Rose Garden Renovations

In recent years, the Dean Bond Rose Garden has been hit hard by rose rosette disease. This is a disease believed to be caused by a virus that has been spreading through much of the wild rose population of the United States for years. It is of great concern to the nursery industry and to many home gardeners because it is known to be lethal to the wild multiflora rose (Rosa multiflora) and it is potentially lethal to many ornamental rose species and cultivars. The disease is known to be spread only by a very small, wind-dispersed eriophyid mite, Phyllocoptes fructiphilus, or by grafting. We ended up with some very big vacancies in what used to be a robust display of roses. As we noticed the virus, we removed affected plants. This experience made us more aware of the hazards of spreading disease in a collection especially when it is a monoculture.

These major openings in the rose garden gave us an opportunity to replant with more disease-resistant and sustainable roses. The disease is not known to reside in soil, so it is fine to replant roses in the same place. There is no treatment for rose rosette disease. The major disease for which we use chemicals in the rose garden is black spot. Some rose species are naturally resistant to the disease, but the more “modern roses” such as hybrid teas or floribundas tend to need chemical intervention to keep them healthy.

Blackspot is caused by the fungus, Diplocarpon rosae, which overwinters on diseased rose canes and fallen infested leaves. Spores produced on fallen leaves are spread via rain or by water splashed to newly emerged leaves and stem tissue in the spring. Under ideal conditions of leaf wetness, humidity, and temperature the spores can germinate and infect in 1 day, cause symptoms in 4 to 5 days, and produce new spores that can infect additional leaves, flowers, and canes within 10 to 11 days. Spores are easily moved by air currents. Bill Costello, our Integrated Pest Management coordinator, rotates the spraying of three different fungicides on a 10 to 14 day basis every season beginning as soon as the roses leaf out until the end of the season. We chose rose cultivars that showed promise of black spot resistance and encouraged increased air circulation by planting roses less densely than they were previously planted.

Since most of the roses that had been affected were modern re-bloomers or shrub roses, we took guidance from the ongoing evaluations at the Peggy Duke Rose Garden at the New York Botanic Garden where they have been replanting their rose garden with disease resistant repeat-blooming modern roses. They share our northeast climate (http://www.nybg.org/gardens/rose-garden-home.php). They have done an excellent job of documenting the replanting and evaluation of roses for disease resistance. We also took recommendations from rose growers and other trial programs. There are several notable programs promoting roses that have been selected and tested for increased disease resistance. A few of the programs that we looked at when deciding what roses to plant are listed below.

Texas Pioneer Roses were developed at Antique Rose Emporium. These are the result of breeding the showiest and toughest antique roses and selecting carefree, repeat-blooming offspring. Disease resistance, thornlessness, and fragrance have also been valued in this breeding program.

Kordes Roses were developed through the breeding program of Germany’s preeminent nursery, W. Kordes Söhne. These are robust, extremely floriferous varieties that have typically won prestigious awards for disease resistance in trials in Europe. With extraordinarily healthy foliage, these roses are stand-outs among “no-spray” varieties. We chose many Kordes selections for replanting the Dean Bond Rose Garden.

EarthKind Roses are the result of testing at Texas A&M University that is ongoing. The tests are designed to identify rose varieties that can be grown well with no or minimal care and are highly disease-resistant and practically immune to blackspot. Stephen George, Ph.D. currently heads the program begun by Robert Basye, Ph.D.

Rose Cultivar Name             Type of Rose                        Flower Traits                                Introduced by: