Dissipation of Pendimethalin in the Garlic (Allium sativum L.) under Subtropical Condition

Abstract

Pendimethalin is the common name of N-(1-ethylpropyl)3,4-dimethyl-2,6-dinitrobenzenamine, a dinitroaniline herbicide that is used widely for selective control of most annual grasses and many annual broad-leaved weeds in crop fields such as rice, peanut, soybean, cabbage, garlic, onion, radish, tomato, pea, and tobacco in Taiwan. Field dissipation studies have revealed that pendimethalin is persistent (Walker and Bond, 1977; Zimdalh et al., 1984; Smith et al., 1995). Walker and Bond (1977) found that the half-life of pendimethalin in a sandy soil, with the moisture at 75% field capacity, is 98 days at 30 C and 409 days at 10 C. The half-life of pendimethalin in a sandy loam soil treated with 1.5 kg a.i./ha in wheat crops in the tropical climate of India ranges from 58 to 63 days (Kulshrestha and Yaduraju, 1987). Singh et al. (2002) have also found that the dissipation of pendimethalin in soil has a half-life of 74 days. Pendimethalin degrades more rapidly in anaerobic soil than in aerobic soil conditions. The T1/2 values of pendimethalin in anaerobic and aerobic soils are 33 and 52 days, respectively (Kulshrestha and Singh, 1992). However, field studies conducted in Greece show that DT50 of pendimethalin in onion fields range from 37 to 39 days (Nicholas and George, 1998). Furthermore, the half-lives of Pendimethalin in cabbage fields with the application rates of 1 kg a.i./ha and 2 kg a.i./ha are 15 and 17 days, respectively (Arora and Gopal, 2004). Besides persistence, the mobility and leaching ability are also important in the environmental study of pesticides. Pendimethalin is classified as a non-leaching compound (Cooper et al., 1994). The field persistence of residues of pendimethalin in soil and garlic (Allium sativum L.) plants in the subtropical conditions of Taiwan have not been examined. This study measures the dissipation and mobility of pendimethalin in a garlic field by the model ecosystem. Additionally, the movement and degradation of pendimethalin in garlic plants are investigated.