Cassava mosaic disease

young leaves show a patchwork of yellow and green on the SAME leaf — pale yellow or whitish blotches mixed with normal green, like paint that was never stirred. This 'mosaic' or mottling is the classic sign and shows up first on the youngest leaves at the growing tip.

the affected leaves twist, curl and pucker, the leaflets grow narrow, crinkled and much smaller than a healthy open cassava leaf, and the whole plant looks stunted and bushy. Below ground the storage roots stay few and thin — a plant sick from planting may give almost no harvest.

plants grown from infected cuttings show mosaic on every leaf from the first sprout; plants infected later by whiteflies show it only on the new top leaves while older lower leaves still look green. Turn a young top leaf over and you may see tiny white insects (whiteflies) underneath — shake the shoot and they lift off in a little white cloud.

nitrogen hunger, which turns a leaf evenly pale all over (usually the old lower leaves) with no green-and-yellow patchwork and no twisting; green-mite damage in the dry season, which is a fine dusty speckling and bronzing at the shoot tips, not big yellow blotches; or cassava brown streak disease — for that one cut a root open: brown streak rots the root brown and dry inside, while mosaic leaves the root small but not rotted.

check hardest in the first 2–3 months after planting — from the moment shoots sprout through early growth. These are the stages when the plant is most vulnerable and when early infection does the most damage. Start right at sprouting: plants from infected cuttings give themselves away with mosaic on their very first leaves.

at least once a week, walk a big 'W' across the field so you cover all four corners and the middle — not just the row beside the path. Make about 10 stops along the way.

look at the youngest top leaves of the plants for the yellow-green mosaic and twisting, and turn a top leaf over to check for whiteflies underneath. Shake the shoot — if a cloud of tiny white flies rises, whitefly pressure is high.

a virus gives no free pass, so there is no 'wait and see' count. The moment you find a single plant with mosaic, pull it out that same day (see control). And when most top shoots throw up a whitefly cloud when shaken, treat the whole field as high risk — spread will be fast, so rogue extra strictly and plan clean, resistant cuttings for next season.

grow an improved CMD-resistant (or tolerant) cassava variety from your national programme or a trusted source. 'Resistant' means the plant can meet the virus and still give a good root harvest. This is the cheapest and most reliable protection of all, and you decide it before you even plant.

the virus rides inside the stem cuttings, so a cutting from a sick plant grows a sick plant. Take cuttings only from healthy-looking plants, or use certified clean planting material, and never cut planting stems from a field that has any mosaic. (Keeping your planting material disease-free like this is called phytosanitation.)

to rogue means to uproot the whole diseased plant — stem, roots and all — and remove it. Burn it, bury it deep, or feed the leaves to livestock; do not leave it lying in the field and never save its stems for cuttings. Do this from sprouting onward: every plant you pull is a loss stopped and one less source the whiteflies can spread from. Keep new plantings well away from old infected fields.

whiteflies are the insects that ferry the virus between plants, and ladybirds, lacewings and tiny parasitic wasps eat them for you. Avoid broad, harsh poisons that wipe out these helpers (and bees) — kill the helpers and the whiteflies only multiply. This slows spread but is a support only; it does not replace clean cuttings and a resistant variety.

a virus cannot be sprayed away the way a caterpillar can, so do not waste money on chemicals hoping to cure infected plants. If mosaic keeps spreading and most of the field is infected, cut your losses: do not save any cuttings from this field (you would carry the disease straight into next season), harvest what roots you can, and start clean next season — certified, healthy cuttings of a resistant variety, ideally on a fresh plot away from the old infected one. A young field heavily infected in the first weeks will give very poor roots; it is better to clear it and replant clean than to nurse a doomed crop.