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DEPARTMENT OF CONSERVATION
Maine Forest Service
Forest Health & Monitoring Division

Forest & Shade Tree
Insect & Disease Conditions for Maine

Issue: May 12, 2005                                                                                Back Issues: April 22, 2005

Here comes the busiest time of spring, ready or not! For our Christmas tree friends in south and central Maine, balsam twig aphid sprays need to be on now! If you haven't planted, this is the time! It's also a good time to prune out those pesky yellow witches' brooms. And if there are any trees left unsheared from last year, it's now or never.

For our nursery friends, take a good hard look at the planting stock your have purchased for resale. Look especially for small stem cankers which may have arrived on infected stock. These may grow to cause problems for homeowners down the road. These small cankers may not cause mortality for several years, well after any warranty has expired. But your customers won't be happy and if your customers ain't happy, ain't nobody happy!

For you landscapers, keep in mind the proper planting depth when you outplant nursery stock. Dig your planting holes wide rather than deep, so that the root ball sits on undisturbed ground at the proper planting depth as you backfill. And check to make sure the top of the root ball, or the top of the potting mixture for container stock, really represents the top of the root system. Often the true root system is buried quite deeply within the container or root ball, and unless the extra layer of soil or potting mix is removed, the tree or shrub may inadvertently be planted too deeply.

For you arborists, please don't give up on us to help you identify your pest problems. We do run behind here during the busiest parts of the season, but accurate diagnosis and appropriate chemical or cultural recommendations are key to effective and responsible insect and disease controls.

For you foresters, technicians, and woodland managers, this is the best time to find and spray Ribes for white pine blister rust control. If you are unsure of techniques, please call for assistance. We will send a blister rust technician to your woodlot for personalized, on the ground help.

And for all, dig out the bug dope. It certainly looks to be a challenging bug season shaping up!

Reminder: Next Week, 15-21 is Arbor Week. You may wish to attend the 9th annual Maine Arbor Week celebration on Tuesday, May 17, from 1:30 - 4:00 p.m at the Maine State Museum in Augusta. A reception with light refreshments will begin at 1:30, with a guest speaker and an awards ceremony starting at 2:00.

Guide to Pest Management for May

Remember that this is just a guide and that conditions will vary

INSECTS

*Balsam Woolly Adelgid (Adelges abietis) - Low winter temperatures in 2003 and 2004 caused heavy mortality of this insect allowing trees that did not die to start rebuilding their foliage. Trees checked this spring displayed a mixture of dead and living adelgids, so there is potential for populations to rebuild this coming season. Christmas tree growers should rogue out any fir showing swelling at the nodes.

Birch Casebearer (Coleophora serratella) - Larvae are now out and feeding on expanding gray birch leaves in southern Maine. Populations are up, at least locally, and also feeding on the slower developing white birch leaves and buds. This pest could cause noticeable foliage browning as the season progresses.

*Browntail Moth (Euproctis chrysorrhoea) - Once again it is browntail moth season along the coast from Boothbay west to Cape Elizabeth. The cool weather has delayed foliage expansion and slowed caterpillar development. Browntail populations will again be heavy from Falmouth to Phippsburg although webs appear to be smaller and fewer in number than in some past years. Scattered populations are present over inland areas of Lincoln, Androscoggin and Cumberland counties. Larvae in those inland webs display about 50% overwintering mortality, which still leaves enough larvae alive to cause significant damage.

This is the time to plan chemical treatment of areas that have webs. (It is too late now to accomplish browntail control through web clipping). Pesticide application should be completed prior to caterpillars developing toxic hairs in early June. We strongly recommend hiring a licensed a licensed applicator to control this pest. Homeowners generally should not attempt control of the browntail with pesticides to avoid both environmental and personal health concerns.

Bruce Spanworm (Operophtera bruceata) - Bruce spanworm larvae have begun to bore into sugar maple buds in Kennebec County and should become evident further north as buds begin to swell.

Eastern Tent Caterpillar (Malacosoma americana) - There seem to be fewer webs of this early season nuisance insect this spring. Bt products are very effective against this pest, or you can simply remove the webs containing the caterpillars and place them in water with a squirt of dishwashing detergent. Either approach will kill the caterpillars, but do not consider burning them out because this process will result in more injury to the tree than the caterpillars could ever cause.

*Gypsy Moth (Lymantria dispar) - Larvae should be hatching now although the egg masses we have been monitoring in central Maine have not shown signs of movement yet. Populations of gypsy moth are expected to be low this season as the rainy weather last summer allowed the fungus Entomphaga maimaiga to decimate the caterpillars. Very few egg masses were found anywhere in Maine when surveys were conducted last fall.

Pear Thrips (Taeniothrips inconsequens) - Pear thrips have begun to move to expanding sugar maple buds in Southern Maine. Populations appear to be low and spotty. Little if any damage is expected this year.

*Yellowheaded Spruce Sawfly (Pikonema alaskensis) - Adults will soon be active around young spruce trees. They are particularly attracted to open grown white spruce under 12 feet tall. The eggs hatch in June and most people do not notice the yellow (orange)-headed, striped, green larvae until substantial amounts of foliage have already been eaten off the tree. If you have spruce that have bare lateral branches especially near the top of the tree, check for larval feeding in June. Three chemicals that will provide control are carbaryl, chlorpyrifos, and spinosad.

DISEASES AND INJURIES

European Larch Canker (caused by Lachnellula willkommii) - European larch canker is a fungal disease that originated in Europe and was first found on native larch (tamarack) in southeastern Maine in 1981. Information gathered from existing cankers indicates this disease has been present in Maine since the 1960's and perhaps much longer. Since larch canker has the potential to cause serious damage to both native larch stands and reforestation projects utilizing non-native larches in Maine and elsewhere, the disease is under state and federal quarantine. In recent years the MFS has contracted to work with Dr. David Houston, a noted forest pathologist, to investigate rates of intensification within and expansion from known infested stands in Maine. While this work is still in progress, it has already become apparent that there is some increase in disease intensity in certain coastal plots in the towns of Addison and Jonesboro.

Salt Damage (caused by movement of deicing salts from road surfaces to susceptible plant species) - Salt damage to roadside white pine is of course very conspicuous at this time. But damage is showing up at locations so distant from roadways that it seems hard to believe salt is involved. Careful analysis of water drainages, snow plowing patterns, and open spaces where wind can blow salt aerosols great distances, however, often show salt to be the primary factor responsible for these spring browning symptoms. So study the situation carefully before concluding that salt damage is not a factor when noting browning in evergreens at this time of year.

Browned pine needles have already begun to drop and most trees will look better as the season progresses. For your clients who experience severe symptoms of salt damage to their pines (or hemlocks) every year, you might consider replacement with less susceptible species, such as spruce.

Sudden Oak Death (caused by Phytophthora ramorum) - We still have no evidence that this disease is presently established in Maine nor any knowledge that it can even survive in this climate. We do, however know that we have some native species which are capable of becoming infected by the sudden oak death pathogen. So it is prudent that we continue to monitor for this disease, and we are planning to conduct forest stand and nursery perimeter surveys again this summer. Therefore some of you will probably be hearing from us in early July when we commence this activity.

Winter Injury - Extremely cold winters are a mixed blessing for those of us in the forest and green industries. On the one hand, harsh winters cause death and/or dieback on tender species and cultivars, and even some of the more hardy sorts, at least until they are well established. On the other hand, cold or "test winters" also are hard on many introduced insects and diseases. This past winter seems to have been neither extremely harsh nor extremely mild with the most tender sorts suffering minor damage, but with most species and cultivars seeming to have performed satisfactorily as of this date. As always, please let me know if your observations are different. We eat crow here if we have to.

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

Compiled by  Clark A. Granger
02/05 Forest Health & Monitoring Division Augusta, Maine