Groundnut rosette disease

a few plants that stay short and bushy while the rest grow tall — the leaves are small, crowded and cupped, and the stem joints are so short the plant looks bunched up in a tight ball (a "rosette"), about the size of a fist instead of spreading out.

most sick plants turn a bright buttery yellow (the leaflets small, twisted and mottled); some instead stay a dark, dull green but are just as stunted and bunched. Either way the plant is dwarfed and never opens out like a healthy one.

on the youngest tips and the undersides of leaves you will find clusters of tiny, shiny black aphids (soft insects smaller than a pinhead) — they carry the virus from plant to plant.

a plant infected early makes few or no pods, and the ones it does make are small and empty — this is the real loss, not just the odd yellow leaf.

plain hunger signs — a nitrogen-short or waterlogged plant yellows all over but is still normal-shaped and spreading, while rosette plants are stunted and bunched into a ball. Yellowing that starts as scattered single plants or small patches and spreads outward from them is the sign of rosette, not of poor soil (which yellows the whole field evenly).

start the day your plants come up and keep it up hard through the first two months — the young, still-growing stage — because plants infected early are the ones that lose everything. Late-planted, thin or gappy fields near older groundnut are the highest risk, so watch those closest.

cross the field in a big "W" shape so you cover all four corners and the middle, not just the row by the path where you always walk.

make about 10 stops along the W. At each stop look closely at a few young plants — check the growing tips and the undersides of the leaves for the little black aphids, and scan around you for any plant that is short, bunched and yellow (or dark-green and dwarfed).

you don't wait for a big count with this disease. As soon as you find aphid colonies settling on young plants, OR the very first stunted, yellow rosetted plant — especially in a late or gappy field — that is your trigger to act the same day. One sick plant left standing is a virus store that feeds the whole field.

the moment you spot a stunted, yellow rosetted plant, uproot it and carry it right out of the field, then bury, burn or feed it to livestock. Do this while plants are still young and few are infected — each one you remove is one less virus store for the aphids to spread from. Also clear any volunteer (self-sown) groundnut nearby, which keeps the virus alive between seasons.

an early insecticide (an aphid-killing spray) can knock down the aphids and slow the spread, but understand clearly: it cannot heal a plant that is already infected — a rosetted plant stays rosetted. Use it only early, while aphids are colonising and plants are still healthy, and only if you cannot get resistant seed. Prefer a systemic spray (one the plant takes up into its sap) over a contact one (which only kills aphids it lands on directly), because aphids hide under leaves.

cover your skin, eyes, nose and mouth; spray in the cool of early morning or evening with the wind at your back so the spray blows away from you; keep it off food, off open water, and away from children and bees; wait the pre-harvest interval (the number of days the label says to leave between spraying and lifting the crop) before you harvest; and wash yourself and your clothes afterwards. If you spray more than once, rotate to a different chemical group each time so the aphids don't build up resistance (stop being killed by it).

keep rogueing hard and keep the aphids down, but be honest early. If most of the field is already stunted and yellow, spraying will not bring those plants back — the nuts are already lost on them. In that case, cut your losses: don't spend more on a crop that can't recover this season, and plan next season to plant early, thick, even, and with resistant seed so it doesn't happen again.