Early season weed competition reduces yield of newly planted matted row strawberries

Competition from weeds and an interplanted sudangrass [Sorghum bicolor (L.) Moensch, formerly S. sudanense (Piper) Stapf.] cover crop was allowed to o ccur in newly-planted strawberries (Fragaria xananassa Duch.) for varying l engths of time, and at different times during the growing season. Newly pla nted strawberries were most susceptible to weed and cover crop competition during the first 2 months after planting, as both runnering (stolon formati on) and subsequent yield were impacted. In 1994-95, 1 month of weed competi tion in June reduced yield by 20%, whereas 2 months of weed competition red uced yield by 65%. However, 1 month of uncontrolled weed growth later in th e growing season had little to no impact on yield, although weed biomass wa s much less then. Herbicide (napropamide) use alone was insufficient to pre vent weed competition and yield reduction. In our study, yield was reduced 0.67 t.ha(-1) or 5.5% for each 100 g.m(-2) of weed biomass. The data sugges t that it is critical for growers to minimize weed competition early in the planting year when weed growth is greatest. Since an interplanted sudangra ss cover crop displaced a portion of the weeds, it could be seeded later in the year to provide some weed suppression without a negative impact on yie ld. Chemical names used: N, N, Diethyl-2-(1-naphthalenyloxy)-propionamide ( napropamide); N-(phosphonomethyl)glycine (glyphosate).