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Phomopsis cane, leaf spot, and fruit rot is widely distributed
in vineyards. The disease can weaken vines, reduce yields, and lower
fruit quality.
Symptoms
This disease was often the first disease of the growing
season to appear in the vineyard. Infected rachises and shoots develop
black, elongated lesions that often split the green tissue. Numerous
lesions give the surface a blackened, scabby appearance. Leaf lesions
often are numerous with brown or black-brown coloration and become
covered with black, pimplelike fruiting bodies. These infections
usually do not become visible until late summer. When infections
on shoots are numerous, they often run together and form dark blotches
that crack. Cluster stems can blight and become brittle if infections
are high. These clusters usually break and the fruit is lost. This
fungus also causes a fruit rot. Infected fruit will turn brown,
shrivel, and eventually drop. In winter, cane infections can be
observed.
Phomopsis Symptoms on Cane and Fruit
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Disease Cycle
The disease is caused by the fungus Phomopsis viticola.
The fungus overwinters in bark and leaf petioles. Black fruiting
bodies of the fungus overwinter in infected canes and rachises.
During early spring rains, spores ooze from fruiting bodies and
are rain splashed onto susceptible young tissue. Shoot and leaf
lesions appear within 3 to 4 weeks after infection but do not form
new spores until the following year. Rachises are susceptible from
the time they first become visible until after pea-sized fruit have
formed. Fruit infections occur primarily from bloom through shatter,
then remain dormant until just before harvest. Thus, severe fruit
rot can develop at harvest if the bloom period is very wet and fungicidal
protection is not provided, particularly in high-risk vineyards.
Disease Management
Phomopsis cane, leaf spot, and fruit rot becomes a problem when
the fungus is allowed to build up on dead canes in the vines. Diseased
canes should be removed during pruning to reduce inoculum. The need
for fungicidal protection programs on susceptible cultivars is heavily
dependent on the level of inoculum within the vineyard and rain
intensity. Because inoculum remains viable in canes for several
years, hedged vineyards are particularly at risk of incurring economic
losses, especially if rachis or fruit infections develop.
Cane blight and leaf spot can be controlled by a combination of
sanitation and fungicide applications. At pruning, remove dead and
diseased wood. Destroy prunings and debris by burning, burying,
or plowing them into the soil. The cane and leaf infections can
be prevented by one or two early season fungicide sprays. The amount
of new shoot infections the previous two years, combined with prolonged
rainy periods the current year, are indications for the need of
one or two fungicide applications. The period from bloom through
fruit set is a critical time to protect against fruit infection
under wet conditions. Fruit and cluster stem infections occur from
bloom until the fruit are pea size. Regular fungicide applications
are necessary to prevent disease. No registered fungicide provides
postinfection control.
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