Striga hermonthica
(witchweed)

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Identity

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Preferred Scientific Name

• Striga hermonthica (Del.) Benth. (1836)

Preferred Common Name

• witchweed

Other Scientific Names

• Buchnera hermontheca Del. (1813)
• Striga hermontheca (Del.) Benth. (1836)
• Striga senegalensis Benth. (1846)

International Common Names

• English: purple witchweed

Local Common Names

• : al boodah; odaar
• Ethiopia: atikur; atkenchera
• Germany: Zauberkraut, Rosarotes
• Italy: erba strega

EPPO code

• STRHE (Striga hermonthica)

Taxonomic Tree

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• Domain: Eukaryota
•     Kingdom: Plantae
•         Phylum: Spermatophyta
•             Subphylum: Angiospermae
•                 Class: Dicotyledonae
•                     Order: Scrophulariales
•                         Family: Orobanchaceae
•                             Genus: Striga
•                                 Species: Striga hermonthica

Notes on Taxonomy and Nomenclature

Top of page There are a number of possible origins of the name Striga, deriving from Latin words meaning 'striate', 'harshly hairy', 'lean' or 'witch' (Raynal-Roques and Salle, 1987). All are appropriate, but the term 'witch' is especially expressive, reflecting the way the weed apparently bewitches the crop and causes damage even before the weed itself emerges above ground.

West African forms of S. hermonthica with slightly smaller flowers were for a long time distinguished as Striga senegalensis, but they are now treated as conspecific with the larger-flowered forms elsewhere in Africa and Arabia.

The alternative spelling, S. hermontheca, is no longer regarded as correct.

Description

Top of page S. hermonthica is a herbaceous annual plant 30-100 cm high, the most robust forms occurring in Sudan and Ethiopia. Larger plants may be much branched. Stems and leaves are clothed in characteristic trichomes giving the plant a harsh texture. Leaves mostly opposite on the lower half of the stem but irregular above, narrowly lanceolate or elliptic, 2-8 cm long, up to 1 cm wide. Inflorescence a terminal spike of sessile flowers, with axillary spikes branching from upper leaf axils. Flowers subtended by bracts 1-2 cm long, up to 3 mm wide, with a fringe of ciliate hairs. Calyx tubular up to 1 cm long with 5 ribs and 5 teeth 2-3 mm long. Flower asymetrically campanulate, the tube 1-2 cm long, bent approximately half way up in West African, Sudanese and Ethiopian populations but usually well above halfway in East African populations (Parker and Riches, 1993). Corolla lobes 4, one bi-lobed almost erect, the others spreading horizontally, up to 2 cm across, pink with some white markings in the throat. The stigma and stamens are hidden in the tube. The main inflorescence spike may bear up to 100 flowers but only 6-10 are open at any one time. The capsules are up to 1 cm long and each develops several hundred minute seeds, approximately 0.3 mm long by 0.2 mm wide.

The root system is weak with little or no ability to absorb materials from the soil, but branches develop from lower nodes of the plant, ramifying and developing secondary haustoria and attachments on contact with other host roots.

Distribution

Top of page S. hermonthica may have developed in north-east Africa (Musselman and Hepper, 1986), but appears to have reached most suitable ecologies in western and central Africa long ago, while its spread in Ethiopia has occurred mainly in the past 100 years; there are parts of that country and of Kenya with a suitable climate to which it has not yet spread. The reasons for non-occurrence in most of southern Africa are not explained and the possibility of further spread southwards should not be ignored. It occurs in the Arabian peninsula but has not yet reached any further east.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Risk of Introduction

Top of page All Striga species are prohibited imports to USA and Israel.

Habitat

Top of page S. hermonthica, in common with most other Striga species, is associated with low-fertility soils, especially those low in nitrogen. Unlike Striga asiatica it occurs not only on light, sandy soils but also on heavy clays and even on vertisols. It is also favoured by low soil moisture, and rarely occurs on irrigated soils, but can tolerate abundant moisture for short periods. It is a plant of African savanna, almost invariably associated with cereal cropping and relatively uncommon in natural vegetation.

Hosts/Species Affected

Top of page The natural host range of S. hermonthica is normally limited to Gramineae [Poaceae], but weak attachment to groundnut, cowpea, lablab and soyabean was obtained in pots by Andrews (1946) and there have been unconfirmed reports of infestation of groundnut and sesamum fields in West Africa. Apart from the wild hosts listed above, S. hermonthica is occasionally observed on Dactyloctenium aegyptium, Panicum walense, Eleusine indica, Paspalum scrobiculatum and Pennisetum violaceum and on Cynodon, Cymbopogon, Ophiuros and Brachiaria spp. Individual biotypes may have a narrower host range than the species. In particular, there are forms which attack sorghum but not pearl millet and vice versa (see Parker and Riches, 1993).

Host Plants and Other Plants Affected

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Growth Stages

Top of page Flowering stage, Fruiting stage, Pre-emergence, Seedling stage, Vegetative growing stage

Symptoms

Top of page S. hermonthica causes characteristic yellowish blotches in the foliage about 1 cm long by 0.5 cm wide. In later stages whole leaves may wilt, become chlorotic and die. Stems are shortened, though leaf number may not be reduced. Inflorescence development is delayed or prevented. Root systems, at least in early stages, may be stimulated, and haustoria 1-2 mm across appear like nodules.

List of Symptoms/Signs

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Biology and Ecology

Top of page The biology and ecology of S. hermonthica are described in detail by Parker and Riches (1993). In brief, S. hermonthica is an obligate hemi-parasite, with green foliage capable of photosynthesis and thus at least partially supporting its own growth once established, but with a minute seed which has inadequate reserves to establish without a host. The germination biology is comparable to that of Striga asiatica. Seeds require after-ripening, sometimes for several months after shedding, and then conditioning in the imbibed state for at least a few days before they will respond to a germination stimulant such as sorgolactone in the root exudate of a susceptible host crop such as sorghum, or a related lactone such as strigol, exuded by a non-host crop such as cotton. In the absence of a stimulant, prolonged imbibition of the seeds usually leads to some degree of 'secondary dormancy'.

Germination occurs within 24 h of exposure to stimulant. The seedling root grows to 4 or 5 mm only before dying in the absence of a host. On contact with a host root, however, elongation stops and sticky hairs develop, anchoring it to the root surface while the intrusive organ develops and penetrates the cortex and endodermis, to make connections with the host xylem. There are no clear connections with the phloem, and most water, minerals and elaborated sugars and amino acids are apparently obtained from the host xylem. Until the parasite emerges, it is totally dependent on the host for all these, while even after emergence and development of green foliage, its photosynthesis is relatively inefficient and it continues to depend on the host for most of its carbohydrate as well as nitrogen requirements (e.g. Press et al., 1987). Rapid transfer of materials from host to parasite depends on high transpiration in the parasite, which is helped by the almost permanently open stomata of the parasite and favoured by low humidity. Germination and growth are generally favoured by low soil nitrogen. High nitrogen, especially in ammonium form, may have direct toxic effects on Striga seedlings (e.g. Pieterse, 1991), but other effects may be more important, including the suppression of stimulant exudation from the host, and other changes in the physiology of the host-parasite relationship (Press and Cechin, 1994).

Relatively high temperatures, 30-35°C, are optimal for germination and for growth. Dry conditions of soil and air are most favourable, and S. hermonthica rarely occurs in irrigated cereals, though wet conditions can be tolerated for short periods. Neither soil type nor pH is critical, S. hermonthica occurring on almost all soil types from sandy acidic to alkaline clay soils, as in Sudan.

Unlike S. asiatica, S. hermonthica is an obligate out-crosser, depending on a range of insects for pollination (Musselman et al., 1983).

Natural enemies

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Notes on Natural Enemies

Top of page The main insect natural enemies of S. hermonthica have been catalogued by Greathead and Milner (1971), Greathead (1984), Markham (1985) and Bashir (1987). Among the commonest are the Smicronyx spp., gall-forming weevils widespread in West Africa, which may greatly reduce seed production. The commonest species are Smicronyx umbrinus and Smicronyx guineanus, while a new species, Smicronyx dorsomaculatus, has recently been described, though this occurs mainly as a stem gall on the related Striga gesnerioides (Anderson and Cox, 1997). These are apparently specific to Striga and closely related genera, but have not yet been successfully exploited for biocontrol. Also widespread are the less specific lepidopteran feeders Junonia orithya and Stenoptilodes taprobanes, often causing conspicuous damage to foliage and flowers, respectively, but with no potential as biocontrol agents.

Records of fungal attack on S. hermonthica have been reviewed by Greathead (1984) and Bashir (1987). A further range of pathogens has been reported from Ghana (Abbasher et al., 1995) and individual species of Fusarium have been identified in Sudan (Kirk, 1993; Abbasher et al., 1996) and Mali (Ciotola et al., 1995). A number of these organisms are under further investigation as possible mycoherbicides.

Impact

Top of page S. hermonthica is almost certainly responsible for more crop loss in Africa than any other individual weed species. Over 5 million ha of crops - mainly sorghum, millets and maize - are affected in six countries of West Africa alone (Sauerborn, 1991), possibly 10 million ha in Africa as a whole. One plant of S. hermonthica per host plant is estimated to cause approximately 5% loss of yield (Parker and Riches, 1993) and high infestations can cause total crop failure. Overall yield losses are estimated at 21% of all sorghum in northern Ghana, 10% of all cereals in Nigeria, 8% in Gambia and 6% in Benin (Sauerborn, 1991). Other countries seriously affected include Cameroon, Cote d'Ivoire, Burkina Faso, Niger, Mali, Senegal, Togo, Sudan, Ethiopia, Kenya, Uganda and Tanzania.

The damaging effect of S. hermonthica on the host plant derives not only from the direct loss of water, minerals, nitrogen and carbohydrate to the parasite, but from a disturbance of the host photosynthetic efficiency (e.g. Press and Graves, 1991) and a profound change in the root/shoot balance of the host, leading to stimulation of the root system and stunting of the shoot.

As S. hermonthica occurs mainly under conditions of low fertility, it is also associated with some of the poorest farming systems in Africa, in which farmers have few resources and very few options in terms of control measures.

Detection and Inspection

Top of page Infestation of a cereal crop by S. hermonthica may be apparent before emergence from the soil, by the chlorotic blotches on the crop foliage. Uprooting may confirm the presence of the haustoria and young parasite seedlings on the root. For detecting the seeds of S. hermonthica in crop seeds, Berner et al. (1994) used a technique involving sampling from the bottom of sacks, elutriation of samples in turbulent flowing water and collection of seeds and other particles on a 90 µm mesh sieve. Striga seeds are then separated from heavier particles by suspension in a solution of potassium carbonate of specific gravity 1.4 in a separating column. Sound seeds collect at the interface and are transferred to a 60 µm mesh for counting.

Similarities to Other Species/Conditions

Top of page S. hermonthica is most often confused with Striga aspera, a common plant in West Africa, occurring on rice, maize and many wild grass hosts. S. aspera has slightly smaller flowers but is readily distinguished (in West Africa) by the bend in the corolla tube occurring two thirds to three quarters up, rather than about half way. Also the bracts in S. aspera are narrower, 1-2 mm only and without a fringe of hairs. S. aspera is rare in East Africa, but there it is less readily distinguished from the local S. hermonthica on the basis of the corolla tube, and the bract character is more important. Other Striga species have different coloured flowers and/or more ribs on the calyx tube (see Parker and Riches, 1993 for a key to the agriculturally important species). Others with 5 calyx ribs include Striga gesnerioides, a short, fleshy parasite of cowpea in West Africa, and Striga densiflora, a white-flowered parasite of cereals in South Asia. Striga asiatica, a white-, yellow- or red-flowered parasite of cereals in Africa and Asia, has 10-14 calyx ribs. Those with 15 calyx ribs include Striga angustifolia, Striga forbesii and Striga latericea.

Striga forbesii differs from S. hermonthica in its 15 calyx ribs, salmon-pink flowers and broader, coarsely toothed leaves. It is widespread but sporadic across Africa and Madagascar, sometimes attacking cereals and sugarcane, especially in Zimbabwe and Tanzania; also on wild hosts, especially Setaria and Echinochloa spp. Biology and ecology are generally similar to those of S. hermonthica, as are the damaging effects on crops, but germination factors may be different (Jackson and Parker, 1991).

Striga latericea is very similar to S. forbesii but is a perennial with deeper brick-red flowers and an underground stolon system, parasitic on a range of wild hosts in East Africa and on sugarcane in Ethiopia.

Prevention and Control

Top of page Varietal Resistance/Tolerance

No completely immune cereal varieties have yet been developed, but many sorghum varieties show high levels of resistance, at least under local conditions. Selection and breeding programmes in India and Africa have led to the development and release of many lines with at least reduced susceptibility, and these may be valuable as components of an integrated control approach (e.g. Carsky et al., 1996; older literature reviewed by Parker and Riches, 1993). However, traditional varieties in Striga-infested areas often show relatively high tolerance, and these may yield well in spite of heavy infestation.

In maize there are no effectively resistant varieties, though some show partial resistance, such as var. Katumani in Kenya (Baltus et al., 1994), and some more tolerant lines have been developed by the International Institute for Tropical Agriculture (Kim and Adetimirin, 1997). Work is now in progress to transfer high-level resistance into maize from wild relatives including Zea diploperennis (e.g. Lane et al., 1997).

Little progress has been possible with the out-crossing pearl millet, but there are promising results from work in progress to select and develop rice varieties with resistance to Striga species (e.g. Riches et al., 1996).

Cultural Control

Characteristics/weaknesses in S. hermonthica which may be exploited in cultural control measures include the following.

- Dependence on a susceptible host for establishment. Crop rotation avoiding a susceptible cereal will prevent new seeding and allow decline of the soil seed bank. In some areas, there may be alternative cereals which are not attacked (e.g. sorghum in a millet-growing area, or vice versa). Among the non-cereal crops, many are known to exude germination stimulant, though they cannot be parasitized. These trap crops, such as cotton, groundnut, cowpea and soyabean, are especially beneficial in causing suicidal germination and accelerating a decline in the soil seed bank. But they need to be sown at a time when Striga germination is likely to be high, usually early in the rainy season, before the onset of any secondary dormancy. Catch crops are susceptible cereals which may be grown at the beginning of the season or in short rains prior to the main season, to stimulate germination of the Striga. However, they need to be destroyed before the weed can mature and set seed.

- Preference for low nitrogen. Additional nitrogen fertilizer usually reduces Striga incidence, though not always, especially when applied as a single dose (see Parker and Riches, 1993). However, improved soil fertility is a vital key to long-term control, whether by organic, inorganic or green manuring, rotation with legumes, or agroforestry techniques involving mulching.

- Preference for dry conditions. Irrigation is rarely an option, but moisture conservation techniques may be beneficial. Any means of raising humidity will reduce Striga transpiration and its ability to draw nutrition from the host. Hence leafy crop varieties, dense, uniform planting and mixed cropping (see e.g. Carsky et al., 1994) all tend to suppress the weed.

None of the methods described above will, alone, provide complete control, and without complete control there is the certainty that surviving plants will mature and replenish the soil seed bank. It is therefore essential that manual, mechanical or chemical methods are used to destroy surviving plants. Hand-pulling is the commonest traditional technique, though a late hoeing or ridging may also be effective.

Chemical Control

2,4-D may be used to kill emerged S. hermonthica or to prevent it from maturing and setting seed in sole-crop cereals, but not where mixed with legumes. Pre-emergence treatment with chlorsulfuron and other sulfonylurea herbicides has proved selective in sorghum and maize in some experiments (e.g. Babiker et al., 1996), but practical field use of these herbicides is likely to depend on combination with herbicide-tolerant crop varieties. For instance, Abayo et al. (1996) report the useful selectivity of imazapyr and chlorsulfuron applied into the planting holes with seed of maize genetically engineered for tolerance of acetolactate synthase-inhibiting herbicides. In a similar study, Berner et al. (1997) applied the herbicides imazaquin and nicolsulfuron to the maize seed before sowing. It is likely that glyphosate will become a useful tool for post-emergence control of S. hermonthica in glyphosate-tolerant maize. It is less likely, however, that herbicide-tolerant varieties of sorghum or pearl millet varieties will be developed.

Biological Control

The reduction in seed production from gall-forming Smicronyx spp. is often substantial (e.g. Kroschel et al., 1995; Traore et al., 1995), but there has been no successful development of a biological control programme based on these weevils. Attempts to introduce Smicronyx albovariegatus (and the moth Eulocastra argentisparsa) from India into Ethiopia apparently failed. Meanwhile, conclusions from a mathematical modelling project have suggested that Simicronyx spp. would in any case be unlikely to have a significant impact on Striga population dynamics (Smith et al., 1993).

There is now rather more interest in the use of soil pathogens as mycoherbicides, especially Fusarium spp., including Fusarium nygamai (Sauerborn et al., 1996), Fusarium oxysporum (Ciotola et al., 1995; Kroschel et al., 1996), Fusarium equiseti (Kirk, 1993), Fusarium semitectum (Abbasher et al., 1996) and Fusarium solani (Kroschel et al., 1996). However, further work is needed before a reliable economic treatment is developed.

Integrated Control

As virtually none of the treatments described above is likely to achieve complete control, integration of one or more is essential for any substantial reduction of the problem. Furthermore, such integrated treatments will almost certainly need to be repeated over a number of years for long-term control. Parker and Riches (1993) propose a range of programmes depending on the initial density of the problem, involving various combinations of rotation, varietal selection, soil fertility enhancement and mixed cropping, supplemented in all cases by hand-pulling, herbicide application or other techniques to prevent seeding.

References

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Abayo GO; Ransom JK; Gressel J; Odhiambo GD, 1996. Striga hermonthica control with acetolactate synthase inhibiting herbicides applied to maize seed with target-site resistance. In: Moreno MT, Cubero JI, Berner D, Joel D, Musselman LJ, Parker C, eds. Advances in Parasitic Plant Research. Cordoba, Spain: Junta de Andalucia, 761-768.

Abbasher AA, 1994. Microorganisms associated with Striga hermonthica and possibilities for their utilization as biological control agents. Plits, 12(1):144 pp.; [Thesis, Hohenheim University].

Abbasher AA; Kroschel J; Sauerborn J, 1995. Microorganisms of Striga hermonthica in northern Ghana with potential as biocontrol agents. Biocontrol Science and Technology, 5(2):157-161; 17 ref.

Abbasher AA; Sauerborn J; Kroschel J; Hess DE, 1996. Evaluation of Fusarium semitectum var. majus for biological control of Striga hermonthica. In: Moran VC, Hoffman JH, eds. Proceedings of the 9th International Symposium on Biological Control of Weeds, Stellenbosch, 1996. Rondebosch, South Africa: University of Cape Town, 115-120.

Anderson DM; Cox ML, 1997. Smicronyx species (Coleoptera: Curculionidae), economically important seed predators of witchweeds (Striga spp.) (Scrophulariaceae) in sub-Saharan Africa. Bulletin of Entomological Research, 87(1):3-17; 32 ref.

Andrews FW, 1946. The parasitism of Striga hermonthica Benth. on leguminous plants. Annals of Applied Biology, 34:267-275.

Babiker AGT; Ahmed NE; Ejeta LG; Butler LG; Mohammed A; El Mana MT; El Tayeb SM; Abdel Rahamman BE, 1996. Chemical control of Striga hermonthica in sorghum. In: Moreno MT, Cubero, JI, Berner D, Joel D, Musselman LJ, Parker C, eds. Advances in Parasitic Plant Research. Cordoba, Spain: Junta de Andalucia, 769-776.

Baltus PCW; Ransom JK; Odhiambo GD; Egbers WS; Borg SJ ter; Verkleij JAC; Pieterse AH, 1994. A comparitive study on the defence mechanism(s) of the maize variety 'Katumani' against Striga hermonthica under field conditions in Kenya. Biology and management of Orobanche. Proceedings of the third international workshop on Orobanche and related Striga research, Amsterdam, Netherlands, 8-12 November 1993 [edited by Pieterse, A.H.; Verkleij, J.A.C.; Borg, S.J. ter] Amsterdam, Netherlands; Royal Tropical Institute, 373-381

Bashir MO, 1987. The potential for biocontrol of witchweeds. Parasitic weeds in agriculture. Volume I. Striga [edited by Musselman, L.J.] Boca Raton, Florida, USA; CRC Press Inc., 183-206

Bengaly M'P; Defoer T; Stoop W; Sanogo ZJL, 1998. Approche méthodologique de lutte integrée contre le striga: processus d'une apprentissage alternatif et participatif de recherche-action (Methodology for the integrated control of Striga: a process of alternative and participatory action-research learning). 56 pp.

Berner DK; Cardwell KF; Faturoti BO; Ikie FO; Williams OA, 1994. Relative roles of wind, crop seeds, and cattle in dispersal of Striga spp. Plant Disease, 78(4):402-406; 23 ref.

Berner DK; Ikie FO; Green JM, 1997. ALS-inhibiting herbicide seed treatments control Striga hermonthica in ALS-modified corn (Zea mays). Weed Technology, 11(4):704-707; 15 ref.

Carsky RJ; Ndikawa R; Kenga R; Singh L; Fobasso M; Kamuanga M, 1996. Effect of sorghum variety on Striga hermonthica parasitism and reproduction. Plant Varieties & Seeds, 9(2):111-118; 13 ref.

Carsky RJ; Singh L; Ndikawa R, 1994. Suppression of Striga hermonthica on sorghum using a cowpea intercrop. Experimental Agriculture, 30(3):349-358

Chaudhary SA; Akram M, 1987. Weeds of Saudi Arabia and the Arabian Peninsula. Saudi Arabia: National Herbarium, Regional Agriculture and Water Research Center, Ministry of Agriculture and Water.

Ciotola M; Watson AK; Hallett SG, 1995. Discovery of an isolate of Fusarium oxysporum with potential to control Striga hermonthica in Africa. Weed Research (Oxford), 35(4):303-309; 19 ref.

EPPO, 2014. PQR database. Paris, France: European and Mediterranean Plant Protection Organization. http://www.eppo.int/DATABASES/pqr/pqr.htm

Estep MC; Mourik TAvan; Muth P; Guindo D; Parzies HK; Koita OA; Weltzien E; Bennetzen JL, 2011. Genetic diversity of a parasitic weed, Striga hermonthica, on sorghum and pearl millet in Mali. Tropical Plant Biology, 4(2):91-98. http://www.springerlink.com/content/q78116547587771u/

Greathead DJ, 1984. The natural enemies of Striga spp. and the prospects for their utilisation as biological control agents. In: Ayensu ES, Doggett H, Keynes RD, Marton-Lefevre J, Musselman LJ, Parker C, Pickering A, ed. Striga. Biology and control Paris, ICSU Press France, 133-160

Greathead DJ; Milner JED, 1971. A survey of Striga spp. (Scrophulariaceae) and their insect natural enemies in East Africa with a discussion on the possibilities of biological control. Tropical Agriculture, 48(2):111-124

Hepper FN, 1963. Scrophulariaceae. In: Hutchinson J, Dalziel JM, Hepper FN, eds. Flora of West Tropical Africa, Volume 2, second edition. London, UK: Crown Agents, 352-374.

Holm LG; Pancho JV; Herberger JP; Plucknett DL, 1979. A geographical atlas of world weeds. New York, USA: John Wiley and Sons, 391 pp.

Jackson MB; Parker C, 1991. Induction of germination by a strigol analogue requires ethylene action in Striga hermonthica but not in S. forbesii. Journal of Plant Physiology, 138(4):383-386

Kim SoonKwon; Adetimirin VO, 1997. Responses of tolerant and susceptible maize varieties to timing and rate of nitrogen under Striga hermonthica infestation. Agronomy Journal, 89(1):38-44; 29 ref.

Kirk AA, 1993. A fungal pathogen with potential for biocontrol of Striga hermonthica (Scrophulariacae). Entomophaga, 38(4):459-460; 5 ref.

Kroschel J; Abbasher AA; Sauerborn J, 1995. Herbivores of Striga hermonthica in northern Ghana and approaches to their use as biocontrol agents. Biocontrol Science and Technology, 5(2):163-164

Kroschel J; Hundt A; Abbasher AA; Sauerborn J, 1996. Pathogenicity of fungi collected in northern Ghana to Striga hermonthica. Weed Research (Oxford), 36(6):515-520; 22 ref.

Kroschel J; Hundt A; Abbasher AA; Sauerborn J, 1996. Pathogenicity of fungi collected in northern Ghana to Striga hermonthica. Weed Research, Oxford, 36(6):515-520.

Lane JA; Child DV; Moore THM; Arnold GM; Bailey JA, 1997. Phenotypic characterisation of resistance in Zea diploperennis to Striga hermonthica. Maydica, 42(1):45-51; 20 ref.

Markham RH, 1985. Possibilities for the Biological Control of Striga Species in the Sahel. Nairobi, Kenya: Commonwealth Institute of Biological Control, 16 pp.

M'Boob SS, 1994. Striga in Africa. In: Lagoke STO, Hoevers R, M'Boob SS, Traboulsi, eds. Improving Striga Management in Africa. Proceedings of the 23nd General Workshop of the Pan-African Striga Control Network (PASCON), Nairobi, 1991. Rome, Italy: FAO, 25-29.

Musselman LJ; Hepper FN, 1986. The witchweeds (Striga, Scrophulariaceae) of the Sudan Republic. Kew Bulletin, 41:205-221.

Musselman LJ; Matteson PC; Fortune S, 1983. Potential pollen vectors of Striga hermonthica (Scrophulariaceae) in West Africa. Annals of Botany, 51:859-862.

Parker C, 2009. Observations on the current status of Orobanche and Striga problems worldwide. Pest Management Science [Managing parasitic weeds: integrating science and practice. Proceedings of a conference held at Apulia, Italy, 21-26 September 2008.], 65(5):453-459. http://www.interscience.wiley.com/pestmanagementscience

Parker C; Riches CR, 1993. Parasitic weeds of the world: biology and control. Wallingford, UK; CAB International, xx + 332 pp.

Pieterse AH, 1991. The effect of nitrogen on the germination of seeds of Striga hermonthica and Orobanche crenata. Progress in Orobanche research. Proceedings of the international workshop on Orobanche research, Obermarchtal, Germany, 19-22 August 1989 [edited by Weymann, K.; Musselman, L.J.] Tubingen, Germany; Eberhard-Karls-Universitat, 115-124

Press MC; Cechin I, 1994. Influence of nitrogen on the Striga hermonthica-sorghum association. Biology and management of Orobanche. Proceedings of the third international workshop on Orobanche and related Striga research, Amsterdam, Netherlands, 8-12 November 1993 [edited by Pieterse, A.H.; Verkleij, J.A.C.; Borg, S.J. ter] Amsterdam, Netherlands; Royal Tropical Institute, 302-311

Press MC; Graves JD, 1991. Carbon relations of angiosperm parasites and their hosts. Progress in Orobanche research. Proceedings of the international workshop on Orobanche research, Obermarchtal, Germany, 19-22 August 1989 [edited by Wegmann, K.; Musselman, K.J.] Tubingen, Germany; Eberhard-Karls-Universitat, 55-65

Press MC; Shah N; Tuohy JM; Stewart GR, 1987. Carbon isotope ratios demonstrate carbon flux from C to C parasite. Plant Physiology, 85(4):1143-1145

Rao VP; Tesfamichael Abraha; Obilana AB; Preston SR, 2002. Sorghum diseases in Eritrea - a survey report. International Sorghum and Millets Newsletter, 43:57-60; 2 ref.

Rao VP; Tesfamichael Abraha; Obilana AB; Preston SR; Abraha T, 2002. Sorghum diseases in Eritrea -- a survey report. International Sorghum and Millets Newsletter, 43:57-60.

Raynal-Roques A; Salle G, 1987. Striga Lour. (Scrophulariaceae), an etymological analysis. Journal d'Agriculture Traditionnelle et de Botanique Appliquee, 34:47-49

Riches CR; Johnson DE; Jones MP, 1996. The selection of resistance to Striga species in upland rice. In: Moreno MT, Cubero, JI, Berner D, Joel D, Musselman LJ, Parker C, eds. Advances in Parasitic Plant Research. Cordoba, Spain: Junta de Andalucia, 673-680.

Robson TO; Americanos PJ; Abu-Irmaileh BE, 1991. Major Weeds of the Near East. FAO Plant Production and Protection Paper 104. Rome, Italy: FAO.

Sauerborn J, 1991. The economic importance of the phytoparasites Orobanche and Striga. In: Ransom JK, Musselman LJ, Worsham AD, Parker C, eds. Proceedings of the Fifth International Symposium of Parasitic Weeds, Nairobi, Kenya, 24-30 June 1991. Nairobi, Kenya: CIMMYT (International Maize and Wheat Improvement Center), 137-143

Sauerborn J; Abbasher AA; Kroschel J; Cornes DW; Zoschke A; Hine KT, 1996. Striga hermonthica control with Fusarium nygamai in maize. Proceedings of the 9th international symposium on biological control of weeds, Stellenbosch, South Africa, 19-26 January 1996., 461-466; 7 ref.

Smith MC; Holt J; Webb M, 1993. Population model of the parasitic weed Striga hermonthica (Scrophulariaceae) to investigate the potential of Smicronyx umbrinus (Coleoptera: Curculionidae) for biological control in Mali. Crop Protection, 12(6):470-476

TraorT D; Vincent C; Stewart RK, 1995. Life history of Smicronyx guineanus and Sm. umbrinus (Col.: Curculionidae) on Striga hermonthica (Scrophulariaceae). Entomophaga, 40(2):211-221; 19 ref.

Distribution Maps

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