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Downy Mildew;
Downy mildew is a fungal disease that is unrelated to powdery mildew see below and only affects outdoor vines
It is spread by wind, but needs water on the leaves e.g rainwater / dew to infect the plants
The symptoms are white patches of fungus that appear on undersides of the leaves,this is seldom serious in the UK, which is fortunate as no control is available.
Grey mould;
The spores unlike powdery mildew spores grow on dead plant material.
Meaning good hygiene around the plants is often the best control i.e. keep the area around the plant/s free from dead leaves and detritus, particularly if the plants have been affected by powdery mildew.
The symptoms initiated by airborne spores are seen as fluffy fungal growth on the fruit.
There are no fungicides available to the amateur gardener to control this disease, but by using the treatment suggested for powdery mildew, damage can be minimized.
Reducing the humidity around the plants can also help to keep the number of spores down.
Powdery mildew.
Grapes grown under glass are the most susceptible to Powdery mildew.
During the winter months spores dwell in fallen leaves or on the vines, then in spring these are spread by the wind / draughts to infect the new emerging leaves.
The fungus is seen as white powdery patches on the leaves and like rust, only lives on living tissue.
The general health of the plant/s deteriorates affecting the yield and quality of the fruit to the point that it can split and become infected by grey mould.(see above)
To control the problem always keep the vines moist and well ventilated at all times during the growing season.
Drought conditions can stress the plants and make them more susceptible the disease.
The only fungicide available to gardeners is sulphur dust, which can be difficult to apply effectively overhead.
Shanking
This is a disorder generally affects grapes grown under glass
The symptoms are shrivelled fruit that fails to ripen and has an unpleasant flavour.
This problem is caused by poor root systems.
For example ;
plants should never be allowed to become pot bound.
they should never be overwatered as this can cause water-logging, over compaction and / or, it may wash out the soil nutrients
Foliar feeding and careful soil improvement is the only control.
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