Results and Discussion No. 14, Fla. Dept. of Agr. & Consumer Ser., Div. of Plant Industry, Talla- hassee, FL. The disease symptoms first appeared as water soaked spots Chupp, C. and A. F. Sherf. 1960. Vegetable diseases and their control. Ronald 10 mm in diameter. After 20 d, necrotic lesions became visible Press, New York. 692 p. Dwivedi, R. P. and S. C. Dubey. 1987. Web blight of Eupatorium cannabinum on the inoculated plants. The spots enlarged to 25 mm or more L. caused by Thanatephorus cucumeris. Indian Jour. Mycology and Plant and then turned dark brown. A whitish mycelium grew rapidly Pathol. 161:309. over the leaves, killing them (Fig. 5), and spread a mycelial web McMillan, R. T., Jr., H. Vande Hei, and W. R. Graves. 1994. First report of web from leaf to leaf. Many small brown sclerotia and web-like blight caused by Thanatephorus cucumeris on Cupaniopsis anacardiopsis in the United States. Plant Dis. 78:317. mycelia were found on the leaves (Fig. 6), typical of the disease McMillan, R. T., Jr., H. Vande Hei, and W. R. Graves. 1994. First report of web symptoms found on the infected nursery plants. Rhizoctonia blight caused by Thanatephorus cucumeris on Sophora tomentosa in the Unit- solani was consistently re-isolated from all the inoculated plants ed States. Plant Dis. 78:317. while no symptoms were observed on the uninoculated plants McMillan, R. T., Jr., M. Borek, and W. R. Graves. 1997. Web blight of dwarf (Fig. 7). Thus Koch’s postulates were thereby fulfilled. Hawaiian snowbush. Proc. Fla. State Hort. Soc. 110:370. Pirone, P. P. 1970. Diseases and Pests of Ornamental Plants. Ronald Press, New York. 546 p. Literature Cited Preston, D. A. 1968. Host index of Oklahoma plant diseases supplement, 1948. Plant Dis. Reptr. 32:398-401. Alfieri, S. A., Jr., K. R. Langdon, J. W. Kimbrough, N. E. El-Gholl, and C. Sharma, J. K. and K. V. Sankaran. 1984. Rhizoctonia web blight of Albizia fal- Whelburg. 1991. Disease and Disorders and Plants in Florida. Bulletin cataria in India. European J. of Forest Pathol. 14:261-264. Proc. Fla. State Hort. Soc. 115:130-133. 2002. PESTICIDE MODE OF ACTION CODES TO AID ORNAMENTAL GROWERS IN DEVELOPING CONTROL PROGRAMS TO MANAGE PEST RESISTANCE ELZIE MCCORD, JR.1 Arthropod resistance to pesticides has been a problem in New College of Florida ornamental crop culture since the early era of synthetic organic Natural Science Division pesticides. A notable example of the problem comes from the 5700 North Tamiami Trail leafminer, Liriomyza trifolii (Burgess) outbreaks of the 1970s. Sarasota, FL 34243-2197 Leafminers were causing losses in chrysanthemum, other annu- al ornamentals (gerbera, aster, gypsophila, and many bedding JAMES F. PRICE AND CURTIS A. NAGLE plants) (Price, pers. comm.) and some vegetables (Parrella et University of Florida, IFAS al., 1981). Several effective pesticides including early organo- Gulf Coast Research and Education Center phosphates (methyl parathion), carbamates (oxamyl), pyre- 5007 60th Street throids (permethrin) (Robb and Parrella, 1984), and triazines Bradenton, FL 34203 (cyromazine) (Price, 1984), were identified for leafminer con- trol during the outbreak period, but pesticide efficacy was lost Additional index words. ornamentals, insecticides, pesticides, due to resistance by the leafminer (Mason et al., 1987). insects, IPM Methods to manage arthropods have included reducing the Abstract. The development of resistance to pesticides has selection pressure of pesticides by emphasizing rotations caused problems in producing high quality, economically among pesticides of different chemical classes and limiting re- competitive ornamental plants in Florida. Presently, there are peated applications of pesticides within identical ones. This approximately 65 pesticide active ingredients involving at method is flawed in that pesticides of multiple chemical classes least 25 different modes of action available for arthropod con- sometimes compromise biological processes (mode of action) trol on ornamental crops in Florida. Resistance management that are identical. Rotation between different chemical classes requires growers to consider product mode of action as a ma- with the same mode of action increases the selection pressure jor factor in rotational schedules. Mode of action information is and can result in more rapid resistance. For example, tradition- not usually found on product labels or in informational fact sheets, thus preventing many growers from developing indi- al rotational schemes could allow rotations between organo- vidualized control programs with emphases on arthropod re- phosphate and carbamate classes, but both are acetyl sistance management. A coding system has been developed cholinesterase inhibitors that interfere with neural transmis- to identify pesticide modes of action. Pesticides of different sion. Additionally, some pesticides within a single chemical class modes of action should be selected to apply in a rotation to a possess different modes of action and rotation between those single arthropod community, thus avoiding selection within should not increase the selection pressure to either. For exam- that community for resistant individuals. ple, carbaryl and fenoxycarb are carbamates, but the mode of action of carbaryl is to inhibit acetyl cholinesterase at the synap- tic cleft and fenoxycarb mimics juvenile hormone. Use of one 1Corresponding author. should not necessarily affect the selection pressure of the other. 130 Proc. Fla. State Hort. Soc. 115: 2002. We propose that Florida ornamental growers alter their plan would provide for applications of the carbamates, car- rotational schemes to follow a plan that provides for rotation baryl (acetyl cholinesterase inhibitor) and fenoxycarb (juve- among pesticides of different modes of action rather than nile hormone mimic) in rotation. chemical class (Bethke, 2002). This rotational plan would se- Adoption of this plan could reduce the selection pressure lect one pesticide between the organophosphates and car- toward pesticides of each mode of action and should result in bamates (acetyl cholinesterase inhibitors) and one among an increased period of usefulness for many pesticides. aminohydrazones, organosulfurs, organotins, pyrazoles, py- Table 1 shows codes, active ingredients, trade names, use, ridazinones, pyrroles, and the rotenoids due to their related chemical class and mode of action of pesticides registered for effects on oxidative phosphorylation. On the other hand, the use in Florida ornamentals. We assigned simple code num- Table 1. Mode of action codes for ornamental insecticides and miticides.zy Codex Active ingredient Trade names Use Chemical classw Mode of action and notes 1 Methyl Bromide Methyl Bromide Biocide Alkyl Bromide Broad biological toxicant. Resistance to fumigants unlikely 2 1,3-Dichloropropene Telone II® Biocide Organochlorine Broad biological toxicant. Resistance to fumi- gants unlikely 3 Metam Sodium Metam®/Metam Sodium® Nematocide Thiocarbamate Broad biological toxicant. Resistance to fumi- gants unlikely 4 Hydramethylnon Probait®/Amdro® IGR Aminohydrazone Blocks ATP synthesis 4 Propargite Ornamite®/Omite® Miticide Organosulfur Inhibits ATPas 4 Fenbutatin-oxide Vendex® Miticide Organotin Oxidative phosphorylation inhibitor/ uncoupler 4 Fenpyroximate Akari® Miticide Pyrazole Electron transport inhibitor 4 Pyridaben Sanmite® Miticide Pyridazinone Electron transport inhibitor 4 Chlorfenapyr Pylon® Insecticide Pyrrole Oxidative phosphorylation inhibitor/ uncoupler 4 Rotenone Rotenone 5% Dust® Insecticide Rotenoid Electron transport inhibitor 5 Fenoxycarb Precision®/Preclude® IGRv Carbamate Juvenile hormone mimic 5 Pyriproxyfen Distance®/Pyrigro® IGR Pyridine Juvenile hormone mimic 6 Halofenozide Mach 2® IGR Diacylhydrazine Ecdysteroid antagonist causing premature lethal molting 6Tebufenozide Confirm® IGR Hydrazide Ecdysteroid antagonist causing premature lethal molting 6 Azadirachtin Azatin®/Ornazin® Insecticide Tetranortriterpenoid Ecdysone metabolism inhibitor and blocks sty- loconic receptors 7 Diflubenzuron Adept®/Dimilin® IGR Substituted Chitin synthesis inhibitor Benzoylurea 8 Hexythiazox Savey®/Hexygon® Miticide Carboxamide Ovicide/larvacide, specific mode of action unknown 8 Clofentezine Ovation® Miticide Tetrazine Ovicide/larvacide, specific mode of action unknown 9 Carbaryl Sevin® Insecticide Carbamate Acetyl cholinesterase inhibitor 9 Bendiocarb Turcam®/Closure® Insecticide Carbamate Acetyl cholinesterase inhibitor 9 Carbofuran Furadan® Insecticide Carbamate Acetyl cholinesterase inhibitor 9 Acephate Pinpoint®/Orthene® Insecticide Organophosphate Acetyl cholinesterase inhibitor Brackett®/Address® Sedagri® 9 Azinphos-methyl Guthion®/Sniper® Insecticide Organophosphate Acetyl cholinesterase inhibitor 9 Chlorpyrifos Dursban®/Duraguard® Insecticide Organophosphate Acetyl cholinesterase inhibitor 9 Diazinon Diazinon®/Knoxout® Insecticide Organophosphate Acetyl cholinesterase inhibitor 9 Dimethoate Dimethoate® Insecticide Organophosphate Acetyl cholinesterase inhibitor 9 Disulfoton Di-Syston® Insecticide Organophosphate Acetyl cholinesterase inhibitor 9 Ethoprop Mocap® Insecticide Organophosphate Acetyl cholinesterase inhibitor 9 Malathion Malathion®/Atrapa® Insecticide Organophosphate Acetyl cholinesterase inhibitor Prozap® 9 Methidathion Supracide® Insecticide Organophosphate Acetyl cholinesterase inhibitor 9 Naled Dibrom® Insecticide Organophosphate Acetyl cholinesterase inhibitor 9 Oxydemeton methyl Metasystox-R ® Insecticide Organophosphate Acetyl cholinesterase