Disease watch: Powdery mildew

Avid gardeners are putting in their zucchini, cucumber, pumpkin, rockmelon and watermelon plants now for the summer harvest. All these plants are susceptible to a fungal disease called powdery mildew, which is better to prevent rather than try to cure.

Powdery mildew looks like white powdery growth on the upper surface of the leaves. The older leaves will turn yellow and go brown and dry. The fruit will eventually be affected and the vitality of the plant goes downhill. The spores are windborn so will spread rapidly through the plant.

You will need to do prevention spraying from seedling stage. There are some sprays you can make yourself or ones such as Ecocarb that are premixed.

Bicarbonate fungicides change the pH of the leaf surface to alkaline. This inhibits the growth of powdery mildew spores, preventing their spread.

You can make your own bi-carb of soda spray by mixing three teaspoons of baking powder in one litre of water and adding a few drops of fish fertiliser to make it stick to the leaf.

Milk is also a good preventive against powdery mildew. Mix one part full-cream milk to five parts water and spray on foliage at fortnightly intervals.

These homemade recipes are purely preventive; once the disease has taken hold, it's a different matter to kill it off.