My roses suffer from black spot. How can I treat this and avoid the problem in future?

Black spot is a common fungal rose disease that's worse in warm, humid climates. The leaves develop dark, irregular spots, then turn yellow and fall off. Some rose varieties are less susceptible than others, so look for these (Brindabella Country Gardens in Queensland has bred the Blackspot Buster range of varieties to be resistant to the disease). Minimise humidity around plants by spacing the roses apart and limiting other plants crowding around them. Plant roses in breezy and sunny spots; they need at least six hours of sun each day. Avoid watering the leaves, especially late in the day. For roses that already have the condition, clean up all fallen diseased leaves. Fungicides such as Yates Rose Gun Advanced prevent attacks if applied fortnightly and after rain. OCP Eco-Rose, an organic treatment based on potassium bicarbonate, also needs fortnightly applications. Alternatively, mix one part full-cream milk with ten parts water and spray regularly. Spraying foliage with Seasol every few weeks increases disease resistance, as does a quarterly dose of sulphate of potash. Keep roses well fed with an organic rose fertiliser every six to eight weeks during the growing season.

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