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New Zealand Plant Protection 57 (2004): 271-276

Effect of rainfall on the movement and persistence of metsulfuron-methyl and clopyralid applied to pasture

T.K. James, A. Rahman, J.M. Mellsop and M. Trolove

ABSTRACT

Metsulfuron-methyl and clopyralid are two herbicides frequently used in pasture. The mobility and persistence of both have been previously reported and showed great variation between overseas and New Zealand results. In a field trial the effect of simulated rain within the first 7 days of herbicide application on the persistence and movement of these chemicals was studied using bioassay methods. Results show that 15 mm of simulated rain on either Day 1, 3 or 7 after herbicide application had no apparent effect on the dissipation of metsulfuron-methyl but natural rainfall that occurred later in the experiment leached it to the 50100 mm soil layer. Glasshouse bioassays of soil samples collected from the field showed that between 75% and 90% of the applied herbicide had degraded by Day 56. Clopyralid stayed in the top 50 mm of soil during the experiment but by Day 56 less than 10% of the applied herbicide remained.

Keywords: metsulfuron-methyl, clopyralid, bioassay, persistence, rainfall.

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