Fire Blight

By Mary Anne Tollefson

Fire blight a disease that is caused by the bacterium Erwinia amylova seriously affects fruit production worldwide and is now present in South America, Europe, UK., Middle East, and Japan. The bacteria overwinters in cankers on the bark formed by the previous year by hail, insect feeding, or other mechanical injury. Since insects are attracted to the ooze that contains the bacteria, they then carry the bacteria to open blossoms and transmit the disease to other favorable trees or shrubs. Such trees and shrubs that are favorable to fire blight are apple, pear, quince, mountain ash, crabapple, hawthorn, cotonaster, serviceberry, and pyracantha.

Fire blight is mostly in its prime during moist periods during the blooming season but the blight can continue to spread later into the season. The blight is more likely to develop when the conditions are favorable. Favorable conditions can include temperatures that are between 70-80 degrees F = 21-27 degrees C and a relatively high humidity above 60%. With favorable conditions such as these trees and shrubs will start to show predominant symptoms

Symptoms would include:

-Branches, twigs, and leaders will turn black and wilt

-Reddish-brown ooze will appear in infected areas

-Areas on the trunk or branches will be discolored and sunken

To control fire blight there are two types for control a person can use. There is cultural control or chemical control. With the cultural control method, first you remove and destroy all the traces of blight. When removing the blighted areas, be sure to sterilize all tools and large cuts with a 10% chlorox or 70% ethyl alcohol solution. Second, you can prevent shoot and sucker growth by using a nitrogen fertilizer. Third, remove trees that are close that can be a source of inoculum. Fourth, avoid overhead watering.

With the chemical control always read and follow the directions on the label. The first recommendation for chemical control is a spray of copper compounds plus oil. This will delay inoculum production in cankers missed after pruning. Another chemical is just a regular bactericide spray that is applied during the main bloom. Some recommendations are streptomycin or teramycin.

With the chemical and cultural controls there is another option which is management. Some options are to grow resistant varieties when possible, do not purchase or plant infected trees or shrubs, remove all plants that are severely infected, and if the disease has all ready begun there are three steps to take:

1. During the dormant season, prune out infected twigs, branches, and flower parts. The best is to prune out when the weather is dry, cutting at least 4 inches below the canker. And remember to sterilize pruning tools between cuts.

2. During the growing season, prune out infected areas by cutting 12 inches below the canker.

3. Spray with either a bactericide or a copper compound containing an oil.

With all the the information listed above should make it easier to distinguish fire blight and ways to handle and treat the disease. Just remember the easiest way to prevent fireblight is to grow resistant varieties.

Links:

http://www.cas.psu.edu/docs/CASDEPT/PLANT/ext/fireblt.html

http://www.orst.edu/dept/botany/epp/guide/P/peafirebl.html

http://www.pi.sa.gov.au/info/factshts/fireblight.htm

http://www.ppathw3.cals.cornell.edu/profiles/fireblight/pa2105+1.html