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

دوره بحراني كنترل علف هرز به دوره اي از چرخه زندگي گياه اطلاق مي شود كه علف هاي هرز بايد كنترل شده تا از كاهش اقتصادي عملكرد محصول جلوگيري شود. به منظور تعيين دوره بحراني كنترل علف هاي هرز لوبيا يك آزمايش مزرعه اي در ايستگاه تحقيقاتي دانشگاه لرستان در سال 1385 انجام شد. آزمايش در قالب طرح بلوكهاي كامل تصادفي با 4 تكرار انجام شد. تيمارهاي آزمايش شامل دوره هاي مختلف تداخل علف هاي هرز، و دوره هاي عاري از علف هرز بودند. در تيمارهاي عاري از علف هرز، علفهاي هرز به مدت 14، 28، 42، 56 و 70 روز بعد از سبز شدن لوبيا كنترل شده و پس از هر دوره تا روز 84 يعني برداشت نهايي به علفهاي هرز اجازه رشد داده شد. در تيمارهاي تداخل به ترتيب 14، 28، 42، 56 و 70 روز به علف هاي هرز اجازه رقابت داده شد و پس از هر دوره تا زمان برداشت نهايي محصول، كنترل شدند. تركيب گونه هاي علف هرز، تراكم، وزن خشك و ميزان كاهش عملكرد لوبيا در هر تيمار محاسبه شدند. علف هاي هرز غالب و مهم در اين مطالعه سوروف، تاج خروس، خارخسك، قياق و پيچك بودند. درصد كاهش عملكرد لوبيا در تيمارهاي كنترل و تداخل به ترتيب با معادله هاي گامپرتز و لجستيك براي تعيين دوره بحراني كنترل علف هاي هرز برازش داده شدند. واحد حرارتي تجمعي در طي فصل براي توصيف دوره هاي بحراني كنترل علف هاي هرز به كار رفت. بر اين اساس، دوره هاي بحراني كنترل علف-هاي هرز براي جلوگيري از كاهش عملكرد 5/2 و 5 درصد به ترتيب از 87 تا 1187 و 137 تا 948 واحد حرارتي تجمعي متغير بوده است. بر اساس روز پس از سبز شدن، اين دوره ها به ترتيب بين 14 تا 62 و 19 تا 52 روز بودند. اثرات رقابت علف هاي هرز قبل و بعد از اين دوره ها روي عملكرد لوبيا در نظر گرفته نشدند.

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 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 < 0.01) on biological and grain yield and number of pod per plants. The maximum and minimum number of pods was obtained in WI1 and WIT at weed-infested period and WFT and WF1 by weed-free period, respectively. The number of pods per plant, biological and grain yield in the weed infested control (WIT) were reduced by 84%, 97% and 98%, respectively, in comparison with the weed-free control (WFT). The Gompertz and logistic equations were fitted to relative yields representing the critical weed-free and the critical time of weed removal, respectively. Accumulated thermal units were used to describe the critical periods. The critical period to prevent yield losses of 2.5 and 5% ranged from 87 to 1187 and 137 to 948 accumulated thermal units, respectively. Based on day after emergence, these periods were between 14 to 62 and 19 to 52 days, respectively. Weed competition before and after these critical periods had negligible effects on grain yield of dry bean. The results of this study suggest that weeds must be controlled during the first half of the dry bean growing season in order to prevent yield losses.