ISHS Acta Horticulturae 704: X International Workshop on Fireblight
PREDICTING THE OCCURRENCE OF FIRE BLIGHT USING LEAF WETNESS IN THE SAN JOAQUIN VALLEY OF CALIFORNIA |
| Authors: | B.A. Holtz, E.W. Hoffman |
| Keywords: | MARYBLYT, leaf wetness |
| Abstract:
Fire blight is a serious disease of apple in the San Joaquin Valley of California. Applications of streptomycin sulfate usually begin after 10% bloom and continue every 5 days until flowering is complete, especially if humid and wet conditions persist. Several models relate the presence of Erwinia amylovora on blossoms to temperature and other meteorological factors to establish thresholds above which disease can be expected to occur. Three fire blight predictive models, Mean Temperature Line, Cougarblight, and MARYBLYT, were compared from 1998 to 2002 and accurately predicted infections when rainfall occurred during the susceptible bloom period and average daily high and low temperatures were above 15.5°C. All three models accurately predicted low fire blight potential during the susceptible bloom period when daily average temperatures were below 15.5°C. However, infections were observed without rain events when average daily high and low temperatures were above 15.5°C. These infection periods were associated with long durations of leaf wetness usually occurring at night. MARYBLYT accurately predicted infections and symptom development when 0.25 mm of rainfall was entered daily into the program when more than two hours of leaf wetness was observed. Quantifying leaf wetness periods associated with dews will provide a more reliable basis for disease prediction in the relatively warm arid climate of California. In six out of the seven years of this study growers eliminated an average of four antibiotic sprays per year when average daily high and low temperatures were less than 15.5°C and low fire blight potential was predicted. Internet obtained 4-8 day predicted temperatures were entered into MARYBLYT to predict infection periods and antibiotic application timings. | |
Download Adobe Acrobat Reader (free software to read PDF files) | |
