Response of canola to simulated diamondback moth (Lepidoptera: Plutellidae) defoliation at different growth stages

Abstract

In field trials conducted during 1995–1998, canola cultivar "Falcon" was subjected to different levels of simulated insect defoliation at four stages of crop growth. Plants were 0, 33, 67 and 100% defoliated at rosette and flowering stages during the 1995–1996 season as well as 2–4 leaf stage during the 1996–1997 and 1997–1998 seasons. Plants were 0, 50 and 100% defoliated at pod filling stage during all seasons. Over all seasons, defoliation did not consistently affect the number of plants per unit area, plant height, 1000 seed weight, and oil content of seeds for most of the defoliation treatments. However, defoliation at the 2–4 leaf and rosette stages made plants more susceptible to cold injury. Generally, canola could withstand a higher level of defoliation as crop development progressed. Maximum yield reductions occurred for defoliations at the 2–4 leaf stage followed by the rosette and flowering stages of the crop. No significant yield losses were recorded for defoliations at the pod filling stage. Results suggest that canola is most sensitive to defoliation in its early stages of growth. Greater amounts of defoliation can be tolerated as crop development progresses. The relationships between defoliation and yield loss were used to establish diamondback moth economic injury levels for canola at different crop growth stages. Key words: Canola, Brassica napus, oilseed rape, simulated defoliation, economic injury level