Friday Ekeleme

Characteristics of speargrass (Imperata cylindrica) dominated fields in West Africa: crops, soil properties, farmer perceptions and management strategies.

Abstract Speargrass is a dominant, competitive and difficult weed to control in tropical Asia, Latin America, and some parts of West Africa. In West Africa, no information is available on the cropping systems and soils most affected by speargrass infestation; Farmers’ perceptions of speargrass and common management strategies employed by farmers are unknown. Surveys were conducted in 1996 and 1997 in the coastal/derived savanna (Benin and Nigeria) and southern Guinea savanna (Cote dIvoire) to characterize farming systems, soils, and farmers’ management strategies in fields dominated by speargrass. Twenty-one crops were found in speargrass dominated fields. Speargrass was ranked as the most serious weed in both agroecological zones. Besides speargrass, Commelina benghalensis L., Digitaria nuda Shumach, Cyperus rotundus L., Tridax procumbens L., Rottboellia cochinchinensis (Lour.) Clayton, Digitaria horizontalis Willd, Striga spp., and Euphorbia heterophylla were also considered as important weeds in major cropping systems. Speargrass was undesirable because it reduces crop yield and quality, limits farm size, causes injury to the skin, increases labour requirement and increases the presence of pathogens and insects of economic crops. Nevertheless, some farmers indicated that speargrass was an important source of cheap roofing material, animal fodder and medicines. Most farmers used labour intensive control strategies to combat speargrass due to, among other reasons, lack of capital. Speargrass occurred in soils with a wide range of chemical properties and particle size distribution.

Field performance of improved cowpea varieties under conditions of natural infestation by the parasitic weed Striga gesnerioides

Cowpea is an important food crop in the dry savannas of West and Central Africa because of its high protein content. Yields are, however, considerably reduced by the parasitic angiosperm Striga gesnerioides. Field trials over 2 years in two localities in northeast Nigeria evaluated the performance of diverse cowpea varieties under conditions of natural infestation by Striga. Grain yield was higher in Tilla than in Damboa where the higher Striga infestation may be caused by the lower rainfall and the sandy nature of the soils. Two varieties (IT97K-499-35 and IT90K-82-2) were confirmed to be resistant to Striga. Yield gain from IT97K-499-35 over the local variety ranged from 30% in Tilla in the northern Guinea savanna to 126% in Damboa in the Sudan savanna. The local variety Borno Brown and two improved varieties were found to be as susceptible to Striga as the susceptible control, TVX-3236, and therefore may not be recommended for cultivation in areas where Striga infestation is a problem. One variety, reported previously to be resistant to one or two races of Striga supported moderate levels of emerged Striga, suggesting that it is not totally resistant to the Striga race in the two localities. However, it produced grain yields that were comparable to the resistant varieties in the locality that was most infested, suggesting that it is tolerant to Striga. There are concerns about the adoption potential of the Striga-resistant variety IT97K-499-35 because of its medium-sized white seeds. Farmers in this zone prefer large-seeded brown cowpea. We recommend that efforts be made to develop Striga-resistant varieties that satisfy end-user preferences.

Weed seedbank characteristics of arable fields under different fallow management systems in the humid tropical zone of southeastern Nigeria

The composition and pattern of weed flora in arable fields are determined by their seedbank structure; but the influence of fallow management practices on weed seedbank structure is presently unknown. The objective of this study was to investigate weed seedbank characteristics and weed population dynamics in arable fields in natural and planted-fallow systems. The study plots were at Mbaise, a densely populated area of southeastern Nigeria, where farmers regenerate their exhausted soils by maintaining planted fallows of Dactyladenia barteri (Hook. F. ex Oliv.) Prance & F. White, and at Umuahia, a less-densely populated area in the same region, where farmers depend on natural bush fallow for soil regeneration. The effect of three years of fallow on the weed flora of arable fields in the two fallow management systems differed remarkably. The first flush of weeds on fields that were cultivated after three years of planted D. barteri fallow (Mbaise) consisted of 80% broadleaf weeds, 7% grass weeds and 13% sedges. On the other hand, the first flush of weeds on the natural bush fallow fields (Umuahia) of the same fallow duration as the D. barteri fallow system consisted of 17% broadleaf weeds, 70% grasses and 13% sedges. Three years of planted fallow caused 36% decrease in weed seedbank at Mbaise relative to the cropped field while the same duration of natural bush fallow caused a 31% increase in weed seedbank at Umuahia. These results show that the planted D. barteri fallow system has a higher potential to reduce weed pressure in smallholder agriculture than the natural bush fallow system and may explain in part why farmers in this humid forest zone have adopted the practice.

Integrating planting date with insecticide spraying regimes to manage insect pests of cowpea in north-eastern Nigeria.

We sought to establish the most effective combination of planting dates with insecticide spraying regimes for the management of insect pests of cowpea in the savannas of northeast Nigeria. The results after 3 sprays, made once each at the bud initiation, flowering, and podding stages, did not differ significantly from those after 2 sprays, made once each at flowering and podding, in terms of reducing insect pest population and increasing grain yield. Despite the reduction in insect infestation, delaying planting beyond mid-August reduced cowpea grain yield by 12.3%, on average. The yield of the medium-maturing variety IT89KD-391 was significantly higher when planted in mid-August and sprayed twice than when planted on the earlier or later dates. The yield of the indeterminate late-maturing variety ITKD89-288 was higher when planted in early August and sprayed thrice. Early- and medium-maturing cowpea varieties should therefore be planted in mid-August and sprayed twice. Late-maturing indeterminate varieties should be planted in early August and sprayed thrice.

Influence of nitrogen fertilization on the performance of early and late maturing maize varieties under natural infestation with Striga hermonthica (Del.) Benth

Field studies were conducted in northeast Nigeria to evaluate the response of early and late-maturing maize varieties infested with natural populations of Striga to different rates of nitrogen (N) fertilizer. There were significant reductions in the number of emerged Striga at 120 kg N ha−1 for the early varieties and at 60 and 120 kg N ha−1 for the late varieties. The number of emerged Striga only significantly differed among the late varieties. Averaged across varieties, grain yield of the early varieties was 144% higher at 60 kg N ha−1 and 192% higher at 120 kg N ha−1 than without added N. For the late varieties the increase in grain yield was 85% higher at 60 kg N ha−1 and 144% higher at 120 kg N ha−1 than without added N. Among the early varieties, TZE COMP4 C3 had significantly lower grain yield than the other varieties. Among the late varieties, grain yields of 8338-1-1 and TZB-SR were significantly lower than in the other varieties. Our results show that the application of 60–120 kg N/ha to Striga resistant or tolerant varieties may reduce damage and increase grain yield. Higher economic rates of return was obtained at N rates of 60–120 kg N/ha than the other rates.

Evaluation of Lumax® for preemergence weed control in maize in Nigeria

The efficacy of various herbicides against weeds of maize was studied in field trials at Ibadan, Nigeria in 2003 and 2004. The formulations were atrazine (Gesaprim® 90 WDG at 3.5 kg a.i. ha−1 and Rhonazine® 80 WP at 3.0 kg a.i. ha−1), a mixture of atrazine and metolachlor (Primextra® Gold™ 660 SC at 4.0 kg a.i. ha−1 and Primextra® 500 FW at 2.5 kg a.i. ha−1), and a mixture of mesotrione, S-metolachlor and atrazine (Lumax® at five rates: 1.88–2.96 kg a.i. ha−1). Unweeded and hoe-weeded treatments were controls. Lumax® at all rates, Rhonazine® at 3.0 kg a.i. ha−1, and Primextra® at 2.5 kg a.i. ha−1 controlled sedges, Commelina benghalensis, and Pueraria phaseoloides as effectively as the weeded control (95–100%). Weed density and biomass were significantly reduced and maize yield increased by 12–22%. The highest yield was in treatments with 2.15 − 2.96 kg a.i. ha−1 of Lumax® and 3.5 kg a.i. ha−1 of Gesaprim®, and the weeded control. Lumax® is more effective for weed control at lower rates than the previously used formulations.