P&PDL Picture of the Week for
February 7, 2005

Fireblight! Now is the time to prune out last year's infected branches!

Gail Ruhl, Senior Plant Disease Diagnostician, Interim P&PDL Director, Department of Botany & Plant Pathology, Purdue University

One of the most destructive diseases of apples and pears is fireblight. This bacterial disease is most damaging during years when above normal spring temperatures are coupled with frequent rains during the blossoming period. Fireblight also infects other trees and shrubs within the Rosaceae family such as mountain ash, hawthorn, cotoneaster, and pyracantha. Trees and shrubs infected with this bacterial disease will look as if their branches have been scorched by a blow torch. Often the tip of the shoot bends over to resemble a shepherd’s crook. If the infection continues down a shoot or flower spur into a larger branch, then a canker may form. The canker is often sunken, with darkly colored bark. The pathogen overwinters in cankers on the trunk and branches and in the spring droplets of sticky, amber-colored bacterial ooze form from these cankers. Insects and splashing rain spread the bacteria from the droplets to blossoms and twigs. Dead wood and cankers should be pruned from the trees during the dormant season—which means NOW!!!

When pruning and removing infected wood, make pruning cuts at least 10 inches beyond the last point of visible infection. DORMANT PRUNING DOES NOT REQUIRE STERILIZATION OF CUTTING TOOLS. Destroy the branches you remove since oozing bacteria can be spashed back onto the tree in the spring from the culled branch sections left on the ground.

 

Click on image to enlarge

Fireblight on
ornamental pear

Fireblight on crabapple

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service