Download pests and diseases of cassava

PESTS AND DISEASES OF
CASSAVA
PRESENTED TO
THE RIO CLARO
FARMER’S
ASSOCIATION .
ANTHONY
SEESAHAI
Consultant to the
CFC/CARDI ROOT
CROP PROJECT.
PESTS AND DISEASES
PESTS
DISEASES
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8.
Thrips
Chinch Bug
Cassava shoot fly
Mites
Cassava hornworm
Whiteflies
Mealy bugs
Grasshoppers
Termites
Cassava bacterial blight
Superelongation
African mosaic disease
Bacterial stem rot
Tuber rotting
Anthracnose
Brown leaf spots
Cassava brown streak
disease
PESTS AND DISEASES
PESTS
10. Fruit flies
11. Leaf cutting ants
12. Lace bugs
13. Cutworms
14. Scale insects
15. Gall midges
16. White grubs
DISEASES
9. Frog skin disease
10. Witches’ broom
11. Cassava ash
12. Rust
13. Concentric ring leaf
spot
14. Root smallpox
disease
15. Bacterial stem gall
16. White leaf spot
THRIPS
Thrips (Corynothrips
stenopterus) – some
species damage growing
points by sucking the
sap of the plant
resulting in loss of
vigour and causes
reduced yields. However
it can be controlled by
chemicals or insect
growth regulators.
CHINCH BUG
Chinch Bug– this pest lives in the soil and
punctures the tubers making them
unmarketable. The Crotalaria plant
prevents damage when planted nearby.
CHINCH BUG-ROOT SMALLPOX DISEASE
This problem is caused by subterranean
sucking insects (Cyrtomerus bergi)
which, while sucking, wounds the
epidermis and cortical zone of the root
with their stylet. The microorganism
penetrating through these wounds cause
rots. Lesions are light to dark brown.
CHINCH BUG
CASSAVA SHOOT FLY
Cassava Shoot Fly (Siblua
pendula)This pest damages the tips of the
young plant causing growth to
be stunted. Mature plants do
not suffer as much as the
younger ones. Heavy
infestations occur in the
beginning of the rainy season.
MITES
The cassava green spider mite (Mononychellus
tanajoa) – this mite is green turning yellow as an
adult. They occur on the lower surface of young
leaves, green stems and auxillary buds and
damages usually appear as yellowish “pinpricks”
on the surface. Heavy attack may cause stunted
and deformed leaves and complete chlorosis.
Green spider mites are major pests in the dry
season and severe attacks often results in 20-80%
loss in tuber yield.
MITES
THE CASSAVA GREEN SPIDER MITE
MITES
The Red Spider Mite
(Oligonychus gossypii) –
this pest usually occur on
older cassava leaves. Initial
symptoms are yellowish
“pinpricks” along the main
vein of mature leaves
which eventually turns
reddish, rusty brown. Most
damages occur in the
beginning of the dry
season.
CASSAVA HORNWORM
Cassava hornworm
(Erinnyis ello) – high
populations can
defoliate large
plantations in a short
time. Yields are
reduced and many
young plants often die.
HORNWORM
LARVAE
WHITEFLIES
Whiteflies – this is the vector of the African
mosaic disease. Yield losses up to 76% due
to serious attack have been recorded. The
whitefly sucks sap from the leaves and
excrete large amounts of honeydew, which
supports the growth of black sooty mould
on the plant, causing premature fall of older
leaves.
WHITEFLIES
CASSAVA MOSAIC DISEASE
WHITEFLY
WHITEFLIES
SPIRAL WHITEFLY INFESTED CASSAVA LEAF
WHITEFLIES
WHITEFLIES
VARIETY RESISTANT TO WHITEFLIES
MEALYBUGS
The cassava mealybug (Phenacoccus manihoti) – this
pest is pinkish in colour and reproduces throughout
the year reaching its peak during the dry season. It
sucks sap from cassava shoot tips on the lower
surfaces of leaves and stem during which they inject
toxins into the plant causing deformation of terminal
shoots which become stunted. Internodes length
reduce and stems are distorted. Mealybug attack
results in leaf loss and poor quality planting material.
Tuber loss have been estimated up to 80%.
MEALYBUG
MEALYBUG
The stripped mealybug (Ferrisia virgata) –
this is a whitish mealybug with two
longitudinal dark stripes, long glassy wax
threads and two long tails. It sucks sap but
unlike the cassava mealybug it does not
inject any toxins into the plants therefore
the attack is not as severe. The stripped
mealybug occurs on the underside of the
leaves near the petioles and on the stems.
MEALYBUG
THE STRIPPED MEALYBUG
TERMITES
Termites – they damage
cassava stems and roots
late or in the dry season.
They chew and eat stem
cuttings resulting in poor
growth, death and rot. In
older cassava plants
termites chew and enter
the stem which weakens
them and cause breaking.
GRASSHOPPERS
Grasshoppers – Adults are usually dark green with
yellow, black and orange markings on their
bodies and the nymphs are black with yellow
markings. The female lay their eggs just below
the surface of the soil under the shade of the
cassava tree. Eggs start to hatch at the
beginning of the main dry season. They feed on
cassava plants, chewing leaves and stems and
may cause defoliation and debark stem.
GRASSHOPPERS
FRUIT FLIES
The female which is yellow oviposits in the
stem tissue and upon hatching the yellowish
white larvae bore their way into the pith
region. Heavy attacks may cause retarding of
the growth and induced formation of lateral
shoots. This pest does not reduce yield but
rather reduce the quality of the propagation
material. Yield have been reduced from 4 up
to 33% when infected material were
planted.
FRUIT FLIES
LEAF CUTTING ANTS
This pest cuts semi-circular pieces of
leaves and sometimes remove the
buds and carry them back to their
nest. Outbreaks usually occur during
the first month of crop growth.
Insecticides are the most effective
means of control.
LEAF CUTTING ANTS
LACE BUGS
Lace bugs attack mainly during the dry
season and are severe during prolonged
droughts. Adults are grey and nymphs are
white both found on the underside of the
leaves. Damaged leaves have small yellow
spots that later turn reddish brown
resembling mite damage. The rate of
photosynthesis decreases and lower leaves
fall.
LACE BUGS
LACE BUG NYMPH
CUTWORMS
Surface Cutworms – The black cutworm feeds on
the basal part of the stem near the surface of the
soil. The larvae are greasy grey to brown with
faint lighter strips.
Climbing Cutworms – These climb the stem feeding
on the buds, foliage and stem causing the upper
part of the plant to wilt and die. The larvae is
dark grey to black with lateral yellow strips.
CUTWORMS
Subterranean cutworms – These remain in the
soil feeding on the roots and underground
parts of the stem. They cause damage to
young plants killing up to 50%.
Crickets – The black cricket or the mole cricket
causes most of the damage by cutting the
young shoots right after germination.
CUT WORMS
SCALE INSECTS
This pest can cause leaves to yellow and fall
out. When damage is severe, the stem is
completely covered with scales causing plant
growth to become stunted and stems may
dessicate causing plant mortality. Heaviest
outbreaks occur during the dry periods and
worsen during prolonged periods of
drought. Yield losses up to 20% have been
recorded.
SCALE INSECTS
SCALE INSECTS
WHITE
SCALE
INSECT
GALL MIDGES
Flies usually induce galls on cassava and
are generally found in the upper surface
of the leaf where they lay their eggs. The
larvae causes abnormal cell growth,
forming galls. The galls are yellowish
green to red in colour and when they
open the larvae can be seen inside.
Severe outbreaks usually retard growth.
GALL MIDGES
WHITEGRUBS
The grubs, whose adult stage is a beetle
attack the cuttings and roots of cassava
plants. Damages are characterized by the
destructions of the bark of the cuttings
and the presence of tunnels in the
woody part. These cuttings may rot and
die, young plants often suddenly wilt and
die.
WHITEGRUBS
WHITE GRUB
BEETLE
CASSAVA BACTERIAL BLIGHT
Cassava bacterial blight (Xanthomonas campestris,
pv. manihotis) – heavy attack causes defoliation
and stems and roots show brownish discoloration.
During periods of high humidity, bacterial
exudation is readily observed. This disease is
spread by infected cuttings and mechanically by
raindrops, use of contaminated farm tools,
chewing insects and movement of man and
animals through plantations. Yield loss range from
20-100%.
CASSAVA BACTERIAL BLIGHT
Cassava leaves showing typical Cassava plant showing shoots
angular, water-soaked spots on typical of the blight stage of
cassava bacterial blight
the lower surface.
CASSAVA BACTERIAL BLIGHT
SUPERELONGATION
Superelongation – there is
exaggerated elongation
of the stem internodes
and the stem is thin,
weak and longer. It may
be spread by using
infected cuttings.
AFRICAN MOSAIC DISEASE
African cassava mosaic disease (ACMD) – this
disease is spread by the whitefly and
infected cuttings and causes heavy yield
losses of up to 90%. Symptoms occur as
characteristic leaf mosaic patterns that
affect discrete areas and are determined at
an early stage of leaf development. Young
plants have yellowish areas, frequent leaf
deformation and reduced young leaf size.
AFRICAN MOSAIC DISEASE
BACTERIAL STEM ROT
Bacterial stem rot – this is characterized by a
pungent, soft stem rot and discoloration of
the woody portion of the plant. Shoots of
infected plants often wilt and die. Diseased
cuttings used for planting do not always
germinate and if they do, they are stunted
with a small number of thick roots.
BACTERIAL STEM ROT
INTERNAL ROTTING
INTERNAL ROTTING
TUBER ROTTING
TUBER ROT – This can
be caused by
pathogens that can
be present in the
soil or water. The
predisposing factors
are heavy soil,
excessive flooding
and poor drainage.
ANTHRACNOSE
Anthracnose (Colletotrichum spp. or
Glomerella spp.) – this disease appears
after long periods of rainfall and is
characterized by the presence of leaf
spots. There is partial or total necrosis of
the affected tissue. The pathogen attack
the green stem producing cankers and
dieback.
ANTHRACNOSE
BROWN LEAF SPOT
Brown leaf spot (Cercosoridium henningsii) –
symptoms are restricted to older leaves.
Brownish round spots with definite borders
appear on the upper leaf surface and on
the lower surface there are brownish-grey
spots. Infected leaves become yellow and
eventually drop. In wet areas the disease
may cause yield reduction of up to 20%.
BROWN LEAF SPOT
BROWN STREAK DISEASE
Symptoms of cassava brown streak disease on the
leaves:
• It appear as patches of yellow areas mixed with
normal green colour commonly referred to as
chlorosis.
• It produces characteristic yellow or necrotic vein
banding on leaves which may enlarge and join to
form comparatively large yellow or necrotic
patches
• The infected leaves do not become distorted in
shape as occurs with leaves infected by Cassava
mosaic disease
BROWN STREAK DISEASE
BROWN STREAK DISEASE
Symptoms on cassava stem –
• The disease appears as dark brown “streaks” and “spots”
on stems, with dead spots on leaf scars
• These streaks are most prominent on upper, green
portions of the stem
• “Streaks” may appear as scratch-like wounds on stems
• The diseased plants may show shoot tip death, which
may progress into cassava stem die-back
• In severe cases there may be leaf drying and shoot dieback.
BROWN STREAK DISEASE
BROWN STREAK DISEASE
Symptoms on cassava tubers –
• The disease may cause cracks and discoloration in the
storage roots and often causes root constriction and
malformation.
• The harvested roots have corky, yellow-brown necrotic
spots and root rot becomes evident.
• In the roots of a susceptible variety, the disease causes a
dry, hard rot which is irregular, yellow blotchy chlorosis.
• Necrosis is most pronounced in the edges of the root
when the root/tuber is cut across with a knife.
BROWN STREAK DISEASE
BROWN STREAK DISEASE
FROG SKIN DISEASE
This disease may cause losses from 50100%. It is characterized by the
thickening of the root epidermis, thin
tubers, the irregular swelling and easy
breakage of the periderm and thick,
cracked, wrinkled skin. This disease is
transmitted by cuttings and grafting.
FROG SKIN DISEASE
WITCHES’ BROOM
Plants affected generally produce up to 80% less than
healthy plants.
Symptoms include –
1. Plants that show stunting and excessive proliferation of
branches, shoots have small leaves and shortened
internodes without showing distortion or chlorosis.
2. Proliferation of shoots from the cuttings and are
generally weak but grow without showing any visible
symptoms.
3. Only a few weak and stunted shoots actually germinate
from the cuttings.
CASSAVA ASH
This disease is common during the dry
season being more prevalent on lower
leaves. It is characterized by the presence
of yellowish leaf spots and a white
mycelium growing on the leaf’s surface.
This disease is however considered to be
of minor importance in yield reduction.
CASSAVA ASH
RUST
This disease is characterized by the
formation of pustules on the veins,
petioles or green stems. These pustules
are orange or light to dark brown
depending upon the age of the pustule
or the type of fungal fructification. They
usually induce distortion of the affected
plant.
RUST
CONCENTRIC-RING SPOT
This disease appears during the rainy
season and causes severe
defoliation, dieback or total death of
the plant. The spots are large and
brown with no well-defined margins.
CONCENTRIC-RING SPOT
BACTERIAL STEMGALL
The symptoms of this disease appear on
the lower part of the stem and in plants
older than seven months. They are
characterized by galls on the stem nodes.
Affected plants may be stunted and may
experience dieback.
WHITE LEAF SPOT
Lesions are small, circular to angular,
white or yellowish brown sunken
from both sides, reducing the
thickness of the normal leaf blade.
THE MOST IMPORTANT CASSAVA PESTS AND
DISEASES IN TRINIDAD AND TOBAGO
1.
2.
3.
4.
5.
6.
7.
CASSAVA BACTERIAL BLIGHT.
THRIPS AND MITES.
SUPERELONGATION.
STEM ROTS.
CYDNID BUG.
SHOOT FLY.
TUBER ROTS.
SUPERELONGATION
SUPERELONGATION
SUPERELONGATION
SUPERELONGATION, THRIPS AND
MITES
THRIPS
THRIPS DAMAGE
THRIPS
SHOOT FLY
ANTHRACNOSE
HORNWORM
BUGS
VIRUS?
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