There is nothing quite as lovely as a rose bud unfurling, framed by lush, healthy, deep green foliage. Rosarians strive to attain and maintain their roses for this often-illusive picture. With the advent of modern roses (post 1867), more and more roses have been hybridized, and the results were variable. Some plants looked healthy no matter what the conditions, and others, while sporting gorgeous blooms, were veritable magnets for disease. Chemical companies responded by developing an arsenal of chemicals to treat the diseases, and fast forward to the last fifty years, and it was not an uncommon sight to see the gardener, instead of wandering through the garden and smelling the roses, gowned up like an astronaut with spray tank in hand, spraying everything in sight in order to have the lovely rose with the lush, healthy, deep green foliage.
There are many good chemicals available to the home gardener, and each one of us has to make a decision about whether or when we want to use them. But there is another option that is to plant disease resistant varieties of roses. There are many varieties to choose from, and planting disease resistant roses is good for the garden - maintaining beneficial insects, butterflies and birds; its good for the gardener as there is less time and money spent on maintenance, and its good for the environment.
So, what is disease resistance? Simply put, it is a plants natural ability to withstand infection from a variety of pathogenic (disease producing) microorganisms - fungi, bacteria, virus and virus like organisms, and pathogenic nematodes. Plants have varying degrees of resistance; some are completely immune to infection by common diseases, others partially susceptible to infection. There are no roses that are completely immune to all diseases under all cultural conditions, though, more than likely, that what hybridizers are working towards.
Infection occurs when the disease-causing organisms make contact with susceptible tissues of the host and begins drawing nutrients from them. The pathogen grows and reproduces inside or on the host plant and disease symptoms appear. Plants have physical defenses that help protect them from infection, for example, leaves have a waxy coating called the cuticle that prevents them from staying wet, making it hard for disease-causing organisms to survive. The leaf cuticle may also prevent spore germination and slow the penetration of disease causing organisms. Plants that have a high degree of disease resistance to infection from fungal infection often have a heavier cuticle layer.
Rugosa and hybrid rugosas are said to be immune to most fungal diseases, and modern shrub roses, generally with such mixed parentage that it is difficult to trace their true origins, are also often more disease resistant. Breeders are constantly striving to produce disease resistant plants and many of the roses introduced during the past decade have shown a remarkable improvement in overall resistance to infection. The big challenge for the hybridizers are developing new varieties of roses that are resistant to the organisms found in the environment today, that will withstand the diseases of the future. Most of the microbes that cause disease either have many different strains that are pathogenic, or, the strains mutate, presenting a constant challenge.
When looking for roses that resist disease (primarily the big three in our climate blackspot, rust and powdery mildew), look at roses with a proven track record in local gardens - you can almost be certain that if a rose is still popular after 10 20 years in commerce, that it is adaptable to climate and reasonable tolerant.
In addition to planting disease resistant varieties, you can also improve the opportunity for success with good cultural habits - healthy roses, ones that are planted in nutritious soil, receive lots of sunshine and good air circulation, are well watered and have leaves dry by evening, are fertilized and mulched, are much less prone to attacks from pests and diseases.
Here are a couple of dozen roses that have great ARS ratings, and generally excellent track records. I developed this list (in part) by observing the roses in my garden during the most challenging weather periods conditions that are conducive to either blackspot and rust or powdery mildew. As I dont use fungicides or insecticides, if the plant remained healthy looking with no significant signs of disease, it was eligible to be included in the list. There are all types of roses to choose from from little roses like Gourmet Popcorn that is covered with clouds of puffy white blooms to the spectacular Kiftsgate that can easily cover a wall or fence in a season or two. Sally Holmes can fit into any garden, whether trained as a climber or trimmed as a shrub. This rose is one of the cleanest roses I grow never a spot of disease.