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Navua sedge (Cyperus aromaticus), a perennial plant native to Africa, poses a significant weed concern due to its capacity for seed and rhizome fragment dissemination. Infestations can diminish pasture carrying capacity, displacing desirable species. Despite the burgeoning interest in integrated weed management strategies, information regarding the efficacy of competitive interactions with other pasture species for Navua sedge management remains limited. A pot trial investigated the competitive abilities of 14 diverse broadleaf and grass pasture species. The results indicated a range of the reduction in Navua sedge dry biomass from 6% to 98% across these species. Subsequently, three broadleaf species—burgundy bean (Macroptilium bracteatum), cowpea (Vigna unguiculata), and lablab (Lablab purpureus), and three grass species—Gatton panic (Megathyrsus maximus), Rhodes grass (Chloris gayana), and signal grass (Urochloa decumbens) were chosen for a follow-up pot trial based on their superior dry biomass performance. These six species were planted at three varying densities (44, 88, and 176 plants/m2) surrounding a Navua sedge plant. Among the grass pasture species, Gatton panic and Rhodes grass exhibited high competitiveness, resulting in a minimum decrease of 86% and 99%, respectively, in Navua sedge dry biomass. Regarding the broadleaf species, lablab displayed the highest competitiveness, causing a minimum decrease of 99% in Navua sedge dry biomass. This study highlights the increasing efficacy of crop competition in suppressing weed growth and seed production, with the most significant suppression observed at a density of 176 plants/m2. [ABSTRACT FROM AUTHOR]

Echinochloa crus-galli (L.) Beauv. is a stronger competitor of rice for resources than other weeds. An adequate knowledge of the biology, ecology and critical period of competition of E. crus-galli with dry-seeded rice (DSR) is fundamental in designing effective, sustainable and integrated weed management programs. Experiments were conducted in the 2013 dry and wet seasons to determine the effect of two E. crus-galli densities (40 and 80 plants m−2) emerging at four intervals (2, 15, 30 and 45 d after rice emergence, DARE) with and without rice interference on the growth and biomass accumulation of both rice and weed, and the productivity of rice. The E. crus-galli plant height decreased with the interference of rice plants. The maximum height of 115–130 cm and number of tillers of 477–508 m−2 in rice plants were recorded when grown alone, and these growth parameters declined to 105–109 cm and 315–352 m−2, respectively, when rice emerged simultaneously with E. crus-galli. Other rice growth parameters (stem, leaf, panicle and shoot biomass, and leaf area) and grain yield attributes (panicle density, per panicle filled spikelets and grain weight) decreased significantly with increases in E. crus-galli density at the early emergence time. A delay in E. crus-galli emergence from 0 to 45 DARE caused a significant reduction in E. crus-galli biomass, which resulted in less reduction in rice biomass and leaf area index. Rice grain yield, grain weight, and harvest index improved significantly with a delay in weed emergence up to 45 DARE. The highest grain yield was recorded when rice was grown alone (6.8–7.3 t ha−1), which was similar to the yield produced in the plots wherein E. crus-galli sown at 40 plants m−2 (6.9–7.0 t ha−1) and 80 plants m−2 (6.4–6.7 t ha−1) emerged at 45 DARE. The lowest grain yield (4.3–4.9 t ha−1) was recorded in the plots wherein E. crus-galli emerged simultaneously with rice. This study established that E. crus-galli emergence at 45 DARE could not cause an economic yield loss because of less biomass accumulation and lower survival rate. [ABSTRACT FROM AUTHOR]