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.
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.