Fireblight! Now is the time to prune
out last year's infected branches!
Gail Ruhl, Senior Plant Disease Diagnostician,
Director, Department of Botany & Plant Pathology, Purdue
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.