The greater attractiveness that has been observed for the north face of traps may be due to greater activity of flies in the afternoon which would relate to greater brightness of north face. Trap efficacy decreases significantly after a week. Traps should never be kept more than a week. Monitoring becomes less predictive because the trap system is based upon the ability to measure traffic into fields that adult flies must leave to seek food. When the crop is mature it is better to err on the side of recommending sprays because mature crop represents mature investment.
Mature carrots can put a root too deep to be marketable.
Clipping should leave about ten inches above-ground to allow for mechanical harvesting. The major pest of carrots in the southern coastal areas of British Columbia. It is a sporadic pest in the Southern Interior and Kootenays. Not present in Terrace, Quesnel, nor in the Peace River area. Larval tunnelling causes a rust-colored etching deforms the root, and permits entry of decay organisms.