Classification of Organisms on Roses
- Several organisms may jeopardize roses.David De Lossy/Photodisc/Getty Images
Roses are perennial plants, some of which bloom throughout the growing season. Although roses are generally tough, they are susceptible to several problems, including infestations with insects and several fungal diseases, which may compromise their health and ability to bloom. Several types of fungal organisms are especially common on roses. Being able to classify these fungi and to distinguish among them will help determine the best course of treatment to restore the plants to health. - Blackspot is the common name for the most troublesome fungal organism that may live on roses. The classification of the fungus is as Diplocarpon rosae, "rosae" indicating the particular fungal strain that lives on the rose plant, explains Cynthia Wescott in her "Plant Disease Handbook." The circular brown or black spots that appear on leaves, sometimes encircled by a lighter yellow halo, readily identify it. The fungus causes the entire leaf to yellow and eventually drop from the plant.
- Powdery mildew is a fungal organism that often appears on rose bushes. According to a newly developed classification system, mildew that grows on roses is a member of one of two genera, either Podosphaera or Sphaerotheca. The distinction is made based on the microscopic structure of the spores, which are produced when the fungus reproduces, says APS.net. It causes a whitish or gray powder to appear on the leaves and on new buds and stems. A severe infestation will cause all the leaves to look as if they were dusted with powder.
- Another fungal organism that may grow on roses, commonly called "rust," is classified in the genus Phragmidium. According to Dr. C. Ritz and co-authors in a paper published in 2005 in "Mycology Research," two distinct species, P. mucronatum and P. tuberculatum, are able to co-exist on rose plants. Other rusts that may live on roses are also members of the genus Phragmidium. The fungus causes small, rust-colored dots to appear on the leaves. Usually these appear on the underside of leaves, and occasionally on the stems.
