Agriculture Reference
In-Depth Information
Reduce humidity within the orchard by pruning trees to
create an open canopy and orienting rows to maximise
breezes.
•
structures (visible with a hand lens) in the centre of older
lesions can be used to diagnose this disease.
Twigs: twig lesions resemble those on leaves, with initially
red spots, developing tan centres and purple edges over
time. Black spore-forming structures can also be observed
on mature twig lesions.
Remove diseased wood and leaves during winter
pruning, and dispose of well away from the orchard.
•
Buds: infected buds turn black and sometimes ooze gum.
Discoloured vascular tissue is seen underneath the affected
buds.
SHOT HOLE
■
Cause
The fungus
Stigmina carpophila
, sometimes referred to as
Wilsonomyces carpophilus
.
Fruit: small, purplish spots become raised and rough with
age, turning into dark brown-purple coloured lesions with
tan centres. Typically, spore-forming structures are not
produced in the centres of older lesions, in contrast with
leaves and twigs.
Symptoms
Leaves: small, circular, red spots enlarge and develop tan
centres with dark red-brown to purple margins. Sometimes
spots have light green-yellow haloes. These spots can fall
out to give a shot-hole appearance. Where many spots
occur together, large, ragged holes result, and premature
leaf fall can occur.
Source of infection and spread
The fungus overwinters on twigs. Substantial levels of leaf
infection in late summer (especially for early harvested
varieties) and autumn can result in increased twig
infections.
Many other diseases can cause shot-hole lesions, including
bacterial spot. The presence of tiny, black spore-forming
In spring, lesions with viable spore-forming bodies will
release spores, which can be splashed onto leaves and fruit
during wet weather. Leaf, twig or fruit surfaces and buds
must remain wet for several hours for infection to occur.
Importance
Shot hole is a common disease that causes leaf yellowing
and premature leaf fall in all stone fruit, but is less severe
on plums. In severe cases, reduced photosynthesis, due
to leaf loss, reduces general tree health, specifically fruit
quality and yield. Infected fruit are unsaleable.
Management
•
Apply recommended fungicides on time during the
growing season. In wet seasons, it may not be possible
to make up for missed sprays.
Fungicides should be rotated according to chemical class,
and a resistance-management plan is essential for
maintaining effi cacy throughout the season.
•
A good orchard hygiene protocol is essential to the
effectiveness of fungicide sprays.
•
Orchard hygiene is essential to reduce the carryover
of this disease from season to season. This requires:
•
-
removing severely diseased branches from affected
trees and applying wound dressings as needed
-
using good orchard ventilation, drip irrigation and
shade minimisation to reduce leaf wetness
Fig 17.24 Symptoms of fungal shot hole.
