Browntail Moth (Euproctis chrysorrhoea) – Browntail moth eggs are hatching, and the caterpillars have started to skeletonize the leaves that will later be enclosed in their overwintering webs.  Sometimes the feeding activity of fall webworm (Hyphantria cunea) is confused with that of browntail moth.  At this time of year, the caterpillars and webs of fall webworm are huge in comparison to those of browntail moth (see photos for comparison).  Later in the fall, the fall webworm tents will become tattered and worn, and the webs of browntail moth will become more tightly woven. Be aware that the cocoons of browntail moth that were formed on trees and shrubs are still present and contact with them could result in exposure to the toxic hairs.

Photos: Development of browntail moth caterpillars and early webbing (left).  Development of fall webworm caterpillars and webs (right).  Photos from southern Maine, week of 8/6/2018, Maine Forest Service.

Emerald Ash Borer (Agrilus planipennis) –  After allowing for public input and completion of the mid-season check of traps, an order to stop movement of ash material from towns with detections of emerald ash borer (EAB) in Maine was put into place last week.  The order covers the towns of Frenchville, Grand Isle and Madawaska.  These are the only towns in Maine with confirmed detections of EAB.  More information about emerald ash borer and the department response can be found at www.maine.gov/eab. 

The public is invited to an informational session on EAB on August 23rd at 6:30 pm at the Frenchville Community Center.  Department of Agriculture, Conservation and Forestry (DACF), USDA Animal and Plant Health Inspection Service and USDA Forest Service staff will be at the meeting to provide an update on EAB and respond to questions. 

Photo: Purple traps similar to the one above captured single adult emerald ash borers in each of two locations in Grand Isle, Aroostook County. 

We have recently finished a mid-season check on the purple traps hung to monitor for EAB.  Approximately 250 traps were hung by DACF throughout the state.  Over 100 of those were hung in northern Maine in the vicinity of the recent EAB find in Madawaska.  Three traps in the town of Madawaska caught EAB, and a single EAB was caught in each of two traps in the adjacent town of Grand Isle (which was not previously known to contain EAB).  The USDA APHIS contractor, Delta 21, is checking an additional 411 traps in the area within 100 miles of the quarantine in New Hampshire (DACF did not hang traps in that area).  No EAB has yet been found in any other part of the state.

We are also monitoring for EAB using biosurveillance with Cerceris fumipennis in the southern part of the state where this non-stinging wasp is found.  No EAB have been found so far. If you find any colonies of wasps (often found on baseball diamonds) you think may be Cerceris fumipennis, please contact us and we will check them out. We are always on the lookout for new colonies of this wasp to help us monitor for EAB and other exotic metallic woodboring beetles.

We have been seeing a lot of declining ash, both as whole stands and as individual trees, throughout the state for several years.  With the recent years of drought, the decline seems to have intensified.  We see many ash with all the classical symptoms of EAB:  decline and branch death from the top down, epicormic growth, woodpecker feeding and bark splitting.  It is very difficult to differentiate this from EAB, and often the only way to be certain is to girdle tree in the spring for use as a trap tree that EAB will be attracted to and then peel it the following winter to look for signs of EAB.  If you have declining ash on your property and think you might want to participate in our girdled trap tree program next spring, please email patti.roberts@maine.gov and ask to be put on our mailing list or call (207) 287-2431.

Minute Pirate Bug (Orius spp.) – Minute pirate bugs (some of which are also called insidious flower bugs), are very small insects in the true bug family.  They are very important predators on a wide variety of garden and tree pests, including aphids, thrips, whiteflies, spider mites, small caterpillars and many other small insects and insect eggs.  Most of the year, they are scattered throughout your yard and fields and one rarely sees them.  However, in states to the south and west of Maine, they are known to congregate in very large numbers near houses and buildings in the late summer/early fall.  In past years we have not received questions about this behavior, but during the last few weeks, we have had several calls about swarms of this insect.  We may be seeing this behavior now because of the hot, dry weather we have had recently.

Photo: Beneficial minute pirate bugs have been reported in large numbers this year (metric ruler). Photo: Maine Forest Service

Minute pirate bugs do sometimes ‘bite’, probing your skin with their stylets.  It is thought they do this to ‘taste’ their environment.  They do not inject any venom, and most people just feel a small pinching sensation (although a few can experience swelling and itching similar to a mosquito bite).  It is important to note that standard insect repellents do not work to keep minute pirate bugs off your skin or structures.  If you find yourself being bitten, covering up with long-sleeves and pants is your best defense.  We do not recommend any chemical control as these insects provide very important natural control for a wide variety of yard, garden and tree pests.  As the weather gets cooler in the autumn, they will disappear and again become unnoticeable. 

Balsam fir mortality Reports of dieback and mortality of balsam fir have been frequent across Maine in 2018.  This seems to be a regional phenomenon with reports from New Brunswick of wider-spread balsam fir mortality and some similar observations in the northern areas of New Hampshire and Vermont.  Inspection of trees in multiple areas of Maine have revealed a number of contributing factors to decline and mortality.  These include salt exposure along roads, bark beetle attack, armillaria root disease/shoestring rot and winter desiccation. As an example, during a recent trip to Aroostook County nearly all inspected trees in various states of decline were infested with a tiny bark beetle (Pityokteines sparsus). As these are all contributing factors to decline, it is important to consider the source of primary stress.  Due to the lack of precipitation from the later part of last year’s growing season and the state-wide drought conditions of this year, drought stress seems to be the major primary source of stress leading to heightened balsam fir susceptibility to various other agents of decline. 

Drought stress in trees describes a condition where there is not adequate moisture in the soil for a tree to extract and carry out necessary life functions. Among other physiological responses, drought conditions can lead to dieback of a tree’s fine roots that are very important for water and nutrient uptake.  Losing the function of these roots leads to reduced tree vigor, making trees less resilient to additional stressors. For example, when a tree suffers drought stress and fine root damage occurs late in a growing season, it becomes more susceptible to winter desiccation. Also, attack by diseases and insects are often more damaging to trees during times of drought, since the trees lack resources for normal defense responses.  In some cases, it has been noticed that even usually weakly pathogenic fungi (those that typically do not cause disease-like symptoms) have caused cankering and branch dieback in drought stressed trees.  This further highlights the significance of regional drought as a primary source of stress predisposing trees to attack by insects and pathogens and reducing a tree’s ability to withstand pressures from additional agents of tree decline.

The Maine Forest Service will continue to look into balsam fir mortality to gain a better understanding of this phenomenon.

Fire blight (Erwinia amylovora) – Fire blight is a bacterial blight of trees and shrubs in the Rose family (Rosacea).  Trees in Maine most commonly affected by this disease are pear, apple, hawthorn and mountain ash (pictured).  On a recent trip to Aroostook County, fire blight on mountain ash was observed multiple times in several towns.  Additionally, samples were received at the lab from southern parts of Maine earlier this year as well.

Photo: Mountain ash with fire blight. Maine Forest Service.

Fire blight symptoms include quite rapid wilting and darkening of branch tips resulting in a characteristic ‘shepherd’s crook’ shape. Soaked-looking, sometimes oozing cankers can be found at the base of symptoms, while other, smaller cankers may be difficult to recognize. Bacterial ooze is the main mode of spreading infection to other parts of the same tree or nearby trees. Spread can occur by rainsplash during warm and moist weather. Insects attracted to the sugary bacterial ooze exuded from cankers also effectively spread this disease. Injuries from hail, pruning or other damage can cause rapid spread of this destructive disease.  

Managing fire blight is challenging and a topic of debate.  Management guidelines for fruit growers can be readily found online, but for the homeowner wishing to keep their planting free of this disease, vigilance and early detection are key.  Infected plant parts should be pruned away and destroyed.  Pruning cuts should be made as far back as possible into older wood, which may harbor the disease, but will not show symptoms – more succulent wood is much more susceptible.  Once fire blight really gets started in a tree, it may require so much pruning that the tree will no longer be aesthetically acceptable, stressing the importance of keeping a close eye on your trees.

White pine needle disease evaluation and monitoring project 2018 field work completed – Field work for the Maine portion of a regional effort by ME, MA, NH, RI and VT to address white pine health issues concluded in early July.  The project, titled “Monitoring eastern white pine decline and its causes in New England and New York through enhanced survey methods” was financially supported through a grant by the US Forest Service.

Map: White pine needle diseases study sites. 

Eastern white pine (EWP) stands with differing levels of symptom severity were evaluated to determine the stand factors associated with WPND incidence and severity and assess the impact that this long-term disease pressure has had on EWP decline and regeneration. The ultimate goal of this work is to use what is learned to develop management practices to improve EWP health in Maine and the overall region. A total of 40 plots (each with 4 subplots) and approximately 700 trees were evaluated by Maine Forest Service Forest Health personnel across the state’s most concentrated white pine resource. Trees were evaluated based on crown health variables such as transparency, density, live crown ratio and disease presence. Other site factors like slope, aspect, basal area, etc., were also recorded. Additionally, diseased needle samples were collected to be identified by a USFS forest pathologist. Currently, data is being entered and will be analyzed this fall/winter with a publication of results is planned for 2019.

Special thanks to all the landowners, managers and foresters who helped this effort and offered their white pine land for our work. Supporters include the University of Maine Demeritt Forest, Maine Bureau of Parks and Lands, Maine Inland Fisheries and Wildlife, Maine Forest Service-- Forest Policy & Management Division, the US Forest Service for use of the Penobscot and Massabesic research forests, Chadbourne Tree Farms, Freeman Ridge Forestry, Hancock Lumber, JD Irving, LandVest, Robbins Lumber and Sappi.