Transformation of aldicarb sulfoxide and aldicarb sulfone in four water-saturated sandy subsoils

The transformation of aldicarb sulfoxide and aldicarb sulfone was studied in incubations with water-saturated subsoils under simulated field conditions at 10°C. The subsoils were collected at four locations from beneath the water table at a depth of 2.5 to 3.5 m. In three of the subsoils, the half-life of sulfoxide, incubated at concentrations of 0.14-0.17 mg litre^?1, ranged from 0.7 to 2.8 years. At higher concentrations (8-13 mg litre^?1), its half-life ranged from 3.4 to 6.4 years. At the lower concentration, a large fraction of sulfoxide was transformed into sulfone. The rates of transformation of the sulfone at the lower concentration in the three subsoils corresponded to half-lives of 3.3 to 8.1 years, but in only one subsoil was a significant transformation rate (half-life 6.7 years) measured at the higher concentration during the 2.3-year incubation period. The half-lives at the lower concentrations were more like those in field studies, and perhaps would still underestimate transformation rates under field conditions. After a year, 2.5-15% of the higher sulfoxide and sulfone doses had been trapped as [¹⁴C] carbon dioxide. In the fourth subsoil, with more anaerobic conditions, the half-life of sulfoxide at both concentrations was less than 0.02 year and that of sulfone was about 0.04 year. Four or five radio-labelled transformation products could be traced in this subsoil and about half of the dose of both compounds was trapped as [¹⁴C] carbon dioxide.     

Inhibition of sterol biosynthesis in cell-free extracts of Botrytis cinerea by prochloraz and prochloraz analogues

The sensitivity of cytochrome-P450-dependent sterol 14α-demethylase (P450_14DM) to prochloraz and several prochloraz analogues was studied in a cell-free assay of Botrytis cinerea Pers. ex Fr. The EC₅₀ values (concentrations which inhibited radial growth of B. cinerea by 50%) of the compounds tested ranged from 3.3 × 10 ?8 to 1.7 × 10 ?5 M. The IV₅₀ values (concentrations which inhibited cell-free C₄-demethyl sterol synthesis by 50%) in cell-free assays of B. cinerea ranged from 2.6 × 10 ?9 to 4.4 × 10 ?7 M. Ranking compounds in terms of their relative inhibitory potencies showed quite similar trends to the order of fungitoxicity, but the IC₅₀ values did not quantitatively reflect the differences in toxicity. Therefore, the differential inhibition of cell-free P450_14DM activity by these compounds cannot fully account for their differences in activity towards B. cinerea. Additional mechanisms must be involved. The compounds tested were generally more potent in the B. cinerea assay than in similar assays developed for Penicillium italicum Wehmer and, in particular, Saccharomyces cerevisiae Meyen. This correlated with the relatively higher activity of most test compounds to B. cinerea. Results suggest that the cell-free assay of B. cinerea is more useful to evaluate candidate fungicides as inhibitors of sterol 14α-demethyiase activity than similar assays from model organisms. The present study confirms that the affinity of prochloraz analogues for P450_14DM depends on the nature of the N-1 substituent of the imidazole and the azole ring. It was also found that addition of an amino group at C-2 of the imidazole moiety of prochloraz gave a compound (6) which inhibited 4, 4-demethyl sterol biosynthesis in B. cinerea at a different site from the P450_14DM. This was confirmed by the observation that laboratory-generated triadimenol-resistant isolates of B. cinerea showed reduced sensitivity to triadimenol and prochloraz, but not to compound 6.     

Isolation of microsomal cytochrome-p450 isozymes from Ustilago maydis and their interaction with sterol demethylation inhibitors

A procedure for the isolation of microsomes containing cytochrome-P450 isozymes from Ustilago maydis is described. Yields of P450 amount to approximately 19(±+ 6) pmol mg^?1 of microsomal protein. The wavelength of maximum absorbance of the reduced carbon monoxide difference spectrum is 448-449 nm. The azole fungicides prochloraz, etaconazole, imazalil, triadimefon and 3-(2,4-dichlorophenyl)-2-(1H-1,2,4-triazol-1-yl)-4(3H)-quinazoline, which differ markedly in toxicity to U. maydis, all induce type II binding difference spectra at extremely low concentrations (10^?9-10^?8 M). The DMI concentrations which cause half saturation of type II binding difference spectra (IC₅₀) do not correlate with the fungicidal activities of the azoles. Binding of carbon monoxide to ferrous cytochrome-P450 was only slightly inhibited to different degrees by the DMIs tested. However, the inhibition of carbon monoxide binding also does not correlate with fungitoxicity of the DMIs. The results in this paper suggest that the spectrophotometric studies with this preparation are not useful for evaluating selective toxicity of DMIs to intact sporidia of U. maydis.     

Sorption, degradation and leaching of the fungicide iprodione in a golf green under Scandinavian conditions: measurements, modelling and risk assessment

In cold climates, fungicides are used on golf greens to prevent snow mould causing serious damage to the turf. However, fungicide residues have been detected in runoff from golf courses, which may lead to restrictions on use. There is therefore an urgent need to improve understanding of the processes affecting leaching of fungicides from turfgrass systems to allow identification of green construction and management practices that minimize environmental impacts. In this study we monitored the leaching of the fungicide iprodione in a putting green. Sorption and degradation of iprodione was measured in batch and incubation experiments, and the simulation model MACRO was used as a risk assessment tool. Degradation of iprodione was bi-phasic, with a rapid initial phase (half-life 17 h) caused by enhanced biodegradation. Degradation rates slowed considerably after 5 days, with half-lives of up to 38 days. Sorption of iprodione was linear, with a K(oc) value of ca 400 cm(3) g(-1). MACRO reasonably accurately matched measured drainflows and concentrations of iprodione in soil and drainflow. However, peak concentrations in drainage were underestimated, which was attributed to preferential finger flow due to water repellency. The results also showed the importance of the organic matter content in the green root zone in reducing leaching. It was concluded that, with 'reasonable worst-case' use, losses of iprodione from greens can occur at concentrations exceeding water quality limits for aquatic ecosystems. Snow mould problems should be tackled by adopting green root zone mixes that minimize leaching and 'best management practices' that would avoid the need for intensive prophylactic use of fungicides.