Studies on weed management in irrigated groundnuts (Arachis hypogaea L.) in the Sudan

A series of field experiments, comprising groundnuts population density, cultivars, Intra-row spacing, timing and frequency of hand weeding and herbicides, was undertaken at the Gezira Research Station during 1997/1998 -2001/2002 seasons. The experiments were undertaken with the objective of developing an integrated weed control strategy for groundnuts. Total and individual weed species were determined in 6 fixed quadrates (20X40 cm) selected at random. Other parameters measured were weed biomass, groundnuts main stem length, shoot biomass, number of primary and secondary branches, leaf area index (LAI), peg and pod numbers, seed weight and pod yield. Common broadleaved weeds irrespective of season, site, intra-row spacing and groundnuts cultivar were Merremia emarginata Dennst., Ocimum basilicum L., Ipomoea cordofana L. and Corchorus spp L. The common grassy weeds were Brachiaria eruciformis Griseb., Commelina kotschyi L., Setaria pallide-fusca (L.) Beauv. and Sorghum sudanense (Piper) Stapf. Weed competition had profound effects on growth and yield of groundnuts. Shoot biomass decreased with the increase of the weedy period and increased with the increase of the weed free period. Groundnuts kept weed free for 10 weeks or more attained the highest shoot biomass, number of primary and secondary branches and pods yield. Conversely groundnuts kept weedy for 8 weeks or more gave the lowest shoot biomass, number of primary and secondary branches, LAI, number of pegs number of pods and pod yield. Hand weeding, 15 or 30 days after sowing (DAS), gave moderate to excellent control (53-93%) of early season weeds, but inconsistent control (19-81%) was achieved for late in the season. Two Consecutive weedings at 15 and 30 DAS gave poor to excellent control (44-93%) of both grasses and broadleaved weeds throughout the season. However, hand weeding, irrespective of time or frequency, significantly, reduced weed biomass. One hand weeding at 15 or 30 DAS yielded groundnut shoot biomass comparable to the weedy check. Clean weeding and weeding twice at 15 and 30 DAS increased shoot biomass significantly. All treatments, often yielded comparable number of primary branches. However, differences between tretments in number of the secondary branches were often significant. The weeded control and two consecutive weedings at 15 and 30 DAS gave significantly higher number of secondry branches than the weedy control. Furthermore, MH 383 was more branchy than kiriz. Leaf area index (LAI) was maximum, irrespective of season, treatment or groundnuts cultivar, at 90 DAS. The unweeded and the weeded control, exhibited the lowest and highest LAI, respectively. Single hand weeding treatments gave LAI comparable to the weedy check. Continuous and two consecutive hand weedings, on the other hand, often resulted in significantly higher LAI. Unrestricted weed growth and single hand weeding treatments reduced peg production and pods number by 11-77% in comparison to the weeded control. Two consecutive hand weedings at 15 and 30 DAS increased peg's production and number of pods significantly in comparison to the weedy check. Differences between treatments in 100 seed weight were often not significant. However, kiriz tended to give heavier seeds than MH 383. Unrestricted weed growth reduced pods yield by 21-91%. In among all treatments the weeded control resulted in the highest pod yield. The herbicides Ronstar (1.07kg a.i./ha), Goal (0.3kg a.i./ha) and Stomp (1.79kg a.i./ha), irrespective of supplementary weeding gave good to excellent control (71-100%) of grasses throughout the season. Satisfactory to excellent control (61-100%) of broadleaved weeds was achieved early in the season. However, the herbicides when not supplemented by hand weeding displayed seasonal variations in performance against broadleaved weeds. The products effected poor to moderate control (39-59%) of broadleaved weeds in season 1998/99 and 1999/2000 and good to excellent control (74-82%) in season 1997/98. Supplementary weeding, invariably, improved late season control (86-96%)of all weeds. The herbicide treatments, irrespective of supplementary weeding, reduced weed biomass significantly and increased groundnuts biomass, secondary branches, LAI, peg number and pod numbers by 8-176, 14-200, 38-259, and 21-310%, respectively in comparison to the unweeded control. Moreover, pod yield was increased by 34-630% over the respective unweeded control