Weather that oscillates between warm and rainy – like we are experiencing now – provides prime conditions for fungal diseases to set up camp on our garden favorites.
Roses, vincas, and even indoor plants can develop fungal infections, which can usually be identified as dark, sometimes soft blemishes arising from damp or humid conditions.
Of course, disease prevention is optimal, but failing that, there are actions to take to prevent it worstening.
This is why it’s recommended to prune and strip roses in winter, followed up with a dose of lime sulfur spray.
It prevents fungal diseases and other pests, and gives the plant a fresh start, with clean new growth emerging in the spring season.
Of course, not everyone gets around to pruning, or maybe you forget the lime sulfur. Maybe your new growth has caught a fungal problem from a neighbouring plant that you overlooked.
If so, remove any leaves that seem affected, and make sure you remove them from the garden completely.
Unattended fungal infections can be transmitted to other plants by wind or water splash: this is why horticulturalists urge you to water plants directly at the base rather than showering them with water from above.
Commercial nurseries do their best to keep fungi under control, but like any growing industry, disease is easily spread.
Check for signs of rot or mould closely, both in the store and in the garden.
If the plant has black spot (Diplocarpon rosae) – which appears as irregular black dots across a leaf, and causes yellowing in the later stages – spray the plant with mancozeb or, if you're looking for an organic alternative, a bi-carbonate solution or a mix of one parts full-cream milk, ten parts water.
This is also effective for powdery mildew (Sphaerotheca pannosa) which appears as a whitish ‘dust’ on the surface of leaves.
Powdery mildew can also be controlled with copper fungicides, which are sold at most garden stores, and are also effective for downy mildew (dark, often angular blotches on the leaf surface, blue-grey ‘powder’ on the underside) and rusts (orange or yellow splodges on the leaf surface).
Of course, if you’re having trouble identifying the disease, it’s always a good idea to take a sample in a plastic bag, or a decent photo, to your local nursery (or friendly garden columnist) for a recommendation.
Do you have a gardening question for Jess? Send your queries to jess.cockerill@fairfaxmedia.com.au