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Apple Powdery Mildew



P_apppowmildew1

Apple Powdery Mildew

Usually appear in

Spring to Summer


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Caused By:-     The Fungus Podeosphaera leucotricha

Description

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.
With Apple Powdery Mildew, which also attacks Pears and other similar trees, the young leaves or flowers which breaks from buds infected the previous year does not reach full size and dies prematurely.
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.
picture by Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org.
See also these other Powdery Mildews Begonia, Hydrangea, 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.


Control

Improve circulation by pruning and keep the tree growing healthily with adequate water and mulching to conserve water as dry conditions exacerbate the conditions.
A winter tar wash may help as this fungus overwinters in the buds.
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.
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.
Succulent tissues are more susceptible to infection.
Once the disease is a problem, avoid late summer applications of nitrogen fertiliser.



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