Harry A. J. Hoitink and Steven T. Nameth, Professors, Department of Plant Pathology, Ohio Agricultural Research and Development Center, The Ohio State University; and James C. Locke, Research Plant Pathologist, U.S. Department of Agriculture, Agricultural Research Service, Application Technology Research Unit, Wooster, Ohio.
Propagation Fungicide Schedule
The fungicide schedule used during propagation must be adjusted to the needs of the crop. On rhododendrons and azaleas, Phytophthora, Cylindrocladium, Botryosphaeria, and Rhizoctonia are the most important pathogens in Ohio. Fusarium, Phomopsis, and Pestalotia are minor pathogens but need to be controlled also to avoid infection of cut stem surfaces on cuttings. Botrytis also can cause problems, and Cercospora leafspot may be present as well. The surface of plants during propagation is continuously wet; therefore, fungicide treatments often have short-term effects.
To obtain effective control of this wide range of pathogens under these high disease-pressure conditions, broad spectrum fungicides must be applied on a preventive basis. Some of the effective fungicides for Pythium and Phytophthora diseases include: Subdue MAXX, Chipco Aliette, Banrot, and Truban. Fungicides such as Domain, Topsin-M, Cleary's 3336 (thiophanate methyl), Banrot, and Terraclor are used for Botryosphaeria, Rhizoctonia, and Cylindrocladium.
Terraguard is an excellent fungicide for control of Thielaviopsis black root rot. Mancozeb (e.g., Dithane or Fore), Stature, chlorothalonil (Daconil Ultrex), Chipco 26019 and copper fungicides such as Kocide 2000, Champ DP, Champion WP, Camelot, Phyton 27, and Bordeaux mixture are excellent broad spectrum fungicides for control of leaf spots. These fungicides need to be applied weekly during mist propagation on crops such as rhododendron. Be sure to follow all instructions on the label. The best procedure is to alternate fungicides with different modes of action.