Karolien Cools

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.

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...

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...