The use of pesticides is sometimes considered to have dated from the latter half of the 19th century. However, a survey of the classical literature (Smith and Secoy, 1975) has shown that there were frequent references to chemicals and natural products which appear to have been used for the control of plant disease and for killing unwanted plants and animals. As a result of further research into contemporary writings, a compendium of inorganic chemicals used for pest control in European agriculture from earliest recorded times until the middle of the 19th century is now presented with attempts to assess their possible success.

Losses of ethalfluralin, trifluralin, and triallate vapors to the atmosphere, following unincorporated surface applications of their granular formulations, were compared over a 14-day period. Then, following two incorporations three days apart into the top 5 cm of the field surface, volatility losses were monitored for a further 10 days. Vapor losses were determined using the aerodynamic method for flux measurement with air samples being collected at 30-, 50-, 75-, 100-, 150-, and 200-cm heights above the soil surface. A total of 21% of the applied triallate, 18% of the applied trifluralin, and 14% of the initial ethalfluralin were lost by volatilization over the 24-day period. Volatility losses were associated with rainfall events, and when the soil surface was dry such losses were negligible. Keywords: Field study; granular formulations; ethalfluralin; triallate; trifluralin; volatility

Studies were undertaken to evaluate the dissipation of pendimethalin (1.1 kg ha(-1)) in two Saskatchewan field soils following applications of an emulsifiable concentrate (EC) formulation in the spring. Persistence of pendimethalin applied as a granular formulation in the fall was also investigated at one of the locations. The EC formulation was applied in May, 1993, and by late September, 0.50 +/- 0.16 kg ha(-1) (41 +/- 13% of that applied) remained at the Estlin site, and 0.34 +/- 0.07 kg ha(-1) (31 +/- 6%) remained at the Regina location. Over the winter, there was little further loss of pendimethalin at either locality. By September, 1994 (479 days after treatment), 0.34 +/- 0.07 kg ha(-1) (28 +/- 6% of the applied herbicide) remained at Estlin and 0.13 +/- 0.05 kg ha(-1) (12 +/- 4%) remained at Regina. Some overwinter dissipation of pendimethalin occurred from a granular formulation (1.51 kg a.i. ha(-1)) applied at Regina on October 4, 1993, with 1.01 +/- 0.15 kg ha(-1) (67 +/- 10% of the initial treatment) remaining in May, 1994. By the third week in September, 1994, 350 days after application, 0.45 +/- 0.08 kg ha(-1) (30 +/- 5% of the initial herbicide) remained. Over the 479-day EC formulation and the 350-day granular formulation study periods, there was no leaching of the herbicide below 10 cm.

The sulfonylurea herbicides are a group of about twenty compounds used for the control of broad-leaved weeds and some grasses in cereal crops. These herbicides are non-volatile, and their water solubilities are pH dependent being greater in alkaline than in acidic solutions. Their soil adsorption is generally low, with leaching potential in alkaline field soils. Sulfonylurea herbicides are degraded in soils by both chemical and biochemical mechanisms. Chemical degradation is particularly important in acidic soils where herbicide degradation is considerably more rapid that in soils of pH >7. Application rates in the order of 10 g ha(-1) necessitate analytical techniques capable of quantifying soil based residues in the sub mu g kg(-1) levels. Analytical methodologies based on plant bioassays, and chemical extraction followed by gas chromatographic (GC), high performance liquid chromatographic (HPLC), and enzyme immunoassay techniques are described and discussed.

A soil bacterium was isolated capable of metabolizing the five phenoxyalkanoic acid herbicides 2,4-D, 2,4-DB, MCPA, MCPB, and 2,4,5-T in mineral solution with the individual herbicides as sole carbon source. The optimum temperature for breakdown was in the range 20-30 degrees C. In a 500-L aerated tank, the organism metabolized kilogram quantities of both 2,4-D and MCPA dimethylamine formulations to inorganic chloride. This bacterium retained activity for at least 18 months after storage in a frozen state at -70 degrees C. When applied to field plots, the organism is able to survive in the soil for at least 615 days and degrade both 2,4-D and MCPA significantly more rapidly than in soil from an untreated control plot.

The field persistence of trifluralin from fall treatments of both emulsifiable concentrate (EC) and granular formulations was investigated at two sites in Saskatchewan over a 2-yr period. At both locations, there were no significant differences (P = 0.05) in trifluralin persistence from fall applications of either formulation. In addition, the carryover of trifluralin residues in farmers’ fields following fall and spring applications of EC and granular formulations was monitored at several Saskatchewan locations to determine their persistence under typical farming practices. Trifluralin residue data indicated that following fall applications, the percent carry-over to the first spring was 83 ± 21(15 fields sampled) and 37 ± 15 (28 fields sampled) to the second spring; and that following spring applications, the percent carry-over to the next spring was 33 ± 12 (14 fields sampled). Key words: Field studies, persistence, formulations, trifluralin, herbicide

The hydrolysis of the herbicide [C-14] amidosulfuron (HOE 075032) was investigated in buffered aqueous solutions with pH values of 5, 7, and 9 at temperatures of 10, 20, 30, 40, and 50 degrees C. Hydrolysis was both temperature and pH dependent following first-order kinetics. The half-lives ranged from 1.1 day in buffer at pH 5 and 50 degrees C to >500 days in solution of pH 9 at 10 OC. Activation energies for the hydrolysis of [C-14] amidosulfuron at pH 5, 7, and 9 were 101, 121, and 135 kJ/mol, respectively. Under all conditions [C-14]-2-amino-4,6-dimethoxypyrimidine was the major degradation product, though a transient C-14 degradation product was formed in all solutions at pH 5. Incubation of [C-14]amidosulfuron in a silt loam (pH 5.2) at 20 degrees C and 85% field capacity (21% moisture) resulted in herbicide degradation that followed first-order kinetics with a half-life of 36 +/- 6 days. [C-14]-2-Amino-4,6-dimethoxypyrimidine did not appear to be a degradation product in the silt loam. Solvent-nonextractable radioactivity associated with the silt loam after 12 weeks of incubation accounted for approximately 33% of the applied C-14.

The degradation of the herbicide [C-14]amidosulfuron (HOE 075032) was studied in three Saskatchewan soils at 0.1 mug/g under controlled temperature and moisture conditions. At 85 % of field capacity, degradation approximated to first-order kinetics at soil temperatures of 10, 20, and 30-degrees-C, with half-life values ranging from 14 +/- 2 days (mean and standard deviation) in a loamy sand incubated at 30-degrees-C to 231 +/- 41 days in a clay at 10-degrees-C. In a clay at 20-degrees-C, herbicide degradation followed first-order kinetics and was directly correlated with soil moisture, with half-life values varying from 246 +/- 21 days at 50 % of field capacity to 63 +/- 17 days at 100 %. There was negligible herbicide breakdown in air-dried soils incubated at 30-degrees-C for 70 days. During the study period, solvent-extractable 14C degradation products accounted for up to 48 % of the applied radioactivity. Solvent-nonextractable radioactivity associated with the soils incubated at 20-degrees-C ranged from 4 to 11 % of the initial treatment.

The relationships between the actual amount of spring-applied trifluralin detected in soil at seeding, initial injury to flax, and crop growth and yield were investigated in southern Manitoba over three growing seasons. As the amount of trifluralin in the soil increased, flax density and dry matter production decreased, such that at a soil concentration equivalent to 1 kg ai ha−1trifluralin, the two were reduced by 40 and 49%, respectively. Recovery from early-season injury was characterized by enhanced crop growth rates (CGRs) and net assimilation rates (NARs) of surviving plants during the remainder of the growing season. Maximum recovery occurred in plots where trifluralin levels in the soil were between 0.8 and 1 kg ha−1at seeding. During the interval between stem elongation and bud initiation, CGRs and NARs of flax in the trifluralin-treated plots exceeded those of flax in the untreated plots by up to 1.5 and 1.2 times, respectively. Additionally, the number of branches per plant increased linearly as trifluralin amounts in the soil increased. Flax seed yield was decreased by trifluralin as described by the equation: flax seed (% of untreated control) = 104.9 - 13.3[trifluralin detected (kg ha−1) at seeding]. Based on this equation, trifluralin levels in the soil of up to 0.7 kg ai ha−1caused less than a 5% reduction in flax yield under weed-free conditions.

Polar solvents based on aqueous methanol and aqueous acetonitrile are good extractants of herbicides from Saskatchewan field soils that had received treatments of the individual chemicals 6 to 17 months previously. The addition of small amounts of acetic acid or ammonium hydroxide to aqueous acetonitrile resulted in greater recovery of most herbicides. In general, 50 ml of the extraction solvent were added to 20 g of soil and the soils were then initially extracted for 1-hr on a wrist-action shaker and then allowed to stand overnight before being shaken for a further 1-hr period.

The degradation of dimethylamine, used extensively in herbicide formulations, was monitored in three Saskatchewan soils at 85% of field capacity under laboratory conditions at 20-degrees-C using [C-14]dimethylamine at rates of 0.5-100 mug/g. In all soils, and at all rates, there was rapid evolution of [C-14]carbon dioxide with between 69 and 89% of the applied radioactivity being released after 7 days. The rapid breakdown of dimethylamine in the loamy sand was confirmed by chemical analysis following solvent extraction. In air-dried loamy sand, <1% of the initial radioactivity was released as [C-14]carbon dioxide after 7 days, with almost quantitative recovery of the dimethylamine. At [C-14]dimethylamine concentrations of 0.5, 10, and 100 mug/g, between 10 and 16% of the applied radioactivity was incorporated into the microbial biomass 7 days after soil treatment.

The extraction of C-14 from air-dried samples of three soils fortified 14 days previously with [C-14]-glyphosate was compared using 10 different solvent systems and an extended-shaking procedure. C-14 recoveries exceeding 73% were reproducibly achieved with 0.35 M H3PO4 (and 0.09 M with respect to CaCl2), 0.1 M NaOH, and 0.5 M NH4OH. With the phosphoric acid and ammonium hydroxide extractants, highest recoveries from a loamy sand were recorded with a soil/solvent ratio of 1:5 or 1:10. With the aqueous sodium hydroxide, highest recoveries were achieved from all soils using a soil/solvent ratio of 1:2.5. Recoveries of C-14 from all three soils, using 0.1 M NaOH, were not significantly different whether fortified 14, 28, or, in the case of a clay, 56 days previously with [C-14]glyphosate. Some loss of extractable radioactivity was noted in two of the soils after 56 days.

The transformation of 2.0-mu-g/g ring-labeled [C-14]-2,4-dichlorophenoxyacetic acid was investigated, in the dark under controlled laboratory conditions, in four soils at 85% field capacity and at 20-degrees-C. The rates of herbicide breakdown were reflected in the numbers of 2,4-D-degrading organisms isolated from the soils at the four sites. Over a 24-day period in soils with no recent herbicide history, more than 89% of the applied 2,4-D was metabolized with 25-31% of the applied C-14 being released as carbon dioxide, 2-10% being solvent recoverable as [C-14]-2,4-dichloroanisole, and 39-43% being associated with soil in a solvent-nonextractable form. In soils with prior 2,4-D treatments herbicide degradation was faster with approximately 50% of the applied radioactivity being released as carbon dioxide, 1-4% being solvent recoverable as [C-14]-2,4-dichlorophenol and 2-5% as [C-14]-2,4-dichloroanisole, and 22-30% of the initial C-14 associated with the soil in a solvent-nonextractable form.

Under laboratory conditions, the rates of breakdown of (C-14)2,4-D (2,4-dichlorophenoxyacetic acid), (C-14)MCPA (4-chloro-2-methyl-phenoxyacetic acid), (C-14)mecoprop (2-[4-chloro-2-methylphenoxy]propionic acid), and 2,4,5-T (2,4-5-trichlorophenoxyacetic acid) in soils from Canadian prairie field plots, 6 wk after receiving the 43rd annual application of 2,4-D formulations or the 37th annual treatment with MCPA, were compared with those in soils from untreated plots. Loss of 2,4-D and MCPA was faster in soils that had received continuous applications with the appropriate herbicide than in soil from the control plots. There was some indication that (C-14)2,4-D was dissipated more rapidly from soils treated annually with MCPA than from the control soils, though breakdown was slower than in soil from the 2,4-D-treated plots. In contrast, (C-14)MCPA breakdown in the 2,4-D-treated plots was similar to that in untreated soils. Breakdown of (C-14)mecoprop and 2,4,5-T in the 2,4-D and MCPA-treated soils was very similar to that in the controls soils. Thus, there was no support for the phenomenon of cross-enhancement. Forty-eight weeks after the last herbicide applications, the field soils still maintained their ability to degrade 2,4-D or MCPA more rapidly than soil from untreated control plots.