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 during which weeds must be controlled to prevent unacceptable yield losses. In order to determine the critical period of weed control in dry bean (Phaseolus vulgaris, Khomein cultivar), a field study was conducted at Agricultural Research Station of Lorestan University on 2004. Experimental treatments were arranged in randomized complete blocks with 4 replications. The treatments consisted of two different periods of 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 maintained weed free until 14, 28, 42, 56 and 70 days after crop emergence (DAE). The weeds were subsequently allowed to compete until final harvest (84 days). In the second series, weed interference treatments of varying duration allowed weeds to compete Correspondence to: rmirzaei57@yahoo.com with dry bean from crop emergence until 14, 28, 42, 56 and 70 days; then the plots were weeded and kept weed-free until harvest. Maximum weed-infested and weed-free periods of 14 weeks after dry bean emergence were maintained by hand weeding. Species composition, density, dry matter of weeds, and relation to reduction of dry bean seed yield were investigated. The major weed species were Amaranthus sp 41.5%, Tribulus terrestris 37.5%, Sorghum halepense 29%, Echinochloa crus-galli 25%, Convolvulus arvensis 24% and other species 21% of the total density. The highest dry matters were recorded for Amaranthus sp, Tribulus terrestris and Sorghum halepense, respectively. Experimental treatments had significant effects (P)