Agriculture Reference
In-Depth Information
GNOMONIA FRUIT ROT
AND LEAF BLOTCH
Cause
The fungus Gnomonia comari (anamorph Zythia
fragariae ).
Symptoms
Two distinct symptoms develop on fruit. One symptom
pattern is a blight of part or of the whole calyx. A firm,
sunken, off-white to tan lesion develops on the fruit
directly under the affected region. This lesion spreads,
becoming softer with a light margin. Internally, vascular
discolouration develops and a firm, rubbery textured, tan
rot (similar to Phytophthora rot) spreads through the fruit
from the initial lesion.
A second symptom involves small, round, off-white to light
pink, sunken lesions appearing at any point on the fruit
and developing as above.
Fig 18.18 Cut strawberry crown showing Fusarium wilt
symptoms.
Unless an off-white to brown, globose pycnidia (fungal
fruiting body) is formed on the fruit, it is very difficult
to distinguish between the fruit-rot diseases caused by
Gnomonia and Phomopsis .
Use a soil fumigant to reduce disease incidence.
On farms with a history of fusarium wilt, pump
irrigation water from the top of dams, away from the
main water inlet.
Leaf symptoms are very similar to Phomopsis leaf blight,
and it is difficult to distinguish between these two diseases
on symptoms alone. An exception is on the new leaves of
runners imported from southern States. On these plants,
Gnomonia leaf blotch produces a large, necrotic area
affecting about one-third of the leaf let and centering
around the leaf let tip. This dead patch is not surrounded
by a halo or margin.
Clean cultivation implements to avoid spreading
infested soil.
Fig 18.20 Stem-end rot caused by the fungus Gnomonia . Note
the wart-like fungal structures (pycnidia).
Fig 18.19 These two varieties of strawberry are susceptible (left) and
tolerant (right) to Fusarium wilt.
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