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Maize chlorotic mottle virus together with a potyvirus ICTV species: Machlomovirus zeae (MCMV), with a potyvirus such as sugarcane mosaic virus (Potyvirus sacchari) · formerly or also: MCMV + SCMV
Maize lethal necrosis is caused when maize is infected by maize chlorotic mottle virus together with a second virus from the potyvirus group, most often sugarcane mosaic virus. Together they kill plants that either virus alone would only weaken. After it appeared in Kenya in 2011, it spread across East Africa within a few years and caused severe losses. There is no cure; control combines tolerant hybrids, clean seed, a maize-free period and vector management.
Maize lethal necrosis is caused by Maize chlorotic mottle virus together with a potyvirus, a virus disease caused by two viruses together (synergistic co-infection) (order Tolivirales (MCMV), family Tombusviridae (MCMV); Potyviridae (partner virus)).
Older or alternative scientific names: MCMV + SCMV.
First reported in the Americas (Peru in the 1970s and the US Corn Belt in 1976 as 'corn lethal necrosis'). In 2011 it appeared in Kenya and spread to Tanzania, Uganda, Rwanda, the Democratic Republic of Congo, Ethiopia and South Sudan. It has also been reported in parts of East Asia and South America. Several countries regulate maize seed for MCMV.
| Region | Status |
|---|---|
| East and Central Africa | Established since 2011-2014 |
| Americas | Reported in the US, Mexico, Peru, Ecuador and others |
| East Asia | Reported in parts of China and Taiwan |
| Other regions | Absent from most; regulated on seed |
Maize chlorotic mottle virus is a small, very stable RNA virus spread by thrips and beetles, through soil and crop residues, and at low rates in seed. Sugarcane mosaic virus and other potyviruses are spread by aphids in seconds of probing (non-persistent). Laboratory tests (ELISA or PCR) identify both viruses.
| Crop stage | What you see |
|---|---|
| Seedling to early vegetative | Fine yellow streaks and chlorotic mottling of young leaves, starting at the base of the leaves. |
| Mid vegetative to tasselling | Leaves dry from the margins inward ('necrosis'); the central whorl dies (dead heart); plants are stunted and may die before tasselling. |
| Ear formation and grain fill | Small, deformed, partly filled or barren ears; husks dry early; cobs rot; whole fields can look scorched. |
Continuous maize cropping keeps both viruses in the field. Thrips and beetles carry MCMV from infected to healthy plants, the virus persists in soil and residues, and a small proportion of seed from infected plants carries it to new areas. Aphids spread the potyvirus partner from grasses and other crops. When both viruses infect the same plant, they multiply far more than either alone, causing necrosis.
| Stage | Duration | Notes |
|---|---|---|
| Introduction | At planting or early growth | Contaminated seed, residues, soil or vectors from nearby fields. |
| Vector transmission | Through the season | Thrips and beetles (MCMV); aphids (potyviruses). |
| Co-infection and synergy | Symptoms within about 2-4 weeks | Earlier infection gives worse disease. |
| Persistence | Between seasons | In residues, soil, volunteers and grasses. |
Warm, dry conditions favour thrips and aphid vectors and therefore spread; the disease is severe across a wide range of altitudes in East Africa.
Spread continues wherever maize is grown continuously.
Continuous or overlapping maize planting (two or more seasons a year with no break), use of recycled or uncertified seed, high thrips and aphid populations, and nearby infected fields and grasses.
There is no economic threshold: once both viruses are present, losses depend on how early infection occurs, and infected plants cannot be cured. Prevention and area-wide measures are applied before planting.
Yield losses of 30-100% have been reported in affected fields in East Africa; during the first years of the epidemic, national losses in Kenya were estimated at around a fifth of the maize harvest in some seasons.
Control works best as a sequence: prevent, monitor, then act only when a threshold or a risk forecast says so, using the least disruptive option that works.
No chemical controls the viruses. Seed treatments and foliar sprays against thrips and aphids in early growth can reduce spread as part of an integrated programme. What is registered differs by country and changes over time; follow the label and your local plant-protection authority.
| Scheme | Group | Mode of action | Notes |
|---|---|---|---|
| IRAC | 4A | Nicotinic acetylcholine receptor competitive modulators (neonicotinoids), seed treatment against vectors | Early-season vector suppression. |
| IRAC | 5 | Nicotinic acetylcholine receptor allosteric modulators, site I (spinosyns), against thrips | Used where registered. |
Maize is the main host. Maize chlorotic mottle virus also infects sorghum, millets and several grasses; the potyvirus partners infect sugarcane, sorghum, wheat and many grasses, which act as reservoirs.
How to grow the crop well is the first line of defence. Laisha's free grow guides cover each crop from sowing to harvest:
Written by Laisha from the sources above, in its own words. This page is general reference, not a prescription: confirm identification locally and follow the label and your plant-protection authority.