Silicon tested in search to defeat the dreaded rose black spot
The velvety petals and sweet scent of a rose make it a classic of the traditional English garden.
But growers and gardeners have long cursed a disease that has ravaged the delicate beauty of their favourite flowers: black spot. Now scientists at the Royal Horticultural Society (RHS) are trying to find an answer to the problem.
They have borrowed prize blooms from the UK’s top rose grower, David Austin, and will inject them with the disease to see whether they can stop it in its tracks by varying the growing medium.
“Roses in RHS gardens, just like gardens all over the UK, commonly suffer from black spot caused by the fungus Diplocarpon rosae,” said Liz Beal, senior plant pathologist at the RHS, who is running the study.
It is a serious disease and symptoms include leaf yellowing, defoliation and a lack of plant vigour.
“A changing climate with more extreme weather leaves plants more vulnerable to attack. Diseases such as rose black spot occur during wet, warm summers. This may mean some gardens that can currently grow roses will struggle in the future,” she added.
Austin has been selectively breeding blooms to be resistant to the disease, but within five years rose black spot can mutate and take hold again.
Rather than using fungicides, which are bad for the environment, the RHS researchers are applying silicon to the soil to see if that can stop the fungus spreading. This has been successfully used to treat another fungal disease, powdery mildew, in strawberries.
Ian Bull, garden manager at RHS Garden Hyde Hall,which has a very wellknown rose garden, said visitors are always asking him how to stop the disease.
He told the Observer: “One of the quintessential featrues of an English garden plants, roses are a big group of plants and can be grown in almost any situation. They can be planted successfully by beginners too, as they are relatively easy to care for, which makes them a very popular choice for gardeners. Sadly, any time we talk about roses, we know we will get questions about rose black spot.
“It can be hugely disappointing for people to see their favourite flowers damaged by such an ugly disease, especially if they only have one or two plants or they have chosen a particular variety for sentimental reasons.”
Bull recommends mixing roses with other plants to reduce the prevalence of diseases. Useful additions are “softcoloured flowers like verbena, salvia and lavender, or grasses, to add interest when roses are not flowering and to compliment your chosen rose.”
Beal hopes that her natural solution to the problem will give gardeners a chance to save their roses.
She said: “Silicon is a mineral naturally present in most soils at low concentrations. This project seeks to learn whether its application can reduce the incidence of rose black spot, and therefore reduce fungicide use.”