Effect of crop rotations on weed control, Bidens cernua and Erigeron canadensis populations, and carrot yields in organic soils

Abstract

Organic coils in Quebec are prone to infestation by nodding beggarticks ( Bidens cernua L.) and Canada fleabane ( Erigeron canadensis L.), and by the root-knot nematode ( Meloidogyne hapla Chitwood). Yield losses can be very severe in fields where carrots have been grown continuously for several years. Six 3-year crop rotations, including onion ( Allium cepa L.), barley ( Hordeum vulgare L.) or a weed fallow, were compared to continuous carrot production to establish their effect on weed control and carrot yield. Weed populations and above ground dry biomass were monitored four times each season. Total and marketable yields of carrots also were measured each year. Results show that weed populations increase when onions are part of the production cycle, and decrease with barley. Beggarticks and fleabane populations were static when cropping sequences included 2 years of carrots with or without onions. Total carrot yield increased by 35–50% and marketable yield increased 17–25-fold due to a drastic reduction in root-knot nematode populations when barley was included in the rotation. The onion-barley-carrot rotation provided good weed control, including nodding beggarticks and Canada fleabane, and yielded high quality carrots.