Blast away the blackspot

By Hannah Stephenson

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 www.which.co.uk/signup

Best of the bunch - Parahebe

Unlike its popular relative, the hebe, you might not find this pretty evergreen sub-shrub at retail chains, but check out local nurseries or online retailers to bag a parahebe.

Parahebes are mainly from New Zealand and more closely resemble veronicas than hebes. They have simple, toothed leaves and small saucer-shaped, four-petalled flowers in loose racemes in spring or summer and should thrive in well-drained soil in sun or partial shade.

Among the most popular is P. catarractae, a spreading plant which grows about 30cm (1ft) high and has white or pale purple flowers with a central crimson ring.

If you want a compact variety which will look great in containers or towards the front of mixed borders, try P. 'Avalanche', a compact variety with deep green evergreen foliage which is smothered by an 'avalanche' of upright flower spikes bearing white flowers with delicate cerise-pink centres in early summer and again in September and October.

It is hardier than other parahebe varieties, to -10C.

Good enough to eat - Peppers

If you're good at growing tomatoes, you should be a whizz with peppers too, and there's a wealth of choice, colours, shapes and sizes from which to choose.

Sweet peppers can be trained easily into neat, bushy plants and yield enough fruits to pay for a prime site in a patio container. They need sowing indoors in March, maintaining a constant temperature of 20C, and when they have been potted on into two-litre pots of compost in May, by June you should be able to pot them on into five-litre pots to produce manageable plants.

When they reach around 20cm high, pinch out the growing tips to encourage bushiness. They can also be planted directly into a greenhouse border or growing bags and trained as cordons.

In July and August, sweet peppers may need some support once the fruits start to swell and you'll need to water the plants twice a day on hot days. When the first flowers form, feed regularly with tomato fertiliser and move the plants to a sunny position outside. Pick peppers when they are ripe, when the skin is still smooth.

Good varieties include 'Gypsy', whose pointed fruits turn from orange to red, and 'Chocolate Beauty', a bell pepper with unusual dark brown fruits. 'Mavras' is also unusual as its fruits start off dark purple but eventually ripen to red.

Three ways to... Make the most of a small garden

1. Carefully position a few vertical plants such as bamboo to give the illusion of divisions.

2. Plant trellis with suitable climbers to divide areas. The trellis can be cut to any size you need.

3. Keep the garden simple if you only have space for a small seating area and a few plants. Select plants with muted shades such as pastels or whites, with a soft foliage effect rather than bright colours.

What to do this week

:: Regularly water newly planted plants, young veg and container plants.

:: Apply and renew mulches to reduce water loss and suppress weeds.

:: Fill gaps in borders with summer bedding to give instant colour to otherwise bare patches.

:: Perk up your lawn by applying a feed using a liquid fertiliser.

:: Thin out aquatic plants and generally tidy up the pond before summer.

:: Prune mature, deciduous shrubs including philadelphus, deutzia and kolkwitzia, once they have finished flowering.

:: Remove faded blooms from rhododendrons and camellias, so allowing the plant's energy to focus on building up buds for next year's flowers.

:: Cut down overgrown lilacs, sawing them down to around 45cm (18in) from the base. A mass of new shoots will regrow and eventually lead to a bushier, better-shaped shrub.

:: Remove suckers from roses, identifiable because the foliage is usually lighter in colour. The suckers should be pulled off the plant at their point of origin on the roots rather than cut off.

:: Remove old leaves and flower stems from hellebores, which start to look tatty once they are over.

:: Cut down the foliage of bulbs naturalised in grass, if at least six weeks have elapsed since flowering.

:: Plant out cannas and lily bulbs, which were potted up when it was too cold to plant outside. They can now be planted in borders.