How to fight Mildew with Neem Oil and a pressure spray bottle

In July we noticed that the maple tree on our terrace was infested with mildew. But that was not enough trouble: the white-mealy leaves of the maple fell into a nearby raised bed and the fungal disease mildew spread to the terrace planting. We take up the fight with neem oil and a squeeze spray bottle.

On a warm day in July, we noticed matte white and floury discoloration on a plant in the flower bed of our terrace. After a short internet research we knew the cause: mildew – a fungal disease that spreads on the leaves of infested plants and can affect the infested plants until they die.

The mildew had attacked the whole maple and spread from here to the lower flower beds.
The mildew had attacked the whole maple and spread from here to the lower flower beds.

The name powdery mildew is a good description of this plant and tree disease. Infested plants look as if the plants have been covered with a mixture of flour and water.

On closer inspection of our terrace planting, we discovered that a large maple tree on our terrace was completely infested. Presumably the spores had spread from here to the raised bed.

If a plant is infested, cutting off the infested parts or treating the plants with neem oil helps. In various forums we also found household remedies such as spraying with milk against the pest. But the latter did not help us. Although we had wasted a few litres of milk, the flower bed smelled unpleasant for a few days, but the mildew remained.

We had to use heavier guns.

Neem oil as natural agent against mildew

Neem oil is a cold-pressed oil of the Indian Neem tree. It has an fungicidal effect, killing fungi and spores and thus combating mildew. Neem oil is usually mixed with water and then sprayed on the infested plants. Supposedly, application in water is also helpful, but we have not tried that. Neem oil does not harm beneficial insects, bees, children or pets.

To dilute Neem oil with water, it is important to use Neem oil that already contains an emulsifier (Amazon Affiliate Link). Because only if the Neem oil is correctly mixed with water can it be reliably sprayed on the plants. Otherwise there is the danger that the plants are only treated with water, but not with enough Neem oil.

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On the other hand, the quantity ratio must be observed: The neem oil-emulsifier mixture should be mixed with water in a ratio of 1:100. Higher dosages can damage the plant. Furthermore, Neem Oil should not be used in direct sunlight or in rain. Otherwise there is a risk that leaves will burn in the sun, similar to normal watering, or that the active ingredient will be washed away.

With spray pressure on the leaves

Gloria spray bottles (Amazon Affiliate Link) are suitable for applying the neem oil mixtures. To be able to spray our almost 3 meter high maple, I had to use a pressure spray bottle. You pump it up with sufficient pressure and thus also master higher or more distant areas of application.

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A small spray bottle (Amazon Affiliate Link) is also sufficient for the ground level flower bed or raised beds.

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We sprayed the infested plants a total of 4 times at intervals of four to five days. We chose days with cloudy weather and little precipitation. After 1 ½ weeks the powdery mildew fell visibly, after two and a half weeks we sprayed one last time and the powdery mildew was history from then on.

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