Agriculture

1. Ryan V. Rasgo
Extension Officer, DA-RFO 6

2. DISEASE TRIANGLE Concept
DISEASE

4.  there are 78 diseases of corn broken
down into 6 bacterial, 54 fungal, 9
nematodal and 9 viral diseases
(Tangonan, 1999) in the Philippines

5. 1. Bacteria
 Single-cell
 Binary fission
 Bacterial ooze

6. 2. Fungus
 Multi-cellular
 Asexual/Sexual
Reproduction
(fragmentation,
budding, fission)

7. 3. Nematodes
 Microscopic worms
(roundworms)
 Sexual/Self-
fertilizing
 Soil-borne

8. 4. Viruses
 RNA/DNA particles
 Intercellular
parasite
 Replicates on living
host
 Transmitted by
vectors

9. Corn Downy Mildew
Occurs during seedling to tasseling
stages
Causal organisms:
Peronosclerospora
philippinensis, P. Sorghi, P.
maydis, P. sacchari, Sclerospora
graminicola, Sclerophthora
rayssaiae var. zee

10. Symptoms
• Infected plants show white-
yellow streaks first at the base
then on entire leaf blade
• Whitish growth on both sides
of the streaks when humidity
is high
• Chlorotic areas on severely
infected plants
• Dwarfing with reduced
elongation of the internodes
• Ears and tassels poorly
formed in advance stages of
the disease
Photo: http://www.fao.org
Downy Mildew

11. Control measures
• Planting of resistant cultivars
• Seed treatment with fungicide-
redomil (apron)
• Destroy alternate hosts
Photo: http://www.fao.org
Downy Mildew

12. Common Name: Banded leaf and sheath blight
Causal organism: Rhizoctonia solani, a soil borne
fungus
Symptoms
• Irregular blotches on leaves,
stalks and ears
• Patches with straw-colored
centers and distinct brown
borders
• Irregular light to dark-brown
fungus lumps known as
sclerotial bodies (less than
1mm) on dead tissues

13. Common Name: Banded leaf and sheath blight
Causal organism: Rhizoctonia solani, a soil borne
fungus
Control measures
• Deep-plowing to bury
sclerotia
• Avoid planting cultivars with
very low ear placement
• Remove leafsheath above the
infected portion below the
earshoot
• In seed production field,
spray with fungicides
Photo: http://gallery.cimmyt.org

14. Common Name: Northern leaf blight
Causal organisms: Setosphaeria turcica,
Helminthosporium turcicum
Symptoms
• Long, elliptical, grayish green
spots or lesions on leaves, 20
mm long and 5 mm wide
• Premature drying of leaves at
early growth stage
• Blackish tiny spots on dead
leaf areas Photo: http://www.ent.iastate.edu

15. Common Name: Northern leaf blight
Causal organisms: Setosphaeria turcica,
Helminthosporium turcicum
Control measures
• Planting resistant cultivars
• In seed production fields,
spray with fungicides
Photo: http://www.ent.iastate.edu
Photo: http://www.ontariocorn.org

16. Helminthosporium maydis=
Cochliobolus heterostrophus (Drechsler) Drechsler
Southern Leaf Blight
Symptoms
• Small to large, tan to
brown, elongated or
oval lesions on leaves
• Lesions may coalesce
to form large blighted
areas that cover the
entire leaf blade

17. Control:
•Destroying or burying crop
residues
•Host-Plant Resistance
• Spraying fungicides if used as
seed production
Helminthosporium maydis=
Cochliobolus heterostrophus (Drechsler) Drechsler
Southern Leaf Blight

18. Brown Spot Common Name: Brown spot
Causal organism: Fungus
(Physoderma maydis)
Symptoms
• Young lesions are very small,
oblong to round, yellowish spots
which turn chocolate brown and
coalesce to form irregular, angular
blotches
• Bigger lesions generally occur in
bands across the leaf blade

19. Photo: http://www.public.iastate.edu
Control measures
• Plant resistant cultivars
• Practice deep plowing
• Deleafing
Common Name: Brown spot
Causal organism: Fungus (Physoderma
maydis)
Brown Spot

20. Corn Rusts
Puccinia polysora
Southern rust
Puccinia sorghi
Common rust

21. Common Name: Leaf rust
Causal organism: Puccina polysora
Undrew.
Symptoms
• Small and circular brown
rusty pustules or blister on
upper and lower surface of
leaves
• Premature drying of leaves
Control measures
• Planting resistant cultivars
• In seed production fields,
spray
with fungicides

22. Common Name: Pythium stalk rot
Causal organism: Pythium spp., soil-borne fungi
Symptoms
• Brown, soft and water-
soaked areas at the based
of the stalk, just above the
soil line
• Lodging of the affected
portion which maybe
twisted or distorted, but
remain green and turgid
• White, cottony mycelium
of the fungus on the
surface of the lesions
Control measures
• Plant resistant cultivars
• Provide good drainage
• Avoid waterlogged areas
Photo: http://www.ctahr.hawaii.edu

23. Common Name: Fusarium stalk rot
Causal organisms: Fusarium species particularly
F. moniliforme
Symptoms
• Sudden death of the plants
before maturity
• Whitish-pink to salmon
discoloration of the pith
• Softening of the affected
stalk which easily get
compressed and crushed
when pinched
Control measures
• Reduce stress factors on the
plant
• Avoid root and stalk injury
• Provide good drainage

24. Common Name: Gibberella stalk rot
Causal organisms: Fungus (Gibberella zeae)
Symptoms
• Reddish coloration starting
from the tip of the ear which
progress down to the ear
• Presence of numerous black
perithecia at the tip of the
outer husk
Control measures
• Plant resistant cultivars

25. Bacterial Stalk Rot
Caused by a bacterium
Erwinia chrysanthemi
pv. zeae
(Sabet 1954) Victoria et al.
1975
SIMILARITIES TO
OTHER SPECIES
Pythium stalk rot
[Pythium
aphanidermatum]
causes similar
symptoms on maize;
to avoid confusion,
the causal agent
should be isolated and
identified. Bacterial
stalk rot may be
accompanied by a foul
odor.

26. Common Name: Bacterial stalk rot
Causal organisms: Erwinia crysanthemi
var zeae
(E. carotovora var zeae )
Symptoms
• Stalk rot starting from the base
progressing upward and eventually
causing wilting of leaves
• Infected inner tissues of older plants
deteriorate and become soft with foul
odor, and later dry, easily disjointed
fibers
• Plants infected and post-detasseling
stage
may remain standing but exhibit wilting
of the leaves
• Wilted leaves at whorl stage can
be easily pulled from the growing point
Photo: http://www.extension.iastate.ed

27. Control measures
• Planting resistant cultivars
• Provide adequate control of borers
• Avoid planting in fields with poor
drainage
Photo: http://www.extension.iastate.edu
• Chlorination of irrigation water,
soil drench with Calcium hydroxide
• Avoid high dose of N fertilizer

28. Corn Smut
Control
Removing maize plants infected with head smut (before
the smuts rupture)
caused by
Ustilago maydis
(DC.) Corda

29. Diplodia ear
rot
Fusarium ear rot
Aspergillus flavus
Ear Rots

30. Common Name: Fusarium ear rot
Causal organisms: Fusarium species particularly
F. moniliforme
Symptoms
• Infected kernels are
scattered randomly on the
entire ear
• Whitish pink to lavender
fungal growth on kernels and
or silks
• “Starbust” symptom
characterized by white
streaks radiating from the
point of silk attachment at the
cap of the kernel or from the
base may also be exhibited
Photo: http://www.agroatlas.ru

31. Common Name: Fusarium ear rot
Causal organisms: Fusarium species particularly
F. moniliforme
Control measures
• Avoid highly susceptible
cultivars
• Control ear infesting insects
Photo: http://www.agroatlas.ru

32. Corn Mosaic
Sugarcane Mosaic virus (SCMV)

33. Maize Dwarf Mosaic Virus (MDMV)
Common Name: Maize Dwarf Mosaic Virus (MDMV)/
Sugarcane Mosaic
Causal organisms: Strain H of SCMV(SCMV-H) and strains
A&B of MDMV (MDMV-A & MDMV-B)

34. Photo: http://extension.missouri.edu
Photo: http://www.agroatlas.ru
Symptoms
• Narrow pale yellow streaks
on leaves parallel to leaf vein
• Pale area later becomes
diffused upon a paler green
background
• Base of infected leaves
produces alternating broad
streaks of green and pale
green areas
Control measures
• Planting resistant cultivars
• Plant early and promptly
remove infected plants early
in the season
4.2

35. Maize Rough Dwarf Virus (MRDV)

36. Purple Sheath Stain
Disease Lesion Mimic
Others (not a disease)

37. That’s all folks
Good Day!!!!