Cassava Farms in Disease ControlIPM Field Guide Disease Control in Cassava Farms 12 Leaf spot diseases Cassava leaf spot diseases are caused by fungi. There are three different types,

Weston Msikita, Braima James, Emmanuel Nnodu,James Legg, Kerstin Wydra, Francis Ogbe

Disease Controlin

Cassava Farms

Disease Controlin

Cassava Farms

International Institute of Tropical Agriculture

About this booklet

This booklet is one in a set of field guides prepared by the International Insti-tute of Tropical Agriculture (IITA) to increase the technical knowledge of exten-sion agents and enhance the integration of plant protection and plant produc-tion practices 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 sys-tems in 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 cen-ters supported by the Consultative Group on International Agricultural Re-search (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 pro-duction while 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 agri-cultural systems causing pest problems and to provide environmentally andeconomically appropriate options for integrated pest management. (IPM)

For more information contact:The Director

IITA Plant Health Management DivisionBiological Control Center for Africa

08 B.P. 0932Cotonou, Republic of Bénin

Fax: (229) 35 05 56Tel: (229) 35 01 88

E-mail: [email protected] visit IITA’s website at: http://www.cgiar.org/iita

Disease Controlin Cassava FarmsIPM Field Guide for Extension Agents

Weston MsikitaInternational Institute of Tropical Agriculture, Plant Health Management Division,Cotonou, Bénin

Braima JamesInternational Institute of Tropical Agriculture, Plant Health Management Division,Cotonou, Bénin

Emmanuel NnoduNational Root Crops Research Institute, Umudike, Umuahia, Abia State, Nigeria

James LeggInternational Institute of Tropical Agriculture, ESARC, Kampala, Uganda

Kerstin WydraInternational Institute of Tropical Agriculture, Plant Health Management Division,Cotonou, Bénin

Francis OgbeNational Root Crops Research Institute, Umudike, Umuahia, Abia State, Nigeria

© IITA 2000ISBN 978-131-176-2Printed in Nigeria by Wordsmithes Printers, Lagos

Contents

What are the objectives of this guide? ------------------------------------------- 4

Introduction -------------------------------------------------------------------------- 4

What are the common cassava diseases? --------------------------------------- 6

Why are cassava diseases important? ------------------------------------------ 18

When are cassava diseases likely to cause severe losses? ------------------ 20

How can I best control diseases in cassava farms? -------------------------- 22

Summary ---------------------------------------------------------------------------- 25

5

IPM Field GuideDisease Control in Cassava Farms

4

Figure 1: Cassava plant damaged bycassava mosaic disease

Figure 3: Cassava storage roots damaged by cassavabrown streak disease

Figure 2: Cankers of cassavaanthracnose disease on stem

Introduction

Many 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 vi-ruses, 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 (Fig-ure 1), stems (Figure 2), and storage roots(Figure 3) of the plant. Cassava diseases arerecognized by their symptoms, such as dis-coloration of leaves, “sores” on the stems,and discoloration of storage roots.

Some other diseases which you may notice incassava are caused by nonliving things. Ex-amples of such diseases are wilting due todrought and poor plant growth because ofpoor soils.

What 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 spr-ead, and

• combine appropriate practices to controlcassava diseases and grow a healthy cropof cassava.

7


6

Figure 6:Adults ofBemisiawhitefly (asseen enlargedunder themicroscope)

Figure 5:Cassava leaf with

chlorotic (pale)spots caused by

cassava greenmite

Figure 4:Cassava leaveswith chlorotic(pale) patchesof cassavamosaicdisease

What are the commoncassava diseases?The common diseases of cassava are cassavamosaic disease, cassava bacterial blight, cas-sava anthracnose disease, cassava bud necro-

sis, and root rots. Some of these diseases at-tack the leaves and stems of cassava plantswhile others attack the storage roots.

Leaf and stem diseases

Common leaf and stem diseases of cassavaare cassava mosaic disease, cassava bacterialblight, cassava anthracnose disease, cassavabud necrosis, and brown streak disease.

Cassava mosaic disease

Cassava mosaic disease is caused by a viruswhich occurs inside cassava leaves and stems.

Damage 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 cas-sava green 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 (Fig-ure 1), 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 white-fly Bemisia tabaci (Figure 6). The virus occursin the saliva of the whitefly. During feeding, theinsect injects saliva containing the virus into

cassava leaves. The virus multiplies and occursin large numbers in the leaves and stems. Cas-sava mosaic disease is also spread by plantingstem cuttings from plants infected with thedisease.

Other crops attacked: Cassava mosaic dis-ease attacks only cassava.

9


8

Cassava bacterial blight

Cassava bacterial blight is caused by a bacte-rium which occurs inside cassava leaves andstems.

Damage symptoms: Initially, damage by cas-sava bacterial blight appears as water-soakeddead spots (lesions). The lesions occur be-tween leaf veins and are most evident on thelower surfaces of the leaves (Figure 7). The le-sions are 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 water-soaked area 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 com-plete death of the shoot. Leaf blighting startsfrom the leaf blade and moves towards thepetiole. The petiole retains a horizontal posi-tion before 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.

The 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 and

leaves. It multiplies and occurs in large num-bers in the leaves and stems. Cassava bacterialblight is therefore spread by planting stemcuttings from plants with the disease symp-toms. 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 in-fected cassava plants should be cleaned afteruse to prevent the bacterium on them fromspreading to other plants.

Other crops attacked: Cassava bacterialblight attacks only cassava.

Figure 9: Leaf blighting and wiltingcaused by cassava bacterial blight

Figure 8: Cassava leaf blighting causedby cassava bacterial blight

Figure 10: Cassava shoot tip die-backcaused by cassava bacterial blight

Figure 7: Cassava leaf with angularleaf spots of cassava bacterial blight

11


10

Cassava anthracnose disease

Cassava anthracnose disease is caused by afungus which occurs on the surface of cassavastems and 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 dis-ease are cassava plants with the disease. Thefungus spreads by wind carrying spores fromcankers on the stems, or by planting stem cut-tings with cankers. The fungus enterscassava plants through wounds and feedingpunctures made by the bug Pseudotheraptus

devastans (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.

Cassava bud necrosis

Cassava bud necrosis is caused by a funguswhich occurs on the surface of cassava stemsand leaves.

Damage symptoms: The disease appears aspatches of brown or grey fungal matter cover-ing the stem. The fungal matter sometimescovers buds (“eyes”) on cassava stem cuttings(Figure 14). The affected buds die, which re-duces the 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 de-stroyed after root harvest. The fungus spreadsby wind, however, planting of infected stemcuttings is the main method by which the dis-ease spreads.

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 petioles

Figure 12: Cassava shoot with wiltedleaves caused by cassava anthracnosedisease

Figure 14: Cassava stem with fungalpatch (arrow) of bud necrosis disease

Figure 13: The bug Pseudotheraptusdevastans on cassava leaf

p

13


12

Leaf spot diseases

Cassava 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 sur-faces (Figure 15). The spots sometimes havepurplish borders around them.

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 be-tween these veins. The dead tissue in the cen-ter of brown spots may fall to give the leafsurface a “shot hole” appearance. Under se-vere attack 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 blight-ing (Figure 17). The blighted leaves lack water-soaked areas, 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 which

then serve as sources for spread of the dis-eases.

Other crops attacked. Not much is knownabout the host crop range of cassava leaf spotdiseases.

Figure 17: Cassava leaf with leaf blight disease

Figure 16: Cassava leaf with brown leaf spotdisease

Figure 15: Cassava leaf with white leaf spotdisease

15


14

Stem and root diseases

Cassava brown streak disease

Cassava 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 dis-ease distorts the shape of the storage rootsand may cause cracks and discoloration inthe storage roots (Figure 20).

Method 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 streakdisease

Figure 18: Cassava leaves with chlorotic (pale)patches of cassava brown streak disease

Figure 20: Cassava storage rootsdiscolored by cassava brown streakdisease

17


16

Cassava root rot diseases

Cassava root rot diseases are caused by vari-ous kinds 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 stor-age roots 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 cas-sava root 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.

Other crops attacked: Cassava root rotfungi attack a wide range of other crops in-cluding maize, soybean, sunflower, and coffee.

Figure 21: Cassava storage root destroyed byroot rot disease

19


18

Why are cassava diseasesimportant?

Cassava pests are important because they re-duce the yield from the crop. They cause foodand income losses from cassava in the follow-ing ways.

Loss of roots: Root rot and cassava brownstreak diseases attack storage roots andcause immediate and direct losses. By damag-ing leaves and stems, cassava diseases gener-ally interfere 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). How-ever, most cassava varieties can lose a lot ofleaves before the root yield is reduced. Farm-ers should be discouraged from rushing totackle control measures at the first signs ofdamage.

Loss of planting material: Many cassavadiseases contaminate cassava stems with vi-ruses, bacteria, and fungi. This makes stem cut-tings unhealthy and unsuitable for planting.Certain cassava diseases, for example, cassavabacterial blight, cassava anthracnose, and cas-sava brown streak diseases, reduce the quan-tity and quality of planting material by causingshoot tip die-back. Cankers of cassava anthra-cnose disease (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 veg-etables (Figure 24). For example, cassava bac-terial blight and cassava anthracnose diseasedefoliate cassava plants; cassava mosaic dis-ease and 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 en-courage weed growth in farms because thecassava plants are no longer able to block sun-light from reaching the weeds growing under-neath. In loose soils, defoliation of cassavaplants will expose the soil to erosion.

Damage to other crops: In addition to cas-sava, 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 root

yield

Figure 24:Good cassavaleaf harvest

Figure 22:Poor cassavastorage rootyield

21


20

When are cassava diseaseslikely to cause severe losses?

The presence of diseases in cassava farmsdoes not always mean that they will cause se-vere losses in food and income. The appear-ance of 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 condi-tions under 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 toler-ance against cassava mosaic disease and cas-sava bacterial 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 hap-pens, 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 pe-riod. 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 provide

fewer and smaller storage roots than if at-tacked later. For example, under cassava mo-saic disease attack, yield losses will be higher ifdisease-free plants became diseased within 4months after planting than if they became dis-eased later 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 compen-sate for the damage. Diseases which causethis kind of damage are mainly cassava rootrots and cassava brown streak disease. How-ever, when diseases attack cassava leaves theplants may produce new leaves and later pro-duce a good root yield.

The season of attack: The effect of seasonon the extent of damage caused by cassava dis-eases varies according to the disease. The dam-age symptoms 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. Dam-age symptoms 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.

Var

iety

Expr

essi

on o

f sel

ecte

d fe

atur

es

Yie

ldpo

tent

ial

% d

ry m

atte

rC

yano

geni

cpo

tent

ial

Gro

und

stor

abili

tyW

eed

supp

ress

ion

Tol

eran

ce t

oC

GM

Tol

eran

ce t

oC

MD

Tol

eran

ce t

oC

BB

IIT

A

TM

S 4(

2)14

25H

igh

Hig

hLo

wG

ood

Goo

dM

oder

ate

Mod

erat

eG

ood

TM

S 30

572

Hig

hH

igh

Mod

erat

eM

oder

ate

Goo

dM

oder

ate

Goo

dG

ood

Ben

in

BEN

860

52H

igh

Hig

hLo

wPo

orM

oder

ate

Goo

dG

ood

Poor

RB

8950

9M

oder

ate

Mod

erat

eLo

wG

ood

Poor

Poor

Goo

dM

oder

ate

Cam

ero

on

8017

Hig

hH

igh

Mod

erat

ePo

orG

ood

Mod

erat

eM

oder

ate

Mod

erat

e

8034

Hig

hH

igh

Mod

erat

ePo

orG

ood

Mod

erat

eM

oder

ate

Mod

erat

e

Gha

na

"Afis

iafi"

Hig

hH

igh

Mod

erat

eM

oder

ate

Goo

dM

oder

ate

Goo

dG

ood

"Aba

sa fi

taa"

Hig

hH

igh

Low

Goo

dG

ood

Mod

erat

eM

oder

ate

Goo

d

Nig

eria

MS

6H

igh

Hig

hLo

wPo

orPo

orG

ood

Goo

dM

oder

ate

NR

808

2H

igh

Hig

hH

igh

Mod

erat

eG

ood

Goo

dG

ood

Goo

d

Sour

ce: I

ITA

IN

RA

B-Be

nin,

MoF

A-C

SD G

hana

, IR

AD

-Cam

eroo

n, a

nd N

RC

RI-N

iger

ia

Tabl

e 1:

So

me

feat

ures

of

com

mo

n ca

ssav

a va

riet

ies

in W

est

and

Cen

tral

Afr

ica

CG

M=

Cas

sava

gre

en m

iteC

MD

=C

assa

va m

osai

c di

seas

eC

BB=

Cas

sava

bac

teri

al b

light

23


22

How 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 prac-tices in growing the crop.

IPM practices at planting

Many integrated pest management (IPM) prac-tices for cassava diseases are applicable atplanting. These include site selection, soil im-provement practices, and selection of appro-priate varieties and planting materials. Thesepractices are covered in the companion fieldguide “Starting a Cassava Farm”. Table 1 listssome cassava varieties that can withstand dis-ease attack 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 va-riety also 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 Cas-sava Farm” 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 chlo-

rosis (Figures 4 and 18), leaf blighting and wilt-ing (Figures 9 and 12), gum exudate, cankers,fungus patches and streaks on the stems (Fig-ures 11, 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 vari-eties that branch, choose the branches assources of planting material. Most of the stemcuttings from these branches will sprout with-out the 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 simi-lar reason. Secondly, after planting, closely ob-serve the stem cuttings as they sprout. Nor-mally, stem cuttings sprout 3–4 weeks afterplanting. Tag all the plants which sprout with-out the 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 are

Figure 26: Cassava stem cutting sprouted withcassava mosaic disease

Figure 25: Unhealthy cassava stem cuttings

25


24

to be used, you should consult the label forguidelines on their application methods andhow to avoid personal and environmental haz-ards associated with their use.

When cutting up cassava stems into stem cut-tings for 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 be-ginning of the rains. Early planting allows thecrop to grow more vigorously and betterwithstand disease damage later in the dry sea-son than late planting.

IPM practices after planting

Good farm sanitation helps to reduce thesources of the pathogens that cause cassavadiseases in farms. For example, after root har-vest you should destroy cassava stems withshoot tip die-back, cankers, fungus patches,streaks or any other disease damage symp-tom. 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 replace

Summary

To control diseases and grow a healthy crop of cassava:

• Identify the common cassava diseases, their damage symptoms, and know the condi-tions under 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, can-kers, 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.

them with healthy stem cuttings. This is calledroguing. Roguing of cassava plants is best doneat 3–4 weeks after planting when controllingcassava mosaic disease.

27


26

Acknowledgements

Special 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 Riv-ers, 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, Ghana

Documents

Cassava Farms in Disease ControlIPM Field Guide Disease Control in Cassava Farms 12 Leaf spot diseases Cassava leaf spot diseases are caused by fungi. There are three different types,