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American Gooseberry Mildew


American Gooseberry Mildew

Usually appear in

Spring and Summer

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Caused By:-     The Fungus Sphaerotheca mors-uvae


There are two mildew that affects gooseberries and related plants as well as Botritis fungi. One is the American(Sphaerotheca mors-uvae) and the other is the European(Microsphaera grossulariae). American Gooseberry Mildew is a much more vigorous fungal disease produces a whitish grey powdery fungal growth that appears on new shoots and quickly spreads to the upper surface of younger then older leaves. The shoots and leaves become distorted and die off. The infected berries turn from a white mould to felty brown as it ages. It can be scraped off an eaten, but the quality of the fruit is severely affected.
Eventually the whole shoot dies from the fungus-like organism which lives on and in the tissues whilst extracting nutrients.
When the infected leaf tissues eventually die, it forms resting spores in the dead material which will then contaminate the soil. If it is sprayed in the early stages only some of the tissues will die and the leaves will be scarred. The youngest leaves and shoots are especially susceptible to the fungus. The white growth on the leaves are the spores which are carried by the wind or plashes from watering.
The fungus overwinters on fallen leaves or as spores inside a chasmothecia which eventually breaks down to release the spores to infect other plants.
Some Mildews are usually host specific, which means they do not spread to other types of plants. There are many types of Mildew fungi and they all produce similar symptoms. Infected leaves may become distorted, turn yellow with patches of green, and fall prematurely, stems may collapse and die and infected buds may fail to open.
The disease is usually observed all over the leaves and stems with a whitish fungal growth in patches which eventually coalesce to cover the leaves, stems or buds which eventually dies.
The severity of the disease depends on several factors such as variety of the host plant, age and condition of the plant.
It is especially severe in cool humid climates and needs wet weather to moisten foliage for up to 8 hours in order for the spores to germinate and infect plants. Therefore if the relative humidity is high the problem will be worse. Crowded plantings where air circulation is poor damp and in shaded areas makes the problem worse. Young growth usually is more susceptible than older plant tissues.
Infected tissues are often colonised by grey mould like Botrytis cinerea and this can lead to further rotting.
See also other Mildews European Gooseberry, Gooseberry.
See also these other Powdery Mildews Apple, Begonia, Hydrangea, Oak, Pansy, Pea, Phlox, Powdery, Quince, Rose.
See also Downy Mildews Brassica, Downy, Hebe, Lettuce, Onion, Pansy, Pea.


This fungus is encouraged by stagnant air around the branches and by excessive use of high nitrogen fertilisers which will only generate soft new growth that's prone to infection. Therefore keep the growth of the plants as open as possible allowing a good airflow through the plants. When planting new bushes, choose an open, sunny spot and do not overcrowd them.
Cut out and burn infected shoots. This fungus overwinters on the branches and in the buds therefore a winter spray wash is helpful.
Potassium sulphide used at a ratio of 60g to two gallons of water and repeated every ten days until the fruit is nearly mature is said to be much more effective as a fungicide than many other propriety fungicides.
Weekly preventative sprays of baking soda( 1 tablespoon of baking soda a few drops of washing up liquid to 1 Gallon of water) makes an inexpensive control for powdery mildew on plants. Once the infection has taken hold baking soda offers only minimal benefits.
Some plants can be burnt by the baking soda therefore test before use on specific plants.
Spraying with a mixture of baking soda(sodium bicarbonate) or potassium bicarbonate combined with a lightweight horticultural oil is said to cure and prevent the problem.
Keep the soil around the roots moist by the use of a mulch. When planting new bushes, choose an open, sunny spot and do not overcrowd them.
The spores are wind blown as will as water splashes.
There are resistant varieties of gooseberry that can be grown.

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