A COMPARISON OF FIRE BLIGHT INCIDENCE AND ENVIRONMENT BETWEEN NEW ZEALAND AND WESTERN UNITED STATES

Fire blight was first reported in New Zealand in 1919 and spread rapidly into all pip-fruit growing areas.
It was quite serious for a few years but then waned and has not been a major threat to the fruit industry since.
Minor outbreaks occur in some of the fruit growing areas almost every year, but major outbreaks are infrequent and occur approximately one out of ten years despite the plantings of susceptible apple and pear varieties.
The Prediction model of Thomson and a modified Billings model were used to estimate the probable years when fire blight would likely be serious.
A high frequency of years appears to be conducive to fire blight in some growing areas of New Zealand and indicates that fire blight should be a frequent problem.
However, the incidence of blight is much less than anticipated and suggests that factors other than environment may be restricting the development of fire blight.
Populations of epiphytic, saprophytic bacteria in pear and apple flowers varied considerably and ranged from 10³ to 10⁶ per flower, whereas in the western U.S. the populations were considerably less at 10² to 10⁴ per flower.
These saprophytic bacteria may be restricting the development of blight in New Zealand by providing some degree of biological control.

IV International Workshop on Fire Blight

S.V. Thomson, C.N. Hale

https://doi.org/10.17660/ActaHortic.1987.217.13