Aerial Survey Notes on Spongy Moth, Winter Moth, and Browntail Moth
With Maine still trapped in a persistent weather pattern of overcast skies and constant precipitation, the aerial survey program has been slow to take off in 2023. Flight coverage would have already been completed for much of the state by now in a normal season; however, now in mid-July, only one flight has been able to be completed safely. The first flight of the season took us to western Maine to evaluate damage from the spongy moth outbreak along the New Hampshire border and see the results of consecutive seasons of drought and defoliation. While it seems the caterpillars might be missing in 2023 due to population collapse, the visible evidence of this outbreak will be long-lasting. While it was not surprising to observe dead white pine and eastern hemlock trees, the extensive hardwood mortality of northern red oak was more than expected, especially in the Kezar Lake basin.
Along the flight route, lingering evidence of mid-May frost damage to oaks over much of Maine was visible from the air, appearing as discolored leaves in the upper canopies reminiscent of early fall colors. This unseasonably late frost event in 2023 could have also contributed to the outcome of the spongy moth outbreak in western Maine. While a lack of leaves at a critical time of development and excessive moisture facilitating the spread of diseases may have spelled doom for local caterpillar populations, it also resulted in a huge loss of resources for affected trees. In certain areas, this could have already been the fourth year where trees were required to produce a second set of leaves in a single season. The cumulative toll of these extreme resource demands on trees due to drought, defoliation, and frost damage appears to have proven too much for many to survive.
The survey then turned to the Midcoast, where winter moth defoliation has once again been prevalent in 2023. Because of the constant uncertainty of being able to fly this season, we attempted to document winter moth damage using roadside surveys. This was useful for documenting damage visible from the road, but the view from the air revealed the overall extent of these defoliated areas, allowing us to fill in the holes in our previous maps from the ground.
The next area of concern was southern Penobscot County, where browntail moth has continued to take hold in 2023. The lateness of this particular survey meant that much of the browntail moth defoliation we were looking for may have already recovered as trees quickly grew new leaves, also aided by the prolific moisture in 2023. While some damage was visible, the true extent of areas affected by browntail moth was masked from the air. We’ll hope for better flight conditions when it comes time to look for leaf discoloration and damage from the next generation of browntail moth caterpillars in late summer and early fall, before the leaves start to turn at the end of the season.
We’ll turn our sights to northern Maine as soon as possible to document the extensive defoliation caused by forest tent caterpillar and large aspen tortrix this spring. However, with trees recovering quickly, the clock is ticking to be able to map damage before full tree recovery. We will hope for clear skies in what’s left of July.
Image: A product produced using satellite imagery that shows abnormalities in expected canopy “greenness” with dark reds and maroons indicating discolored or missing leaves. Much of this damage is due to frost or spongy moth in western and southern Maine. Dark red and maroon areas in Midcoast Maine are the result of winter moth defoliation. (U.S. Forest Change Assessment Viewer, forwarn.forestthreats.org)
An Atypical Season for Ash Foliage
While we are impressed at the large volume of public reports for potential EAB sightings this year, many of the poor-quality canopies that have been reported as dieback from EAB appear to have been caused by other mostly abiotic issues. As some of you might already be aware, ash is one of the very last tree species in the Northeast to fully leaf out in the spring, meaning that your ash is not necessarily suffering just because other species are in full foliage weeks ahead of time. With the extended cool and wet weather, it appears this leaf out may have been delayed even longer in 2023. In some locations more than others, we’ve also observed an extra heavy seed set in 2023, meaning many trees have forgone some leaf production in exchange for resources and branch space for bearing seeds. These seeds are in large clusters and while they remain on the tree, the canopy appears quite full. Once they drop, this can present the illusion of rapid leaf loss or canopy dieback. Some of this seed loss may have been aided by frequent, heavy rainfall in many areas of Maine. Look carefully however, and you can still see the fine structures attached to the twigs where the seeds themselves were once attached. Other more concerning causes for leaf loss can include things like ash anthracnose induced by excessive moisture in the environment (see Anthracnose Diseases of Broadleaved Trees and Ash Leaf and Stem Rust below).
Being aware of the possibility of EAB is an important first step that many Mainers have already proven by picking up the phone and checking in with us. In a year like this one, another important requirement is patience and giving ash trees time to rebound, even if this winds up not being until next spring. While woodpecker feeding on ash trees is usually a red flag, there are many other symptoms we might now associate with EAB that in the past have been caused by normal abiotic stressors like unusual weather patterns. So, if you think you might have EAB, keep letting us know about it, but don’t be surprised if the advice is to wait and see so we can all avoid unnecessary actions before they are truly required when EAB is confirmed. So if you think you might have EAB, keep letting us know about it, but don’t be surprised if the advice is to wait and see so we can all avoid unnecessary actions before they are truly required when EAB is confirmed.
Image: An example of an ash branch with heavy seed set and bare twigs where seeds have already been dropped. When the remaining seeds fall, this branch may have roughly 50 percent of its normal foliage. Apply this to an entire tree and many ash canopies in Maine are looking thinner than usual in 2023. Pittston, ME.
No Dought No Drought!
So far this growing season, much of Maine has experienced more than adequate rainfall. This condition is markedly different from previous years where many parts of Maine experienced prolonged dry periods during the early growing season. However, this increased wet weather has not been a reality for all of Maine as the northern regions of Maine bordering Canada (northern Aroostook County) and western Washington County have experienced abnormally dry conditions earlier this spring according to the National Drought Monitor. As can be seen in the colorless map below, thanks to increased rains in Maine’s drier areas, the whole state is currently within adequate moisture status.
Images: (left) As of July 4, none of Maine is under a drought; (right) Heading into July 2023, a large portion of Maine received one and a half to two times the normal amounts of precipitation in June.
Our first staff update is the departure of long time Forest Health & Monitoring employee Jeff Harriman. Jeff’s dedication, selflessness, and outstanding work ethic have landed him a well-deserved position as executive director of the Downeast Lakes Land Trust. While we miss Jeff tremendously, he has done a thorough job of preparing us for his departure and equipping others with the diverse skillset needed to perform his duties in the interim. The Downeast Lakes Land Trust will certainly benefit from Jeff’s leadership and we wish you all the best in your new role – congratulations Jeff!
Ronna Coleman was promoted to Entomology Field and Mapping Supervisor with the FHM Division in March of this year. The position was vacant after the November 2022 departure of Aron Bishop for work in the private sector. This position leads the Forest Inventory and Analysis (FIA) crews and assures timely, safe, and accurate collection of the National FIA dataset within the state. Ronna graduated from the University of Maine at Fort Kent with a degree in forestry and previously worked as a Conservation Aide and then an Entomology Technician with the FIA program. She has already employed her extensive knowledge of FIA to assist with training current and past employees. This experience, her familiarity with the program, and her drive to continue improving program delivery and employee well-being has already served her well in her new role.
We are pleased to welcome two summer student interns this season, Johanna McGinley and ConorBoyan. Johanna works out of the Insect & Disease Lab in Augusta and is currently enrolled at University of Southern Maine, where she studies environmental policy and planning. Conor works out of our Old Town office and is currently enrolled at University of Maine – Orono, where he studies wildlife ecology. We welcome their enthusiasm for forest health and the extra assistance these two provide during an especially busy time of year.
Finally, we welcome new entomology technician Zoe Albion, who started working with us in July of this year. Zoe works out of the Old Town office and received her BS in wildlife biology from the University of Vermont. She comes to us most recently from the Field Museum in Chicago, IL. Zoe has extensive experience in managing insect collections and we welcome her organizational skills and taxonomic expertise.
Browntail Moth (Euproctis chrysorrhoea)
As caterpillar development came to a close for the season, we confirmed viral and fungal pathogens at some monitoring sites. Although we documented some mortality from disease, please note these pathogen outbreaks were localized. Many of the deceased caterpillars observed had died right before pupation either in or just outside the pupal packet.
Image: A pupal pocket contains multiple browntail pupae, where they rest and metamorphize before emerging as adult moths. Outside of this pupal pocket is a dead browntail caterpillar that likely died from a viral pathogen. Unity, ME.
We received the first report of a browntail moth adult on Friday, July 7, in Penobscot county with other confirmed sightings in Turner and Skowhegan later that same day. This means that you may soon see these white-colored moths flying around in an area near you. Many species of white moths in the northeast are often confused for browntail moth; most notably the Virginian tiger moth, satin moth, and fall webworm (see chart below). Browntail moths have white wings and legs and reddish-brown hairs on their abdomen, which gives this species it’s common name of brown “tail” moth. This brown abdomen peeks out from under its wings when at rest.
We expect to see the peak of adult browntail moths in the middle of July. Although the brown hairs on the moth are not the toxic barbed hairs on the caterpillars, you don’t want to attract adult browntail moths to your property: more moths = more caterpillars. To dissuade these adult moths from flying onto your property, turn off unnecessary outdoor lights (or switch to yellow-colored bulbs) from now until the beginning of August. We don’t recommend the use of bug zappers or other devices to control browntail moths; these devices often use light to attract insects which will result in more browntail moths being attracted to that area. These devices also kill insects that can help reduce browntail populations.
Sign up for our Browntail Moth Updates to stay informed about this insect.
Hemlock Woolly Adelgid (Adelges tsugae)
The extreme cold much of Maine experienced in January and February led to high mortality of overwintering hemlock woolly adelgid (HWA). In some locations, over 95% of adelgids died during the winter. Since there were fewer adelgids this spring, many hemlock trees that had been declining because of HWA have put on good new growth. The ample rain this year should also favor hemlock recovery.
Image: Adults with fresh ‘wool’ are easy to see on last year’s growth in July (photo credit: Maine Forest Service)
However, this respite will only be temporary. We expect most adelgid populations to rebound quickly. The adelgids that survived the winter laid eggs in March. Those eggs quickly grew into adults which are now present and are laying their own eggs. After these eggs hatch, the crawlers will move onto the new growth and settle. Once they are settled and firmly attached to the new growth in August, it will again be safe to work in hemlock stands with minimal chance of spreading HWA.
Image: Crawlers move onto new growth after hatching and become settled nymphs by the beginning of August (photo credit: Maine Forest Service).
HWA is very easy to see at this time of year, if you wish to monitor for it.
Diseases and Environmental Issues
Anthracnose Diseases of Broadleaved Trees
The prolonged, cool and wet weather pattern seen throughout much of Maine this May and June has provided optimal conditions for the spread of fungal leaf and needle diseases. This general period of wetness has spanned the spore dispersal period of many of our common, and not so common, fungal pathogens. Observations and reports have yielded the following list anthracnose pathogens on hosts in late June/early July:
Ash: Ash anthracnose (Gnomoniella fraxini) was observed causing severe premature defoliation in Boothbay harbor and various levels of severity in other parts of Maine.
Beech: Beech anthracnose (Discula umbrinella) has been observed causing various severities of leaf lesions. Beech leaves damaged by the freeze event in mid-May are perhaps more susceptible to damage. Beech anthracnose damage is sometimes mistaken for symptoms of beech leaf disease.
Birch: Birch anthracnose (Discula betulina) has been observed on river birch in several areas of southern Maine causing lesions and in some cases partial defoliation.
Maple: Maple anthracnose (potentially caused by Aureobasidium apocryptum,Discula campestris or Colletotrichum gleosporoides) has been seen very commonly in red maples, although it has also been seen in striped maple and sugar maple. Sometimes the dead leaf tissue caused by maple anthracnose infection drops out of the leaf, leaving a hole sometimes mistaken for insect feeding.
Oak: Oak anthracnose (Discula quercina) has been observed causing various severities of leaf lesions on multiple oak species in Maine. Oak leaves damaged by the freeze event in mid-May are perhaps more susceptible to damage. Oak anthracnose causes deformation of leaves and necrosis of leaf tissues causing them to turn brown and dry out.
Sycamore: Sycamore anthracnose (Apiognomonia veneta) was observed in the Augusta area, causing moderate damage and defoliation. A severe infection accompanied by defoliation was also recently seen in York County. Sycamore trees are not common in Maine, but they are highly susceptible to this disease and full defoliation has been documented here when spring wet weather conditions favor disease development.
These diseases often look more serious than they are, however multiple years of heavy defoliation may degrade the vigor of impacted trees leading to dieback and decline. Refer to the article in the previous Condition Report “Caring for Defoliated Trees” for tips on how to help trees recover from defoliation.
Images: (top left, right) Ash anthracnose on white ash, maple anthracnose on red maple; (bottom left, right) Heavy defoliation of birch leaves due to birch anthracnose, oak anthracnose-infected tree with a scorched appearance due to severe infection.
Apple Scab (Venturia inaequalis) and Frogeye Leaf Spot (Botryosphaeria obtusa)
The prolonged wet periods of weather this early growing season have created prime conditions for several fungal leaf diseases. Apple scab and frogeye leaf spot are two such diseases that have caught people’s attention on their apple and crabapple trees due to their appearance on leaves and the premature defoliation they cause. These diseases have been observed in several areas of Maine. Heavy apple scab infection has in many cases led to premature defoliation. The disease causes non-uniform blotches on leaves and leaf yellowing. Frogeye leaf spot has caused high levels of conspicuous, round leaf lesions, characterized by a distinctly round brown center of dead leaf tissue surrounded by a slight halo of yellow leaf tissue, resembling an ‘eye’ responsible for the disease’s common name. The fungus that causes frogeye leaf spot, Botryosphaeria obtusa, can also cause cankers and impact fruit – it is unusual for a fungus to be able to attack multiple tissues on a host species. Cultural control for both diseases is to clean up and dispose of fallen leaves and infected fruit (apples with scabs and shriveled and mummified fruits in the case of B. obtusa). Pruning out dead wood and cankers caused by B. obtusacan help toward managing the disease as well. Do take care when pruning and make sure to sterilize pruning equipment between cuts to prevent unintentional spread of other diseases in your trees.
Images: (left) The round fungal lesions of frogeye leaf spot, sometimes coalescing to form less symmetrical lesions; (right) Dropped leaves showing symptoms of apple scab (and a few frogeye leaf spot lesions as well).
Ash Leaf and Stem Rust (Pucciniastrum sparaginoides)
In early June, the forest pathologist and field staff surveyed Columbia Falls and Cherryfield areas one year after severe defoliation of ash from ash leaf and stem rust. Many ash trees in the area showed extensive dieback and even some mortality was noted. Survey of shoreline vegetation of nearby waterways in early June revealed signs of the rust on the alternate hosts (marsh and cord grasses in the Spartina and Distichlis genera, respectively) near infected areas, indicating that damage to ash in the area could be severe again this year. During another visit to the same areas in late June, symptoms of ash leaf and stem rust were readily found on ash trees in the area that resembled the early phases of rust infection – before the formation of the orange structures that produce spores to reinfect the coastal grasses. The wet weather and fogs common so far this growing season have been favorable for ash leaf and stem rust infection. Severe infection by the pathogen again this year will lead to increased dieback and mortality of ash trees in the affected areas.
Images: (left) A residence in Columbia Falls, Washington County Maine, where ash leaf and stem rust wilted and defoliated a whole tree in 2022 and the same tree in 2023 showing extensive crown dieback; (middle and right) Impacts of ash leaf and stem rust on ash foliage.
Beech leaf disease (BLD) continues to be found in an increasing geographical area in the southern half of Maine. A large acreage was found to be infected in York County and Washington and Cumberland counties were added to the list of counties with positive BLD finds in late June and mid-July, respectively, marking the presence of BLD in over half of Maine’s 16 counties. We continue to welcome reports of BLD in new towns. A new map will be on the Maine Forest Service Beech Leaf Disease webpage soon.
A BLD treatment trial was recently initiated in cooperation with the MFS Policy and Management Division and Viles Arboretum. BLD was recently detected at the arboretum and a decision was made to try the trial, modeled after one in progress in Ohio using a high potassium fertilizer. The liquid fertilizer has been shown to be therapeutic, keeping symptoms from progressing. The trial comprises a total of 19 treated trees and 12 controls. The first application has been made and a second application is planned for the end of the month.
Images: (left) Beech leaf banding is an easily seen symptom indicating the presence of beech leaf disease; (right) MFS technician Abby Karter and summer intern Johanna McGinley record data and prepare a tree for treatment during the first round of the BLD treatment trial at Viles Arboretum in Augusta, Maine.
Dutch Elm Disease (Ophiostoma ulmi; Ophiostoma novo-ulmi)
Dutch elm disease symptoms have begun to show up in elms in the various location where they grow in Maine. Characteristic symptoms of the disease are yellowing and wilting of foliage, which tends to happen quite suddenly. This sometimes results in reddish-to-brown desiccated foliage that is fragile to the touch and may be dropped from the tree. Damage is typically seen higher in the tree where the insect vectors spread the disease during their maturation feeding, although flagging branches (symptomatic branches) can be seen anywhere on the tree where the causal fungus is introduced by beetles. The disease can also spread below ground via natural root connections (root grafting), leading to rapid death of trees in close vicinity. American elm trees continue to persist on Maine’s landscape but seldom reach the age and stature that once made them an invaluable shade tree in urban and rural settings. However, an increasing number of disease-resistant cultivars can be found in the nursery trade, representing an opportunity to plant elms for short- and long-term tree services and enjoyment.
Images: (right) The crown of an American elm tree infected with DED; (left) Leaves dropped from a DED-infected tree.
The prevailing wet weather this growing season (anyone picking up on the recurring theme in this pathology section?) has led to increased reports of needle rusts in hemlocks and true firs compared to previous years. These rusts are seldom of serious concern with regard to tree health, although aesthetic impacts may cause Christmas tree growers to take notice and consider management.
Rust fungi (with a few exceptions) need two species of plants to cause disease: the primary host of concern and an alternate host. In the case of hemlock rust, the two hosts are, of course, hemlock, and other host can be blueberry, hydrangea or poplar, depending on the particular hemlock rust species. The infection cycle can be broken by removing one of the two hosts. Hemlock rust is seldom severe, so tree damage and aesthetic impacts often do not warrant management. Removal of the alternate hosts is a possibility, but the specific species would need to be confirmed in order to do this. Protective fungicides in spring to prevent infection would likely be the most straightforward management practice.
For fir rusts, management is a bit less complicated. One can mow/remove ferns, as they are the alternate host to this rust fungus impacting true fir trees (Doug-fir is not a true fir). Target ferns nearest to the plantings – you don’t need to eradicate every fern in the area.
Use protective fungicides in spring as new growth emerges and again after 2 weeks. Fungicides with the active ingredient Chlorothalonil or other copper-based fungicides are effective at protecting needles from infection.
Images: (left) Hemlock rust spore-producing structures on the underside of needles (Conor Boyan, Maine Forest Service 2023 Intern); (middle) Fir rust-impacted planting showing mild infection and needle discoloration; (right) A close-up of the spore producing structures of fir rust on the underside of needles. (Heather Rodrigue).
Spruce Needle Cast Diseases (Rhizosphaera kalkhoffii and Stigmina lautii)
Spruce needle cast fungi typically release spores in June when the new growth of spruce is about 1.5 inches long. The spores of Stigmina lautii are thought to be released earlier, broadening the window of infection for this needle cast fungus. These diseases lead to greatly reduced needle retention and lower branch dieback in the lower third of trees. This often diminishes the use of white spruce and Colorado blue spruce as privacy screens. Norway spruce shows greater resistance to these diseases but is not immune and can be impacted in areas with high disease pressure and weather conditions that favor disease development.
Image: Colorado blue spruce trees impacted by spruce needle cast disease. The lower third of the tree is usually the worst impacted, diminishing the trees’ use for privacy screens and aesthetic plantings.
Three Taphrinas: Plum Pockets (Taphrina communis), Peach Leaf Curl (Taphrina deformans) and Oak Leaf Blister (Taphrina caerulescens)
This year three species of fungi in the genus Taphrina have been increasingly seen. This is likely due to the wet weather much of the state has experienced this spring. Early June observations of peach leaf curl were observed in Knox, Kennebec and Cumberland counties. Symptoms include deformed, twisted and blistered leaves with yellowish to reddish coloration. This is usually followed by premature defoliation of severely infected leaves.
Late June observations of plum pockets were made in wild plum (Prunus spp.) in northwestern Waldo County. This disease can cause leaf blister and fruit deformation.
These two diseases are not typically serious tree health issues, but when severe can represent considerable tree stress. They can also represent a problem for fruit growers, requiring management to preserve healthy leaves (luckily, the fruits of many commercial plum varieties are not affected by plum pockets). The third species of fungus in the genus Taphrina described here is oak leaf blister, which is usually not a serious health issue and has not been commonly reported in Maine in the past. However, this year the disease was spotted on northern red oak in Kennebec County and we received one report of serious infection and defoliation in York County on white oak (see images). The blistering of the leaves caused by this disease differentiates it from the typically more common fungal leaf disease of oak, oak anthracnose, mentioned earlier in this report.
Cultural management for all three of these diseases includes cleaning up leaves and debris from the impacted trees, pruning out dead twigs and branches and rogueing out infected wild plum (in the case of managing plum pockets) from nearby areas. Chemical management involves fungicide applications in the dormant season after leaf-off, and potentially again in spring before budbreak if the disease was severe in the previous year. With a little effort, proper fungicide applications and yearly scouting, damage from these diseases can be mitigated and even eliminated. In the case of oak leaf blister on larger trees, treatment is seldom practical or warranted. Trees that were healthy prior to infection will be resilient and may even send out a new flush of leaves following defoliation.
Images: (left) Blistered, curled and discolored leaves of a peach tree infected with the peach leaf curl fungus (orange arrows, image by Michael Collin). Deformed plums are a symptom of infection by the plum pockets fungus (yellow arrows).
(left) Oak leaf blister symptoms on white oak; (right) One branch of a tree that was severely infected with the oak leaf blister fungus. The tree had dropped many of its leaves, which prompted the landowner to call MFS.
Venturia Blight of Poplar (Venturia populina or Venturia moreletii)
Venturia blight of poplars was documented in a handful of spots in Kennebec County this June and July; however, occurrence of the disease is likely more widespread in Maine, with dispersal and infection enhanced by the wet spring/early summer weather. Venturia blight is characterized by dark blotches on leaves and wilting and blackening of new growth tips resulting in a shepherd’s crook with a scorched appearance. The blight has not been documented causing significant damage in Maine, although serious impacts have been reported in Canada.
Image: Venturia blight of aspen, orange arrows pointing to shepherd’s crook symptoms.
This Month in History
From the July 26, 1988 Conditions Report:
“European Earwig (Forficula auricularia): This is probably the “bug of the year” as far as homeowners are concerned and a real nuisance. Populations in many areas are the heaviest seen in years and are real difficult to control.”
July 21, 2023, 9:00AM-10:00AM, Virtual Webinar: Forestry Friday: Firewood Alert, the Control and Prevention of invasive insects: What can you do?
A Maine Forest Ranger and Entomologist will discuss the rules of importation of firewood into and throughout Maine. Learn how to help prevent the spread of invasive insects by limiting the movement of firewood. Invasive insects can have a huge impact on our forests, home, and life. Everyone who enjoys our forests and/or works and depends on our forests have a stake.
August 10, 2023, 9:00AM-3:00PM, Skowhegan (exact location being finalized): Using Forests as a Tool Statewide to Engage Students in Climate Discussions and Community Science
The Forest Ecology Research Network (FERN) guides students, teachers, and non-formal educators through creating a 1/10 of an acre plot and infusing the data collection and study of the plot with cross-cutting concepts, current events, and the exploration of natural phenomena. FERN activities are inquiry-based and align with the Maine Science Learning Results and Project Learning Tree Curriculum, and guide students to generate their own questions and use forests as a lens to discuss climate tangibly. This workshop will provide forestry professionals with the tools and experience they need to guide students and teachers through FERN curricula. Presenters are Lena Ives, Director of Education of the Maine TREE Foundation, and Shane Duigan, District Forester with the Maine Forest Service.
This event is approved for 5 SAF Continuing Forestry Education Credits
August 11, 2023, 8:30AM- 3:30PM, Governor’s Events Center, 376 Main Street, Waterville, Maine: Maine Sugarbush management conference
The University of Maine Cooperative Extension’s Maple Program is hosting the 2023 Maple Sugarbush Management Conference at the Governor’s Events Center in Waterville, ME. At this full-day program, maple and forestry research specialists, and maple sugarbush managers will share information about optimizing the health and productivity of maple sugarbushes. Among the presenters will be Entomologist Colleen Teerling and District Forester Jim Ferrante from the Maine Forest Service.