ISHS Acta Horticulturae 338: VI International Workshop on Fireblight
A PREDICTIVE MODEL FOR FORECASTING FIRE BLIGHT OF PEAR AND APPLE IN WASHINGTON STATE. |
| Author: | T.J. Smith |
| Abstract:
Fire blight outbreaks are sporadic in apples and pears grown in the Northwest United States. Pears are the most common host, and infection usually occurs through secondary blossoms from mid-May through July. Since most damage is relatively minor, and all common models are over-predictive, most growers tend to ignore models except during the full bloom period. To develop a more accurate fire blight predictive system, temperatures that occurred prior to known isolated infection periods were analyzed. A simple degree hour based method for estimating the relative growth rate of Erwinia amylovora (Burr.) Winsl. et. al., in blossoms was developed. Degree hours over 15.5°C are totaled for the four days preceding a blossom wetting event. Daily degree hours peak at 31°C and decline as the daily high approaches 40°C. Infection of blossoms is rare when degree hours total less than 240 when blossoms are wetted. Risk of infection increases with higher degree hour totals. Most serious fire blight has occurred when four day degree hour totals are between 270 and 350 when flowers are wetted. Severity of the disease in any specific orchard depends on relative presence of flowers, cankers, and the disease susceptibility of the pear or apple variety. | |
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