February 15, 2013
By Jen Llewellyn,
OMAFRA nursery crops specialist

The Ministry of Natural Resources (MNR) hosts the Annual Forest Health Review in Orillia each fall. Foresters and researchers come together to hear about forest health issues and network. It is always time well spent, with a lot of the information that relates to the arboriculture industry. A team of forest health technicians collects data and observations throughout the growing season, which helps everyone better understand, and hopefully manage, these issues.

Defoliation from forest tent caterpillar (Malacosoma disstrium) was detected in scattered pockets over the last few years. There was 8,000 hectares of light defoliation in the Owen Sound area in 2012, but 10,000 hectares of moderate to heavy defoliation took place in other areas. Caterpillar egg mass counts are quite high in some of these areas, suggesting that populations are likely building and damage will be more severe in 2013. This is a common pest of oak, and recently an arborist found a heavy infestation on ornamental crabapple.

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

Larch casebearer (Coleophora laricella), another pest introduced 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 were detected on over 3,000 hectares of forests in northwest Ontario. The eastern larch beetle is associated with larch tree mortality. In Minnesota, they detected this pest on a whopping 46,000 hectares of larch forest trees. This was the first I’ve heard of this pest. I hope I don’t ever meet one.  

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 lifecycle and damage is down to 2,000 hectares. Pine false webworm (Acantholyda erythrocephala) has caused some small pockets of defoliation on white pine and is on the incline in Ontario. In 2012, more than 6,000 hectares of defoliation were mapped out in the Lake Nipissing area. In order to help survey, a sex pheromone has been developed and Sylvar Technologies out of New Brunswick supplied pheromone to MNR 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.

There’s no question that 2012 was a wickedly hot and dry growing season. Spring started in mid-March with lots of early spring growth that got hit by hard frosts in May. Many conifers that had foliage killed by spring frost, actually leafed out again in late July.

Several areas went from six to eight weeks without any precipitation this summer. MNR staff saw several signs of stress on deciduous and evergreen trees from 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. MNR also noticed significant populations of ips beetles 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 the Canadian Shield).  

Cedar leafminer (various species of moths) is still an issue in some areas of southern and south-eastern Ontario. The MNR fielded a lot of media calls about this pest, and so did I. The ministry 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 pest. Damage was much more severe on sandy, drier soils. I have never seen cedar leafminer injury so severe.   

MNR 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 hectares 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.  
Jennifer Llewellyn may be contacted at the Bovey Building, University of Guelph, at 519-824-4120, ext. 52671, or jennifer.llewellyn@ontario.ca.