Jean Rouchaud

Effects of fertilizer on insecticides adsorption and biodegradation in crop soils.

Recent organic fertilizer treatments (cow manure, pig slurry, composts, or green manure) simultaneously increase insecticide adsorption onto soil and the insecticide soil persistence, indicating a mechanism of slow release of insecticide into soil by the organic matter. This occurred in sugar beet crops with aldicarb, thiofanox and imidacloprid; also, in leek, cauliflower and brussels sprouts crops with chlorpyrifos and chlorfenvinphos. In contrast, organic fertilizer treatments applied once or repeatedly in the past, have no significant influence on adsorption or persistence of insecticides; the same is observed for the old soil organic matter, when its soil concentrations change in limited ranges.

DISSIPATION OF THE TRIKETONE MESOTRIONE HERBICIDE IN THE SOIL OF CORN CROPS GROWN ON DIFFERENT SOIL TYPES

The new triketone herbicide mesotrione corresponds to the older sulcotrione in which the 2‐chloro benzoyl substituent is replaced by a nitro group, generating an herbicide of greater efficiency and a broader spectrum of activity. Mesotrione has been applied within the same 15 days period pre‐emergence at the rate of 150gha‐1 to four corn crops made at different sites located 40 km apart in Belgium and of soils of different textures, but similar pH and organic matter (old humus) contents. The mesotrione soil half‐life in the 0–10 cm surface soil layer (which contained more than 90% of the residue) was 50 days in loam soil (at Zarlardinge), 41 days in sandy loam soil (at Melle) and in clay soil (at Koksijde), and 34 days in sandy soil (at Zingem). The cumulative effects of the recent organic fertilizer treatments and of the soil texture could explain the differences between the soil half‐lives. The time for the 90% dissipation of mesotrione was between 3.6 (in the sandy soil) to 4.7 months (in the sandy loam, loam and clay soils). The low mesotrione soil residues remaining after the corn harvest should disappear with the usual heavy rains in autumn, and the tilling which precedes the following crop and dilutes the mesotrione soil residue. These low mesotrione soil residues thus should have no phytotoxicity toward the following crop, especially at the lower application dose of 100 g mesotrione ha‐1 used in practice.

Hydrolytic Biodegradation of Chlorothalonil in the Soil and in Cabbage Crops

Broccoli and Chinese cabbage crops were treated at planting by pouring an emulsion of the fungicide chlorothalonil around the stem of the plant. During culture, chlorothalonil was biodegraded in soil into l,3‐dicarbamoyl‐2,4,5,6‐tetrachlorobenzene (compound 1), l,3‐dicyano‐4‐hydroxy‐2,5,6‐trichlorobenzene (compound 2), and l‐carbamoyl‐3‐cyano‐4‐hydroxy‐2,5,6‐trichlorobenzene (compound 3). Compounds 1 and 2 were the major metabolites in soil. In the harvested broccoli (in the flower) and Chinese cabbages (the leaves), the concentrations of chlorothalonil and of compounds 1 and 2 were lower respectively than 0.1, 0.1 and 0.5mg/kg fresh weight.

Soil organic matter ageing and its effect on insecticide imidacloprid soil biodegradation in sugar beet crop

Imidacloprid insecticide was applied in pelleted seed dressing at sugar beet sowing in March 1993. The field was divided into plots. On some plots, one cow manure treatment (50 tons ha‐1) had been applied either 18 or 6 months before sugar beet sowing. On other plots, two cow manure treatments (2 × 50 tons ha‐1) had been applied: either at 18 and 6 months, or at 18 and 1 months before sugar beet sowing. During the first two crop months period, the imidacloprid soil half‐lives in these plots were 40, 85, 112 and 121 days, respectively. The single cow manure treatment applied 18 months before sugar beet sowing almost had no more influence on the rate of imidacloprid soil biodegradation. The cow manure treatments applied either 6 or 1 months before sowing slowed down the imidacloprid soil biodegradation with similar intensities. To the greater imidacloprid soil concentrations corresponded greater imidacloprid concentrations in the leaves of sugar beet. After the first two months crop period, the rates of imi...

New Trends in the Studies About the Metabolism of Pesticides in Plants

During the past 15 years, many reviews have been published concerning the metabolism of pesticides in plants. They usually study the problem according to the different types of pesticides (Frear et al. 1972 a and b, Kearney 1975, Klein 1972, Kuhr 1976, Menn 1972, Naylor 1976, Sijpesteijn et al. 1976), or according to the different types of biochemical reactions which generate the degradation products (Baldwin 1977, Matsunaka 1972, Menn and Still 1977). These last times, more and more new types of pesticides are studied; these studies show that the previous generalizations frequently do not correspond to reality. The present work studies the factors which influence the biochemical pathways of pesticide metabolism, the rate of metabolism, and the possible phytosanitary and toxicological properties of the metabolites. This work is based on recent researches; it thus shows the new trends of the studies about pesticide metabolism in plants.

Persistence of the sulfonylurea herbicide iodosulfuron-methyl in the soil of winter wheat crops

On four winter wheat fields grown on soils of different textures in Belgium, 10 g a.i. ha−1 of the sulfonylurea herbicide iodosulfuron-methyl-sodium was applied post-emergence in the spring. A procedure was developed for the analysis in field soils of iodosulfuron-methyl 1 and of its metabolites iodosulfonamide 2 and iodosaccharin 3 with a sensitivity limit of 0.3 µg of equivalents of iodosulfuron-methyl 1 kg−1 dry soil. GC and GC-MS was used after purification of the soil extracts by repeated TLC, and methylation. The results of the chemical analyses were confirmed by means of bioassays using sugar beet as test plants. On a winter wheat crop grown on sandy loam soil of pH 6.2 at Melle, iodosulfuron-methyl-sodium 1 was applied at the beginning of April. The iodosulfuron-methyl 1 soil half-life in the 0–10 cm surface soil layer was 60 days. At the end of June, the sum of the concentrations of the metabolites 2 and 3 in the 0–10 cm surface soil layer attained a maximum corresponding to 27% of the applied dose. Green manures were sown after the harvest of the wheat at the end of August. No phytotoxicity at all was observed during the growth of the green manures, in spite of the very low residues of iodosulfuron-methyl 1 remaining in soil in September and October. At the mid of November, iodosulfuron-methyl 1 and its metabolites 2 and 3 were no more detected in soil. On three other winter wheat crops grown on clay soils of pH of about 8 at Leke, Gistel and Zevekote, iodosulfuron-methyl-sodium 1 was applied at the beginning of May. The soil half-life of iodosulfuron-methyl 1 in the 0–10 cm surface soil layer was between 30 and 44 days. Since the application and until the mid of November, in all the trials made on sandy loam or clay soils, iodosulfuron-methyl 1 (and its metabolites 2 and 3 in the trial made on sandy loam soil) were never detected in the 10–15 and 15–20 cm surface soil layers, indicating their low mobilities in the field soils.

Influence of cow manure and composts on the effects of chlorfenvinphos on field crops.

Cauliflower crops were grown in several regions and seasons (spring and summer). Five days after planting, the plants were treated against the root fly by pouring onto soil around the plant stem an emulsion of chlorfenvinphos [2-chloro-1-(2,4-dichlorophenyl) ethenyl diethyl phosphate] in water. The fields were divided into plots. Onto each plot, one of the organic fertilizers, city refuse compost, mushroom cultivation compost, or cow manure was applied at the rate of 100 tons/ha, 1 or 3.5 months before the insecticide treatment. There were also control plots which were not treated with any of the organic fertilizers. During the first 50 days crop period which followed the insecticide treatment, the chlorfenvinphos soil concentrations were always greater in the organic fertilizer-treated plots, than in the untreated ones (controls). The intensity of the organic fertilizers effect as to the increase of chlorfenvinphos soil persistence was in the following increasing order: city refuse compost < cow manure < mushroom cultivation compost. The organic fertilizer effects were greater when they had been soil-incorporated 3.5 months—instead of 1 month—before the chlorfenvinphos soil treatment. The increase of the insecticide soil concentrations—due to the organic fertilizers treatments—should increase the plant protection efficiency during the period of the first 50 days, during which time the young plants are the most sensitive to insects. During the following period of the 2 or 3 last crop weeks, the effects of the organic fertilizers onto the rate of chlorfenvinphos soil metabolism were levelled off; at harvest, the very low soil-resting residues were similar in the organic fertilizers treated and untreated plots. At harvest, no chlorfenvinphos nor its metabolites were detected in the ‘flower’ of cauliflower of all the plots, the analytical limit of sensitivity being 0.02 mg kg−1 fresh weight for all of these compounds.

Concentrations of the Herbicides Propyzamide, Chlorpropham, and of Their Metabolites in Soil and Lettuce Under Field Conditions

Propyzamide [3,5-dichloro-N-(l,l-dimethyl-2-propynyl)benzamide] is a useful and effective herbicide which is widely used for weed control in the cultures of lettuce, endive, witloof, scorzonera, and alfalfa. As witn most pestlcides, propyzamide possesses properties which make it necessary to establish rules for its safe use. Propyzamide has some carcinogenicity (Reuber 1980); tnat activity would correspond to the inactivation of hepatic cytochrome P-450 in animals (Montellano and Kunze 1980). Following dietary administration of propyzamide to a lactating cow, about 5% of the administered dose was detected in the milk (St John and Lisk 1975). To reduce these risks, the lettuce tolerance for the combined residues of propyzamide and its metabolites has been reduced to i ppm in most of the countries (USEPA 1983). winter crops, planted in the year of herbicide application to the preceding crop, were especially sensitive to herbicide residues; winter wheat and barley, grasses, spring cereals and other crops were injured by resldues of propyzamide (Eagle 1981). The half-life of propyzamide in different soils has been measured in laboratory experiments; thus in the absence of any crop culture; it varied from I0 to 40 days at 25vC, and from 60 to 120 days at 15~

Metsulfuron‐methyl soil persistence and mobility in winter wheat and following green manure crops

A procedure has been developed for the analysis of metsulfuron‐methyl in the soil of field crops. The soil extracts are cleaned by repeated TLC, and metsulfuron‐methyl is simultaneously separated from its soil metabolites. Metsulfuron‐methyl is transformed by diazomethane into its N,N ‘‐dimethyl derivative which in the GC (electron capture detection) and GC‐MS apparatus is transformed into a benzisothiazole compound which is measured with great sensitivity. The sensitivity limit is 0.3 μg metsulfuron‐methyl kg‐1 dry soil. The results of the chemical analyses are confirmed by bioassays using sugar beet as test plant. Metsulfuron‐methyl was measured in the soil of two winter wheat crops after post‐emergence application in the spring of 6 g metsulfuron‐methyl ha‐1. In the 0–8 cm surface soil layer, the metsulfuron‐methyl soil half‐life was 78 days in 1997, and 67 days in 1998. During crop, metsulfuron‐methyl remained in the 0–8 cm surface soil layer. There, it was at a maximum concentration and herbicide eff...

Effects of organic fertilizers on aldicarb soil biodegradation in sugar beet crops.

In the present work, the influences of several organic fertilizer treatment regimens were compared as to their slowing down effect on aldicarb soil metabolism in a sugar beet crop. The organic fertilizers treatment schemes had been repeatedly applied in the past 30 years, according to a 3-year rotation cycle. The following organic fertilizers treatment regimens—which are the main ones used in the agronomy practice—were compared: Treatment 1: no organic fertilizer at all; treatment 2: 40 tons cow manure ha−1; treatment 3: 40 tons pig slurry ha−1 + green manure + crop wastes; treatment 4: green manure + crop wastes; treatment 5: straw cereal wastes alone. A sugar beet crop was sown in April 1991, 1 kg aldicarb ha−1 being applied in granulates in the sowing furrow. During the 2.9 first crop months, the soil half-lives of the sum of the insecticide S- +SO- +SO2-aldicarb in the sowing line in the 0–25 cm surface soil layer were 21.6, 44.4, 39.6, 35.7, and 30.3 days in the treatments 1, 2, 3, 4, and 5 treated plots, respectively. The organic fertilizers soil treatments thus increased the persistence of the total insecticide compounds soil concentrations, and probably also the insecticide protection efficiencies. Comparison of the results obtained here with the ones previously obtained with other crop trials, herbicides and soil insecticides, suggests that the soil organic matter is the most efficient to slow down the insecticides soil biodegradation, compared to the old humus originating from the organic fertilizers treatments made more than one year ago. After the three first sugar beet crop months, the effect of the organic fertilizers treatments on the aldicarb and its insecticide metabolites soil persistences disappeared, their soil concentrations become very low and similar in the organic fertilizers treated and untreated control plots.