Agriculture Reference
In-Depth Information
Ensure good ventilation and rapid drying of the foliage
by pruning lower limbs so that the canopy is at least
500 mm above the ground.
•
Prune out dead twigs and branches before fl owering.
Remove dead leaves entangled in the tree canopy.
Remove infected fruit from the tree.
•
Control insect pests, such as fruit-spotting bugs and
Queensland fruit fl y, which damage fruit.
•
Do not harvest during wet weather.
•
Handle fruit carefully to avoid damaging the skin.
•
Plant resistant cultivars. Fuerte, Rincon and Wurtz are
more susceptible to anthracnose than Hass.
•
Select a rootstock such as clonal Velvick, which gives a
low N:Ca ratio in the fruit skin.
•
Fig 4.6 Early symptoms of Phellinus infection showing trunk rot
as the fungus advances upwards from the roots.
Postharvest
•
Spray fruit after harvest with a recommended fungicide.
Cool fruit promptly after harvest to 7°C. Lower
temperatures after harvest could cause chilling injury.
Delays of more than six hours before cooling and higher
pulp temperatures will increase anthracnose.
•
Temperature is critical to anthracnose development
during the fruit-ripening stage. Once fruit starts to
ripen, temperatures of 24°C and above will accelerate
development of anthracnose. The fi rst onset of ripening
cannot be detected by the eye or by feel. At the wholesale
level, fruit should be ripened at 16-18°C with the addition
of ethylene to reduce the variation in ripening between
fruit and the amount of anthracnose development. Once
avocados have ripened to an easily detectable softening
stage, fruit may be held between 2°C and 4°C, and as low
as 2
•
Fig 4.7 Advanced symptoms of Phellinus showing a white margin on
the brown, hyphal stocking.
°
C for ripe and ready-to-eat avocados.
BROWN ROOT ROT AND TRUNK-ROT
■
Cause
The fungus
Phellinus noxius
.
Symptoms
Leaves wilt, yellow and become necrotic and trees
eventually die. Decline can be rapid where leaves turn
brown within days and drop. An external cinnamon-
coloured fungal stocking is often present girdling the trunk
at the base of the tree. This stocking may exude a sticky
f fluid, which causes soil to adhere to affected roots and the
lower trunk. When the fungus is growing actively, a broad,
white margin forms at the front of the brown stocking.
Fig 4.8 Bark removed to reveal the margin between healthy and
infected tissue.
