Posted: 06/08/2014 at 22:26
Not having read all the posts. IMHO Dave the Gardener has provided the most reliable answer. If I may. I speak from experience. I have over a hundred different roses in my postage stamp sized garde, I have plenty of black spot etc. How come, if you are an expert? As with so many gardeners, I tend to follow on. So at the start of the season all looks good. Flower buds develope and in time present a grand array of colour. Then the weather takes it's toll. Wet days, scorching days. Yes these elements do play havoc with our gardens. At the end of the day however who is most at blame. SIR, Me Sir. I failed to spray and protect in advance. Agreed the labels on the chemicals usually say. As soon as you notice, TOO late. Try and develop a kind of schedule. Early spring. Liven up the soil around the plant base, add a good quality rose feed. Top Rose is fine. Keep weeds well away from the rootbase. Like going to the doctors. Why have you left it so long? Thankfully 'Black spot seldom infects the main structure of the plant. It attacks the leaves, which in turn really do spoil the appearance of the plant. The disease after contacting the outermost point of the leaf, it the rapidly travels along the leaf stalk, then spreads outwards to infect the secondary and following leaflets. Even without your intervention. As soonas the infection reaches the main or semi main stem. It's had enough. One might say. Mission accomplished. It has played it's role in defoliation. So in conclusion. Don't wait until you see black spot, or for that matter anything else. Especially with roses. Your are after all dealing with 'Hybrids' Much weaker than natural forms. So act fast. As soon as growth starts, get spraying.