The Current Status of Imazalil: a Post Harvest Fungicide for Citrus

Since 1974 the Decco-Tiltbelt Division of Penn walt Corporation has been conducting research programs on the experimental fungicide l-[2-(2,4-dichlorophenyl)-2-(2propenyloxy) ethyl]-IH-imidazole (Imazalil) at their Mon rovia, California Research Laboratory. Tests have proven the efficacy of this fungicide against postharvest diseases of citrus. It is especially effective in sporulation and decay control of Penicillium digitatum Sacc. and Penicillium italicum Wehmer, green and blue mold of citrus. Tests have demonstrated that Imazalil is equally effective against strains of Penicillium possessing resistance to current commercial fungicides. On March 12, 1979, the Environmental Protec tion Agency issued to Pennwalt a temporary tolerance and an experimental permit which allow the commercial appli cation of Imazalil. This paper updates the information base on Imazalil, and presents early results from the current ex perimental program. Pests such as fungi, bacteria, insects, nematodes, weeds and rodents are estimated to cause serious crop losses. Esti mates of such losses of more than 30% of the potential pro duction in the world are frequently cited, the situation being more serious in warmer and humid regions. An addi tional 10% of the crops are typically lost due to biological decay after harvest (29). Prevention of even a portion of such losses would markedly increase the world food supply. A broad attack on pest control problems is essential and the intelligent and safe use of pesticides has become a key component in all integrated pest management systems. Re search activities on pesticides precedes the commercial use of pesticides; these activities are directed at two general areas, 1) to improve the efficiency for existing known pesti cides and to learn more about their safe and judicious uses and 2) to discover and develop newer pesticides that are safe and effective where the present ones fail or are no longer available. According to available data from a USDA report (29) losses of fresh fruits and vegetables in the U. S. during shipment and retail marketing are estimated at more than $200 million annually. A substantial portion of this loss is attributed to diseases caused by fungi and bacteria. Ac cording to Eckert (8) the most serious post harvest diseases are those which cause rapid and extensive breakdown of fresh produce items, often soiling the entire packed carton or box as exemplified by attacks of Penicillium species in citrus and pome fruits; Rhizopus species in stone fruits, Proc. Fla. State Hort. Soc. 92: 1979. strawberries; and Erwinia species in potatoes, tomatoes and other vegetables. Eckert has also thoroughly reviewed the role of chemical control of post harvest pathogens. The post harvest industry has developed and marketed products with fungicides such as sodium-o-phenyl phenate (SOPP), 2-aminobutane (2-AB), 2-(4-thiazolyl) benzimidazole (TBZ), methyl l-(butylcarbamoyl)-2-benzimidazolecarbamate (Benomyl), and dimethyl 4, 4, -Ophenylenebis (3-thioallophanate) (Topsin-M) for the treatment of most food crops to reduce losses caused by fungal decay. However, one of the common problems in the chemical control of plant pathogens is the ability of pathogenic fungi to develop resistance to these chemicals (7, 9, 10, 11, 13, 14, 19, 21, 26, and 32). These reports document the widespread occurrence of resistant Penicillium strains to commercially available citrus fungicides in diverse citrus growing areas. McDonald, et al (18) reported strains of Penicillium species resistant to TBZ and Benomyl isolated from decaying citrus fruits obtained from a terminal market in Rotterdam. These citrus fruits originated from 18 different countries; decayed lemons and grapefruits were more often sources for the resistant isolates than decayed