Forest & Shade Tree - Insect & Disease Conditions for Maine

June 15, 2010

Emerald Ash Borer (Agrilus planipennis) - Although emerald ash borer (EAB) has not yet been found in Maine, now is the time to start keeping our eyes open for it.  Degree-day calculations show that if EAB were in Maine, adults would be emerging now throughout most of the state.  EAB is a small, narrow-bodied bright metallic-green beetle, and poses a very serious threat to all ash trees.  If you think you see an EAB, please capture the insect and call us.

There is another bright metallic-green beetle which is often mistaken for EAB:  the native green tiger beetle, which is a beneficial predator.  This beetle is much wider in the body than EAB, and has definite ‘shoulders’.  However, its behavior is an easy way to tell it apart from EAB.  It is usually found on the ground and as it is approached, will usually fly away and land 10-20 feet farther.  As it is approached again, it will again fly away in front of the one approaching.  It is very difficult to catch.  EAB does not behave like this. 

Volunteer Trainings-If they become established here, the Asian longhorned beetle (ALB) and the emerald ash borer (EAB) will be two very serious threats to Maine’s trees and forests. The best defense is early detection. The Maine Department of Agriculture is offering training workshops to individuals who are interested in learning about these forest threats and sharing that information with others. The more people familiar with these invasive pests, the better chance we have of saving our trees. Participants will be asked to conduct outreach activities in their communities this summer. Details on outreach activities and assistance will be discussed, but the time commitment is not large. Trainings run from 9am to 3pm: Bowdoin College, Brunswick, Tuesday, June 22nd; Auburn Land Lab, Auburn (Co-sponsored by the Lewiston-Auburn Community Forestry Board), Thursday June 24th; Maine Department of Agriculture, Augusta, Tuesday, June 29th. Contact Anne Bills to register or for more information:, 207-287-3892.


Arborvitae Leafminer Complex – Cedar across the state is showing browning from the feeding of arborvitae leafminers as well as other problems (see also Diseases and Injuries section).  There are four species of leafminers that feed on cedar in Maine.  The larvae feed inside the needles causing them to turn brown.  There will be a small hole in each mine that can be seen with a hand lens. The larvae overwinter in the needles then resume feeding in the spring.  The moths will be flying soon to mate and lay eggs.

High value trees can be monitored for the presence of leafminer adults.  From the end of June into early July periodically shake the branches of the trees and if clouds of tiny moths fly out, it is time to treat.  Use a contact insecticide to kill the moths – they do not feed.

*Browntail Moth(Euproctis chrysorrhoea) - The browntail moth caterpillars are finishing up feeding for the season and are starting to pupate.  This, and the rain, will begin to provide relief for people suffering from the browntail moth rash.  People still need to be cautious mowing, raking and removing cocoons from buildings or trees.

Cinera Aphids (Cinera spp.) – A number of reports of aphids infesting fir and spruce trees have been received in the past few weeks.  Cinera aphids are large aphids that feed in masses on the trunk and branches.  They do not harm the tree but can create a mess with their honeydew and accompanying sooty mold.  Ants usually tend the aphids and wasps are also attracted to the honeydew.  They also alarm people when they see a tree covered with insects, as occasionally happens.  No treatment is needed unless they are overwhelming on ornamentals and then an insecticidal soap should take care of the problem.

*Hemlock Woolly Adelgid (Adelges tsugae) – In the last month additional hemlock woolly adelgid infestations have been confirmed in Harpswell, South Portland, Brunswick (Cumberland Co.) and Phippsburg (Sagadahoc Co.). We are working through calls in other towns as time allows. Reports to the MFS and Maine Department of Agriculture have come from forest landowners, homeowners and Asplundh right-of-way arborists doing line clearing for CMP. Please keep them coming and be patient—we will get to your call.

Larch Casebearer (Coleophora laricella) – Casebearer damage showed up more broadly then expected through central Maine and into northern Maine. The browning is fading now as the needles drop off and the elongating branches mask the damage.  Although the damage looks severe for a few weeks it does little lasting harm to the trees. (USDA FIDL)

Large Aspen Tortrix (Choristoneura conflictana) – This early season defoliator has come and gone stripping scattered stands of quaking aspen in Aroostook county.  The large aspen tortrix has been defoliating trees in Quebec for the past four years and we have been seeing the moths in our light traps. This is the first time we have found defoliation on our side of the border though. This insect overwinters as a larva at the base of the tree and feeds as soon as the foliage is out. It rolls and ties leaves together for protection and pupates in the leaves. (USDA FIDL pdf)

Satin Moth (Leucoma salicis) – Poplar yard trees from Houlton to Fort Fairfield are being attacked by satin moth caterpillars. The satin moth caterpillars are quite striking – brown with large white dots running down their backs and hairy red bumps sticking out from their sides.  They have been mostly absent in the past few years.  The caterpillars overwinter so they are ready to eat as soon as the leaves come out and will completely consume the leaves except the larger veins. They make their cocoons on the trees and the moths emerge in July.  The eggs hatch, the tiny caterpillars skeletonize leaves in late summer and then hibernate on the trees.

If it isn’t one thing it is another attacking poplar this year!

Striped Alder Sawfly (Hemichroa crocea) – Paper birch in Boothbay had larvae of this sawfly feeding heavily on the foliage. (image)  The larvae feed gregariously along the leaf margins of birch (or alder or willow.)  They first skeletonize the leaves and then as they get larger completely consume the leaves moving as a group from one leaf to another.  There are two generations a year so control of the first generation is advisable on high value ornamentals. 


Diseases and injuries

Cedar-Apple Rust (Gymnosporangium juniperi-virginiana) – Every year, the cedar-apple rust draws the attention of homeowners who see golf-ball sized, conspicuous, bright-orange, jelly-like masses in junipers, (including varieties of eastern red-cedar Juniperus virginiana  and Rocky Mountain juniper J. scopulorum)(image). The disease causes insignificant damage to the juniper hosts.  However, these gelatinous galls produce spores that can infect and cause leaf spots and premature defoliation of apple and crabapple varieties. While there are fungicides available to protect apple hosts (applied earlier in the spring), removal of the galls from the junipers will reduce the risk of apple infection.  Inspection and removal of juniper galls can be done at any time of year; the non-sporulating galls appear as small, reddish-brown dimpled structures on the juniper branches when the bright-orange tendrils are no longer present. (Cornell Fact Sheet)

Frost Injury Recovery – Many species of woody plants were damaged after the hard frosts that occurred during the period from May 10 – 12. (image) Numerous reports were received of “spot” locations of frost damage throughout north-central, central, and southern Maine.  For the great majority of affected trees, a rapid recovery has been observed.  Significant long-term damage is unlikely to have occurred. Trees on which primarily the leaf tissue alone was frosted, the re-foliation is well underway.  In some individual cases, it has been observed that if the succulent, new shoot growth (in addition to the leaves) was frosted, a slower recovery is occurring.  In these cases, new buds first have had to develop before the re-foliation could begin.  Some branch dieback on these trees may occur, but damage will be minor.

Needlecast of Spruce (Rhizosphaera kalkhoffii) - The needlecast of white and Colorado blue spruces has continued to be prevalent again this year.  Most recent reports have come from Saco and York (York Co.), Augusta (Kennebec Co.), and Eastport (Washington Co.), but the disease can be found anywhere the host trees are growing.  The early spring season required that the recommended fungicide applications be made before now.  However, infection levels for this season should be lower than in the recent past, due to the dry weather during the month of May, coupled with the earlier maturation of new growth.

Northern White-Cedar Decline - The condition of northern white-cedar (Thuja occidentalis) in many areas of the state again appears poor to moderate at best.  Decline in northern white-cedar has been a concern for several years, with examinations and surveys defining a multitude of problems in a variety of combinations.  A significant level of arborvitae leaf miners is apparent again this year, with damage appearing as “flags” of yellow to light brown branch tips throughout crowns of affected trees.  In addition, needle pathogens have been observed on some foliage.  Neither the insect damage nor the needle diseases are believed to account for the general, off-color appearance and more severe dieback of many trees.  Northern white-cedars left as residual trees in partial harvests often suffer root and bole mechanical damage.  There are also several root and stem decay pathogens which commonly affect trees of all ages.    The decline appears chronic and widespread, and the assessments are continuing.

Phomopsis Branch and Stem Galls on Oaks (Phomopsis spp.) – Branch galls on oaks (image) (primarily red oaks Quercus rubra) have been reported from several towns this spring, including Paris (Oxford Co.), Sydney (Kennebec Co.), and Waldoboro (Lincoln Co.).  Some individuals in the oak stand in Paris had multiple and severe branch infections, with branch mortality very evident.  Some previous tree mortality was reported by the landowner.  Management recommendations are limited to pruning affected branches, or removal of severely infected trees, including trees with galls located on the main stem.

White Pine Needlecasts (Canavirgella banfieldii and Mycosphaerella dearnessii) – The majority of public assistance requests for tree disease concerns over the past month have been due to the yellowing, browning, and premature needle loss of white pines. (image) The condition has been observed throughout the state, but appears to be most severe in western and southern counties.  The occurrence of needle diseases and needle browning on white pine has been reported from throughout New England.

There are two diseases (caused by fungi) of particular importance, and trees may be affected by either or both. The first is called Canavirgella needle cast (Canavirgella banfieldii); the second is called “brown spot” (Mycosphaerella dearnessii). We have seen a great deal of Canavirgella in the past four or five years, and suspect it is the result of the very wet springs and summers we have had. The fungi require free moisture to germinate and grow into the needles, and the last few years have been very wet. The yellowing needles are one-year-old needles – those produced last year. The current-season needles are elongating now and are green. Infection (if it occurs) of the new needles will take place this spring and summer, and these eedles will then yellow and turn brown next year. In addition to the fungi, some observers feel that the late spring frosts may have played a role in the development of the yellowing symptoms of one-year old needles. There are no fungicides recommended for managing either brown spot or Canavirgella, primarily because they have not been a serious problem before.

To date, there has been no documented tree mortality from these diseases, but some trees do appear to be very thin in the crown. Younger, regenerated trees in the understory are also affected, and may be more at risk of succumbing than the mature overstory trees.  On a more positive note, this year so far has been a bit drier than last year, so infection of current-year needles may be reduced compared with last year’s levels. 

Tree condition and disease development continues to be closely monitored.  Foresters and landowners who observe white pine mortality which may be related to the condition described here are encouraged to call the Maine Forest Service Entomology Laboratory at (207) 287-3008.

Conditions Report No. 3, 2010
Maine Forest Service
Forest Health and Monitoring Division