Roses have a second season of flower in the autumn and on cool evenings their scent is especially clear. Their leaves are another matter. Notoriously, they suffer from the disease called black spot, which scatters black spots over them and encourages roses to drop all their greenery. It looks a mess and can become an obsession for the roses’ owners. I know gardeners whose one crusade at weekends is to limit the ravages of black spot by spraying with whatever is the fashion of the moment. Alternative remedies are their favourites. As Christmas approaches they corner me at charity gardening evenings and tell me that since February they have been “applying” doses of antiseptic Jeyes fluid, sprayed around each rosebush once a week. When I ask if it works they say that it does seem to have had an effect, at least if compared with the previous year.

The dreaded black spot

Black spot is a bore but technically it is the result of a spore. To help you in the worldwide fight against it I have been consulting two of the most thoughtful rose growers, one in Britain and one in New York, a tough site for any sensitive rose bush. I will give the upbeat message from the US this week, little of which is familiar to European gardeners. In the “old world” ideas of an ideal rose involve long French names like Madame Legras de St Germain and a heavily petalled flower with a scent beyond anything devised by Coco Chanel. I will give a British reaction next week and indicate where a spot-free future might lie.

Over in New York the fight against rose diseases has become hampered by public opinion. Within Manhattan there are now legal bans on the chemical spraying of garden plants. Green lawmakers have never sprayed and loved a Malmaison rose and in their view it is up to responsible rose-growers to find other varieties of deterrent that do not depend on a chemical drench. How can we rail against traffic fumes and pine for clean air while wanting to scent a spot-free “old-fashioned” rose? Green gardening sounds so much more friendly to the future.

Pink Traviata in the New York Botanical Garden

Up in the Bronx, the New York Botanical Garden lies outside the city’s inner chemical-free zone but can hardly ignore the new climate of opinion. Last year 1,300 rose bushes were removed from the iconic Peggy Rockefeller Rose Garden and were replaced by disease-resistant alternatives, results of a worldwide search. On June 12 next year the garden will be hosting a Great Rosarians of the World event. The curator of the Peggy Rockefeller Rose Garden, Peter Kukielski, did not wish to preside over a display of nothing but old French beauties starting to develop their yearly spatter of black marks. Next June, attentive visitors to this event will see his first line of attack.

Healthier suggestions have poured in from Germany to Texas. I have asked Kukielski and the garden president to reveal their top performers of the year. None of them features in the British gardeners’ sourcebook, the RHS Plant Finder. Some of them come from US breeders whose websites are cheerleading us into a new dawn, now that the old rose New Dawn is so shamefully prone to mildew. At Bailey Nurseries, breeder Ping Lim has come up with Easy Elegance roses, which promise almost everything. So does the nursery, which backs it with a two-year “homeowner guarantee” against all the familiar diseases. “Let it be known – these are not your grandmother’s roses. You don’t have to spend all day in the yard to make them last. All you have to do is plant them and enjoy the beauty. And there is nothing easier than that.”

From this year’s showing in the Peggy Rockefeller rosarium I have photos of the top performers in action. Outside the US, who has heard of classically formed Belinda’s Favourite with tea-shaped flowers like the old Madam Butterfly and a “fully raspberry fragrance”? She attaches to another US initiative, the Earthkind programme, whose name is bestowed on a plant after years of scientific trialling by the Texas AgriLife Extension Service in the state’s agricultural service. Earthkind is the top environmentally aware programme for plant trials in the US and now has links with Canada, India and New Zealand. The New York Botanical Garden leads the Earthkind education and research programmes for the north-east US and has dedicated an entire rose garden for Earthkind trials, to be planted this autumn. There is nothing comparable at Kew Gardens in the UK.

Among the US data I like the look of four healthy finds from Germany. All are bred by the great firm of Kordes and none is listed by British sources in the current Plant Finder. In their Fairy Tale series, creamy-white Elegant Fairy Tale has flat flowers like a camellia with a darker centre and leaves that see off the bad black spot witch. Kordes Moonlight is a vigorous climber with glossy leaves, large apricot-yellow flowers and very few thorns, also resisting the usual mildew and spotting on old yellow varieties. I do not like the glare of the orange-pink Brothers Grimm Fairy Tale but Kosmos, in the same series, looks a white winner, so much so that it has been adopted by the Rotary Club, with profits to go to the battle against polio.

This year the winner in the Peggy Rockefeller Rose Garden has been the light pink Larissa. Reports are that she has arched to the ground with flowers along her branches. She has no scent but she has acted as a beautiful ground-cover with no hint of disease. Years ago a whiskery lady gardener tried to bully me into planting a ground-cover rose called Grouse. It was not even double-flowered and I ignored it with pleasure. Larissa is in a different class.

Over in France, not all is historic and struggling like mossy Madame de La Roche-Lambert of the past. The distinguished team at Meilland nursery has bred two robust winners. Easter Basket has beautifully shaped flowers of pale yellow with lavender tinges on their edges; and the superb apple-scented Traviata has leaves that Kukielski calls “perfect”. Both are current stars in the New York garden.

What about the US’s national favourite, Knock Out? Bred by Bill Radler, its kin have become bestsellers, totalling nearly 12m plants at the till in the past eight years. Knock Out is certainly disease-proof but are its flowers sufficiently refined? Here, British voices begin to answer back. I asked the sales team up at David Austin Roses, the breeders of our best-loved modern shrub roses. “A good enough shrub, which happens to look rather like a rose,” was their knock-out verdict. Next week I will be giving a British response to the black spot problems that New York’s Botanical Garden and its worldwide search have been addressing with such panache.