Beating the problem of the powdery mildew pest
It seems this year’s number one pest is powdery mildew, caused by our very dry spring – here’s how to identify it and treat outbreaks organically without buying expensive products. Powdery mildew is a white film that grows on leaves, stems and sometimes flowers and fruit when there isn’t enough air circulation between plants.
It’s a fungal disease affecting apples, blackcurrants, gooseberries, grapes, brassicas, curcubits, peas, grasses, Acanthus, delphiniums, phlox, the daisy family, honeysuckle, Rhododendrons, Azaleas, roses and oaks.
Each mildew has a narrow range of host plants – the fungus affecting peas is different from the one attacking apples. Symptoms are: White, powdery spreading patches on upper or lower leaf surfaces, stems, flowers and fruit.
Tissues sometimes become stunted or distorted.
Most infected tissues show little reaction in the early stages, but in a few cases, tissue turns dark brown.
Spores produced on both sides of leaves.
It thrives in warm weather when foliage is dry – wind spreads the spores, which can’t germinate or grow when foliage is wet. Organic control: Destroy fallen infected leaves. Mulching and watering reduces water stress. Prune out infected shoots. Try to buy resistant cultivars. Spray weekly with a 10 per cent milk/water solution, upping the concentration to 50 per cent.
Wash off spores early in the day so foliage has time to dry quickly.
One part ethanol-based mouthwash to three parts water but this can damage new foliage.
A mix of 2-3 tablespoons of apple cider vinegar, containing 5 per cent acetic acid mixed with a gallon of water is the dose, but too much vinegar can burn plants.
Garlic spray: Blend two bulbs in a quart of water with a few drops of liquid soap, strain and refrigerate. This makes a concentrated solution that should be diluted 1:10 with water before spraying.
Oils: Vegetable seed oils such as canola can be used, at a rate of 2.5 to 3 tablespoons per gallon of water, plus a quarter-teaspoon of liquid soap to emulsify the oil. Spray every seven to 14 days.
Powdery mildew is often confused with downy mildew but occurs in totally different conditions – but more of that next time!