Destructive spruce budworm being monitored
The last outbreak, decades ago, saw 50 million cubic metres of wood lost
There hasn’t been a major outbreak of spruce budworm in the province for more than 30 years, but that doesn’t mean the province isn’t keeping an eye on them.
“Budworm is one of our major forest pests,” said Dan Lavigne, supervisor of insect and disease control with the Department of Natural Resources in Corner Brook.
Because of that, the department conducts annual surveys to monitor the spruce budworm population in the province. Lavigne said this is in addition to monitoring for other forest pests like the hemlock looper, balsam fir sawfly and spruce beetle.
Lavigne said the last outbreak of budworm in the province started in the early 1970s and didn’t collapse until the mid to late 80s. At the time it was estimated that 90 per cent of spruce and fir forests in the province were infested by the budworm.
“During the outbreak there’s an estimate that we lost 50 million cubic metres of wood (spruce and fir) to the spruce budworm,” said Lavigne.
Trees weaken and die
The budworm feeds on both new and old foliage and most of the damage to trees occurs when the budworm are in the larval or caterpillar stage. After three to five years the trees start to weaken and die off.
The main method used to track the budworm population is a pheromone trapping survey where plastic traps containing a synthetic lure are placed in trees. The lure is similar to the scent emitted by female budworm moths when they are ready to mate.
“The number of moths that we catch from year to year gives us some indication as to what’s happening with our populations.”
Lavigne said the department has a network of 100 locations across the island in spruce-fir forests where pheromone trapping occurs annually. Within the last couple of years the department has been recording an increase in the number of male budworm moths caught in those traps. He said the average has gone from 19 per trap in 2011 to 34 in 2012.
Two areas on the west coast in the area of Gros Morne National Park actually saw trap catches of 500 and 200 moths. Lavigne said those areas were then subject to weekly monitoring.
The results showed an increase in catches and then a sudden drop and this suggested some dispersal event may have occurred to bring the moths, which can travel hundreds of kilometres, to the area. He noted, however, that the local population is not a level that would predict any kind of defoliation.
Lavigne said in areas with high trap catches the department will do followup branch sampling to look for eggs and larvae.
This surveying has yet to find any egg masses on the island. He said the department will also do aerial surveying to look for damage to forests from the air.
Lavigne said the department uses the information it gathers in a reactive way.
“The branch sampling that we do will tell us if we start getting above a certain threshold of egg masses on our branch samples then we know that we’re gonna expect moderate to severe defoliation in those areas.”
He said from that they will look at the impact that will have on forests in the area, and noted a normal outbreak lasts about 10 years and a severe one 15 years. If the impact is above a certain threshold, he said government may decide it is necessary to take some protective measure which would involve a control program using an insecticide like BT.
Conditions in Labrador are a little different than on the island. Lavigne said an outbreak of spruce budworm was first detected in the Goose Bay area in 2006-07. Last year, the insect caused 30,000 hectares of moderate to severe defoliation in that area.