On August 9, Maine Forest Service (MFS) staff performed the fifth and final year of ground survey as a follow-up to the Anoplophora macularia specimen submitted to our department in spring 2019. The beetle was reported to have been collected two to five years prior at a wooded property in North Berwick (York County), although the collector could not remember the exact year.
During this survey, trees along the road near the presumed point of collection were observed from the ground. Trunks and branches were closely inspected for any signs of adult beetle activity, including egg-laying sites and emergence holes. The surveyors did not find any signs of A. macularia infestation; however, outreach materials were handed out to neighbors in the area to keep an eye out for any large beetles matching the description of A. macularia.
Unfortunately, very little is known about A. macularia and its potential risk to Maine’s trees. To our knowledge, the 2019 specimen was the first time this species had been reported in the United States. Like its cousin, the Asian longhorned beetle, this species appears to be able to survive on a wide variety of trees. In Asia, the most significant hosts appear to be citrus, litchi, and mulberry, but it is also documented to attack willow, chestnut, and maple.
Asian long-horned beetle (Anoplophora glabripennis)
On a related note to the previous article, we ask for your assistance in looking out for A. macularia’s more well-known cousin, the Asian long-horned beetle (ALB). Thankfully, ALB has not been detected in Maine to date and the closest confirmed infestation is in the Worcester area in Massachusetts. That being said, firewood movement is one of the primary sources of new ALB infestations (among many other forest pests and pathogens) and Massachusetts is on our doorstep. As a reminder to all out-of-state visitors to Maine, all out-of- state firewood is prohibited from entering the state.
This is the time of the year that ALB adults are most active and can be readily spotted on the branches and trunks of a variety of trees including one of their preferred hosts, maples. Look for trees weeping sap from egg-laying sites and frass/sawdust from large pencil-sized exit holes up to ½ inch in diameter.
One novel way of looking for ALB is to check pool filters to see if any beetles wound up going for a dip. If you suspect you’ve found one of these invasive insects, try to capture it (at least in a picture, but preferably the beetle itself), accurately record where and when you found it, and report it. The Department of Agriculture, Conservation and Forestry has an extensive resource page on Asian longhorn beetle and other exotic Anoplophora, including reporting instructions.
Image: Asian longhorned beetle adults look similar to some of our native woodborers. Check out the resource page for more information. (Donald Duerr, USDA Forest Service, Bugwood.org)
Browntail moth (Euproctis chrysorrhoea)
Browntail moth (BTM) egg masses across the state began hatching the week of August 7. As this new generation of caterpillars grows, they will begin to construct the web in which they will spend the winter. These webs start off looking thin and translucent but will become more compact as the end of their feeding period approaches, typically in late September or early October, depending on the weather.
Image: BTM caterpillars hatching from their egg mass; note the tiny caterpillars and the exposed white eggs. (Maine Forest Service)
As the young caterpillars feed, they graze on the outer surface of the leaf without consuming the entire leaf. This damage is called skeletonization and causes the leaf to die and turn a copper color. When we perform our aerial BTM surveys in the late summer, we use this damage to help identify where BTM populations are severe. We are starting to see some skeletonization damage visible from the ground. In these trees, leaves on the outer tips of the branches are a copper hue. Staff have noted this damage on the I-95 corridor in southern Penobscot County, southern Somerset County, northern Kennebec County, and northern Sagadahoc County. It is likely also visible elsewhere.
Image: BTM caterpillar skeletonization damage; note the small caterpillars in the upper center of the photo. (Maine Forest Service)
Although it is much less common this time of year, exposure to hairs from previous seasons’ caterpillars can still cause skin irritation. These exposures often happen during activities that stir up hairs in the environment during dry conditions such as performing yardwork or closing camp. Caterpillar hair exposure can also happen through contact with old pupal cocoons which are often still attached to host foliage, in sheltered areas, or on surfaces where hairs settled that have not been washed clean. The caterpillars now feeding on the leaves are unlikely to cause a reaction in most people.
Late summer treatment of the very young browntail caterpillars can be difficult for a few reasons:
The leaf skeletonization damage from the younger caterpillars can be difficult to detect.
Caterpillars in late summer are not necessarily found on the same trees they defoliated in the spring, although this is possible in areas with high populations. If you can’t tell if there are newly hatched caterpillars in your trees, plan to observe them more closely over the winter and decide whether and how to treat them before spring. Do not treat trees with no evidence of browntail moth activity.
Caterpillars produce silk and feed under it, therefore, pesticides sprayed on leaves or other non-systemic pesticides may not be as effective.
Trees injected in late summer may be less effective at absorbing and spreading pesticides throughout the leaves and therefore treatment may not be as effective.
Small caterpillars in August: Browntail or Fall Webworm?
Our native fall webworm (Hyphantria cunea) is a moth that has a caterpillar form that can be easily mistaken for the browntail moth caterpillar. Both insects are active in August and these small caterpillars can be found eating the same host plants and trees, and both insects create filmy silken webs. So how can you tell the difference?
Image: Browntail moth caterpillars have emerged from their egg mass to construct silk webs and skeletonize leaves of their host tree. Old Town, ME. (Maine Forest Service)
(Carefully) Check the web! Oftentimes, fall webworm webs will be larger than browntail webs during late summer.
Look at the caterpillars! If you can safely reach the area where the caterpillars are, check for two dark spots toward the head of the caterpillar. If present, these are browntail caterpillars. If not present, the caterpillars may be fall webworm. Young browntail caterpillars also tend to be smaller (about a quarter of an inch) compared to fall webworm (often longer than a quarter of an inch).
Are there silk ‘highways’? In late summer, browntail caterpillars will build white silk highways to help them travel in their host trees. In trees with fall webworm, although there is silk, they do not create readily observed trails.
Image: Fall webworm caterpillars can be the same color as young browntail caterpillars and may be found underneath silk, they do not have two dark spots near their head.(Maine Forest Service)
If you are still struggling to identify the caterpillars, you can wait until later this fall, when the silk ‘highways’ and small winter webs of the browntail moth are created (see photo below). Unlike the browntail caterpillars’ silk creations, webs of fall webworm will break down through fall and winter, because they do not get used during this time. Finding intact silk ‘highways’ and winter webs in fall may be a good indicator of browntail caterpillar activity.
Image: In late fall, browntail caterpillars create silk ‘highways’ they use for traveling in their host tree and to their recognizable winter webs that protect them during the winter season. Webs from fall webworm will breakdown during fall and winter, so finding intact silk webs and ‘highways’ may be a good indicator of browntail caterpillar activity. (Maine Forest Service)
Coneworms (Dioryctria spp.)
Eastern white pine cones are beginning to brown a bit too early this year and it’s actually due to moth larvae. Coneworms (Dioryctria spp.) bore into the cones of conifers to feed on the internal tissue and seeds, occasionally causing problems in seed orchards. The pinecone below was gathered during routine forest management efforts in Old Town when coneworm signs were observed.
Images: (left) A white pine cone showing signs of coneworm infestation, including premature browning, entry/exit holes, and accumulations of frass and resin; (right) A cross section of an infested pine cone showing a light brown coneworm surrounded by frass. (Maine Forest Service)
In addition to partial browning, 1-2 mm entry and exit holes are seen on the immature cones, often surrounded by a noticeable clumping of frass and resin. The larvae themselves appear light brown with a darker, amber-colored head. Depending on the species, multiple generations can occur over the course of a year, and larvae may enter and exit multiple cones before pupating. Keep an eye out during your summer travels, as this pest has been spotted from Penobscot County to York County and likely is found elsewhere.
Many of the insects of greatest concern for forest health in Maine are notoriously difficult to monitor for, but sometimes you wind up in the right place at the right time. A report from a tree care company in Brunswick in early August alerted us to the presence of adult emerald ash borers emerging from infested trees. When we went to follow-up on the report the next day, this tip did not disappoint, as trees at the reported location were still covered with newly emerged adults. Distracted by mating, they were easy to observe and collect. No matter how much time we spend looking for insects like emerald ash borer, visual encounters like these are still relatively uncommon.
Image: Adult male and female emerald ash borer collected during mating from an infested ash tree flagged for immediate removal in Brunswick, ME. (Maine Forest Service)
Even though Brunswick is within the area currently regulated for emerald ash borer, this detection marks a notable inroad into Maine’s Midcoast region and fills in a relatively open area of our statewide detection map. We have continued survey efforts in neighboring Bath, as this would represent another new county on Maine’s growing list. This significant detection is also timely as we are now in a public comment period on the potential expansion of three forest pest quarantines, including hemlock woolly adelgid and European larch canker, in addition to EAB.
Image: Latest map of areas regulated for emerald ash borer in Maine, including the most recent EAB detection in Brunswick and including proposed expansion area to be deliberated upon during the public comment period. (Maine Forest Service)
To participate in these public hearings and offer comment, please join us on Wednesday, September 6, from 10:00 AM to 12:00 PM. More information is available in the events section at the end of this newsletter.
Biosurveillance for Emerald Ash Borer with Cerceris fumipennis
When it comes to monitoring and surveying for emerald ash borer (EAB), there is no silver bullet. We use several methods, each with its own strengths and weaknesses, and each contributes to our overall goal of understanding where EAB is established. One of the more intriguing methods of monitoring is biosurveillance –using one organism to help search for another. In this case, we locate colonies of Cerceris fumipennis, a native ground-nesting wasp that specializes in hunting beetles from the same family as emerald ash borer, Buprestidae. Conveniently, colonies of this wasp are often found in baseball diamonds, although they can be found in other areas with hard-packed sandy soil and lots of sunlight.
In July and August, we carefully monitor colonies as female wasps are returning to provision their nests with paralyzed beetles. If a wasp returns carrying a beetle that we can clearly identify as a native species, we allow her to return to her nest without interference. If she is carrying a smaller species that cannot be identified in the air, we temporarily capture her with a net to collect the prey she is carrying in the event it could be EAB or other invasive buprestids. This gives us a clear picture of what buprestid beetles are in the area and we have even discovered a few new buprestid record for Maine in this way. We examine the captured, paralyzed beetles to ensure no EAB are among the prey or other invasive buprestids not yet found in Maine, such as the oak splendor beetle. This survey is funded through the USDA APHIS Plant Protection Act Section 7721.
If you think you may have seen these helpful wasps, we are always interested in learning the locations of new colonies. The nest entrances are round holes about the diameter of a pencil, and when the wasps are not hunting or excavating their nests, you can often see their black faces with three yellow patches peering up at you as they guard their nest entrances.
Image: Cerceris fumipennis guards the entrance to her nest. (Maine Forest Service)
Image: Cerceris fumipennis carrying a native buprestid beetle. (Mike Bohne)
The northeast is home to many native species of longhorn beetle. One subfamily, the flower longhorns, (Lepturinae) is especially diverse in eastern North America. One eye-catching species that lacks a common name is Gaurotes cyanipennis. This species comes in two color phases, a metallic purple or green; both color phases have yellow legs. Adults can be found May through August in or near wooded areas as they wander on flowers in search of pollen and nectar. Many species in this subfamily can be found on plants that produce large, somewhat flattened white flowers which are shaped like an umbrella (think Queen Anne’s lace, gray dogwood, or hydrangea). The larval habits of this species are not well-known; however, they do feed beneath the bark of declining deciduous trees and shrubs.
Image: The purple phase of Gaurotes cyanipennis. (Maine Forest Service)
Hemlock Woolly Adelgid (Adelges tsugae)
This is just a quick reminder that hemlock woolly adelgid (HWA) crawlers have settled and are now firmly attached to the hemlock twigs where they will spend the rest of their lives. They are currently aestivating (a type of summer ‘hibernation’). These tiny, almost invisible settled nymphs will remain dormant until October. As the cooler weather arrives, they will begin feeding and growing their white waxy ‘wool’ and will start to become more visible. They will feed throughout the winter but will not start laying their eggs until the beginning of March. Until then, there is very little risk of accidentally moving HWA, and this is a good time of year to do any work needed in your hemlock stands or trees.
Recently, we have received multiple reports of leaf damage caused by the oak leaf tier. While its impact on the overall forest landscape is usually limited, it is known to cause localized defoliation in areas of central Maine. Primarily an insect affecting red oak, this caterpillar will affect other oak species and has also been observed this year on beech.
Images: (Left) two oak leaves attached to each other by silk, with skeletonization evident where overlapping; (right) oak leaf tier larvae exposed when leaves are pulled apart. (Maine Forest Service)
As the name suggests, the oak leaf tier uses silk to fasten leaves together or create folds within them. This allows the larvae to remain concealed while they feed on the leaves, creating skeletonized portions that appear brown from the outside. If peeled apart, the leaves often reveal multiple life stages of caterpillar surrounded by black frass. The larvae tend to vary in appearance, ranging from the striped neonates to later instars which have green bodies and black heads. Mature larvae have pale heads and variable markings along the body.
As oak leaf tier damage progresses, skeletonized portions of leaves may fall away, causing foliage to appear ragged or distorted. Trees can typically survive multiple years of infestation before branch mortality occurs, though often the caterpillar population collapses after only a couple years.
Diseases and Environmental Issues
Beech leaf disease (BLD) continues to be found in new places in Maine, with the disease confirmed in the following counties: Cumberland, Hancock, Kennebec, Knox, Lincoln, Penobscot, Piscataquis, Waldo, Washington, and York. BLD may be established elsewhere, and efforts continue to determine disease distribution through survey and reports from the public.
Data collection on long-term monitoring plots, tracking the progression of the disease at the stand level, have concluded for the year. Nine plots have been established in Maine, some already being impacted by BLD, some that have not. This year marked the first occurrence of finding BLD on a long-term monitoring plot where it was not detected in the previous year (the plot in Acadia National Park). BLD has not been detected on three of the nine plots. While we have not recorded any overstory (mature tree) mortality attributable to BLD on the plots, seedling and sapling mortality has been noted. This is consistent with the timeframe of decline in other states impacted by BLD. There is some speculation that the speed of decline may be accelerated in mature trees already impacted by the beech bark disease complex.
Image: (left) Darkened interveinal tissue, referred to as ‘banding’, is an early symptom of beech leaf disease. (right) The ‘crinkling’ symptom is typical of a more advanced infection and is characterized by smaller leaves and thicker leaf tissue with a rough texture. (Maine Forest Service)
The fungal canker disease, butternut canker, is readily found in native butternut trees throughout their range in the United States and Canada. The disease has led to the gradual decline of the species over the past several decades. Butternut canker is characterized by numerous root flares and both main stem and branch cankers that appear black and often water soaked. There seems to be no resistance to the disease in the native population of butternuts, although some hybrid butternuts occur (crossed naturally or purposefully with closely related species) that show high levels of resistance to butternut canker disease.
This summer, the MFS forest pathologist received a request from a Canadian researcher with Atlantic Forestry Centre Natural Resources Canada to collect butternut canker and leaf tissues for an investigation of genetic aspects of butternut trees and the butternut canker fungus. The request was approved and recently efforts began to sample butternut trees in three different locations in Maine. Butternut trees are not particularly common in Maine due to the specific site requirements of the species and mortality due to butternut canker disease. Despite this, a sufficient number of butternut trees have been located and collections have been successful.
Images: (left) Orange arrow pointing to a small ‘water-soaked’ area of bark indicating a butternut canker; (middle) Extensive necrotic tissue revealed after removing the bark above the water-soaked area; (right) A butternut tree showing many butternut cankers. (Maine Forest Service)
Cherry leaf spot (Blumeriella jaapii)
In addition to numerous other foliar pathogens reported to MFS in 2023, cherry leaf spot has recently been added to the growing list. Cherry leaf spot is a fungal disease that causes patches of necrotic (dead) tissue to form, expanding at the point of infection. These parts of leaves dry and drop out of the leaf, leaving a roundish hole. Similar symptoms can also be caused by a bacterial leaf spot, the abundance of which would also be favored by wet weather. However, reports and observations have not been consistent with bacterial disease.
Image: Fungal lesions caused by the cherry leaf spot fungus. (Zhenya Shevchenko)
General Fungal Leaf Diseases
Fungal leaf diseases were reported in the previous Forest & Shade Tree – Insect & Disease Conditions for Maine. This topic has been raised again in this report due to the high prevalence of leaf diseases that continue to be observed and reported by the public throughout a large portion of Maine. Overall, most of Maine has been unusually wet this year with frequent rains (and increased fogs in coastal areas). This has led to a continued higher volume of fungal leaf disease reports on a variety of hosts. Among the most frequently seen and reported diseases are maple anthracnose, birch anthracnose, apple scab, and cherry leaf spot. Although these diseases look very serious and even cause significant defoliation, serious tree health impacts are not expected unless severe damage occurs in at least two subsequent years. However, more serious impacts may occur in trees affected by these foliar pathogens that already have preexisting conditions like root disease or stem cankers.
Many fungal diseases can be brought under control through cultural practices like raking and composting leaves in the fall since many fungal leaf diseases can overwinter on previously infected foliage. In cases of high-value trees and smaller trees, protective fungicides can be used in spring. These are general recommendations that do not apply to all fungal diseases of trees and shrubs, so confirming diagnoses before treatment is important and will save time and money.
Images: Thin crowns from cherry leaf spot on cherry (left), apple scab on crabapple (middle) and Septoria leaf spot on willow (right). (Maine Forest Service)
MFS received a request for assistance from a landowner in Searsport concerning a weeping variety of white pine that was losing its needles prematurely. Defoliation would not typically be expected at this time (early August) as it does not fit with the defoliation associated with the white pine needle damage complex that often occurs in late June/early July or the natural defoliation of older needles that occurs in white pine in the mid- to late autumn. A site visit occurred and samples were taken for closer evaluation. The fungus present was determined to be from the genus Hendersonia. Interestingly, a Hendersonia species was also identified by the University of Maine causing current defoliation on white pine cultivars in another coastal area of Maine. This is a curious situation of a needle fungus that is not typically considered a significant pathogen, showing pathogenic traits. Literature indicates that Hendersonia species can infect needles previously impacted by other needle diseases. This may well be the case since the wet weather of 2023 has been favorable to fungal disease development of various kinds. Even though the most common white pine needle diseases’ prevalence depends more so on the moisture levels of the previous spring/early summer, the location of the occurrences of Hendersonia in coastal areas could be significant, since coastal fogs provide adequate moisture for development of many needle diseases of conifers. This is an interesting situation that will be monitored in the future.
Images: (left) White pine needles with fungal lesions and spore producing structures; (right) the fungal spores of Hendersonia sp. under magnification. (Maine Forest Service)
Slime Flux and Bacterial Wetwood Staining Trees
Sometimes liquid can build up inside a tree and/or enter from external sources, typically occurring at a branch crotch, or near the lower stem and roots, often at the site of an injury. Liquid containing sugars in these areas can be colonized by a combination of microorganisms, usually yeasts and bacteria. Subsequently, fermentation and other biological processes occur and the liquid may ooze or bubble out of openings near the site. In some cases pressure can buildup in a tree causing the liquid to bubble out, even making a hissing sound in rarer cases. The liquid may be slimy, foul smelling, dark in color and may leave a stain on the trunk. Bacterial wetwood is more often associated with bacterial colonization. Alternatively, yeasts are more commonly associated with slime flux. Occasionally, the liquids associated with these disorders can clog vascular tissues leading to leaf scorch or wilt and even crown dieback.
Some trees have these disorders for years and it never causes more than an aesthetic issue. In trees impacted by wetwood or slime flux, assessing parameters like live crown ratio and crown density/transparency may offer a better indication of general tree health to inform management decisions.
Image: Stained wood from slime flux associated with a pruning wound. (University of Minnesota)
Unexplained defoliation of Maples and other trees
Maple trees have been observed dropping seemingly healthy green leaves in several parts of southern Maine. The species that seems to be primarily affected is sugar maple, although observations have been made of this phenomenon in poplar and oak. There is some speculation that this may be due to the very wet summer. Interestingly, tree responses to overwatering are very similar to tree responses to drought, such as scorched leaf margins (independent of disease signs) and dry and brittle leaves. This may impact fall foliage quality in areas where this occurrence is most common. MFS Forest Health and Monitoring will continue to assess this situation.
Image: Maples dropping leaves that appear slightly scorched (left), ones that have been dropped (middle) and those that are green and apparently healthy (right). (Maine Forest Service)
This Month in History
From the August 15, 1979, Conditions Report:
“American Chestnut: New records of native American chestnuts were listed from Manchester and Hampden. We are interested in receiving reports of American chestnuts even if diseased. Such trees may be useful to researchers testing hypovirulent strains of the fungus against the virulent strain which is still killing off many trees. Many of these trees are just reaching the fruit-producing stage.”
September 6, 2023, 10:00 AM to 12:00 PM: Draft Rulemaking Public Hearing: Quarantine Expansion for EAB, HWA and ELC the Spread of Three Tree Killing Invasive Species
Location: Bolton Hill Regional Office, 2870 N Belfast Ave, Augusta, ME, AND Maine Forest Service Regional Office, 87 Airport Rd, Old Town, ME
The Maine Department of Agriculture, Conservation, and Forestry proposes expanding three forest protection quarantines to slow the spread of emerald ash borer, hemlock woolly adelgid, and European larch canker. A virtual option using the Microsoft Teams platform will be available during those hearings.
The adjustments to the European larch canker quarantine, Chapter 272, extend a state quarantine against the European larch canker to prevent its movement from Hancock, Knox, Lincoln, Sagadahoc, and Waldo Counties and parts of Androscoggin, Cumberland, Penobscot, and Washington counties to other parts of the State to protect Maine’s forest and landscape tree resources. The European larch canker is federally regulated, and this rule fulfills the requirement that Maine must have a similar state quarantine in place because the state is partially regulated for European larch canker. Chapter 272 Proposed Rules Draft (PDF) / Proposed ELC Quarantine Expansion Map (PDF).
Written Comments: If commenters cannot attend the public hearings in person or virtually, written comments must be submitted by 5:00 PM on September 22, 2023. Those attending the live sessions are welcome to submit additional written comments. Comments can be submitted to:
Gary Fish, State Horticulturist Department of Agriculture, Conservation & Forestry 28 State House Station, Augusta, ME 04333-0028 Email: firstname.lastname@example.org Telephone: (207) 287-7545 Fax: (207) 287-7548
September 10, 2023,8:30 AM to 3:30 PM: Maine Woodland Owners Forestry Field Day
September 22, 2023, 1:00 PM: Maine Forest Pest and Disease Update
Location: Common Ground Fair, Unity, Maine
Emerald ash borer in Maine presents a significant threat to millions of ash trees in Maine and other forest pests have made their way to our state, including the spongy moth and browntail moth. Find out how to identify signs of these pests and learn about management strategies you can take. Presented by Tom Schmeelk, MFS entomologist.