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Ethnobotanical Leaflets 12: 784-800. 2008.
Weed Flora of a Maize/Cassava Intercrop under Integrated Weed Management in an Ecological Zone of Southern Guinea Savanna of Nigeria
1Olorunmaiye, P. M. and 2Olorunmaiye, K. S.
1St. Augustine`s College, P.O. Box 54, Kabba. Kogi State, Nigeria 2Dept of Plant Biology University of Ilorin, P.M.B. 1515 Ilorin, Kwara State, Nigeria
Issued 04 October 2008
ABSTRACT Weed flora of different management techniques under different cropping systems have been reported but no sufficient information on weed flora of integrated weed control method in maize/cassava intercrop in southern Guinea savanna of Nigeria. This study assessed the weed flora and relative frequencies of weeds in a maize/cassava intercrop under integrated weed management involving two pre-emergence herbicides (Primextra and Galex, each at 2.5 kg/ha alone or with one or two supplementary hoe-weeding, at 6 weeks after planting (WAP) or 6 and 12WAP, a hoe-weeded check (hoeing at 3, 6 and 12WAP) and a weedy control. A total of 41 weed species belonging to 35 genera and 19 families comprising of Poaceae, Euphorbiaceae, Asteraceae, Rubiaceae, Cyperaceae among others were encountered in the experimental plots during 2002 and 2004 cropping seasons. The very abundant weed species included Paspalum obiculare Forst, Digitaria horizontalis Willd and Brachiaria deflexa (Schumach) while those with moderate abundance were Bulbistylis arbotiva (Steudel), Cleome viscosa L., Croton lobatus L., Dactylocternium aegyptium (L) P. Beauv., Tridax procunbens L. and Vernonia galamensis (Cass.) Less. The remaining weed species had rare abundance. The relative frequency of the weed species was generally reduced under all the weed control treatments except Paspalum obiculare whose relative frequency was consistently high in all the assessment periods under all the weed control treatments.
INTRODUCTION In Nigeria and in many other developing nations, intercropping has remained the traditional farming practice. It is a wide spread food crop production system in the humid and subhumid tropics of West Africa (IITA, 1981; Akobundu, 1980; Anuebunwa, 1991). Cassava/maize seems to be the most common crop combination preferred by small-scale farmers (Akobundu, 1980; Unamma and Ene, 1984; Unamma et al., 1986). Okigbo and Greenland (1976) estimated that about 50% of the cassava grown in tropical Africa is intercropped with cereals, legumes, leafy vegetables and fruits as well as tree crops. Weed seeds are abundant in cultivated fields and many species will germinate independent of the crop density, spatial arrangement and species (Akobundu, 1987). Both maize and cassava have been shown to be sensitive to weed infestation, maize in the first 4 weeks and cassava in the first 10-12 weeks after establishment (Onochie, 1975). It has been estimated that yields of crops can be reduced by between 60-90% in cases of poor weed management practices (Ogunremi, 2005). Uncontrolled weed growth causes yield loss of 40-60% in maize in the tropics (Akobundu, 1980). Yield components of cassava most affected by weeds are tuber number and weight. The most damaging effects of weeds were reported to occur during early canopy formation and when tuberization is taking place (Onochie, 1975). Whereas yield losses due to weeds is put at about 50% or more in the developing countries (Anon 1982), in Nigeria, yield losses due to weed interference vary between 40 and 100% depending, among other things, on type of crops, type of weeds and weed density (Fadayomi, 1991). Weed flora of different weed management techniques under different cropping systems have been reported (Ekeleme, et al., 2004) but no sufficient information on weed flora of integrated weed control method in maize/cassava intercrop in southern Guinea savanna of Nigeria. This study therefore investigated the weed flora of maize/cassava intercrop using integrated weed control methods.
Materials and Methods Each year, the experimental site was ploughed and harrowed, after which ridges which are approximately 1.3 m apart were made. The experiment consisted of eight main treatments and six sub treatments. The main treatments were made up of the application of two pre-emergence herbicides [Primextra and Galex, each at 2.5 kg a.i./ha alone or with one or two supplementary hoe weedings at 6 weeks after planting (WAP) or 6 and 12WAP], a hoe-weeded check (hoeing at 3, 6 and 12WAP) and a weedy control. The size of each main treatment was 280mē with 6 ridges of 6m long. Maize (var. DMRY) and cassava (Okoyawo a local var.) were planted after land preparation. The herbicide treatments were applied as pre-emergence sprays at the rate of 2.5 kg.a.i/ha, one day after planting of maize using a CP3 knapsack sprayer, fitted with a green deflector nozzle, which was calibrated to deliver a spray volume of 240L/ha. Weed sampling was carried out at 6 and 12WAP in 2002 and at 6, 12, 20, 36, 44 and 48WAP in 2004 from each main treatment using wooden quadrats (0.5mē). Twelve throws were made per main treatment and weed species within each quadrat were uprooted, sorted into grasses and broad leaves and identified to the species level using a standard text by Akobundu and Agyakwa (1987). Thereafter, each weed species was counted and the value recorded to compute the Relative frequency.
RESULTSA total of 41 weed species belonging to 19 families and 35 genera were found in the experimental plots during the 2002 and 2004 cropping seasons. The weed species consisted of 13 Poaceae, 5 Euphorbiaceae, 4 Asteraceae, 3 Rubiaceae and 2 Cyperaceae. The remaining families: Amaranthaceae, Commelinaceae, Nyctaginaceae, Papilionaceae, Portulacaceae, Cleomaceae, Leguminoceae, Lamiaceae, Acanthaceae, Solanaceae, Malvaceae, Loganiaceae, Fabaceae and Tiliaceae had one (1) each (Table 1). The very abundant weed species included Paspalum obiculare, Digitaria horzontalis and Brachiaria deflexa while those with moderate abundance were Bulbostylis arbotiva, Cleome viscosa, Croton lobatus, Dactyloctenium aegyptium, Tridax procumbens and Vernonia galamensis. The remaining weed species had rare abundance. In both cropping seasons grasses were the predominant weeds in the experimental plots. Broadleaved weeds were, however, more abundant in 2004 than in 2002, while sedges were very few in both cropping seasons.
Table 1. Weed species composition of the experimental plots in 2002 and 2004, at Ilorin, Nigeria.
Note: AG = Annual Grass PG = Perennial Grass ABL=Annual Broadleaf PBL= Perennial Broadleaf +++ = Very abundant (60-100%) ++ = Moderate abundant (40-59%) + = Rare abundant (<10-39%) - = Absent
In 2002, a total of 8 weed species were recorded at 6WAP from the experimental plots across the main treatments. Digitaria horizontalis had the highest relative frequency across all the weed control treatments (63.8 94.4%) followed by C. lobatus (11.1 88.8%), B. arbotiva (0 61.1%). Brachiaria deflexa, C. viscosa and T. procunbens were rare in all the main treatments at this sampling period (Table 2). At 12WAP, more weed species were encountered under the weed control treatments (Table 3). Just as it was observed at 6WAP, D. horizontalis had the highest frequency (77.7 94.4%). This was, however, followed by P. obiculare (38.9 72.2%) which occurred at very low frequency at 6WAP. Weed species with relative frequencies of 5.6 55.6% included B. deflexa, B. arbotiva, C. viscosa D. aegyptium, M. villosus, and T. procumbens. Those weed species with relative frequency of 10% included Celosia sp. C. benghalensis, C. rotundus, E. hyssopifolia, I. cylindrica, Pennisetum violaceum, Physalis angulata and Spigellia anthelmia. In 2004, a total of 20 weed species were encountered at 6WAP (Table 4) with P. obiculare, B. arbotiva, D. horizontalis and T. procumbens occurring at relative frequencies of 22.8 72.2%, while B. deflexa, C. benghalensis, E. herterophylla, Oldenlandia herbacea, Rhynchelythrum repens and Vernonia galamensis had relative frequencies of 11.1 66.7%. The rest of the weeds had less than 10% relative frequencies.
Table 2. Relative frequencies of weed species encountered in the main treatment plots at 6WAP in 2002 at Ilorin, Nigeria.
Table 3. Relative frequencies of weed species encountered in plots the main treatment at 12WAP in 2002 at Ilorin, Nigeria.
Table 4. Relative frequencies of weed species encountered in the main treatment plots at 6WAP in 2004 at Ilorin, Nigeria.
At 12WAP, 28 weed species were recorded in the various weed control treatments (Table 5). Again, P. obculare had the highest relative frequency of 94 100% in all the weed control treatments. Brachiaria deflexa, B. arbotiva, D. aegyptium, D. horizontalis, and Tridax procumbens had relative frequencies of 27.7 88.8%. Others with low relative frequencies of 5.6 44.4% included B. jubata, C. benghalensis, C. rotundus, E. heterophylla, M. villosus, O. herbacea, S. anthelmia, V. galamensis, V. cinerea, A. gayanus, C. ciliata, C. lobatus, E. hirta, I. cylindrica, Mariscus sp., P. hirsuta, P. violaceum, P. angulata, R. repens and Vernonia perottetti. At 20WAP, the number of weed species encountered had reduced to 18 but P. obiculare still had the highest relative frequency of (44.4 66.7%) followed by O. herbacea, T. procumbens, D. horizontalis, V. galamensis, M. villosus with relative frequencies of 11.1 - 55.6%. The other weed species occurred at low relative frequencies of 5.6 16.7%. These included B. deflexa, C. benghalensis, C. ciliata, C. rotundus, Monecma ciliatum, R. repens, Stylosanthes sp., Tephrosia bracteolata, Triunmfetta cordifolia, D. aegyptium, Hyptis suaveolens and I. cylindrica (Table 6). The relative frequency of occurrence of the weed species was generally reduced under all the weed control treatments.
Table 5. Relative frequencies of weed species encountered in the main treatment plots at 12WAP in 2004 at Ilorin, Nigeria.
Table 6. Relative frequencies of weed species encountered in the main treatment plots at 20WAP in 2004 at Ilorin, Nigeria.
At 44WAP, 15 weed species were recorded under all the weed control treatments (Table 7). Paspalum obiculare had the highest relative frequency (88.8 94.4%) followed by T. procumbens (11.2 65.6%).and B. deflexa (5.6 22.2%). Many of the other species that were recorded had low relative frequencies of 5.6 16.7%. These weeds were B. diffusa, E. heterophylla, E. hirta, C. benghalensis, C. lobatus, H. suaveolens, O. herbacea, P. indica, R. repens, Stylosanthes sp. and I. cylindrica. At 48WAP, 17 weed species were recorded in the weed control treatments (Table 8). Paspalum obiculare and B. deflexa occurred at fairly high relative frequencies of 33.3 66.7% and 16.7 66.7%, respectively while the rest of the weed species (B. jubata, C. benghalensis, D. aegyptium, D. horizontalis, E. heterophylla, H. suaveolens, I. cylindrica, Phillanthrus amarus, R. repens T. bracteolata and E. hirta) occurred at frequencies of 5.6 33.4%.
Table 7. Relative frequencies of weed species encountered in the main treatment plots at 44WAP in 2004 at Ilorin, Nigeria.
Table 8. Relative frequencies of weed species encountered in the main treatment plots at 48WAP in 2004 at Ilorin, Nigeria.
DISCUSSION The weed flora for both years were of great species diversity and richness as was reported by Olofintoye and Fadayomi, 2005 and Olorunmaiye and Olorumaiye, 2007. Weed species common to all the weed control treatments were: Grasses B. deflexa, B. arbotiva, D. horizontalis and P. obiculare for both years though D. horizontalis was much more prominent in 2002 and P. obiculare in 2004. In addition to 2004, broadleaved weeds: T. procumbens and V. galamensis were abundant along with the grasses. Out of all these weeds mentioned in the weed control treatments, P. obiculare seems to be difficult to control by these integrated weed control treatments as its relative frequency was consistently high in all the assessment periods. Earlier study by Akobundu (1987) has shown that P. obiculare being an annual grass can behave as a perennial grass if given enough moisture. In this present study, it regenerated easily from the old stump and became much more prominent than others at 44WAP where its relative frequency ranged between 88.8% - 94.4% and at cassava harvest with 33.3 66.7%. Akobundu (1987), observed that P. obiculare and D. horizontalis have tendency to grow densely around economic plants and are adapted to overcrowding hence they are able to compete better with crops because of the numerical superiority they have over weeds.
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