Agriculture Reference
In-Depth Information
FIRE BLIGHT - BIOSECURITY THREAT
Fire blight is a destructive disease of apple and pear,
recognised by severe blighting in blossoms, shoots, limbs
and fruit. The numerous diseased shoots make the tree
appeared burned, hence the name 'fire blight'.
Cause
The bacterium
Erwinia amylovora.
Symptoms
Fire blight can affect all parts of the plant:
Blossom blight: f lowers appear water-soaked and grey-
green in infected parts.
Ooze may be present as milky drops on the surface of
infected tissue. Sepals of infected f flowers change from
red to brown to black as the disease progresses.
Leaves and shoots: infected leaves become discoloured
and desiccated, and often remain attached to branches,
even in winter.
Blighted pear shoots are black while blighted apple shoots
are usually a lighter shade of brown. Infected shoots wilt
rapidly and often form a shepherd's crook shape at
their tips.
Fig 3.3 Bacterial ooze in fruit affected by fire blight.
Woody plant parts: symptoms can be difficult to see,
especially on older trees with rough bark. Bark of
infected branches or trunks is sunken and darker than
usual. Initially, the inner tissues are water-soaked, and
can have reddish streaks that turn brown as the disease
progresses. These areas eventually turn into cankers.
Fig 3.2 Symptoms of fire blight on stem and leaves. Inset: note
bacterial ooze.
Fig 3.4 Mummified pear fruit (left) and an advanced lesion caused
by fire blight.
