How to combat fungal disease in your vege patch

Lots of our summer plants are being affected by fungal diseases this month — these include tomatoes, potatoes, zucchini, squash, cucumbers and capsicums to name a few.

The highly-prevalent foliar diseases around at the moment are downy and powdery mildew that affect the cucumbers, squash and zucchini families. These appear on leaves and stems as a white powdery substance that spreads rapidly throughout your plants, causing leaves to curl and the overall health and production of the plant to suffer.

Powdery mildew
Powdery mildew is an airborne fungus spread by wind, rain, humidity, yellow and black ladybirds and humans. Preventing its rapid spread is the key, and good hygiene with your tools and hands is very important as it can get on your tools or gloves then spread to the next plant you touch.

Wipe your tools with methylated spirits and wash your gloves regularly. Spray plants with a good organic oil before removing the leaves as this will stick the fungus to the leaf to prevent spreading when the leaf is removed.

Downy mildew
Downy mildew is a different fungus affecting the above plants and is again spread by airborne spores. There are many different types of this fungus and they are plant-specific — so the one attacking your cucumbers is a different species from the one attacking your brassicas. The difference between downy and powdery mildew is that downy mildew can overwinter in your soil waiting for you to plant next spring.

Make sure your plants are well fed and watered as plants that are weak will be affected more.

To make an organic homemade spray for controlling the spread of these fungi, take one tablespoon of baking soda, half a teaspoon of natural liquid soap and four litres of water and mix. Spray this mixture all over your plants — on the leaves, under the leaves and down the stem — on a weekly basis.

Early blight in advance stage on tomato leaves

Blight is a fungal disease that affects tomatoes, potatoes, capsicums and eggplants. It appears as black or brown spots on the older leaves of your plants, and as they grow, round rings will develop and leaves will curl and turn yellowy-brown. Blight will kill the tissue in leaves, stems and fruit, and stunt the growth of your plant. Blight is spread by fungal spores that can be carried by the wind, insects and overhead watering.

Spray the plant with a good oil or soap spray to stick the fungus to the leaves, pull the plant out and discard, but avoid putting it in your compost.

A good way to process your diseased plants is through Bokashi fermentation which I have had great success with to control the above diseases.

This article was published in the New Zealand Herald’s food and wellbeing magazine, Be Well. Look out for my monthly column in the New Zealand Herald’s Monday food and wellbeing magazine Be Well and on

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