Forest & Shade Tree – Insect & Disease Conditions for Maine
July 11, 2022
Plan for pine. If those who don’t suffer from allergies are skeptical of whether pollen season is real, look at this photo captured during an aerial survey. Hundreds of feet tall, those plumes are neither dust nor smoke but massive clouds of airborne pollen. This flight through a white pine heavy area occurred at just the right time and place to observe this phenomenon. The clouds were distinctly yellow to the naked eye. For those managing eastern white pine, monitor for a coming seed year in 2023 (fertilization happens about 13 months after pollination, and seeds mature soon after, learn more in the Silvics of North America)!
Image: Plumes of primarily white pine pollen tower hundreds of feet above the trees during the peak pollen season.
Publication available. Are you feeling nostalgia for last year? The Forest and Shade Tree Insect and Disease Conditions for Maine Summary 2021 (aka 2021 Annual Summary Report) was finalized last month and is available for download.
Webinar posted. June’s Forestry Friday Webinar, an overview of beech leaf disease presented by US Forest Service Pathologist Cameron McIntire, is available for “on demand” viewing on the Maine Forest Service YouTube Channel.
Earthworms in the Forest. The Maine Forest Service and our Jumping Worm Work Group partners want to know if you see earthworm damage in your forest.
Do you think you have jumping worms in any setting? Learn the keys for identification and report your observations here. Learn where in Maine jumping worms have been confirmed.
Do you think you have earthworm damage in your forest? Report your observation to the Maine Forest Service.
Earthworms are non-native in Maine due to our glacial history. Their presence in forests that have developed without earthworms can lead to negative outcomes, including faster nutrient cycling and eventual nutrient loss, depletion of duff layers that hold nutrients and water while preventing soil erosion, and other changes that reduce soil integrity, plant growth, and regeneration. Additionally, the loss of forest duff leads to fewer spring ephemeral plants in the understory and ruins the habitat needed for some salamanders, birds, and other wildlife species. The University of Minnesota provides a nice overview of earthworm impacts on forests.
Many are surprised to learn earthworms can be damaging. Some earthworms are considered helpful in managed places such as fields and gardens, but others are damaging even in those settings. Populations of the latter species, the invasive Amynthas, or jumping worms, are expanding in the state. They can quickly turn soil into a loose, coffee ground-like texture, limiting root development and nutrient availability and leading to erosion.
There are no proven management practices for reducing the impacts of earthworms on forests once they are introduced. Preventing the spread of all earthworms into forest settings is key to limiting their damage. To prevent new introductions, consider cleaning soil from your boots and equipment, including deeply treaded tires, before entering forested areas. Don’t dump live worms used for bait; dispose of them in the trash. Don’t assume soil in pots from purchased plant material is free from earthworms’ tiny eggs (cocoons); do not discard it in the forest. Monitor tree nurseries for the presence of earthworms and only use planting media sources known to be earthworm free.
The Maine Forest Service is part of Maine’s Jumping Worm Work Group, led by Maine Bureau of Agriculture’s State Horticulturist, Gary Fish, with members from the University of Maine. The group is interested in knowing about forest sites impacted by earthworms, especially Amynthas worms (jumping worms). Please help us out and let us know where you observe jumping worms or forests with earthworm impacts in Maine. Please provide pictures with your reports.
Browntail moth (Euproctis chrysorrhoea)
Since our last Conditions Report in May, much has happened with browntail moth (BTM). In late spring, we inoculated three sites (Deer Isle, Cumberland, and Chelsea) with fungus-killed BTM caterpillars to test if this would be a viable method for assisted disease dispersal to manage populations. All three sites later showed signs of fungus-related caterpillar mortality. This was confirmed at two of those sites within a week of inoculation and from the third site in Deer Isle by the week of June 20.
Image: Adult moths attracted to an outdoor light.
During the last week of June and early July, we got our first reports of adult BTM. Around the same time that browntail moths start showing up on lampposts, posts on social media abound, encouraging the use of a light trap to “eradicate” BTM. This is not something we encourage for many reasons, including the following:
- Bright lights will draw in more BTM dispersing from other areas.
- People who have tried this method report that they notice more BTM winter webs in their trees, particularly those around the lights, the following winter.
- Many parasitic flies and wasps that attack BTM are also drawn to light, reducing their impacts on browntail moth populations, not to mention other non-target effects.
- Female moths attracted by lights generally hang out on nearby host foliage, with more males drawn directly to the light.
Unfortunately, the females are crucial in keeping the population levels high, so killing just the males won’t make a dent in the population, especially in heavily impacted areas. We recommend keeping unnecessary outside lights off between 9:00 PM and midnight until the beginning of August to avoid attracting more BTM to your yard.
Image: Adult browntail moth resting on a wall. Note the large brown abdomen or “tail”.
People often ask if the adult moths have the same toxic hairs as the caterpillars. The answer is no. The hairs on the abdomens of the adult moths are not hollow and filled with the toxin, nor are they barbed. That being said, some people can experience irritation from exposure to the moths. Keep in mind that many moth species in their adult and larval forms have hairs that can cause a reaction in sensitive individuals.
Many white moth species in the northeast are active around the same time as the BTM. This simple chart can be used to differentiate lookalikes from BTM. Please note that other species may also be confused for BTM.
 Even though we are starting to see adults, both recently vacated and still inhabited pupal cocoons are still present. The coarse silk cocoons surrounding the pupae contain the last cast skin of the caterpillar, or caterpillars, and are full of toxic hairs. Many people become exposed to the hairs through encounters with the cocoons. Cocoons may be found on buildings, vehicles/ trailers, other outdoor equipment, plant stems, branches, and foliage. To prevent browntail from hitching a ride, check vehicles, trailers, and other materials for cocoons or adult moths before moving them.
Emerald Ash Borer (Agrilus planipennis)
There were several significant developments to Maine’s emerald ash borer situation in late June. Within the already regulated area of southern Maine, there were additional finds in towns with known populations and the addition of the town of Fryeburg. These new finds in the already regulated area are becoming a common occurrence. Still, the big news came with two new detections outside the regulated areas in the Oakland/Waterville area and Lewiston/Auburn area. These detections represent the first county detections for Kennebec and Androscoggin counties.
The Oakland/Waterville detection began as a suspicious tree on the side of the interstate with obvious woodpecker damage viewed from a moving vehicle. A follow-up visit soon after revealed emerald ash borer galleries, likely several years old. This is typical, as trees often show no sign of infestation until woodpecker activity reveals the presence of insect larvae. The site is near Exit 127 on I-95 North near Kennedy Memorial Drive. Ground surveys revealed the visible extent of the infestation is limited to that general area. However, there are undoubtedly infested trees nearby that currently show no signs of impact. We will continue to survey the general area and ask that the public report any suspicious ash trees in this general area.
In Lewiston, declining ash and other species were seen from the highway. A follow-up survey detected light EAB damage, with the decline primarily related to site factors. However, further survey found one area heavily infested with EAB less than a mile from the first detection, with many ash trees dead or near death. It appears this infestation started about 6–8 years ago.
One of the most significant impacts of these two finds is the effect on Maine’s EAB regulatory boundaries. Until more information can be gathered, a new emergency order was enacted to stem the flow of potentially infested ash from these infested areas. New regulatory maps and full details of the new emergency order area can be viewed at www.maine.gov/eab.
Forest Tent Caterpillar (Malacosoma disstria)
In an eventful season for all sorts of defoliators, forest tent caterpillar has been active throughout northern Aroostook County. The core damage area spans from Fort Kent to Caribou, though there are likely other scattered pockets in the region. Forest tent caterpillar experiences occasional outbreaks in Maine. The last recorded small outbreak of forest tent caterpillar activity was several years ago in Blue Hill, Hancock County. That was a localized but intense outbreak, resulting in a small area of extensive overstory oak mortality. Though we had hoped to perform a special aerial survey trip to document this latest outbreak area, we, unfortunately, missed the weather window. We did an extensive ground survey and documented just over 8,500 acres of defoliation. Additionally, forest ranger support provided some excellent UAV aerial photos. Caterpillars have now pupated, and recent reports indicate aspen are recovering well from this early season defoliation, and the damage is becoming less noticeable. We will try to document any additional damage when we conduct an aerial survey for spruce budworm impact in the upcoming weeks; however, expect the bulk will no longer be visible.
 |
Image: Two examples of the current forest tent caterpillar defoliation on aspen in northern Aroostook County. Photo Credit Ranger Keith Draper, MFS.
Hemlock Woolly Adelgid (Adelges tsugae)
During June, the Maine Forest Service worked with several individuals and organizations to release Sasajiscymnus tsugae, a tiny predatory beetle that feeds on hemlock woolly adelgid (HWA). These entities, including cities, parks, land trusts, schools, and private citizens, raised money and ordered the predatory beetles last year. During the winter, we worked with them to select the best sites for release and assisted with the releases throughout June. In some of these areas, an integrated pest management program will be initiated with the targeted use of pesticides on selected trees in conjunction with predator releases. This will help keep trees alive long enough for the predator numbers to build up, which may give those more mature trees a chance to survive without chemical protection. We have been releasing these beetles in southern Maine for many years and have recovered them from most of our release sites. The beetles are expensive, and the numbers released in almost all cases cannot control the extremely high populations of HWA. This is the reason for using pesticides – to keep trees alive and healthy as predator populations grow to the point where they can feed on enough HWA to provide control.
 |
Image: (left) A hemlock branch with adelgid from an area where Sasajiscymnus tsugae was not released. You can see the ‘wool’ covering many healthy adelgids; (right) A branch from the same general area, but from a tree on which the predators were released. You can see where they fed on adelgids, disrupting the ‘wool.’ Images Courtesy of Joan Ray.
Large Aspen Tortrix (Choristoneura conflictana)
Swarms of large aspen tortrix, a relative of spruce budworm, descended on the city lights of Fort Kent in late June, and large piles of dead moths accumulated. The larvae of this periodic pest are leafrollers and feed primarily on aspen. However, they can feed on other hardwood host species during outbreaks. Despite occasional mentions of large aspen tortrix in our historical records, it has infrequently reached pest status in Maine. More dramatic outbreaks of this species tend to occur further north in Canada. Urban moth invasions like this have made regular headlines in Canadian news. The tattered, torn condition of the moths seen in Fort Kent indicates they may have had a long and arduous flight and, similar to spruce budworm, could have arrived from a distant location. No damage has been reported, and the widespread aspen defoliation in northern Maine is due to forest tent caterpillar, not large aspen tortrix.
 |
Image: (left) A pile of countless dead large aspen tortrix moths beneath a gas station light in Fort Kent, ME; (right) A pair of tattered large aspen tortrix moths with no wing scales remaining alongside a characteristic large aspen tortrix egg mass. Images courtesy Neil Thompson, UMFK.
Red Pine Scale (Matsucoccus matsumurae)
In June, an infestation of the red pine scale was confirmed to be associated with red pine mortality in the northern end of Deblois in Washington County. This is the furthest inland damage from the red pine scale confirmed in Maine. This insect has been associated with a high level of mortality in planted and natural red pine in coastal Hancock and Washington counties and has been observed in southern York county. Often this insect is noticed only after significant tree mortality begins. Those who manage red pine for commercial products should monitor stand health regularly to be able to capture volume before degradation caused by the attack of this insect. Work on control of red pine scale in ornamental systems is minimal, but measures against similar sucking insects may be effective.
Image: Red pine scale-impacted red pine trees in this stand in Deblois give a red hue to the tree line in this photo.
Spongy Moth (Lymantria dispar)
The continued spongy moth outbreak in southern Oxford County and other scattered locations throughout Maine has brought widespread and intense defoliation in some areas. An estimated 35 thousand acres were documented during mid-June aerial survey. Overall, about 55 thousand acres of damage were documented in 2021. We decided to fly over the damage as soon as possible in 2022 to take advantage of available flight time and provide prompt information. However, these flights probably underestimate the full extent of the damage. This is evident from road travel through the core affected areas over the past several weeks when we’ve observed damage progression.
The damage has remained centered on southern Oxford County, from Brownfield to Stoneham, but extends into other towns. There remains another large outbreak area in the Jay and Canton area, with several additional small pockets scattered around the State. This was the first year we received a damage report in Enfield and Bradley (Penobscot County), both in aspen stands dominated by root sprouts.
 Image: An example of spongy moth defoliation in Oxford County. Note the Fryeburg Fairgrounds in the background.
Damage is nothing short of dramatic in certain areas. While some other defoliators get close, spongy moth caterpillars can truly achieve 100% defoliation of trees with not a single leaf remaining. This is because partially consumed leaves are clipped from trees as caterpillars move onto new ones. This behavior is evident on the forest floor, scattered with a thick carpet of these partially consumed leaf fragments. Despite these odds, hardwood trees can still recover under the right circumstances. We are fortunate that the areas affected this year have not simultaneously experienced drought conditions as they were last year.
Mature spongy moth caterpillars can switch from hardwood hosts to conifer hosts once the preferred hardwood food source has been exhausted. Unlike hardwoods, conifers cannot respond to defoliation by producing additional foliage later in the season, meaning this damage is more often lethal. Many pines and hemlocks especially will succumb to the defoliation damage. As for hardwoods, if we experience a population collapse, chances for overall recovery remain good, but it’s difficult to say how long an outbreak will last. From a forest management perspective, one of the most important things we can do is allow trees time to recover from the damage. Any hardwood harvesting using partial harvest systems in spongy moth affected stands should be delayed until several years after the outbreak has subsided, if possible.
Spongy moth outbreaks are fast and furious. As we’ve already witnessed, the damage went from minimal to off the charts from one year to the next. Now that the outbreak has been present for two seasons, the massive population of caterpillars becomes more prone to natural pathogens contributing to population crashes. One of the most important fungal controls is Entomophaga maimaiga, a fungal disease similar to the one that impacts browntail moth caterpillars (Entomophaga aulicae). If you observe dead caterpillars hanging straight down, chances are this fungus has killed them. Another important control is a nucleopolyhedrosis virus (NPV). If you see dead caterpillars hanging in an upside-down “V,” this virus has likely affected them. Fortunately, we’ve seen widespread evidence of both in areas like Fryeburg and Lovell, and they are probably present throughout the core affected area this season, given, in part, more normal precipitation patterns. Higher levels of disease were observed in both the Bradley and Enfield infestations.
At this point in the season, most caterpillar feeding has concluded in most areas, and the spongy moth is pupating. Adults will emerge in a few weeks towards the end of the month. Hardwood trees should show the first signs of recovering along generally the same timeline. There will undoubtedly be spongy moth in 2023; an approximation of how bad it will be where you are can be made using simple egg mass surveys.
Image: At extreme populations, spongy moth caterpillars are vulnerable to viral and fungal epizootics. An example of caterpillars that have succumbed to disease in Fryeburg, ME.
Spruce Budworm (Choristoneura fumiferana)
The spruce budworm monitoring season has begun with the installation of our pheromone trap network throughout Maine. With our cooperators, around 360 sites have been installed this season. A huge thank you is due to our cooperators for their help with this massive undertaking. Observations of vacated pupae and automated pheromone traps operating in northern Maine that provide daily data indicate that the earliest moths have emerged. We look forward to seeing what our seasonal pheromone traps reveal when retrieved in the fall.
A limited amount of aerial spraying occurred during June 2022 at two locations on private landholdings in northern Maine. These areas were identified as “hot spots” through the 2021/2022 overwintering larval survey and have been treated following the Early Intervention Strategy being tested in Atlantic Canada, with the management goal of preventing more significant defoliation issues in the future. Overall, total treatment acres dropped to less than 2,000 in 2022 compared to around 5,000 in 2021. The single area treated in 2021 did not require follow-up treatment in 2022.
Aerial and ground surveys for SBW defoliation damage are planned for the upcoming weeks. We plan to fly over known damage areas documents in 2021 for comparison and search for visible defoliation in new areas. On the ground, 60 sites evaluated for SBW defoliation in 2020 and 2021 will be re-evaluated in 2022 using the Fettes method. These sites showed little variation in defoliation levels between 2020 and 2021.
For a complete review of last season’s statewide SBW monitoring activities, please read our complete Spruce Budworm in Maine 2021 Report.
Winter moth (Operophtera brumata)
We have received many reports of winter moth damage this year from across coastal Maine. Reports have come in from Phippsburg, Kittery, Casco Bay Islands, South Portland, West Bath, and Harpswell. A field crew also ground surveyed severe defoliation in South Bristol and moderate defoliation in Mount Desert and confirmed winter moth damage in those places. Collection efforts were conducted by Forest Health and Monitoring Staff and staff from Rachel Carson National Wildlife Refuge, an intern (Gianna) from the MFS Forest Protection Division, and Joe Elkinton and Jen Chandler from the University of Massachusetts. Over 6,700 caterpillars were collected from 6 field sites (2 additional sites yielded no collectible material). Half of these caterpillars were reared to pupation in Maine. They will be transferred to the Elkinton Lab at the University of Massachusetts to assess the level of parasitism by Cyzenis albicans, a host-specific species of fly that serves as a biocontrol agent for winter moth.
The remainder of the caterpillars were brought back to Massachusetts by their lab’s staff. The parasitic flies that result from these efforts will be released at a site yet to be determined in Maine in the spring of 2023. Some of this work in the coming years will be supported by a grant from the USFS to the Elkinton lab announced in late June of this year.
Join us September 9 at 9:00 am for a Forestry Friday Webinar on winter moth biocontrol from the Elkinton Lab. Details will be added to the Maine Forest Service Calendar of Events at www.maineforestservice.gov
Ash Rust (Puccinia sparganioides)
Recent reports of a severe disorder affecting many ash trees in Columbia Falls (Washington County) prompted a visit by MFS staff in late June. The disorder impacting the trees was severe ash rust. Like most other rust fungi, this disease requires two hosts to complete its life cycle: any of Maine’s three native ash species (white, green, or black) and a cord grass (Spartina spp.) which are commonly found in coastal tidewater areas. The effects on the grasses are seldom noticed or reported; however, symptoms on ash, especially those as severe as seen in Cherryfield and Columbia Falls, are hard to miss. Symptoms typically appear mid-June as small yellow to yellow-orange spots on upper leaf surfaces. Bright orange clusters of fungal spore-producing structures (aecia) develop within two weeks and become apparent on stem and leaf undersurfaces, causing swelling and distortion of tissues. By early July, affected tissues may begin to die and fall from trees, causing severely infected trees to appear scorched – resembling herbicide exposure or extreme drought stress. More vigorous trees may flush new growth that will be smaller, causing crowns to appear thin. Severe infections occasionally result in the mortality of smaller trees. Ash rust rarely kills large landscape specimens. Although as with any tree stressor, impacted trees can become susceptible to secondary agents of decline. Management of ash rust is seldom warranted but may be attempted on high-value trees. Applications of fungicides containing myclobutanil starting at bud break and repeated at two weeks and four weeks post-bud break may provide some control, but this approach has not been thoroughly tested under Maine conditions.
 |
Image: (top left) A branch with light/moderate symptoms of orange pustules and deformed growth from ash rust; (top middle) An ash leaflet with rust pustules on the leaves and rachis; (top right) Multiple rust pustules and severe deformation of leaves and twigs; (bottom left) A moderately infected ash tree with about half of its leaves remaining green, appearing a bit brown/orange next to healthier trees of other species; (bottom middle) An ash tree showing the scorch-like symptoms and lack of green leaf tissue associated with severe infection and peak symptoms; (lower right) A leaflet dropped from a tree with severe scorch-like symptoms.
Beech Leaf Disease (Litylenchus crenatae mccannii)
The range of where beech leaf disease (BLD) can be found in Maine has expanded significantly since the initial find of the disease last year in Lincolnville (Waldo County). To date, BLD has been detected in Hancock, Knox, Lincoln, Penobscot, and Waldo counties, with the furthest north report from south of Burlington (Penobscot County), the southernmost report from Rockland (Knox County), the easternmost reports from Aurora and Ellsworth (Hancock County) and furthest west report from Somerville (Lincoln County). BLD is expected to occur at varying levels of severity within these geographic boundaries and may occur beyond these boundaries in areas not yet detected.
Images: Known BLD distribution in Maine as of July 1, 2022.
Symptom severity has increased considerably in the areas where beech leaf disease was discovered last year, consistent with the rapid progression of the disease, also seen in Massachusetts, Connecticut, and Rhode Island. The reason for this is unclear and differs from disease progression, for example, described in Ohio. For up-to-date information about BLD in Maine, visit the Maine BLD website.
Researchers in Ohio have been conducting BLD treatment trials since 2017. Some encouraging preliminary results have been noted through these trials involving several products and modes of application. To date, the most effective BLD treatment includes using phosphite products, essentially high-potassium fertilizers. Several phosphite products are available on the market and available to the public. These products are not restricted-use substances, like many pesticides, and can be applied by homeowners. The product used in the Ohio trials is called PolyPhosphite 30. In the trials, small trees (<4-inch-diameter trees) were treated with the PolyPhosphite 30 twice a year for five years. Treatment resulted in improved tree health and canopy characteristics. Treatment information can be found on the MFS BLD website in the ‘Treatment’ section.
 |
Images: (left two photos) Comparison of natural shading (red arrows) to the banding symptom of BLD (green arrows); (right two photos) The lower- and upper-side of a beech leaf with a single BLD band, highlighting the challenge of detecting BLD in areas where the disease occurs at trace levels. Photo Credit: Kelby Leary, MFS Intern.
Beech Anthracnose (Discula umbrinella)
Compounding beech tree health issues recently is an increase in June reports of beech anthracnose, both in areas with beech leaf disease and areas where the disease has not yet been found. Beech anthracnose causes brown lesions on leaf tissue. Symptoms can vary greatly depending on the stage of leaf expansion when the beech anthracnose spore landed on the leaf and initiated infection. Leaves infested early tend to have larger lesions, and a greater degree of leaf deformation as the leaf expands around leaf tissue killed by the fungus. Leaves that have already expanded when infection occurs will have smaller, more uniform lesions. Typically, beech anthracnose, like the several other specialized anthracnose diseases impacting the leaves of other tree species in Maine, can be a significant stressor when severe but is usually not a danger to trees. Trees are seldom severely defoliated and can be expected to leaf out the following year, and they may even set new buds and leaves in the same year as defoliation. Beech anthracnose is sometimes mistaken for beech leaf disease. For images of other beech leaf disease look-alikes, see the MFS BLD website.
 |
Images: Beech anthracnose damage to a beech tree and a close-up image of a damaged leaf showing large and small lesions/necrotic (dead) leaf tissue.
Birch Anthracnose (Cryptocline betularum or Discula betulina)
Birch anthracnose is a fungal disease of birch leaves characterized by symptom development from mid-June to July. Like beech anthracnose described above, birch anthracnose causes necrotic lesions on leaves, often noticed as brown spots surrounded by a light-colored ring (referred to as a ‘halo’). Like other anthracnose diseases, defoliation may occur and is almost always worse in the bottom third of the crown – this is where relative humidity stays higher for the longest duration, allowing for greater success by these moisture-dependent fungi (most fungal forest pathogens are highly dependent on moisture). Because of this, avoid planting birch trees (and other susceptible hosts of other anthracnose diseases) in low-lying/moist areas or areas where airflow is inhibited. Preventing vegetation from growing into the lower crown will also encourage more rapid drying of foliage and may reduce disease. Also, avoid lawn irrigation practices that directly wet foliage, which prolongs leaf wetness and may promote disease development.
 |
Images: (left) A river birch leaf with anthracnose lesions; (middle) Birch leaves shed due to fungal infection; (right) River birch trees showing severe defoliation with worsening symptoms from top to bottom, a pattern typical of fungal leaf diseases. Images Courtesy Donald Paine.
Drooping New Growth and Purplish Foliage in Red Oak
Drooping oak foliage has been witnessed and reported in Kennebec and Lincoln counties and may exist elsewhere in Maine. The foliage of affected oaks has appeared reddish, leading to reports from concerned foresters, land managers, and the public. In mid-June, a landowner in Waldoboro reported this symptom, worrying it was an early symptom of oak wilt (oak wilt has not been found in Maine, but we are on the lookout for this potentially serious fungal pest of oak). Upon visiting the site, no typical oak wilt symptoms were seen, such as wilting or summer defoliation, and the reason for the drooping appearance of oak crowns became clear. The oaks exhibiting this character had been growing at a remarkable pace for the species. The new growth had been growing so fast that it was not becoming sufficiently rigid and, as a result, was flopping over, leading to a droopy or wilted appearance. The rapid growth in some areas is assumed to be due to the ample moisture supply up to that point in the growing season. The reason for the reddish growth coloration is unclear, although it could be nutrient deficiency related to the rapid growth or increased production of reddish anthocyanin pigments due to environmental conditions. This demonstrates the growth potential of oaks in good growing conditions.
 |
Images: (left) A partial section of new growth from an oak tree in Lincoln County showing purple coloration; (right) The long new growth of oak drooping over to give the tree a weeping/wilting appearance. This new growth measured 22 inches in early June.
Dutch Elm Disease (Ophiostoma ulmi, Ophiostoma novo-ulmi)
Dutch elm disease (DED) symptoms have been visible since mid-June throughout Maine, which seems to be a bit early compared to previous years. Also, this year the disease seems to be spreading very effectively, with more trees in a given area becoming infected instead of the typical scattered pattern of infection. Symptoms of DED often start as a yellowing or wilting branch (referred to as a flagging branch or ‘flag’) often (but not always) near the outer portion of elm tree crowns. These initial infections occur when elm bark beetles that emerge from elm trees recently killed by the DED fungus carry spores of the causal fungus to healthy elms when they feed before mating. Symptoms progress at varying rates toward the inner crown, with smaller and eventually larger branches dying. When the DED fungus reaches the main stem, more extensive crown symptoms are seen, and tree death occurs soon after. Most elm trees infected with DED die within a year or two of infection. The fungus that causes DED will eventually spread throughout the tree following infection, including the roots. Like several other tree species, elms growing next to each other have a habit of connecting their root systems (called root grafting). This can allow DED to spread to adjacent trees underground. When neighboring trees’ root systems are infected, whole-tree symptoms and mortality occur rapidly. There is no cure for trees infected with DED. Attempts to prune out infected limbs are very seldom effective. Although there are ways to protect high-value elm trees from DED, these methods need to be administered with specialized equipment by a trained arborist and can be very costly. If you wish to plant an elm tree, select a disease-resistant cultivar and plant it where it can grow vigorously. Several cultivars have been developed that resemble the iconic American elm and provide services similar to this once abundant tree on the landscape and in urban environments.
 Image: (left) An American elm tree in the early stages of infection in Littleton, August 16, 2021; (right) The same tree in June 2022. Disease progression is expected to advance through July and August. Images Courtesy Dan Jacobs MFS.
White Pine Needle Damage
The white pine needle disease complex (WPND) is impacting white pine trees throughout Maine again in 2022. This is seen as the yellowing of diseased foliage that is cast from trees prematurely accumulating on roads, driveways, gutters, etc. – much like the natural process of needle shedding that occurs in healthy trees in the autumn. Fungal spores of the four potential diseases involved in the white pine needle disease complex (WPND; Brown Spot Needle Blight, Mycosphaerella dearnessii / Lecanosticta acicola); Bifusella linearis; Dooks needle blight, Lophophacidium dooksii; Septorioides strobi) are released in May and June. This fungal reproduction process depends on water, as it is a critical resource for spore production, dispersal, and spore germination leading to infection.
The life cycle of the diseases involved in WPND is such that the spores released now infect newly emerging needles. These newly infected needles will not show visible symptoms until next year, when they will turn yellow/orange and be shed from the tree. With these aspects in mind, conventional thought is that the weather conditions of the previous spring dictate the severity of disease in the following year. As many will recall, May and June of 2021 were very dry. Despite this, WPND symptoms are widespread and reported from many areas throughout the white pine resource in Maine this year. The reasons for this are unclear, leading to speculation about the moisture requirement for the diseases causing WPND. Perhaps the higher relative humidity from dews and fogs is enough to drive the disease cycle. While this remains unclear, WPND symptoms are clearly seen this year in Maine, and the diseases continue to impact tree health and growth. For more information on white pine needle damage, please check out this fact sheet on our website.
 |
Images: (left) The yellow to orange coloration of a tree severely impacted by WPND; (right) Infected and shed needles accumulating on a driveway in mid-June.
From our July 12, 1990 Conditions Report: “Euonymus caterpillar (Yponomeuta sp.)- This unusual (at least for Maine) species has certainly generated a lot of interest this season in addition to stripping foliage from euonymus in many ornamental plantings. We now have a pretty good idea how much euonymus is grown in Maine and where. Following our last issue and some press coverage, calls were received from many towns throughout southern Maine from south of Rte. 2 and west of the Penobscot River. These caterpillars seem to be busy everywhere… We would like to thank our readers for their many reports. We now have specimens of the adults for our collection. The infested shrubs should recover without any serious long-term effects.”
July 12, 9 am and July 14, 6 pm: Jordan Hall, 46 Temple Ave, Guild Park, Old Orchard Beach. Join Colleen Teerling, MFS Entomologist and Dave Parker, Forester, Parker Forestry Associates, for an educational session on management of the forest and an infestation of hemlock woolly adelgid in Guild Park. A guided walk will follow. July 14 program is a repeat of July 12.
July 15, 2022, 9 am: Maine's Wildfire Weather Program - Forestry Friday Webinar
August 5, 2022, 8:30 am: North Country’s Forest Health: Hands on with Today's Insects & Diseases Workshop. Lancaster, NH. Credits: 5.5 SAF Cat. 1 CFEs available; NHPLP Certification – 6.0 CEUs. Cost: $25/ person; registration is required. Registration Deadline: Friday, July 29, 2022
August 5, 2022, 9 am: Overview of Maine's Forestry Regulations - Forestry Friday Webinar
August 29, 2022, 10 am: Emerald Ash Borer (EAB) and other Tree Health Concerns: Update for Maine Cities and Towns
Conditions Report No. 3, 2022
On-line
Department of Agriculture Conservation & Forestry, Maine Forest Service – Forest Health and Monitoring
Contributors: Aaron Bergdahl, Amy Emery, Allison Kanoti, Mike Parisio, Thomas Schmeelk, and Colleen Teerling.
Unless otherwise noted, images by Maine Forest Service, Forest Health and Monitoring, DACF.
|
