manage their aesthetic impacts. For early intervention, periodically scout your dogwood leaves for eggs and the skeletonizing damage from the gregarious young larvae (photos: http://www.ipm.iastate.edu/ipm/hortnews/2009/8-12/sawfly.html). Dogwoods do tend to survive attacks well so if you miss this window of opportunity, don’t fret, begin scouting earlier next year.  The last instar of this insect wanders in search of a pupation site in soft wood.  This can create a nuisance for homeowners when that soft wood is siding, favorite outdoor furniture or very occasionally structural wood—the nuisance can be compounded by woodpecker activity.  

Photo: Dogwood sawfly larvae are invading the top of this deck post in Rangeley, ME.  (Photo Courtesy David Fuller, UMaine Coop. Ext.)

Fall Webworm (Hyphantria cunea) – The webs of fall webworm caterpillars are quite visible now; building of the webs was underway by mid-July but additions will continue until the caterpillars pupate later this season.  Although unsightly, feeding from this insect does not cause significant damage to its host.  If you want to reduce aesthetic impacts it is best to start looking for this pest in early July.  Two low impact ways to reduce aesthetic damage are to relocate webs or wash them from the tree with a concentrated blast from a garden hose. Both methods may require follow-up and should be employed when the webs first begin to form.  These webs are much looser and larger than those of the early larval instars of browntail moth.  Another way to distinguish the webs is to look at their occupants.  Browntail moth caterpillars are tiny (~ 1/8th inch), the two bright orange glands on their tail-ends aren’t orange in these early instars, but they are there as yellow spots.  Fall webworm caterpillars, just like their webs, are larger (>1/2 inch in most places by now).  

Photo: A look inside a nest of fall webworm caterpillars on gray birch.  These larvae were approximately ½” long on August 26th in Old Town, ME. (MFS Photo)

Leaf-miner on Holly Species (Possibly Rhopobota dietziana) – The mines of a tortricid leaf-miner and –tier on holly (Ilex spp.), possibly Rhopobota dietziana, were seen in abundance in Orono (Penobscot County) and Lincolnville (Waldo County) this month.  Hosts included the understory shrubs winterberry (Ilex verticillata) and mountain holly (Ilex mucronata).  Although the mining itself was abundant enough to be eye-catching in places, the “hook” was a small tube of frass extending out of the mine on the undersurface of affected leaves.  At first glance this resembled spindle-galls found on cherry, but close examination revealed that the hook was made of digested, not galled, plant tissue.  The moth had already departed all examined mines and tied leaves.  

Photo: Leaf-mine possibly created by Rhopobota dietziana on mountian holly (Ilex mucronata). (MFS Photo)

Locust Leaf Miner and Locust Digitate Leafminer (Odontota dorsalis and Parectopa robiniella) – Similarly to the attention given to the scorched appearance of alders, people have been noting, some with alarm, the scorched appearance of black locusts.  Some locusts appear untouched by damage and others have scant green leaves.  Significant skeletonizing and mining is being done by a leaf-mining beetle—Odontota dorsalis.  However some mines of a delicate moth species, the locust digitate leafminer, can also be found on the foliage of affected trees.  The previous outbreak of locust leaf mining beetles in Maine caused branch dieback and some locust mortality.

Photo: A mine of the locust digitate leafminer, a gracillariid moth (left) and larval mines and adult skeletonizing damage caused by the locust leaf miner, a chrysomelid beetle (right), Old Town, ME.

Stigmina and Rhizosphaera Spruce Needle Cast Diseases (Rhizosphaera kalkoffii and Stigmina lautii) – Spruce needle cast diseases are commonly encountered throughout Maine where spruce trees are planted.  Needle cast fungi were also recently noticed during a survey of a naturally forested area in central Maine, although symptom severity in most instances in the forest was less than typically seen in landscape situations. The most susceptible host species are Colorado blue spruce and white spruce, with red, black and Norway spruces showing varied levels of resistance.  

Photo: A tree with needle cast symptoms.  Note the lack of needle retention. (Aaron Bergdahl, North Dakota Forest Service)

Photos: (Left image) Current-year needles (1) are infected but do not show symptoms. Second-year needles (2) were infected last year and have begun to show discoloration, spore producing structures appear on some needles and some needles are beginning to fall off. The third-year needles (3) have mostly been cast; the remaining needles contain many spore-producing structures. Trees heavily infested with needle cast disease fungi will not have needles on any growth that is older than three years.

(Close-up needle images) (L) A healthy needle and (R) a needle infected with the Stigmina needle cast fungus showing the fuzzy-looking round spore producing structures.

Aaron Bergdahl, North Dakota Forest Service

Tip Dieback of Red Oaks (Botryosphaeria sp.) – Branch tip dieback of red oaks has been observed in several locations in Kennebec County and a particularly severe site was visited in the Limington area in York County.  The typically observed symptoms include a random pattern of dead branch tips with wilted orange leaves.  Branch samples were taken from the Limington site and a site on the East Side Campus in Augusta (Kennebec County, pictured). Upon closer observation of these samples, cankers were noticed below all symptomatic branch tips and fruiting structures were present near the canker margins. On the Augusta sample, physical characteristics such as staining of the sapwood, the fruiting structures on the canker margins and spore characteristics strongly indicate that the dieback was caused by a fungus in the genus Botryosphaeria (likely Botryosphaeria quercuum).

Photo: Dieback symptoms of red oak twig infected with a Botryosphaeria spp. and (lower right) a typical ‘Bot canker’ (pictured canker is about 1/2inch long). 

The condition caused by these fungi is more generally referred to as ‘Bot canker’.  Typically, disease outbreaks caused by the fungi in this group only last a few years and result in minor damage.  This is because the pathogen is not particularly aggressive and typically does not spread into larger branches causing mortality.  It is believed that outbreaks usually result from some kind of initial stress, weakening trees enough for the Botryosphaeria fungus to cause symptoms. However, the oaks at the Limington site were severely affected and the condition appeared to be leading to large branch and even whole tree mortality of oaks throughout a wooded neighborhood.  For management of high-value trees, the affected branches can be pruned back 8 to 10 inches below the nearest visible symptom.  To avoid spreading the fungus, pruning equipment should be sanitized between cuts with either 70% alcohol or 1:9 bleach to water solution.

While this disease is presently not a widespread phenomenon of great concern, the Maine Forest Service will continue to monitor this outbreak. Anyone with oaks showing similar symptoms is encouraged to report the location and extent of the damage to the Maine Forest Service Insect and Disease Lab. For further information about this topic, please contact aaron.bergdahl@maine.gov.