Some effects of weed control on the numbers of the small cabbage white (Pieris rapae L.) on brusseb sprouts.
The following is based largely on the author's summary. During investigations in Britain in 1968 on the effect of weed control on the incidence of Pieris rapae (L.) on brussels sprouts, the presence of weeds within the crop was found to increase the suitability of-the habitat for some of the arthropod predators of Pieris. Harpalus rufipes (Deg.) [cf. RAE A 57 1969] was particularly dependent on ground cover. With the higher number of predators, survival of larvae of Pieris was significantly poorer on weedy than on hoed plots. Fewer eggs were laid on plots with many flowering weeds, but the difference was not significant at the 5% level. The numbers of Pieris were low, and the advantageous effects of weeds were outweighed by the harmful effect of competition between the weeds and the crop. The yield was highest on plots kept free from weeds.