Soil residues of picloram applied aerially to New Zealand brushweeds

MacDiarmid, B.N.

Proceedings of the 28th New Zealand Weed and Pest Control Conference: 109-114


Accession: 000500068

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Soil samples were collected from 28 gorse (Ulex europaeus) locations sprayed aerially with 1.1 kg/ha picloram and 7 manuka (Leptospermum scoparium) locations receiving 0.5 kg/ha. Trifolium subterraneum bioassays showed picloram residues fell from 1.1 kg/ha to a safe level which would enable white clover establishment in 75% of the locations after 15 months. Residues from 0.5 kg/ha were safe after 3 to 6 months. Soil types varied in their capacity to adsorb picloram, requiring a loss of between 73 and 98% from an initial treatment of 1.1 kg/ha before becoming safe. Picloram levels were highest in the top 0 to 75 mm soil but did not vary between samples from pasture and bareground sites. From summary. Following aerial spraying of gorse and manuka (Leptospermum scoparium), bioassays and field sowings of white clover showed that in 75% of locations treated, picloram residues had fallen within 15 months from 1.1 kg/ha to a level which allowed white clover establishment. Soil types varied in their absorption capacity. Picloram concentrations were highest in the top 0-75 mm of soil but did not differ between pasture and bare ground sites.