How to avoid black spot

WITH the sustained hot weather, it is understandable that we need to be on the lookout for diseases that would once have been confined to the south of England.

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It is important to note that as much as we will be required to water, we need to be careful we don't overdo the watering on any of our plants, especially roses, which can suffer from black spot, an unsightly disease which is difficult to eradicate.

Black spot is identified by dark patches turning black as the disease progresses, leaf tissue may turn yellow around the spots and the leaf is likely to drop.

It is important to give roses the best start in life when you bring them home from the garden centre, with good cultivation, feeding, good drainage and irrigation the best ways to avoid the disease.

With the exception of rust affecting roses, black spot is the most pernicious problem. Persistent attack on some varieties can leave the shrubs more jaded each year and ultimately a fraction of their true selves.

The disease attacks the leaves, usually from mid-summer but each affected leaf that falls carries millions of spores which overwinter in the soil, ready for an attack the following season.

When the weather is as hot as this week, overhead irrigation with a fine spray helps to reduce the attack of black spot but this must be done in late evening, avoiding the heat of the day. If your plant is not showing signs of disease, water the soil around the plants but be careful not to over-water them.

Good resistance to the disease is found in newer roses and also bush-type roses.

It is also important to keep your roses well fed. High potash is important, as is iron, and, in alkaline soil, use fertilisers which contain magnesium.

There are many rose fungicides available from garden centres that are good at controlling this disease if spotted early.

If you do start a fungicide treatment continue the spraying and avoid watering over the leaves as this will move the fungicide, if it has not been managed, to be taken in by the plant.

If you do not want to go down the chemical control route then look towards your feeding method and make sure you incorporate high potash fertiliser and pick off affected dead leaves.

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 hopefully we will not experience too much rain soon.

Home and Garden

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