Effect of Temperature, Moisture, and Soil Texture on DCPA Degradation

Turf managers sometimes experience poor or early loss of control oftargeted weeds, even when herbicides are applied at recommended rates. This study was conducted to determine the influence of soil temperature and moisture on the rate of DCPA (dimethyl tetrachloroterephthalate) degradation in soil. The effect of six soil temperatures, three soil moistures, and three soil textures on the degradation of DCPA was measured in the laboratory through HPLC analysis. Soil temperature influenced the rate of DCPA degradation in the following order: 10< <15< <20<25=30>35°C. The average half-life ranged from 92 d at 10°C to 18 d at 30°C. Soil moisture content influenced the rate of degradation in the following order: low (0.1 kg H 20 kg ., soil)<medium (0.2 kg H20 kg-' soil) = high (0.4 kg H 20 kg I soil). The average half-life values of DCPA were 49, 33, and 31 d for the low, medium, and high soil moisture levels, respectively. A mathematical model of DCPA loss was utilized to determine the relative contribution of time, soil moisture, and soil temperature to the rate of degradation. Faster degradation of DCPA was observed from a sand/soil moisture (47.5:52.5, w/w) than from either a sand or a soil (Flanagan silt loam [fine, montmorillonitic, mesic Aquic ArgiudollJ). It was concluded that the dissipation rate of DCPA is largely dependent on soil environmental conditions including soil temperature, soil moisture, soil texture, and the time interval since the application to the soil. Thus, it is suggested that soil environmental factors be considered in determining the timing of second or subsequent applications when necessary rather than following a fixed application schedule. Additional index words: Crabgrass, Digitaria spp., Turfgrass, Preemergence herbicide, Pesticide fate. THE CHEMICAL control ofannual grasses is regarded as one of the most important procedures in turfgrass maintenance. The use of preemergence herbicides has been very effective for the short-term control of this group of weeds. To maintain a sufficient concentration ofherbicide in the soil for continued control ofgrass weeds from early spring through mid-summer, it is necessary to apply the herbicide in concentrations above that required for initial control. J.S. Choi, Dep. of Ornamental Horticulture, Dankuk Univ., Korea; T.W. Fermanian, DJ. Wehner, and L.A. Spomer, Dep. ofHorticulture, Univ. of Illinois at Urbana-Champaign, Urbana, IL 61801. Contribution from the Dep. of Horticulture, Univ. of Illinois at Urbana-Champaign. This study was part of Project no. 65-167 of the Agric. Exp. Stn., Univ. of Illinois at Urbana-Champaign. Received 25 Feb. 1987. *Corresponding author. Published in Agron. J. 80:108-113(1988). Turf managers sometimes experience poor or early loss of control of targeted weeds even when the herbicides are applied at recommended rates. This may be attributed to herbicide concentration dropping below the threshold level for control before the weed season is over. Many papers have discussed the effectiveness ofpreemergence herbicides (Johnson, 1976; Miller et al., 1978). DCPA, introduced in 1959, has been used in a wide range of crops including turf (Weed Science Society of America, 1983). Many studies have been conducted to examine the performance of DCPA under different cropping conditions, reporting effective suppression of annual weed germination by DCPA (Menges and Hubbard, 1970; Miller et al., 1978; Walker, 1978). However, inconsistent control in comparison to other preemergence herbicides was reported by Johnson (1976). Various half-life values of DCPA in the soil have also been reported by several investigators (Roberts et al., 1978; Branham, 1983; Hurto et al., 1979; Walker, 1978). Those half-life values ranged from 13 to 295 d depending on the prevalent soil environment. The rapid and inconsistent degradation rate of DCPA requires reexamination of the factors affecting its fate in soil to maximize its effective use in turf. The primary DCPA degradation mode is proposed . to be microbial degradation (Hurto and Turgeon, 1979; Lewis et al., 1978; Fields et al., 1967). Many researchers have reported a relatively small contribution of volatilization, photochemical decomposition, leaching, adsorption, or uptake by plants to the dissipation ofDCPA (Branham, 1983; Glofelty et al., 1984; Miller et al., 1978; Iyer et al., 1969). Ifmicrobial degrad~ti~n is a major mechanism for the loss of DCPA actIVIty in soil, factors such as soil temperature, soil moist';lre, and soil type affecting microbial activity would be Important in understanding the rate of loss of DCPA. Walker (1978) reported that soil temperat~re a~d soil moisture affected the degradation rate of eIght dIfferent herbicides under controlled laboratory condItions. A general trend of faster degradation rates was observed with increasing soil temperatu~e up !o. ~p-­ proximately that optimal for soil microbIal actlvltles