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 investigated at Lincoln University, Canterbury, New Zealand in 1994-95. The proportion of damaged carrots resulting from late sowings (mid November-late December) and harvested before the third carrot rust fly generation was lower than those sown earlier (early-late October). However, a reduction in growing time for later sowing dates resulted in roots which were not of a marketable size. There were low numbers of first-generation flies caught from early November to late December, and very high numbers of third-generation flies caught from late March to late June. An early sowing (October) in combination with a harvest before the peak of third-generation flight activity (mid April-early May) resulted in a higher proportion of marketable carrots.