Disease Control in Cassava Farms Disease ... - Cassavabiz.org

About this bookletDisease ControlinCassava FarmsThis booklet is one in a set of field guides prepared by the International Instituteof Tropical Agriculture (IITA) to increase the technical knowledge of extensionagents and enhance the integration of plant protection and plant productionpractices in farmers’ efforts to grow a healthy crop of cassava. The bookletis based largely on the extension and farmer training experience of the regionalproject “Ecologically Sustainable Cassava Plant Protection” (ESCaPP), 1993–1997. ESCaPP was executed by IITA’s Plant Health Management Division(PHMD), in collaboration with national agricultural research and extension systemsin Bénin, Cameroon, Ghana, and Nigeria, and funded by the Division ofGlobal and Interregional Programmes of the United Nations DevelopmentProgramme (UNDP).IITA is one of 16 nonprofit international agricultural research and training centerssupported by the Consultative Group on International Agricultural Research(CGIAR). Their shared mission is the alleviation of hunger and poverty intropical developing countries by generating appropriate plant production andprotection technologies which benefit the poor and enhance agricultural productionwhile preserving the natural resource base. At IITA, PHMD is dedicatedto sustainable plant protection of primary food crops in Africa. The division’sresearch philosophy is to identify and correct the ecological imbalances in agriculturalsystems causing pest problems and to provide environmentally andeconomically appropriate options for integrated pest management. (IPM)For more information contact:The DirectorIITA Plant Health Management DivisionBiological Control Center for Africa08 B.P. 0932Cotonou, Republic of BéninFax: (229) 35 05 56Tel: (229) 35 01 88E-mail: IITA-benin@cgiar.orgOr visit IITA’s website at: http://www.cgiar.org/iitaWeston Msikita, Braima James, Emmanuel Nnodu,James Legg, Kerstin Wydra, Francis OgbeInternational Institute of Tropical Agriculture

Disease Controlin Cassava FarmsIPM Field Guide for Extension AgentsWeston MsikitaInternational Institute of Tropical Agriculture, Plant Health Management Division,Cotonou, BéninBraima JamesInternational Institute of Tropical Agriculture, Plant Health Management Division,Cotonou, BéninEmmanuel NnoduNational Root Crops Research Institute, Umudike, Umuahia, Abia State, NigeriaJames LeggInternational Institute of Tropical Agriculture, ESARC, Kampala, UgandaKerstin WydraInternational Institute of Tropical Agriculture, Plant Health Management Division,Cotonou, BéninFrancis OgbeNational Root Crops Research Institute, Umudike, Umuahia, Abia State, Nigeria

ContentsWhat are the objectives of this guide? ------------------------------------------- 4Introduction -------------------------------------------------------------------------- 4What are the common cassava diseases? --------------------------------------- 6Why are cassava diseases important? ------------------------------------------ 18When are cassava diseases likely to cause severe losses? ------------------ 20How can I best control diseases in cassava farms? -------------------------- 22Summary ---------------------------------------------------------------------------- 25

Disease Control in Cassava FarmsIPM Field GuideWhat are the objectives ofthis guide?This field guide has been prepared to help youto:• recognize common cassava diseases andspecify their causes,• specify how the diseases damage cassavaplants,• identify the sources of cassava diseases,and understand how cassava diseases spread,and• combine appropriate practices to controlcassava diseases and grow a healthy cropof cassava.IntroductionMany diseases are caused by very tiny livingthings called pathogens. Pathogens are so tinythat you cannot see them even with the aidof hand lenses. Examples of pathogens are viruses,bacteria, and fungi. When a pathogenattacks a cassava plant, it multiplies andspreads inside or on the plant. As it spreads,it destroys the plant. The plant will show signs(symptoms) of attack. Damage symptoms ofcassava diseases appear on the leaves (Figure1), stems (Figure 2), and storage roots(Figure 3) of the plant. Cassava diseases arerecognized by their symptoms, such as discolorationof leaves, “sores” on the stems,and discoloration of storage roots.Some other diseases which you may notice incassava are caused by nonliving things. Examplesof such diseases are wilting due todrought and poor plant growth because ofpoor soils.Figure 1: Cassava plant damaged bycassava mosaic diseaseFigure 2: Cankers of cassavaanthracnose disease on stemFigure 3: Cassava storage roots damaged by cassavabrown streak disease45

Disease Control in Cassava FarmsIPM Field GuideWhat are the commoncassava diseases?The common diseases of cassava are cassavamosaic disease, cassava bacterial blight, cassavaanthracnose disease, cassava bud necrosis,and root rots. Some of these diseases attackthe leaves and stems of cassava plantswhile others attack the storage roots.Leaf and stem diseasesCommon leaf and stem diseases of cassavaare cassava mosaic disease, cassava bacterialblight, cassava anthracnose disease, cassavabud necrosis, and brown streak disease.Cassava mosaic diseaseCassava mosaic disease is caused by a viruswhich occurs inside cassava leaves and stems.cassava leaves. The virus multiplies and occursin large numbers in the leaves and stems. Cassavamosaic disease is also spread by plantingstem cuttings from plants infected with thedisease.Other crops attacked: Cassava mosaic diseaseattacks only cassava.Figure 4:Cassava leaveswith chlorotic(pale) patchesof cassavamosaicdiseaseDamage symptoms: The leaves of cassavaplants with the disease are discolored withpatches of normal green color mixed withlight green, yellow, and white areas (Figure 4).This discoloration is known as chlorosis. Thechlorotic patches can be confused with cassavagreen mite feeding damage (Figure 5).When cassava mosaic attack is severe, theleaves are very small and distorted and theplants are stunted. The disease symptomsare more pronounced on younger plants (Figure1), usually under 6 months, than on olderplants.Method of spread: The main sources of thevirus which causes cassava mosaic disease arecassava plants with the disease and the whiteflyBemisia tabaci (Figure 6). The virus occursin the saliva of the whitefly. During feeding, theinsect injects saliva containing the virus intoFigure 5:Cassava leaf withchlorotic (pale)spots caused bycassava greenmiteFigure 6:Adults ofBemisiawhitefly (asseen enlargedunder themicroscope)67

Disease Control in Cassava FarmsIPM Field GuideCassava bacterial blightCassava bacterial blight is caused by a bacteriumwhich occurs inside cassava leaves andstems.Damage symptoms: Initially, damage by cassavabacterial blight appears as water-soakeddead spots (lesions). The lesions occur betweenleaf veins and are most evident on thelower surfaces of the leaves (Figure 7). The lesionsare small, not completely round in shape,and have a few angles at their edges. Theseangular lesions later join together into largerpatches killing the leaf blade as they enlarge.The leaf blade turns brown with the watersoakedarea at the leading edge of the brownpatch. This damage symptom is known as leafblighting (Figure 8). Severely blighted leaveswilt (Figure 9), die, and fall causing defoliationand shoot tip die-back (Figure 10) or completedeath of the shoot. Leaf blighting startsfrom the leaf blade and moves towards thepetiole. The petiole retains a horizontal positionbefore leaf fall (Figure 9). This is unlikecassava anthracnose-damaged leaves whosepetioles droop before leaf fall (Figure 12).Drops of brownish gum may occur on theleaves, petioles, and stems of plants infectedwith cassava bacteria blight.leaves. It multiplies and occurs in large numbersin the leaves and stems. Cassava bacterialblight is therefore spread by planting stemcuttings from plants with the disease symptoms.Dead cassava stems and leaves with thebacterium also serve as sources of the diseaseif they are not destroyed after root harvest.The disease is spread naturally by raindropswhich splash the bacterium from infectedplants to healthy plants. Insects, for example,grasshoppers become contaminated with thebacterium and spread it to healthy cassavaplants. Farm tools that are used to cut infectedcassava plants should be cleaned afteruse to prevent the bacterium on them fromspreading to other plants.Other crops attacked: Cassava bacterialblight attacks only cassava.Figure 7: Cassava leaf with angularleaf spots of cassava bacterial blightFigure 8: Cassava leaf blighting causedby cassava bacterial blightThe damage symptoms of cassava bacteriablight are more evident in the wet than in thedry season. The disease is more severe inyoung plants than in older ones.Method of spread: The main sources of thebacterium which causes cassava bacterialblight are cassava plants with the disease. Thebacterium enters cassava plants throughwounds and scratches on the stems andFigure 9: Leaf blighting and wiltingcaused by cassava bacterial blightFigure 10: Cassava shoot tip die-backcaused by cassava bacterial blight89

Disease Control in Cassava FarmsIPM Field GuideCassava anthracnose diseaseCassava bud necrosisCassava anthracnose disease is caused by afungus which occurs on the surface of cassavastems and leaves.Cassava bud necrosis is caused by a funguswhich occurs on the surface of cassava stemsand leaves.Damage symptoms: Cassava anthracnosedisease appears as cankers (“sores”) on thestems and bases of leaf petioles (Figure 11).Cankers weaken the petioles so that the leafdroops downwards (Figure 12) and wilts. Thewilted leaves die and fall causing defoliationand shoot tip die-back or complete death ofthe shoot. Soft parts of cassava stems becometwisted under severe attack by the disease.The disease usually starts at the beginning ofthe rains and worsens as the wet seasonprogresses.Method of spread: The main sources of thefungus that causes cassava anthracnose diseaseare cassava plants with the disease. Thefungus spreads by wind carrying spores fromcankers on the stems, or by planting stem cuttingswith cankers. The fungus enterscassava plants through wounds and feedingpunctures made by the bug Pseudotheraptusdevastans (Figure 13). Dead cassava stems andleaves with the fungus also serve as sources ofthe disease if they are not destroyed afterroot harvest.Other crops attacked: The fungus thatcauses cassava anthracnose disease affectsother crops as well as cassava, for example,coffee, pepper, and pawpaw.Damage symptoms: The disease appears aspatches of brown or grey fungal matter coveringthe stem. The fungal matter sometimescovers buds (“eyes”) on cassava stem cuttings(Figure 14). The affected buds die, which reducesthe sprouting ability of stem cuttings.Method of spread: The main sources of thefungus that causes bud necrosis are cassavaplants with the disease. Dead cassava stemsand leaves with the fungus also serve assources of the disease if they are not destroyedafter root harvest. The fungus spreadsby wind, however, planting of infected stemcuttings is the main method by which the diseasespreads.Other crops attacked: The fungus thatcauses bud necrosis causes leaf spots on avariety of plants including grasses, cerealcrops, banana, and mango.Figure 11: Cankers of cassavaanthracnose disease at the bases ofcassava leaf petiolesFigure 12: Cassava shoot with wiltedleaves caused by cassava anthracnosediseasepFigure 13: The bug Pseudotheraptusdevastans on cassava leafFigure 14: Cassava stem with fungalpatch (arrow) of bud necrosis disease1011

Disease Control in Cassava FarmsIPM Field GuideLeaf spot diseasesCassava leaf spot diseases are caused by fungi.There are three different types, namely whiteleaf spot, brown leaf spot, and leaf blight.Damage symptoms: Cassava white leafspot disease appears as circular white orbrownish-yellow spots on the upper leaf surfaces(Figure 15). The spots sometimes havepurplish borders around them.then serve as sources for spread of the diseases.Other crops attacked. Not much is knownabout the host crop range of cassava leaf spotdiseases.Cassava brown leaf spot disease appears assmall brown spots with dark borders on theupper leaf surfaces (Figure 16). The brownspots occur between leaf veins, and their sizesand shapes are limited by the distance betweenthese veins. The dead tissue in the centerof brown spots may fall to give the leafsurface a “shot hole” appearance. Under severeattack the infected leaves become yellow,dry, and die prematurely.Cassava leaf blight disease appears as lightbrown lesions on the upper surfaces of theleaves. The lesions are not limited by veins,therefore they are usually larger than brownleaf spots. The lesions may enlarge to covermost of the leaf surface and cause leaf blighting(Figure 17). The blighted leaves lack watersoakedareas, which are typical of leaf damageby cassava bacterial blight (Figure 8). Leafblight lesions also lack the dark borders ofbrown leaf spots and they do not develop into“shot holes” on the leaf surface.Method of spread: The main sources of thefungi that cause leaf spot diseases are infectedcassava leaves on the plant or those fallen onthe ground. The fungi spread to new plantsfrom these sources by wind or rain splashes.Leaf spot fungi can occur on weeds whichFigure 15: Cassava leaf with white leaf spotdiseaseFigure 16: Cassava leaf with brown leaf spotdiseaseFigure 17: Cassava leaf with leaf blight disease1213

Disease Control in Cassava FarmsIPM Field GuideStem and root diseasesCassava brown streak diseaseCassava brown streak disease is caused by avirus. Presently the disease is reported onlyfrom cassava-growing regions in East andSouthern Africa.Damage symptoms: Damage symptoms ofcassava brown streak disease appear on theleaves, stems, and storage roots of cassavaplants. On the leaves, the disease appears aspatches of yellow areas mixed with normalgreen color (Figure 18). The yellow patchesare more prominent on mature leaves thanon young leaves. The damaged leaves do notbecome distorted in shape as occurs withleaves damaged by cassava mosaic disease(Figure 1). On the stems, the disease appearsas dark brown “streaks” (Figure 19) withdead spots on leaf scars. These streaks aremost prominent on upper, green portions ofthe stems. The diseased plants may showshoot tip die-back. Cassava brown streak diseasedistorts the shape of the storage rootsand may cause cracks and discoloration inthe storage roots (Figure 20).Figure 18: Cassava leaves with chlorotic (pale)patches of cassava brown streak diseaseMethod of spread: The main sources of thevirus that causes cassava brown streak arecassava plants with the disease. The disease isspread through the planting of stem cuttingsfrom diseased plants. The virus is also believedto be spread from plant to plant by insects.Other crops attacked: Cassava brownstreak disease is not known to attack othercrops.Figure 19: Cassava stem with“streaks” of cassava brown streakdiseaseFigure 20: Cassava storage rootsdiscolored by cassava brown streakdisease1415

Disease Control in Cassava FarmsIPM Field GuideCassava root rot diseasesCassava root rot diseases are caused by variouskinds of fungi living on or in the soil. Thefungi occur mainly in soils that do not drainproperly and in forest fallow land that hasbeen recently cleared.Damage symptoms: The leaves on cassavaplants affected by root rot disease turnbrown, wilt, and the plant appears scorched.The leaves may or may not remain attached tothe plant, but the plant loses a lot of water anddies. If you suspect a cassava plant as havingroot rot disease, you should confirm this byuprooting it and examining the roots for thedamage symptoms. Root rot diseases kill bothfeeder and storage roots of cassava. The storageroots may swell unusually and developlight brown coloration which you can see ifthe roots crack in the soil or if you cut themopen (Figure 21). The roots may give out a badsmell as they rot.Method of spread: The important sourcesof cassava root rot fungi are soils, and cassavaroot and stem debris contaminated withthe fungi. The fungi enter cassava plantsthrough wounds caused by pests or farmingtools or by piercing the roots by themselves.Farm tillage tools used in cassava farms withthe disease should be cleaned after use toprevent the fungi on them from spreading toother areas. Similarly, cassava plant debris infarms with the disease serve as sources ofroot rot fungi and should be destroyed byburning.Figure 21: Cassava storage root destroyed byroot rot diseaseOther crops attacked: Cassava root rotfungi attack a wide range of other crops includingmaize, soybean, sunflower, and coffee.1617

Disease Control in Cassava FarmsIPM Field GuideWhy are cassava diseasesimportant?Cassava pests are important because they reducethe yield from the crop. They cause foodand income losses from cassava in the followingways.Loss of roots: Root rot and cassava brownstreak diseases attack storage roots andcause immediate and direct losses. By damagingleaves and stems, cassava diseases generallyinterfere with the way by which the plantmakes food for storage in the roots. This willreduce the growth of the plants, the numberof storage roots they can form, and the abilityof the storage roots to swell with food andmature for harvest (Figures 22 and 23). However,most cassava varieties can lose a lot ofleaves before the root yield is reduced. Farmersshould be discouraged from rushing totackle control measures at the first signs ofdamage.Loss of planting material: Many cassavadiseases contaminate cassava stems with viruses,bacteria, and fungi. This makes stem cuttingsunhealthy and unsuitable for planting.Certain cassava diseases, for example, cassavabacterial blight, cassava anthracnose, and cassavabrown streak diseases, reduce the quantityand quality of planting material by causingshoot tip die-back. Cankers of cassava anthracnosedisease (Figure 11) cause cassava stemsto break easily. Fungal matter of cassava budnecrosis (Figure 14) kills the buds (“eyes”) onstems and reduces the ability of stem cuttingsto sprout.Loss of leaves: In areas where cassava leavesare used as food, leaf diseases “rob” farmersand other consumers directly of the leafy vegetables(Figure 24). For example, cassava bacterialblight and cassava anthracnose diseasedefoliate cassava plants; cassava mosaic diseaseand cassava brown streak discolor theleaves, and cassava mosaic disease distorts theleaf shape and size. These kinds of damage willalso reduce the ability of cassava plants tomake sufficient food for storage in the roots.Increase in weeds and erosion: Diseasesthat defoliate and kill cassava shoot tips encourageweed growth in farms because thecassava plants are no longer able to block sunlightfrom reaching the weeds growing underneath.In loose soils, defoliation of cassavaplants will expose the soil to erosion.Damage to other crops: In addition to cassava,the diseases can damage other crops.Examples of cassava diseases that attackother crops are cassava anthracnose, cassavabud necrosis, and cassava root rot diseases.Figure 23:Good cassavastorage rootyieldFigure 22:Poor cassavastorage rootyieldFigure 24:Good cassavaleaf harvest1819

Disease Control in Cassava FarmsIPM Field GuideWhen are cassava diseaseslikely to cause severe losses?The presence of diseases in cassava farmsdoes not always mean that they will cause severelosses in food and income. The appearanceof disease damage can be misleading. Forexample, leaf spot diseases are unlikely tocause severe losses in root yield because theyusually attack plants close to maturity. It istherefore very important to know the conditionsunder which diseases can be seriousproblems. The following pointers will help youto know when the diseases are likely to causesevere losses in cassava farms.The cassava varieties you grow: Lossescaused by diseases are less severe on somecassava varieties than on others. Table 1 listssome varieties with different levels of toleranceagainst cassava mosaic disease and cassavabacterial blight.The stage of plant growth at attack:Generally, yield loss is greater if stem cuttingssprout with the diseases than in disease-freesprouts. Disease-free sprouts can, however, beinfected with pathogens later on. If this happens,young cassava plants suffer more fromdisease attack than older plants. At 3–4months after planting, the storage roots ofmost cassava varieties start to swell withfood. At about 7 months after planting, theplants have formed the number of storageroots they will carry during their growing period.This number will not increase much afterthis time, but the storage roots will continueto swell with food until they are harvested.Therefore, if diseases attack cassava farmsaged 7 months or less, the plants will providefewer and smaller storage roots than if attackedlater. For example, under cassava mosaicdisease attack, yield losses will be higher ifdisease-free plants became diseased within 4months after planting than if they became diseasedlater on. Also, leaf spot diseases occurmainly on mature and older cassava leaves,and normally on older cassava plants, usuallymore than 5–9 months old. Leaf spot diseasesare therefore unlikely to cause severe lossesin root yield.The plant parts attacked: Diseases whichdamage the plant parts that you harvest “rob”you directly of food and income. For example,when cassava storage roots are damaged, theplants do not replace them with more rootsnor do the roots become bigger to compensatefor the damage. Diseases which causethis kind of damage are mainly cassava rootrots and cassava brown streak disease. However,when diseases attack cassava leaves theplants may produce new leaves and later producea good root yield.The season of attack: The effect of seasonon the extent of damage caused by cassava diseasesvaries according to the disease. The damagesymptoms of cassava brown streak diseaseare more serious in the dry than in the wetseason. Root rot damage can be severe eitherin the wet or in the dry season, depending onthe type of fungi that causes the disease. Damagesymptoms of cassava bacterial blight andcassava anthracnose disease occur more in thewet than in the dry season. In the dry seasonyou can notice plants with shoot tip die-backand defoliation caused by any or both of thesediseases. However, these symptoms are carriedover from the wet season attack.Table 1: Some features of common cassava varieties in West and Central AfricaExpression of selected featuresVarietyTolerance toCBBTolerance toCMDTolerance toCGMWeedsuppressionGroundstorabilityCyanogenicpotential% dry matterYieldpotentialIITATMS 4(2)1425 High High Low Good Good Moderate Moderate GoodTMS 30572 High High Moderate Moderate Good Moderate Good GoodBeninBEN 86052 High High Low Poor Moderate Good Good PoorRB 89509 Moderate Moderate Low Good Poor Poor Good ModerateCameroon8017 High High Moderate Poor Good Moderate Moderate Moderate8034 High High Moderate Poor Good Moderate Moderate ModerateGhana"Afisiafi" High High Moderate Moderate Good Moderate Good Good"Abasa fitaa" High High Low Good Good Moderate Moderate GoodNigeriaMS 6 High High Low Poor Poor Good Good ModerateNR 8082 High High High Moderate Good Good Good GoodCGM = Cassava green miteCMD = Cassava mosaic diseaseCBB = Cassava bacterial blightSource: IITA INRAB-Benin, MoFA-CSD Ghana, IRAD-Cameroon, and NRCRI-Nigeria2021

Disease Control in Cassava FarmsIPM Field GuideHow can I best controldiseases in cassava farms?The best way to control diseases is to grow ahealthy crop of cassava. This is especially sobecause you do not see the viruses, bacteriaand fungi which cause diseases. In order togrow a healthy crop you will need to combineplant production and plant protection practicesin growing the crop.IPM practices at plantingMany integrated pest management (IPM) practicesfor cassava diseases are applicable atplanting. These include site selection, soil improvementpractices, and selection of appropriatevarieties and planting materials. Thesepractices are covered in the companion fieldguide “Starting a Cassava Farm”. Table 1 listssome cassava varieties that can withstand diseaseattack better than others. A similar tablecan be prepared by scientists and extensionagents for other cassava varieties in particularlocalities. In selecting a variety to grow againstdiseases you should find out if the selected varietyalso has other features you may want.Almost all cassava diseases are spread byplanting infected stem cuttings. The viruses,bacteria and fungi which cause the variousdiseases survive on or inside cassava stemsand are easily carried to new fields in this way.The companion field guide on “Starting a CassavaFarm” presents the general guidelines onhow to select healthy stem cuttings. Theguidelines will assist you to avoid unhealthystem cuttings (Figure 25) as planting materialand grow a healthy cassava crop. In selectingplanting material, you should avoid cassavaplants which show leaf discoloration or chlorosis(Figures 4 and 18), leaf blighting and wilting(Figures 9 and 12), gum exudate, cankers,fungus patches and streaks on the stems (Figures11, 14, and 19) and defoliation, shoot orshoot tip die-back (Figure 10). Stem cuttingsfrom such plants can sprout into diseasedseedlings or not sprout at all.In the control of cassava mosaic disease, youcan select good planting material and reducethe level of disease in the farm by following anumber of other steps. Firstly, in cassava varietiesthat branch, choose the branches assources of planting material. Most of the stemcuttings from these branches will sprout withoutthe disease. On the other hand, most ofthe stem cuttings from the main stem willsprout with the disease (Figure 26). In cassavavarieties that do not branch, avoid the basalstem portions as planting material for a similarreason. Secondly, after planting, closely observethe stem cuttings as they sprout. Normally,stem cuttings sprout 3–4 weeks afterplanting. Tag all the plants which sprout withoutthe disease. At harvest time select theseplants as your planting material to controlcassava mosaic disease. Even if the plantssprouting without cassava mosaic disease areattacked by the disease later on, they willgrow into healthier plants than those whichgrow from stem cuttings sprouting with thedisease.If it is difficult to get sufficient quantities ofhealthy stems for planting, you should treatthe stem cuttings against certain diseases. Forexample, you can dip cassava stem cuttingswith cankers in dilute solutions of Benlate (afungicide) to clean them of the fungus thatcauses cassava anthracnose. If fungicides areFigure 25: Unhealthy cassava stem cuttingsFigure 26: Cassava stem cutting sprouted withcassava mosaic disease2223

Disease Control in Cassava FarmsIPM Field Guideto be used, you should consult the label forguidelines on their application methods andhow to avoid personal and environmental hazardsassociated with their use.When cutting up cassava stems into stem cuttingsfor planting, you should select the middlebrown-skinned portions of cassava stems.These parts sprout and ensure more vigorousplants than the top green stem portions. Thetop green stems dehydrate quickly and areeasily damaged by disease.It is advisable to plant cassava early, at the beginningof the rains. Early planting allows thecrop to grow more vigorously and betterwithstand disease damage later in the dry seasonthan late planting.IPM practices after plantingGood farm sanitation helps to reduce thesources of the pathogens that cause cassavadiseases in farms. For example, after root harvestyou should destroy cassava stems withshoot tip die-back, cankers, fungus patches,streaks or any other disease damage symptom.Crop debris of storage roots, leaves, andstems with these symptoms harbor thepathogens and should be destroyed to reducethe sources of disease spread. Farm toolsshould be cleaned before and after tillage toreduce the spread of root rot fungi throughtools contaminated with the pathogen.If only a few stem cuttings sprout with diseaseit is advisable to remove them and replacethem with healthy stem cuttings. This is calledroguing. Roguing of cassava plants is best doneat 3–4 weeks after planting when controllingcassava mosaic disease.SummaryTo control diseases and grow a healthy crop of cassava:• Identify the common cassava diseases, their damage symptoms, and know the conditionsunder which they will cause severe losses.• Select sites with dense vegetation, deep loamy soils, and flat or gently sloping land togrow cassava.• Improve the soils by manuring, mulching, and intercropping to encourage cassavaplants to grow vigorously and offset damage by cassava diseases.• Grow cassava varieties that tolerate the common cassava diseases in your area.• Plant stem cuttings from healthy plants without leaf chlorosis, shoot tip die-back, cankers,fungus patches, or streaks on the stems.• After root harvest destroy discarded cassava stems and storage roots showing anysymptom of disease.• In the control of cassava mosaic disease, select planting material mainly from stembranches; avoid the basal and main stem portions as sources of stem cuttings.• Plant cassava mainly at the beginning of the wet season; try and avoid late planting.2425

Disease Control in Cassava FarmsIPM Field GuideAcknowledgementsSpecial thanks to the United Nations Development Programme and the Austrian governmentwhich provided funds, and to the following institutions which provided materials, information, andservices for the production of the set of cassava IPM field guides:• Agricultural Development Programs (ADPs) in Abia, Akwa Ibom, Anambra, Benue, Cross Rivers,Rivers, Delta, Edo, Enugu, Imo, Kogi, Kwara, Ogun, Ondo, Osun, Oyo, and Plateau StateGovernments, Nigeria• Centre d’Action Régionale pour le Développement Rural (CARDER), Bénin• Centro International de Agricultura Tropical (CIAT), Cali, Colombia• Crop Services Department (CSD), Department of Agricultural Extension Services (DAES),and Plant Protection and Regulatory Services Department (PPRSD), Ministry of Food andAgriculture, Ghana• Federal University of Technology, Owerri, Nigeria• Fourah Bay College, University of Sierra Leone, Freetown, Sierra Leone• IITA Eastern and Southern African Regional Centre (ESARC), Uganda• Institut de Recherche Agronomique et du Développement (IRAD), Cameroon• Institut National de Recherche Agronomique du Bénin (INRAB), Bénin• National Root Crops Research Institute (NRCRI), Umudike, Nigeria,• Rural Training Centre (RTC, Presbyterian Church) in Fonta and Kumba, Cameroon• Sasakawa Global 2000, Bénin• Service de Protection des Végétaux et du Contrôle Phytosanitaire (SPVC), Bénin• Southern African Root Crops Research Network (SARRNET), Malawi• University of Agriculture, Abeokuta, Nigeria• University of Buea, Buea, Cameroon• University of Cape Coast, Cape Coast, Ghana2627