The virus, the blueberry, and the scientist

It is coming for the Fraser Valley’s blueberries. 

It hitches a ride on the needle-like mouth of an aphid and then it’s gone. Within the structure of the blueberry bush, it goes into hiding, replicating itself and passing copies onto other plants through the willing mouths of other aphids.

It is a scourge that has grown significantly since 2000, when the disease was first found in Abbotsford. Once infected, the blueberry bushes succumb to an inevitable death. When spring comes, leaves and flowers shrivel. Season after season they weaken, with some plants lingering for years before withering entirely. 

Blueberry scorch knows no mercy.

What is Blueberry Scorch?

Plants, like people, are vulnerable to an array of diseases—some deadlier than others. For blueberries, the most dangerous comes from a miniscule rod-shaped virus called blueberry scorch virus or BIScV.

This virus was first identified in Washington in 1980, when a number of blueberry plants were found with necrotic leaves and flowers. (A similar blighting disease had been noticed 10 years earlier in New Jersey, but it wasn’t until the late 1980s that scientists linked the New Jersey discovery to the virus ravaging berries in Washington.) By 1987, researchers had begun to monitor fields across BC and the western United States, but it wasn’t until 2000 that the first plants in BC were diagnosed with blueberry scorch. By the end of 2001, the disease had been found in 60 fields in the province. Three years later, it had spread to 140 fields.

The virus is an efficient killer. It is carried between blueberry bushes  by aphids. When the aphid inserts its needle-like mouth into a leaf, the virus is transferred to the plant, where it begins to replicate. 

The following spring, the leaves and flowers of the blueberry bush begin to decay. By that time, the plant will have been infectious for a year or more, and new aphids will have landed on the bush, picked up the virus, and flown on to dozens of other plants. Each year, more and more of the infected bush withers. Eventually, the virus has colonized the entire plant, from the leaves to the roots, and it dies.

Scorch symptoms are almost identical to blueberry shock, a related virus that is spread through pollen. Visually, it is nearly impossible to tell the two apart—the only way to tell is either through a lab test or through time. While blueberry plants will eventually recover from blueberry shock, scorch is lethal.

This is a major challenge for blueberry growers—particularly in the Fraser Valley, which produces nearly 42% of Canada’s cultivated blueberries. (The Fraser Valley is also responsible for roughly 2% of the world’s total blueberry output.) 

BC’s Blueberry Council has declared that scorch infections are “reaching a critical point” and that if left unmanaged, the virus will impact the entire blueberry industry.

Currently, the only way to manage scorch is to dig up and burn infected plants. If left unchecked, the disease will spread to all the plants in a field—and soon bushes in neighbouring fields. Farmers can also use pesticides to kill aphids, but that only happens at certain times of year to protect pollinators.

“There is no cure for this virus,” Michelle Franklin, an entomologist at the federal Agassiz Research and Development Centre, said. “It is quite a devastating virus to the blueberry growers.”

That is why Franklin, fellow federal scientist Bryan Brunet, and others on their team have been entrusted to analyze blueberry scorch—and more specifically, the aphids that transmit it.

The research project

Michelle Franklin is not a stranger to the Fraser Valley’s berry fields—and the invaders that threaten them. She joined the Agassiz Research Centre four years ago, and since then has spent summers trapping strawberry weevils on sticky yellow sheets and finding natural enemies to an Asian fruit fly. She is an advocate for biovigilance, an agricultural response that focuses on proactive prevention and natural predators to manage pests.

She will need every ounce of that vigilance to figure out what is going on with blueberry scorch.

Despite the impact on the blueberry industry, relatively little is known about BIScV. Some significant work was done in the 2000s on aphids and the scorch virus, but much has changed in the years since.

“Our blueberry acreage has increased, climate has changed. We also have some new pests and blueberries,” Franklin said. “We thought this was a really good time to … see how it has changed from when scorch virus was really first detected in our blueberry fields.”

Over the next four years, Franklin will study eight blueberry fields between Agassiz and Delta. Fieldwork will take place during the spring and summer, when aphids are active and blueberries are blooming. The winters will be spent analyzing genetics and morphology in the lab, in collaboration with Canada’s national curator of aphids Bryan Brunet. 

The project is co-funded by the Agriculture and Agri-Food Canada and the Lower Mainland Horticulture Improvement Association, and research has already gotten underway, with Franklin and her team starting some preliminary fieldwork last summer. Now, she has returned to the fields to investigate how aphids transmit scorch between plants. 

The aphids

There are more than 400 species of aphids in British Columbia; at least 80 of them like to hang out in blueberry fields in the Fraser Valley. But one has been the centre of focus for blueberry scorch research in British Columbia: Ericaphis fimbriata.

The species was first described by Brunet’s scientific forebearer W.R. Richards, who held the position of aphid curator at the Canadian National Collection of Insects, Arachnids, and Nematodes in 1959. 

Like many aphids, Ericaphis frimbriata survive the winter as eggs on a plant, emerging in the spring as translucent sap-sucking insects. These aphids produce clones of themselves in April, and whole colonies congregate on the underside of leaves where they can feed on the veins of the plant. Some of these clones end up as winged aphids, which can travel up to a kilometre in search for new plants. 

It is the aphids who are responsible for the transmission of blueberry scorch. While aphids suck up a plant’s juices, the virus secures itself on the outside of the aphid’s mouth. If the aphid moves to a new blueberry bush within 15 minutes, the virus will leave the aphid and infect the new plant. 

The aphid essentially uses the plant like a napkin, wiping the viral residue off its mouth using the inside of a leaf. One of the things Franklin and Brunet will be studying is how much virus actually makes it onto the aphid’s mouth. They will also look at how aphid populations have changed since the early 2000s, and what species prey on them. 

First, though, they need to collect the aphids. 

During the first three years of the study, Franklin and her team will roam fields picking aphids off blueberry leaves. They will use a variety of traps, including one that is essentially an aphid vacuum cleaner, to collect the insects.

Once collected and sent to Brunet’s lab in Ottawa, scientists will either smash up the aphids to collect their DNA for analysis, or slice them up like mini cadavers for examination.  

The hope is that once the study is complete, Franklin and Brunet will have a better understanding of what aphids are actually living in the Fraser Valley’s blueberry fields—as well as what insects growers can team up with to curb aphid spread. 

Pest management

Today’s blueberry growers have a list of 10 insecticides they can use to get rid of aphids. All are toxic to bees, and have explicit instructions to avoid use during bloom, when bees are present. 

The guidelines were developed in the early 2000s, when scorch was first found in BC. But, Franklin noted, the climate has changed a lot since then. In Abbotsford in 2000, the average maximum temperature in May—when blueberry bushes are typically flowering—was 16.3C. In 2023, the average temperature for that month was 21.7C, with the intervening data showing that was not an isolated hot year. Across the Lower Mainland as a whole, the average winter temperature has increased by 1.2C over the last century. And data suggests that without the moderating influence of the nearby ocean, the Fraser Valley has been warming at an even faster rate. (You can read our story on the Fraser Valley’s changing climate here.)

The climatic changes may also be accompanied by potential changes to the local bug population. Aphids are prey for a number of different insects, including lady beetles, ant-like parasitoid wasps, lacewing flies, hoverfly larvae, and minute pirate bugs. These insects are important but relatively unstudied—and it’s not clear how climate change has affected them and their aphid lunches.

“Getting an idea of what the natural pest control in the fields can offer is an important piece,” Franklin said. “If we tap into some of these sustainable pest control options that are free of charge to growers, then that’s going to be a real benefit.”

It’s not just a financial benefit. Blueberry scorch’s favourite aphid, Ericaphis fimbriata, is native to the Fraser Valley and plays an important role in the local ecosystem. Although farmers could do their best to wipe it out entirely, that would wreak havoc on lesser known aspects of BC’s natural ecosystems—not to mention harm  crucial insects like bees.

“Yes we want to control it, but we want to control it responsibly,” Brunet said, “because it does belong to the environment, the ecosystems here.”

The virus

Along with their aphid work, Franklin and Brunet will also be looking at the virus itself, and the unusual things it does to aphids as it strives to replicate itself in blueberry hosts.

There is evidence that the scorch virus can change how aphids act by pushing them to prefer certain plants. To test that theory, Brunet and Franklin will need to perform tiny experiments with tiny aphids. 

The team will present aphids with an array of infected and clean blueberry plants—all from different varieties available in commercial fields. Then, they’ll watch to see which ones the aphids prefer.

“I’m excited to see what happens,” Brunet said about the experiment. 

They will also be looking at how much virus an aphid picks up each time it sips from the plant, and whether that changes depending on the time of year.

The plants

Although Franklin and Brunet are most excited to tackle aphids, the blueberry plants themselves will also play an important part in their research. And so they’ll be engaging in a century-old tradition for the Agassiz Research Centre: breeding better plants. 

Currently, there are no blueberry varieties that are resistant to aphids. But, Franklin plans to screen the more than 100 varieties growing at the research centre to see which ones aphids tend to avoid. 

With those findings, she can tell farmers’ groups which types of blueberry bushes they should consider if they want to have fewer aphids—and reduce the likelihood of encountering blueberry scorch.

Saving BC’s blueberries

Franklin’s research won’t solve BC’s blueberry scorch problem. It won’t develop a vaccine or promise the end of aphid transmission. 

But when her work is complete four years from now, it will mark an important step in understanding the comparatively unknown dynamic of aphids, blueberries, and virus in the province. 

It’s not entirely clear how widespread the virus is in British Columbia, and there are indications that it can be present in related plants like cranberries without symptoms. Other scientists are working to answer some of these questions. (In the coming weeks, we will have an interview with one researcher who is looking at how climate change is affecting cranberries.)

But for now, Franklin’s research will give growers at least one more tool to battle the virus.

“If we have this understanding, then we hope to be able to give them more input on how they can manage aphids in their field, in a sustainable way,” she said.

A scorched earth policy isn’t always the best way to manage blueberry scorch. Franklin, Brunet, and the rest of their team are doing their part to give growers more tools to make ecologically sustainable choices.