Agriculture Reference
In-Depth Information
At leaf fall in autumn, bacteria enter leaf scars and remain
dormant until late winter, when buds swell. Bacteria then
spread from the scars and the branch cankers formed in
the previous season.
During spring rain, bacteria are washed from cracks in
branch cankers to the young twigs and foliage, allowing
new branch cankers and leaf spots to develop. Bacteria
invade and kill young, swollen buds, and may blight young
branches. Further spread occurs in spring and early
summer, affecting leaves, twigs, branches and fruit.
Importance
Bacterial spot is a major disease of susceptible stone fruit in
Queensland, and in coastal production areas, particularly
in wet seasons. The disease is also becoming more common
in inland production areas. Japanese plums are most
severely affected, while peaches, apricots and nectarines are
affected to a lesser extent.
Fig 17.7 Lesions of bacterial spot on nectarine (left) and peach (right).
Lesions appear in late spring as circular greasy spots that
become sunken and darken as the fruit enlarges. The
centre of each spot frequently cracks and may ooze gum.
Roughened cork tissue develops on the edges of lesions as
the fruit continues to expand.
The Japanese plum cultivars Doris, Santa Rosa, Red Ace,
Mariposa, Friar and Laroda as well as those imported from
the Californian breeding program are very susceptible.
Some Japanese plums (e.g. Wilson, Narrabeen and
Burbank) appear resistant to the disease, and have been
used in Queensland breeding programs to produce
bacterial spot-resistant, high-quality plum cultivars.
Source of infection and spread
Bacterial spot is favoured by high summer rainfall, high
humidity and moderate temperatures. The bacteria are
spread by rain and wind from diseased trees to adjacent
trees through the growing season, especially during
hailstorms, which damage plants and provide entry points
for bacteria.
European plums, a different species from Japanese plums,
are unaffected by the disease.
Management
Plant resistant varieties.
Plant only vigorous, disease-free trees from a reliable
source. All bacterial diseases are diffi cult to control once
established, and it is important to prevent the disease
from entering orchards, where possible.
Remove nearby wild or neglected Prunus trees, because
they can act as reservoirs of the disease.
Avoid planting new blocks very close to existing blocks
that have the disease.
Plant windbreaks to reduce the chance of disease spread
by wind-blown rain.
Apply copper products as recommended for each region.
Apply copper products after hail damage to reduce
disease levels and prevent build up of inoculum in
wounded tissues.
Do not plant orchards in exposed locations.
Prune diseased wood and twigs, and dispose of the
prunings well away from the orchard.
Fig 17.8 Bacterial spot on a peach.
Search WWH ::




Custom Search