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 1Olorunmaiye, P. M. and 2Olorunmaiye,
K. S. 1St. Augustine`s
College, P.O. Box 54, Kabba. pmmoji@yahoo.co.uk 2Dept of Issued 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 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 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 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 280m² 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 (0.5m²). 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. RESULTS
A 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
Note: AG = Annual Grass PG = Perennial Grass 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,
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
Table 3. Relative frequencies of weed species encountered in
plots the main treatment at 12WAP in 2002 at
Table
4. Relative
frequencies of weed species encountered in the main treatment plots at 6WAP in
2004 at
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 Table
5. Relative frequencies of weed species encountered in the
main treatment plots at 12WAP in 2004 at
Table 6. Relative
frequencies of weed species encountered in the main treatment plots at 20WAP
in 2004 at
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 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
Table 8.
Relative frequencies of weed species encountered in the main treatment plots
at 48WAP in 2004 at
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. REFERENCES AKOBUNDU,
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