EFFECTS OF SOWING AND HARVEST DATES ON CARROT-RUST-FLY (PSILA-ROSAE) DAMAGE TO CARROTS IN CANTERBURY, NEW-ZEALAND

The effects of manipulating sowing and harvest dates on the degree of carrot rust fly (Psila rosae) damage on carrots (Daucus carota) was in vestigated at Lincoln University, Canterbury, New Zealand in 1994-95. The proportion of damaged carrots resulting from late sowings (mid Nov ember-late December) and harvested before the third carrot rust fly ge neration was lower than those sown earlier (early-late October). Howev er, a reduction in growing time for later sowing dates resulted in roo ts which were not of a marketable size. There were low numbers of firs t-generation flies caught from early November to late December, and ve ry high numbers of third-generation flies caught from late March to la te June. An early sowing (October) in combination with a harvest befor e the peak of third-generation flight activity (mid April-early May) r esulted in a higher proportion of marketable carrots.