PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Wood rots
Scientific name
Several orders of the Phylum Basidiomycota, eg
Heart rot (Schizophyllum commune)
Pink limb blight (Corticium salmonicolor)
Red wood rot (Pycnoporus coccineus)
Yellowish wood rot (Trametes versicolor)
Many other species, eg Fomes, Phellinus, Poria,
Ganoderma, Peniophora, Lenzites
Keane et al (2000) described comprehensively wood,
stem and butt rots of eucalypts.
Host range
Most have a wide host range and can attack ageing
ornamental, native, forest and fruit trees, sometimes
found on younger trees. Many can also attack and
reproduce on dead branches, fallen logs.
Symptoms/Damage
General. Infected trees may live for many years but
eventually they die or blow over during storms and
temperature extremes due to internal rotting wood
which structurally weakens the tree. Check that the tree
will not cause any physical damage if it falls.
Trunks.
Older decaying trees may drop branches, break or
shatter without warning in gales or storms endangering
life and property. Inspection may indicate wood rot.
External symptoms include:
– Die-back of twigs, branches or the whole tree.
defoliation, lack of vigour (which could also be
caused by root rot, insect attack or mismanagement).
– Fungal fruiting bodies may develop on outside of
affected limbs and trunks, usually during autumn or
winter, one to many years after infection. They may
be the only indication that there is a well established
wood rot infection (Fig. 202). They vary in colour
and size depending on the species. Common names of
wood rot fungi often describe the type and colour of
fruiting body (or rot) produced, eg white rot, pink
limb blight. Fruiting bodies may be annual or
perennial and ‘mushrooms’ or ‘toadstools’.
White
yellowish
wood rot
(Polyporus
versicolor)
Some fruiting bodies
Internal decay
Fig. 202. Fruiting bodies and internal
decay of some wood rotting fungi.
Internal symptoms. Soft wood, no structural
strength, when dry is extremely light in weight.
– Rotted wood when dry is soft and very light in
weight. Any exposed woody tissue is readily
attacked by wood rot fungi and, once infection
becomes established, a tree has no protective
mechanism to stop the rot. Wood decay generally
spreads longitudinally within the trunk mainly
because this is the way of ‘least resistance’. The
extent and exact location of the decay within a trunk
depends on the species of wood rot fungus and the
species of tree attacked.
– Some wood rotting fungi, eg Schizophyllum,
are weak pathogens and are usually only important
in older neglected trees.
– In living trees most wood rots are confined to
older central dead wood (heartwood). Depending
on the part of the tree attacked, wood rots are also
called root, butt or stem rots.
– Brown rots decompose cellulose causing a brown
rot with a cubical pattern of cracking and crumbly
texture. They preferably attack softwoods, eg
conifers. White rots decompose cellulose and
lignin, reducing wood to a pale spongy mass. They
preferably attack hardwoods normally resistant to
brown rot fungi.
– Termite damage often follows fungal decay on old
living trees (page 178). There are exceptions.
Potting mixes/lawns.
Wood rot fungi may grow on improperly composted
material in potting mixes (page 391, Fig. 212). The
fungi are not parasitic on the plants in the pots.
Similarly fungi growing on chips and bark used for
mulches, feed on organic matter in the soil and are not
parasitic on plants.
Diagnostics.
All assessments of large trees should be carried
out by a professional arborist to avoid confusion with
possible borer or termite damage (page 178, Table 35).
As a generalization an arborist can get some indication
of the health of a tree from external symptoms and
‘sounding’ the tree, eg
– External signs of decay may include dieback and
fruiting bodies which may be easier to see during
winter on deciduous trees.
– A composite hammer is used to ‘sound’ trees as
this can indicate if there is a hollow and some idea of
how big the hollow is.
– As a generalization, if a problem cannot be seen
or sounded then it is not an important factor in tree
failure. If it can be seen or sounded then the
principle of Visual Tree Assessment (VTA) must be
engaged to see if hollows are likely to cause failure.
Visual Tree Assessment (VTA) is the method of
evaluating structural defects and stability in trees
including the detection and extent of decay in older trees
(Matheny et al. 1994).
Many tools are available to assist with tree assessment
in certain situations, eg
– Internal diagnosis of decay. Resistographs are
invasive and involve drilling a small hole into the
trunk. The drill hole may pass through both sound and
decayed wood. The small drill holes with remaining
sawdust create a highway for spread of fungal decay.
Older types of drilling equipment were better because
the holes were large and not full of sawdust. Not
commonly used to diagnose internal diagnosis of
decay. Some arborists refuse to use it on trees that are
not definitely being removed.
– Picus sonic tomography is non-invasive and
measures the structural integrity of trees and extent of
fungal invasion. Variations in the velocity of sound in
the tree’s wood measure density and elasticity.
– Electronic fracture meters can conduct accurate
wood strength testing of trees on site.
– Ground penetrating radar technology scans tree
roots 3-5m deep in soil which can used in saving trees
on construction sites by locating roots before design.
– Chlorophyll Fluorescence Analyzers are suitable
for large scale screening of trees in the field for
diagnostic research and teaching applications.
– GPS and GIS computer equipment can map assets.
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Fungal diseases - Examples of fungal diseases 361