The little-known, parasitic mistletoe stunting B.C. trees

Every so often, David Ruschclimbsinto his white pickup truckand rumbles up a gravel forest service roadinto theendless lodgepole pine forests surrounding Williams Lake, B.C.

He's on the hunt for mistletoe, and not the festive kind.

Rusch is tracking local dwarf mistletoe because it's a destructive, explosive parasite that races through the woods and sucks the life from trees at a blistering pace. Rusch, a veteran forest pathologist with province's Ministry of Forests, can spot bristly clusters of infection sapping strength from a single, free-standing tree as the truck lurches past.

"You get the eye for it after a bit," he said.

Managed properly, dwarf mistletoe is a normal,even healthypart of B.C.'s forest ecosystem, but improper management and natural disasters can clear the way forinfestations thatstuntfledgling trees and wreckup to 40 per cent of the volume and profitability of aforest.

It's such a troublesome pest because failure to consider the mistletoe will doom young trees before they have a chance to grow and replenish the forest. It plays a role in howcompanies plan to regenerate an areaafter harvesting its lumber.

"Plants are good, but if they're onwrong plants in your garden, then they're weeds," said Rusch,whose work as a forest pathologist centres on researching disease that affects the health of a forest.

Spreads 'like a water cannon'

The dwarf mistletoe in B.C.'s forests isn't the same leafy planthung in doorframesas lead-into aChristmas kiss;that version is European and doesn't exist in Canada. The leafless North American species needs an evergreen host to survive. Trees with the disease areleft swollen and distorted, their growth impaired.

The parasite isdevilishly hard to get rid ofbecause of the way it spreads.

When seeds mature inside dwarf mistletoe berriesin the summer, the fruit explodes. Countless sticky seeds are sent flying in an arcat up to 85 km/h an hour, travellingup to 15 metres away from the host tree. The pelletsrain down and latch on toshorter, defencelessyoung trees in the line of fire, and anew infection begins.

"It's kind of crazy," explained Rusch. "It's like a water cannon."

To prevent the spread of dwarf mistletoe in the province, harvesters have to ensure saplings are kept out of the seeds' range.

Regeneration goals

Forestry has traditionally been B.C.'s most lucrative natural resource. Lumber companies taking trees from B.C.'s forests are obligated, under agreements with the province,to ensure an area is reforested in good health after a harvest, so the forest remains environmentally and economically sound.

Mistletoe threatens that objectivebecause infected saplings fail to grow up properly, making them unfit for market.

So, for decades, harvestershave tried to avoid theproblem by chopping down any dwarf mistletoe host trees as crewsgather their lumber. Companiesalso leave a buffer between infected treesand replanting zones, to keep young treesout of the parasite's reach.

"If you can eliminate that 15-metre radius spread around these overhead trees, then you can go a long way in reducing the impacts of mistletoe over time and slowing down the spread rate," said Rusch, who helped write the province'sdwarf mistletoe management handbookin 2016.

Another forest pathologist, Harry Kope, said paper-like barriers wrapped around mistletoe are also used tointercept sticky seeds flying out of the berries.

"It's like a cone of shame for dogs," Kopeexplained.

Despite best efforts, mistletoe persists.Ungovernable wildfires and outbreaks of pine beetle devouring swaths ofB.C.'s forests in recent years leave host trees behind, towering over young trees that will eventually sprout vulnerable below.

Parts of B.C.'s Cariboo-Chilcotin region, where Rusch works, are dealingwithan excess of mistletoe.The issue is so widespread, B.C. Timber Salesis hiring contractors to trek into the woods in the new year and chop down diseased trees to give saplings a fair chance.

The pest exists in the other Canadian provinces, but Natural Resources Canada says B.C. is the most afflicted. The pest isn't found in any of the territories.

Pathologists like Rusch and Kope monitor the parasiteand track outbreak of disease. Both agree dwarf mistletoe has a rightfulplace in the ecosystem,as food forbirds, insects and butterflies, but moderation is crucial.

"We're like pediatricians. We're making sure that the environment is correct and that these young plants get a chanceto get up and become good participating trees in the forest," said Kope.

"Mistletoe hasalways been a problem but we cantry to avoid setting up bigproblems."