The crop may suffer from a number of bacterial and fungal diseases which are described below:
Northern Leaf Blight (Exserohilum turcicum, Helminthosporium turcicum) :
In Sikkim, it is the most important disease.
Symptoms: Elliptical, grayish-green or tan lesions 1 to 6 inches
long with smooth margins. During damp weather, greenish-black fungal sporulation
is produced in lesions. Older leaves are affected first. Severely affected leaves
can be killed when lesions coalesce.
The fungus survives in undecomposed corn residue. Spores are spread by
air currents. Spores germinate and infect leaves during wet weather with moderate
(18° to 27°C) temperatures. Severe yield loss can occur when leaves become blighted
during early grain fill. More severe in fields with corn following corn under reduced
tillage. Also infects sorghum.
Control Measures: Use resistant hybrids, especially when grown
without rotation under conservation tillage. Hybrids with either single-gene (Ht)
or multiple-gene resistance are available. Rotate away from corn and sorghum for
one to two years.
Southern Leaf Blight (Helminthosporium maydis): Like southern leaf
blight it is also an important disease of maize.
Symptoms: Elliptical, tan to light brown, small lesions (1/8 to
1/4 inch by 1/4 to 3/4 inch), often with somewhat parallel sides, and sometimes
with a brown border. Older leaves are affected first; severely affected leaves can
be killed when lesions coalesce.
Disease Cycle: The fungus survives in corn residue. Spores are
spread by air currents. Spores germinate and infect leaves during warm (20° to 32°C),
wet weather. More severe in fields with corn following corn under reduced tillage.
Greatest yield loss can occur when leaves become blighted during early grain fill.
Control Measures: Plant resistant hybrids, especially when grown
without rotation under reduced tillage. Rotate away from corn for one to two years.
Seedling blight (Diplodia maydis):
The young seedlings get infected by various fungi and they start drying.
- Uprooting and burning of infected plants as
soon as detected in the field.
- Clean cultivation is another method to check
- It can also be controlled by seed treatment
and soil application with Trichoderma formulations @ 2% and 5% respectively.
Soft rot (Erwinia carotovora var. zeae): This is a bacterial disease.
The bacteria dissolve middle lamella of the cells and disintegrate the whole tissues. The symptom appears first at collar region and spread upward. Pale white ooze out
may be seen in the collar region with foul smell.
Control Measure: The disease spread quickly in poorly drained soil
during hot weather period and during high humidity. Therefore, provide an efficient drainage.
In severe case, spray antibiotic, Streptocyclin, at the base of the plant.
Stalk rot (Cephalosporium sp.): The fungi which cause stalk rot
is a very week parasite, enter into plants through injuries/wounds by mechanical
operations and by insect injury.
- Avoid mechanical injury to plants.
- Control stem borer/stalk borer.
- Wherever possible grow resistant varieties.
Charcoal rot (Macrophomina phaseoli): The disease appears after
tasselling. The affected part becomes dry and brittle having innumerable pycnidia.
The disease may be controlled by adopting a long term rotation of 4 to 6 years duration, roughing out diseased plant and by growing crop in poorly drained light textured soil.
Leaf spot (Helminthosporium carbonum):
Small water soaked elliptical lesions or spots are formed on the leaf blade which may be extended into the leaf sheath. It is light brown and finally turns to straw colour when the tissue dries out.
a) Rouging of infected plants as soon as it is detected in the field.
b) Use of resistant variety.
Smut (Ustilaginoidea virens):
It appears in the ears and tassels by which they are partially transformed into galls.
Control Measure: The disease may be controlled by applying lower dose of nitrogen, uprooting of smut affected plant and adopting long duration crop rotation.
There are some pathogens that affect the cob at all stages including storage. These Cephalosporium sp. Infect the grains by showing a characteristics feature of fan- like streaks on the stigmatic side of the endosperm
and 5 to 10 percent grains in each cob are found to be affected by this pathogen, Rhizoctonia sp. and Curvularia sp. Fusarium sp. are seen on the cobs during storage conditions if the cobs are moist Aspergillus sp. are also common on cobs in the
There are many insect pests which attack the crop and cause a considerable damage to the crop if not controlled at an appropriate time. Following are the important insect pests that need due care.
Stem borer (Chilo partellus):
Nature of attack: It attacks the crop right from seedling stage to the older plants. In case of seedling the insect makes dead heart while in older plants the larvae bore into the stalk through apex and makes the tunnel that result into a considerable reduction in the grain yield. The cobs are also attacked by the borer and grains are damaged.
- Hand-picking or light trapping of adult moths
and collection of their eggs for destruction.
- Burning of stubbles and trash which harbour
borers and acts as a source of infestation for the next crop.
- Use of higher seed rate to compensate for the
young infested plants that are pulled out and destroyed.
- Changing the sowing and harvesting timings
reduce infestation, an early sowing will make the vulnerable seedlings unavailable
to the pests when they are born and it will need early harvesting before adults
emerge thereby preventing spread of the pest to the next crop.
- Prophylactic spray of Neem oil 2 to 3% before
and after knee high stage will minimize the incidence. In case of emergency, apply
2 to 3 granules of Thimet or Furadon on the whorl of maize plants.
- Growing resistant varieties like, Antigua Gr.
I, Jawahar composite, Hybrid Ganga 5, Colombian Hybrid H 207 etc.
- Trichogramma minutum may be employed as egg
- Apanteles flavipes and Bracon brevicornis is
used as larval parasitoid.
- The lady bird beetles, Coccinella septempunctata
and Menochilus sexmaculata have been recorded predating on early stages of the larvae
of this pest.
Shoot fly and Aphid:
It can be controlled by the following measures:
- There should be no water logging in the field.
- Use of neemgold, nimbicidine, neem cake etc. gives good results.
Besides, grain weevil and grain moth are the important storage pests which are carried
over from infested field. Dry cob in hot sunshine.
Note: For the control of pests we can use bio-pesticide like neemgold, nimbicidine, neem cake etc.
Non-insect pests: Jungle pigeon and a long tailed blue bird are
the major threat to farmers. They pick away germinating seeds/seedlings during March-April
and damage matured cob before harvest.
The attack of crows can be effectively reduced by using
scare-crow placing at different places in the maize field.
Rats: The rats damage the maize right from grain formation stage
to harvest. it is also serious problem in storage. The attack of rats can be reduced by using trap and poison baits.