Occurrence and damage characteristics of weeds and influence on yield of green vegetables in Shanghai.
This study investigated the occurrence and damage status of weeds in green vegetable fields in nine counties of Shanghai. The investigations in spring/summer and autumn/winter found 67 weed species, belonging to 24 families and 54 genera, most of which are grassy and compositae weeds. Annual and perennial weeds are 82.1% and 17.9% respectively. Native weeds accounted for 80.6%, while 19.4% of alien species. Grassy weeds such as Echinochloa crusgalli, Digitaria sanguinalis, Eleusine indica and broadleaf weeds such as Chenopodium serotinum, Amaranthus lividus, Eclipta prostrata, Stellaria media, Capsella bursa-pastoris appeared more frequently in these weeds. Influence of Echinochloa crusgalli and Stellaria media on the yield of Chrysanthemum coronarium and Brassica campestris ssp. Chinensis var. communis was measured. The results showed that Chrysanthemum coronarium yield loss rate were up to 48.7% and 49.5% respectively when the growth density of Echinochloa crusgalli was 300/m2 or Stellaria media was 250/m2. The yield of Brassica campestris ssp. Chinensis var. communis was effected obviously when the growth density of Stellaria media was 150/m2, while the loss rate of Brassica campestris ssp. Chinensis var. communis was up to 42.0%-48.1% when the growth density of Stellaria media was 200/m2-250/m2.