Agriculture Reference
In-Depth Information
Native and orchard
tree stumps and roots
are colonised by
Armillaria.
Spores produced by mushrooms
can colonise stumps and cause
infection through wounds.
In established infection, thick,
white mycelial sheathing grows
between the bark and the trunk;
this may kill the tree.
Infection is spread by:
1 rhizomorphs,
2 root-to-root contact or,
occasionally, spores
Bark removed to expose fungal
sheeting.
1
2
Fig 2.9 Disease cycle of
Armillaria
species.
irrigated rows. Abundant rhizomorphs then grow around
the roots and through the soil to infect roots of adjacent,
healthy trees.
called rhizomorphs or 'shoestrings', often occur on the
surface of the roots, forming a branched network that may
extend 200 to 300 mm into the soil.
Honey-coloured mushrooms with widely separated gills
can form at the base of an affected tree during wet, cold
weather in early winter.
Management
•
Prepare soil thoroughly before planting new orchards
and vineyards. Preparation involves deep ripping
and cultivation with discs and tines to remove as
many roots and infested root residues as possible.
Thoroughly clear soil in old orchards before
replanting. Where this is not possible, plant resistant
crops into the area.
Source of infection and spread
The fungus can survive in the soil for many years on
stumps and roots. Infection occurs by root contact with
infected plants or more commonly, by rhizomorphs present
in the soil. Rhizomorphs on small, infected root pieces are
distributed by f flowing water or by moving cultivating
implements from infested areas, which is the main source
of infection. Rhizomorphs grow through the soil, attaching
to young roots and infecting the outer root tissues.
Mushrooms of Armillaria do not have a role in the
infection cycle.
A r m i l l a r i a
is common in native vegetation where it can
cause considerable damage. When native vegetation is
cleared for orchards and vineyards, the fungus survives on
decaying roots and stumps of infected plants. Introduced
crops planted into these locations often sustain serious
damage, particularly high-density, irrigated orchards where
vigorous growth of the fungus occurs along the moist,
When re-planting low-density orchards, locate rows
midway between previous orchard rows to reduce the
risk of carryover of infested root residues not removed by
deep ripping and cultivation. For high-density plantings,
replant orchards, construct mound rows with soil that is
free from root residues. This will increase soil volume
that promotes root growth. This improves early tree
growth and allows early recovery of the costs of
management.
•
Use rootstocks resistant to Armillaria when replanting
plum, pear and grape into high-risk areas.
•
Fumigate infested soil with a recommended fumigant.
•
