Seeing spots? Here's help for your roses

| 29 Sep 2011 | 09:17

MILFORD - Every year was the same. In early spring, my roses would start off nicely enough. Nice green canes, nice fat buds, and healthy leaf growth. But spring rains would arrive and not long after that, my roses would practically be defoliated, and whatever leaves were left behind would have black spots all over them. Last year I was ready. I sprayed them in time and they fought off the dreaded fungal disease: black spot. But this year I wasn’t ready. Nearly all my time was spent working on my lawn, repairing major swaths that had been devastated by grubs last year. Then the Poconos, along with the rest of the East Coast, were deluged with a solid week of rain, which was great for my newly seeded lawn, but not so great for the roses. And my roses succumbed. What is black spot? Black spot is a plant disease caused by the fungus Diplocarpon rosae. It’s a big problem with roses. High humidity, moisture, and warm temperatures help the spores to germinate, which are spread by water drops, tools, and clothing. Most often, the disease is spread by rain, splashing up spore-laden water droplets from fallen leaves that had been infected the season before. Leaves get irregularly-shaped, dark brown or black spots on them and these leaves will typically drop off. The canes, too, become infected with brownish spots. The plant has difficulty making food for itself with the loss of green leaves, and the quantity and quality of the blooms suffer. How can black spot be controlled? The first thing to do is to change your gardening practices. Clean up all leaves that have fallen right now, and make sure to do this in autumn, too. Overwintered rose leaves are a major source of reinfection. Avoid overhead watering as well as watering too late in the evening. If your roses are growing too close together, prune them or remove some of them to improve ventilation. Prune out badly infested canes. Finally, keep weeds down - better yet, use mulch. Ideally, start a spray schedule in the early spring, right after pruning. Spray your roses for black spot with a product containing chlorothalonil, a fungicide, according to label directions. Look on the label for this active ingredient. I’ve used Ortho’s Garden Disease Control (formerly called Daconil) with great success in the past, and although I’ve started very late in the season, I’m hoping to save the second flush of growth that I’m now getting on my roses. Besides chlorothalonil, the active ingredients in other recommended chemical controls are captan or mancozeb. If you prefer to use an organic spray, another product I’ve found in my research is called Rose Defense, by the Green Light Company. It’s made from the oils of Neem tree seeds, a native tree of India. If you want to plant new roses this fall, look for varieties resistant to black spot; read the plant descriptions in the catalogs, and read the labels at your garden center or nursery. Keep in mind that resistant does not mean the rose variety will never get the disease - it’s just less susceptible to it. So continue with your good rose gardening practices, and continue looking out for black spot. For more information, see Penn State’s website at