ELSEVIER Permeability of plastic films to methyl bromide: field study Abraham Gamliel§*, Avi Grinstein”, L.Klein+, Y. Cohen+ and Jaacov Katan* *Laboratory for Pest Management Application, AR0 The Volcani Center, Bet Dagan 50250, Israel, Qromine Compounds Ltd., Agricultural Department, P.O.B. 180 Beer Sheva, Israel and *Department of Plant Pathology and Microbiology, The Hebrew University of Jerusalem, Faculty of Agricultural, Food and Environmental Quality Sciences, Rehovot 76100, Israel The use of gas-impermeable films to minimize methyl bromide (MB) emission into the atmosphere from soil fumigation was studied in the field. Three experiments evaluated various plastic films during fumigation with a reduced dosage of MB. The concentration of MB decreased sharply in the soil during the first 24 h when polyethylene-based films were used. In contrast, films having a layer of barrier material, such as polyamide or ethylene vinyl alcohol, were significantly less permeable, shown by a gradual decrease in the MB concentration in the soil, a relatively higher concentration in deeper soil layers, and higher concentration (C) by exposure time (T) (C x r) values. A significant correlation was obtained between permeability values obtained in the laboratory and C x 7’ values in the field. Fumigation under impermeable films at the reduced dosage of 20-25 g m 2 was effective in killing propagules of five pathogenic fungi to a depth of 40 cm. The significant correlation obtained between C x T values and the level of fungal killing suggests that using impermeable films reduces MB dosage and emission to the atmosphere while maintaining effective pest control. 0 199X Elsevier Science Ltd. All rights reserved Keywords: Fusarium oxysporum; Sclerotium rolfsii; soil fumigation; impermeable film Methyl bromide (MB) is the most widely used fumigant for soil disinfestation due to its broad spectrum activity against soil-borne pests and high penetration ability. In recent years, concern regarding this fumigant’s potential role in ozone depletion (Anon., 1995) and regulations to reduce its use and eventually phase it out altogether, have prompted a need for methods to reduce MB dosage and emission into the atmosphere. The commonly used films for MB fumigation, e.g. low-density polyethylene (LDPE) or high-density polyethylene (HDPE), provide poor barriers (Anon., 1995; Daponte, 1994; De Heer et al., 1983; Gamliel et al., 1997a,b), allowing MB to escape into the atmosphere within a short time after its application (Yagi et al., 1995). Previous studies have shown that gas-impermeable films slow this escape, resulting in the maintenance of a relatively higher MB concentration for a certain period of time in the soil (Anon., 1995; Daponte, 1994; De Heer et al., 1983; Gamliel et al., 1997a,b). Pesticide toxicity is a function of its concentration (C) and exposure time (T) (Knight, 1925; MacDonald and Reichmuth, 1996). Therefore, extending a pathogen’s exposure to a reduced dosage of fumigant would result in a C x T product which is similar to that obtained with high %orresponding author. dosages of MB under permeable films, and conse- quently enable effective pathogen control. Thus, films that are less permeable to MB may enable increased exposure time and reduced concentration without affecting pest control (Van Wambeke, 1983; Gamliel et al., 1997a). This has been shown recently in the control of Verticillium wilt in potatoes (Gamliel et al., 1997b) and in other studies (Cebolla zyxwvutsrqponmlkjihg et ul., 1996; Gullino et al., 1996; Van Wambeke et al., 1983). The objectives of the present study were to evaluate, under field conditions, the permeability properties of polyethylene-based and impermeable films to MB, and to relate C x T values to mortality of fungal propagules under these conditions. Materials and methods Selection of films Various LDPE, HDPE, and multilayer films with barrier materials (e.g. ethylene vinyl alcohol-EVOH, or polyamide) (Table I), were tested for their perme- ability to MB in the laboratory using the variable- volume method (Anon., 1982) with permeability cell (CS-135, Custom Scientific Instruments, Whippany, NJ, USA). The cell consisted of the tested plastic film Crop Protection 1998 Volume 17 Number 3 241