BROOKS, Alta. – As a plant disease detective, Ron Howard spends his days looking at discoloured beans, wilting cucumbers and potatoes succumbing to blight.
Based at the crop development centre in this southern Alberta community, the plant pathologist is responsible for new disease surveillance and works with federal government and university groups to identify new pests that strike a variety of valuable crops.
Operated by Alberta Agriculture, the centre studies the production and marketing needs of horticultural crops, forages and specialties such as spices, oilseeds and pulses.
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The total acreage of many of these crops is small, but their value is high. Ongoing research is needed to find better ways to manage costly disease through chemical, management or biological controls.
“It is impossible and impractical to eradicate a pest. What you want to do is keep it below an economic threshold,” Howard said.
An economic threshold is an acceptable loss. Controls are considered necessary once a disease crosses that limit.
Howard and his team culture diseases in their laboratory and use them to infect seeds and plants so they can study the diseases’ progress and look for controls.
“The process of putting the disease on the plant and looking at the reaction can be done in a few months,” he said.
“What takes the time is once you identify that resistant plant, moving the gene for resistance to a new plant.”
The centre is currently on the alert for several new diseases of tomatoes, edible dry beans and geraniums.
Pepino mosaic virus has been most recently reported in greenhouse tomatoes. The virus is known in Ontario and British Columbia, and has appeared in two Alberta greenhouses, probably arriving on infected transplants.
It is not poisonous to people but can kill plants. Growth is stunted, leaves are discoloured and the fruit is marbled in appearance.
It does not do well in hot environments and during the summer the plants seem to outgrow it.
Badly diseased plants need to be removed and destroyed.
Growers are discouraged from visiting each other’s greenhouses because people can carry the virus on their hands and clothes.
This disease can be a problem even among those with smaller greenhouses that supply farmers’ markets or sell from the farm.
A geranium bacterial disease known as Ralstonia solanacearum has been found in a greenhouse in Saskatchewan and possibly other locations in the West. It can cause brown rot in potatoes and wilt in tomatoes, but so far has been detected only on greenhouse geraniums.
It started in the United States and may have come to North America from Kenya. Many growers get plants already started from outside sources that they finish as full-grown plants.
The symptoms look like another disease called bacterial wilt.
Geranium bacterial blight is easily spread mechanically with pruning shears and machinery.
When people set out their geraniums, infected plants are likely to die. However, most greenhouse growers are likely to cull them before they reach the home gardener.
A new disease found in edible dry beans may have arrived on contaminated seed from the U.S. two years ago.
The seeds turn yellow and look spoiled.
The best cure is to use chemically treated seed containing the antibiotic streptomycin.
However, Health Canada does not favor antibiotic seed treatments, but has agreed to allow streptomycin on seed from the U.S. This is likely the last year this antibiotic may be used. A newly registered treatment containing copper sulfate is the likely substitute.
