As if aphids, vine weevil and lily beetle aren't trouble enough for us all at this time of year, when your roses show signs of blackspot you may wonder if it's time to throw in the trowel.

While blackspot used to be a disease confined to the south of England, now it's all over the UK, causing defoliation and stunted growth to roses nationwide.

This unsightly fungal disease is hard to eradicate as it lurks over winter on fallen leaves and diseased stems, spreading on to healthy new leaves as spring returns.

There are many blackspot sprays on the market, claiming to provide a protective barrier which kills fungal spores on the leaves as they germinate. A recent trial by Which? Gardening, the Consumers' Association magazine, put eight such products to the test between April and October last year.

The products were tested on 'Silver Jubilee' roses as they are a modern variety, more resistant to blackspot than older varieties and more typical of the roses you might buy today. The roses were planted at a site known to carry the blackspot fungus and by June blackspot had appeared on the plants, at which point treatment was started, following the instructions supplied, while a number of bushes were left untreated.

The trial found that any chemical-based product was better than nothing and that they all slowed the progress of the disease to a similar degree.

While none of the products completely stopped the disease, testers recommend Bayer Garden Systhane Fungus Fighter Concentrate (£5.99 for 300ml, makes 15 litres, available from Amazon, Wilkinson, garden centres); Scotts Fungus Clear Ultra (£6.99 for 225ml, makes 15 litres, available from Amazon, garden centres); and Bayer Garden Multirose 2 Ready-to-use (£5.75 for 1 litre, available from B&Q, Homebase and garden centres).

However, trials found that the organic product which was tested, Vitax Organic 2-in-1 Pest and Disease Control ready-to-use spray, comprising a blend of sesame oil and fish oils, didn't make any difference to the roses and blackspot took hold of them in the same way as the untreated plants.

You will have to be persistent with spraying to keep the barrier on the leaves in place, and spray early, as the leaf buds burst if the blackspot was present the previous year.

If you don't want to go down the chemical route, there are other ways of controlling blackspot.

Pick off affected leaves and burn fallen leaves, and give plants a high potash feed, as potash deficiency may make blackspot worse.

Buy disease-resistant varieties such as the gallicas and albas and modern shrub roses like the rugosas. Good resistance to disease is also found among newer varieties of English and Modern bush roses. Good choices include Rosa gallica 'Versicolor', with its semi-double, pink flowers striped crimson, Rosa alba 'Konigin von Danemark', which produces glowing pink blooms, and the wonderfully fragrant English rose 'Gertrude Jekyll', which bears beautiful rich pink flowers.

If you keep your plants well fed and in the right place - preferably in a sunny spot with good drainage - they'll be less susceptible to disease. Remember, roses are hungry feeders so you would do well to apply a thick mulch of well-rotted organic matter and ensure good air circulation.

When watering, water the soil, not the leaves, and prune in spring to remove infected stems.

:: The full report is in the June issue of Which? Gardening. Sign up to Which? for a one-month trial for £1, with access to all its product reviews, test scores and Best Buy or Don't Buy ratings. For more information, visit