Impact of broom twig miner on broom growth and florifory in Canterbury, New Zealand

The broom twigminer (Leucoptera spartifoliella) is widely distributed in New Zealand and was believed to be damaging broom plants (Cytisus scoparius) in some regions. A simple exclusion experiment was designed to investigate the impact of the broom twigminer on broom growth and floriflory. The twig miner was chemically excluded from 15 broom bushes, each bush being paired with an adjacent untreated bush. Significant differences in broom growth were observed after three months: the bushes without the twig miner increased in height by 39%, while bushes with the twig miner increased by 11 %. No significant effects in broom growth were observed six or eleven months after the twig miner was excluded. After eleven months there was a trend towards greater florifory in the bushes without the twig miner, but the difference was not statistically significant.