INVESTIGATIONS ON THE BIOLOGY AND CONTROL OF THE CARROT FLY (PSILA ROSAE F.)

Abstract

Records were obtained for the emergence of the first and second generation flies at Chatteris and Cambridge. There is a correlation between the age of the carrot crop and the commencement of the emergence of the second generation from it. The first generation was successfully controlled by killing the flies with a poison bait sprayed on the dikesides of the carrot fields. This treatment reduced the population of second generation flies and also their attack. Spraying the dikesides and/or the headlands of eight maincrop carrot fields in August and September greatly reduced the second generation damage. Very high kills of carrot fly were obtained on the headlands of treated fields. Poor results were given by the treatment on three very weedy fields which were incompletely treated. A marked increase in attack occurred in three untreated areas in 1942 as compared with the previous year. Application of the poison bait spray in the field is discussed. Creosote-treated string gave promising results in small-scale experiments for the control of the second generation. Calomel dust (4°) with and without grass cuttings caused no reduction in attack. In hot sunny weather the flies shelter in the vegetation around carrot fields from about 10 a.m. until about 5 p.m. In the cooler conditions of early morning and evening there is a movement of flies into the field. This rhythm is not maintained in dull warm weather Seedling carrots may be attacked in the field any time after the cotyledon stage. This enables the first generation of flies to propagate on main crop carrots. Soil sections about carrot rows showed that pupae of the overwintering generation are closely congregated around the carrots. Various insecticides were tested for the destruction of pupae in the soil. A creosote-sawdust mixture gave the best results. Storage experiments showed that clamped carrots deteriorate much less than those unlifted. The population of flies is greatly increased by allowing attacked carrots to remain unlifted throughout the winter or by ploughing in.