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New Zealand Plant Protection 65 (2012): 295

Assessing damage by manuka beetles (Pyronota spp.) in "flipped" West Coast pastures

J.E. Dunbar, P.W. Hateley, R.J. Townsend, S.M. Zydenbos and T.A. Jackson


Manuka beetles (Pyronota festiva and P. setosa) have become a major problem in dairy pastures developed on "flipped" soils on the South Island's West Coast. The beetles rapidly invaded these new pastures and signs of damage appeared within 1-3 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 2-3 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.

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