In U of G’s Pest Diagnostic Clinic, Melody Melzer, left, and Shannon Shan identify pests and diagnose plant diseases for Ontario’s horticulture and agriculture industries.

“My job is sort of like triage.” No, Melody Melzer doesn’t work in a hospital emergency room. She’s a plant disease diagnostician in U of G’s Pest Diagnostic Clinic (PDC), now marking 35 years on campus.

That’s more than three decades’ worth of poring over plant, water and soil samples to help identify pest organisms that can ravage ornamental plants and food and forestry species vital to our health and economy.

To find the clinic, head for the Agriculture and Food Laboratory of Laboratory Services, located at 95 Stone Road West. There, four PDC staffers test for diseases caused by fungi, bacteria and viruses, and look for infestations of parasitic nematode worms and insects.

They use microbiological and DNA-based methods and enzyme assays to narrow down likely candidates from among long lists of potential pests. They usually start with a hunch about the culprit and use the disease symptoms to recommend and run tests to confirm the problem.

Says Xuechan (Shannon) Shan, PDC supervisor and plant diagnostic pathologist, “As a diagnostician, you have to have an idea what it is. You’re almost like a doctor: Let’s do the test to confirm it.”

After that, it’s up to the client to decide what to do about an infection. Key clients include industry growers, government agencies, crop consultants and farmers. Most samples are sent from Ontario, although others come from elsewhere in Canada and the United States.

Besides testing plant material, the clinic looks at water samples – typically from greenhouses – and soil samples sent by farmers or by the Ontario Ministry of Agriculture and Food (OMAF) and the Ministry of Rural Affairs (MRA).

Last year, the clinic tested OMAF samples to confirm that a soybean virus had entered the province from the United States. It also helped the ministry identify a new fruit fly in samples last fall and worked on screening for strawberry virus.

Some of PDC’s diagnostic tests are homegrown. In 2012, the clinic developed a test for boxwood blight, a disease worrying nursery growers of the popular boxwood shrub. A PDC technician is now validating a genetic test for identifying the culprit fungus. Earlier, the clinic devised similar tests for organisms causing cucumber wilt and tomato bacterial canker.

Laboratory Services staff, including those within PDC, have used enzyme-based assays to identify plum pox virus in southern Ontario. That testing program, done during much of the past decade, stems from disease surveys by the Canadian Food Inspection Agency (CFIA).

Along with OMAF and the Ontario Apple Growers, clinic members tested fruit for fungal resistance to fungicides used to treat apple scab.

For additional help, clinic employees also call on other labs and resources within Laboratory Services, as well as insect experts on campus, particularly in the School of Environmental Sciences (SES).

The clinic gets the odd call about pests making headlines, such as emerald ash borer, but it’s not a hotline service. Other groups, notably CFIA, look after quarantines and programs to stem invasive species and disease outbreaks. PDC staff members alert those other agencies to such problems, says Todd Marrow, manager of the Laboratory Services diagnostic unit.

“The clinic serves as the provincial diagnostic lab for pests,” he says. “It’s an early warning sign for the CFIA as well. If we find something in our province, we have to alert the CFIA to that.”

The U of G clinic uses quality assurance protocols that follow guidelines set by the Standards Council of Canada.

PDC’s busiest time – perhaps not surprising – is April to October. Speaking in late January, Melzer said: “This is the quiet time of the year. Summer can get pretty hectic.”

Genetic testing has become increasingly useful here. Some of those diagnostic tests rely on DNA barcoding of the sort developed by U of G biologists and now used routinely to identify species of organisms at the Biodiversity Institute of Ontario on campus.

“One of the coolest methods is the DNA multi-scan,” says Melzer. That technology uses prepared membranes containing DNA probes targeting dozens of pest species that can quickly and accurately match a bit of genetic material from an unknown sample.

Much of that technology was unheard-of when the clinic began in 1978. Demand grew, with thousands of samples arriving each year.

The clinic became part of OMAF’s Agriculture and Food Laboratory Services Centre, which was transferred to the University in 1997 under U of G’s enhanced partnership with the ministry.

Melzer, B.Sc. ’90 and M.Sc. ’93, joined the clinic about a year ago. She studied fungal diseases in plants for her graduate degree in environmental biology and worked as a research associate with Prof. Greg Boland, who recently retired from SES.

She and Shan work with technicians Honghe Cao and Jessica van Frankenhuyzen.

What do clinic members do about plant pests in their own gardens?

Melzer resists any urge to use pesticides: “I will dig it up and plant something else there.”

So does Shan, who confesses to a perverse fascination that carries over from work to home. She was thrilled, for instance, to identify a crown gall infection on her euonymus shrub. “I like to see disease in my garden.”