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Pea Downy Mildew



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Pea Downy Mildew

Usually appear in

Spring to Autumn.


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Caused By:-     The Fungus-Like Peronospora viciae

Description

Pea Downy mildew is caused by the fungus-like plant pathogen Peronospora viciae which is worldwide in distribution. It is a fungus-like microorganism which overwinters on diseased plant debris in soil and is most severe on young plants.
The symptoms is greyish white mouldy spore producing growth on the lower leaf surface and on pods, mould may also grow inside pods. Lighter areas appears on the top of the leaf's surface.
Eventually the whole leaf dies from the fungus-like organism which lives within the tissues of the leaves 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. Although with Pansies it is usually usually fatal.
The fungus overwinters on fallen leaves or as spores inside a chasmothecia which eventually breaks down to release the spores to infect other plants.
Downy mildews are usually host specific, which means they do not spread to other types of plants. There are many types of Downy 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 on the under sides of the leaves with a whitish fungal growth 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. It is especially severe in cool humid climates and needs wet weather to moisten foliage for 2-4 hours and a temperatures of 10- 12°C 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 Downy Mildews Brassica, Downy, Hebe, Lettuce, Onion, Pansy.
See also other Mildews American Gooseberry, European Gooseberry, Gooseberry.
See also these other Powdery Mildews Apple, Begonia, Hydrangea, Oak, Pansy, Pea, Phlox, Powdery, Quince, Rose.


Control

Good hygiene is the first line of defence. Always remove all plant debris and allow enough spacing for good ventilation. Burn or destroy infected leaves preferably before the spores are produced. Copper fungicides may give some protection. Spraying with a good fungicide will control this disease, but thorough coverage of foliage is important in the control of downy mildew.
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.
The timing of planting is also a factor in prevention of this disease.
High nitrogen fertiliser produces lush soft growth which is easier for the fungus to infect.
Crop rotation will prevent build up of the the area..
Some varieties of onion sets show some resistance to this disease.



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