Early field experience with microencapsulated zinc phosphide paste for possum ground control in New Zealand

In New Zealand we need to develop new control tools for the overabundant brushtail possum, which is an agricultural and environmental pest. In this study we evaluated the performance of a new microencapsulated zinc phosphide (MZP) paste (1.5% w/w nominal conc.) in a captive study and at six North Island field sites. In the captive study 14 out of 16 possums fed MZP paste bait died (87.5% kill ± 8.3% SE) with death occurring on average 165.4 minutes (± 5.5 SE) after first eating the bait. At all field sites relative possum abundance was estimated using a residual trap catch index, and contractors were able to choose their preferred ground-control technique. Pre-feeding non-toxic paste (using 200–320 g/ha) was carried out over 2 weeks with at least one top-up after 7 days. Toxic bait was then deployed using the same baiting regime, and the average decline in possum abundance at the field sites was 82.2% (± 3.2% SE). This trial demonstrates that experienced contractors can get good kills using MZP and a refinement of best practice techniques could further improve control efficacy.