In general, the number and type of fungicides registered for use on ornamental crops is limited. Estimating the economic impact of the loss of fungicides to the commercial ornamental crops industry [i.e., nurseries and greenhouses] is difficult because there are hundreds of plant species grown as ornamental plants and each has its own complex of diseases. Estimating the economic impact of one to several diseases on a given host without a key fungicide is not practical and may not be possible.
The important issues for disease management in commercial nurseries and greenhouses are the compatibility of any one fungicide on the multitude of plant species being grown, the spectrum of activity of a single product against many diseases, and flexibility of the label. Consequently, products that are effective against a number of diseases, are safe to use on many different plant hosts, and have a broadly written label are the ones used most frequently. In a recent publication, National Agricultural Pesticide Impact Assessment Program (NAPIAP) Report No. 1-CA-96: Biologic and Economic Assessment of Pest Management in the United States Greenhouse and Nursery Industry, thiophanate-methyl, chlorothalonil, and mancozeb were the three fungicides used in greatest quantities for managing foliar diseases in the Southeast. The dicarboximides [vinclozolin & iprodione] were fourth in line. Coppers are broad spectrum in activity but can cause phytotoxicity and are less effective than the three most popular fungicides. Most of the other fungicides registered for use on ornamental crops in nurseries can be very effective but have limited spectra of activity and narrowly defined labels. For root disease management, metalaxyl, fosetyl-Al, and etridiazole are used in the greatest quantities.
Loss of any one of these heavily used fungicides would pose a major negative economic impact on this industry because replacement products are not available. More frequent applications of fungicides with narrower spectra of activity would be necessary, and disease management across the nursery or greenhouse would be less effective and more costly.
The Ornamental industry will be impacted [by FQPA]. Because of the broadly written labels of dicarboximides and thiophanate methyl and chlorothalonil, they become the products of choice for an industry that grows a wide diversity of plant material in the same sites. Resistance and double resistance to thiophanate methyl and dicarboximides is wide spread in the industry. Mancozeb, also broadly labeled is an alternative but efficacy is considerably less, providing 20 to 30% less control than chlorothalonil. Other dithiocarbamates with much more limited labels also offer similar lower levels of control. Captan also a much more limited label is not available due to FQPA. Some copper labels are reasonably broad but they also lack efficacy. Since the loss of oxamyl, Nemacur is the only post plant nematicide for ornamentals. Each state must seek a 24C to enable use of Nemacur. Nematodes are estimated to cause 10% loss to none greenhouse nursery industry.