Influence of annual forages on weed dynamics in a cropping system

Abstract

Alternatives to herbicides are needed for weed control. Field studies were conducted in 1994/1995 and 1995/1996 to investigate the nature of forage crop-weed dynamics and to test the effect of single year forage crops on the density and community composition of annual weeds in a following field pea (Pisium sativum L.) test crop. Five spring-seeded forage treatments were compared with wheat (Triticum aestivum L.) grain crops (with or without herbicides for grassy and broadleaved weeds): winter triticale (Triticosecale) (simulation grazed); spring triticale (silage); spring/winter triticale intercrop (silage, then simulation grazed); alfalfa (Medicago sativa L.) (hay); sorghum-sudangrass (Sorghum bicolor [L.] Moench × Sorghum sudanese [Piper]) (hay); and a weedy fallow (silage). A fall rye (Secale cereale L.) grain crop and a sweet clover (Melilotis officinalis L.)/winter triticale double crop (hay, then simulation grazing) were included in the 1995/1996 trial. All forage systems were at least as effective as the sprayed wheat control in suppressing wild oat (Avena fatua L.); however, effects on other weeds, especially broadleaved species, were variable. Biennial crops provided the best early season weed control, while long-season systems such winter triticale and the triticale intercrop provided the best late season weed control. Forages shifted the weed community composition away from wild oat and green foxtail (Setaria viridis L. Beauv.) to a similar or greater extent than herbicide-treated wheat. Forage systems that did not provide season-long crop competition tended to have more broadleaved weeds. Some forage systems increased pea grain yield the following year (relative to the sprayed wheat control); however, forages alone did not eliminate the need for herbicides in the pea crop. Annual forages may play an important role in integrated weed management, especially for wild oat, however further research to refine forage-based weed management systems is needed. Key words: Integrated weed management, alfalfa, intercropping, double cropping, organic farming