Watch out for fungal diseases


Summer and early autumn are peak seasons for fungal diseases, especially if humidity levels are high and showers are frequent. Most fungal diseases are very host specific (a certain disease only affects a particular type of plant) and all are spread by means of tiny, dust-like particles called spores. Here are some of the most prevalent to look out for:

Powdery mildew (pictured)

The name refers to the powder-like coating that develops on the leaves and stems. Powdery mildew is a particular problem with cucurbits, the members of the cucumber/pumpkin family, but can attack a wide range of other plants, including roses. Control mildew on vegies with Yates Lime Sulfur. Use Yates Rose Shield Insect & Disease Spray on ornamentals.

Soft, sappy growth is the most likely to be attacked by mildew, so cut back on heavy watering and reduce applications of nitrogen-rich fertilisers. Instead, choose a fertiliser that’s high in potassium, because potassium is the nutrient that builds up resistance to disease. Thrive Flower & Fruit, for example, not only promotes blooming but gives the plant a good dose of potash.


The fungal disease rust has nothing to do with the breakdown of old iron, but is named for the rust-like pustules that develop on the leaves. Certain plants are more susceptible to rust problems than others. Frangipani rust, a relatively new arrival in Australia, can be treated with Yates Rose Shield Insect & Disease Spray.

Black spot

Black spot is best known as the number one spoiler of rose leaves, but various versions of black spot attack other plants. A severe case of rose black spot will cause leaf drop and subsequent weakening of the plant. Use Yates Rose Shield Insect & Disease Spray.

Root rot

Root rot, where the root system becomes infected and rotten, is usually associated with overwatering, poor drainage or prolonged wet spells. Once established, the disease is almost always lethal and an affected plant may die suddenly for no clearly obvious reason. Often the disease is caused by a pathogen called Phytophthora, which travels through the soil water. Plants from dry climates should always be grown in well-drained conditions, which may mean planting them either in a container or a raised bed.

Use Yates Anti Rot regularly (say, twice a year) to protect susceptible plants such as avocadoes, citrus, daphne and dry-area natives.

Controlling fungal diseases

Prevention of fungal diseases is better than cure, so try to avoid the conditions that promote disease. Water plants in the morning, rather than the evening, so that the leaves stay as dry as possible. Have suitable plant fungicides on hand to combat disease as soon as it appears. Some products – e.g. Yates Rose Shield Insect & Disease Spray – contain a systemic fungicide and will treat existing disease. Other fungicides, such as Fungus Fighter and Lime Sulfur, are better regarded as protectants that stop diseases from spreading.


This area is for general comments from members of the public. Some questions or comments may not receive a reply from Yates. For specific gardening advice visit Ask an expert Alternatively you may wish to contact us.