Disease Resistant Roses
Q. Mike: I live in Europe and am having trouble with my roses. The leaves are getting black spots and then falling off some of my bushes. Any idea what the disease could be, and how I can control it without chemicals? Thanks,
- ---Gene in Slovenia (" a nice little country just south of Austria")
- ---Roberta in Chicago, Illinois
Hello Mike: What are the names of some good disease resistant roses? It's ordering time, and I am 'new' to this region after 40 years in Bay Area of California. I'm aware of the rugosas, Knockouts, old roses etc., but am more interested in 'modern' hybrid teas, floribundas, grandifloras, etc. Are any of them worth trying? Thanks,
- ---Todd; now in Stratford, NJ
A. Well, thank you, Todd! It's been a while since I had an excuse to call my old friend Dr. Tommy Cairns, noted author, former President of the American Rose Society and Immediate Past President of the World Federation of Rose Societies. (If roses grew on the moon, odds are Dr. Tommy would be a President of the LUNAR Rose Society…) He's the rosarian I trust to name names; and to provide sage advice on keeping that dreaded black spot at bay.
That's the disease Gene in Slovenia and Roberta in Chicago are facing—and the one that you'll likely have the most troubles with. "In a really moist climate, you're always going to be battling black spot," explains the good Dr. Cairns. It first appears as—no surprise—black spots on the plants' leaves, and is often so severe it can defoliate entire plants by the end of the season. In contrast, notes Dr. Tommy, the damage caused by most of the other common rose diseases, like powdery mildew, tends to be more cosmetic.
Before we move on to naming the best varieties for avoiding the problem, let us first quickly list the basic things you should do to prevent rose diseases in general.
- Always plant in open, uncrowded areas where the rose will get lots of airflow and the first morning sun.
- NEVER prune in the Fall.
- Prune off all dead, damaged and diseased canes in the Spring, just as new growth appears.
- Clean up and discard the old mulch underneath your roses every Spring, and replace that disease-spore ridden material with an inch of high-quality compost.
- NEVER use bark, wood or rubber mulch.
- Prune throughout the summer to keep the plants open and uncrowded.
Naturally disease-resistant varieties? In general, Dr. Cairns reminds us that the older the rose, the more likely it will be disease-resistant; that roses with waxy leaves will always be more disease-resistant than roses with papery leaves; and oddly, the lower growing the rose, the more resistant it should be.
That said, the 'Knockout' series of roses, mentioned by our California transplant, "has become synonymous with disease resistance", says Dr. Cairns. Created by Bill Radler, an amateur interbreeding old roses, the Knockouts are shrub roses that reach three to four feet in height, come in a variety of colors, have the unique ability to rebloom without any deadheading, and perhaps most importantly, "are virtually immune to black spot."
Next in line is 'Kardinal', a red hybrid tea that Dr. Tommy says "never gets black spot, rarely gets mildew, and lasts a very long time in the vase, which is unusual for home-grown roses. It was developed by Kordes, a German company that's really paying attention to disease resistance."
He also likes the brand-new 'Moon Dance', a white "rain proof" floribunda from Jackson & Perkins with a unique fragrance ("perfume with a hint of raspberry"); it's a 2007 AARS winner. Another relatively new white floribunda, called 'Fabulous', is also very disease resistant, he notes, and it grows a little taller than Moon Dance.
Getting back to unique smells, Dr. Cairns says that the 'Julia Child' yellow floribunda released last year has a "very strong licorice and spice fragrance", good disease resistance and an enormous number of petals per flower. And 'Wild Blue Yonder', a deep purple grandiflora, has a very strong citrus fragrance, he notes. Described as only lightly fragrant but much more disease resistant is 'Cabana', an orangey-yellow hybrid tea from Jackson & Perkins. And 'Bolero', a short, "rain proof white floribunda from France" has a strong "pure rose fragrance", he notes.
Dr. Tommy continues his surprisingly long list of naturally healthy roses with 'Amber Queen', an apricot colored floribunda whose glossy foliage is "highly disease-resistant"; 'Passionate Kisses', a floribunda that produces big clusters of neon pink flowers; and 'Ronald Reagan', a nicely disease-resistant hybrid tea with flowers the color of the late President's hair that tends to lean a bit to the right in the garden.
He adds that he really likes the 'Easy Elegance' series of VERY hardy (down to zone 4 without winter protection) shrub roses, especially 'Fiesta' (aka 'Golden Jubilee') which Dr. Tommy says "is like an explosion of pink and white blooms"; 'Macy's Pride', whose "creamy white flowers age gracefully to develop a hint of pink"; 'Snow Drift', whose white flowers contain an astounding 50 petals apiece; and 'Showtime', a clear red climber with bright gold stamens that, says the good Dr. Cairns, "is as hardy as it gets."
And finally, he closes with two new varieties that have earned the title of "World's Favorite Roses" and thus entrance into the World Rose Hall of Fame: 'Eden Rose' (aka 'Pierre de Ronsard'), a medium pink climber; and 'Elina' a pale yellow hybrid tea.