observations on the current status of orobanche and striga problems worldwide

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ReviewReceived: 17 October 2008 Accepted: 23 October 2008 Published online in Wiley Interscience: 10 February 2009

(www.interscience.wiley.com) DOI 10.1002/ps.1713

Observations on the current statusof Orobanche and Striga problems worldwideChris Parker∗

Abstract

Species of Orobanche and Striga are among the most damaging parasitic weed species worldwide, but there are few reliablestatistics on the full extent of the economic losses they cause. The distribution, host range and economic importance of themajor species of Orobanche and Striga are briefly summarised. A review of literature over the period since 1991 suggests thatmany million hectares are infested and that the losses amount to $US billions annually. Unfortunately there are almost nofully reliable figures on which to base these figures precisely. Meanwhile, there is little evidence of any significant changein intensity, range or losses caused over this period. Any reduction in the importance of these damaging weeds is sporadic,and alleviation of the problems is mostly localised. Furthermore, while the importance of Orobanche species may be broadlystatic, Striga species on cereals continue to become more serious in many countries owing to continued loss of soil fertility. Itis suggested that new techniques may be needed for measurement of the extent of losses caused by these genera and theireconomic impact. There is continued urgency to develop control measures appropriate to the farming systems involved, andto reduce the risk of spread of both groups of parasite to new areas.c© 2009 Society of Chemical Industry

Keywords: parasitic weeds; Striga; Orobanche; crop losses

1 INTRODUCTIONThis paper discusses the current status of the two main parasiticweed genera, Orobanche (including Phelipanche) and Striga.It reviews, very briefly, the areas affected and the estimatedlosses caused by each species, and then considers evidence for(i) intensification of the problems within the areas already infested,(ii) spread to new areas, (iii) alleviation of the problem withininfested sites and (iv) reductions in the area of infestation.

There are no reliable global figures, based on rigorous sampling,for the total area affected by Orobanche or Striga, but anestimated 16 million ha were considered to be ‘at risk’ ofOrobanche attack in the Mediterranean and West Asia regionin 1991.1 The corresponding figure for Striga in Africa was44 million ha ‘endangered’, and the total loss of revenue frommaize, pearl millet and sorghum ‘could total’ $US 2.9 billion.More recent figures suggest that 50 million ha and 300 millionfarmers are affected by Striga species in Africa, with losses of $US7 billion.2

The accuracy and validity of all these figures must be regardedwith some reservation, but they suggest a massive problemrequiring urgent attention. Some more detailed estimates aregiven under individual species.

2 OROBANCHE SPECIESEarlier reviews1,3,4 outline the seriousness of Orobanche problemsand the major crops affected by each species. One of these bringstogether estimates of the extent of infestation and crop losses fora number of problem species, as noted below.1

One more recent review has compiled information and views onthe extent and seriousness of Orobanche spp. in Europe and NorthAfrica.5 Seven species are described as ‘major’ weeds in Europe,

the most damaging being O. crenata Forsk., O. cumana Wallr., O.ramosa L. (= Phelipanche ramosa) and O. (= P.) aegyptiaca Pers.The remaining three are O. foetida Poir, O. cernua Loefl. and O.minor Sm. This is very much in line with previous appraisals, withthe exception of O. foetida, which has only become a significantproblem in the past 10–20 years. There is no attempt to quantifythe losses, which would allow comparison with those presentedearlier.1 Other recent reviews6,7 again confirm the major problemsbut make little attempt at any updated quantification of losses.

2.1 Orobanche crenataOrobanche crenata has its greatest economic impact on fababean. In 1991, some 180 000 ha were estimated to be infestedin Morocco, Portugal, Spain and Syria, representing 50–70% ofthe areas grown in those countries.1 In Morocco, the losses wereestimated at 12% in the infested areas, or 7.8% of the nationalyield.1 Some estimates of yield loss were even higher: in Egypt(33%), Malta (50–100%) and Turkey (30–70%). Other countriesin which O. crenata is a significant problem on legumes includeAlgeria, Cyprus, Iraq, Italy, Jordan, Lebanon and Tunisia. In Israelit mainly affects Umbelliferae – parsley, carrot and celery.8 It hasbeen estimated that over 4 million ha of legumes could be at riskfrom Orobanche (mainly O. crenata) across the Mediterranean andWest Asia.1 Peas, lentil, chickpea and carrot are among other cropsmost seriously affected.5 Its importance in pea has apparentlyincreased in recent years.9

∗ Correspondence to: Chris Parker, 5 Royal York Crescent, Bristol BS8 4JZ, UK.E-mail: [email protected]

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A recent report10 includes comments on a survey in 1993 showing12% losses of faba bean in Egypt and Morocco on account of O.crenata. It then states that ‘the spread and impact of the parasiteare increasing ever since’, such that a recent survey in those twocountries indicated that the losses were by then 30–40%. Thereis also comment that ‘most of the farmers do not apply any kindof control against O. crenata’. In Egypt, some tolerant varietiesof faba bean are available,11 but the loss figures mentionedabove suggest that these varieties are of limited effectiveness.Furthermore, Egypt is now having to import faba bean becausethe crop was abandoned in Upper Egypt owing to pest problemsincluding O. crenata.10 In Syria, ‘extensive research on crop andweed management practices have had no impact on Orobanchealleviation’. Adoption of recommended herbicide treatments infaba bean and lentil is low ‘due to lack of effective extension’.12

Another review in 1994,13 based on correspondence with in-country experts, concluded that, since the 1991 review,1 there hadbeen no significant change in levels of infestation in faba beanin Spain or Syria, while levels were increasing in Morocco, andsome 5000–10 000 ha were infested in Tunisia. In Syria 40 000 haof lentil were thought to be infested, with an average 10% yieldloss.1 Three years later, it was thought to be getting worse thereand in Morocco, where over 50% of the crop (15 000 ha) wasseriously infested.13 Also in Morocco, 50% (25 000 ha) of peas wereestimated to be affected, with an overall 12% loss in yield. Atthat time, 72% of farmers thought the problem of O. crenata wasincreasing, while only 28% thought it was decreasing.14 From thelimited evidence available it appears that the problems from thisspecies have perhaps stabilised in most countries but have notdecreased significantly, and, in spite of intensive research overseveral decades, there is no convincing evidence that availablecontrol methods are having any widely successful impact, andcrop losses presumably continue to be severe.

While there is limited evidence for intensification of pre-existinginfestations, there are a number of instances of spread to new areas.One report refers to a continuing spread of the problem westwardsalong the coast of Algeria.10 In Spain, it has now spread from thesouthern, eastern and western regions into the central regionof Salamanca, where it is attacking lentil and vetch.15 Eruptionsof the problem in completely new regions have been especiallydisturbing: in Ethiopia,16 and most recently in Sudan,17,18 whereit was first observed on 2 ha in 2000 and spread rapidly along160 km of the Nile to infest over 3000 ha at well over 100 separatesites by 2006.

The main way in which the problem is being reduced is byavoidance. A decrease in the area of infestation by O. crenatain one region of Sudan ‘is due to abandonment of faba beanplanting’.18 The same phenomenon has been reported from Italy.19

In Morocco,20 losses of 33% in yields of faba bean were recordedin 1999 across five zones of the country, but losses in productionwere even greater because of the reduced area of legumes plantedin infested areas. It had earlier been recorded that 30% of farmersquestioned had decided to give up growing faba bean, while 50%were giving up chickpea, lentil and pea.14 Similarly, in Tunisia,76% of farmers in one area had already abandoned faba beanproduction, and growing of lentil and caraway had also beenreduced.21

2.2 Orobanche foetidaThis species has been recorded for many years in western NorthAfrica and southern Europe, but has only relatively recentlybecome a significant problem weed in faba bean, chickpea and

vetch in Tunisia.22 In Morocco it has occurred widely on wild hosts,but there is disturbing evidence that it is now evolving forms ableto attack vetch.23 This observation should be of concern in theother countries around the western Mediterranean, where as yetit only occurs on wild hosts.

2.3 Orobanche cumanaAlthough sometimes included under O. cernua in earlier publica-tions, O. cumana is now agreed to be a distinct species.24 It isimportant in Russia, Ukraine, Moldavia, Romania, Turkey, Bulgaria,Spain, Israel and Hungary.25 Its importance also in the former Yu-goslavia is reflected in a recent report from Serbia.26 While there isa preponderance of the problem in eastern Europe, in the easternMediterranean and in Bulgaria, Romania, Turkey, Syria and Egypt,it also occurs along the North African coast and in Spain.5

The problem of O. cumana in sunflower has been the subjectof research for almost 100 years,4 and the breeding of resistantvarieties has resulted in some stabilisation or temporary alleviationof the problem at the local level. However, there has been asteady emergence of yet more virulent biotypes of the parasitethat overcome the resistance of the established crop varietiesand require yet more selection and breeding, often based onintrogression from wild Helianthus species.7 In Spain, it was firstobserved in 1958 and was still spreading and intensifying rapidlyup to 1993.27 By 1998 it was estimated to affect 40 000 ha.28

Sunflower growing was abandoned locally in Spain becauseof the problem.1 It was stemmed somewhat after that bythe development and introduction of more tolerant sunflowervarieties for oil production.29 Resistance in confectionary varietieshas not been so readily developed, and, whereas in Spainonly about half the oil sunflower area was affected, almost allconfectionary sunflowers were infested, 20 000 ha seriously.13

In Greece, 10 000 ha of sunflower were moderately or severelyinfested, with an estimated 60% yield loss; in China, 20 000 hawere infested, with 20–50% yield loss; in Turkey, over 50%of the crop area was moderately infested in spite of the useof tolerant varieties.13 In the 1950s, the sunflower area in theformer Yugoslavia was reduced by 37%, before the introductionof resistant varieties.1 Presumably, this pattern will have beenrepeated in many other countries in which O. cumana is aproblem, but it is not well documented, and the degree to whichlosses are now minimised, and by what means, is far from clear.Although resistant varieties are the main means of alleviating O.cumana in sunflower, herbicides are also contributing, especiallyin Israel where imazapic is now being widely used by farmersfor control of O. cumana in confectionary sunflower, contributingto a substantial reduction in the problem there.30 Other relatedherbicides are also being used in conjunction with commerciallyavailable imidazolinone-resistant lines of sunflower.31

2.4 Orobanche cernua‘Typical’ O. cernua is almost exclusively a parasite ofSolanaceae – tomato, tobacco, pepper and eggplant. Distributionextends from southern and eastern Europe and North Africa east-wards through southern Asia into China and Australia. Orobanchecernua (in the strict sense) has been especially troublesome as aproblem on tobacco and tomato in Pakistan, India, Nepal, Iran,the Arabian Peninsula and Egypt.4 The problem in South-EastIndia affects about 50% (40 000 ha) of the crop.13 Yield losses havebeen estimated as 25–50% in tobacco, depending on the timeand intensity of infestation and the availability of soil moisture.

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The quality of tobacco is also seriously reduced.32 The problemin tobacco in India apparently continues to increase because ofmonocropping of tobacco,33 while it is also a significant compo-nent of the Orobanche complex in tomato, tobacco and eggplantin Ethiopia, Jordan and Israel.

In sub-Saharan Africa there are sporadic occurrences in bothWest Africa (in Niger) and Tanzania, presumably as a result ofintroduction. Most recently, severe damage was reported ontomato in Kenya, and some farmers are abandoning their crops asa result of the infestation.34

2.5 Orobanche ramosaThe Solanaceae tomato, potato and tobacco are the crops mostseverely affected by O. ramosa, while a large number of other cropsare affected to a lesser extent.4,5 Rapeseed and hemp are nowincreasingly affected in France, where there has been a ‘dramaticspread’ of the problem.35 In 1986, 15 000 ha of tomato in Greecewere thought to be infested (30% of the total area), with yieldlosses averaging 25%.13 Orobanche ramosa had previously beenreported from a number of countries outside its native area aroundthe Mediterranean, as in Nepal and Cuba4 and in Chile.36 In Cuba,up to 20 000 ha of tobacco was infested in 1994, with yield lossesof 10–50%.13 Up to 80% crop loss has been measured in tomato inChile.36 There are no recent reports of its status in those countries,but there has been a relatively new infestation in Australia,37 whereit infests rapeseed and other hosts on some 6000 ha in WesternAustralia. It is now the subject of an eradication campaign, andnearly 200 000 ha are under quarantine. It is an economic problemin that it can endanger the export of produce out of the country.Another new infestation of O. ramosa has been reported from theUSA, where it has been found for the first time in Virginia.38 It isnot currently of any economic significance in the USA, but it isa reminder of the ability of this and other Orobanche species tobe accidentally introduced and become established across a widegeographic range.

Solarisation has been used with success in some countries,13

but there have been very few other successful control methods.The wide host range of O. ramosa means that control by rotationinto other crops is rarely a practical method, and, where highinfestations have built up in large-scale tomato farms in Sudanand Ethiopia, the crop has had to be abandoned, together withthe associated canning factories.13

2.6 Orobanche aegyptiacaOrobanche aegyptiaca has a similar host range to that of O.ramosa, but a somewhat more eastern geographical range, fromthe eastern Mediterranean through to Afghanistan, Pakistan, Indiaand Nepal. Orobanche aegyptiaca is the most widespread andtroublesome Orobanche species damaging tori (Brassicacampestrisvar toria Duthie) and tobacco crops in Nepal.39 The main rangein the ‘European’ context is from Greece through Turkey to theBlack Sea and down through Syria and Israel to Egypt.5 The maincrops affected include all the Solanaceae, rapeseed, chickpea andvetch. Cucurbitaceae are more frequently attacked by this speciesthan by O. ramosa,4 and in 1994 there were reports of extensiveand increasing infestation of musk melon and water melon in theXinjiang province of China, with 20–70% yield loss.13

No evidence for any change in the status of O. aegyptiaca hasbeen reported, except that Joel (Joel DM, private communication)reports ‘successful chemical control of O. aegyptiaca in processingtomato with sulfosulfuron and imazapic, leading to the ability

of farmers to grow tomato in highly infested fields throughoutthe country. The yield in treated infested fields is the same as innon-infested fields’.

2.7 Orobanche minorThis is indeed a more minor problem than those discussed above.Clovers and lucerne (alfalfa) are the main crops affected, althoughnot severely.5 It is broadly distributed throughout most of Europe(other than Scandinavia) and the Middle East, and also along thewestern coast of North Africa.5 It has been introduced furtherafield in the USA, South America, Japan, Australia, New Zealandand southern Africa. It is less clear whether occurrence in thehighland tropics of eastern Africa is natural or introduced, but it isespecially abundant in Ethiopia where it affects a number of cropsincluding noog/niger seed [Guizotia abyssinica (L. f.) Cass] and fababean, although rarely causing more than minor damage.40

It is mainly a problem in clovers and lucerne crops grown forseed, where it has the opportunity to shed seed and build up tohigh populations. Resultant contamination of the crop seed mayprevent it being sold. The harvesting or grazing of forage cropsprevents this. The importance of O. minor as a weed has declinedwith the reduced cultivation of Trifolium seed crops, as in theNetherlands41 and in the UK.4

New infestations continue to appear. In Oregon, USA, O. minorwas first identified in a single field in 1998. By 2001 it was knownfrom a further 15 sites.42 In pot experiments, up to 50% reductionin clover biomass was measured, while inflorescence mass couldbe reduced by 80%.43

3 STRIGA SPECIESThe main agriculturally important Striga species are S. hermonthica(Del) Benth. and S. asiatica (L.) Kuntze in cereal crops and S.gesnerioides (Willd.) Vatke in cowpea. Striga aspera Willd. Benth.,S. forbesii (Benth.) and S. densiflora (Benth.) Benth. are alsosporadically significant problems in cereals in limited locations.In 1991 it was estimated that in just six West African countriesover 5 million ha were infested, causing an overall 12% yieldloss of cereals.1 Locally, as in North Ghana, the estimated lossof sorghum and pearl millet averaged over 20%. ThroughoutAfrica the financial loss was estimated at over $US 300 million,while the potential loss, assuming infestation of all areas atrisk, could be 10 times that figure.1 There are few more recentestimates to compare with these, although a ‘rough estimate’ wasrecently given of 50 million ha now infested by Striga in Africa.2

There is a general consensus that in most areas the problem isincreasing owing to lack of capital, poor soil fertility, infestationof previously uninfested land by Striga seeds and continuouscropping of host crops.44 Between 1989 and 1992 the infestedarea of cereals in North Ghana increased from 12% to 27%, whilethe intensity of infestation increased by 15–45%.45 An FAO reportfrom 2006 (http://www.fao.org/ag/AGP/AGPP/IPM/Weeds/Issues/striga2006.htm) refers to the ‘aggravation’ of the problem in thesix West African countries of Benin, Togo, Burkina Faso, Niger,Senegal and Mali. Over 6 million ha of maize are now estimated tobe infested in East, West and southern Africa, representing 24% ofthe overall maize area.46 The level is higher in West Africa (31%)than in East Africa (21%), but the intensification of the problem isthought to be especially severe in East Africa.2 These observationsmostly relate to S. hermonthica, but S. asiatica is also a significantpart of the picture, especially in southern and East Africa.

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The author has not seen publications referring to the avoidanceof Striga problems by abandoning the growth of susceptiblecereals, but it is assumed that this must occur quite widely wherethere is the option of alternative crops. However, for subsistencefarmers it is rarely an acceptable option.

3.1 Striga hermonthicaThis is by far the most damaging of all the Striga species, affectingmost of the staple cereal crops grown in Africa, across tropicaland northern subtropical regions from Gambia in the west toKenya, Tanzania and Ethiopia in the east. Previously, the mostwidely affected crops were sorghum and pearl millet, but theproblem has apparently increased in maize, which is due in partat least to the increased area of this crop being grown. A usefultable of estimated areas of maize being infested by Striga spp.across 25 African countries has recently been published.46 WhereS. hermonthica is the assumed species, these estimates vary upto 20–30% in Ethiopia, Cameroon, Cote d’Ivoire and Guinea,30–40% in Togo, Mali and Nigeria and 65% in Benin. There areno comparable recent estimates for the infestation of sorghumor pearl millet, or more direct comparison with the total infestedareas estimated in 1991.1 The proportion of all cereals thought tobe infested at that time varied from 40 to 50% in Ghana, Cameroonand Nigeria to over 70% in Benin and Gambia.

In maize fields that are not infested by Striga, farmers wouldexpect an average maize yield of 1.5 t ha−1 in the Nyanza Provinceof Kenya. In fields moderately infested by Striga, the expectedyield is about half of this, and only about 20% in situationswhere there is high Striga infestation. The corresponding figuresfor Western Province are 1.8 t ha−1 and again half and 20%respectively.47 Following the introduction of herbicide-treatedseed of herbicide-resistant maize, farmers estimated their yieldsto have been approximately doubled in those areas.48

Most of the studies quoted above for increased intensity ofthe problem relate mainly to S. hermonthica, especially thosefrom West Africa, and there can be no doubt that the continuingintensification of agriculture, lack of rotation and limited use offertilisers are all contributing to falling soil fertility and an inevitablechange in the habitat in favour of Striga. A further indication ofintensification of S. hermonthica comes from Ethiopia.49

Recent reviews2,6 suggest continuing severity of the problemand make no reference to declining importance as a resultof successful control measures, while estimates of about 70%infestation of all cereal fields in northern regions of Ghana byStriga do not suggest any general improvement.50 One possibleexception to this generalisation comes from a comparison of theproportion of maize crops infested by S. hermonthica in NorthGhana, estimated at 40% in 19911 but only at 14% 15 yearslater.4 This could perhaps be a reflection of the intensive researchand extension efforts applied in this area over the past 15 years,leading to improved agronomic practices, but it is not being clearlyclaimed. There are also a number of developments that suggestthat the problem is being reduced, at least locally. From EastAfrica there are promising reports of S. hermonthica control bythe introduction of the Desmodium intercrop technique,51,52 nowbeing used by at least 7000 farmers in Kenya, Uganda and Tanzania,and the use of herbicide-treated maize seed53 or a combination ofboth approaches.54 Farmers are apparently adopting both of theseprocedures, and there is likely to be a positive outcome on farmsthat can afford these more sophisticated approaches. Farmersadopting the push-pull technique are achieving approximatelydouble the yields of maize by comparison with the farmer controls.

Most of this benefit is apparently from Striga control.55 Thetechnique has been shown to work in sorghum as well as inmaize.50 Greatest benefit is in situations where the forage can beutilised by livestock and where the dry season(s) are not severeenough to kill the Desmodium. In West Africa, IITA have developeda number of tolerant maize hybrids, but their impact has not beenclearly described, while, for sorghum, resistant varieties have beenwidely released in Ethiopia,56 where it is estimated that some100 000 farmers are growing Striga-resistant sorghum varieties aspart of a package of measures for Striga control. Again, there areno available appraisals of their impact to date. While the evidencefor any general alleviation of the problems from S. hermonthica isvery thin indeed, there are these glimmers of hope that progressis being made, at least locally.

3.2 Striga asiaticaStriga asiatica as a weed problem (usually with red flowers)occurs only sporadically across West Africa, but becomes thepredominant species towards the East African coast southwardsthrough Tanzania, Malawi, Mozambique and southern Africa.Northern Tanzania is a transition zone where both S. hermonthicaand S. asiatica occur.50 The red-flowered form of S. asiatica was alsoaccidentally introduced into eastern USA some time before 1950and was the subject of an expensive but eventually successfuleradication campaign. A white-flowered form occurs widely inIndia but does not seem to cause such acute problems as itsAfrican relative. Rice is attacked in Africa, in addition to maize,sorghum and millets.There are a number of reports suggesting intensification of theproblems from this species. In Tanzania, the increase is attributed toa continuing decline in soil fertility throughout Striga-prone areas,inevitably contributing to an enhancement of the problem.57

Likewise, in Swaziland there are increasing infestation and croplosses.58 In Malawi, a country-wide survey found 63% of maizefields infested.45 This figure has since increased to 80%.46 Thisdoes not suggest a declining problem. There are also estimates of10% maize crops infested in Namibia, and 25% in Angola.46

One country in which some impact is being seen from researchefforts is Tanzania, where there has been promising uptake of greenmanuring for improvement of soil fertility and control of S. asiaticain rice.57 Another area in which the problem is apparently beingbrought under control is Kwazulu in South Africa, where there hasbeen a government eradication campaign based on herbicides.50

It is not clear to what extent other research approaches, includingthe use of Desmodium species or herbicide-coated seeds, are beingapplied successfully to the S. asiatica problem.

3.3 Striga gesnerioidesStriga gesnerioides occurs very widely in Africa in a number ofdistinct biotypes. Many of these are specific to wild plants only,but in West Africa a number of biotypes attack cowpea, causingsevere crop loss. Other biotypes attack tobacco and sweet potato,but only on a very local basis. In north-eastern Nigeria, an estimated81% of cowpea fields are infested.59 Other countries with a seriousproblem include Mali, Burkina Faso, Niger, Benin and Cameroon. Itwas observed to be spreading quite rapidly in the 1980s, apparentlyassociated with an increase in the crop area. Any recent estimationsof crop loss are curiously lacking, but there were average lossesof 30%, with up to 56% loss in one local variety in a 1989 study.60

Total crop loss can also occur.4

Fortunately, immunity or high levels of resistance have beenfound in a range of varieties, and plant breeders have released


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varieties with combined resistance to the various biotypes of S.gesnerioides, together with resistance to other pests or diseases andto the further parasitic weed problem – Alectra vogelii Benth.61,62

Research in this direction is being helped by the development ofmarker-assisted selection.63 Unfortunately, there is as yet a lack ofpublished evidence for any substantial uptake of these varietiesand corresponding reduction in the problem.

4 CONCLUSIONSGood evidence for inclusion in this review has been scant. Hence,conclusions are largely tentative. Very few of the estimates ofextent or occurrence, or of yield losses caused, are based on anydetailed survey and measurement. For more reliable data, newtechniques may be needed. One approach to the assessment ofdistribution is that of sampling soil for the presence of parasiteseeds.64 This could help to define the areas of infestation, butcorrelations with emergent parasite population and damagecaused are unlikely to be good enough to allow deduction ofeconomic impact. Scanning of aerial or satellite images could alsobe of value. Two of the recent studies on Striga quoted above46,47

represent some of the more thorough attempts at quantificationof the problem and deserve to be replicated in other areas andfor other species, although even here most of the quantificationcomes from farmer opinion rather than direct measurement. Whilemore precise estimates of economic damage would be of valuein convincing donors to support research, it is also questionablewhether the cost of such studies would be justified on any but alocal basis.

While the quantitative evidence is at no stage fully reliable, thereis little indication of significant alleviation of either Orobanche orStriga problems, other than on a localised and/or specific basis. Itcan be confidently stated that both groups of parasite continueto cause immense losses. Many million hectares, and many millionfarmers, are affected, and the annual economic losses are measuredin millions if not billions of $US. These statistics raise enormouschallenges. One of these challenges is to ensure that availableresearch results are implemented for the benefit of the farmer,to reduce the losses in the infested areas. A second challengeis to minimise the risk of new infestations. Two publications65,66

analyse the climatic requirements of Orobanche and Striga speciesand suggest that very large areas of new territory are at risk ofinvasion if care is not taken to limit the introduction of seeds andto educate farmers and others to be alert for new infestations.

The author sincerely hopes that these somewhat pessimisticconclusions will be challenged, and that new, more encouragingdata will be brought to our attention.

REFERENCES1 Sauerborn J, The economic importance of the phytoparasites

Orobanche and Striga, in Proceedings of the Fifth Symposium onParasitic Weeds, Nairobi, Kenya; 24–30 June 1991, ed. by Ransom JK,Musselman LJ, Worsham AD and Parker C. CIMMYT, Nairobi, Kenya,pp. 137–143 (1991).

2 Ejeta G, The Striga scourge in Africa: a growing problem, in IntegratingNew Technologies for Striga Control: Toward Ending the Witch-hunt, ed. by Ejeta G and Gressel J. World Scientific Publishing Co.,Hackensack, NJ, pp. 3–16 (2007).

3 Parker C, Scope of the agronomic problems caused by Orobanchespecies, in Biology and Control of Orobanche, Proceedings ofWorkshop in Wageningen, The Netherlands, 13–17 January 1986.LH/VPO, Wageningen, The Netherlands pp. 11–17 (1986).

4 Parker C and Riches CR, Parasitic Weeds of the World: Biology andControl. CAB International, Wallingford, UK, 332 pp. (1993).

5 Schneeweiss GM, List of Actual and Potential Broomrape Pest Species.[Online]. Available: http://www.botanik.univie.ac.at/plantchorology/PestSpeciesOrobanche.pdf [10 January 2009].

6 Elzein A and Kroschel J, Progress on management of parasitic weeds,in Weed Management for Developing Countries, Addendum 1, ed. byLabrada L. FAO Plant Production and Protection Paper 120, Add. 1.FAO, Rome, Italy, 30 pp. (2003).

7 Joel DM, Hershenhorn Y, Eizenberg H, Aly R, Ejeta G, Rich PJ, et al,Biology and management of weedy root parasites. Hortic Rev33:267–349 (2007).

8 Eisenburg H and Joel DM, Orobanche species in Israeli agriculture.COST Action 849, Parasitic Plant Management in SustainableAgriculture Workshop ‘State of the Art in OrobancheControl’, 18–20 October (2001). Bari, Italy. [Online]. Available:http://cost849.ba.cnr.it/BARI%20ABSTRACTS.pdf [10 January 2009].

9 Rubiales D, Perez-de-Luque A, Cubero JI and Sillero JC, Crenatebroomrape (Orobanche crenata) infection in field pea cultivars.Crop Prot 22:865–872 (2003).

10 Abu-Irmaileh BE and Labrada R, The Problem of Orobanchespp. in Africa and Near East. [Online]. Available:www.fao.org/ag/AGP/AGPP/IPM/Weeds/Issues/orobanche.htm)[10 January 2009].

11 Emeran AA, El-Rodeny WM and Fernandez-Aparicio M, Orobanche cre-nata control in Egypt workshop. Parasitic Plant Management inSustainable Agriculture, Final Meeting of COST Action 849, 23–24November (2006). ITQB Oeiras-Lisbon, Portugal. [Online]. Avail-able: http://cost849.ba.cnr.it/Abstracts%20Lisboa%2002%20Nov%202006.pdf [10 January 2009].

12 Haddad A and Pala M, Significance of parasitic weeds for food legumesin Syria, in Proceedings of the 9th World Congress on Parasitic Plants,Charlottesville, VA, 3–7 June 2007. Virginia Tech, Blacksburg, VA,CDRom (2007).

13 Parker C, The present state of the Orobanche problem, in Biology andManagement of Orobanche, Proceedings of the Third InternationalWorkshop on Orobanche and Related Striga Research, ed. byPieterse AH, Verkleij JAC and ter Borg SJ. Royal Tropical Institute,Amsterdam, The Netherlands, pp. 17–26 (1994).

14 Lutzeyer HJ, Kroschel J and Sauerborn J, Orobanche crenata in legumecropping: farmers’ perception, difficulties and prospects of control,in Biology and Management of Orobanche, Proceedings of the ThirdInternational Workshop on Orobanche and Related Striga Research,ed. by Pieterse AH, Verkleij JAC and ter Borg SJ. Royal TropicalInstitute, Amsterdam, The Netherlands, pp. 432–441 (1994).

15 Rubiales D and Fernandez-Aparicio M, First report of crenatebroomrape (Orobanche crenata) on lentil (Lens culinaris) andcommon vetch (Vicia sativa) in Salamanca Province, Spain. PlantDisease 92:1368 (2008).

16 Reda F, Orobanche crenata in Ethiopia. Haustorium 49:3 (2006).17 Babiker AGT, Ahmed EA, Dawoud DA and Abdrella NK, Orobanche

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observations on the current status of orobanche and striga problems worldwide

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