The rose is probably the icon of the English garden. There is nothing quite like the bloom of bush, patio and climbing roses in June. They add elegance, colour and scent to the summer garden. On the whole I find roses quite easy to grow. Many of my old English specimens are grown in containers as well as the ramblers and bush roses I have growing in borders throughout the garden. However, the one problem even the most experienced gardener can't avoid is that of a black spot.
Although common to roses, a black spot can also be found on other plants. But it is the most serious disease for roses. Popular varieties such as hybrid teas, floribundas, climbers and patio types are usually the most susceptible. Caused by the fungus Diplocarpon rosae, a black spot appears as purple or black spots on the leaves which eventually drop off thus greatly reducing the vigour of the plant. Badly affected plants can shed almost all their leaves in a very short time. First signs of a black spot are usually seen in early spring when new leaves begin the sprout. Because the fungus is very diverse and new strains form all the time, it is difficult to create lasting resistance in new rose varieties.
Treating and controlling a black spot
There is not really very much you can do if you don't want to use chemicals. Old varieties of rose tend to be less susceptible to a black spot, so as a form of prevention is might be a good idea to do your home work and select old varieties of rose when buying new plants or replacing lost ones. For new varieties, go for those that have shown some evidence of resistance to the disease - that's not to say the plant will be free of a black spot for its entire life, but you will have a head start. If your rose does show signs of a black spot, remove and destroy the affected leaves immediately. Don't put them on the compost heap as the fungus will survive and affect other plants when spread with the compost. To reduce the chance of re-infection the following year, prune affected plants back hard in autumn.
If you have to resort to chemical control, then start spraying with a suitable fungicide as new leaves open and repeat at fortnightly intervals. Continue to spray the plant every two weeks throughout the season. It is also a good idea to alternate several different products in order to maximise their effectiveness. This is especially relevant for roses grown in garden planters which will always be slightly compromised when grown in a container rather than in open ground.
Jo Poultney is one of two people behind Garden Planters. I have an RHS general certificate in horticulture. Garden Planters source unusual outdoor and indoor planters, and other garden related gifts - whatever your taste, be it traditional, modern or just a bit quirky, we will have something for you. I believe garden planters are an integral part of any garden - they enhance the overall design and say a little something about the person to whom the garden belongs. If you would like to know more about Garden Planters, visit our website at http://www.gardenplantersshop.co.uk
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