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Hydrangea Powdery Mildew


Hydrangea Powdery Mildew

Usually appear in

Spring to Autumn.

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Caused By:-     The Fungus Microsphaera polonica


Powdery mildews are one of the most widespread plant diseases. They affect virtually all kinds of plants from cereals and grasses, to fruit trees, and broad-leaved shade trees.
The symptoms are usually the same or very similar regardless of the specie of fungus and plant host and the fungi needs living tissue in order to grow.
With Hydrangea the fungus is Microsphaera polonica. Eventually the entire leaf branch or stem may be covered in the fungus. In some cases the fungus causes yellowing(chlorosis) of infected tissues, but eventually the infected tissues dies and becomes brown. 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. Although it usually is not usually fatal, the infected plant may become extremely unsightly and is weakened. The fungus overwinters as growth in buds, on fallen leaves or as spores inside a chasmothecia which eventually breaks down to release the spores.
Powdery mildews are usually host specific, which means they do not spread to other types of plants. There are many types of Powdery Mildew fungi and they all produce similar symptoms on stems, leaves and buds. Infected leaves may become distorted, turn yellow with patches of green, and fall prematurely, stems and twigs may collapse and die and infected buds may fail to open.
The disease is usually observed on the upper sides of the leaves with a whitish fungal growth developing on the leaf surfaces in patches which eventually coalesce to cover the leaves, stems or buds. The infected areas dies or may become soggy.
The severity of the disease depends on several factors such as variety of the host plant, age and condition of the plant, and is especially severe in warm, dry climates. This is because the fungus does not need the presence of water on the leaf surface to infect it. However, if the relative humidity is high the problem will be worse, but it does not tend occur when leaf surfaces are wet. Therefore, 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.
See also these other Powdery Mildews Apple, Begonia, Oak, Pansy, Pea, Phlox, Powdery, Quince, Rose.
See also Downy Mildews Brassica, Downy, Hebe, Lettuce, Onion, Pansy, Pea.
See also other Mildews American Gooseberry, European Gooseberry, Gooseberry.


The best method of control is good hygiene and growing conditions, plenty of sun and a good airflow, as many fungicides are ineffective in getting rid of most Powdery Mildew.
Choose a fungicide which specifically says it combats Powdery Mildew.
When spraying spray above and below leaves.
Prune out severely infected branches and burn.
This fungus is encouraged by stagnant air around the branches and leaves. 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.
Spray as soon as it is seen which usually stops the infection.
Potassium sulphide used at a ratio of 60g to two gallons of water and repeated every ten days is said to be much more effective as a fungicide than many other propriety fungicides.
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.
This fungus overwinters on the fallen leaves so good hygiene, by raking up fallen leaves, will usually prevent this disease. Dry conditions may make this disease more capable of attacking gooseberries therefore keep the soil around the roots moist by the use of a mulch.
The asexual spores are wind blown as will as water splashes. There are resistant varieties that can be grown.

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