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Managing fire blight in the Maritimes

From minor, isolated outbreaks in 1986, primarily based in an Annapolis County apple orchard, fire blight has spent the past 20 years spreading the entire lengt


March 13, 2008
By Dan Woolley

Topics

From minor, isolated outbreaks in
1986, primarily based in an Annapolis County apple orchard, fire blight
has spent the past 20 years spreading the entire length of the
Annapolis Valley, Nova Scotia’s premier apple-producing region.

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A branch from a Gala apple tree, complete with fruit, with scorched leaves caused by a severe fire blight infection. Fire blight infections are spreading in the Annapolis Valley of Nova Scotia. Photo courtesy of USDA-ARS 

From minor, isolated outbreaks in 1986, primarily based in an Annapolis County apple orchard, fire blight has spent the past 20 years spreading the entire length of the Annapolis Valley, Nova Scotia’s premier apple-producing region.

“All orchards in the valley are at risk,” says Bill Craig, a horticultural consultant with Agra Point International, adding infected blossoms appeared in most areas of the Annapolis Valley during 2006, which was a bad year for the disease in the Atlantic region. “Maybe global warming is coming back to bite us.”

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Warm temperatures in early spring, coupled with heavy rains in May and June, encouraged fire blight to develop, explains Craig. “If you have enough innoculum and rain, you will get infection.”

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Fire blight infects the terminal leaves on an unpruned and uncovered apple tree. Warm temperatures in early spring, coupled with heavy rains in May and June, encouraged fire blight to develop. Photo courtesy of USDA-ARS 


Based on a prediction model, there were three days of extreme infection risk in late May and early June 2006, he notes. “If you didn’t apply streptomycin in that period, you were going to have problems.”

Craig stresses it is weather conditions – heat and rain particularly – that drive the prediction models for fire blight

He advises growers to clear infected shoots out of their orchards during the next few months and apply copper sprays to reduce the ooze from any over-wintering cankers on shoots.

Dr. Gordon Braun, an Agriculture and Agri-Food Canada plant pathologist based at the Atlantic Food and Horticulture Research Centre in Kentville, says that, until recently, only two control agents were available for fire blight – streptomycin and copper. Unfortunately, streptomycin has developed resistance problems and copper’s usefulness is limited based on application timing.

But Dr. Braun notes there are two new biological control agents available – Blight Ban C9-1 and Bloom Time E325. The application rate of both products is the same – 370 to 500 grams per hectare in 1,000 litres of spray solution – but they are only effective when applied at specific stages during the bloom period.

Fire blight bacteria increase in number by growing on nutrients found on the stigma of the blossom. The bacteria eventually infect the blossoms through the nectaries. Dr. Braun says Bloom Time and Blight Ban protect against this type of infection by also growing on the stigma of the blossom, feeding on nutrients produced by the blossoms and displacing the fire blight bacteria. Because of this timing issue, the bio-controls must be applied 72 to 96 hours before the fire blight bacteria arrive on the stigma.

The products are applied when 15 to 20 per cent of bloom development has occurred and again at full bloom. A third application of Blight Ban can also be applied during periods of high risk at the 50 per cent bloom development stage or on late (rattail) bloom.

Both products can be tank sprayed or alternated with streptomycin, adds Dr. Braun, although he warns biocontrols are less effective under high disease pressure and not as effective streptomycin.

He recommends growers use a predictive model – such as Cougarblight or Maryblight – to determine when to apply bio-controls, applying them during a low risk period but prior to a predicted time of high risk and using the streptomycin a day before a period of high risk.

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Dr. Gordon Braun (left), a plant pathologist with Agriculture and Agri-Food Canada, and Bill Craig, a horticultural consultant with Agra Point International, are interested in informing Maritime apple producers how to prevent fire blight outbreaks. Photo courtesy of Dan Woolley
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Bernie Solymár, a consultant with EarthTramper Consulting Inc., suggests growers with fire blight concerns may want to consider using the growth regulator Apogee, which has been shown to not only reduce the vigour of new growth shoots on apple trees but also toughen the shoots to fire blight infection – rapidly growing, succulent plant tissue is more susceptible to the disease. Photo courtesy of Dan Woolley


But growers should be forewarned. Supply of the two new bio-controls is likely to be limited in Canada during the 2007 season, says Bernie Solymár, a consultant with EarthTramper Consulting Inc. He adds that growers with fire blight concerns may want to consider using the growth regulator Apogee, which has been shown to not only reduce the vigour of new growth shoots on apple trees but also toughen the shoots to fire blight infection – rapidly growing, succulent plant tissue is more susceptible to the disease.

Dr. Braun says there is talk of organizing Canada-wide trials involving the use of Bloom Time and Blight Ban. Growers with a significant amount of fire blight infection are invited to host trials in their orchards. “We hope to trial over the next two years.”

Other trials are also scheduled over the coming years as part of the national Phase III Integrated Fruit Production (IFP) on-farm demonstration program administered by the Canadian Horticultural Council. Five Maritime apple growers – four in Nova Scotia and one in New Brunswick – are collaborating in these trials, which, according to Craig, will evaluate various mulches and orchard grasses as ground cover to reduce herbicide use and improve soil health.

The Phase III trials are part of a reduced risk strategy aimed at reducing the use of broad-spectrum chemistries through the use of new products, such as Surround and Ignite, plus other lower risk products. Five years of funding is available for demonstration field trials in conjunction with provincial IFP advisory teams and consultants in Nova Scotia, New Brunswick, Quebec, Ontario and British Columbia. The trials are based in commercial orchards under commercial conditions. Participating growers are compensated for their involvement in the trials.

Solymár, project coordinator of the national trials and reduced risk strategy, says IFP is a system to achieve sustainability by reducing impacts on the environment, all while maintaining the economic viability of production. It seeks to reassure retailers, consumers and the world they are buying safe, healthy and environmentally responsible grown fruit, he adds.¶