Hemlock woolly adelgid on the move in Nova Scotia

July 9, 2020

By: The Working Forest Staff

LUNENBURG, N.S., The Chronicle Herald — An invasive insect from Asia appears to now have a foothold in southwestern Nova Scotia — and it is on the move.

The hemlock woolly adelgid (HWA), a pint-sized sap-sucking pest, feeds on the storage cells located at the base of hemlock needles. The insect leaves severely damaged or dead hemlock trees in its wake.

According to a report in The Chronicle Herald, Ron Neville, a plant health survey biologist with the Canadian Food Inspection Agency (CFIA), said the organization is working to slow the spread of the insect.

“With this pest, it reproduces very quickly, and in a short period of time, you can have thousands of these on one tree, all feeding at the same time,” said Neville.

“This kind of mass attack of a tree can cause it to severely decline and eventually die.”

And left unmanaged, the insect could do serious damage to the province’s landscape.

“Hemlock is an ecologically-significant tree species. There are many other species that rely on it for habitat — other species of plants and animals and insects and things that only exist on hemlock,” Neville said.

The pest was first identified in the province in the summer of 2017 in five counties: Digby, Yarmouth, Shelburne, Queens, and Annapolis.

This year, the CFIA has confirmed its presence in Lunenburg.

Neville said it appears the insect is restricted to one small area in the northwestern part of Lunenburg County. However, a survey is underway to determine if the HWA has spread to other areas.

“The strategy of the CFIA is to slow the long-distance spread of HWA within Canada,” said Neville.

“When we find it in an area, we will put in movement restrictions on different products.”

According to the CFIA, the hemlock woolly adelgid was first reported in the Eastern United States in 1951. It was thought to have arrived in the region via infested nursery stock from Japan. In Canada, the adelgid is currently found in British Columbia and N.S.

A close up of hemlock woolly adelgid eggs

SLOWING THE SPREAD

The public is already prohibited from transporting any untreated firewood or hemlock products, such as nursery stock, roots and other plant parts, outside of southwestern Nova Scotia.

Neville said HWA spreads relatively slowly on its own, however, with the aid of humans, an infected item can travel long distances in a short period of time.

And that could spell trouble.

“The biology of HWA is kind of unique in the insect world where they don’t need to find mates to reproduce. They’re all clones of each other,” said Neville.

“Technically, you could have a new population arise just from one individual being moved from one area to another. If it were to land on a hemlock tree and start feeding, it could produce eggs and just reproduce that way.”

Neville said an individual HWA could produce up to 5,000 progeny in one year.

“That’s one of the reasons why it can explode in population very quickly is because of this ability to lay eggs without mating, and it also has two generations per year as well.”

Neville said one of the easiest ways people can avoid unknowingly transporting the insect is by using firewood native to the area.

“We encourage people to buy their firewood where they burn it. When you get to the campground or get to where you’re traveling to, get your firewood there,” he said, noting that “moving firewood is a way to spread a whole variety of invasive species long distances and we really discourage that activity.”

Neville said the eastern hemlock makes up “a large component of the Acadian forest of Nova Scotia,” with certain areas having more dense populations than others.

Neville said both Lunenburg and Colchester County have considerable hemlock populations.

The eastern hemlock, a coniferous tree native to eastern North America, is the state tree for Pennsylvania.

A hemlock woolly adelgid infestation would kill trees throughout Victoria Park in Truro. LYNN CURWIN/TRURO NEWS

Stan Kochanoff, a Hants County arborist, said he hasn’t seen any evidence of the hemlock woolly adelgid locally and doesn’t think it would cause as much devastation here as it would elsewhere in the province.

“We don’t have a lot of hemlocks in Hants County but certainly it’s a threat,” said Kochanoff, who has planted hemlock hedges — a cultivar of the tree — in Wolfville in the past.

“It’s certainly one that hasn’t concerned us as much as the emerald ash borer that is on its way,” Kochanoff said, alluding to another invasive Asian insect that destroys trees.

That beetle was discovered in New Brunswick in 2018, and later that year in Bedford, N.S.

Kochanoff said the province has a lot of ash trees, and he has a nursery full. All are at risk if that beetle can’t be contained.

“There’s always insect problems. Unfortunately, we have to let nature take its course now because there’s no spraying,” said Kochanoff.

Over the years, the government has banned or restricted many pesticides, insecticides, and fungicides that may have been used to address infestations.

“Nobody is spraying anymore so it’s hard to control this stuff,” Kochanoff said.

According to the CFIA, the HWA does not pose a threat to human health.

Hemlock woolly adelgid eggs are found in sacs that resemble tiny cotton swabs. They often go unseen because they’re laid in the upper canopies of trees. USDA PHOTO

ERADICATION NOT THE ANSWER

Neville said the CFIA is looking to the U.S. for ways to control the spread of the insect.

“The focus is more on a management strategy than an eradication,” said Neville.

He said there are three methods currently being reviewed: a silviculture strategy where a stand is thinned to make it healthier; applying pesticides to the trees to protect them from attack, and introducing a bio-control predator that feeds on HWA.

There are no known local predators of the HWA.

“In its native range, which is in Asia, it doesn’t really cause much damage at all (to the trees) and the main reason they feel that’s the case is because of the predator relationship with it. The predators keep the population down low enough that it doesn’t cause much damage,” said Neville.

The same is true for B.C., where there’s a predator that feeds on the adelgids.

Neville suggests residents with hemlocks on or near their property inspect them regularly.

“Flip over the branches and look at the underside of the branches. Look for these small, white, cottony balls,” said Neville. “They look just like cotton balls that are stuck to the twig at the base of the needles. If they see that, I’d encourage them to take a picture, and please report it to their local CFIA office.”

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