Determination of the Critical Period of Weed Control in Dry Bean Using a Thermal Basis

The critical period for weed control is the period in the crop growth cycle duringwhich weeds must be controlled to prevent unacceptable yield losses. In order todetermine the critical period of weed control in dry bean iPhaseolus vulgaris,Khomein cultivar), a field study was conducted at Agricultural Research Station ofLorestan University on 2004. Experimental treatments were arranged in randomizedcomplete blocks with 4 replications. The treatments consisted of two different periodsof weed interference, a critical weed-free period, and a critical time of weed removal.In the first series, treatments of increasing duration of weed control were maintainedweed free until 14, 28, 42, 56 and 70 days after crop emergence (DAE). The weedswere subsequently allowed to compete until final harvest (84 days). In the secondseries, weed interference treatments of varying duration allowed weeds to compete with dry bean from crop emergence until 14, 28, 42, 56 and 70 days; then the plotswere weeded and kept weed-free until harvest. Maximum weed-infested and weedfreeperiods of 14 weeks after dry bean emergence were maintained by hand weeding.Species composition, density, dry matter of weeds, and relation to reduction of drybean seed yield were investigated. The major weed species were Amaranthus sp41.5%, Tribulus terrestris 37.5%, Sorghum halepense 29%, Echinochloa crus-galli25%, Convolvulus arvensis 24% and other species 21% of the total density. Thehighest dry matters were recorded for Amaranthus sp, Tribulus terrestris and Sorghumhalepense, respectively. Experimental treatments had significant effects (P