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Abstract
Potato mirid, Calocoris norvegicus, commonly occurs in white clover, Trifolium repens, crops in Canterbury, New Zealand. Its potential to reduce seed yield by feeding injury was investigated in field cage plots in a cv. Huia white clover seed crop. Third to fifth instar nymphs were released at five intensities ranging from 0 to 2 mirids per 5 stolons. Plant growth and inflorescence production were determined by regular measurements of 15–20 tagged stolons per cage. Seed was harvested in late summer and dressed into first and second quality seed for which thousand seed weights were recorded. No differences between plant growth and flowering pattern were observed between treatments, but inflorescence numbers were quad‐ratically reduced as mirid numbers increased. When total plot flowering and yield components were compared, a significant negative quadratic relationship between total inflorescences and first quality seed yield with increasing mirid intensity was demonstrated. For second quality seed yield a negative linear relationship was observed. A positive linear relationship between undamaged inflorescences and total yield per plot was also demonstrated. On the basis of current returns for white clover seed ($4 kg−1), losses of up to $740 ha−1 were estimated.