Floristic Composition of the Weeds and Efficacy of PRE Herbicides in a Black Locust (Robinia pseudoacacia L.) Nursery

Abstract

Field trials were conducted in 2010 and 2011 to evaluate floristic composition of weeds and the efficacy of pre herbicides in black locust (Robinia pseudoacacia L.) nurseries. The weed population in both years was consisted mainly of annual spring and summer weeds, and some perennial weeds. The weediness in both years was relatively high. Weed density in the untreated control plots was 106.5 plants per m2 in 2010 and 87.4 plants per m2 in 2011. The most dominant weeds were Chenopodium album, Polygonum aviculare and Amaranthus retroflexus in 2010 and Polygonum aviculare, Tribolus terestris and Cynodon dactilon in 2011. By taxonomic aspect, the weed flora was distributed in 11 families. 15 weed species were dicotyledons and 2 weed species were monocotyledons. Terophytes were the dominant life form weed category in black locust nurseries. Efficacy of herbicides 28 days after treatment (DAT) ranged from 91.0% (pendimethalin) to 95.3% (linuron) in 2010, and 74.5% (linuron) to 88.0% (pendimethalin) in 2011, respectively. Efficacy of herbicides 56 DAT ranged from 93.6% (pendimethalin) to 98.3% (linuron) in 2010, and from 74.8% (linuron) to 83.1% (pendimethalin) in 2011, respectively. Prevailing weed control by herbicides was not consistent over the years. However, efficacy of herbicides in control of prevailing weeds 28 and 56 DAT ranged from 88% to 100% in 2010 and 7% to 86% in 2011, respectively. Lower herbicide efficacy in 2011 was most likely due to high precipitation occurred immediately after herbicide application and domination of perennial weeds, particularly Cynodon dactilon.