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African Crop Science Journal
African Crop Science Society
ISSN: 1021-9730 EISSN: 2072-6589
Vol. 4, Num. 2, 1996, pp. 263-273
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African Crop Science Journal
Vol.5. No.2, pp. 263-273 1997
FORUM
INTEGRATED MANAGEMENT FOR STRIGA CONTROL IN MALAWI
H. R. MLOZA-BANDA and V. H. KABAMBE^1
University of Malawi, Bunda College of Agriculture, P.O.Box
219, Lilongwe, Malawi
^1 Department of Agricultural Research, Chitedze Research
Station, P.O.Box 158, Lilongwe, Malawi
(Received 25 March, 1996; accepted 30 June, 1996)
Code Number: CS96065
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ABSTRACT
In Malawi, Striga asiatica (L.) Kuntze infestation
presents a serious constraint to small-scale farmers who must
grow cereals, in particular, maize, for food. The successful
introduction of highly productive and acceptable flint maize
hybrids is under threat from Striga. Little is known of the
economic importance of Striga in other host crops. When the
control of this weed is reviewed, it appears that information
applied on the management of Striga asiatica is largely
based on extensive work on Striga species infesting sorghum.
It is, however, generally agreed that the best solution in the
control of Striga is an integrated approach that includes a
combination of methods that are within reach of the farmer and
considered worthwhile by the farmer. This paper attempts to
mould a topical inventory of work on S. asiatica in the region
into a research perspective for the small-scale farmer in
maize-based cropping systems in Malawi.
Key Words: Maize, Malawi, small-scale farmer,
Striga
RESUME
Au Malawi, l'infestation des cereales par le Striga
asiatica (L.) Kuntze, en particulier sur le mais, produit
alimentaire de base, constitue une contrainte importante pour
les petits producteurs. La reussite des efforts destines e
introduire des hybrides de mais acceptables et a haut
rendements est ainsi compromise. Il n'existe pas beacoup
d'information sur l'importance economique de Striga sur
d'autres cultures htes. Lorsque l'on evalue les methodes de
contrle de cette herbe, on constate que l'information
appliquee a sa gestion est largement basee sur le travail
extensif mene sur les especes de Striga infestant le sorgho.
Il est, toutefois, generalement accepte que la meilleure
solution pour son contrle s'est trouve dans une approche
integree qui comprend une combinaison des methodes abordables
par le petit paysan et considerees valorisantes par celui-ci.
Ce document, tente de constituer en inventaire des themes de
recherches qui peuvent etre menees sur le S. asiatica dans la
region, pour les petits producteurs au Malawi, dans des
systemes de cultures incorporant le mais.
Mots Cles: Mais, Malawi, petit producteur, Striga
INTRODUCTION
Small farming families occupy 68.7% of total cultivated land
in Malawi (ICLARM and GTZ, 1991). They rely on maize and grain
legume cropping systems to provide their staple food.
Extensive damage and yield losses are inflicted upon these
major food crops grown on small scale farms by insects, weeds,
and diseases. The problem of pests and diseases and how to
control them remains a challenge. There are indications that
one of the most important and intractable pest problem in
maize-based production systems in Malawi is Striga.
Striga infestation is apparently wide-spread in maize
which is the predominant staple cereal crop in Malawi. The
detrimental effects of this weed is well known to farmers who
associate increasingly wide-spread infestation with declining
soil fertility (Riches et al., 1993). This is in
agreement with research findings from trials in Malawi
(Johnson, 1971; Ngwira and Nhlane, 1986) and other locations
in Africa (Hassan et al., 1994). Although there has
been some evidence of increased adoption of hybrid maize
varieties and inorganic fertilizer in recent years in Malawi
(Conroy, 1992), a number of socio-economic factors have forced
farmers into using lower rates of fertilizers, maintaining the
production of local open pollinated varieties with low yield
potential, and weed late and ineffectively (Mkamanga, 1986;
Ngwira et al., 1989). As a result of increasing
population pressure, crop rotation has been displaced by
continuous cropping of maize leading to decline in soil
fertility and maize productivity with a concomitant emergence
of the Striga problem.
Control of Striga has been attempted through the
integration of various measures into simple control packages
deemed appropriate to local farming systems (Ogborn, 1987).
However, when research on the control of this parasitic weed
is reviewed, the most important unsolved Striga spp. control
problem in Southern Africa is the attack of Striga
asiatica (L.) Kuntze on maize grown by smallholder
farmers. It appears that information applied to Striga
asiatica is largely based on extensive work on Striga
hermonthica infesting sorghum in East and West Africa. There
is a persuasive case, however, for increased understanding of
these parasitic weeds, and application of a remedy for the
small-scale farmer, particularly at a time when increased crop
production must be weighed against a deteriorating natural
environment exemplified by loss of soil productivity and
weather anomalies in the region.
OCCURRENCE OF STRIGA IN MALAWI
Banda and Morris (1985) described Striga as a common and
widely distributed weed in Malawi in cultivation as well as
Brachystegia woodlands below about 1350 m. Binns (1968)
provided the first listing of various genera of the
Scrophulariaceae family identified in Malawi based on a
floristic survey. The following Striga species were identified
in the wild or on cultivated land: Striga asiatica (L)
Kuntze (= S. lutea Lour, red witchweed), Striga aspera
(Willd.) Benth; Striga gesnerioides (Willd.) Vatke (tobacco
witchweed) and Striga orobanchoides Benth. Moriarty (1975)
noted the existence of S. pubiflora Klotzsch. while Riches
et al. (1987), described the presence of S.
euphrasioides in Malawi. The distribution and extent of crop
infestation by these species in Malawi is largely unknown
except for S. asiatica which is noted to be the most
widespread of all witchweeds.
Striga forbesii is described as a pink-flowered giant
witchweed with toothed leaves and restricted to moister sites
and generally of less common occurrence in the region (Terry,
1988; Musselman, 1994). In Tanzania, it has been reported as
a parasite of Setaria sphacelata (Schumach.), rice and
sorghum, while in Zimbabwe it has been reported in maize
(Terry, 1988). Striga euphrasioides has been reported to be
an occasional parasite of rice, maize, sorghum, sugarcane, and
wild grasses in both Tanzania and Malawi (Riches et
al., 1987). Striga gesnerioides lacks developed leaves
and uses scales and stems of the plant for photosynthesis
(Musselman, 1994). Further, infestation is restricted to
broadleaf crops, mainly cowpea, but also tobacco and sweet
potato.
Striga asiatica is prevalent throughout Malawi and
the East and Central Africa region where it parasitises upland
rice, maize, sorghum, the millets and sugarcane (Terry, 1988).
It is known to be the most variable in morphology and taxa.
In Malawi, although the red-flowered type predominates field
infestations, small proportions of the yellow-flowered types
have been noted (Parker and Riches, 1993). Physiological
variation within this species has also been reported between
populations that form distinct ecotypes differing in
morphology, vigour, leaf size, and even host range.
Bharathalakshmi et al. (1990) reported work in India
which showed S. asiatica populations that specifically
attacked sorghum, pearl millet, or Paspalum spp. They
suggested that host-preference was based upon different
germination stimulant requirements. Parker and Riches (1993)
argued that, because of the autogamous nature of S. asiatica,
this species adapts less readily from its wild hosts to crop,
or from crop to crop; rather, it displays an overlap of
different morphotypes in different areas.
The prevalence of Striga has also been ascribed to changes
in seasonal weather, such as drought or locations with
unreliable rainfall (Ayensu et al., 1984; Ogborn,
1984). Ogborn (1984) gave an example of the savannas of
southern Guinea where, in particular areas, successive seasons
of maize were completely free from Striga attack, while in
another season the maize was widely attacked to the point of
total crop failure. The seasonality of the severity of Striga
attack has also been observed in Malawi. Banda and Morris
(1985) describe Striga as less common in high rainfall areas.
This demonstrates the need for a fundamental study of the
interaction between climate and incidence of Striga attacks on
all susceptible crops. In Malawi, maize is grown in a very
wide range of ecologies including areas marginal for its
production. If Striga control is to be achieved by the
integration of various methods into simple control packages
(Ogborn, 1987), then all relevant fundamental information
about the ecological range of the parasite and its host
species must be included.
ECONOMIC IMPORTANCE OF STRIGA IN MALAWI
The current maize yield levels in Malawi range from 2000 to
3000 kg ha^-1 for hybrids, 1400 to 2400 kg ha^-1 for
composites, and 880 to 1300 kg ha^-1 for unimproved (local)
maize. It is perceived that with proper production practices,
including timely and effective weed control, smallholder
farmers' yield can be increased to more than 8000, 5000, and
3000 kg ha^-1 for hybrid, composite, and local maize,
respectively (Anonymous, 1994).
Striga species were already clearly recognised as
parasitic weed problems in Malawi four decades ago (Anonymous,
1959, 1963) and experimental work on control methods appear to
have begun in the early 1960s (Anonymous, 1965). However, data
on yield losses caused by Striga on maize in Malawi is very
limited. A recent survey showed that 63% of the 295 fields
surveyed in Malawi were infested with Striga, with 25% of the
plants per field being infested. This represented an average
total yield loss of 2.5% for maize production due to S.
asiatica occurrence (Kroschel et al., 1996). In the
Southern African region, visual estimates for grain yield loss
due to Striga in farmers' fields has been put at between 15%
(in tolerant cultivars) and 95% (in susceptible cereals)
(Obilana, 1988). Estimating yield loss due to Striga within
the agronomic weed complex has been reported to be very
difficult. Parker and Riches (1993) cited the difficulty of
creating Striga-free plots, the serious non-uniformity of
natural infestations, both within and between fields, and the
confounding micro-variability of soil fertility which
interacts with the level of damage caused to host plants.
Nevertheless, economic justification for working on the
problem arises from farmer perception of the problem (Riches
et al., 1993). In heavily infested areas of the
Southern Region of Malawi, farmers frequently identified
Striga as the most important weed and have described having to
abandon fields when infestation levels become severe. Thus,
Striga also causes indirect production losses when farmers
change production strategies to respond to heavy
infestations.
EFFICACY OF AVAILABLE CONTROL METHODS
Resistant varieties. Development of resistant varieties of
susceptible plants has been attempted in a number of crops
including sorghum, maize, cowpeas, rice, and millet (Pieterse
and Pesch, 1983). Resistance in sorghum materials has been
confirmed for S. asiatica and S. forbesii in Southern Africa
and has been incorporated into testing and breeding programmes
(Riches et al., 1987; Obilana et al., 1991).
One of the major problems though, is that resistance to
witchweed has been associated with low grain yield and poor
grain quality (Parker and Riches, 1993).
Considerable variability in resistance or tolerance has
been reported in maize for S. asiatica (Ransom et al.,
1990). At IITA, some maize lines with partial tolerance and/or
resistance to both S. hermonthica and S. asiatica (in U.S.A.)
were identified and hybrid lines developed (Kim et
al., 1985; Kim and Winslow, 1991). However, there are no
maize cultivars specifically developed with resistance or
tolerance commercially available in East and Southern Africa
(Ransom and Odhiambo, 1995). Development of resistant maize
genotypes is further complicated by the existence of biotypes
and the presence of three different and economically important
Striga species in Africa that infest maize, and the potential
build up of the parasite where tolerant maize lines are used
(Efron et al., 1989; Parker and Riches, 1993). Ogborn
(1987) suggested that sources of tolerance may exist among
locally adapted African maize varieties because of the longer
exposure to Striga attack. Farmers in the lake region in Kenya
reported that their local yellow maize variety showed some
tolerance to Striga (Hassan et al., 1994).
It is suggested that combined with other methods of
control that prevent the seeding of Striga, resistant
varieties of crops are compatible with the low-cost input
requirements of the small-scale farmer. Additional research is
needed to confirm the role of some genotypic traits of the
crop along with other host-parasite interactions and their
contribution to Striga resistance (Ogborn, 1987; Ejeta and
Butler, 1993; Ransom and Odhiambo, 1995).
Manual methods. Hoe weeding remains the most common
method of weed control in Malawi. Farmers will normally weed
twice, the second time is through the banking operation where
soil is pulled-up the ridge. Inconsistent results have been
obtained in Malawi in the effectiveness of hoe-weeding for
Striga control. District witchweed control trials were
conducted to examine the effectiveness of simple cultural
techniques in the control of Striga and in rehabilitating
badly infested fields (Anonymous, 1976). Ordinary hoe weeding
(twice) followed by spot spraying of Striga with gramoxone
every ten to fourteen days showed higher yields than ordinary
hoe weeding (twice) alone or hoe weeding coupled with hand
pulling. However, earlier results (Anonymous, 1965) had shown
that normal hoe weeding gave best average yields contrasted
with spraying 2,4-D. It appears that success of hoe weeding in
controlling Striga infestation depends largely on the timing
of the operation itself which is often done following
appearance of weed plants. For Striga, this would mean after
the parasite has already attached to the host crop. Hoe
weeding seems to be of limited application for Striga control
except where any general late weeding is practised and
incidental Striga control resulting from it.
Handpulling of witchweed at fourth-nightly intervals till
harvest has been recommended for controlling light
infestations of the parasite in Malawi (Anonymous, 1974).
Several investigators have reported possible benefits from
handpulling (Ramaiah, 1985). However, this has been with the
larger Striga species, namely, S. hermonthica, S. forbesii and
S. aspera. In trials conducted in Malawi on S. asiatica,
Kabambe (1991) reported that handpulling did not improve grain
yield or reduce Striga incidence. Parker and Riches (1993)
suggested that handpulling of S. asiatica plants may be more
difficult and expensive because plants are individually small,
less conspicuous, and may be much more numerous. The high
labour input demanded of handpulling would always lead to
control being protracted and therefore ineffective in reducing
crop losses (Carson, 1988). Handpulling of S. asiatica, may
however, be used as part of a long-term strategy to prevent
seeding of residual populations of the weed plants after other
control measures have been applied.
Cropping systems. Another means by which the number of
witchweed seeds in the soil can be reduced is crop rotation or
intercropping with trap or catch crops (Wild, 1948; Robinson
and Dowler, 1966; Ogborn, 1987; Parkison et al., 1989; Bebawi
and Michael, 1991). Kroschel and Sauerborn (1996) reported a
case study which showed that crop rotation with trap crops was
thought to be a feasible Striga control strategy by farmers
from three districts (out of twenty-four) surveyed in Malawi.
The feasibility of using trap crops in rotation is limited to
very few areas in Malawi owing to population pressure. The
fact that at least three years of rotation are likely to be
needed emphasizes the practical limitation of the rotation
option (Parker and Riches, 1993). Both trap crops and catch
crops do not bring about complete eradication and it may take
several years before an effect becomes apparent. However, for
heavily infested fields, trap crops can accelerate the
depletion of the reservoir of Striga seed in the soil
(Robinson and Dowler, 1966).
In Malawi, 21% of the maize crop is grown in association
with other crops mainly pulses and oilseeds (ICLARM and
GTZ,1991). Inter-cropping maize with these potential trap
crops represents a ready made strategy owing to current crop
diversification extension messages. Parker and Riches (1993)
observed that even though Saunders (1933) showed a
considerable reduction in S. asiatica from intercropping maize
with cowpea as early as 1933, intercropping has received less
research emphasis as a viable method for reducing the weed
despite the importance of the intercropping system in many
Striga-infested regions. Work on S. hermonthica has shown that
intercropping significantly reduced Striga (Carson, 1989;
Hassan et al., 1994; Odhiambo and Ransom, 1995). In
these studies, intercropping was effective where the intercrop
was within the cereal crop row. It is not clear, however, how
mixed cropping results in reduced Striga incidence (Parker
and Riches, 1993). Further, it is suspected that multiple
infestation by the parasites and their wide host range may
preclude effective control through the use of crop mixtures or
even rotation with trap crops. It also appears there is no
clear distinction between trap crops efficacious for Striga
asiatica and those for other witchweed species.
Soil amendments. Striga infestation on cereal crops has
often been reported to be most severe on soils of low
fertility and that nitrogen can reverse this effect (Farina
et al., 1985; Ogborn, 1987). However, the results of
field trials with basal applications of nitrogen fertilizer
over many years in many countries have not been consistent in
terms of crop yields or Striga numbers (Parker and Riches,
1993). Only where ÒhighÓ levels of nitrogen have been applied
has there been a more distinct and consistent beneficial
effect in reducing parasite numbers (Agbobli, 1991). It is
also not clear how high levels of nitrogen suppress Striga
(Ogborn, 1984; Bebawi, 1987; Parker and Riches, 1993). The
reduction in stimulant exudation by the host and the
concomitant reduction in numbers of emerged and maturing
Striga is reported to be the best documented nitrogen effect
(Parker and Riches, 1993).
In Malawi, Ngwira and Nhlane (1986) recommended an
application rate of 11,000 kg per hectare of farm yard manure
and 100 kg N and 10 kg P ha^-1 from inorganic fertilizers to
improve the nutrient status of the soil and to allow the maize
crop to compete better against the parasite. Kabambe (1991)
reported 50-75% reduction of S. asiatica in maize using 112 kg
N ha^-1 as ammonium sulphate. However, even in traditional
cattle raising areas of Malawi, there is never enough farmyard
manure to protect more than a small fraction of the crop from
Striga. In terms of fertilizer, such rates appear uneconomic
for the smallholder farmer whose most immediate reason for
investing in nitrogen fertilizer is the prospect for increased
yield with marginal costs. Data from two long term experiments
in Kenya suggest that inputs of fertilizer and organic
materials are essential in the control of Striga even while
other methods of control to stop Striga reproduction are
practised (Odhiambo and Ransom, 1995). There is a clear need
now, in Malawi, to integrate recent recommendations on optimum
time, rate, and method of fertilizer application in maize into
a witchweed control package. The potential role of soil
fertility improvement by alley cropping being recommended for,
and practised in, different areas in Malawi needs to be
explored to restore the fertility of Striga infested soils.
Chemical control methods. Various chemicals, such as
fumigants, germination stimulants, antitranspirants, or
host-crop seed hardening with organic acids, have been
employed to destroy either the quiescent Striga seed in the
soil, the germinating seed, or the emerged weed (Lagoke et
al., 1991). Invariably, however, no method has yet been
devised for making practical use of those natural or synthetic
substances under field conditions for the control of Striga
(Parker and Riches, 1993).
Most farmers will not for the time being be able to take
advantage of herbicides for general weed control owing to the
cost of the chemicals, skills required for their safe
application, and because they carry a greater risk of crop
damage which preclude their use in most mixed crop situations
(Parker and Riches, 1993). However, herbicides may be one
single solution where it is feasible for them to be
introduced, in particular, as an aid to prevent seeding and as
an alternative to handpulling for destruction of the emerged
parasite.
Herbicides, such as trifuralin and pendimethalin, have
been effective against S. asiatica when incorporated shallowly
in a layer above the cereal seed by inhibiting shoot growth of
the parasite. Translocated herbicides, such as 2,4-D or
Dicamba, or soil-acting herbicides, such as 2,4-D itself,
MCPA, or benazolin, have shown unsatisfactory results in the
control of Striga before or immediately after attachment. The
success of soil-acting herbicides largely depends on
irrigation or rainfall washing the chemical into the soil at
the critical time of Striga germination. The ineffectiveness
of translocated herbicides is ascribed to the absence of a
phloem bridge in the cereal/parasite haustorium which has been
shown to be present in other parasitic relationships such as
that between cowpea and S. gesnerioides (Parker and Riches,
1993).
A number of alternative herbicides safe enough for mixed
cropping and control of Striga on grass weeds in rotational
crops have been evaluated (Ogborn, 1987; Langston and English,
1990). It is particularly significant that, in USA, herbicides
are used intensively for control of grass weeds on which S.
asiatica might grow and seed (Parker and Riches, 1993). Ogborn
(1984) observed that in Africa and Asia, where Striga spp. are
endemic, reinfestation from wild hosts may make it very
difficult to eradicate the weed.
Biological control. Various insects which feed on
witchweed have been described and include: the weevil,
Smicronyx spp., the moth, Eulocastra argentisparsa, and the
stem mining fly, Ophiomya strigalis (Pieterse and Pesch,
1983). The species of Smicronyx are seed, pod, and root
gallers of S. hermonthica and have been observed to cause
severe damage reducing seed production by the weed by 80% or
more. A butterfly Gunonia orithya, which occurs in Africa and
Asia, feeds voraciously on witchweed leaves while O. strigalis
only causes superficial damage (Pieterse and Pesch, 1983).
Microbial antagonists mainly of the genus Fusarium, have been
shown to penetrate and parasitise Striga seeds and attacking
germ tubes and Striga shoots thereby reducing seed germination
(Kroshel et al., 1996b). A suitable product has not
been developed for field testing. The possibility for
deliberate use of insects or bioherbicides for classical
biological control remains attractive but may not be of
immediate importance in Malawi.
STRIGA CONTROL RESEARCH IN MALAWI
A review of Striga control methods at present available to the
small-scale farmer shows that there is no single method
against Striga that is both effective and economically
feasible (Ogborn, 1984). Parker and Riches (1993) argue that
there is a feeling that the available solutions are deemed
inadequate and that the only hope is some dramatic research
breakthrough such as resistant varieties, genetic engineering,
or a miracle herbicide. Instead, control measures must involve
a long-term, integrated approach. With adequate knowledge
about Striga asiatica and its relationship to crops in
different agroecological zones in Malawi, it is feasible to
support an approach in which Striga prevention and control
have companion roles. There are a number of research and
extension activities which can generate and deliver
information from which farmers in Malawi can be helped towards
solution of the Striga problem. These include synthesis and
communicating optimum decisions on rotation and/or
intercropping maize with trap crops, soil amendment practices
to restore fertility, and weed control methods that are
relevant to the prevailing farming/cropping systems for Striga
control.
Ecogeographical study of Striga in Malawi. First, the
occurrence and distribution of Striga asiatica in
Malawi is believed to be widespread and severe in some areas
while that of other species is largely unknown despite two
recent surveys (Kroschel et al., 1996a; Munthali et
al., 1992). Little is known about the genetic diversity of
Striga in Malawi nor is there descriptive information.
Specimen collections have been limited to those at the
National Herbarium being preserved for floristic purposes. A
comprehensive documentation of species occurrence,
distribution, and severity of Striga in Malawi is the basic
tenet for research. Second, the general belief that Striga is
a problem associated with low rainfall seasons and low
fertility soils needs to be validated. Quantified information
on the influence of various environmental factors on Striga
will be useful for simulating these factors in research
methodologies and/or avoiding the occurrence of some factors
while formulating cultural practices to reduce Striga
attack.
Evaluation of trap crops for Striga control. Kroschel
and Sauerborn (1996) argue that in regions with possibilities
for marketing Striga trap crops such as cotton or soybeans,
farmers have an advantage in their Striga control efforts.
However, rotating the cereal and other crops as sole crops in
succeeding years rather than as mixed crops every year is
viewed as a better option. There exists variations in cropping
systems in Malawi for which the adoption of different
trap-crop control methods can be expected.
Agroforestry remains a critical component in an
integrated approach to soil fertility improvement in
maize-based cropping systems in Malawi (Wendt et al.,
1991). There is need to investigate the efficacy of
multipurpose trees being employed in agroforestry systems in
the control of Striga. For instance, Thijssen (1995) reported
that trees of the species Croton megalocarpus have been shown
to be an effective trap crop, inducing germination of Striga
seeds.
Weeding practices. Farmers weeding practices in Malawi
seem to be aimed at preventing crop losses from current weed
infestation without regard to subsequent infestations. Striga
plants may escape the first two weedings in absence of any
late weeding or may mature and shed seed where weeded Striga
and other weeds are left between crop rows as practised in
Malawi (Kroschel and Sauerborn, 1996). Most smallholder
farmers only have a hand hoe and family labour at their
disposal. There is often conflict in the amount and timing of
labour allocated to crop establishment practices such as land
preparation, planting and weeding whose labour requirement and
timing coincide at the beginning of the season. The notion
that more than two weedings, or handpulling, may be required
to stop Striga reproduction is not just a biological issue but
a socio-economic one as well, as it will entail a shift in the
amount and timing of labour requirement for Striga control.
Farmers will have to be aware of the biology of Striga, the
limitation of present weed control practices, and the
long-term practices to be followed to control Striga
effectively given the resources at their disposal.
Striga control package for small-scale farmers in
Malawi. Several packages for the control of Striga have
been developed and tested based on integrated control
practices (Carson, 1988; Mboob, 1989; Matthews, 1989; Parker
and Riches, 1993; Oryokot, 1994; Odhiambo and Ransom, 1995;
Kachelriess et al., 1996). Ogborn (1984) argued that
the ability to measure Striga seed populations from the soil
seed bank is the only way in which success of integrated
control of Striga in smallholder systems can unambiguously be
evaluated.
In Malawi, for the small-scale farmer, an effective Striga
control programme would include four aspects: (1) elimination
or reduction of Striga seed numbers from heavily infested
soils; (2) prevention of flowering and seed shed of Striga;
(3) restoration of soil fertility for direct benefit of the
host crop; and (4) communication and training for Striga
control. Lack of relevant information remains a constraint to
adoption of perceived Striga control methods. Shaxson et
al. (1993) and Debrah (1994) argue that providing
information to farmers on why a control method works rather
than merely recommending which ones to use is essential for a
successful crop protection programme. This is because farmers'
knowledge about the parasite is generally very limited. With
the present understanding of Striga and potential control
strategies, a dissemination package and a training package can
be developed for farmers through an interactive and creative
process with them, researchers, and extension agents
(Kachelriess et al., 1996).
ACKNOWLEDGEMENTS
Thanks are due to the Rockefeller Foundation Forum for
Agricultural Resource Husbandry for a preparatory grant that
was used in a literature survey and creation of a Striga
database at Bunda College of Agriculture, Lilongwe. Comments
of Dr. G.K.C. Nyirenda, Dr. S. Snapp, and Dr. S. Waddington
during preparation of an earlier manuscript are acknowledged.
Thanks are also due to Dr. C. Riches for an earlier synopsis
on Striga research in Malawi, to Dr. M.A.R.Phiri for
translation of the abstract and to Mr. A.M.Z. Chamango for
work on the database.
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