Persistence of Terbutryn and Atrazine in Soil as Affected by Soil Disinfestation and Fungicides

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Abstract
The effect of soil disinfestation with methyl bromide (MB) or by soil solarization (solar heating) and the fungicides TMTD (tetramethylthiuram disulfide) and fentin acetate (triphenyltin acetate) on the degradation of terbutryn [2-(tert-butylamino)-4-(ethylamino)-6-methylthio)-s-triazine] and atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] were investigated. The degradation of terbutryn appeared to follow first-order kinetics with a half-life of about 2 weeks and was much slower in MB-treated or solarized soils, i.e. half-life of about 11 weeks. Suppression of terbutryn degradation in the MB-treated soil was still evident 8 months after soil fumigation, similar to that found in autoclaved soil. TMTD and fentin acetate at 20 μg/g soil strongly inhibited degradation of terbutryn in soil. Degradation of atrazine was affected to a lesser extent by soil disinfestation. Results from the present study suggest that biocidal soil treatments may slow herbicide degradation. Thus, herbicide dosages in disinfested soil should be adjusted in order to avoid phytotoxicity. Moreover, lower dosages might be sufficient to attain weed control, and combined disinfestation or fungicides with herbicide treatments might be intentionally used to extend herbicide activity.