Highlights on MLN management

1. Dr. Suresh, L.M.
Maize Pathology Lead – Sub saharan Africa
CIMMYT – Kenya
Nairobi
‘MLN Disease and its
Management’
Global Maize Program

2. History of MLN
• First report of viral co-infection (MCMV+MDMV) leading to MLN was reported in
Kansas and Nebraska (USA) in 1976 (Niblett). Disease was termed Corn Lethal
Necrosis (CLN)
• In the 1990s, co-infection of MCMV+MMV was reported to cause extensive
damage to temperate seed production in Hawai.
• First report of MLN in Africa made in 2011 in Kenya (Wangai et al, 2012).
Causal agents identified to be MCMV and SCMV by tissue blot immuno-
assay and PCR.

3. MLN Disease Development
Vectors:
Presence of
aphids and
thrips
Environment:
Conditions
favoring
vectors and
disease
Susceptible
Germplasm
Virus: Either
individual or
compound

4. MCMVMCMV
Potyvirus
SCMV
MDMV
WSMV
MLNMLN
• Individual infection with mixture of viruses can also cause disease
• Typically, infection with one virus results in milder symptoms than MLN but
reaction depends on germplasm and viral strain.
Maize Lethal NecrosisMaize Lethal Necrosis

5. Why is the MLN devastating in EA?
• MCMV is new to the region
• Potentially new strains of SCMV/MDMV
• Widespread cultivation of susceptible germplasm
that has never been screened for MCMV
• Characterization of viral populations will reveal
identify of strains in the region.

6. Disease Symptoms
• Dying leaves, leading to premature plant death
• Failure to tassel and sterility in male plants
• Malformed or no ears
• Rotting cob

7. Symptoms of the disease
• Symptoms observed vary widely depending on;
-Germplasm
-Time of infection
-Prevailing environmental conditions
-Ratios of the viruses infecting the plant
• The symptoms can easily be confused with drought ,
micro- nutrient deficiency or stalk borer infestation

8. Symptoms in artificially inoculated maize plants in
screen house
MCMV SCMV

9. Early Symptoms
Mild mosaic and mottling Mild mosaic and mottling

10. Chlorosis and Mottling Diffuse mottling and chlorosis
Early MLN Symptoms

11. Severe chlorosis and leaf necrosis

12. Shortened internodes and severe chlorotic mottle

13. ‘Dead Heart’ symptoms

14. Premature drying of the husks

15. Poor or no grain filling

16. 16
VIRULANT PATHOGEN
SUSCEPTIBLE
HOST
CONGENIAL
ENVIRONMENT
TIME
DISEASE

17. Recommendation for prevention for disease spread

18. 18
SUCKING PESTS ROLE
Aphids
SuckingPests
Whitefly
Thrips
Transmits
Viruses

19. 19
Initial inoculum source
(Weed)
Vector – Transmits Virus
Rapid spread due to vector
movement and Host susceptibility Disease

20. 20
SeedSeed
SoilSoil
WaterWater
Market
Analysis
Pest /
Disease
Pest /
Disease
WeedWeed
NutritionNutrition
Healthy
Crop
INTEGRATED CROP MANAGEMENT

21. IPM
Integrated Pest Management

22. Over-the-Top
Over-the-Top
Over-the-Top
Under
Dose
Optimum
Dose
Over
Dose
Under
Dose
Optimum
Dose
Over
Dose

23. 1.Vehicles or machinery can introduce pathogens to production area from outside.
2.Vehicles can visit many places and agricultural area so wheels and car body can be contaminated by
pathogen
Precaution
1. Disinfect all vehicles and machinery before entering to our research /production area
2. If disinfection is not available, prepare parking lots isolated from
production area to prevent contamination. Red zone is allowed.
Risk:
Vehicle or agricultural machinery not disinfected

24. 1.All waste materials came from our GH/field area must be dumped at designated area only and
it should not throw away near facility or near walk way. Rain or people can carry pathogen and
this mechanism will cause disease again. If facility is poor without fence or less depth, plant sap
can overflow in rainy season and its sap can come to the field.
Precaution
1.Designate waste area far away from our field.
2.If it is not available, waste area will fenced and covered. Putting chemical or lime will stimulate
decomposing
2. Plant materials will bury or burn
Risk:
No waste designated area

25. MLN - infected MLN - free

26. Spread of Maize Lethal Necrosis (MLN) in
Eastern Africa
Country Year Reference
Kenya 2012 Wangai et al. (2012
Tanzania 2012 CIMMYT TF Report to Ministry of Agriculture,
Tanzania
Uganda 2012 G. Asea, Workshop (Nairobi; Feb 12-13, 2013)
Rwanda 2013 C. Ngabiyasonga, MLN Training Workshop (Nairobi;
2013)
DRC 2014 Kumar , FAO Regional Meeting, Nairobi, 2014
Ethiopia 2014 CIMMYT T-Force Report to Ministry of Agriculture,
Ethiopia
Next ????

27. MLN Transmission
Can be transmitted through:
1.Infected seed: reported transmission rates
•MCMV = 17/42,000 plants (0.04%)
•SCMV = 21/72,897 plants (0.03%)
2. Insects
•Aphids (Aphis gossypii, Myzus persicae )
•Corn Thrips(Frankliniella williamsi)
•Corn flea beetle (Chaetocnema pulicaria)
•Southern corn rootworm (Diabroticaundecimpunctata)
•Northern corn rootworm (D. lonicornis)
•Western corn rootworm (D. virgifera)
•Flea beetle (Systenafrontalis)
•Cereal leaf beetle (Oulemamelanopa)
3. Infected soil and plant debris
4. Mechanically

28. Corn thrips(Frankliniella williamsi)
DESCRIPTION OF THE PEST
Thrips are small insects, about 0.04 inch long. Immature thrips are wingless, whitish to yellowish in
color, and are most commonly found in whorls, tassels, ears, or on the underside of leaves. Adults
emerge continuously throughout the warm months. Adults and immatures may be found in corn at
any time during the growing season. Eggs are deposited in plant tissue and hatching occurs in about 5
days during the summer months; the immature stages take about 5 to 7 days to complete
development.
DAMAGE
Thrips are most noticeable and of greatest concern at two periods during the corn growing season: on
young seedling plants and a2t ear formation. On young seedlings their feeding makes the plants look
stunted. A common sign of a heavy thrips infestation is distorted leaves that turn brownish around
the edges and cup upward. Usually the plants will grow away from the problem, just as they outgrow
severe ragging resulting from wind damage. At ear formation, thrips and thrips injury to developing
kernels provides entry for infection by Fusarium spp. The actual thrips injury does little damage;
however, the ear rot diseases can be devastating.
Foliage-feeding thrips are effective predators on early-season spider mite infestations. Both adult and
immature thrips may be found in spider mite colonies feeding on spider mite eggs.

29. Corn thrips(Frankliniella williamsi)
MANAGEMENT
Treatment is usually not necessary on seedlings because plants recover from thrips injury.
Thrips are also beneficial at this time because of their role as mite predators. No threshold
has been established for damage from thrips at ear formation.
Biological Control
Minute pirate bugs (Orius tristicolor) play a major role in controlling thrips populations.
Cultural Control
Thrips populations tend to build up on weeds. Cultivating nearby weedy areas before corn
emerges will reduce the potential of a thrips problem when the weeds begin to dry out.
Cultivating weedy areas after corn emergence will increase thrips problems.

30. Corn flea beetle (Chaetocnema pulicaria
Adult
The corn flea beetle is a tiny pinhead-sized [1.6 mm) in length black insect with
thickened hind legs that enable it to leap considerable distances when disturbed.
Flea beetle eggs are deposited on weeds, corn, other cultivated crops, or in the soil
near the host plant. Larvae hatch, feed on the roots of plants, pupate in the soil and
emerge as adults
Damage
Badly damage plants appear frosted. The corn flea beetle feeds on corn leaves by
stripping away the top layer of plant tissue. This feeding leaves gray to brown lines or
"tracks" etched on the leaf surface. Heavily infested plants may appear gray as their
leaves shrivel and die.

31. Southern corn rootworm
(Diabroticaundecimpunctata)
larvae go through three instars, or developmental stages, that each lasts seven to ten
days.
The first instar is less than 1/8 inch in length. By the third instar larva can measure up to
1/2 inch in length.
After the larvae have completed the three developmental stages (instars), they will
pupate in the soil. The pupal stage is a dormant stage when no feeding takes place.
During this stage the larva is developing into an adult.

32. Flea beetle (Systenafrontalis)
Adult
Shiny black adults are nearly twice as long as With a hands lens and good light, you can see
the reddish head. Antennae are light colored near the head and dark near the tips. The
enlarged femur on the hind leg allows adults
Eggs
Pale yellow eggs are laid singly in the soil.
Larvae
Creamy white larvae have a brown head capsule, three pairs of jointed legs and can get
to just under a ½” at maturity. The last body segment has a fleshy upward projection that
has hairs on the tip

33. Cereal leaf beetle (Oulemamelanopa
Adult cereal leaf beetles are about 5-mm long and have metallic bluish-black heads
and elytraEggs are about 1-mm.
Eggs darken and turn black as hatching approaches. Larvae are yellowish-orange, but
this color is usually obscured by a layer of feces and mucus, giving them a shiny
appearance.
The larval stage passes in about two weeks. Mature larvae burrow into the ground to
pupate. Adults emerge about two weeks later, and will feed in small-grain and corn
fields for a short time before remaining inactive for most of the summer.
Adult feeding in small grains and corn has not been shown to be economically
significant and targeting adults

34. Corn Leaf Aphid
Rhopalosiphum maidis
Heavily infested corn leaves may wilt, curl, and show yellow patches of discoloration. When
tassels and silks are covered with honeydew, the pollination process may be disrupted.
The corn leaf aphid is a blue-green or gray, soft-bodied, spherical insect about the size of a
pinhead (1.6 mm) in length].
It has approximately 9 generations per year.
Female corn leaf aphids do not lay eggs, as do most other insects, but give birth to living
young.
These young, called nymphs, resemble the adults except that they are smaller and are sexually
immature.
Adults and nymphs can often be found clustered within the whorls or upper parts of corn
plants over isolated or wide areas of a field.

35. Integrated Management
of MLN
Awareness creation to all stakeholders
•Policy makers, researchers, extension staff, seed producers and
farmers.
Use clean seeds
•Use certified MLN- free seeds
•Grow nurseries in MLN free regions
•Regularly send samples for viral diagnostic verification
•Treat seed to provide early stage protection against vectors using:
 Clothianidin (Poncho),
 Thiamethoxam (Cruiser),
 Imidacloprid (Gaucho)
 Imidacloprid + thiodicarb (Aeris)

36. Integrated management of MLN cont.
Reduce inoculum level
• Maize- free “Break” seasons
• Early planting. Plant at the onset of main rainy season
• Crop rotation with non-host crops (legumes)
• Crop diversification
• Scout daily, record, rogue and destroy symptomatic plants
• Farm planning –plant first nurseries as far downwind as possible
• Weed fields regularly to control alternate weed hosts (esp. grassy weeds)

37. Integrated management of MLN cont.
Control spread of the virus
•Visit non- infected fields before visiting infected fields
•Use farm implements/ machinery in non- infected fields first and disinfect
after use.
•Avoid unnecessary people and machines in the field
Use MLN-resistant varieties.
•Screening of maize germplasm for MLN resistance at CIMMYT Naivasha
MLN facility
Control Vectors
•Scout and monitor daily for presence of potential vectors.
•Erect insect sticky traps
•Apply insecticides 1-2 weeks to control insect vectors
•Alternate insecticides molecules and chemistries to prevent insects from
developing resistance.
•Use appropriate chemical dosage and ensure proper coverage of the crop
when spraying.

38. Safety measures while applying
insecticides
Use proper PPE’s when spraying
•Gloves
•Spraying suits
•Closed shoes
•Spray early in the morning or in the evening when the wind is less
•Observe Re-entry periods (REI) after spraying.

39. Managing MLN in the maize seed increase/
Breeding Nursery at Kiboko
Maize free period:
At least one-month maize free period within 5km radius
Seed treatment
•Treat seed before planting using Clothianidin (Poncho)/ Thiamethoxam
(Cruiser)/ Imidacloprid (Gaucho)/ Imidacloprid + thiodicarb (Aeris)
Monitoring of vectors and viral diseases
•Daily monitor, record, rogue out, and destroy plants
•with viral symptoms
•Weekly monitor for vectors (thrips/aphids)
Purpose of seed increase and breeding nursery
• The source of seed for the next generation
• Beginning of large seed increases
• The source of seed to be distributed to large areas

40. Managing MLN in the maize seed increase/
Breeding Nursery at Kiboko
Control of vectors
•Spray the first spray immediately after germination and continue up to
physiological maturity
•Spray insecticides 1-2 weeks while changing their chemistries over
time.
Phytosanitary measures by KEPHIS
•Regular field inspections by KEPHIS
•Testing of seed for MLN by KEPHIS before distribution (DH facility and
nurseries)
Farm planning
•Planting early nurseries far downwind to avoid spread of vectors by
wind from old to younger crop
Control alternate hosts
•Fields weeded regularly

42. Thank you
for your
interest!