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Mononychellus tanajoa (Bondar, 1938) · formerly or also: Tetranychus tanajoa
The cassava green mite is a tiny spider mite that feeds on the young leaves at the tips of cassava shoots, especially in the dry season. Leaves become speckled yellow, small and deformed, and shoot tips can lose all their leaves, leaving 'candlestick' stems. After it arrived in Africa from South America in 1971, it became one of the main pests of cassava there until predatory mites and a fungus from its native range were introduced. Its story is one of the clearest examples of how carefully chosen natural enemies from a pest's homeland can protect a staple crop across a continent without any spraying.
The scientific name of cassava green mite is Mononychellus tanajoa (Bondar, 1938), in the order Trombidiformes, family Tetranychidae.
Older or alternative scientific names: Tetranychus tanajoa.
Native to South America (north-eastern Brazil and nearby). It was found in Uganda in 1971 and spread across the cassava belt of sub-Saharan Africa within about 15 years. Its spread followed the movement of cassava cuttings and wind-borne dispersal of mites between fields.
| Region | Status |
|---|---|
| South America | Native |
| Sub-Saharan Africa | Invasive since 1971; widespread; partly controlled biologically |
| Other regions | Not established; regulated in some countries |
Adults are about 0.3-0.5 mm long, green to yellowish green, and live mainly on the undersides of young leaves and on shoot tips; a hand lens is needed. Unlike many spider mites they produce little webbing. Mites cluster on the youngest leaves and growing points, where the leaves are most tender; Typhlodromalus aripo, the introduced predator, hides by day in the shoot tips.
| Crop stage | What you see |
|---|---|
| Early infestation | Fine yellow-white speckling on young leaves at the shoot tips; mites on leaf undersides. |
| Heavy infestation (dry season) | Small, mottled, deformed and stunted young leaves; shoot tips lose their leaves, leaving 'candlestick' stems. |
| Crop level | Reduced leaf area, slower growth and smaller roots; plants recover when the rains return. |
Females lay eggs on the undersides of young leaves. The mite passes through larval and two nymphal stages before adulthood in about one to two weeks in warm weather. Populations explode in the dry season and crash when heavy rains wash mites off and fungal disease spreads. Mites disperse between plants by walking along touching leaves and by being carried on wind currents, and they are moved over long distances on infested planting material.
| Stage | Duration | Notes |
|---|---|---|
| Egg | About 3-4 days | On young leaves. |
| Larva and nymphs | About 5-8 days | Feed on leaf undersides. |
| Adult | About 2-3 weeks | Females lay several eggs a day. |
Development is fastest in hot, dry conditions; a generation takes about 10-14 days at around 27-30 °C.
Many overlapping generations; numbers peak in the dry season.
Long dry seasons, drought-stressed crops, susceptible varieties, and absence of introduced predatory mites. Crops planted late, so that young plants face the dry season with few leaves, are particularly vulnerable, and leaf loss is worst on poor soils.
There is no numeric economic threshold for smallholder cassava; management relies on biological control and tolerant varieties, which make action rarely necessary.
Thresholds are local. They depend on crop price, control cost, variety and natural-enemy activity, so use the figure your local extension service publishes where one exists.
Before biological control, root yield losses of about 13-80% were reported in Africa depending on variety and dry-season length; losses are now lower where introduced predators are established. Damage reduces leaf area and photosynthesis at the time roots should be bulking, and leaves eaten as a vegetable in many African households are also lost.
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.
Acaricides are not economical in smallholder cassava and would destroy the introduced predators that provide lasting control. What is registered differs by country and changes over time; follow the label and your local plant-protection authority.
Cassava and other Manihot species.
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.