O Neus

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.

Analysis of the sulfonylurea herbicide metsulfuron-methyl and its metabolites in the soil of cereal crops. Comparative analytical chemistry of the sulfonylureas

Abstract For the analysis of metsulfuron-methyl in the crop soils with a sensitivity limit of 0.3 μg kg−1 dry soil, in the soil extract metsulfuron-methyl was separated from its soil metabolites and the soil impurities by repeated thin-layer chromatographies (TLC). In the cleaned soil extract, diazomethane transformed metsulfuron-methyl 1 into N,N′ -dimethyl metsulfuron-methyl 2 (methyl 2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)methylamino]carbonyl]methylamino]sulfonyl]benzoate). In the gas-liquid chromatograph with detection by electron capture (GC-EC) and in the combined gas chromatograph-mass spectrometer (GC-MS), 2 was transformed into 1-dioxy-2-N-methyl-3-keto-1,2-benzisothiazole 3 which was measured by GC-EC with confirmation by GC-MS. The metsulfuron-methyl soil metabolites 2-sulfonamido-methylbenzoate 6, 1-dioxy-3-keto-1,2-benzisothiazole (saccharin) 7 and 2-sulfonamidobenzoic acid 8 were analyzed in the soil of winter wheat crops by a procedure similar to the one for metsulfuron-methyl. After their separation and purification in the soil extracts by TLC, 7 and 8 were methylated, and analyzed as 3 in the GC-EC and GC-MS apparatus where the generated 6 was quantitatively transformed into 3; 6 was analyzed as such with the GC and GC-MS apparatus wherein it was transformed into 3. The sensitivity limit for each metabolite was 0.3 μg of equivalents of metsulfuron-methyl kg−1dry soil. The syntheses of the analysis standards of the metsulfuron-methyl derivatives 2 and 3, and of the metsulfuron-methyl metabolites 6, 7 and 8 are described. The transformation pathways of metsulfuron-methyl and of its derivatives are different from those of the pyridine-pyrimidine sulfonylurea herbicides flupyrsulfuron-methyl and rimsulfuron. The soil analysis of a sulfonylurea -by means of one of its transformation product- needs a previous study of the chemical reactivity of the sulfonylurea. This leads to the analysis procedures for the main soil metabolites of the sulfonylurea.

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...

Persistence and Movement of the Herbicide Propoxycarbazone-Sodium in Winter Wheat Crops

The new herbicide propoxycarbazone (sodium methyl 2-[[[(4,5-dihydro-4-methyl-5-oxo-3-propoxy-1H-1,2,4-triazole-1-yl)carbonyl]amino]sulfonyl]benzoate, 1 ) has been measured in the soil of winter wheat crops. In the soil extract, propoxycarbazone was separated from its potential soil metabolites by repeated TLC. Propoxycarbazone was methylated with diazomethane. In the GC and GC-MS apparatus, the N -methylpropoxycarbazone 2 (methyl 2-[[[(4,5-dihydro-4-methyl-5-oxo-3-propoxy-1H-1,2,4-triazole-1-yl)carbonyl]methylamino]sulfonyl]benzoate) generated N -methylsaccharin 4 (1-dioxy-2- N -methyl-3-keto-1,2-benzisothiazol) which was measured. Propoxycarbazone has been applied in the spring at the rate of 70 g ha m 1 post-emergence on winter wheat crops grown in several sites different as to their soil texture and composition. In the 0-10 cm surface soil layer of the winter wheat crops grown on sandy loam (Melle) or on clay loam (Zevekote) soils, the half-life of propoxycarbazone was 54 days. In the winter wheat crop grown on loam soil (Cortil-Noirmont), the propoxycarbazone soil half-life was 31 days. The difference between the propoxycarbazone soil half-lives at the different sites was related to the organic fertilizer treatments applied in the past. After the winter wheat harvest at the end of August, the concentration of propoxycarbazone in soil was very low at Cortil-Noirmont; at the end of September, propoxycarbazone was no more detected. At Melle and Zevekote, the concentration of propoxycarbazone in soil was very low in September, and disappeared completely at the end of October. Since the treatment and until the end of October, propoxycarbazone was not detected in the 10-15 and 15-20 cm surface soil layers of the three trials.

Cyanazine soil dissipation in leek crops: Combined influences of rain and organic fertilizer treatment

The herbicide cyanazine has been applied at the rate of 750 g a.i. ha‐1 15 days after planting of a leek crop in July 1994. The field was divided into plots. Control plots were not treated with an organic fertilizer. The other plots were treated either with a green manure, or with 100 tons ha‐1 cow manure applied either in November or in March before planting, or with 100 tons ha‐1 mushroom cultivation compost applied in March. The same organic fertilizer treatments ‐and only this one‐ had been applied once a year on the same field plots since 4 years before planting the crop of July 1994, except the control plots which were left organic fertilizers untreated. During the 2.5 months period following the cyanazine treatment, the cyanazine soil half‐lives in these field plots respectively were 26, 32, 37, 43 and 37 days. The trial was repeated in 1995 on the same field plots, each of the organic fertilizer treatments being applied again on the same plots. The corresponding cyanazine soil half‐lives respectiv...

Diuron and chlorotoluron herbicides dissipation and leaching out from the peat substrate of containers of ornamental plants in nursery

One year old conifer plants were grown on peat substrate in containers in a field nursery. One of diuron (1.25 kg ha‐1) or chlorotoluron (1.5kg ha‐1) were applied on separate field plots (one herbicide per container and per plot). For the herbicide treatment, some pots were set in a temporary location away from the rest of the experiment; thereafter these pots were placed on lysi‐meter tables set in the center of the plots treated with the same herbicide applied at the same dose and date. The overhead sprinkler irrigation (180 mm month‐1, to which added the rainfall) was the same above the lysimeter and the field plot. The water collected from the lysimeter was only the one which leached through the peat of the containers set on the lysimeter. During the 7 months which followed the herbicide treatment, diuron and chlorotoluron mainly remained ‐ for more than 98% of the herbicide residue remaining in peat at each analysis time ‐ in the 0–5 cm peat surface layer, their half‐lives there being 3.3 and 2.6 mon...

Herbicide flurochloridone soil biodegradation in potato crops

Flurochloridone herbicide has been applied pre‐emergence in potato crops at the rate of 500 g a.i. ha‐1. The field was divided into plots. Each plot was treated either with 50 tons ha‐1 cow manure or pig slurry, or with green manure. Control plots were not treated with organic fertilizers. During the 2.5 months period following flurochloridone application in the 1994 potato crop, in the control plots, and in the plots treated either with green manure, pig slurry or cow manure, flurochloridone soil half‐lives respectively were 41, 48, 67 and 74 days. In the potato crop repeated in 1995 on the same field plots, each being treated again with the same organic fertilizer, the corresponding flurochloridone soil half‐lives respectively were 50, 58, 80 and 70 days. In both 1994 and 1995 crops, after the first 2.5 months period following flurochloridone application, the rates of flurochloridone soil biodegradation increased, and its soil residues became very low and similar in the plots treated or not with organic...