How to Manage Pests
Interactive Tools and Models: About the Fire Blight Risk Assessments
The Fire Blight Risk Assessments are computer representations of the Zoller (degree-hour) and Schroth (mean temperature) disease models for controlling fire blight, Erwinia amylovora, in apple and pear crops in California.
Gubler, W.D, Lindow, S., Zoller, B., and Duncan, R. 1999. Pear Diseases in Production and Handling of California Pears.
University of California, Division of Agriculture and Natural Resources Publication.
This degree-hour fire blight model assesses actual conditions for Erwinia amylovora bacterial growth and infection. It also indicates when treatment is unnecessary. It takes into account early bloom and periods of continuous cool weather, allowing adjustments in treatment timings.
The model was dveloped from five years of field observation on the development of Erwinia amylovora in Bartlett pear blossoms. It is based on the correlation between the number of accumulated Fahrenheit-degree-hours and the incidence of random new blight infections per holdover infection during an 11 year period.
Use of the degree-hour method requires a recording thermograph to obtain a continuous thermometer reading in the orchard beng managed.
If possible, growers should start the season with a full soil water profile so irrigation during bloom can be avoided.
Growers can track the degree-hours for your orchard and take into account the spray applications. The UC IPM Pest Management Guideline for Fire Blight on Apple and Pear explain the current recommendations for applying the results of the model in a spray program.
Thomson, S.V., Schroth, M.N., Moller, W.J., and Reil, W.O. 1982. A Forecasting Model for Fire Blight of Pear. Plant Disease 66:576-579.
Prediction of flower colonization by Erwinia amylovora bacteria is based on
the daily mean temperature rising above a line drawn from 62°F (16.7°C) on March 1 to
58°F (14.4°C) on May 1. Subsequent applications should be made every five days until the
end of bloom.
The UC IPM Pest Management Guideline for Fire Blight on Pear explains the current recommendations for applying the results of the "UC" or mean-temperature model in a spray program.