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Brassica Downy Mildew



P_brassicadnymldw

Brassica Downy Mildew

Usually appear in

Spring to autumn


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Caused By:-     The Fungus Peronospor parisitica

Description

Downy mildews are a common plant disease. They affect virtually all kinds of plants.
Brassicas Downy mildew is a disease of seedlings and also mature plants. It is caused by a fungus Peronospora parasitica which penetrates the tissues under wet conditions and grows out to produce fuzzy whitish patches of spores under the leaves. There is a yellowing of the leaf in patches coinciding with the whitish fungal growth on the underside of the leaf.
This fungus is specific to brassicas including: cabbages, cauliflowers, Brussels sprouts, radishes, swedes and turnips and the wild relatives, including: horseradish, Cheiranthus (wallflowers), Matthiola (stocks), Aubrieta (aubretia) and Capsella bursa-pastoris (shepherd's purse).
Brassica Downy Mildew often occurs together with Brassica White Blister (Albugo candida), another another fungus. The spores resides in plant debris which carry it through winter
Spores are produced on the fungal mycelium early in the season, which are wind or water splash borne to infect other plants or leaves. The effect of this fungus is to reduce the vigour of the plant, which can eventually die.
Spores are produced on the fungal mycelium early in the season, which are wind or water splash borne to infect other plants or leaves.
It is associated with the weather conditions at that time and relative humidity is high the problem will be worse. 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.
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.
Powdery 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 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.
Picture by Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org.
See also Downy Mildews Downy, Hebe, Lettuce, Onion, Pansy, Pea.
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

The best method of control is prevention therefore good hygiene and cultural practices are essential to avoid this disease.
Raking up fallen leaves, placing plants in full sun with pruning that allows good airflow through the plant, Winter tar, oil or fungicide wash and pruning out severely infected branches and burning them will all help in preventing attack from these fungi.
Fungicides are often ineffective and special systemic fungicides will have to be used.
A weekly spray of milk at a concentration of at least 10% (1 part milk to 9 parts water) is said to significantly reduced the severity of some mildew infection.
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.
Mulching the plants should help in preventing many mildews.



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