DEPARTMENT OF CONSERVATIONMaine Forest Service
Forest Health & Monitoring Division
DEPARTMENT OF CONSERVATION
Maine Forest Service
Forest Health & Monitoring Division
Forest & Shade
Tree
Insect & Disease Conditions for
Maine
Issue: June 8, 2005
Back Issues: May 12, 2005
April 22, 2005
In wet springs such as this we often get many inquiries asking whether all this rain is good or bad for the trees. The answer seems to be "It all depends!"
Christmas tree growers always note the lush new growth that is produced on their trees following rainy springs. Plenty of water, together with the dissolved nitrogen this precipitation contains ("poor man's fertilizer"), combine to push vigorous new growth. The same is true for other tree species.
But there are also down sides to all this water. Most significant is the fact that abundant rainfall usually provides for optimal infection periods for plant diseases, especially foliage diseases. The current expression of maple anthracnose in Southern and Central Maine (see "Diseases and Injuries" section of this report) is a prime example. And maple anthracnose may be just the beginning of our tree disease woes this season. Certainly the stage is now set for outbreaks of ash, oak, birch and catalpa anthracnoses. We may see high levels of horse-chestnut leaf blotch, ash leaf and twig rust, apple scab and fir-fern rust this season as well. Stay tuned.
Among other problems associated with abundant precipitation are "wet feet" among trees growing in poorly drained areas. Tree roots require ample oxygen for good root development, and the ability to assimilate certain soil nutrients. So expect poor growth, off color foliage, and perhaps the development of root rots among trees growing on more poorly drained sites this spring.
Nurserymen will want to be especially careful with their nursery stock watering regimens this spring. We repeatedly caution garden center managers not to apply overhead irrigation water in the evening because of the potential for creating infection periods for nursery stock pathogens. Soaker hoses are fine, as is early morning watering. But all the rain this spring has already built inoculum levels in many nursery holding areas, so extra caution with overhead sprinkler irrigation is advised.
I'd like to take this opportunity to thank those of you who have contributed information to our reports so far this year. First and foremost I'd like to recognize our eminent entomologist emeritus Richard Dearborn who, despite his retired status, continues to contribute substantially to this publication. Thanks also go to Marty Folsom, Didier Bonner-Ganter, Steve Murch, Hartley Marsh, Brianne O'Leary, Ted Armstrong, Bruce Watt, Don Ouellette, Charlene Donahue and a host of others for their support and contributions.
Insects
*Balsam Gall Midge (Paradiplosis tumifex) - Populations of gall midge are expected to remain low in 2005. Check Christmas tree plantings now for signs of galls. Treatment with Diazinon or chlorpyrifos (Lorsban) after the new growth flares should do the trick.
*Birch Leafminers (Messa nana and Fenusa pusilla) - The black fly sized adults are now evident and laying eggs on the leaves of white and gray birch respectively. Developing mines are now becoming evident in birch leaves in central and southern Maine and will be by mid June elsewhere. Soil systemics for these miners should already have been applied. Foliar treatments to preserve aesthetic quality of birch should be made as soon as the tiny mines appear. Don't confuse developing blotch mines of the leafminers with translucent spot mines of the casebearer. Acephate and carbaryl are registered for this purpose.
Black Locust Problems - Black locust flushes new foliage late in the season, the last of our species to do so. The small ¼ inch long flat, red and gray black striped locust leaf miner (Odontota dorsalis) adult beetles are now wandering over and feeding on emerging foliage. As soon as the foliage unfolds the beetles will be laying eggs which will hatch into leafmining larvae. By July browned, mined foliage is expected to be evident on trees throughout the range of black locust in Maine. Most trees will survive, but some excessively stressed trees may succumb to secondary attack by the locust borer (Megacyllene robiniae).
*Browntail Moth (Euproctis chrysorrhoea) - Most browntail moth caterpillars are now in the fourth or are about to enter the fifth instar and are at the stage where the danger to people of developing dermatitis and respiratory problems from contact with toxic hairs has increased significantly. In infested areas, be especially careful on windy days or when mowing the lawn. It might be advisable to wear a surgical nose/mouth mask in such cases. The "browntail itch" will become more of a problem over the next two to three weeks. Once pupation is complete (early to mid July), the hairs will begin to settle to the ground and the incidence of the rash should diminish. Bathing exposed skin in cold water immediately after exposure to the browntail will help limit the rash, but if a severe rash develops it is best to consult your family physician for medical assistance. Inhaling these toxic hairs may also cause respiratory distress in some individuals.
Lacebugs (Corythucha spp.) - Lacebugs are now very active and adults are blowing around and landing on cars, laundry, etc. Of these the walnut or butternut lacebug (C. juglandis), the birch lacebug (C. pallipes) and the elm lacebug (C. ulmi) are the most common. Where populations are high, the foliage of infested host trees tend to become off color and messy by mid summer.
*Conifer Sawflies (Various) - A variety of sawflies should now be laying eggs on their respective conifer hosts across the state. Early detection and control should prevent serious and often rapid defoliation later. Larvae of most species feed gregariously at first so it is fairly easy to spot them. Where a problem is expected, treat with acephate or carbaryl, while larvae are still small. Of those species listed on the attached chart, the ones which are most likely to cause a problem this season are:
Introduced Pine Sawfly - A local problem on white pine. No widespread damage expected.
Jack Pine Sawfly - This species can be a problem along the coast in eastern Maine.
Larch Sawfly - A local problem, larvae show up by mid summer.
Yellowheaded Spruce Sawfly - A continuing problem in and on trees in open grown or ornamental situations. Eggs should be laid in southern and central Maine by mid June and should hatch by the end of the month.
*Gypsy Moth (Lymantria dispar) - The eggs of this species hatched later than expected. Tiny larvae began emerging and blowing around the wind (ballooning) in most areas of southern Maine during the third week of May. Trees in infested areas of southwestern Maine should be monitored now for current populations. Acephate, Bt and carbaryl are among the pesticides registered for use in controlling gypsy moth.
*Mountain Ash Sawfly (Pristiphora geniculata) - Adults are now out in southern Maine and should be laying eggs along the margin of leaflets causing bladder-like swellings. Larvae will become evident in a week to ten days and defoliation occurs rapidly. In small trees control can be achieved by prompt removal and destruction of infested leaves. Otherwise you may wish to treat infested trees with carbaryl, spinosad, or acephate when larvae are present.
*White Pine Weevil (Pissodes strobi)- Infested terminal shoots on pine and spruce should begin wilting by the end of the month. Early detection and corrective pruning can minimize the long term impact of this pest.
Diseases and Injuries
Cones in Christmas Trees - The production of cones in fir Christmas trees is highly undesirable, because cones displace desirable foliage growth, often become infested with insects leaving behind a pitchy mess in trees, drain vigor from trees which often results in yellowish foliage in tree tops, and disintegrate just before harvest to leave behind an unattractive cone axis. Fortunately for most growers this is not a heavy cone year. Cones seem not to be abundant in balsam fir Christmas tree plantations. Fraser fir growers always seem to have cone challenges, but probably will experience a somewhat reduced problem this year.
"Cone years" often follow dry or droughty growing seasons, so the past couple of relatively moist summers seem to provided Christmas tree growers a reprieve.
Dutch Elm Disease (caused by Ophiostoma ulmi and Ophiostoma novo-ulmi) - The next few weeks will provide an opportunity for astute arborists to attempt to prune incipient Dutch elm disease infections from high value landscape trees. With the onset of hot, dry weather over the next few weeks, Dutch elm disease symptoms will become evident in infected trees as tree branches flag and wilt, the result infection by the Dutch elm disease fungus.
Incipient infections, apparent as limited areas of wilting at branch tips, may often be successfully pruned from trees if caught sufficiently early. Immediately prune out these flagging branches, and peel back the bark from excised branches to look for the stained or streaked sapwood which is a telltale sign of infection. Prune back the branches until only clean sapwood is located for a distance of 5-10 feet, taking care to sterilize pruning tools between cuts. Make the final cut at a branch junction to avoid leaving a branch stub. This procedure will not work on trees where the disease is well established throughout the tree, but is worth a try in early stages of infection.
Maple Anthracnose (caused by the Discula state of Apiognomonia errabunda ) - Maple anthracnose is presently causing heavy defoliation of maple trees, especially Norway maple, in southern and central Maine. This problem became conspicuous last Friday as leaves began dropping from trees, and our telephones have been ringing off the hook ever since. Infected leaves have a blotchy blackened or brown scorched appearance, are often curled, and often display vein necrosis (darkened veins). Typically, lower portions of tree crowns exhibit greater defoliation than upper crowns, but all crown portions may be affected. The first calls came in to us from the Falmouth, Cumberland and Gorham areas southward to Wells and Berwick, but by Tuesday of this week calls from Lewiston, Rockland and points north to Bangor indicate that more northerly areas are affected as well.
Our damp spring has provided excellent conditions for infection of emerging growth. And the past two spring seasons were quite moist as well, which apparently has provided optimum conditions for inoculum buildup. So everything has seemingly fallen into place to create this year's epiphytotic (plant disease epidemic).
It is too late now for fungicidal sprays to be effective, but trees will recover as the season progresses. This disease will not kill trees. Trees are expected to refoliate within a month or so. Crowns of affected trees may appear a bit sparse later this summer, but enough new leaves will be regenerated to provide for the trees' photosynthetic needs going forward.
Compiled by Clark A. Granger
03/05 Forest Health & Monitoring Division Augusta, Maine