PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Disease cycle
See Fig. 203 below.
‘Overwintering’
As mycelium in diseased or dead trees, logs and
stumps, and sometimes as perennial fruiting
bodies. Infected trees, plant debris, stumps.
Spread
Fruiting bodies release spores (basidiospores)
during or soon after rain and are spread by wind,
rain, animals, pruning and harvesting tools to
other trees. Spores lodge on crevices in dead
bark, borer damage, pruning and natural wounds,
germinate, invade the plant and the mycelium
grows slowly through the woody tissue. A tree
has no protective mechanism to stop infection
progressing.
Some wood rotting fungi, eg Fomes can also
enter through roots, others, eg Rigidoporus
muroporus, important in some tropical and
subtropical areas, spread as mycelium in the soil.
Conditions favoring
Any exposed woody tissue is readily attacked by
wood rotting fungi. Wood rot fungi commonly
infect trees through wounds and large dead or
dying branches.
Wounds, eg
– Mechanical injury, wind, stress fractures due to
drought. broken branches in storms, heavy winter
pruning, dead projecting stubs (poor pruning
techniques), re-worked trees, root damage, lawn
mower or whipper-snipper injury.
– Borer damage.
– Butt and stem rots may be associated with termite
tunnels in eucalypts.
– Excavations causing tree root damage, change in
soil moisture.
Environment, eg
– Frost or spray injury may kill twigs.
– Hail may damage limbs.
– Sunburn scalds exposed surfaces, bark is killed and
is an entry point for wood rot fungi. Small trunks
and branches facing west may be scalded by heat
reflection from chip bark. Larger limbs and butts
especially are at risk if they are exposed to the sun
by premature leaf fall following diseases or pests,
drought or unsuitable pruning.
Stress due to drought, poor nutrition and
ventilation, overcropping, waterlogging. Some
wood rot fungi will only attack trees weakened
by root injury or drought.
Ageing trees, eg Ganoderma is mainly a
problem on ageing trees.
Fig. 203. Disease cycle of a wood rot fungus (adapted from Agrios, 1997).
362 Fungal diseases - Examples of fungal diseases