Photo: LWK Vorarlberg
Fire blight in Austria
Fire blight is a destructive bacterial disease caused by the bacterium Erwinia amylovora. It appears on various fruit trees and ornamentals of the Rosaceae family and is extremely difficult to control.
Fire blight is said to originate from the United States, where it was reported already 200 years ago. In Europe, it occurred first in 1957 in South England and, since then, has been identified in almost all European countries.Fire blight is a serious threat to pome fruit and susceptible ornamental plants! It constitutes a danger for commercial horticulture and the scattered fruit trees characteristic of our landscape just as much as for tree nurseries, kitchen gardens and public parks.
In Austria, the presence of fire blight was first proved in May 1993 in Vorarlberg. Since then, further centres of infestation have been detected also in all other Federal Provinces.
The host plants most susceptible to fire blight are apple (Malus), pear (Pyrus), quince (Cydonia), cotoneaster (Cotoneaster), hawthorn (Crataegus), fire thorn (Pyracantha), mountain ash (Sorbus), flowering quince (Chaenomeles), and medlar (Mespilus).
Disease patterns
The development of fire blight is the same in all host plants, their symptoms may however vary depending on growing stage, variety, or climate. Leaves and flowers of infected plants shrivel suddenly, turning brown or black. Infected shoots first appear pale-green, then, as the infection progresses, shrivel and blacken. Tips of infected twigs hang down and curl over due to lack of water, causing the characteristic shepherd’s-crook appearance. During humid weather infected twigs exudate whitish, later brown, droplets of a gummy substance containing bacteria. Under the bark of newly infected trees the wood is discoloured reddish brown in most cases and contains a sticky bacterial ooze which is soon forced through cracks to the bark surface. At the end of the vegetation period the bacteria stop spreading. Blighted parts of the bark appear as slightly sunken places with a clear edge between the diseased and the healthy tissue. Inside cankers bacteria die but for a few exceptions which multiply rapidly in spring and resume activity. During the winter time dead leaves and mummified fruit cling to the branches which look as though scorched by fire.
Spread
At larger distances fire blight is frequently spread by contaminated planting material or contaminated objects. Also migratory birds (starlings, thrushs) may pick up the bacteria on their beaks and talons and inadvertently carry it over wide distances. At smaller distances the disease is spread through rain, wind, and insects. Carriers are either bees, bumble-bees, wasps, and flies, which cause infections in flowers, or sap feeders (aphids, bugs, cicadae), which infect shoots. However, shoots can be infected also through injuries created mechanically, e.g. by hail storms. If fire blight spreads in an orchard special attention has to be paid to the pruning tools. During the vegetation period warm and humid weather provides particularly favourable conditions for the rapid spreading of fire blight (temperatures above 18°C and air humidity of over 70%).
Infection processes
In the blossom the stigma is the preferred gateway. Bacteria migrate from the blossom via the pedicel down to the young twigs, from there down to the stronger branches, the stem and, finally, the roots. After the bacteria have reached the shoots of susceptible host plants the pathogen enters through natural openings (air openings, lenticels) or through wounds. The pathogen spreads considerably more rapidly in young shoots of a host plant than it does in older ones. 100 hours after the infection at the earliest first symptoms of dying tissue may appear. A young pear tree, for example, may have died after two to three weeks.
Measures
The transport of fire blight hosts is regulated in the Federal Law on Measures for the Protection against the Transport of Harmful Agents of Plants and Plant Products (Plant Protection Act 1995), Federal Law Gazette No 532/1995, and the 1996 Ordinance on Plant Protection, Federal Law Gazette No 253/1996. To prevent infection with contaminated plant material it is important that the material originates from an area which is not affected by fire blight. Fire blight hosts should be checked for potential symptoms from the beginning of the flowering period to the end of the vegetation period. After warm and humid weather orchards, tree nurseries, parks, and kitchen gardens in susceptible places have to be checked several times for potential infections with fire blight. The planting of fire blight hosts as ornamentals should be minimised. As the application of large amounts of nitrogen makes plants extremely susceptible to fire blight, attention has to be paid also to balanced fertilisation. Severely infected plants have to be removed immediately and burned on the spot, as the pathogen is able to survive for several months even on plants which have been cut down. For plants which are less severely infected it may suffice to remove the infected branches, with the cut having to be made in healthy wood. In order to prevent the spread of the disease, the pruning tools, hands and shoes have to be disinfected (e.g. alcohol 70%, 30 minutes) after each and every work carried out in the infected area.
Control:
At present, controlling fire blight by means of chemical agents is possible only with restrictions. In the treatment of susceptible ornamental plants copper compounds have proved effective when applied during the flowering period or right after periods of increased danger of infection. In the case of pome fruit caution is required for reasons of plant tolerance.
For a certain diagnosis of fire blight, laboratory tests are required!
Contact:
For legal questions and international issues:
Federal Ministry of Agriculture, Forestry, Environment and Water Management, Division III/9, Mr Michael Kurzweil, phone: 01/711 00 / 2819, email: michael.kurzweil@lebensministerium.at
For technical questions (biology of the pathogen, diagnosis, control measures, etc.):
Austrian Agency for Health and Food Safety, Prof. Sylvia Blümel, phone : 01/73216 / 5154, email: pflanzengesundheit@ages.at
Links of topic:
- http://www13.ages.at/servlet/sls/Tornado/web/ages/content/C8C0A6C5A58420CEC1256E24006AC48D
- http://www.feuerbrand.com/
20.05.2009, Lebensministerium III/9