WEEDS AND WEED MANAGEMENT IN IRRIGATED LENTIL IN NORTHERN SUDAN

Weeds are a major constraint to increasing production of lentil (Lens culinaris Medik.) in Sudan. Field studies were conducted to determine the yield loss due to weeds, to identify the critical period of weed i nterference, to evaluate the activity of different herbicide mixtures in controlling weeds and their selectivity for lentil, and to evaluate different methods of weed control for developing an integrated weed m anagement practice. At Rubatab, unrestricted weed growth accounted for up to 84% loss in yield. The critical period of weed control was betw een 2 and 4 weeks after sowing. However, a weeding regime experiment a t Dongola, a cooler location with a longer growing season, indicated t hat the critical period was between 4 and 6 weeks after sowing, sugges ting that the critical period might vary with the environmental condit ions. The herbicides imazethapyr (0.05 kg a.i. ha(-1)), terbutryn (1.0 kg a.i. ha(-1)) and prometryn (1.0 kg a.i. ha(-1)), each in a tank mi xture with pendimethalin (1.2 kg a.i. ha(-1)), were tolerated by lenti l, controlled weeds effectively and significantly increased yields at Wad Hamid. Their efficacy in controlling weeds at Rubatab was low, how ever, because of the presence of Tephrosia apollinea (Del.) DC. and Me lilotus indica (L.) All., which tolerated these herbicides. Efficacy w as also reduced, in heavier soils. One supplementary hand-weeding at 4 weeks after sowing enhanced the performance of these herbicides under such conditions. A tank mixture of oxyfluorfen (0.24 kg a.i. ha(-1)) with either terbutryn (1.0 kg a.i. ha(-1)) or prometryn (1.0 kg a.i. h a(-1)) also provided good weed control and increased yield of lentil a t Wad Hamid. Application of a higher dose (1.5 kg a.i. ha(-1)) of terb utryn and prometryn caused phytotoxicity. Irrigation before seed-bed p reparation reduced grass and broad-leaved weeds by! 58% and 40% respec tively, and gave a 30% increase in grain yield over no irrigation. Pre -emergence application of oxyfluorfen (0.24 kg a.i. ha(-1)) and a supp lementary hand-weeding at 4 weeks after sowing gave excellent control of weeds and increased lentil yield by 57% over the weedy control. Thu s, use of presowing irrigation, pre-emergence herbicide and one hand-w eeding form an effective integrated package for controlling weeds in n orthern Sudan.