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Pea Powdery Mildew



P_peapowmildw

Pea Powdery Mildew

Usually appear in

Summer to Autumn


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Caused By:-     The Fungus Erysiphe pisi

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.
The fungus “Erysiphe pisi” causes powdery mildew of peas and beans. This fungus causes white powdery patches to appear mainly on both sides of the older leaves and stems of plants.
Eventually the whole leaf or stem dies from the fungus-like organism which lives within the tissues of the leaves whilst extracting nutrients.
Heavily infected leaves become yellow, then become dry and brown, before dropping off with a corresponding loss or reduction of the pea crop. The pods are covered with white patches which may develop purplish spots and become distorted.
It usually appears in July to August and is associated with the weather conditions at that time. Dry warm days from this time seem to start it off first on the foliage and eventually on the pods.
When the infected leaf tissues eventually die, it forms resting spores in the dead material which will then contaminate the soil. This disease can not grow in the absence of living plant tissues.
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.
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 Gerald Holmes, Valent USA Corporation, Bugwood.org.
See also these other Powdery Mildews Apple, Begonia, Hydrangea, Oak, Pansy, 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

Attacks of powdery mildew start in dry seasons and are worst in sheltered humid gardens.
Plants with a rich soil is less likely to be attacked by this fungus, but too much nitrogen allowing soft growth and poorly fertilised soil increase the likelyhood of attack by this fungus.
Plant early-maturing cultivars and keep the plants well watered as these are ready for harvesting before the dry spell which tend to initiate an attack.
There are resistant varieties which will help reduce the disease.
Remove infected leaves as soon as the discolouration on the upper surface is seen. This will prevent infected leaves from contaminating the soil. Also reduce humidity wherever possible. If possible do not grow pansies on the same site in consecutive years.
Spraying with fungicides is often ineffective as the infection is within the leaves therefore the only fungicides that may have an effect is a systemic type.
Baking Soda, Bicarbonate of Soda, is said to be preventative treatment for most any fungal infection, and is not harmful to the soil. It works best in the early days of infection, and should halt downy mildew. Dilute about 6 teaspoons in a litre of water, and spray on, covering the whole plant, and even the soil around. re-spray after 2 weeks, as a further preventative measure.
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.



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