The effect of tillage regime on emergence of root maggots (Delia spp) (Diptera: Anthomyiidae) from Canola

The effect of four tillage regimes on the emergence of root maggots (Delia spp.) (Diptera: Anthomyiidae) was determined on experimental plots seeded the previous year to either Brassica rapa L. or Brassica napus L. The tillage regimes evaluated comprised no tillage, tillage in the spring only, tillage in the fall only, and tillage in both the fall and the spring. Emergence trap collections of Delia radicum (L.) and Delia floralis (Fallen) were made from;he experimental plots from early May to mid-July of 1991 and 1992. In both years, emergence from untilled plots significantly exceeded that from plots subjected to any other tillage treatment. Tillage resulted in a decrease in emergence of 55-64% for D. radicum, and a reduction of 53-72% for D. floralis. For D. floralis, greatest reductions in emergence following a tillage treatment occurred in plots tilled only in the fall or in plots tilled in both the fall and the spring; however for D. radicum, tillage in the fall, the spring, and in both the fall and the spring reduced emergence to approximately the same extent. Results of our study indicated that canola growers in regions of high population densities of root maggot should cultivate infested fields, preferably in fall, to reduce the emergence success of Delia spp.