Agriculture Reference
In-Depth Information
Fig 4.10 Leaf symptoms of Cercospora spot showing angular lesions
on the underside of a leaf (right) and lesions surrounded by halos on
the upper surface (left).
Management
•
Apply appropriate fungicides. Spraying should start
when fl oral buds begin to swell and continue at monthly
intervals until harvest. Inoculum can develop on
prunings and these should be removed from the
orchard.
Do not move nursery trees from the Atherton Tablelands
to other growing regions in Australia.
•
The disease is under active control in Western Australia,
which restricts import of fruit from affected areas by
legislation.
•
Fig 4.11
Cercospora
spot on fruit. The cut-away section shows
sub-surface corking and limited penetration into the flesh.
LAUREL WILT - BIOSECURITY THREAT
Cause
The fungus
Raffaelea laurelensis
.
colonise the galleries that the beetles bore in infested
trees, and larvae graze on the 'lawns' of fungi that
develop. The ambrosia beetles benefit from the fungal
breakdown of indigestible lignified cellulose, and fungi
benefit by being transported to new trees. Laurel wilt is
different in that the beetles attack healthy trees and the
fungal symbiont
R. laurelensis
is an aggressive plant
pathogen. The fungus moves systemically through the
vessels of the tree and causes a vascular wilt disease. The
pathogen can spread in two ways. The beetle can extend
its range by 12-18 km per year, and can also be spread in
infested firewood.
Symptoms
The fungus causes a vascular wilt disease. Symptoms
include wilted stems and leaves, black streaking in the
wood and eventual death of the tree.
Source of infection and spread
Laurel wilt affects members of the Lauraceae. The
pathogen is vectored by the ambrosia beetle
Xyleborus
glabratus
. Ambrosia beetles typically have symbiotic
relationships with fungi they carry in specialised
pouches known as mycangia. As the ambrosia beetles
attack dead or dying trees, their fungal symbionts
Importance
Laurel wilt is present in the south-eastern United States
where it has been observed, often causing extensive
