Agriculture Reference
In-Depth Information
Management
•
Plant resistant varieties, such as Delicious, Firmgold, Gala,
Golden Delicious and Royal Gala. Avoid susceptible
varieties, such as Granny Smith and Jonathon.
Apply recommended fungicides during dormancy and
the growing season.
•
Remove diseased twigs and terminals in winter during
pruning and diseased blossom trusses in spring.
•
Remove heavily infected leaves, twigs and fruit during
the season to increase the effectiveness of fungicides and
reduce the potential for the development of fungicide
resistance.
•
Fig 3.28 Powdery mildew on a young apple leaf.
Reduce vegetative growth during autumn to help reduce
spread (secondary infection of powdery mildew can only
occur on very young tissues).
•
Infection is favoured by high relative humidity and
temperatures between 19°C and 25°C. The risk of infection
decreases as summer temperatures rise; mildew spores are
short-lived at temperatures above 28°C. Further outbreaks
can occur during autumn when favourable cool conditions
return.
RIPE FRUIT ROT OF APPLE
■
Cause
The fungus
Neofabraea alba
(previously
Pezicula alba
).
Importance
This is a serious disease, particularly in susceptible
cultivars in dry seasons. Powdery mildew reduces vigour,
yield and fruit quality. It is very severe in orchards where
minimal winter pruning retains diseased twigs and
terminals on trees.
Symptoms
On fruit, brown, pinpoint-sized spots develop slowly and
become black and sunken with creamy white spore masses in
moist weather. This fungus is often confused with bitter rot.
Source of infection and spread
The fungus survives in fruiting bodies in cankers formed
on branches and twigs. It is spread by spores released
during cool, wet or humid weather. The fungus also
survives on diseased fruit left on the orchard f loor.
Fig 3.29 Fruit scarring caused by a powdery mildew infection
in the developing fruit.
Fig 3.30 Ripe fruit rot appears as sunken spots containing white
masses of fungal spores.
