Last week I looked at how the New York Botanic Garden was responding to black-spotted roses There, newly resistant varieties from around the world have been tracked down and tried. What does a great British breeder think of the problem? For answers, I approached David Austin Roses as the nursery’s flowers are among the 900 replacements that the New York Botanic Garden introduced last year.

I learnt at once that I did not understand black spot’s habits. On a steaming July day 30 years ago, I remember standing in the Norfolk nursery of Peter Beales, Britain’s great old rose champion. He told me how he recalled his early days in nursery work, when a revolving water spray would turn across an arc of roses in the stock beds and, as if by magic, black spot would be much less prevalent on rose leaves within the water’s reach. It was a passing remark, probably prompted by the volume of water we were both sweating at the time, but it has stayed with me since. In wet summers, is black spot really less prevalent? I have been telling myself that it will be, only to find that it is not.

Nowadays, the scientific view is rather different. Black spot is a spore that is activated by damp conditions in relatively warm weather, at least by British standards. If the air is between 15°C and 20°C the spore is in its element. The moral, as Beales was implying, is to water roses in hotter weather but not to water them at night or in the cool early morning. Since our conversation, irrigation systems have been installed in many more gardens, let alone in expatriate bolt-holes across the Mediterranean. Many of them run at night or in the small hours of the morning, partly to avoid soaking the owners, partly so as to conceal the fact that they are running at all. For roses, this timing is not well aimed. It is better to water them in the greater heat of the day when the air temperature is above the level that the black spot spore appreciates.

As a precaution, we can do two things. We can mulch rose bushes with decayed manure or compost in the spring. The spore decomposes quickly in this rich blanket, which is much more effective than an early spray with soapsuds or disinfectant fluid. We can also revert to old practice and prune some of our varieties to within an inch of the ground. This savagery was the standard practice of park-keepers before the fashion for tall older shrub roses came in. It was not just a military urge for order. The hard pruning and clearing of the debris gave the spores less of a surface area on which to survive. None of us wants to prune a shrub rose such as the lovely Madame Hardy or a hybrid Musk such as Buff Beauty within an inch of ground level because too much flowering growth is lost to the clippers. Our light pruning, however, favours black spot’s habits.

Lady of Shalott

What can we use as a spray outside regulated Manhattan? There are two possibilities. One is to attack with systhane, a compound available to alert amateurs. The other is to feed early and late in the season with the homely Uncle Tom’s Rose Tonic. It is not successful because it sounds so folksy and alternative. It contains potassium phosphite, which promotes healthy growth and keeps black spot at bay. If you cannot find it locally, the concentrated liquid Maxicrop is the next best thing.

A word, too, about mildews. They bother gardeners more in Britain and they come in two brands. Powdery mildew shows up grey and dusty on the leaves in late summer and is the result of dryness at a rose’s roots. Mulching in the early season helps to keep it out, as does watering in hot conditions. Downy mildew thrives on warm days followed by cool nights. The answer here is not to compound it by irrigating the roses in cool nights during hot weather.

Most of this advice is for prevention, not cure. Much of the best advice is to choose the most resistant varieties, rather than the climbing pink Zephyrine Drouhins and Kathleen Harrops, which are such martyrs to these disfiguring diseases. Michael Marriott, sales director of David Austin Roses, has kindly advised me on British roses that are more dependable.

Kew Gardens

Naturally, David Austin himself has always been aware of the black spot problem during his breeding programme of the past 50 years. He feels that his newer varieties are much more able to shake off the disease and points particularly to innovations of the past five years. Among soft pinks, he recommends Gentle Hermione, a very free-flowering shrub. Among apricot-yellows, the choice is Port Sunlight, while Munstead Wood is not spot-prone among the dark reds. Nor is the new Darcey Bussell. Others to pick are Lady of Shalott and this year’s novelty, Kew Gardens, if you like the flowers’ distinctive shape.

From both sides of the Atlantic, the advice is progressive and wonderfully modern. Myself, I would add a less gung-ho note. It is simply not true that all older roses go black and lose their leaves after midsummer. If you make shrewd use of Peter Beales’ current catalogue, you will find that it makes a similar point. The precondition is to cultivate well, to mulch, regulate the irrigation times and feed with Uncle Tom’s. I have no problems with the excellent old Rose de Rescht, probably because it was found growing wild in Iran and has no hybrid blood in it. I have a little trouble with disease on Jacques Cartier but, as it is the greatest repeat-flowering old rose, I simply forgive the few spots and enjoy it. American breakthroughs such as Rainbow Knockout have none of its scent, tightly petalled shape and pink charm. Among the prickly once-flowerers, I look no further than two wonderful pinks with wild American blood, picked out long ago and named Rose d’Amour and Rose D’Orsay. They have never had a hint of disease, even though my soil is abominable for roses. Among climbers, I head straight for the wonderful white Long John Silver, another rose with older American parents and leaves that never go spotty.

My advice is that there is still all to play for as breeders wake up to a new spray-conscious age. For too long many of them messed about trying to produce the ever-elusive blue-flowered rose. They have failed but now they are aware that healthy, unsprayed roses are indeed Earth Kind, as the Texas category calls them. Not all old roses are, therefore, villains. American breeders need to look closely at the exceptions that already existed in each class and then try to capitalise on them too. Past and present, as always, need to co-operate on either side of the Atlantic. We must not throw out old classics in the race to dispense with the need for soapy, disinfected watering.