ISHS Acta Horticulturae 338: VI International Workshop on Fireblight
THE RELATIONSHIP BETWEEN FLOWERING HAWTHORN AND FIRE BLIGHT INCIDENCE IN HAWTHORN AND IN PEAR ORCHARDS |
| Author: | M. Rien van Teylingen |
| Abstract:
In 1984 in the Netherlands a new fire blight policy came into force. The legislative regulations i.a. obliged the destruction of infected plants, and prohibited the flowering of the native hawthorn (Crataegus calycina, C. laevigata and C. monogyna) in designated areas where fruitgrowing or nurseries were important (Netherlands, 1984). A three years field research was carried out to study the effectiveness of the flowering prohibition in protecting pear trees against fire blight infection. Five test areas with hawthorns as well as pear orchards were chosen. These areas contained 51 000 hawthorns and 126 pear orchards larger than 0.2 ha. In two of these areas the hawthorns were not allowed to bloom. During the research fire blight infections were light to moderate in the test areas. In 16.4% of the flowering hawthorn sites once or more often infection was detected, while in the non-flowering hawthorns fire blight occurred in 2.3% of the sites. Of the pear orchards in the areas with no or little flowering 53% had blighted trees and in the other areas in 59% of the orchards diseased trees were present. This difference was not significant. The reason that flowering prevention decreased fire blight infection in hawthorn but not in pear, can be found in the way the control measures were taken. Diseased hawthorns had to be removed completely as soon as possible, but the measures taken by the fruitgrowers concerned proved to be inadequate to eradicate the disease in the orchard. In the study it was assumed that new infections were initiated by the nearest existing infection. It appeared that infections in pear mostly were initiated by old infections in pear trees which were not removed adequately by the grower. Spread of fire blight from hawthorn to pear could hardly be demonstrated during the study. In contrast with this, pear played a more important role in infecting hawthorn. Spread between pears and between hawthorns often occurred. The information from this research led to a change in the Dutch fire blight control policy in 1991. | |
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