December 15, 2008
By Jen Llewellyn,
OMAFRA Nursery Crops Specialist

Robert Kennaley The annual forest health review took place in Orillia this year. Members of the forestry, arboriculture and nursery industry came out to hear about this year’s surveillance activities and research.

Traditionally, forest health monitoring has been conducted by forest health specialists from Ontario’s Ministry of Natural Resources (MNR) and the Canadian Forest Service (CFS). Tony Hopkins of the CFS announced that in the future, MNR will take complete control of forest health monitoring. In return, the CFS plans to enhance its efforts in diagnostics, systematics and research to support forest health issues.

Gypsy moth populations were on a slight incline this year at 31,000 HA (up from 10,000 HA in 2006). Aerial applications of B.t. (Bacillus thuringiensis, a biological insecticide) have been helpful in reducing populations of these leaf-chewing caterpillars. Because of all the rain during late larval development in June, background populations of pathogenic fungi and viruses were also able to significantly reduce larval populations.

You probably noticed the plethora of stretched caterpillar carcasses hanging lifelessly from trunks and branches with their heads down. That’s the work of the entomopathogenic fungus, Entomophaga maimaiga. Just like other pathogenic fungi we know, this fungus thrives in wet conditions. We’ll also see them hanging from their middle in an upside down ‘V’ position, which is usually characteristic for those infected with NPV (a type of viral pathogen). The virus (Gypchek) is not registered for use in Canada, but you’ll be encouraged to know that there is a very progressive company out of New Brunswick, Sylvar Technologies, that has been conducting efficacy studies at various sites in Canada with an emphasis on spray deposition technology. By inoculating with Gypchek, larval populations crashed much sooner, thus reducing defoliation significantly from untreated plots.

Taylor Scarr of the MNR gave an update on the successful jackpine budworm management program. Very similar-looking to the spruce budworm, this caterpillar feeds on the pollen and the current season’s growth of pine, especially at the top of the crown. Feeding damage turns foliage red and sometimes, jackpine budworm damage can kill a tree in just one year. Current hot spots include Sudbury and North Bay, and a little further north.

Traditionally, the industry has dealt with the damage by performing salvage cuts in the infested areas. That way, the wood can be harvested before the value is compromised. In the last decade, the area of infestation has become so large that regional sawmills are not able to handle the number of logs from these salvage operations. In 2006, industry and government decided to combine salvage cuts with an insecticidal spray program using the bio-control agent Bacillus thuringiensis (B.t., Dipel). An aerial spray program using state-of-the-art GPS technology was able to achieve uniform spray deposit at incredibly low rates (1.5 L B.t. per hectare). Defoliation was reduced down to 37 per cent in treated areas compared to 70 per cent in untreated areas. The spray program was repeated quite successfully in the last couple of years. The team reduced jackpine budworm infested areas to 166,000 HA in 2008, which is down from 740,000 HA in 2006.

Sawyers attacking healthy pines

Blow-down damage is something we see every year. Once they dry, toppled trees can pose a significant fire hazard. Where stands of white pine have been subject to blow-down, forest health technicians are seeing native white spotted sawyers, a long horned beetle, often confused with the invasive Asian long horned beetle. The white spotted sawyer beetles are reproducing on blow-down and slash piles of white pine. The populations have grown so high in some areas, that the white spotted sawyers have been observed attacking healthy pines. It’s something which I’m starting to get more calls about.

Except for a pocket near Sudbury, forest tent caterpillars are still at a relatively low level at 42,000 HA. Pine false webworm, cedar leafminer and larch casebearer outbreaks are also few and far between.

Surveys for sirex wood wasp (Sirex noctilio, European wood wasp, EWW) were conducted again in 2008 by the MNR. The purpose was to determine the northern limit for this invasive alien species. In 2006, multiple trap sites across southern Ontario uncovered positive detections of sirex wood wasps. In 2007, survey efforts were largely concentrated in the countries outside of the 2006 positive detections. According to the MNR, no positive sites were detected north of the 2007 detections. This wood wasp was first found in New York state in 2004 and consequently detected in eastern Ontario in 2005. Sirex wood wasp has since been detected in several counties of New York and has also been found in Pennsylvania, Michigan and Vermont. Currently, the Canadian Food Inspection Agency is working on a regulatory document to limit the spread of sirex host material (Pinus sp.). This directive is due to soon be released for comment.

Emerald ash borer (EAB) is a popular topic of discussion. This invasive alien species has been detected at several new locations across Ontario, Quebec and several parts of the U.S. this year. CFIA staff members are currently engaged in delimitation surveys in order to determine the extent of these new infested sites. As you know, detecting EAB infestations in ash trees has been the most significant hurdle for surveys. Trees quite often don’t show symptoms until the infestation is quite advanced.

Dr. Krysta Ryall from the Canadian Forest Service gave an excellent report regarding her research team’s efforts to improve sampling techniques. The team focused its efforts on sampling live trees that were found next to those that were heavily infested. They felled the trees, cut them up and labelled them to help track samples in relation to their position on the tree. For instance, they tracked N-S-E-W orientation, as well as upper crown, lower crown and general branch diameter groupings. They took 59 trees back to the lab and dissected 938 subsamples — painstakingly shaving back layers of bark and cambium in search of the signs of EAB (can you imagine?). Early EAB larvae are so tiny and flat, they are easy to miss. So to check the level of error, they held all the dissected sub-samples in sealed rearing cages and monitored for EAB adult emergence, based on established rearing techniques. And yes, they proved that current sampling techniques produce false negatives: only about 50 per cent of the trees had obvious external signs, but it turned out that a whopping 89 per cent were actually infested! It was also discovered that 40 per cent of the trees had numerous galleries in the branches of the crown with no galleries in the boll (better get out your step ladder and binoculars this winter). The group determined that most of the infested branches were in the five- to six cm-diameter range, although they found EAB in branches as small as 1.75 cm in diameter. The EAB tunnels often tended to be found under five mm of bark.

Dr. Barry Lyons, also of CFS, gave a whirlwind overview of some of the EAB bio-control research going on in North America. CFS and U.S. scientists are screening host tree volatiles to determine if EAB adults respond to certain host chemicals moreso than others. They hope to use this information to develop more EAB-specific attractants to facilitate trapping in the fiel. As you can imagine, bark peeling is extremely cumbersome. They did isolate a few volatiles that attract the EAB adults. They also found that the males seem more responsive to these compounds than females. A grad student at the University of Guelph has been working with a parasitic wasp, Cerceris fumipennis. The adult wasp will actually hunt for EAB adults, capture them and take them back to their ground nest to feed their developing maggots. Researchers constructed a mobile colony of Cerceris, complete with ground nests on a trailer. They were able to tow the colony around the province, and monitor the nests for EAB adults. It turns out that Cerceris could actually be used as a bio-surveillance tool. The effectiveness of Cerceris compared to other monitoring techniques (e.g. purple prism traps) is currently being investigated.

An alternative to green ash?

In the last issue, I wrote about some new research regarding the “tolerance” of blue ash (Fraxinus quadrangulata) to emerald ash borer (Agrilus planipennis, EAB). A University of Guelph study conducted in Point Pelee National Park (Essex County) investigated potential infestation of EAB in blue ash and green ash (F. pennsylvanica) standing side-by-side. The research team discovered that all green ash trees at this site exhibited symptoms of EAB infestation and reduced health. In contrast, they found no evidence that EAB had infested the blue ash at this site; the blue ash trees were all in excellent health. I thought: this is great news! Since then I’ve had some discussion with forestry specialists and found out that blue ash trees have been found infested in the city of Windsor. How can this be?

Although it can somehow regenerate itself through seed in the wild, nursery growers say that blue ash is probably one of the most challenging species of trees to propagate from seed or cuttings. Because of this, nursery growers are often forced to propagate the tree by grafting it onto other ash rootstock. While the trees growing in natural forests are pure blue ash from seed, it could be that the blue ash trees planted in our urban areas are a combination of blue ash and other susceptible ash species. Perhaps the ash rootstock is imparting some attractiveness to the emerald ash borer. Blue ash may be the answer, but we first need to work out its propagation in order to retain the true species and its tolerance to this destructive beetle.
Jen Llewellyn can be reached at (519) 824-4120, ext. 52671 or by e-mail at
See her Nursery-Landscape Report at

Caption: Gypsy moth larva infected with virus