ISHS Acta Horticulturae 489: VIII International Workshop on Fire Blight
FIRE BLIGHT RISK ASSESSMENT: BILLING'S INTEGRATED SYSTEM (BIS) AND ITS EVALUATION |
| Author: | E. Billing |
| Keywords: | Erwinia amylovora |
| Abstract:
Billing's integrated system (BIS) evolved from earlier systems described by Billing and others. The primary intents were: simplicity, flexibility and useful guidance on risk and disease limitation actions. Computer use is not essential. BIS weather analyses, when used in conjunction with good field risk records, aim to assess risks for all hosts over the whole growing season, including low and high incidence risks but, some assessments are easier to achieve than others. For simplicity, degree day sums are used, pending evidence that degree hour sums would significantly increase precision. Warm, wet infection risk days which lead to localized, low incidence disease need to be distinguished from conditions favouring a high incidence of blossom blight where, following a warm period, wetting of flowers by dew may suffice for infection. When temperatures are high (>= 27°C), blossom infection may occur without wetting. Degree day sums above a temperature of 13.0°C, have given good guidance on times when, following infection, early signs of disease may be seen. Judged by 74 test cases, the critical degree day sum for most apple blossom blight is >=47 but, for blossom blight on pear and hawthorn, and for shoot blight, it is only >= 17. As with other systems and models, BIS remains a combination of working hypotheses that require further testing; about 200 cases is the aim. Meanwhile, BIS offers useful guidance to users who take full account of field risks. It does not provide rules for novices or for those who, unrealistically, rely on weather analyses alone. The quality and quantity of the output of any system depends on the quality and quantity of the input of both field and weather data. | |
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