Credits: Biovision-Infonet
(c) Cimmyt
A serious new disease of maize appeared in the farmers’ fields in eastern Africa in 2011. Called maize lethal necrosis (MLN; or corn lethal necrosis, CLN), it can devastate maize crops. Infection rates and damage can be very high, seriously affecting yields and sometimes causing complete loss of the crop.
The disease is difficult to control for two reasons:
1.It is caused by a combination of two viruses that are difficult to differentiate individually based on visual symptoms.
2.The insects that transmit the disease-causing viruses may be carried by wind over long distances.
MLND is mainly spread by a vector, transmitting the disease from plant to plant and field to field. The most common vectors are maize thrips, rootworms, leaf beetles and aphids. Hot spots appear to be places where maize is being grown continuously.
In Africa, the disease was first reported in Kenya, (South Rift Valley – Bomet and Naivasha districts) in September 2011 although its extent at that point suggested that the disease has been present for some time. According to the Kenyan Ministry of Agriculture, two percent of the maize harvest was affected in 2012. MLND has also spread rapidly into Tanzania, Uganda and South Sudan in the meantime.
National and global research and extension organizations, laboratories, and seed companies are working together to control the spread of the disease and to develop and deploy disease-resistant maize varieties for the farmers as soon as possible.
Currently, all maize varieties at every stage appear to be susceptible to the disease. The symptoms include: – Mild to severe mottling on the leaves, usually starting from the base of young leaves in the whorl and extending upwards toward the leaf tips. – Stunting and premature aging of the plants. – Dying (known as ‘necrosis’) of the leaf margins that progresses to the mid-rib and eventually the entire leaf. – Necrosisof young leaves in the whorl before expansion, leading to a symptom known as ‘dead heart’ and eventually plant death
What to do:
Prevention:
- MLN does not occur on crops other than maize; so avoid growing maize after maize. Diversify your farm enterprise by planting different crops each season.
- Do not plant a new maize crop near an infected field. Wind-blown insect vectors can transmit the disease from the infected field to the new crop
- Plant maize at the onset of the main rainy season, rather than during the short rain season; this creates a break between maize crops and interrupts the disease cycle
- Weed fields regularly to eliminate alternate hosts for insect vectors. Use maize varieties that are resistant to MLN
Control:
- Immediately remove diseased plants from your fields. You can feed the leaves to livestock
- Do not allow humans or animals to eat infected ears or grains, which may contain secondary fungal infections and harmful mycotoxins. Burn infected ears and grains.