Assessing damage by manuka beetles (<i>Pyronota</i> spp) in flipped West Coast pastures

Abstract

Manuka beetles (Pyronota festiva and P setosa) have become a major problem in dairy pastures developed on flipped soils on the South Islands West Coast The beetles rapidly invaded these new pastures and signs of damage appeared within 13 seasons Damage is caused by beetle larvae feeding on the roots of grasses and clovers creating damage patches of dead and dying plants A visual damage scale has been prepared to assist farmers to grade damage and provide a basis to make control decisions Damage rankings were estimated by assessing both the proportion of the paddock with obvious damage patches and the overall vigour of the pasture Increasing damage severity was shown to be strongly correlated with numbers of beetle larvae in the soil Pastures invaded by manuka beetles had lower autumn production and if untreated overall pasture production declined to very low levels within 23 seasons due to poor pasture composition and low pasture covers It is estimated that milk yields on affected farms have been depressed by 30 where no controls have been implemented It is recommended that pastures with high damage gradings should either be treated with insecticide or renewed