With the improvement in the weather the last week it should set as a reminder we need to be on the lookout for disease of plants that would once have confined to the warmer climates. As summer approaches and much longer and hotter days we will be required to water, we need to be careful we don’t overdo the watering on any of our plants especially our rose plants. Black Spot is a very unsightly disease and is very difficult to eradicate. It is important to give your roses the best possible start in life when they have been brought home from the garden centre therefore good cultivation, adequate feeding and especially good drainage and irrigation are the best methods of avoiding problems with the disease.

With the exception of rust affecting roses, black spot is the most pernicious. Persistent attack on some varieties can leave the shrubs somewhat jaded each year and ultimately reduce them to a fraction of their true selves. The disease attacks the leaves, usually from mid-summer onwards although it lurks over winter on fallen and diseased stems, spreading on to healthy new leaves as spring returns. Each affected leaf that falls carries with it millions of spores which overwinter in the soil, ready for an attack the following season. When the hot weather arrives overhead irrigation with a fine spray helps to reduce the attack of black spot but this must be done in late evening and important to avoid the heat of the day, alternatively if your plant is not showing signs of any disease then water the soil around the plants but being careful not to overwater them too much.

Good resistance to the disease is found in newer roses and also bush type roses. It is important to keep your roses well with good nutrient applications as roses are hungry feeders so a good high potash is important along with iron and if your soil is alkaline then look towards applications of fertiliser containing magnesium.

There are many good rose fungicides available now from garden centres that are very good at controlling this disease if spotted at an early stage. There are also organic based fungicides available If you do start a fungicide treatment make sure you continue the spraying and avoid watering over the leaves as this will move the fungicide if it has not managed to be taken in by the plant. If you do not want to go down the chemical control route then perhaps look towards your feeding method and make sure you incorporate high potash fertiliser and pick off any dead leaves that have been affected. Black Spot is identified with dark patches eventually turning black as the disease progresses, leaf tissue may turn yellow around the spots and the leaf is likely to drop .

The disease will infect plants again in subsequent years if control methods such as removing infected leaves are not carried out. Spores can also be blown in with rain but given we are in the middle of some lovely weather we will hopefully not experience too much rain soon.

Paul Brannan