Articles
A RISK ASSESSMENT MODEL FOR FIRE BLIGHT OF APPLE AND PEAR
Article number
411_22
Pages
97 – 104
Language
Abstract
Fire blight generally causes very little damage to Washington State apples and pears, but can cause serious loss in a low percentage of orchards in about one year out of five.
Infection of pear usually occurs through the late blossoms produced on the side of primary blossom clusters about 5 to 14 days past petal fall, or through secondary blossoms produced sporadically during the two months after primary bloom.
Apple infection has been very uncommon, even in highly susceptible varieties.
However, weather conditions in 1993 and 1994 were abnormally warm and wet during portions of the apple and pear primary blossom period, resulting in severe fire blight outbreaks in a small percentage of the orchards, and wide-spread incidence of light infection.
A predictive system, used in Washington since 1990, effectively identified key infection periods.
Growers and advisors who used the model in 1993–94 sprayed far less frequently with better control than those who followed more traditional control methods.
The model requires the fruit growers to: 1) evaluate host condition, such as the number of flowers present, tree age, vigor, stage of growth, and varietal susceptibility, 2) judge the relative presence of active fire blight cankers in the area, 3) add the total degree hours that have occurred during the past four days (using high and low daily temperatures and a look-up chart), and 4) watch for conditions that would cause blossom wetting.
The model assigns a level of risk to the various orchard and weather situations, and the growers make personal decisions about the level of risk they are willing to take during a potential infection period.
Growers and advisors have been taught to effectively use this model in classes of less than one hour duration.
Infection of pear usually occurs through the late blossoms produced on the side of primary blossom clusters about 5 to 14 days past petal fall, or through secondary blossoms produced sporadically during the two months after primary bloom.
Apple infection has been very uncommon, even in highly susceptible varieties.
However, weather conditions in 1993 and 1994 were abnormally warm and wet during portions of the apple and pear primary blossom period, resulting in severe fire blight outbreaks in a small percentage of the orchards, and wide-spread incidence of light infection.
A predictive system, used in Washington since 1990, effectively identified key infection periods.
Growers and advisors who used the model in 1993–94 sprayed far less frequently with better control than those who followed more traditional control methods.
The model requires the fruit growers to: 1) evaluate host condition, such as the number of flowers present, tree age, vigor, stage of growth, and varietal susceptibility, 2) judge the relative presence of active fire blight cankers in the area, 3) add the total degree hours that have occurred during the past four days (using high and low daily temperatures and a look-up chart), and 4) watch for conditions that would cause blossom wetting.
The model assigns a level of risk to the various orchard and weather situations, and the growers make personal decisions about the level of risk they are willing to take during a potential infection period.
Growers and advisors have been taught to effectively use this model in classes of less than one hour duration.
Publication
Authors
T.J. Smith
Keywords
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