Four things decide whether a cassava crop survives and sells: 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 percent 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: the share of surveyed fields with any mosaic fell from the 94 to 98 percent range of the earlier cycles to 66.5 percent in 2022, and in most infected fields a quarter or fewer of the plants showed it, 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 percent of a harvest, and unlike mosaic it had not been reported in Ghana or anywhere in West Africa as of early 2026.3 It is spreading westward across Africa, its main route of entry is infected planting material carried across borders, and in May 2026 Ghana validated a National Response Plan Against Cassava Viral Diseases, covering brown streak as well as mosaic.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.
Share of surveyed fields with cassava mosaic across four national surveys: 95.3 percent in 2015, 97.8 in 2016/17, 94.1 in 2019/20 and 66.5 in 2022; in most infected fields a quarter or fewer of the plants showed symptoms. Mean whiteflies per plant ranged 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 its main long-distance route 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 no recent outbreak has been reported, 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 In November 2023 eleven institutions signed an agreement to operationalise a national early-warning and rapid-response system for pests and diseases, under the plant-protection powers of the Plants and Fertilizer Act, 2010 (Act 803), which 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.8In practice a fresh root can be held only two to three days before it must be eaten or processed.
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. In practice a fresh root can be held only two to three days before it must be eaten or processed, 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 a field study of the 2011 chain putting outright physical loss at about 12.5 percent of national production (over 1.7 million tonnes of fresh roots), rising to 29 percent once roots sold at a discount for damage or spoilage are counted, at a combined cost of about US$520 million a year.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 while more roots are sold at a discount than are thrown away, about three quarters of the money lost is outright spoilage, most of it in households and at retail.
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 over a two-month store, at about GH¢9 (US$2) a bag at 2018 prices.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 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 who owns the kit decides who gains; sell it as a service |
| Hermetic bags for the dried form | Cuts storage losses in dried cassava chips over a two-month store, against ordinary sacks | About GH¢9 (US$2) a bag at 2018 prices | Helps the dried form only, leaving the fresh root untouched; the gain is in the protocol more than the kit |
| Deterioration-tolerant varieties | Tolerant lines delay spoilage; yellow, high-carotenoid roots gain about one to two days | 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 at about 3 to 10 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.
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 Codex Alimentarius maximum for total hydrogen cyanide is 10 milligrams per kilogram for cassava flour and 2 milligrams per kilogram for gari. 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 on average across studies from Nigeria and Malawi, the only common product below the flour limit, though still above the 2 mg/kg Codex limit set for gari itself.12
The traditional processing that makes gari also detoxifies it, which is why gari is the cassava product closest to formal and export standards, provided each batch is tested against the 2 mg/kg gari limit. Food safety here is a market-access question as much as a health one. Ghana does have national product standards, GS 237:2017 for gari and GS 762:2008 for edible cassava flour, sold by the Ghana Standards Authority; a processor targeting export should buy them, work to the Codex limits (2 mg/kg for gari, 10 mg/kg for flour) and document every batch.
Average hydrogen cyanide by product against the Codex limits (10 mg/kg for cassava flour, 2 mg/kg for gari): 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 flour limit, though still above its own 2 mg/kg limit, 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 | About a fifth of roots sold fresh are lost outright, and over a quarter are sold at a discount; 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; fewer fields infected in 2022 | Over 20 percent yield loss; up to 30 to 40 percent of Africa's harvest | Carried in infected cuttings and by whitefly; the national surveys found no direct link between whitefly numbers and disease severity | Clean, tested planting material and resistant varieties; the 2022 national survey found fewer fields infected than the three before it |
| Cassava brown streak disease | Watch-list, not yet here | Up to 70 percent where present; roots scored 3 or worse on the severity scale cannot make high-quality flour | 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 Codex limit (10 mg/kg for flour, 2 mg/kg for gari), and even average gari at 5.7 mg/kg misses the gari limit | 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) on the clock and Naziri et al. (2014) on loss; Chikoti and Tembo (2022) and Oppong et al. (2025) on mosaic and brown streak; Forkum et al. (2025) on cyanide by method. Severity ratings are the authors' judgement of business impact.
Already widespread and carried in cuttings and by whitefly, mosaic claims 30 to 40 percent 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 percent 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 most of it, and well-made gari can meet the standard.
Any processor moving from the informal stall to a formal buyer, exporter or institutional caterer, where the product is tested against the Codex limits (10 mg/kg for flour, 2 mg/kg for gari).
Ferment, dry and roast properly; work to the Codex limit for the product; document safety for buyers.
Two viruses set the ceiling: mosaic is here and being managed (the share of fields infected fell to 66.5 percent in 2022), while brown streak is not yet here and would take up to 70 percent 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 raw root carries cyanide, on average about six times the flour limit; proper processing removes it, and gari averages 5.7 mg/kg, the lowest of the common products, but that is still above the 2 mg/kg Codex limit for gari, so only well-processed, tested batches are 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).