FIRE BLIGHT CONTROL UNDER TEMPERATE ZONE CLIMATOLOGY

Fire blight has been present in Belgium since 1972 and new infections have been reported every year on apple and/or on pear trees.
The flowering period of fruit trees is generally considered to be the most riskful period of the year for fire blight infections.
Most years, the mean flowering period of pear trees occurs under very variable weather conditions.
The temperature accumulation before bloom, which is necessary for a sufficient bacterial inoculum build up, is often under the critical level.
More important for the host susceptibility of pear trees is the presence of secondary blossoms.
Four different types of secondary bloom can be distinguished on pear trees.
The structure of three different types of secondary bloom on pear trees is discussed and correlated with possible fire blight infection risks.
On apple trees, the flowering period occurs 2 to 4 weeks later than on pear trees and the risk for a primary bloom infection is considered to be higher.
Two types of secondary bloom have been found on apple trees.

Only when critical climatological conditions are combined with a critical phenological stage (primary or secondary bloom) is a chemical treatment with streptomycin sulphate recommended.
Different risk assessment systems are compared to evaluate the daily fire blight infection risk : Billing’s revised system (BRS), Maryblyt 4.2 C and Parefeu.
These systems are very useful as a basis for prediction of fire blight infections and of fire blight development in the orchard during bloom and during the season.
Some suggestions for improvement of these systems are formulated.

VII International Workshop on Fire Blight

T. Deckers, E. Daemen, I. Hayen

https://doi.org/10.17660/ActaHortic.1996.411.86