EFFECTS OF FLEA BEETLE FEEDING ON TRANSPLANTED AND DIRECT-SEEDED BROCCOLI

Abstract

The effects of flea beetle (Coleoptera: Chrysomelidae) feeding on transplanted and direct-seeded broccoli (Brassica oleracea var. italica Pl.) were studied for 2 yr in field plots in south central Manitoba. Flea beetle populations were monitored in biweekly broccoli plantings and the plots were assessed for stand loss, plant damage and yield. Transplants of 4-, 3-, or 2-wk-old seedlings, direct-seeded plants and direct-seeded plants with carbofuran granules in furrow were compared. The earliest plantings had the greatest mortality, delayed harvest and most prolonged harvest period because of high beetle populations early in the season. Small transplants and newly emerged seedlings were the most severely defoliated by the beetles while broccoli plants beyond the 6- to 8-leaf stage suffered negligible damage. Direct-seeded plants without insecticide had the fewest and generally lowest-quality heads. Over both years direct-seeded broccoli yielded only 37% of the marketable harvest of direct-seeded, insecticide-protected broccoli. The old transplants were the most tolerant to flea beetle attack. Feeding on bud florets of the mature heads by the large summer generation of flea beetles in the second year of the study reduced marketable yields of all treatments.Key words: Flea beetle, broccoli, transplant, direct seed, carbofuran, Brassica oleracea var. italica Pl.