title: Isoxaben soil biodegradation in pear tree orchard after repeated high dose application.
abstract: During the past nine years, each of the plots of a pear tree orchard were treated annually with the same herbicide treatment. The following herbicide treatments were compared, each being made by application of a mixture of two or three herbicides: 1a, no herbicide at all, weeds being hoed (control 1a); 2, diuron + paraquat 3 + 1 kg/ha; 3, simazine + paraquat 2 + 1 kg/ha; 4, isoxaben + diuron + paraquat 0.5 + 1.6 + 1 kg/ha; and 5, isoxaben + simazine + paraquat 0.5 + 1.25 + 1 kg/ha. In March 1996, one year after the final orchard herbicide treatment, isoxaben could not be detected in the soils of any field plots; isoxaben was incorporated at 0.74 mg/kg in the loamy soils sampled separately in each of the field plots, and the soils were incubated in the laboratory. Isoxaben soil half-lives were 92 days in the soils treated previously with herbicide treatments 1a, 2, or 3 and 42 days in the soils treated with herbicide treatments 4 and 5. The repeated isoxaben treatments applied in the past thus enhanced the isoxaben soil biodegradation; diuron, simazine, and paraquat had no influence on this rate enhancement. On the other hand, herbicide treatments 4 and 5 were applied in the orchard in April 1996 on the corresponding plots treated in this manner for the last nine years. Isoxaben + paraquat 0.5 + 1 kg/ha was applied simultaneously on other plots (control 1b) not treated in the past with isoxaben. During the growth season in the orchard, the isoxaben soil half-lives in the control plots 1b was 101 days, and 41 days in the plots where herbicide treatments 4 or 5 were applied.
authors.affiliation: Laboratory of Phytopharmacy, Catholic University of Louvain, 3, Place Croix du Sud, SCI 15D, 1348 Louvain-la-Neuve, Belgium.
authors.forename: J
authors.initials: J
authors.lastname: Rouchaud
authors.forename: O
authors.initials: O
authors.lastname: Neus
authors.forename: R
authors.initials: R
authors.lastname: Bulcke
authors.forename: D
authors.initials: D
authors.lastname: Callens
authors.forename: T
authors.initials: T
authors.lastname: Dekkers
mesh_terms: D001549:Benzamides / Q000737:chemistry*; D001673:Biodegradation, Environmental; D006540:Herbicides / Q000737:chemistry*; D012989:Soil Pollutants / Q000032:analysis*; D014197:Trees
chemical_list: D001549:Benzamides; D006540:Herbicides; D012989:Soil Pollutants; C057467:isoxaben