cassava pests and disease

A member of CGIAR consortium www.iita.org

Cassava pests and disease

Rachid Hanna, A. Fotso

+Numerous colleagues, students and partners

Contract review presentation, IITA-Ibadan, 18 February. 2015


Importance of cassava for Africa

> 50% of world production in Africa

> 90 million tons fresh production; > any other crop in Africa

Vital to livelihoods of > 200 million people

Key food security role

Huge untapped potential for commercial development.


Major constraints of production

Pests and diseases

Local varieties with low yield potential

Poor agronomic practices

Poor soil fertility and other soil characteristics

Relative lack of commercialization

Cassava mosaic disease

Cassava green mite


Component of an integrated management

programs of cassava pests and diseases

Factors affecting abundance

Incidence/severity

Distribution, seasonality,

Diversity

Knowledge dissemination, training, and grower adoption

Biological control

Cultural controls

Host plant resistance

Chemicalcontrols Monitoring


Ecologically-based pest management

Use of multiple

tactics to

manage pests

in the

agroecosystem

www.sare.org


Major cassava pests and diseases in

Central Africa

African root

and tuber scale

Cassava green

mite

Cassava mosaic

virus disease

Cassava

mealybug

Climate change Cassava brown

streak virus disease

Whitflies

Cassava

Anthracnose and

Bacterial Blight


Major challenges to African Agriculture:

Accidental introduction and spread of

cassava mealybug and cassava green mite

UgandaVenezuela

Brazil

Colombia

Peru

Bolivia

Paraguay

Kenya

AFRICA

S. AMERICA

Early 1970s


Cassava mealybug

Phenacoccus

manihoti


Anagyrus lopezi in Africa

A. lopezi

provided

excellent

control

Some

challenges on

poor soils

where

outbreaks can

still occir


Cassava Green Mite

Mononychellus

tanajoa


Typhlodromalus aripo in Africa

1st released

In Benin

Typhlodromalus aripo


T. aripo in cassava apex

Typhlodromalus aripo attacking cassava

green mite

Conservation biological control of cassava

green mite – hairy cassava


But displays a strong

pattern of diurnal vertical

migration at night

apex

leaf 2leaf 1

leaf 7

leaf 20

leaf 8

apex

leaf 2leaf 1

leaf 7

leaf 20

leaf 8

Predator resides in apex of cassava branches

Day

Night

(Onzo et al. 2003)


TMS 30572 AgricOdoungbo

0.0

0.2

0.4

0.6

0.8

1.0

1 2 3 4 5

Apex hairiness

Pro

port

ion

of

ap

ices

wit

h T

. ari

po

Preference for hairy

cassava genotypes

(Hanna et al. unpubl)


Complementary strategies for

CGM biocontrol

Conservation biological control – using hairy

cassava varieties

Use of entomopathogenic fungus Neozygites

tanajoae from Brazil

Fungus present in Africa but Brazilian isolates

much more virulent

First introduced in Benin 1999

Increased infection but we lacked tools to

distinguish isolates.

Primers recently developed to identify isolates

(Cornell and Gottingen Universities).

Potential to introduce fungus to other countries


African root and tuber scale

in Central Africa

Countries with S. vayssiereiApproximate distribution

Hot spot

Cassa

va

Coco

ya

m

Afr

am

om

um

First described from Manihotesculenta (Richard 1971)

Reported as pest on cassava in Cameroon in 1981 (Mutsaers et al.) & later as major constraint to cassava production in Cameroon and the DR Congo

But until recently very little was known about its biology, ecology, and management

Crop losses can reach 70% in severely affected areas.


Types of damage


Likely factors in rise

in scale problem:

shorter fallow and

abundance of host

plants in the young

fallows

+2.4 fold

Sca

les p

er

pla

nt

Prior vegetation type

All blocks179

74

0

50

100

150

200

Young fallow Secondary

Forest

Yaounde Block

Cassava

Likely factors in rise in scale problem


Anoplolepis tenella

Scale-ant association

>200 morphospecies (35 genera) of ants found in scale habitat - cassava fields and surrounding forest and fallow vegetation

Anoplolepis tenella (brown crazy ant) most frequently associated with S. vayssierei(98%)

Laboratory and field experiments showed that ant is essential of scale survival

Tends the scale (for honeydew); shown experimentally to be agent of dispersal - it carries crawlers to new infestation sites

Factors affecting abundance and distribution of A. tenella and underlying factors affecting its close association to the ARTS

Developed a bait to disrupt ant-scale association.

S. vayssierei


ARTS management summary

Shorter fallows coupled with higher frequency of left-

over cassava and other host plants contribute to

scale/ant reservoir which exacerbate scale problem.

Follow management – i.e., reducing host residues during

fallow period and/or host plant residue removal before

planting – can help in reducing scale infestations and

improve cassava yield.

Host plant tolerance – no resistance yet found – but large

variations in suitability to the scale

Several tolerant varieties are presently being promoted;

should be tested in other affected countries; local

germplasm should be screened for susceptibility to the

scale

Ant management: use of boric acid + sugar bait can be

effective in reducing the ant and therefore the scale


Cassava whiteflies

Bemisia and Aleurodicus

B. tabaci B. afer Spiralling whitefly


Damage caused by SWF

Direct feeding can cause

premature leaf drop,

reduces plant vigor and

yields

Indirect damage - sooty moulds

(reduce photosynthesis and

yields.


Serendipitous parasitoid

introductions

1993

Encarsia dispersa

E. guadeloupea


Bemisia tabaci

Worldwide distribution

Exists in many types – now being split into species.

Very large host range but types closely associated with specific host plants

Young and adults feed by sucking on leave

Generally not much direct damage

Principal economic importance is vector of many viruses: cassava mosaic and cassava brown streak viruses

But new superabundant species


Physical damage to upper leaves


26

Insects and mites for whitefly control


True resistance to B. tabaci not found yet among African cassava

varieties – but lots of variability.

Early flowering and susceptibility to mites – possible factors.

Presently working with clones from CIAT that are resistance to

another whitefly - Aleurotrachelus socialis

Parasitism by several aphelinid parasitoids can reach 40% at

time and likely play a important role in whitefly control – need to

better understand diversity and role of the parasitoids and

develop ways to promote their control of whiteflies.

Surveillance and containment of spread of B. tabaci

superabundant biotypes.

Biotechnology – RNAi (gene silencing)

Summary B. tabaci management


Cassava mosaic virus diseases

Healthy Cassava

Diseased cassava


Pandemic of sever CMD

CMD pandemic zonesNot surveyedPandemic affectedUnaffected

James Legg - IITA

Eastern Cameroon

Alabi et al 2010.

N. Angola – Kumar et al., 2009

Tabora

Ndyetabula

et al., 2008

Uganda 1990s


Severe cassava mosaic disease in Cameroon

Distribution of

EACMV-UG in

Cameroon. Each

point represents a

location from which

cassava samples

were collected for

EAMCV-UG, ACMV

and EACMV

analysis. Locations

where EACMV-UG

positive samples is

indicated in red; and

the sites where only

ACMV/EACMV was

detected is

indicated in blue.

EACMV-UG found first time in 2009

Alabi et al. 2010


Severe CMD in Cameroon

2015/2016

A member of CGIAR consortium www.iita.orgJ. Legg - IITA

Cassava Brown Streak Virus Disease


1930s

2009

2004

20052005

New Outbreaks of CBSD


Plenty of resistance to CMD; some resistance for CBSD (IITA

working on transgenic cassava for both disease and whitefly

resistance); varieties must be disseminated;

Vigorous campaigns in DRC and Cameroon, but other countries

– CAR, Tchad, Gabon, Congo, Eq. Guinea need more

investment in variety dissemination.

CMD spread in CAR, Tchad, Gabon, Congo, Eq. Guinea

requires updating (information is old); surveillance and actions

to reduce spread into unaffected areas;

Similar efforts are needed for CBSD;

Need more information on whiteflies diversity and associated

parasitoids from all CA countries;

Farmer training on disease recognition and management.

CMD and CBSD management


Resistant/tolerant varieties: TMS

96/0023; TME 419, TMS

96/1414, TMS 92/0067);

Use cuttings that do not show

symptoms of the disease

(cankers)

Remove severly affected plants

Keep your field clean (weed-

free).

CAD management

Cassava Anthracnose Disease


Resistant/tolerant varieties:TMS

92/0067) and use cuttings from

unaffected fields.

Remove symptomatic leaves an bury

infected leaves and debri.

Rotate cassava with other crops.

Remove severly affected plants

Keep your field clean (weed-free).

Reduce grasshopper abundance –

vectors.

CBB management

Cassava Bacterial Blight (CBB)


Implementation of developed IPM for

Africa root and tuber scale

Conservation biological control of

cassava green mite

Surveillance of severe cassava

mosaic disease (CMD) and CBSD

especially unaffected countries, and

development and promotion of

cassava resistance to CMD

Host plant resistance and biological

control of Bemisia tabaci, vector of

cassava mosaic viruse

Information dissemination sand

capacity development

Cassava IPM outlook

A member of CGIAR consortium www.iita.orgA member of CGIAR consortium

Projected global effects on

agriculture due to climate change

www.iita.org


Why? Impact of climate change

An increase in extreme climate events, changes in moisture

conditions, temperature increase, elevated CO2 concentrations

expected to magnify pest pressure on agricultural systems

Accelerated pest development leading to more pest cycles per

season.

Susceptibility to pests increases in drought stressed plants.

Asynchronization of pests and antagonists - > risk of pest outbreaks.

Range expansion - existing pests and invasion by new pests

Increase damage potential from invasive alien species.

Exacerbate already existing food security problems.

Numerous examples of increasing pest status have been

documented and modeled.

Level of vulnerability may be agroecosystem specific hence the need

to understand and predict climate change effect Adapted from J. Kroschel


Phenology modelling for climate change and

adaptation planning

Cassava mealybug

& A. lopeziCassava green mite

& T. aripo

Banana aphid

Bactrocera invadens & Fopius arisanus


Divide into groups – by country (of if too few, join neighboring

country).

Elect an animator and rapporteur.

Develop a priority list of interventions for pest and disease

management – do not to forget capacity building.

Provide a list of on-going programs, research and development

organization active in cassava sector, and present and potential

donors.

Present summary of discussion: 5-8 min/country.

Rapporteur should provide soft version of each country summary.

Way forward for our session

A member of CGIAR consortium www.iita.orgA member of CGIAR consortium www.iita.org

Thank you very much for your kind attention

Merci beaucoup pour votre amiable attention

Thank you et Merci

cassava pests and disease

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