Maize Lethal Necrosis disease, plant a different crop this year
Farmers whose maize was affected by
Maize lethal Necrosis disease are advised to change to another crop
during the current season because pests carrying the disease are still
in the soil and will reinfect any maize crop planted on the same land
this year.
The disease first shows in the upper leaves of the maize plant.
One reason why the Maize Lethal Necrosis
Disease (MLND) is spreading to new areas in the country is that many
farmers are not willing to practise crop rotation by planting other
crops that do not belong to the grass family. The fact that maize is the
main food crop in the country is one reason why many farmers find it
difficult to plant other crops that are not affected by the disease.
The disease is spread by crop pests such
as thrips, which remain in the soil after the maize is harvested.
Immediately the maize is planted, the pests still in the soil will
attack and infect the maize that is germinating. Although the disease is
not soil borne, the pests in the soil are carriers of the disease and
will transmit it to the next maize crop if farmers plant maize in the
same shamba that was affected last year. This is one of the reasons why
it has become difficult to break the disease cycle in all maize growing
areas in the country. Below are a few measures on how to identify the
disease and ways to control it:
How to identify the disease
The MLND disease is caused by a
combination of two viruses; the Maize Chlorotic Mottle Virus (MCMV) and
the Sugarcane Mosaic Virus (SCMV). Since viruses can only survive on
living plant material, new research findings show that the disease is
able to survive in the soil through pests mainly thrips, which undergo
part of their lifecycle in the soil. The main mode of transmission of
the disease is through insect pests, which transfer it from one crop to
the other. Farmers can identify the disease by looking for the following
symptoms:
● When the maize is at knee height, the
upper maize leaves start yellowing and later dry up, turning brown in
colour from the mid-rib towards the edge of the leaf (leaf margin).
● The stem and the nodes turn brown.
● In some cases, the maize produces many shoots (excessive tillering).
● At the beginning, it is only the upper leaves that appear brown in colour.
● As the maize matures, the cob shrinks and does not put on any grains.
● In some cases the maize plant may appear stunted.
How to control the Maize Lethal Necrosis disease
As research into MLND continues,
scientists have found new facts about the disease and how farmers can
control it. Below are important measures that farmers can take to
eradicate the disease in their farms and also reduce its spread to new
areas.
● So far, the disease has no cure.
Therefore farmers should be wary of people promising to sell them
chemicals that can control the disease.
●The situation in most growing areas is
that farmers plant maize at different times such that we have maize at
different stages of growth; when this happens the disease is easily
transmitted from the older crop to the younger maize, which leads to a
continuous infection of maize and persistence of the disease in the
affected areas and even its spread to new areas. Farmers should avoid
this practice.
● Crop rotation has been identified as
one of the options that can help reduce the incidence of the disease
considerably. Crop rotation or planting of alternative crops that are
not affected by the disease such as beans, Irish potatoes, sweet
potatoes, sorghum peas, bananas for two or three seasons can help break
the disease cycle and prevent its spread to new areas.
● Farmers are advised to use only
certified maize seed. At present all maize seed in the country has been
fortified with stronger pesticides, but research shows that this is not
helping either as the virus-carrying pests still manage to survive and
attack the next crop. Farmers in areas not affected are advised to
continue spraying their maize with plant extracts or biopesticides to
control pests such as stemborers, thrips, aphids and maize beetles which
are the main vectors of the disease.
● Farmers are advised to inspect their
crops ever day for signs of the disease. If they notice any of the signs
mentioned above, they should uproot the infected maize stalk and bury
it to prevent the disease from spreading to the rest of the maize.
● Infected maize can be fed to animals
except the rotten maize; farmers have to protect the animals from
mycotoxins that can cause poisoning. Animals and people who consume
animal products such as milk and meat can be affected by aflatoxin
poisoning.
● Ensure that your maize field is clean
and free of weeds that act as hosts to insect pests. The pests carry the
disease-causing viruses and transfer the disease from plant to plant.
Plants in the grass family such as Napier grass have been found to be
the main reservoirs of the disease. Napier grass or other pasture
grasses near maize fields are partly responsible for passing the disease
to any maize crop planted in the vicinity.
● Destroy all volunteer maize, weeds or
crops in any field where you intend to plant maize, as they may harbor
insect pests that can transfer the disease to your new maize crop.
● Dry maize stocks or composited material cannot transmit the disease and is therefore safe for animal feed. Farmers can also use the affected maize as silage as long as the rotten part of the maize is cut off and discarded or buried to prevent animals from eating it
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