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Maine Forest Service
Forest Health & Monitoring Division

Forest & Shade Tree
Insect & Disease Conditions for Maine

Issue: July 8, 2005                                                                                  Back Issues: May 12, 2005
                                                                                                                                       April 22, 2005
                                                                                                                                        June 8, 2005

In our last Conditions Report we wrote of the potential impact that the abundant rain we received during the past spring season might have on the development of plant diseases. Maple anthracnose was rampant at the time, but other foliage diseases also seemed poised to develop.

Now a month later, the picture has clarified considerably. While ash anthracnose defoliation seems to have been less severe than we feared, other foliage diseases, particularly fir-fern rust, have become epiphytotic (see Diseases and Injuries). And the cool, damp spring seems to have had an effect on insect populations as well. It seems likely that weather was a significant factor in this spring’s apparent collapse of browntail moth populations.

Despite our success to date in halting artificial establishment of hemlock woolly adelgid in Maine, we continue to note an expansion of the area infested with hemlock woolly adelgid in southern Maine where the insect has migrated into our state from infested areas to the south. We have included a special update on this insect by State Entomologist Dave Struble in this issue.

And once again we would like to thank those of you whose reports contribute to the success of this report. Special contributors this month include Phil Norris, Ken Fowler, Walter Gooley, Ralph Dow, Jim Pearson, Dave Linney, Bob Morrell, Pete Lammert, Clem Meserve, Robert Moody, Didier Bonner-Ganter, Todd Murphy, Doug Johnson, Bob Tooley, Jeff Smith, Jeff Ewing, Bob Monette, Dana Graves, Sharon Lloy, Brian Ketchum, Rand Stowell, Charlene Donahue, and Len Price, among many others. 

Special Update on the Status of Hemlock Woolly Adelgid

by State Entomologist Dave Struble

Hemlock Woolly Adelgid (HWA) was first found in the wild in Maine on native hemlocks on Gerrish Island in Kittery in 2003. Earlier this year we reported that it had subsequently spread to infest portions of three towns in southern York County: Kittery, York and Wells. We now find it necessary to add a fourth town to the list. Last month HWA was found in the Town of Eliot, also part of York County. 

The Eliot infestation appeared last week to be confined to five, closely spaced understory hemlocks in a single roadside wooded area. However, earlier this week Maine Forest Service personnel located another spot infestation in Eliot on two trees about a mile away. Delimitation surveys are now underway to more closely define infested areas within Eliot. At this time somewhat over 4000 acres in southern York County display either trace or light infestations of HWA.

The Maine Forest Service continues agressive efforts to contain or slow the spread the movement of this pest in Maine.

We are enlisting the services of landowners, landowner groups, and the general public to help locate new infestations in their early stages. The first finding of HWA in Eliot last month was due to the vigilance of a small woodland owner.

We continue to eradicate HWA infested trees which have been introduced to Maine on imported nursery stock. While this effort to date has been successful, we remain constantly vigilant. Just this spring, staff at three separate nurseries detected and informed state officials of hemlocks originating in Oregon that were included in shipments they had received. Because Oregon is an infested state whose hemlock stock is not allowed to come to Maine, this material has been secured and is being destroyed.

The Maine Forest Service is working with local and regional researchers (academic and USFS) on impact assessment, host resistance, remote sensing, and biocontrols.

While HWA has caused significant mortality in mid-Atlantic and southern states, forest impacts and population intensification have been slower at the northern edge of the infestation. We are hopeful that climatic conditions in Maine will ameliorate HWA's impact and slow its spread.

In the meantime we will continue to monitor any further spread of HWA in Maine, attempt to project its impact on the hemlock resource, and recommend changes in forest management practices if they become warranted.


Ash Defoliator (Palpita magniferalis) - This is a little known moth that has been defoliating ash trees in the Owls Head/Islesboro area for the past two years. Moth numbers are high again so defoliation from the larvae is expected this year as well. Larvae can be found feeding on the undersides of ash leaves under a thin film of silk. The damage becomes pronounced in late July to early August.

Aspen Leafrollers probably (Pseudexentera oregonana) and others - Moderate levels of leafroller damage have been reported in New Limerick. Leafroller damage was heavy in this area in the early 1990’s and may be on the rise there again.

*Browntail Moth (Euproctis chrysorrhoea) - This past winter’s browntail moth survey showed a marked decline in the number of overwintering webs but there were still more than enough to cause significant defoliation and human rashes in most areas. The larvae, as we reported in earlier newsletters, emerged on time and began to feed. Then the cold wet weather settled in and with it brought perfect conditions for transmitting diseases through the population. Ground surveys in late June came up with unexpected results - minimal defoliation and few rashes in people! The browntail were not completely gone; there were still healthy larvae to be found but in very low numbers. Occasional trees had noticeable defoliation but that damage was not apparent in aerial surveys. Samples of dead larvae have been sent off for confirmation of the disease causing agent, most likely Entomophaga aulicae.

At the same time that the browntail moth population was collapsing around Casco Bay, there were two incidents in Augusta where people came into close contact with browntail moth caterpillars. One population was controlled due to it’s close proximity to a manned fire station and summer day camp.

Clipping out any webs you can reach this winter will help to keep the populations down next year.

Eastern Tent and Forest Tent Caterpillars (Malacosoma americanum and M. disstria) - Caterpillars have moved to pupation sites but not all of them made it through the year. The wet spring does have a silver lining in that many caterpillars were infected with fungal and viral diseases that will reduce the populations for next year.

*Gypsy Moth (Lymantria dispar) - Populations of gypsy moth are generally low and many caterpillars were infected with a fungus spread by wet weather. Anticipate low levels of gypsy moth again next year.

Oak Leafrolling Weevil (Attelabus bipustulatus) - The damage from the first generation of leafrolling weevils is evident now on oaks in central Maine. Leaves, particularly at the tips of branches, have both small holes from weevil damage as the leaf was expanding and larger holes chewed after expansion. The adult weevil lays an egg and then forms a rolled packet around it for the larva to eat. Most of the packets fall to the ground but some are left hanging on the tree; these often contain eggs that do not make it. A second generation of adult weevils is now present on the leaves so more damage is expected.

*White Pine Weevil (Pissodes strobi) - It’s not too late to correctively prune infested white pine leaders. Corrective pruning helps trees to retain their upright stature. Prune back to the first healthy whorl of branches. Then select the best lateral of this top whorl and prune off all remaining laterals leaving the single best lateral to form a new leader.

*Yellowheaded Spruce Sawfly (Pikonema alaskensis) - Larvae are gaining size now and defoliation is becoming obvious on roadside spruces. Control now with Spinosad or carbaryl to limit damage. The population appears to be staying low overall.

Diseases and Injuries

Ash Leaf and Twig Rust (caused by Puccinia sparganiodes) - Ash trees in certain portions of coastal Maine display weak crown foliage growth this season. This symptom is perhaps most apparent in the Thomaston area, and is the result of past and present ash leaf and twig blight infection. Trees which were heavily defoliated by ash leaf and twig rust in previous years, such as those along Route One in Thomaston, did not and probably will not rebuild good crowns with strong foliage for several years.

The recent outbreak of ash leaf and twig rust in coastal Maine areas is still ongoing, and many more ash trees from Kittery to the Ellsworth area and perhaps beyond may be expected to continue to drop leaves over the next week or two due to this disease. Affected leaves display yellow to orange spots which darken to brown or black over time.

Ash leaf and twig rust generally does not kill trees but does cause considerable crown dieback when infection levels are high.

Fir-Fern Rust (caused by Uredinopsis mirabilis) - Fir-fern rust has been more prevalent this year than any previous year in our memory. We have received many calls from all over southern Maine. Christmas trees have been the most heavily impacted, but landscape and woodland fir trees are affected to varying degrees as well.

This disease first became apparent to many Christmas tree growers about June 24, when infected balsam fir needles began displaying an off color light yellow appearance among the healthy green needles. Closer inspection revealed tiny, white aecial cups protruding from the underside of affected needles. But many growers did not notice anything wrong with their trees until about a week later when they observed clouds of white dust (fungal aeciospores) drifting from trees as they were disturbed through contact during mowing or shearing activity.

Many growers have called us with concerns about marketability of affected trees and whether controls are appropriate at this time. Generally if no more than about 20% of needles of current year growth are infected, marketability will not be affected. Needles will turn brown shortly and fall from trees by the end of next month. Unless a tree is heavily infected, these needles will not be missed. Very heavily infected trees may have to be held over until next year. But all needles which will be infected this year have already been infected, so no additional needles will be lost. No chemical controls are practical at this time.

While this disease is severe on balsam fir, Fraser fir has generally been spared. Probably the later flushing nature of Fraser kept this species tight in bud while infective spores from ferns were being released (mid May in southern Maine). Concolor fir does display some infection, however.

This disease, like many (not all) rust fungi, has two hosts: true firs, and certain species of fern, especially sensitive fern. The causal fungus will not spread from fir to fir, but must infect the fern alternate host first. So this provides an opportunity for growers to break the disease cycle in and around their plantation by destroying the alternate host plants. Now is the time to eradicate the infective ferns. Glyphosate products such as Roundup work well at the same rates as used for other weed management activities in Christmas tree plantations. So spray those ferns in and around your plantations within the next few weeks. Expect to re-spray the few ferns next summer which survive this summer's control efforts.

For growers who do not wish to employ herbicides, frequent fern mowings throughout the summer may be helpful.

Pine Needle Cast (cause uncertain, possibly a species of Lophodermium) - Large stands of pitch pine in portions of Western Maine display brown needles this season. We have noted this problem in these same areas in some past years, and while the disease is striking it does not seem to cause mortality. MFS personnel have aerially mapped affected stands. The most conspicuous symptoms are in the Fryeburg, Brownfield and Waterboro areas, with a total of 7,650 acres affected.

Sudden Oak Death (caused by Phytophthora ramorum) - We continue our efforts to monitor for this disease. To date all our surveys have been negative, but we are aware that planting stock from infested West Coast nurseries occasionally makes its way to Maine. MFS has commenced forest and nursery perimeter surveys for evidence of the Sudden Oak Death, and plan to complete surveys on ten sites before the end of this month.

Insect and Disease Laboratory, 50 Hospital Street, Augusta, Maine 04330-6514
Phone (207) 287-2431, Fax (207) 287-2432.

Compiled by  Clark A. Granger
03/05 Forest Health & Monitoring Division Augusta, Maine