Agriculture Reference
In-Depth Information
17
STONE FRUIT
The main stone fruit crops grown in Australia are peaches
and nectarines
(Prunus
persica
), apricots
(P. armeniaca),
plums (
P. domestica
) and cherries
(P. avium)
. All are
members of the Rosaceae family.
The major production areas are the Goulburn Valley
in Victoria, the central west of New South Wales, the
Riverland area of South Australia, Sunraysia in Victoria
and the Granite Belt of south Queensland. In central-
western New South Wales, Young produces nearly 50%
of the Australian cherry crop.
Stone fruit are propagated by budding varieties onto
rootstocks.
The fungal disease brown rot is the most serious disease of
stone fruit, while several bacterial, fungal and viral pathogens
require good crop management to minimise losses.
BACTERIA
BACTERIAL CANKER (BACTERIAL BLAST)
■
Cause
The bacterium
Pseudomonas syringae
pv.
syringae
or
P
.
syringae
pv.
morsprunorum
.
Symptoms
The disease can affect most parts of the plant including the
trunk, branches, shoots, buds, f flowers, leaves and fruit.
Leaves: the bacteria infect young leaves causing water-
soaked spots that turn brown with age, separate from the
surrounding tissue and drop out, giving the leaf a shot-hole
appearance. Other symptoms include thin, narrow, often
rolled yellow leaves, particularly on peach and plum trees.
Fig 17.1 Bacterial canker on a twig in early summer causing new
growth to wither and die.
Branches: circular to more elongated cankers form on the
limbs and trunk. The bark is killed, and when removed, the
underlying tissue is orange to brown in colour, and often
has a strong, sour smell. The cankers often exude large
amounts of gum, especially in winter when the cankers
are most active. Dead areas of tissue become sunken as
surrounding areas of healthy tissue continue to grow, giving
a typical canker effect. This can appear similar to other
bacterial stone fruit diseases, such as bacterial spot.
Shoots: young shoot growth wilts, turns brown and dies
back from the tip. Sunken spots (cankers) may develop on
twigs and production of gum is common.
Buds: dormant buds become brown and fail to break. Behind
the bud an area of dead tissue develops on the shoot. This area
may be sunken and appear brown and damp underneath.
Flowers: infected f flowers turn brown and die. These
symptoms can be confused with brown rot. If fungicides
do not control these symptoms, the cause may be canker.
In susceptible cherry cultivars, whole trees or limbs may be
killed at any stage of growth. In peaches, cankers may not
be visible externally but weaken the tree throughout its life.
