The Pro Farmer

How to treat downy mildew

It’s a fungus attacking cucumber, melon, pumpkin and squash, severely.

Severe infestation of downy mildew on cucumber leaves

It appears in high humidity conditions, as small chlorotic lesions.

Yellow spots on the upper side of the cucumber leaf are a symptom to downy mildew fungus on the backside
symptoms of downy mildew on melon leaf

In cucumber it’s defined on the lower side by the leaf veins.

Black fungus downy mildew colonies, between the veins, on the backside of a cucumber leaf
Downy mildew on basil leaves

They continue to expand until the leaf dies.

Expanding necrotic lesions caused by downy mildew on cucumber leaves

If you are using head irrigation with sprinklers,

you are increasing the chance of the appearance and spreading out of this fungus.

If you can, it is better to use drip irrigation.

It is recommended to use at least 3 kinds of different pesticides,

and alternate between them every 4 days, in order to overcome pest’s resistance,

and completely exterminate them.

For further information about this, read this post , and this post also.

There are 2 ways to eliminate downy mildew: Chemical, and organic.


Best pesticides for downy mildew,

Active ingredients:

Fosethyl Aluminium


Copper sulfate –

It is an inorganic compound that combines sulfur with copper.

It can kill bacteria, algae, snails, and fungi.

It controls fungal diseases by damaging enzymes and proteins critical to fungal growth.

It has been registered for use as pesticide product in the United States since 1956.

Hydrogen peroxide –

Well known as an ingredient in disinfectant products, it’s now also approved for controlling microbial pests, on crops growing indoors and outdoors, and on certain crops after harvest.

This active ingredient prevents, and controls bacteria, and fungi by destroying essential components of the cells.

Neem oil –

A naturally occurring pesticide, found in seeds from the neem tree.               

Azadirachtin is the most active component here.                                                         

It reduces insect feeding and acts as a repellent.

It also interferes with insect hormone systems, making it harder for insects to grow and lay eggs.

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