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Canker cause scrutinized


Weather plays big role in spread of Godronia in blueberry fields, but scientists want to know a lotmore.


By Judie Steeves A


lthough blueberry canker is not new to B.C., it recently has begun causing very serious problems in some parts of the Fraser Valley, so efforts are underway to learn more about it and how best to counter it.


At first, it was misdiagnosed as bacterial blight, notes plant pathologist Siva Savaratnam of the agriculture ministry’s Abbotsford office.


However, a survey two years ago showed that, some fields were really hammered by Godronia cassandrae, he said.


There is less in Delta and Richmond, but in some parts of Aldergrove, Abbotsford and Pitt Meadows it has made a patchy appearance in as much as 20 percent to 30 percent of a field.


Savaratnam says he is working with provincial berry specialist Mark Sweeney to look into just what environmental conditions aid it, although they know it is dispersed by rain or overhead irrigation, and that it requires moisture on the surface for the spores to germinate. That means fall’s rainy weather makes it a key time for the infection to spread, usually attacking leaf or floral buds at the nodes, he said. He is now analyzing two seasons of data on the biology of the disease to establish when it begins, its progress and when the spores are produced. It would appear that spores are produced throughout the season, though, although mature cankers seem to produce more at the beginning of the season.


In early spring, growers should be able to see the initial growth of a canker on new wood and they should be pruned out immediately to prevent spread of the disease.


Dry, brown leaves are evidence of Godronia infection. Pruning to remove the canker (inset) will prevent its spread the following season.


However, most of the cankers should be pruned out in the fall during regular pruning, and the spread can be reduced by opening up the canopy to provide good air circulation.


The symptoms are brown and dry leaves because the canker girdles the stem and blocks water and nutrients from circulating. It’s too late then, but pruning does remove the canker and prevent its spread the next season.


Management practices can prevent


spore production and spread of the mycelium.


There are no chemicals registered for use against Godronia, he said, but he is working on that. It will take at least two years though, for the registration process.


Godronia inoculum may be impacted by fungicides used as part of a grower’s regular spray program. They believe some varieties may be more susceptible than others. For instance, Duke and Bluecrop seem to be affected.


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Contact: John Gibeau President, Honeybee Centre Cellular (604) 317-2088


Email: Gibeau@HoneybeeCentre.com British Columbia Berry Grower • Spring 2011 11


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