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New Zealand Plant Protection 64 (2011): 288

Plant-back safety of fodder beet (Beta vulgaris) following the application of tribenuron-methyl

C. Dowsett, T.K. James and A. Rahman

ABSTRACT

Tribenuron-methyl is a sulfonylurea herbicide for control of certain broadleaf weeds in cereal crops and prior to conservation tillage. Safe plant-back periods for this herbicide are expected to be shorter in acid soils compared to neutral or alkaline soils due to a faster rate of degradation at low pH levels. This research was conducted to determine the safe plant-back period for fodder beet following use of tribenuron-methyl in New Zealand soils. Two similar sedimentary soils from Hawke's Bay were used in this glasshouse study, one with a pH of 7.0 and the other with a pH of 5.5. Residual activity of the herbicide was measured by bioassay using fodder beet as the test species. The plant-back times were 14, 28, 42 or 56 days after spraying. Assessments included number of plants emerged, plant vigour scores and dry matter weights 8 weeks after planting. The results showed that in the low pH soil a plant-back period of 14 days is sufficient, although the best growth and vigour was noted if planting was carried out 28 days after spraying. In the high pH soil even the longest period of 56 days tested in this study was not safe for planting of fodder beet.

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