What decides whether a cassava crop survives and sells is not the weather. It is four things you can name: the mosaic virus that is already here, the brown streak virus that is not yet, the clock that starts the moment a root leaves the ground, and the natural poison inside every root. Each is manageable. Each mismanaged is a business destroyed.
The useful part is that the same processing that adds the most value also removes the poison. The pages that follow set out each of the four in turn, price the loss, and point to the service a practitioner can sell against it. None of the four is a farming problem you solve with a better season. Each is a business decision, and each is currently made by default.
Two virus diseases set the ceiling on cassava yield in Ghana. Cassava mosaic disease is already here and everywhere. It is carried in infected cuttings and spread field to field by the whitefly, and across Africa it still claims 30 to 40 per cent of the harvest.1 Four national surveys between 2015 and 2022 found it in the great majority of fields, though the last brought better news: mean incidence fell from the 94 to 98 per cent range of the earlier cycles to 66.5 per cent in 2022, which the surveyors read as a sign that awareness and cleaner planting material are starting to work.2
The second virus is the one to fear. Cassava brown streak disease rots the root itself and can take up to 70 per cent of a harvest, and unlike mosaic it is not yet present in Ghana as of late 2025.3 It is spreading westward across Africa, its main route of entry is infected planting material carried across borders, and Ghana validated a national response plan against it in 2026.4The defence against both is the same, and it is Pillar 1’s defence: clean, tested planting material of resistant varieties, plus vigilance on imported stems. Managing the whitefly that carries them is the other half.
Mean cassava mosaic incidence across four national surveys: 95.3 per cent in 2015, 97.8 in 2016/17, 94.1 in 2019/20 and 66.5 in 2022, with mean whiteflies per plant ranging from about 1.4 to 11.4. The surveys found no direct relationship between whitefly counts and disease level, a reminder that the infected cutting carries mosaic as surely as the insect does.
Mosaic is a management problem: resistant varieties and clean seed hold it down, and the 2022 survey shows that working. Brown streak is a biosecurity problem: it is not here, it must not arrive, and the only thing that brings it is an infected cutting crossing a border. Anyone trading planting material regionally is the risk, and anyone building a tested clean-seed system is the country’s first line of defence.
Cassava carries a familiar set of pests: the cassava mealybug, the green mite, the variegated grasshopper and the whitefly. Most of them are, quietly, a solved problem. Classical biological control introduced natural enemies that brought the mealybug and green mite under control decades ago, and they remain managed today rather than devastating, with resistant varieties doing much of the rest.5
The exception that still matters is the whitefly, because it is more than a pest: it is the vector that carries both mosaic and brown streak from plant to plant. Whitefly numbers per plant in the national surveys ran from about one to eleven, and the surveys found no direct relationship between whitefly numbers and disease levels, a reminder that infected cuttings carry mosaic as surely as the whitefly does.6 Ghana now runs a national early-warning and rapid-response system for pests and diseases, backed by the Plants and Fertilizer Act, that gives cassava surveillance an institutional home.7 So pests as such are mostly handled by resistant varieties and established biocontrol; the one worth spending money and attention on is the whitefly, because controlling the vector is how you control the viruses.
Cassava has a problem no cereal has. Within 24 to 72 hours of harvest the root begins to spoil from the inside, a blue-black streaking of the flesh called post-harvest physiological deterioration, and the chemistry that drives it starts within 15 minutes of the root being cut or bruised.8A root that is not eaten or processed within two to three days is unmarketable.
This single fact shapes the entire cassava economy. It is why cassava is grown, harvested and eaten close to home, why the value chain is short and local, and why a farmer cannot store the crop or ship it raw to a distant buyer the way a maize farmer can. The clock is a constraint and an opening at once. The constraint forces processing within days and near the farm. The opening is everything that beats the clock: rapid on-farm processing, simple storage that buys a few more days, and the PPD-tolerant varieties now in breeding. Whoever shortens the distance between harvest and processing captures value that currently rots.
Post-harvest physiological deterioration begins within 24 to 72 hours of harvest, and the biochemistry that drives it starts within 15 minutes of a root being cut or bruised. A root not eaten or processed within two to three days is unmarketable, which is why the cassava chain is short, local and built around beating the clock.
The clock turns into money lost. Post-harvest losses along Ghana’s cassava chain are large, with commonly cited estimates of measured physical loss running from around 10 to 26 per cent of the crop, rising toward half once roots left unsold for want of a market are counted (Pillar 6), and an economic cost put near US$500 million a year, though these figures are dated and secondary and should be treated as directional until confirmed against primary data.9Ghana’s loss profile is distinctive: because a high share of roots reach the consumer fresh, most of the loss lands at the last, fresh-market stage, and much of it is quality and price discounting rather than outright weight loss.
Storage helps at the dried-product end, where hermetic bags of the kind used for grain have been shown to cut losses in stored dried cassava chips in Ghana at a cost of a few cedis a bag.10 The losses are real, concentrated at the fresh end, and fixable by moving the crop into a stable processed form fast. Loss reduction is not charity; it is a service business, and the operator who offers rapid processing or reliable dried storage is selling time.
| The intervention | What it does | What it costs | The catch, and who should sell it |
|---|---|---|---|
| Convert near the farm | Turns a root that rots in days into a storable product (chips, gari, flour); the one durable answer to the clock | A shed and simple processing kit | It works, but it shifts labour from women to men unless ownership is designed first; sell it as a service, not as advice |
| Hermetic bags for the dried form | Cuts storage losses in dried cassava chips over a two-month store, against ordinary sacks | About GH¢9 a bag | Helps the dried form only, leaving the fresh root untouched; the gain is in the protocol more than the kit |
| Deterioration-tolerant varieties | Some genotypes stay symptom-free far longer than susceptible ones, buying days at the farm | Chosen at planting, at no extra cost | A breeding pipeline rather than an off-the-shelf fix, and it trades against dry matter (Pillar 1) |
| Cold and simple storage | Cold storage below four degrees, and low-tech ground storage, slow the clock at the margin | A cold room, or straw and soil | Cold storage is almost nowhere in the chain; the low-tech methods are cheap but buy only a little time |
Sources: Baral and Hoffmann / IFPRI (2018) on hermetic bags for dried chips; Dankwa et al. (2025) on the deterioration clock and tolerant varieties. Loss-reduction percentages are not quoted here: the held sources carry no cassava-specific field figures for these interventions in Ghana, and this playbook does not invent them.
Every cassava root contains cyanogenic compounds that release hydrogen cyanide when the flesh is damaged. Eaten raw or poorly processed, cassava causes acute poisoning and, over time, chronic neurological disease, including konzo, a paralytic condition, and tropical ataxic neuropathy.11 The internationally used safe level is 10 milligrams of cyanide per kilogram. A review of cyanide across cassava products found raw roots at about 61 milligrams per kilogram, cassava flour at 71 and chips at 47, all well above the safe line, while gari, which is grated, fermented, pressed and roasted, came in at 5.7, the only common product below the limit.12
The point is worth stating plainly: the traditional processing that makes gari also detoxifies it, which is exactly why gari is the cassava product ready for a formal or export market, where raw roots and simple flour are not. Food safety here is a market-access question as much as a health one. The catch is that Ghana has no confirmed national cyanide standard of its own for cassava products yet, so a processor targeting export should work to the international 10 mg/kg limit and document it.
Average hydrogen cyanide by product against the WHO/FAO safe level of 10 mg/kg: cassava flour 71.1, raw roots 61.0, chips 46.6, paste or dough 38.1, biscuits 12.0 and gari 5.7. Only gari, the fully fermented and roasted product, falls below the line, which is what makes the processing method, more than the crop, the thing that decides safety.
| Threat | Severity | The loss | The mechanism | The fix to sell |
|---|---|---|---|---|
| Post-harvest deterioration | Critical | Up to half the fresh crop; roots turn unmarketable within two to three days | Harvest wounds trigger rapid internal spoilage the root cannot seal; months in the ground become days out of it | Near-farm conversion to a storable form; dried storage; PPD-tolerant varieties |
| No buyer, and a clock | Critical | Not separately counted; it shows up as the price the farmer takes every morning | Harvest is irreversible and roots waste fast, so a grower with no buyer accepts the day's price | A lifting calendar and a forward offtake; the scarce thing is a credible date rather than a machine |
| Cassava mosaic disease | High, and falling | Over 20 per cent yield loss; up to 30 to 40 per cent of Africa's harvest | Carried in infected cuttings and by whitefly; severity is set by the cutting more than the insect count | Clean, tested planting material and resistant varieties; national surveys show prevalence already falling |
| Cassava brown streak disease | Watch-list, not yet here | Up to 70 per cent where present; it disqualifies flour outright when severe | Invisible in the plant, a dry rot in the root; moves in stems over long distances | Surveillance, diagnostics, stem quarantine and pre-emptive breeding; the lead time is the asset |
| Cyanide and the certification gap | High for any formal sale | Market access; a poorly processed product fails the 10 mg/kg limit even though standard gari passes at 5.7 | The toxin hydrolyses to hydrogen cyanide; the processing method, more than the crop, decides the residue | Controlled fermentation and drying, a defined starter culture, and testing at intake |
Sources: Dankwa et al. (2025) and Ghana News Agency (2025) on loss and the clock; Chikoti and Tembo (2022) and Oppong et al. (2025) on mosaic and brown streak; Forkum et al. (2025) on cyanide by method. Ranked by evidence of business impact, not by menace; severity ratings are this playbook's judgement.
Already widespread and carried in cuttings and by whitefly, mosaic claims 30 to 40 per cent of Africa's harvest and sets the yield ceiling in Ghana.
Anyone budgeting for insecticide against the whitefly instead of clean cuttings, and every yield forecast that assumes clean material without checking the source.
Plant resistant varieties from certified clean seed; rogue diseased plants; manage the whitefly vector.
Not yet in Ghana but spreading westward, brown streak rots the root and can take up to 70 per cent of a harvest; it enters on infected stems.
Every processor whose model depends on flour, which the disease disqualifies where it is severe, and every breeding or surveillance programme that has not yet started.
Border vigilance on imported planting material; report suspect plants; back the national response plan.
Roots spoil within 24 to 72 hours of harvest, so the whole value chain bends around the clock and any delay is a direct loss.
Every farmer without a contracted buyer and every aggregator far from a processor; the harvest is irreversible and the root wastes within days.
Process within days and near the farm; use simple storage for dried forms; plant PPD-tolerant varieties as they come.
Raw and poorly processed cassava carries unsafe cyanide and can cause acute and chronic illness; proper processing removes it and gari is safe.
Any processor moving from the informal stall to a formal buyer, exporter or institutional caterer, where the product is tested against the 10 mg/kg limit.
Ferment, dry and roast properly; work to the 10 mg/kg limit; document safety for buyers.
Two viruses set the ceiling: mosaic is here and being managed (incidence fell to 66.5 per cent by 2022), while brown streak is not yet here and would take up to 70 per cent of a harvest if it arrived.
The defence against both viruses is Pillar 1's: clean, tested planting material of resistant varieties, plus whitefly control and border vigilance.
Most pests are already handled by resistant varieties and long-standing biocontrol; the whitefly matters because it carries the viruses.
Cassava spoils within 24 to 72 hours of harvest, which is why the chain is short and local and why beating the clock is the core post-harvest opportunity.
Every root is mildly poisonous raw; proper processing removes it, and gari at 5.7 mg/kg is the only common product under the 10 mg/kg safe limit, which is what makes it export-ready.
Where this connects.The clean planting material and resistant varieties that hold the viruses down are Pillar 1’s business. The processing that beats the clock and removes the poison is Pillar 6’s. And the value that currently rots between harvest and market is the gap the value chain has to close (Pillar 6).