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Maine Forest Service

Forest & Shade Tree ? Insect & Disease Conditions for Maine

May 17, 2024

Welcome to our 2024 seasonal Conditions Reports bulletins. We are borrowing inspiration from colleagues in the region, especially Vermont Forest Health [ [link removed] ], and including a feature on invasive plants through a partnership with Maine Natural Areas Program [ [link removed] ] biologist Chad Hammer and one on climate. Although we can?t always respond to feedback, we do value it; please let us know what you think <[email protected]?subject=Conditions%20Report%20Feedback>.

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In This Edition:

* This Month in Conditions Report History: May 14, 1980 [ #link_1 ]
* Living with Caterpillars [ #link_2 ]
* Climate Summary [ #link_3 ]
* Insects [ #link_4 ]
* Diseases and Environmental Issues [ #link_5 ]
* Maine Invasive Plant Control Grant Program Applications Now Open [ #link_6 ]
* Invasive Plant Spotlight [ #link_7 ]
* Calendar [ #link_8 ]

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This Month in Conditions Report History: May 14, 1980

"Fiddleheads- fiddleheads are now variable but in most areas range from peak of picking conditions to just past picking range. In the far north picking has not yet begun."

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Living with Caterpillars

Spring has arrived in Maine, and with it, the Maine Forest Service and others have been fielding caterpillar questions. Caterpillars are essential food for many other animals, including insects, birds, mammals, and even fish! However, sometimes caterpillars from our trees and shrubs become nuisances around our homes and workplaces, and outbreak populations can threaten tree health. Maine Forest Service urges you to take a responsible approach to living with the caterpillars in your developed landscape. Read more in our recent bulletin [ [link removed] ].

Caterpillars on a leaf

Image: Forest tent caterpillars on expanding aspen leaf, Caribou, ME, May 15, 2024.

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Climate Summary

Most of Maine saw above average precipitation levels in the last twelve months (May 2023?April 2024). For 2023, the state average precipitation was about 54 inches, 11.25-inches greater than average precipitations for the state since 1895. In the northernmost region of the northern climate division, precipitation totals for 2023 were about average based on the 1991-2020 average precipitation levels. However, southern interior and coastal climate divisions saw precipitation levels 150-200 percent above normal.

Maps of Maine showing precipitation levels

Images: (left) Maine?s climate divisions; northern (blue), southern interior (red), and coastal (green) showing annual temperature increases statewide since 1895. Source: Fernandez et al. 2020; (right) The percent departure of precipitation in the past year (May 2023-April 2024) from normal values (an average precipitation from 1991-2020 in Maine. Note a ?100? indicates that precipitation levels were not different from the 1991-2020 average. Source: Northeast Regional Climate Center.

This past winter (Oct 2023?April 2024), Mainers statewide experienced a warmer and milder winter compared to previous winter seasons. Maine?s March 2024 had average temperatures 6 to 9 F degrees higher than normal. According to NOAA climate data, it was the second warmest winter recorded with an annual winter temperature of 24.3?F statewide, with the warmest winter recorded occurring in 2016 with an annual winter temperature of 24.4?F. In the northern climate division, some areas saw seasonal snow totals that were 50 inches less than the average, although other areas near Baxter State Park experienced about 10 inches more snow than the seasonal average. Conversely, snowfall totals in the coastal climate division were 60 inches below average, though some areas experienced average snowfall totals. Late season snowfall made up for early season shortfalls in some areas in western Maine.

Map of Maine showing snowfall departure from average

Image: The departure in statewide snowfall totals from normal (1991-2020 averages). Note a ?0? indicates snowfall totals were not different from the 1991-2020 average. Source: Northeast Regional Climate Center.

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Insects

*Browntail moth* ("Euproctis chrysorrhoea")

We are running our network of monitoring sites again this year to observe browntail moth (BTM) caterpillar development over the season. The purpose of these monitoring sites is to capture trends and developmental differences of the BTM population throughout Maine and to track disease outbreaks of the pathogens that infect BTM caterpillars. The ten monitoring sites for this year are Bangor, Belfast, Bridgton, Brunswick, Dover-Foxcroft, Hancock, Lincoln, Newport, Turner, and Unity. Sign up for our Browntail Moth Updates [ [link removed] ] for monitoring reports and to stay informed about this insect.

Browntail caterpillars have been active for about a month now. We received the first report of emerged caterpillars on Monday, April 15, which is right on schedule. Since then, their webs have grown a bit with caterpillars adding some silk to the outside.

Caterpillars on web

Image: Browntail caterpillars on their dew-covered web, Brunswick, ME.

We have not yet observed diseased browntail caterpillars at our monitoring sites this year. We welcome any reports from the public [ [link removed] ] of *_diseased_ *caterpillars. Please include a photo or two in your report so we may confirm pathogen presence.

Some signs of pathogens may be:


* White or yellow fungal spores on caterpillars (Fungus)
* Caterpillars hanging onto branches with just their rear prolegs (leg-like extensions of the exoskeleton) (Fungus)
* Liquid expulsion of the caterpillar guts (often the caterpillar rests in an upside-down "V" shape) (Virus)
* Swollen, puffy caterpillars (Virus or Fungus)
* Dead caterpillars (Virus or Fungus)

Four photos of dead caterpillars

Images: Examples of pathogen-killed caterpillars; note the upside down ?V? shape indicative of virus in the top right photo.

Based on aerial survey data from last summer and fall and data from this past winter?s BTM web survey [ [link removed] ], the counties that may be the most impacted are Penobscot, Knox, Hancock and Waldo. Weather-wise, precipitation seems more ?normal? this spring than the last several, with rain events interspersed with sunny days. Weather patterns through June will influence disease development. People should not count on disease-related collapses to save them from the rash. Please plan ahead for managing populations, avoiding exposure to hairs and treating symptoms related to exposure.

Where population management has been deemed necessary, plans should be in place by this time. The time for web clipping efforts ended in early-April. For pesticide treatments like spraying, it is still too early in many locations since sufficient leaf surface area is needed to hold the spray. For some systemic treatment approaches, however, the time is now: budburst or newly emerged leaves are a sign the tree is transporting water to the crown and pesticide will be moved within healthy trees when soil moisture is adequate, and product is correctly applied. We recommend working with a licensed pesticide applicator for this management approach. Please note that AceCap? is not registered for use in Maine and is therefore unlawful to use. Please check the Maine Board of Pesticides Control website [ [link removed] ] for up-to-date information regarding which pesticides are registered in Maine. In most years, treatments should be timed to be effective in killing the caterpillars before the end of May to limit the buildup of toxic caterpillar hairs and host foliage loss.

Typically, we have our first reports of caterpillars on the sides of houses or decks in late May. To remove those caterpillars from your dwelling you can put a couple of inches of soapy water in the bottom of a wet/dry vacuum that has a good HEPA filter installed in it and vacuum them. This will both kill and contain the caterpillars and they can be disposed of away from the house. If you are doing yard work and are sensitive to the hairs, we recommend that you wear proper protective gear, including long pants and long-sleeved shirts taped at the wrist, gloves and closed-toed shoes.

On an interesting note, browntail caterpillars have been confirmed in New Hampshire. We last received anecdotal reports of their presence in the Seacoast Region of New Hampshire from a USDA Animal and Plant Health Inspection Service biologist at a professional meeting in 2010. This year?s report came to our NH forest health colleagues from NH Division of Plant Industry staff. The browntail caterpillars were found on Star Island on the NH side of Isle of Shoals. The webs are present on low shrubs as the island is largely devoid of trees.

*Emerald Ash Borer ("Agrilus planipennis)"*

*Preparations for Emerald Ash Borer Monitoring Season Underway*

As we head into the field season, one of the important early milestones we watch out for is the emergence of emerald ash borer (EAB) adults. This usually occurs around 450 growing degree days (GDD), an agricultural measurement tool that has been adopted for many phenological events in the natural world like flowering dates or insect emergence. Depending on the year, this can happen as soon as mid- to late May in Maine, but more often this occurs from late May to early June, with peak EAB emergence typically occurring in mid- to late June. A good natural visual aid is the blooming of black locust trees, also right in step with that 450 GDD mark. With this in mind, and with USDA APHIS funding support, we are currently installing traps all over the state in preparation for the first flights of EAB, with the hopes that our monitoring network might find new infestations of EAB early on, allowing for better management in new localities. So, if you happen to view a strange purple or green object in a roadside tree, chances are it?s one of our Maine Forest Service traps.

Unfortunately, much of southern Maine is already living with EAB populations, and the expansion of EAB?s range in Maine led us to expand our regulatory areas to try to contain existing populations and prevent the unrestricted movement of things like ash logs and firewood which can rapidly spread EAB. If you did not catch the most recent regulatory revisions that happened in December of 2023, please have a quick look at the map below and refer to our webpage [ [link removed] ] for more information on EAB rules and regulations in Maine.

And, as always, let your friends and relatives visiting from out-of-state know that all untreated firewood from out-of-state is banned from Maine in an effort to protect our forests from a growing number of forest health concerns.

Map of Maine and photo of a trap in a tree

Images: (left) Most recent extent of Maine?s emerald ash borer quarantine zones as of the December 2023 revision; (right) an ash tree with a green funnel trap deployed for emerald ash borer monitoring in Maine.

*Emerald Ash Borer Insecticide Demonstration*

As EAB continues to spread throughout the state, one effective set of tools used to protect individual ash trees are systemic insecticides. Products such as those containing the active ingredient emamectin benzoate can be injected into the base of an ash tree, which then travels up through the phloem and into the crown. This can prevent EAB larvae from developing over the winter and can protect an ash for several years. However, there are a number of factors that must be considered before deciding on a chemical treatment, including the size, health, and location of a tree, as well as its proximity to active EAB infestations. More information can be found in this guide for saving high-value ash [ [link removed] ].

The treatment process is no trivial endeavor. It requires specialized equipment and should be conducted by a licensed pesticide applicator. This month, Arborjet regional technical manager Kevin Brewer gave the Maine Forest Service staff a private demonstration of the process. ?This training was timely, as MFS will be implementing an ash seed-tree treatment project in the coming months. The strategy of this project is to treat small pockets of ash across the landscape to help maintain genetic diversity of ash adapted to our environment. These sites will act as refugia of seed-bearing trees for subsequent repopulation of ash forests following the initial destructive wave of EAB.

People standing around a tree; one person kneeling next to the tree

Images: (left) Some injection devices require small plugs to be inserted at the base of the tree; (right) Maine Forest Service Staff receive a demonstration of the Quikjet Air injection system.

*Emerald Ash Borer Parasitoid Releases*

In 2023, Maine Forest service began monitoring the sites where EAB biological control agents had first been released in southern Maine. We were looking for evidence that parasitoids had become established. Trapping efforts to detect adult parasitoids were unsuccessful. We felled and peeled trees to look for larval parasitoids under the bark, which was also unsuccessful. Lengths of wood from each tree we felled were placed in rearing barrels and held for several months to allow any parasitoids under the bark to emerge as adults. These samples were recently processed, and both larval parasitoids, "Spathius" "galinae" and "Tetrastichus planipennisi," were detected in Limington. "T. planipennisi" alone was detected in Shapleigh and Acton.

Two close up photos of insects

Images: Adult parasitoids from rearing barrels; (left) Spathius galinae; (right)Tetrastichus planipennisi.

A few weeks ago, we again felled and peeled trees from each southern release site, and this time, we recovered an EAB larva parasitized by multiple "S. galinae "from South Berwick. We have not yet detected any of the egg parasitoid, "Oobius agrili", but they are so tiny that they require specialized monitoring methods.

Larvae in wood

Image: Multiple pupae of the ectoparasitoid, Spathius galinae, feeding on an emerald ash borer larva under the bark. Healthy larva to the right.

Adding these recent finds to the "T. planipennisi" found a few years ago in Madawaska, Maine, we have recovered biological control agents from five of the ten completed release sites. We are still in the very early stages of establishing biological control throughout the area where EAB is established in Maine, but these recent results are encouraging.

*Forest Tent Caterpillar* ("Malacosoma disstria)"

Forest tent caterpillars (FTC) are the larvae of a native moth species, locally also referred to as armyworms. Their name is misleading, they make no tent. They normally feed on oak, maple, aspen, or birch, where they may be a serious pest. Mature larvae can be identified by a row of white keyhole spots on their backs, as opposed to the eastern tent caterpillar, which has a solid white line.

Over recent years, significant FTC activity has been observed in Aroostook County. Defoliation of aspen occurs early in the growing season, along with large aggregations of FTC reported on roads and buildings. There does not yet appear to be any obvious mortality among the affected trees however, as recovery has been aided by several seasons of regular or abundant rainfall in northern Maine. FTC outbreaks are known to last up to five years at a time, with large populations often collapsing sooner due to natural controls like pathogens. Nevertheless, based on the population levels observed this year and the year prior, we expect damage to persist in 2024.

Though management of FTC is not always necessary, in addition to the controls outlined in our Caterpillar Season bulletin [ [link removed] ], there are insecticide control options available to private and commercial applicators. Products containing the microbial agent "Bacillus thuringiensis" var. "kurstaki" (Btk) are a popular method of controlling moth and caterpillar larvae which remain relatively safe to other insects. Other options include products such as those containing the active ingredients Spinosad and others labeled for both caterpillar control and the target site of application.? Control is most effective when the caterpillars are still small and have not caused serious tree defoliation. As such, treatments should be applied by the end of May for best results.

Comparison of browntail, eastern tent, forest tent and spongy moth caterpillars.

Image: Comparison of browntail, eastern tent, forest tent and spongy moth caterpillars.

*Hemlock Woolly Adelgid ("Adelges tsugae)"*

Maine Forest Service has been tracking the mortality rates of hemlock woolly adelgid (HWA) at various sites throughout its range in Maine for the past decade. During some years with cold winters and polar vortices, over 90 percent of the overwintering generation died. Several recent winters have been mild, leading to much lower rates of death, and only around 60 percent of the overwintering adelgids died. The brief, record-breaking cold spells in January and February of 2023 did lead to high mortality rates in many, but not all sites. However, the mild winter this past year allowed the majority of adelgids to survive, and the average mortality rate was just under 33 percent. This is the lowest we have ever recorded. It is likely that HWA populations throughout the state will rebound quickly and spread may be hastened by these higher populations.

Graph showing average mortality of hemlock woolly adelgid from 2013 to 2023. Most years are between 60 and 95%.

Graph: Average winter mortality of hemlock woolly adelgid from 2014?2024.

We are now well into the high-risk period for transmission of HWA. Crawlers and eggs are likely to be present until the beginning of August. Crawlers have the potential to live up to three weeks off the tree and only one is needed to start a new infestation, so be careful when you are working or recreating in hemlock areas that you do not pick up crawlers on your pets, clothing or vehicles/equipment and move them to uninfested areas. A few minutes in a hot dryer will kill crawlers on clothing; washing your vehicle, or just being aware of where you park, will reduce the likelihood of transmitting hitchhiking crawlers to new trees. As with so many invasive species, prevention of new infestations and slowing the spread of existing populations, are some of the most effective things we can do to protect our trees.

*Spruce Budworm *("Choristoneura fumiferana")

Although things have appeared to be relatively stable and quiet the past few seasons, the spruce budworm (SBW) monitoring network has picked up on an area with heightened SBW activity in northern Aroostook County adjacent to defoliation in Quebec. Pheromone trap monitoring and larval sampling sites operated by cooperators picked up both higher moth counts, and of greater concern, higher larval counts in some locations. Given the nomadic nature of adult SBW, traps can pick up moths that may have originated in distant forests, but the larval recoveries speak to more local populations. The map below illustrates elevated pheromone trap captures from 2023 in relation to areas of Quebec with active SBW defoliation. Unfortunately, the weather kept survey aircraft grounded during critical time periods in 2023, meaning this area was not surveyed. Survey plans for 2024 include the usual monitoring techniques, but special ground surveys of this area of concern are also expected to happen as soon as possible. The complete 2023 SBW annual report is available for viewing here [ [link removed] ].

Map of Maine and Quebec

Image: Map illustrating that spruce budworm defoliation areas in neighboring Quebec may have finally reached Maine?s border and spilled into forests in far northwestern Aroostook County.

*Winter Moth* "(Operophtera brumata)"

The annual release of "Cyzenis albicans" flies, the biocontrol agent for winter moth, occurred on April 26 in West Bath. This year we had 1,323 fly pupae from our caterpillar collection efforts at our previous release sites. These adult flies will feed on nectar from a variety of flowers, including red maple, while the females undergo maturation. Female flies will seek out host volatiles from damaged oak, maple, and other host leaves. Once their eggs have matured, they will lay eggs on the damaged leaves, and some eggs will be consumed by winter moth caterpillars. After the caterpillars mature and drop off the tree into the soil, they will spin a cocoon that looks like a small dirt clod that is about the size of a Tic Tac mint. It is then that the fly larvae inside the parasitized caterpillars become active and consume the caterpillars from the inside. Eventually, the fly larvae will pupate inside the cocoons of the winter moth caterpillars and emerge from the soil the following May.

Later this month, we will perform our annual collection of caterpillars from our previous release sites. Flies reared from any parasitized caterpillars collected will serve as the source for next year?s release. In addition, these collections will show where the parasitoid has been established successfully and what proportion of the winter moth population in those areas is being parasitized.

If you observe hardwood trees with more than a quarter of their leaves consumed by small green inchworms from Penobscot Bay, eastward, or away from coastal towns throughout Maine, we would be interested in your reports through our online form [ [link removed] ].

Green caterpillar on a hole-riddled green leaf

Image: Winter moth caterpillar on a damaged leaf, June 8, 2023.

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Diseases and Environmental Issues

*Anthracnose Diseases* ("Apiognomonia "spp., "Colletotrichum" spp., "Discula" spp., "Gloeosporium "spp.)

The spring and early summer of 2023 were unusually and consistently wet. In some areas this led to increasing levels of Anthracnose diseases. This translates to higher amounts of overwintering inoculum for springtime infections. Thus, spring is the time to apply fungicides to reduce this year?s infections of newly emerging leaves. The first application of an appropriate fungicide for a specific Anthracnose pest is required?at the?time?of budbreak to protect?leaf tissues as they grow and expand. A second application is suggested?about 14 days later when?the?foliage is nearly fully developed.?Specific information regarding reapplication is listed on the fungicide label and should be strictly followed. For most hardwood species, budbreak?usually occurs by the?first?week?of May. Unfortunately, by the time this report is received, the timing of the first application will have passed for most of southern and central areas of Maine; however, the timing may be just right for northern parts of Maine.

Hand holding bunch of leaves

Images: (left) Dark lesions on red maple leaves resulting from maple anthracnose infections; (right) Tan lesions on northern red oak leaves resulting from oak anthracnose infections.

*Salt damage and Winter-burn*

In a typical year, a number of reports of salt damage and winter-burn would prompt a Conditions Report article documenting the locations and severity of these abiotic tree disorders. However, weather conditions have combined nearly perfectly such that the Insect and Disease Lab has not received a single report of salt damage or winter burn yet this year.

Reddish trees next to a road

Image: Roadside salt damage from a previous year showing more prevalent symptoms than in many places in early 2024.

On a recent drive on I95, a low degree of salt damage was noticeable in places (orange-tinted conifer foliage), but much less so than in past years where spans of bright-orange conifer foliage have raised public concern. It is hypothesized that the late winter rainstorms washed away deposits of deicing chemical on roadside conifers, minimizing damage. Similarly for winter-burn, the ample late fall and winter rains kept soil moisture availability high. So, even those of us who forgot to water-in and/or wrap our landscape conifers in the fall were spared from winter-burn symptoms, even to the most susceptible species like arborvitae.

*Scouting for Currants*

Early spring is an ideal time to scout woodlots for currants and gooseberries (plants in the genus "Ribes"). These serve as the primary host for the fungus that causes white pine blister rust ("Cronartium ribicola").?"Ribes "plants are some of the first vegetation to leaf out in early spring (mid-April in southern Maine, with later emergence in more northerly latitudes) and are, therefore, easily located for removal by pulling them up or treating them with herbicide.

Removal of all "Ribes" species plants within 900 to 1000 feet of susceptible pines or pine stands will greatly reduce the likelihood of infection of white pine by the white pine blister rust pathogen.?"Ribes" spp. eradication around white pine stands has been an effective control measure for this disease since the practice was first initiated in Maine around 1918.

A leaf

Images: (left) A diagram from Report of Forest Commissioner Maine 1935?1936 depicting and explaining details of the white pine blister rust disease complex; (right) A currant plant from the genus Ribes. Image: Dale Bergdahl

Some other New England states and New York have allowed the cultivation of "Ribes" specifically bred to be resistant or immune to white pine blister rust. However, a more virulent strain of the pathogen was discovered in 2011 in New England, and cultivars of "Ribes" once resistant are now susceptible. These pose a significant risk of spreading the disease. This is why plants in the genus "Ribes" are restricted in Maine, to preserve our ecologically and economically valuable State Tree.?

Plants in the genus "Ribes "are subject to quarantine rules in Maine [ [link removed] ]. The *"importation, possession, planting, and culture of "*"currants, gooseberries, Jostaberries, Worcesterberries "and all other species of*" Ribes"* is prohibited by law in the quarantine area of Maine. In addition, the *"importation, possession, planting, and culture of any Ribes nigrum "*(European black currant) *"or its varieties or cultivars"* is prohibited throughout the entire state.

*Spruce Needle Cast Diseases "(Rhizosphaera kalkhoffii and Stigmina lautii)"*

These are two very common diseases of spruce trees in Maine, especially impactful to Colorado blue spruce and white spruce trees (all spruce can be affected to varying degrees). These diseases cause premature needle loss that negatively impact tree health and aesthetics. Needle loss and branch dieback occur from the bottom up, leaving thin lower crowns with advancing branch dieback.

Four close up pictures taken through a microscope of spores

Image: A close-up comparison of the fruiting structures and spores of the two spruce needle cast fungi, Rhizosphaera (top) and Stigmina (bottom).

Close up of fir twig; several fir trees

Images: (Left) Current-year needles have no visible symptoms, although they are already infected following early spring spore dispersal and will show symptoms next year (1 in the image). Needles from the previous year remain attached to the tree, appear discolored and are responsible for spore release and new infections (2 in the image). Needles from three years ago are typically brown and begin to fall off the fine branches; many of these needles are gone by late summer (3 in the image), while needles from four years ago or older are absent (4+ in the image); (right) Needle loss in the bottom third of blue spruce crowns due to needle cast disease infection leading to decreased function as a road-side privacy barrier.

This article is included in this issue to remind people that these needle diseases can be managed with appropriate cultural practices and treated with specifically timed fungicide applications. Needle cast diseases require moisture for infection and spread, so improving spacing and air-flow are important cultural practices for management. Care should be taken to avoid wetting spruce foliage during lawn irrigation. Needles on at least the bottom half of the crown of infected tree should be protected with fungicide containing chlorothalonil for at least two months after bud break. Needles must be protected as they begin to emerge, and shoots have elongated about one-and-a-half inches. Management is much more effective if needle cast is found early, so keep a close eye on your spruces for needle loss. Correctly identifying the specific disease impacting your tree is important to designing a management strategy that will yield the best results. This can be accomplished by contacting and/or sending foliage samples to the MFS Insect and Disease Lab or University of Maine?s Plant Diagnostics Lab.

It is important to understand that to rehabilitate trees severely or even moderately impacted by these diseases, treatment must be done accurately for a few years before enough new growth is protected to provide noticeable results. Lastly, if you are thinking of planting a new tree on your landscape or planning a privacy screen planting, avoid tree species that are highly susceptible to spruce needle cast diseases and consider a diverse group of species rather than relying on just one.

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Maine Invasive Plant Control Grant Program Applications Now Open

The Maine Forest Service (MFS) is providing assistance for local governments, municipalities, educational institutions, non-profit organizations, and private family woodland owners interested in obtaining Invasive Plant Control Practice Plans (IPCPP) for their woods. The invasive plant management program is administered by the MFS and the Maine Natural Areas Program [ [link removed] ].

Funded by a Landscape Scale Restoration Program grant from the USDA Forest Service, financial incentives for IPCPPs are available to public and private woodland owners with ten to one thousand wooded acres in Maine. The program will reimburse up to 50 percent of the cost based on the number of acres. An average small woodlot may receive up to 500 dollar maximum incentive; larger lots will be eligible for higher incentives. The IPCPP provides woodland owners with maps and treatment recommendations for invasive plants. Funds for treatment of invasive plants are also available, on a competitive basis, for those lands with an approved IPCPP.

For those interested in applying, please see the updated application instructions [ [link removed] ].

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Invasive Plant Spotlight

*Japanese Stiltgrass *("Microstegium vinimeum)"

Biologists from the Maine Department of Agriculture, Conservation and Forestry (DACF) are asking for the public?s help locating and reducing the spread of severely invasive Japanese stiltgrass. Populations of stiltgrass are only known from a handful of sites in Maine. Two large populations of stiltgrass were first detected in southern Maine in 2020. These populations are being actively managed, but due to a prolific seed bed and dispersal of new seed, new populations appear every year. Stiltgrass is an annual grass that takes over the forest floor and reduces biodiversity and regeneration of native flora. Stiltgrass thatch can also build up and make it difficult for native trees, shrubs, and wildflowers to regenerate. The thatch also raises fire risk. Infestations grow rapidly as each plant can produce up to a thousand seeds that can be spread by moving water, deer, contaminated soil, dirty boots, or dirty equipment. New populations are most likely to be found along trails, roadways, wetlands, and in moist forest sites.

Newly detected stiltgrass should be removed to prevent it from damaging Maine?s treasured forests and wetlands. DACF will offer support and guidance to affected landowners. If you think you have found stiltgrass on your property or on public land, take great care not to spread plant propagules and seed. This can be achieved by hand-pulling before it sets seed, using boot brushes and cleaning equipment when leaving the site, and properly disposing of plant material. If you would like more information or believe you have found Japanese stiltgrass, please send an email <[email protected]> with photos and location or map the location with photos in the online mapping tool iMapInvasives.

iMapInvasives [ [link removed] ] also allows you to see other mapped locations, explore invasive species near you, and set up email alerts for your area or species of concern. Please visit the Maine Natural Areas Program?s website [ [link removed] ] under the Invasive Species tab to view their invasive plant field guide for identification tips and to sign-up for a free iMapInvasives account.

Grass growing in a forest

Images: (left) Stiltgrass can form large, dense infestations in forests (Georgetown, ME); (right) Stiltgrass leaves alternate along the stem and have a silvery midrib.

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Calendar

*May 20?26, 2024: Emerald Ash Borer Awareness Week 2024 Webinar Series*

Don?t Move Firewood will be hosting a series of webinars next week: Emerald Ash Borer Awareness Week nationally, and Arbor Week here in Maine. Two webinars will be held each day from May 20 to 22 highlighting emerald ash borer. You can learn more and register on Don?t Move Firewood's website [ [link removed] ].

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*Conditions Report No. 1, 2024*

*On-line* [ [link removed] ]*
*

Department of Agriculture Conservation & Forestry, Maine Forest Service ? Forest Health and Monitoring

Contributors: Aaron Bergdahl, Amy Emery, Chad Hammer, Allison Kanoti, Gabe LeMay, Mike Parisio, Brittany Schappach, Jan Santerre, Thomas Schmeelk, and Colleen Teerling.

Forest Pest Index [ [link removed] ]



Maine State Government is an equal opportunity provider and employer.

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