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About this booklet<strong>Disease</strong> <strong>Control</strong><strong>in</strong><strong>Cassava</strong> <strong>Farms</strong>This booklet is one <strong>in</strong> a set of field guides prepared by the International Instituteof Tropical Agriculture (IITA) to <strong>in</strong>crease the technical knowledge of extensionagents and enhance the <strong>in</strong>tegration of plant protection and plant productionpractices <strong>in</strong> farmers’ efforts to grow a healthy crop of cassava. The bookletis based largely on the extension and farmer tra<strong>in</strong><strong>in</strong>g experience of the regionalproject “Ecologically Susta<strong>in</strong>able <strong>Cassava</strong> Plant Protection” (ESCaPP), 1993–1997. ESCaPP was executed by IITA’s Plant Health Management Division(PHMD), <strong>in</strong> collaboration with national agricultural research and extension systems<strong>in</strong> Bén<strong>in</strong>, 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 <strong>in</strong>ternational agricultural research and tra<strong>in</strong><strong>in</strong>g centerssupported by the Consultative Group on International Agricultural Research(CGIAR). Their shared mission is the alleviation of hunger and poverty <strong>in</strong>tropical develop<strong>in</strong>g countries by generat<strong>in</strong>g appropriate plant production andprotection technologies which benefit the poor and enhance agricultural productionwhile preserv<strong>in</strong>g the natural resource base. At IITA, PHMD is dedicatedto susta<strong>in</strong>able plant protection of primary food crops <strong>in</strong> Africa. The division’sresearch philosophy is to identify and correct the ecological imbalances <strong>in</strong> agriculturalsystems caus<strong>in</strong>g pest problems and to provide environmentally andeconomically appropriate options for <strong>in</strong>tegrated pest management. (IPM)For more <strong>in</strong>formation contact:The DirectorIITA Plant Health Management DivisionBiological <strong>Control</strong> Center for Africa08 B.P. 0932Cotonou, Republic of Bén<strong>in</strong>Fax: (229) 35 05 56Tel: (229) 35 01 88E-mail: IITA-ben<strong>in</strong>@cgiar.<strong>org</strong>Or visit IITA’s website at: http://www.cgiar.<strong>org</strong>/iitaWeston Msikita, Braima James, Emmanuel Nnodu,James Legg, Kerst<strong>in</strong> Wydra, Francis OgbeInternational Institute of Tropical Agriculture
<strong>Disease</strong> <strong>Control</strong><strong>in</strong> <strong>Cassava</strong> <strong>Farms</strong>IPM Field Guide for Extension AgentsWeston MsikitaInternational Institute of Tropical Agriculture, Plant Health Management Division,Cotonou, Bén<strong>in</strong>Braima JamesInternational Institute of Tropical Agriculture, Plant Health Management Division,Cotonou, Bén<strong>in</strong>Emmanuel NnoduNational Root Crops Research Institute, Umudike, Umuahia, Abia State, NigeriaJames LeggInternational Institute of Tropical Agriculture, ESARC, Kampala, UgandaKerst<strong>in</strong> WydraInternational Institute of Tropical Agriculture, Plant Health Management Division,Cotonou, Bén<strong>in</strong>Francis 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 <strong>in</strong> cassava farms? -------------------------- 22Summary ---------------------------------------------------------------------------- 25
<strong>Disease</strong> <strong>Control</strong> <strong>in</strong> <strong>Cassava</strong> <strong>Farms</strong>IPM 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• comb<strong>in</strong>e appropriate practices to controlcassava diseases and grow a healthy cropof cassava.IntroductionMany diseases are caused by very t<strong>in</strong>y liv<strong>in</strong>gth<strong>in</strong>gs called pathogens. Pathogens are so t<strong>in</strong>ythat 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 <strong>in</strong>side 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. <strong>Cassava</strong> 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 <strong>in</strong>cassava are caused by nonliv<strong>in</strong>g th<strong>in</strong>gs. Examplesof such diseases are wilt<strong>in</strong>g due todrought and poor plant growth because ofpoor soils.Figure 1: <strong>Cassava</strong> plant damaged bycassava mosaic diseaseFigure 2: Cankers of cassavaanthracnose disease on stemFigure 3: <strong>Cassava</strong> storage roots damaged by cassavabrown streak disease45
<strong>Disease</strong> <strong>Control</strong> <strong>in</strong> <strong>Cassava</strong> <strong>Farms</strong>IPM 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.<strong>Cassava</strong> mosaic disease<strong>Cassava</strong> mosaic disease is caused by a viruswhich occurs <strong>in</strong>side cassava leaves and stems.cassava leaves. The virus multiplies and occurs<strong>in</strong> large numbers <strong>in</strong> the leaves and stems. <strong>Cassava</strong>mosaic disease is also spread by plant<strong>in</strong>gstem cutt<strong>in</strong>gs from plants <strong>in</strong>fected with thedisease.Other crops attacked: <strong>Cassava</strong> mosaic diseaseattacks only cassava.Figure 4:<strong>Cassava</strong> 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 feed<strong>in</strong>g 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 ma<strong>in</strong> sources of thevirus which causes cassava mosaic disease arecassava plants with the disease and the whiteflyBemisia tabaci (Figure 6). The virus occurs<strong>in</strong> the saliva of the whitefly. Dur<strong>in</strong>g feed<strong>in</strong>g, the<strong>in</strong>sect <strong>in</strong>jects saliva conta<strong>in</strong><strong>in</strong>g the virus <strong>in</strong>toFigure 5:<strong>Cassava</strong> leaf withchlorotic (pale)spots caused bycassava greenmiteFigure 6:Adults ofBemisiawhitefly (asseen enlargedunder themicroscope)67
<strong>Disease</strong> <strong>Control</strong> <strong>in</strong> <strong>Cassava</strong> <strong>Farms</strong>IPM Field Guide<strong>Cassava</strong> bacterial blight<strong>Cassava</strong> bacterial blight is caused by a bacteriumwhich occurs <strong>in</strong>side cassava leaves andstems.Damage symptoms: Initially, damage by cassavabacterial blight appears as water-soakeddead spots (lesions). The lesions occur betweenleaf ve<strong>in</strong>s and are most evident on thelower surfaces of the leaves (Figure 7). The lesionsare small, not completely round <strong>in</strong> shape,and have a few angles at their edges. Theseangular lesions later jo<strong>in</strong> together <strong>in</strong>to largerpatches kill<strong>in</strong>g the leaf blade as they enlarge.The leaf blade turns brown with the watersoakedarea at the lead<strong>in</strong>g edge of the brownpatch. This damage symptom is known as leafblight<strong>in</strong>g (Figure 8). Severely blighted leaveswilt (Figure 9), die, and fall caus<strong>in</strong>g defoliationand shoot tip die-back (Figure 10) or completedeath of the shoot. Leaf blight<strong>in</strong>g startsfrom the leaf blade and moves towards thepetiole. The petiole reta<strong>in</strong>s 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 <strong>in</strong>fectedwith cassava bacteria blight.leaves. It multiplies and occurs <strong>in</strong> large numbers<strong>in</strong> the leaves and stems. <strong>Cassava</strong> bacterialblight is therefore spread by plant<strong>in</strong>g stemcutt<strong>in</strong>gs 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 ra<strong>in</strong>dropswhich splash the bacterium from <strong>in</strong>fectedplants to healthy plants. Insects, for example,grasshoppers become contam<strong>in</strong>ated with thebacterium and spread it to healthy cassavaplants. Farm tools that are used to cut <strong>in</strong>fectedcassava plants should be cleaned afteruse to prevent the bacterium on them fromspread<strong>in</strong>g to other plants.Other crops attacked: <strong>Cassava</strong> bacterialblight attacks only cassava.Figure 7: <strong>Cassava</strong> leaf with angularleaf spots of cassava bacterial blightFigure 8: <strong>Cassava</strong> leaf blight<strong>in</strong>g causedby cassava bacterial blightThe damage symptoms of cassava bacteriablight are more evident <strong>in</strong> the wet than <strong>in</strong> thedry season. The disease is more severe <strong>in</strong>young plants than <strong>in</strong> older ones.Method of spread: The ma<strong>in</strong> 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 blight<strong>in</strong>g and wilt<strong>in</strong>gcaused by cassava bacterial blightFigure 10: <strong>Cassava</strong> shoot tip die-backcaused by cassava bacterial blight89
<strong>Disease</strong> <strong>Control</strong> <strong>in</strong> <strong>Cassava</strong> <strong>Farms</strong>IPM Field Guide<strong>Cassava</strong> anthracnose disease<strong>Cassava</strong> bud necrosis<strong>Cassava</strong> anthracnose disease is caused by afungus which occurs on the surface of cassavastems and leaves.<strong>Cassava</strong> bud necrosis is caused by a funguswhich occurs on the surface of cassava stemsand leaves.Damage symptoms: <strong>Cassava</strong> 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 caus<strong>in</strong>g 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 beg<strong>in</strong>n<strong>in</strong>g ofthe ra<strong>in</strong>s and worsens as the wet seasonprogresses.Method of spread: The ma<strong>in</strong> sources of thefungus that causes cassava anthracnose diseaseare cassava plants with the disease. Thefungus spreads by w<strong>in</strong>d carry<strong>in</strong>g spores fromcankers on the stems, or by plant<strong>in</strong>g stem cutt<strong>in</strong>gswith cankers. The fungus enterscassava plants through wounds and feed<strong>in</strong>gpunctures 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 cover<strong>in</strong>gthe stem. The fungal matter sometimescovers buds (“eyes”) on cassava stem cutt<strong>in</strong>gs(Figure 14). The affected buds die, which reducesthe sprout<strong>in</strong>g ability of stem cutt<strong>in</strong>gs.Method of spread: The ma<strong>in</strong> 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 w<strong>in</strong>d, however, plant<strong>in</strong>g of <strong>in</strong>fected stemcutt<strong>in</strong>gs is the ma<strong>in</strong> method by which the diseasespreads.Other crops attacked: The fungus thatcauses bud necrosis causes leaf spots on avariety of plants <strong>in</strong>clud<strong>in</strong>g grasses, cerealcrops, banana, and mango.Figure 11: Cankers of cassavaanthracnose disease at the bases ofcassava leaf petiolesFigure 12: <strong>Cassava</strong> shoot with wiltedleaves caused by cassava anthracnosediseasepFigure 13: The bug Pseudotheraptusdevastans on cassava leafFigure 14: <strong>Cassava</strong> stem with fungalpatch (arrow) of bud necrosis disease1011
<strong>Disease</strong> <strong>Control</strong> <strong>in</strong> <strong>Cassava</strong> <strong>Farms</strong>IPM Field GuideLeaf spot diseases<strong>Cassava</strong> leaf spot diseases are caused by fungi.There are three different types, namely whiteleaf spot, brown leaf spot, and leaf blight.Damage symptoms: <strong>Cassava</strong> 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.<strong>Cassava</strong> brown leaf spot disease appears assmall brown spots with dark borders on theupper leaf surfaces (Figure 16). The brownspots occur between leaf ve<strong>in</strong>s, and their sizesand shapes are limited by the distance betweenthese ve<strong>in</strong>s. The dead tissue <strong>in</strong> the centerof brown spots may fall to give the leafsurface a “shot hole” appearance. Under severeattack the <strong>in</strong>fected leaves become yellow,dry, and die prematurely.<strong>Cassava</strong> leaf blight disease appears as lightbrown lesions on the upper surfaces of theleaves. The lesions are not limited by ve<strong>in</strong>s,therefore they are usually larger than brownleaf spots. The lesions may enlarge to covermost of the leaf surface and cause leaf blight<strong>in</strong>g(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 <strong>in</strong>to“shot holes” on the leaf surface.Method of spread: The ma<strong>in</strong> sources of thefungi that cause leaf spot diseases are <strong>in</strong>fectedcassava leaves on the plant or those fallen onthe ground. The fungi spread to new plantsfrom these sources by w<strong>in</strong>d or ra<strong>in</strong> splashes.Leaf spot fungi can occur on weeds whichFigure 15: <strong>Cassava</strong> leaf with white leaf spotdiseaseFigure 16: <strong>Cassava</strong> leaf with brown leaf spotdiseaseFigure 17: <strong>Cassava</strong> leaf with leaf blight disease1213
<strong>Disease</strong> <strong>Control</strong> <strong>in</strong> <strong>Cassava</strong> <strong>Farms</strong>IPM Field GuideStem and root diseases<strong>Cassava</strong> brown streak disease<strong>Cassava</strong> brown streak disease is caused by avirus. Presently the disease is reported onlyfrom cassava-grow<strong>in</strong>g regions <strong>in</strong> 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 prom<strong>in</strong>ent on mature leaves thanon young leaves. The damaged leaves do notbecome distorted <strong>in</strong> 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 prom<strong>in</strong>ent on upper, green portions ofthe stems. The diseased plants may showshoot tip die-back. <strong>Cassava</strong> brown streak diseasedistorts the shape of the storage rootsand may cause cracks and discoloration <strong>in</strong>the storage roots (Figure 20).Figure 18: <strong>Cassava</strong> leaves with chlorotic (pale)patches of cassava brown streak diseaseMethod of spread: The ma<strong>in</strong> sources of thevirus that causes cassava brown streak arecassava plants with the disease. The disease isspread through the plant<strong>in</strong>g of stem cutt<strong>in</strong>gsfrom diseased plants. The virus is also believedto be spread from plant to plant by <strong>in</strong>sects.Other crops attacked: <strong>Cassava</strong> brownstreak disease is not known to attack othercrops.Figure 19: <strong>Cassava</strong> stem with“streaks” of cassava brown streakdiseaseFigure 20: <strong>Cassava</strong> storage rootsdiscolored by cassava brown streakdisease1415
<strong>Disease</strong> <strong>Control</strong> <strong>in</strong> <strong>Cassava</strong> <strong>Farms</strong>IPM Field Guide<strong>Cassava</strong> root rot diseases<strong>Cassava</strong> root rot diseases are caused by variousk<strong>in</strong>ds of fungi liv<strong>in</strong>g on or <strong>in</strong> the soil. Thefungi occur ma<strong>in</strong>ly <strong>in</strong> soils that do not dra<strong>in</strong>properly and <strong>in</strong> 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 rema<strong>in</strong> attached tothe plant, but the plant loses a lot of water anddies. If you suspect a cassava plant as hav<strong>in</strong>groot rot disease, you should confirm this byuproot<strong>in</strong>g it and exam<strong>in</strong><strong>in</strong>g 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 <strong>in</strong> 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 contam<strong>in</strong>ated withthe fungi. The fungi enter cassava plantsthrough wounds caused by pests or farm<strong>in</strong>gtools or by pierc<strong>in</strong>g the roots by themselves.Farm tillage tools used <strong>in</strong> cassava farms withthe disease should be cleaned after use toprevent the fungi on them from spread<strong>in</strong>g toother areas. Similarly, cassava plant debris <strong>in</strong>farms with the disease serve as sources ofroot rot fungi and should be destroyed byburn<strong>in</strong>g.Figure 21: <strong>Cassava</strong> storage root destroyed byroot rot diseaseOther crops attacked: <strong>Cassava</strong> root rotfungi attack a wide range of other crops <strong>in</strong>clud<strong>in</strong>gmaize, soybean, sunflower, and coffee.1617
<strong>Disease</strong> <strong>Control</strong> <strong>in</strong> <strong>Cassava</strong> <strong>Farms</strong>IPM Field GuideWhy are cassava diseasesimportant?<strong>Cassava</strong> pests are important because they reducethe yield from the crop. They cause foodand <strong>in</strong>come losses from cassava <strong>in</strong> the follow<strong>in</strong>gways.Loss of roots: Root rot and cassava brownstreak diseases attack storage roots andcause immediate and direct losses. By damag<strong>in</strong>gleaves and stems, cassava diseases generally<strong>in</strong>terfere with the way by which the plantmakes food for storage <strong>in</strong> 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 rush<strong>in</strong>g totackle control measures at the first signs ofdamage.Loss of plant<strong>in</strong>g material: Many cassavadiseases contam<strong>in</strong>ate cassava stems with viruses,bacteria, and fungi. This makes stem cutt<strong>in</strong>gsunhealthy and unsuitable for plant<strong>in</strong>g.Certa<strong>in</strong> cassava diseases, for example, cassavabacterial blight, cassava anthracnose, and cassavabrown streak diseases, reduce the quantityand quality of plant<strong>in</strong>g material by caus<strong>in</strong>gshoot 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 cutt<strong>in</strong>gsto 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 k<strong>in</strong>ds of damage willalso reduce the ability of cassava plants tomake sufficient food for storage <strong>in</strong> the roots.Increase <strong>in</strong> weeds and erosion: <strong>Disease</strong>sthat defoliate and kill cassava shoot tips encourageweed growth <strong>in</strong> farms because thecassava plants are no longer able to block sunlightfrom reach<strong>in</strong>g the weeds grow<strong>in</strong>g 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
<strong>Disease</strong> <strong>Control</strong> <strong>in</strong> <strong>Cassava</strong> <strong>Farms</strong>IPM Field GuideWhen are cassava diseaseslikely to cause severe losses?The presence of diseases <strong>in</strong> cassava farmsdoes not always mean that they will cause severelosses <strong>in</strong> food and <strong>in</strong>come. The appearanceof disease damage can be mislead<strong>in</strong>g. Forexample, leaf spot diseases are unlikely tocause severe losses <strong>in</strong> root yield because theyusually attack plants close to maturity. It istherefore very important to know the conditionsunder which diseases can be seriousproblems. The follow<strong>in</strong>g po<strong>in</strong>ters will help youto know when the diseases are likely to causesevere losses <strong>in</strong> 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 toleranceaga<strong>in</strong>st cassava mosaic disease and cassavabacterial blight.The stage of plant growth at attack:Generally, yield loss is greater if stem cutt<strong>in</strong>gssprout with the diseases than <strong>in</strong> disease-freesprouts. <strong>Disease</strong>-free sprouts can, however, be<strong>in</strong>fected with pathogens later on. If this happens,young cassava plants suffer more fromdisease attack than older plants. At 3–4months after plant<strong>in</strong>g, the storage roots ofmost cassava varieties start to swell withfood. At about 7 months after plant<strong>in</strong>g, theplants have formed the number of storageroots they will carry dur<strong>in</strong>g their grow<strong>in</strong>g period.This number will not <strong>in</strong>crease much afterthis time, but the storage roots will cont<strong>in</strong>ueto 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 with<strong>in</strong> 4months after plant<strong>in</strong>g than if they became diseasedlater on. Also, leaf spot diseases occurma<strong>in</strong>ly 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 losses<strong>in</strong> root yield.The plant parts attacked: <strong>Disease</strong>s whichdamage the plant parts that you harvest “rob”you directly of food and <strong>in</strong>come. 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. <strong>Disease</strong>s which causethis k<strong>in</strong>d of damage are ma<strong>in</strong>ly 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 accord<strong>in</strong>g to the disease. The damagesymptoms of cassava brown streak diseaseare more serious <strong>in</strong> the dry than <strong>in</strong> the wetseason. Root rot damage can be severe either<strong>in</strong> the wet or <strong>in</strong> the dry season, depend<strong>in</strong>g onthe type of fungi that causes the disease. Damagesymptoms of cassava bacterial blight andcassava anthracnose disease occur more <strong>in</strong> thewet than <strong>in</strong> 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 <strong>in</strong> 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 GoodBen<strong>in</strong>BEN 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 = <strong>Cassava</strong> green miteCMD = <strong>Cassava</strong> mosaic diseaseCBB = <strong>Cassava</strong> bacterial blightSource: IITA INRAB-Ben<strong>in</strong>, MoFA-CSD Ghana, IRAD-Cameroon, and NRCRI-Nigeria2021
<strong>Disease</strong> <strong>Control</strong> <strong>in</strong> <strong>Cassava</strong> <strong>Farms</strong>IPM Field GuideHow can I best controldiseases <strong>in</strong> 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 comb<strong>in</strong>eplant production and plant protection practices<strong>in</strong> grow<strong>in</strong>g the crop.IPM practices at plant<strong>in</strong>gMany <strong>in</strong>tegrated pest management (IPM) practicesfor cassava diseases are applicable atplant<strong>in</strong>g. These <strong>in</strong>clude site selection, soil improvementpractices, and selection of appropriatevarieties and plant<strong>in</strong>g materials. Thesepractices are covered <strong>in</strong> the companion fieldguide “Start<strong>in</strong>g a <strong>Cassava</strong> 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 <strong>in</strong> particularlocalities. In select<strong>in</strong>g a variety to grow aga<strong>in</strong>stdiseases you should f<strong>in</strong>d out if the selected varietyalso has other features you may want.Almost all cassava diseases are spread byplant<strong>in</strong>g <strong>in</strong>fected stem cutt<strong>in</strong>gs. The viruses,bacteria and fungi which cause the variousdiseases survive on or <strong>in</strong>side cassava stemsand are easily carried to new fields <strong>in</strong> this way.The companion field guide on “Start<strong>in</strong>g a <strong>Cassava</strong>Farm” presents the general guidel<strong>in</strong>es onhow to select healthy stem cutt<strong>in</strong>gs. Theguidel<strong>in</strong>es will assist you to avoid unhealthystem cutt<strong>in</strong>gs (Figure 25) as plant<strong>in</strong>g materialand grow a healthy cassava crop. In select<strong>in</strong>gplant<strong>in</strong>g material, you should avoid cassavaplants which show leaf discoloration or chlorosis(Figures 4 and 18), leaf blight<strong>in</strong>g and wilt<strong>in</strong>g(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 cutt<strong>in</strong>gsfrom such plants can sprout <strong>in</strong>to diseasedseedl<strong>in</strong>gs or not sprout at all.In the control of cassava mosaic disease, youcan select good plant<strong>in</strong>g material and reducethe level of disease <strong>in</strong> the farm by follow<strong>in</strong>g anumber of other steps. Firstly, <strong>in</strong> cassava varietiesthat branch, choose the branches assources of plant<strong>in</strong>g material. Most of the stemcutt<strong>in</strong>gs from these branches will sprout withoutthe disease. On the other hand, most ofthe stem cutt<strong>in</strong>gs from the ma<strong>in</strong> stem willsprout with the disease (Figure 26). In cassavavarieties that do not branch, avoid the basalstem portions as plant<strong>in</strong>g material for a similarreason. Secondly, after plant<strong>in</strong>g, closely observethe stem cutt<strong>in</strong>gs as they sprout. Normally,stem cutt<strong>in</strong>gs sprout 3–4 weeks afterplant<strong>in</strong>g. Tag all the plants which sprout withoutthe disease. At harvest time select theseplants as your plant<strong>in</strong>g material to controlcassava mosaic disease. Even if the plantssprout<strong>in</strong>g without cassava mosaic disease areattacked by the disease later on, they willgrow <strong>in</strong>to healthier plants than those whichgrow from stem cutt<strong>in</strong>gs sprout<strong>in</strong>g with thedisease.If it is difficult to get sufficient quantities ofhealthy stems for plant<strong>in</strong>g, you should treatthe stem cutt<strong>in</strong>gs aga<strong>in</strong>st certa<strong>in</strong> diseases. Forexample, you can dip cassava stem cutt<strong>in</strong>gswith cankers <strong>in</strong> dilute solutions of Benlate (afungicide) to clean them of the fungus thatcauses cassava anthracnose. If fungicides areFigure 25: Unhealthy cassava stem cutt<strong>in</strong>gsFigure 26: <strong>Cassava</strong> stem cutt<strong>in</strong>g sprouted withcassava mosaic disease2223
<strong>Disease</strong> <strong>Control</strong> <strong>in</strong> <strong>Cassava</strong> <strong>Farms</strong>IPM Field Guideto be used, you should consult the label f<strong>org</strong>uidel<strong>in</strong>es on their application methods andhow to avoid personal and environmental hazardsassociated with their use.When cutt<strong>in</strong>g up cassava stems <strong>in</strong>to stem cutt<strong>in</strong>gsfor plant<strong>in</strong>g, you should select the middlebrown-sk<strong>in</strong>ned 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 beg<strong>in</strong>n<strong>in</strong>gof the ra<strong>in</strong>s. Early plant<strong>in</strong>g allows thecrop to grow more vigorously and betterwithstand disease damage later <strong>in</strong> the dry seasonthan late plant<strong>in</strong>g.IPM practices after plant<strong>in</strong>gGood farm sanitation helps to reduce thesources of the pathogens that cause cassavadiseases <strong>in</strong> 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 contam<strong>in</strong>ated with the pathogen.If only a few stem cutt<strong>in</strong>gs sprout with diseaseit is advisable to remove them and replacethem with healthy stem cutt<strong>in</strong>gs. This is calledrogu<strong>in</strong>g. Rogu<strong>in</strong>g of cassava plants is best doneat 3–4 weeks after plant<strong>in</strong>g when controll<strong>in</strong>gcassava 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 slop<strong>in</strong>g land togrow cassava.• Improve the soils by manur<strong>in</strong>g, mulch<strong>in</strong>g, and <strong>in</strong>tercropp<strong>in</strong>g to encourage cassavaplants to grow vigorously and offset damage by cassava diseases.• Grow cassava varieties that tolerate the common cassava diseases <strong>in</strong> your area.• Plant stem cutt<strong>in</strong>gs 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 show<strong>in</strong>g anysymptom of disease.• In the control of cassava mosaic disease, select plant<strong>in</strong>g material ma<strong>in</strong>ly from stembranches; avoid the basal and ma<strong>in</strong> stem portions as sources of stem cutt<strong>in</strong>gs.• Plant cassava ma<strong>in</strong>ly at the beg<strong>in</strong>n<strong>in</strong>g of the wet season; try and avoid late plant<strong>in</strong>g.2425
<strong>Disease</strong> <strong>Control</strong> <strong>in</strong> <strong>Cassava</strong> <strong>Farms</strong>IPM Field GuideAcknowledgementsSpecial thanks to the United Nations Development Programme and the Austrian governmentwhich provided funds, and to the follow<strong>in</strong>g <strong>in</strong>stitutions which provided materials, <strong>in</strong>formation, andservices for the production of the set of cassava IPM field guides:• Agricultural Development Programs (ADPs) <strong>in</strong> 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), Bén<strong>in</strong>• 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), M<strong>in</strong>istry 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 Bén<strong>in</strong> (INRAB), Bén<strong>in</strong>• National Root Crops Research Institute (NRCRI), Umudike, Nigeria,• Rural Tra<strong>in</strong><strong>in</strong>g Centre (RTC, Presbyterian Church) <strong>in</strong> Fonta and Kumba, Cameroon• Sasakawa Global 2000, Bén<strong>in</strong>• Service de Protection des Végétaux et du Contrôle Phytosanitaire (SPVC), Bén<strong>in</strong>• 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