The beginning of a new season of outdoor recreation brings new focus to the dangers posed to our forests by invasive forest pests, often spread by infested firewood.  Recreationists and camp owners from out-of-state must be aware of the threats invasive forest pests pose to Maine’s natural resources. Currently, the emerald ash borer (EAB) and Asian longhorned beetle (ALB) are of greatest concern, but there are dozens of other threats to our forest that can move in or on firewood that the public will be less likely to recognize.  These range from tiny bullet-shaped beetles and large longhorned beetles, that look nearly identical to our native beetles, to microscopic fungi.  

The message, “use local firewood,” is less complicated than enumerating hosts and descriptions of some key insects of concern. However, we will continue to provide information about these few “charismatic megafauna” with the hopes that you can help us find them, but with the caveat that they are merely the tip of the iceberg when it comes to new forest threats.  Learn to identify those insects, their signs and symptoms, but keep aware of changes in tree and forest health, and report concerns beyond the most wanted list.  Public detections are important in finding these insects in our forest and ornamental trees as quickly as possible.  

We also ask the concerned public to help us spread the word about firewood. Maybe you know a neighbor who looks at a trip to camp as a frugal and environmentally sensitive alternative to disposal of suburban tree waste.  Consider helping your neighbor recognize the costs associated with that activity.  If a neighborly chat is not enough to convince him or her to burn the wood immediately, or there is too much wood for immediate consumption, you can report your concerns to the MFS Forest Protection Division by phone at 1-800-750-9777 or online at http://www.maine.gov/dacf/mfs/rpt_concerns.html.

Because there is a quarantine on EAB in most states in the Eastern US, transporting firewood into Maine from out-of-state is often not only a violation of State rules, but also of Federal quarantine.  Learn more at emeraldashborer.info and www.maine.gov/firewood.  

If you are a landowner and have ash trees on your land, consider creating a girdled trap tree to monitor for EAB.  All trap trees girdled last year were negative for signs of EAB and efforts have begun this year to girdle trees to continue monitoring. If you have an ash tree of any species (not mountain ash) over four inches in diameter at 4.5 feet that you would be willing to sacrifice as a trap tree, please email Colleen Teerling at colleen.teerling@maine.gov with the subject line “Trap Tree” and we will help you create a trap tree. More information can be found on our website.

Photo: Evidence of woodpecker feeding on ash. Image: Maine Forest Service

This is one of the best times of year to watch for signs of EAB.  During the winter until the trees start to leaf out in the spring, woodpeckers often find and feed on overwintering EAB larvae, which are fat and make good eating at this time of year.  As the birds feed, they flick off the gray outer bark, and expose the light-blond inner bark, leaving a distinctive signature (although not unique to woodpeckers feeding on EAB).  It is primarily the smaller woodpeckers, like the hairy and the downy, that feed on EAB; although even smaller birds like nuthatches do as well.  When you are out and about, watch for signs of woodpecker feeding on ash and let us know if you see any.  If you can, take a picture of any feeding you see on ash and pass it on to us.  

Eastern Tent Caterpillar (Malacosoma americanum) – Watch for the developing tents of these hairy caterpillars in cherries and apples in late April and early May in southern Maine (later as you move farther north).  In Maine, this native insect is primarily a nuisance and aesthetic pest.  It does not significantly impact forest health, but repeated defoliation can affect host growth and vigor, which can be important on ornamental and orchard trees. On valued fruit and ornamental trees, you can look for and destroy egg masses of this caterpillar.  Also, monitor for developing tents on these trees and consider removing them when they are small. The caterpillars return to their tents in the evening, so this and early morning are good times to remove tents.

Photo: Eastern tent caterpillar egg mass.  Maine Forest Service

Delphinella shoot blight (Delphinella abietis) affects true firs (Abies spp.) and is an occasional pest of firs in Christmas tree plantations and horticultural plantings in Maine. Historically, the disease has been recorded in several locations throughout Maine and has resulted in some losses in plantations. Delphinella shoot blight is characterized by blighted tips, usually affecting early season new growth. At first glance, the damage can resemble that caused by late frost. Newly affected tips turn a reddish-brown color and may twist and turn irregularly as they dry (this symptom can also be mistaken for chemical injury). In time, numerous black fungal spore-producing structures can be seen on the needles on the dry blighted tips. These needles persist for a year or more and are the source of reinfection during prolonged periods of moisture in the following spring/early summer.

Photo: Delphinella shoot blight symptoms in Penobscot County, Maine in 2018. Maine Forest Service

Any management practices that encourage air-flow in the vicinity of trees, thus enhancing needle drying (decreasing the period of needle wetness), may limit disease. Pruning of lower, infected branches reduces the source of reinfection (inoculum) and helps increase drying in the lower crown. Other cultural practices like maintaining proper spacing (for instance in a Christmas tree plantation) and controlling vegetation around trees is recommended where this disease is a problem. 

Some Christmas tree growers in the Pacific Northwest have used chlorothalonil-based products to control this disease, however in some cases they have noted chlorotic stippling and discoloration associated with this chemical management approach.  Since needles capable of producing spores causing reinfection persist on trees for two (possibly more) years, chemical and cultural management practices should be conducted for as many years as it takes to eliminate the disease from the area.

Oak wilt (Bretziella fagacearum, formerly Ceratocystis fagacearum) has not been detected in Maine but is a pathogen of significant concern and therefore a focus of early detection efforts.

Photo: Oak wilt symptoms on prematurely defoliated leaves in Pittsburgh, PA. Maine Forest Service.

The oak wilt fungus kills water-conducting tissues, first leading to discoloration and early defoliation of leaves followed by wilting and killing of branches (flagging).  As the disease progresses in the tree, wilting and branch mortality expands, with trees dying in the same year or the following year

Oak trees have a habit of connecting their roots with neighboring oak trees (root grafting).  This can allow the oak wilt fungus to spread from tree to tree rapidly, causing pockets of oak mortality in a stand.

The causal agent of oak wilt has been confirmed in three locations on Long Island, New York, one location in eastern and one location in western New York State. This disease has caused mortality of oaks in the Midwestern United States for decades and is a threat to oaks in forest and residential settings. Oak wilt disease can also spread via firewood, further highlighting the importance of not bringing firewood from out of state and instead relying on local sources for firewood needs.

Please report any early defoliation of oak trees to the insect and disease lab in Augusta and keep an eye out for unusual dieback and unexplained oak mortality in your area.