For example, Morden Sunrise is what I call a “blackspot magnet”. I loved the color of that rose and planted several in a cluster in one of my terraced beds, several years ago. The first summer they were covered with blackspot and almost immediately every other rose around them, including disease-resistant Buck roses on which I’d never seen blackspot, became infected as well. So I had no choice other than getting out my fungicides and spraying the whole garden periodically for the rest of the summer; something I really don’t like to do as an organic gardener.
So, lesson number one in controlling blackspot is to find out which roses are most susceptible and, either don’t plant them in the first place or, if you already have them, shovel prune them like I did with Morden Sunrise. In my opinion, there are so many great, disease-resistant roses that there really is no justification for growing susceptible plants and polluting your garden (and neighborhood) with fungicides. The Buck roses, for example, are beautiful and quite disease resistant. That’s what Dr. Griffith Buck’s work was all about: hybridizing beautiful, disease-resistant, winter-hardy roses. He was phenomenally successful and we are heirs to his legacy. This lesson is an integral part of practicing Integrated Pest Management (IPM), which all of us should be doing, for our own health, as well as the health of those around us.
Lesson number two is, if you have roses that are susceptible to blackspot and you just can’t part with them (yet), or if you have an outbreak on your resistant plants that you need to fix, be sure to use the right fungicide and practice IPM, which means that you must spray only the right fungicides and spray them as infrequently as possible.
So, what are the right fungicides and how often should you spray them? Fact: To my knowledge, there is only one fungicide that actually KILLS blackspot spores; and that’s Manzate (also known as Mancozeb). So, if you are going to spray for blackspot (and most of us will have to spray at least once in a summer), get yourself some Manzate. It’s available on-line at Rosemania.com and the shipping is free. I find that the liquid product is easier to use than the wettable powder, albeit a bit more expensive. To the best of my knowledge, all of the other products labeled and sold for the treatment of blackspot are fungus inhibitors, not killers.
The late Howard Walters, past president of the American Rose Society, wrote a wonderful column known as “Rosarian Ramblings” in the American Rose for many years. One of his favorite subjects was treating blackspot and he always recommended using Manzate, which is a surfactant, in combination with Banner Maxx, which is the best systemic inhibitor (also available at Rosemania.com). The combination of the strong inhibitor with the proven killer is a one-two, knockout punch, which allows you to spray only once every two or three weeks, depending on how bad your infestation is. Using Manzate alone would require weekly spraying, until all spores were killed. In my garden, where blackspot occurs only once or twice in a summer, the Manzate/Banner Max combination does the trick in only one or two sprayings for the whole summer, which is good IPM.
Now, let’s look at another fungus, spot anthracnose, which I have found to be more deadly than blackspot, in that it will take out an entire rosebed, if left uncontrolled. A lot of people mistake it for blackspot, even though it really doesn’t look much like it. It’s important to recognize anthracnose before it does irreparable damage in your garden. Fortunately, the treatment is exactly the same as for blackspot, i.e., Manzate and Banner Maxx, so mistaking it for blackspot is usually not fatal, as long as you spray it a couple of times. Here are two good pictures of spot anthracnose:
Last but not least, let’s talk about powdery mildew. Banner Maxx inhibits powdery mildew but Manzate does nothing. Fortunately for us IPMers, powdery mildew can be controlled, without a fungicide, by using strong doses of baking powder. Just mix three tablespoons of baking powder, per gallon of water, spray it on several times over a few weeks time, and powdery mildew usually goes away. Another little-known fact is that powdery mildew doesn’t like to be wet, so you can give your roses a good washing before applying the baking powder mixture. Unfortunately, if you are also fighting blackspot or anthracnose, washing your roses (or top watering) isn’t the best idea.
Finally, and this is more important than anything else I’ve said here, you must wear protective equipment and clothing when spraying fungicides (and insecticides). First and foremost, use a respirator so you don’t breathe any of the chemicals. Paper dust masks just don’t cut it here (if you can smell it, you are breathing it into your lungs). I wear a full-face 3M respirator, which is preferable, but partial-face respirators will work, if you also wear protective goggles. Check out 3M’s website for their respirator products and where you can buy them: http://solutions.3m.com/wps/portal/3M/en_US/PPESafetySolutions/PPESafety/
I also recommend wearing inexpensive Tyvek coveralls (also available at Rosemania.com). These can be hosed off and dried in the sun after each using, so that one or two sets of coveralls will be enough for a whole summer of spraying. Also, wear protective nitrile or rubber gloves for both mixing and spraying chemicals. I wear nitrile “milking” gloves sold by Fleet Farm, but any medical/surgical glove will do. And…It should go without saying that if you get any of this “stuff” on you, go wash it off!