GRAPE - Diseases of Fruit Crops in Australia - page 139

Importance
Grapevine rust has a wide distribution throughout the
tropics from India to Indonesia and in Florida and
several countries of South America. Although
considered a disease of the tropics and subtropics, the
pathogen also occurs in northern temperate regions,
including Japan and North and South Carolina in the
United States. It was first found in Darwin in 2001 but
has since been eradicated from Australia.

Fig 9.22 Grape rust pustules on a leaf showing light (left) and
severe (right) infection.

What to do if you suspect leaf rust
This pathogen is a biosecurity risk to Australia. Any
suspected affected plants should be reported to the
nearest Department of Primary Industries or the Plant
Health Australia hotline [phone]).

fungal threads (mycelium) in buds and as spores
(urediniospores) on green tissue. The spores are dispersed
by wind and are produced more abundantly in warm,
humid weather.

PHOMOPSIS CANE AND LEAF SPOT

Symptoms are similar to those caused by black spot, but in
that disease, the black spots are red-brown to deep purple
in colour, up to 4-5 mm in size and do not have a marked,
yellow halo (the latter occurs with Phomopsis).

Cause
The fungus Phomopsis viticola .

On shoots, small spots with black centres develop and
gradually enlarge into brown to black, oblong, scabby scars
that crack as the shoots swell. When girdled near the base,
shoots may break off in the wind or during pruning. Badly
diseased shoots fail to mature, and often are stunted and die.

Symptoms
The characteristic symptoms are bleached internodes on
dormant canes in winter, elongated black cracks and scars
on the lower three to four internodes of green shoots,
which may be stunted and, importantly, on the leaves,
small black spots surrounded by thin yellow halos. The
halos (less than 3 mm wide) surround pinhead-sized dark
brown to black spots, rarely more than 1 mm in diameter.
These are most likely to occur during wet springs and are
more abundant on lower leaves of shoots.

Source of infection and spread
The fungus overwinters as fungal fruiting bodies (pycnidia)
on previously infected canes, spurs or wood. During wet
weather in spring, spores from pycnidia are splashed onto
young foliage where infection occurs. Spots appear three to
four weeks later on the leaves and subsequently on the
shoots. Cool, wet conditions favour the disease. In autumn
and winter, the disease progresses, discolouring infected
areas on canes. Infected canes and spurs may provide
inoculum (the source of disease) for at least three seasons.

Importance
The disease is more common in cooler areas, particularly
when there is cool, wet weather in spring. Yield losses depend

Fig 9.24 Phomopsis cankers are shallower and more elongated than
black spot. Fig 9.23 Phomopsis leaf spot (right) differs from black spot (left).