Plant Diseases Crossing Borders

Eric Allen October 2003

Speaker Biographies

As a research scientist, Eric Allen leads the Forest Health Unit at the Pacific Forestry Centre. Their purview involves everything from ozone effects, tree diseases and various pests that plague our western forests. Eric received his advanced education from the University of Alberta: B.Sc., M.Sc., and Ph.D in Forestry and Plant Science. Karen Morrison is a long-time successful gardener and an active of The Victoria Rhododendron Society.

Eric Allen provided a masterful treatise on plant diseases and the growing menace they pose to our gardens, parks, forests, and countryside. Sudden Oak Death phytophthora ramorum (SOD) has been the focus of recent concern as its inexorable advance has been reported from California northward, posing threats to rhododendrons among other key species, vital to our interests. But it is only one of a broad array of alien scourges that have wrought changes to our environment in the past, and will do so in the future.

The White Pine Blister Rust Beetle has wiped out the white pine forests in Canada. The Gypsy Moth is a well-known destroyer of many forest species. The Pinewood Nematode has reportedly caused $600 million in annual losses to the green lumber trade. Pests follow few boundaries of life forms: zebra mussels from European ships have clogged the St. Lawrence Seaway; blue-green algae poisons lakes in the Canadian Shield; weeds are ubiquitous on the planet, but who would have predicted the noxious spread of Scotland’s beloved broom, imported to our Island by a homesick gardener, himself transplanted from away.

Alongside SOD, new destroyers seem to strike at random. The Asian Long-horned Beetle was first noted in New York City in 1996. It exists now in a Halifax enclave. It has been reported in Toronto, and recently in Vancouver. The Emerald ash-borer has appeared in the Detroit-Windsor region. How do these invasions happen? Their vectors are insidious: wood ‘dunnage’ – the pallets, wire and cable spools and the like – accompany the thousands of tons of imports throughout our continental ports. One large piece of Norway Spruce used to hold imported granite blocks in place was inspected microscopically and seen to house several hundred species of insects and fungi.

The horticulture trade can be an unknowing importer of malevolent organisms. Plant collectors may successfully thwart official inspections when they innocently carry plants across borders. (Following the meeting, more than one person was heard to admit, “we’ve all done it and maybe we shouldn’t in future”). But the enormous increase in world trade with thousands of containers being unloaded every day in scores of ports on every continent, probably presents the greatest hazard. Are we facing vegetative Armageddon when not only our precious garden plants but also our forests will be wiped out by an array of new diseases? Or is this merely a new surge of the pathological onslaughts that have occurred over millions of years. We may take some comfort in such phenomena as the survival of most specimens of our precious Garry Oaks from a combined attack of fungus and aphids over several years in the 1990s. But then we may think of the Dutch Elm disease that wiped out the whole population of the splendid American Elm in the eastern region of our continent, not 50 years ago.

Dr. Eric Allen counselled patience over panic, stressing the importance of communication, especially with the Canadian Forestry Inspection authority, in reporting new incidences of disease. His presentation was outstanding, stimulating a torrent of questions from an enthusiastic audience. His message deserves a broad dissemination. (the Editor)

In her ‘5 Minute’ offering, Karen Morrison spoke of her favourite rhododendron. Confessing her difficulty in making this choice, she presented a fine array of some fourteen candidates, some familiar and some not. She narrowed her list to three: (in reverse order) ’Seta’, a spinuliferum x moupinense early bloomer; then R spinuliferum, a four month spring blooming lepidote with lots of firecracker-red flowers and hairy-edged puckery (a lovely word!) leaves. Then came her very favourite, R.moupinense. Almost a first-bloomer in January, this lepidote was introduced in 1909 from Sichuan. The charm of its cinnamon-brown peeling bark, its oval leaves with ciliate margins, its white flowers with kissy-red smears and dark brown stamens combined to qualify as Karen’s earliest rhodo love. Among so many.