Determination of The Critical Period of Weed Control in Fall-grown Safflower (Carthamus tinctorius)

به منظور تعيين دوره بحراني علف هاي هرز در گلرنگ، دوآزمايش صحرايي در ايستگاه تحقيقاتي دانشكده كشاورزي دانشگاه شيراز در دو منطقه باجگاه و كوشكك انجام شد . تيمارهاي آزمايشي شامل حفظ و يا حذف علف هاي هرز تا مدت زماني مشخص پس از كاشت گياه زراعي بود . شروع د وره بحراني كنترل علف هاي هرز به صورت مرحله اي از رشد گياه زراعي كه رقابت علف هرز منجر به كاهش 10 درصد عملكرد گرديد، تعريف شد . همچنين انتهاي دوره بحراني به صورت مرحله اي از رشد گياه زراعي تعريف شد كه در آن براي جلوگيري از كاهش عملكرد تا سطح 10 درصد، مزرعه بايد عاري از علف هرز نگهداري شود . دوره بحراني كنترل علف هاي هرز براي باجگاه بين مراحل ابتداي ساقه رفتن تا گلدهي (144 تا 220 روز پس از كاشت) و براي منطقه كوشكك بين مراحل ابتداي ساقه رفتن تا ابتداي ظهور جوانه گل (135 تا 184 روز پس از كاشت) بود. نتايج نشان داد كه شروع دوره بحراني، در قياس با انتهاي آن، تغييرات كمتري دارد كه تاييد كننده اين موضوع است كه مهار زود هنگام علف هاي هرز در گلرنگ امري ضروري است .همچنين با افزايش طول دوره تداخل علف هاي هرز، اجزاي عملكرد (تعداد قوزه در بوته و تعداد دانه در قوزه) بطور معني داري كاهش يافت.

To determine the critical period of weed control in safflower (Carthamus tinctorius), two field studies were conducted in 2002 at the Bajgah and Kooshkak Experimental Stations, College of Agriculture, Shiraz University. Each experiment consisted of two series of treatments. In the first series, weeds were kept in place until crop emergence, leaf formation, stem elongation, lateral stem emergence, head emergence, flowering and ripening, and were then removed and the crop kept weed-free for the rest of the season. In the second series, crops were kept weed-free until the above growth stages after which weeds were allowed to grow in the plots for the rest of the season. The beginning of the critical period was defined as the crop stage in which weed interference reduced crop yield by 10%.Similarly, the end of the critical period was defined as the crop stage in which the crop had to be weed free to prevent more than 10% yield loss. The Weibull and MMF models were used to determine the critical period. The critical period of weed control occurred between safflower early stem elongation and flowering stages (144-220 days after planting, DAP) at the Bajgah site and between early stem elongation and early head emergence stages (135-184 DAP) at Kooshkak. The onset of interference seems to be less variable than its conclusion, indicating that early weed control is necessary to prevent yield loss. Also, with increase in as the weed interference period increased so yield components (number of heads per plant and number of seeds per head) decreased significantly.