Agriculture Reference
In-Depth Information
established, and disease prevention is the best means
of management.
Avoid tree damage, especially during autumn, and protect
trees from wind-driven rain.
In badly affected orchards, avoid pruning in winter when
cankers are active. Instead, prune after harvest, well
before leaf fall, or in late winter, up to budburst.
Disinfect secateurs (using bleach or alcohol) frequently
during pruning, at least between every tree.
When pruning discrete cankers, ensure the cut is at least
15 cm below the visible lesion. Disinfect secateurs or
saws before cutting into clean tissue.
Apply wound paint to large pruning wounds.
Fig 17.2 Sunken canker associated with gumming on a limb. The
lesion area is sunken compared with healthy tissue.
Spray with the recommended copper bactericides
as registered in each state. In susceptible stone fruit
cultivars, winter spraying before and after pruning
is essential.
The disease can also cause death of young stone fruit
plants. There is often extensive suckering after infection.
Fruit: sunken spots with dark centres may occur on fruit,
particularly cherries. Sometimes underlying gum pockets
are also present.
Remove and dispose of severely affected trees well away
from the orchard.
BACTERIAL SPOT
Source of infection and spread
Bacterial canker is favoured by wet, windy weather in
autumn and early winter before and during leaf fall.
Damage to trees and limbs during this period increase
the risk of infection.
Cause
The bacterium Xanthomonas arboricola pv. pruni
(previously Xanthomonas campestris pv. pruni ).
The bacteria overwinter in the cankers on twigs and
limbs. In spring, large numbers of bacterial cells are
produced and are spread during wet, windy weather.
Twig infection commonly occurs through leaf scars in
the autumn. The bacteria may be spread in infected buds
used for budding.
Symptoms
In Australia, bacterial spot symptoms are found on buds,
leaves, stems and fruit of apricots, nectarines, peaches and
plums.
Buds: expanded buds become blighted and may fail
to unfurl.
Importance
Bacterial canker is a serious disease of all stone fruit grown
in high spring/summer rainfall production districts in
Australia. The level of damage caused ranges from reduced
yields to tree death. Cherries are particularly susceptible,
especially when grown on deep, sandy soils. The disease
also causes losses in apricots; peaches, plums and
nectarines are less affected. Management is difficult.
Leaves: leaf spots appear in spring as greasy or water-soaked
angular areas, partly confined by leaf veins. Spots dry to a
light tan, then darken with age and become dark brown to
black. As the leaves expand, diseased tissue separates from
the surrounding healthy tissue and may drop out to give a
shot-hole symptom. This is easily confused with fungal
shot-hole caused by the fungal pathogen, Wilsonomyces
carpophilus , or symptoms of copper phytotoxicity. The
bacterial disease can usually be recognised by the oily sheen
and sharp angles of the young lesions.
The spots often join, and where infection is heavy, affected
areas become pale yellow-green or reddish. Extensive
spotting results in ripping and tattering of the leaves.
Premature defoliation may occur.
Management
Avoid planting apricots and cherries in orchards prone
to bacterial canker.
Plant only vigorous, disease-free trees from a reliable
source. All bacterial diseases are diffi cult to control once
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