Striga hermonthica (witchweed)
Index
- Pictures
- Identity
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Description
- Distribution
- Distribution Table
- Risk of Introduction
- Habitat
- Hosts/Species Affected
- Host Plants and Other Plants Affected
- Growth Stages
- Symptoms
- List of Symptoms/Signs
- Biology and Ecology
- Natural enemies
- Notes on Natural Enemies
- Impact
- Detection and Inspection
- Similarities to Other Species/Conditions
- Prevention and Control
- References
- Distribution Maps
Don't need the entire report?
Generate a print friendly version containing only the sections you need.
Generate reportIdentity
Top of pagePreferred 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
- Arab countries: al boodah; odaar
- Ethiopia: atikur; atkenchera
- Germany: Zauberkraut, Rosarotes
- Italy: erba strega
EPPO code
- STRHE (Striga hermonthica)
Taxonomic Tree
Top of page- 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 pageWest 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 pageThe 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 pageDistribution Table
Top of pageThe 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.
Last updated: 12 May 2022Continent/Country/Region | Distribution | Last Reported | Origin | First Reported | Invasive | Reference | Notes |
---|---|---|---|---|---|---|---|
Africa |
|||||||
Angola | Present | ||||||
Benin | Present, Widespread | ||||||
Burkina Faso | Present, Widespread | ||||||
Burundi | Present | ||||||
Cameroon | Present, Widespread | ||||||
Central African Republic | Present | ||||||
Chad | Present, Widespread | ||||||
Congo, Democratic Republic of the | Present, Widespread | ||||||
Congo, Republic of the | Present, Localized | ||||||
Côte d'Ivoire | Present | ||||||
Egypt | Present, Widespread | ||||||
Eritrea | Present | Original citation: Rao et al. (2002) | |||||
Eswatini | Present | ||||||
Ethiopia | Present, Widespread | ||||||
Gambia | Present | ||||||
Ghana | Present, Widespread | ||||||
Guinea | Present, Widespread | ||||||
Guinea-Bissau | Present | ||||||
Kenya | Present, Widespread | ||||||
Madagascar | Present | ||||||
Malawi | Present, Localized | ||||||
Mali | Present | ||||||
Mauritania | Present | ||||||
Morocco | Present | ||||||
Mozambique | Present, Widespread | ||||||
Namibia | Present | ||||||
Niger | Present, Widespread | ||||||
Nigeria | Present, Widespread | ||||||
Rwanda | Present | ||||||
Senegal | Present, Widespread | ||||||
South Africa | Present, Widespread | ||||||
Sudan | Present, Widespread | ||||||
Tanzania | Present, Widespread | ||||||
Togo | Present | An estimated 30–40% of maize growing areas infested | |||||
Uganda | Present, Widespread | ||||||
Zambia | Present | ||||||
Zimbabwe | Present, Widespread | ||||||
Asia |
|||||||
Cambodia | Present | ||||||
India | Present | ||||||
Saudi Arabia | Present, Widespread | ||||||
Yemen | Present, Widespread |
Habitat
Top of pageHosts/Species Affected
Top of pageHost Plants and Other Plants Affected
Top of pagePlant name | Family | Context | References |
---|---|---|---|
Brachiaria (signalgrass) | Poaceae | Wild host | |
Cymbopogon | Poaceae | Wild host | |
Cynodon (quickgrass) | Poaceae | Wild host | |
Dactyloctenium aegyptium (crowfoot grass) | Poaceae | Wild host | |
Eleusine coracana (finger millet) | Poaceae | Main | |
Eleusine indica (goose grass) | Poaceae | Wild host | |
Eragrostis tef (teff) | Poaceae | Other | |
Hordeum vulgare (barley) | Poaceae | Other | |
Oryza sativa (rice) | Poaceae | Main | |
Panicum (millets) | Poaceae | Main | |
Panicum walense | Poaceae | Wild host | |
Paspalum scrobiculatum (ricegrass paspalum) | Poaceae | Wild host | |
Pennisetum glaucum (pearl millet) | Poaceae | Other | |
Rottboellia cochinchinensis (itch grass) | Poaceae | Wild host | |
Saccharum officinarum (sugarcane) | Poaceae | Main | |
Sorghum | Poaceae | Unknown | Marley et al. (2004); Marley et al. (2004) |
Sorghum bicolor (sorghum) | Poaceae | Main | |
Sorghum halepense (Johnson grass) | Poaceae | Wild host | |
Zea mays (maize) | Poaceae | Main |
Growth Stages
Top of pageSymptoms
Top of pageList of Symptoms/Signs
Top of pageSign | Life Stages | Type |
---|---|---|
Leaves / abnormal patterns | ||
Leaves / yellowed or dead | ||
Stems / stunting or rosetting | ||
Whole plant / dwarfing | ||
Whole plant / early senescence |
Biology and Ecology
Top of pageGermination 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
Top of pageNatural enemy | Type | Life stages | Specificity | References | Biological control in | Biological control on |
---|---|---|---|---|---|---|
Alternaria alternata | Pathogen | |||||
Athelia rolfsii | Pathogen | |||||
Cladosporium oxysporum | Pathogen | |||||
Cochliobolus spicifer | Pathogen | |||||
Curvularia fallax | Pathogen | |||||
Curvularia fallax | Pathogen | |||||
Eulocastra argentisparsa | Herbivore | Ethiopia | ||||
Eurytoma | Parasite | Plants|Stems | ||||
Fusarium oxysporum | Pathogen | Plants|Leaves; Plants|Stems | ||||
Gibberella intricans | Pathogen | Plants|Leaves; Plants|Seeds; Plants|Stems | ||||
Gibberella nygamai | Pathogen | Plants|Leaves; Plants|Seeds; Plants|Stems | ||||
Haematonectria haematococca | Pathogen | Plants|Leaves; Plants|Stems | ||||
Junonia orithya | Herbivore | Plants|Leaves | ||||
Macrophomina phaseolina | Pathogen | |||||
Mycosphaerella holci | Pathogen | Plants|Leaves; Plants|Seeds; Plants|Stems | ||||
Nodulisporium gregarium | Pathogen | |||||
Ophiomyia strigalis | Herbivore | Plants|Roots; Plants|Stems | ||||
Phoma sorghina | Pathogen | |||||
Smicronyx albovariegatus | Herbivore | Ethiopia | ||||
Smicronyx guineanus | Parasite | Plants|Stems | ||||
Smicronyx umbrinus | Parasite | Fruits|pods | ||||
Stenoptilodes taprobanes | Herbivore | Fruits|pods; Plants|Inflorescence |
Notes on Natural Enemies
Top of pageRecords 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 pageThe 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 pageSimilarities to Other Species/Conditions
Top of pageStriga 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 pageDue to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
Varietal Resistance/ToleranceNo 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
Top of pageAbayo 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; 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.
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.
EPPO, 2014. PQR database. Paris, France: European and Mediterranean Plant Protection Organization. http://www.eppo.int/DATABASES/pqr/pqr.htm
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.
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.
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.
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.
Distribution References
CABI, Undated. Compendium record. Wallingford, UK: CABI
CABI, Undated a. CABI Compendium: Status as determined by CABI editor. Wallingford, UK: CABI
Hepper FN, 1963. Scrophulariaceae. In: Flora of West Tropical Africa, 2 (second) [ed. by Hutchinson J, Dalziel JM, Hepper FN]. London, UK: Crown Agents. 352-374.
M'Boob SS, 1994. Improving Striga Management in Africa. Proceedings of the 23nd General Workshop of the Pan-African Striga Control Network (PASCON), Nairobi, 1991. In: Improving Striga Management in Africa. Proceedings of the 23nd General Workshop of the Pan-African Striga Control Network (PASCON), Nairobi, 1991, [ed. by Lagoke STO, Hoevers R, M'Boob SS, Traboulsi]. Rome, Italy: FAO. 25-29.
Distribution Maps
Top of pageSelect a dataset
Map Legends
-
CABI Summary Records
Map Filters
Unsupported Web Browser:
One or more of the features that are needed to show you the maps functionality are not available in the web browser that you are using.
Please consider upgrading your browser to the latest version or installing a new browser.
More information about modern web browsers can be found at http://browsehappy.com/