Managing Diseases on Ornamental Crops - A New Program at Clemson

Steven N. Jeffers Department of Plant Pathology and Physiology Clemson University

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I joined the department of Plant Pathology and Physiology at Clemson University in July of 1995 to work on diseases of ornamental crops grown commercially in nurseries and greenhouses in South Carolina. My predecessors here at Clemson, Dr. Luther Baxter, retired 6-7 years ago after an illustrious career working primarily on diseases of Camellias. Consequently, Clemson has been without research and extension efforts focused specifically on diseases of ornamental crops for some time. Prior to joining the faculty at Clemosn, I was a Senior Scientist at EcoScience Corporation in Worchester, Massachusetts where I worked on the development of biological control products for managing postharvest diseases of fruits, primarily apples, pears, and citrus. Before joining EcoScience, I was an Assistant Professor and Extension Specialist in the Department of Plant Pathology at the University of Wisconsin-Madison with both research and extension responsibilities for diseases of fruit crops. My graduate education was done at Cornell University in Ithaca, NY where I earned both M.S. and Ph.D. degrees in Plant Pathology while working at the New York State Agricultural Experiment Station in Geneva, NY. My thesis topics dealt with Phytophthora crown rot of apple trees.

Here at Clemson, I have both research and extension responsiblities for diseases affecting commercially-grown ornamental crops. I am interested in working with growers to find practical solutions to plant disease problems through applied research and extension education. My program will focus on developing integrated disease management systems to improve crop production. To develop these systems, we need to optimize fungicide use, take advantage of cultural practices and host resistance whenever possible, and explore the potential and practicality of biological controls. I have been visiting nursery and greenhouse operations around the state to become familiar with the ornamental plant industry in South Carolina and to canvass growers on the more economically important disease problems currently at hand. People growing ornamental crops commercially are encouraged to send disease problems into our Plant Problem Clinic for diagnosis and to contact me directly so I can be aware of the problems affecting our industry and assist with disease management recommendations.

Based on information provided by growers, the Plant Problem Clinic here on campus, and fellow extension colleagues, I have initiated two projects on which to concentrate my efforts over the next several years. One of these will focus on Phytophthora root rot of woody ornamentals grown in containers. This is a disease that affects many of the woody nursery crops grown in South Carolina, in the Southeast, and throughout the country. It is caused by a number of different species in the fungus genus Phytophthora, most commonly P. cinnamomi and P. nicotianae var. parasitica. The first stage of this project will be to determine which species of Phytophthora are present and causing problems in South Carolina nurseries and where these fungi are coming from. Much of this research will be conducted by a graduate student, Ms. Andrea Ferguson, for her thesis research. I have been working with the Plant Problem Clinic and nurserymen to collect isolates of Phytophthora species from diseased nursery plants. We will be visiting nurseries around the state regularly throughout the year to collect samples from both healthy-appearing and diseased plants as well as from potting media and irrigation water so we can determine what are the sources of primary inoculum. The second stage of this project then will be to devise ways to eliminate these sources of inoculum and, therefore, reduce the number of plants becoming infected.

The other project that has been initiated focuses on Botrytis blight (or gray mold) of greenhouse-grown crops. Botrytis cinera , the fungus pathogen that causes the disease, is ubiquitous in greenhouses around the world. It affects many different species of ornamental plants as well as plants grown for food and fiber use. In the greenhouse, the disease is particularly problematic on geranium, poinsettia, Cyclamen, and African daisy. It also can persist in greenhouses saprophytically on senescing and dead plant parts; it colonizes senescing flowers very readily. Consequently, it is difficult to eliminate Botrytis from the greenhouse environment.

One unfortunate characteristic of Botrytis is that it can develop resistance to several of the fungicides that are most effective and , therefor, used exstensively against this pathogen. Resistant isolates of Botrytis have been documented on a number of host crops around the world. In the first stage of this project, islates of Botrytis will be collected from greenhouses around the state to obtain a representative sample of the population of this pathogen in South Carolina greenhouses. These isolates will be tested for resistance to thiophanate-methyl (a benzimidazole-class fungicide) and vinclozolin (a dicarboximide-class fungicide) both in the laboratory and in the greenhouse. Results from this investigation should be available within the year and will have a direct impact on our recommendations for managing Bortrytis blight in South Carolina greenhouses. Preliminary results indicate that isolates resistance to one or both of these fungicides is not uncommon. Once the resistance status of silates in ur representative sample of the population has been determined, appropriate studies on the biology of the fungus and on the epidemiology and management of the disease will be conducted. This research is being conducted by Mr. Len Yourman, a Research Associate and Graduate Student, as part of his Ph.D. thesis project.

Much of my first year here at Clemson has been spent establishing our research facilities. In Dr. Baxter's former laboratory in 201 Long Hall, a new, modern laboratory and office complex was constructed. The laboratory is equipped with state-of-the-art technology--including compound and stereo microscopes, and autoclave, a programmable controlled environmental chamber, incubators, ultra-low freezer, shaker, spectrophotometer, and both transfer and fume hoods--for safely working with mocroorganisms and chemicals, respectively. Funding for the laboratory/office complex came from Public Service Activities monies provided by the South Carolina Legislature for research and extension programs in environmental horticulture. In addition to the laboratory, a greenhouse on campus has been completely renovated to accommodate research on diseases of ornamental crops.

Last Updated 2/1/97