Agriculture Reference
In-Depth Information
time your sprays in relation to wetting events.
Fire Blight
Fire blight is caused by a bacterium that attacks many pome fruits and
is a serious challenge to orchardists. The bacterium is particularly serious
with pears and quince, and it can also be a serious problem for apples, may-
haw, medlar, and saskatoon. Fire blight also infects apricot, cherry, plum,
crab apple, raspberry, blackberry, strawberry, chokeberry, cotoneaster, pyr-
acantha, mountain ash, photinia, potentilla, roses, and other members of
the rose family. The pathogen attacks the flowers, leaves, fruits, stems, and
trunks. Infected trees, particularly young trees, can be killed. The bacterium
overwinters in cankers on infected stems and trunks.
Fire blight is easily spread in splashing rain or irrigation water, on bees
and other insects, and on pruning tools. Infection usually occurs through
young flowers, but the pathogen can also infect young shoot tips and leaves.
Wounds offer excellent entry sites for the bacterium. Infection only occurs
when temperatures are 65°F (18°C) or greater and the humidity is at least 65
percent or the plant tissues are wet. In western North America, fire blight is
not usually a serious problem except during unusually wet growing seasons.
In eastern North America, fire blight is a common problem.
The increased use of fire blight-susceptible varieties in commercial orch-
ards has increased disease problems. Most commercially important pear
varieties are susceptible to fire blight, especially 'Bosc'. Apple varieties res-
'Enterprise', 'Goldrush', 'Jonafree', 'Liberty', 'Melrose', 'Northwestern Greening',
'Nova Easygro', 'Prima', 'Priscilla', 'Pristine', 'Quinte', 'Red Delicious', 'Red Free',
'Sir Prize', 'Sundance', and 'William's Pride'. Moderately resistant pear variet-
ies include 'Kieffer', 'Magness', 'Moonglow', 'Harrow Delight', 'Honeysweet', and
'Blake's Pride'. Fire blight resistance in other fruit crops is not well documen-
ted.
