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.
This unsightly fungal disease is hard to eradicate as it lurks over winter on fallen leaves and diseased stems, spreading as spring returns.
There are many blackspot sprays, claiming to provide a protective barrier which kills fungal spores on the leaves as they germinate. Which? Gardening, the Consumers’ Association magazine, put eight products to the test last year.
The products were tested on Silver Jubilee roses planted at a site known to carry the fungus. By June blackspot 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 any chemical-based product was better than nothing and they all slowed the progress of the disease to a similar degree.
While none 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, from B&Q, Homebase and garden centres).
However, 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 and blackspot took hold of them in the same way as the untreated plants.
Be persistent with spraying to keep the barrier on the leaves and spray early as the leaf buds burst if the blackspot has been present
If you don’t want to go down the chemical route, pick off affected leaves and burn fallen leaves. 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 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 fragrant English rose Gertrude Jekyll, which bears beautiful rich pink flowers.
Water the soil, not the leaves, and prune in spring.
JOBS FOR THE 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 bare patches.
Perk up: your lawn by applying a feed using a liquid fertiliser.
Thin out: aquatic plants and generally tidy up the pond.
Prune: mature, deciduous shrubs including philadelphus, deutzia and kolkwitzia, once they finish flowering.
Remove: faded blooms from rhododendrons and camellias.
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.
GOOD ENOUGH TO EAT:
If you’re good at growing tomatoes, you should be a whizz with peppers too.
Sweet peppers can be trained into neat, bushy plants and yield enough fruits for a prime site in a patio container. They need sowing indoors in March, maintaining a 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.
When they reach around 20cm high, pinch out the growing tips. They can also be planted directly into a greenhouse border or growing bags and trained as cordons.
In July and August, theymay need some support once the fruits start to swell and you’ll need to water the plants twice a day on hot days. When flowers form, feed regularly with tomato fertiliser and move to a sunny position outside.