Beware, lethal maize disease is still on prowl

What you need to know:

  • Although MLND has ability to attack maize irrespective of growth stage, the severity of disease depends on stage of crop growth at the time of attack.
  • The symptoms are observed on plants as early as two weeks after germination up to cob formation stage and even during storage of infected grains. Leaves turn bright yellow starting with upper leaves.
  • Partial grain or no grain filling formed while the grains formed become moldy with brown discoloration. Insect vectors are observed on the infected plants including thrips, aphids and stalk borers.

Farmers have reported signs of the much dreaded Maize Lethal Necrosis Disease (MLND) and it is crucial that we revisit this subject.

MLND is currently the single most serious threat to food security in Kenya.

It was first reported in Kenya in September 2011 in the low altitude zones of Bomet before spreading to Sotik, Chepalungu, Narok South, Narok North and Naivasha.

What causes this disease?

The lethal necrosis disease involves synergism between two viruses namely Maize Chlorotic Mottle Virus (MCMV), and any of several potyviruses including: Sugar Cane Mosaic Virus (SCMV), Wheat Streak Mosaic Virus (WSMV) and Maize Dwarf Mosaic Virus (MDMV). The virus is spread by insect vectors.

Although MLND has ability to attack maize irrespective of growth stage, the severity of disease depends on stage of crop growth at the time of attack.

Infestation at early stages of crop growth produces severe effects on yields compared to late entry which allow plant to partially escape. Insect pests are the major transmitters with leaf hoppers, aphids and maize thrips being the main vectors which transmit the disease mechanically.

High colonies or masses of aphids are noted on maize leaves particularly in the funnel. Thrips can be observed inside the maize plant funnel. MCMV can be introduced into maize growing areas through seeds.

SYMPTOMS

Affected plants show symptoms on all above ground parts of the plant (tassels, leaves, stem and cobs).

The symptoms are observed on plants as early as two weeks after germination up to cob formation stage and even during storage of infected grains.
Leaves turn bright yellow starting with upper leaves.

There is chlorosis and mottling of leaves, usually starting from the base of the young leaves and extending upwards toward the leaf tips.
Dwarfing and premature aging of plants.

Necrosis of the inner parts, leading to ultimate death of the entire field.

Cob husks appear mature and turn brown while the grains inside are still milky and the rest of plant is green.

Partial grain or no grain filling formed while the grains formed become mouldy with brown discoloration.

Insect vectors are observed on the infected plants including thrips, aphids and stalk borers.

SUGGESTED SOLUTIONS

Design and enforce a maize closed season in all regions.

Design and implement a crop rotation schedules for all regions.
Maintain field sanitation removal of alternative hosts plants.

Consider altitude, rainfall, temperatures, the soil type and nutrient levels before selecting a maize variety for planting.

Early planting should be a must, not an option.

Pesticide applications on seed and foliar for vector control. Spray against the insect vectors as soon as they are noted to avoid further spread to other crops.

Rouging and destroying affected plants in the field. It is advisable to spray against vectors before rouging to kill the vectors that before the infect new plants.

Observe phytosanitary regulation import regulations.

Prof Paul Kimurto and Lilian Jeptanui, Egerton University.