“Impatiens downy mildew is a destructive foliar disease of Impatiens walleriana that is capable of causing complete defoliation or plant collapse, especially in landscape plantings under moist conditions and cool nights. . . . By the end of the 2012 season [the disease] had been confirmed in 33 states.”
Dr. Colleen Warfield, January 2013
DR. Colleen Warfield, corporate plant pathologist for Chicago-based Ball Horticultural, posted her warning about impatiens downy mildew disease in the company's Guidelines for Growers Bulletin.
In this case, "growers" refers to the greenhouse and field propagators throughout North America who provide nurseries with the plants we look forward to each spring.
But this spring was different.
This year, if you bought Impatiens walleriana to brighten your shady North Shore spaces and then spent hours on your knees planting them, you may well be disappointed with the results - and with this story.
For years, I have enjoyed helping to plant hundreds of "busy lizzie" impatiens in a Lynn Valley garden - sometimes lilac and fuchsia, in other seasons a riot of salmons and white.
After they settled in, all we had to do was watch as one patch of plants blended with the next until the shadegarden was a rainbow of colours from one end of the arc to the other.
Unfortunately, we had no way of knowing trouble was looming for the plant that has served us so well for so long, because gardeners weren't warned about the fungal epidemic in time to avoid buying and introducing already-infected impatiens to our gardens.
CanadianGardening.com posted an article on May 3, but the alert still isn't mentioned on the websites of the three North Shore nurseries I checked today.
So somewhat later than usual, the Lynn Valley family bought this year's impatiens from a Langley grower. Busy reclaiming another garden patch, I bought my two dozen locally.
Not in the habit of checking online before heading out, I knew I wanted geraniums for the sunny spots, impatiens for the shade and had no reason to change my mind.
At the first nursery I tried, very few impatiens were displayed. Asked why colour choices were so sparse, a staff member replied, "Oh, we'll be getting more next week." No further explanation about the uncharacteristic lack of stock.
On the way home, I checked the benches at Walmart. No impatiens. Then, just as I was thinking I was out of luck, I finally found enough at a hardware store.
Planted, they looked much as usual and I thought no more about it - until two to three weeks later when I realized the plants weren't thriving and chastised myself for buying poor quality stock instead of waiting for my favourite nurseries to replenish their supplies.
Not until August was a week old did I catch sight of a July 31 Vancouver Sun story as I was putting the paper in the Lynn Valley blue-bag.
Killer Fungus Brings Fear of 'Death of Impatiens as We Know Them' in B.C." read Steve Whysall's headline that, too late, drove me to some online research.
The problems in my garden space and in the Lynn Valley plantings were clearly symptomatic of the disease described by Warfield and in the Pacific Northwest Plant Disease Handbook (pnwhandbooks.org/plantdisease/node/6644).
Widely separated geographically, the plants failed to thrive in either garden. Yellow, curled leaves and stems were soon followed by flower loss and dead or dying plants.
Worse, we had imported the disease to our flowerbeds.
Scientifically speaking, the PNW handbook says the cause is Plasmopara obducens - "a host-specific, funguslike organism."
It goes on to say that the disease is spread by "airborne spores [that] find their way into greenhouses as well as landscapes."
Although growers can take preventive measures by adhering to stringent best practices and using approved fungicides, once a plant is infected there is no cure.
Unwittingly, regional water conservation measures make matters worse because, if we use overhead sprinkling in the evening when the plants have little time to dry off, we create ideal conditions for the fungus to spread.
And spread it has - to the soil in any and every garden or landscape that has been home to even one diseased impatiens plant.
Horticultural websites say discarded plants should not be composted but secured in a bag for garbage collection. Is that warning too late for your compost box? Although Warfield emphasizes that "other (types of) garden plants are safe from the disease," the PNW handbook warns gardeners against reusing flower-beds for impatiens for at least three years.
Much of this grief could have been avoided. The disease was evident in the UK in 2002. By 2004, the march through North America had begun and growers in Washington, Oregon and California were named among the 33 states that saw it in 2011.
In view of the online advisories authored by Ball Horticultural and others, it seems inconceivable Fraser Valley growers remained unaware of the problem - especially after Warfield posted her analysis in January.
For a nursery to tell Whysall that "We don't want to cause a panic.. . ." is not warning enough. Nor is it enough to alert only those gardeners who question the quality of the plants they bought - rather than blaming themselves.
Because as Warfield marks with an uppercase CAUTION: "Infected plants not yet showing symptoms may result in the inadvertent movement of the pathogen."
To protect consumers and the health of their gardens, it would have helped to have these warnings posted at the checkout counters of all plant retailers in the region.
All we can hope for now is that scientists and growers will find a "green" way out of this sad horticultural misfortune.
