As its name suggests, plant rust is characterised by rust coloured spots and irregular discolouration on a plant’s leaves and stems. Rusts are fungal garden diseases and there are many different species affecting a variety of garden and greenhouse plants.
How to spot plant rust
Look at the infected foliage closely and you’ll see dark orange, brown, yellow or red spots or pustules on the undersides of the leaves. These spots can vary in colour according to the rust species and the type of spore that it is producing. These pustules spread to all areas of foliage and sometimes down the stem. The infection can develop very quickly in the right environment and spores will only germinate on wet leaves.
To complicate matters, most garden rust cycles have a latent period, which means the plant can be infected without showing any symptoms for a long period of time.
How to treat plant rust
Remove any infected leaves immediately. However, be careful not to remove too many, as removing them in large numbers is likely to do more harm than good. It is important to move the fallen leaves before they start to decompose. As is the case with many garden diseases, do not compost infected plants.
The plant rust spores spread through the air, so separate infected plants from healthy ones to avoid cross-contamination. Water in the early morning to allow the plants to have a chance to dry out during the day. Water plants from the base, as watering from overhead will cause the spores to be carried back up to the plant by splashing water.
Prevent rust on plants by keeping greenhouses well ventilated and by pruning and thinning plants. Finally, you can use a sulphur-based fungicide but always check the manufacturer’s recommendations for use.