Short Stories From OMNR’s Forest Health Review

Nov-Dec 2012


Each October, the Ontario Ministry of Natural Resources (OMNR) hosts the Annual Forest Health Review in Orillia. Foresters and forest researchers come together to hear about forest health issues and to network. It is always time well spent and a lot of the information relates to the arboriculture industry. A team of Forest Health Technicians collect data and observations throughout the growing season and this information is reported to help everyone better understand, and hopefully manage, these issues. Here’s a synopsis of some of the key findings.

Forest Tent Caterpillar
Defoliation from forest tent caterpillar (FTC, Malacosoma disstrium) was detected in scattered pockets over the last few years. There were 8,000 hectares (ha) of light defoliation in the Owen Sound area in 2012 and another 10,000 ha of moderate to heavy defoliations in other areas. Egg mass counts for FTC are quite high in some of these areas suggesting that populations are likely building and damage will be more severe in 2013. FTC is a common pest of oak and recently an arborist found a heavy infestation on ornamental crab-apple.

Gypsy Moth
Gypsy moth (Lymantria dispar) populations are still low and much of the population collapse can be attributed to their fungal disease, Entomophaga maimaiga. In 2012, there were some pockets of severe defoliation in Sudbury and Manitoulin Island (~8,000 ha) but the 50-year trend line indicates that we are still on the bottom of the outbreak scale. When conditions are dry (such as this past spring), insect pathogens are much less successful and insect survival can be much greater. We’ll see how the spring of 2013 treats these gypsy moth populations. 

Larch Casebearer & Eastern Larch Beetle
Larch casebearer (Coleophora laricella), another introduced pest in Canada, was found in several pockets last year and doubled its geographical range in 2012 to encompass over 5,000 hectares. Eastern larch beetle was often found associated with these infested trees as well and was detected on over 3,000 hectares of forests in NW Ontario. The eastern larch beetle has been associated with larch tree mortality and in Minnesota, they have detected this pest on a whopping 46,000 ha of larch forest trees. This was the first I’ve heard of this pest. I hope I don’t ever meet one. 

Other More Northern Pests
Spruce budworm (Choristoneura fumiferana) is still a significant pest in the Sudbury and Espanola areas, causing an estimated 5,000 hectares in tree mortality this past year. Forest health technicians say it is moving into Manitoulin Island. Large aspen tortrix is still causing damage in the Sudbury and Manitoulin Island areas but it is in the collapse phase of its life cycle and damage is down to 2,000 ha. Pine false webworm (Acantholyda erythrocephala) has caused some small pockets of defoliation on white pine and is on the increase in Ontario. In 2012, more than 6,000 ha of defoliation were mapped out in the Lake Nippising area. In order to help survey, a sex pheromone has been developed and Sylvar Technologies out of New Brunswick supplied pheromone to OMNR staff to test as a survey technique for male adults. Pine false webworm is also a periodic pest in conifer nursery production and this pheromone could be useful for monitoring this pest in tree nurseries. 

Cedar Leafminer
Cedar leafminer (various species of moths) is still an issue in some areas of southern and southeastern Ontario. The OMNR fielded a lot of media calls about this pest and so did I. OMNR mapped over 31,000 hectares of cedar leafminer damage in the province. I saw several eastern white cedar trees in the landscape and in field production nurseries totally decimated by this leaf-mining pest. Damage was much more severe on sandy, drier soils and I have never seen cedar leafminer injury so severe.  

Emerald Ash Borer
OMNR forest health technicians mapped over 67,000 hectares of ash trees exhibiting either decline or mortality due to Emerald ash borer (Agrilus planipennis). Over 1,000 ha were mapped in the Ottawa area, where it is killing ash trees. We can probably expect this area to increase significantly as EAB moves into more and more forest stands with a significant ash component.  

Weather Implications
There’s no question 2012 was a wickedly hot and dry growing season. Spring started in mid-March and we had lots of early spring growth that got hit by those hard frosts in May. Conifers whose foliage was killed by spring frost actually leafed out again in late July. Several areas went for 6-8 weeks without any precipitation this summer and many of us were getting sick of the sun. 

OMNR staff saw several signs of stress on deciduous and evergreen trees from their aerial survey activities in mid-summer. Needle mortality was especially high on red pine and we also saw foliar desiccation on red pine seedlings in nursery production. OMNR also noticed significant populations of Ips beetles associated with the symptomatic red pine, often with blue stain fungi associated with the wood. About 174,000 hectares of “desert” injury was detected aerially across southern Ontario. In some cases, it was severe enough to cause tree mortality (especially on shallow soils around Canadian Shield). 


Long Horned Beetles
Krysta Ryall from the Canadian Forest Service is working with other international entomology researchers to test the efficacy of a new chemistry of pheromone lures for cerambycid (long horned) beetles. Concern over additional introductions of long horned beetles through wood packaging has prompted investigation of some male sex pheromones that attract various species of female long horned beetles. My natural tendency is to insert a funny joke at this point but I couldn’t think of one that was politically correct so I’ll just giggle to myself and continue on. 

Dr. Ryall found the pheromones to attract 10 out of the 19 species found in Ontario. These pheromones have great potential to be used as a surveillance tool and perhaps a mating disruption tool for Integrated Pest Management. Incidentally, the Canadian Food Inspection Agency has been surveying the Asian long horned beetle quarantine zone in North Toronto and has found no signs of active populations in the last four years. The CFIA is hoping to declare eradication in this zone in 2013.  

Dog Strangling Vine
A research team from the University of Toronto is evaluating some plant feeding insects for the biocontrol of dog strangling vine (Cynanchum rossicum), an introduction from the Ukraine. The entomology team is evaluating leaf feeding moths, beetles and entomoparasitic flies from the Ukraine to see if any of them might be efficacious in managing dog strangling vine in controlled lab experiments. This approach is similar to the very successful biocontrol program for purple loosestrife where University of Guelph researchers evaluated Galerucella beetles and introduced them at over 400 locations across Ontario in partnership with several other organizations. 

Beech Bark Disease & Scale
John McLaughlin of the OMNR Ontario Forest Research Institute has been observing beech bark disease (Neonectria faginata) and its vector, the beech scale (Cryptococcus fagisuga) on American beech in Ontario for several years now. Field staff and arborists have noticed beech blight and scale to be spreading more quickly and more severely on beech in central Ontario (the northern edge of the outbreak) and scientists can’t explain this phenomenon.

Beech scale is believed to be a vector for this disease and its white, woolly egg masses are easily detected on beech bark in late summer to fall. The beech bark canker disease is noticed 1-3 years following scale infestation and often results in tree mortality. Large trees seem to fall victim to this disease first. Some trees are able to fight the canker disease (small, “eye”-shaped cankers on bark) while others decline faster (larger, general cankers on bark). Researchers are advising woodlot managers to harvest large DBH trees at the early signs of infestation. They advise thinning out high densities of American beech and retain trees that show no signs of scale/canker infestations (show potential for disease resistance), regardless of age or structural health.

Researchers at the Canadian Forest Service are finding that when woodlots have >30% ash species, it is enough to see significant ecological changes after the emerald ash borer causes ash mortality in that woodlot.

The effects include disturbances in forest structure, plant diversity, songbird populations, soil and nutrient recycling, shoreline habitat and aquatic ecosystems. The increased light on the forest floor opens up new habitat for a lot of competitive plants, including invasive species such as European buckthorn. To try and avoid this, many foresters are considering managing these future forest gaps through strategic cutting, underplanting and early removal of some ash trees.    

That critical threshold of >30% ash species is something that Martin Streit, OMNR Kemptville District Forester, is watching closely. Streit reports that of the 215,000 hectares of forest in his district, a whopping 70,000 hectares have an ash component of over 30%. Most of the areas infested by emerald ash borer in Ontario are private lands and so Streit works closely with private landowners to help them manage their woodlots to lessen the potential impact of EAB once it arrives. Streit is a private woodlot owner himself and has been trialing some of these practices in his own backyard.  

It has already been demonstrated that EAB cannot be eliminated through widespread removal of ash trees. In fact, indiscriminate removal of all ash species ahead of the borer would be devastating to woodlots, especially those with >30% ash content. In addition to the negative side effects listed above, removing that many ash trees in a short period of time has been known to cause flooding and the proliferation of ash seedlings. In their article “Managing Ash in Farm Woodlots,” Williams and Schwan state that it is important to retain some ash in the forest as EAB moves through to provide for diversity, wildlife habitat and a future seed source. However, the trees need to be managed to become more resilient to EAB and to retain as much of their ash resource value as possible.

Williams and Schwan advise the woodlot owner to evaluate the risk: get an estimate of the number of years before the ash in the stand will be threatened or killed by EAB infestation. For example, if a scattered EAB population has been found 50 km away, it may be 10 years before that woodlot is affected. If a dense population EAB front was 50 km away, it may be only five years. This will give the woodlot manager a more accurate time frame to put an action plan in place. 

Last words of warning: diversify the forest and kiss your ash goodbye. Thinning out the ash component of a forest should be done so as to maintain as much canopy closure as possible. Streit says that it is more important to keep crown closure than it is to harvest valuable ash trees ahead of an EAB infestation. Low value ash trees and ash saplings should be removed so that only healthy, mature ash trees are maintained. Underplanting and seeding with other desirable species will speed up regeneration, recovery and help increase species diversity. Unfortunately, deer will eat hemlock and white pine seedlings so make sure you have a good mix of species. Streit says that when thinning, if you have to choose between removing a decent ash tree versus a less valuable specimen of another species (e.g. elm, popular), it might be a good idea to take the ash. There are some excellent resources available at   


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