Divisi
Algal leaf spot
Cephaleuros virescens · Other
Photo: Malcolm Manners from Lakeland FL, USA · CC BY 2.0
Algal leaf spot is caused by a parasitic green alga — a simple, water-loving plant, not a true fungus — called Cephaleuros virescens. It settles on the leaves and twigs of woody perennial trees such as coffee, tea, mango, citrus, avocado and guava, forming raised, velvety spots that turn rust-orange as it fruits. It spreads by tiny spores that swim in a film of rainwater and are splashed and blown from tree to tree in warm, wet, humid weather. It does the most harm on weak, crowded, shaded or poorly fed trees, where it moves onto the twig bark and kills fruiting wood.
iNaturalist user (via Wikimedia Commons) · CC BY 4.0 
Edward L. Barnard, Florida Department of Agriculture and Consumer Services, Bugwood.org · CC BY 3.0 us
Why it matters
Algal leaf spot rarely kills a tree outright, but on a weak, crowded coffee, tea, mango, citrus, avocado or guava it quietly eats into the leaves and creeps onto the twigs — and a bad case can cost you up to a fifth (20%) of your crop. The velvety spots stop the leaf from making food, and where the alga bites into the twig bark it cracks the wood and kills the branch tips — the very wood that carries next season's fruit. It is stubborn once it settles in: it lives on the tree all year and throws out fresh spores every wet season, and a copper spray only shields new leaves — it cannot scrub off what is already there. So the real fix is to change the damp, shady, crowded, hungry conditions it thrives on, not to wait and spray it away.
When to act
Treat when orange-green velvety spots appear on more than a few leaves of stressed or shaded trees.
This guidance is general, compiled from published agronomic references including FAO and CABI. Thresholds and timing shift with your crop, your variety and the season.
In much of the region a spray is simply called mushonga — medicine. But a chemical group you cannot name is one you cannot rotate, and a product you did not write down has no pre-harvest interval you can observe. Mushonga, and other farming words →
The full algal leaf spot field guide
- Identify it
- Scout for it
- Control it
14 field-guide sections in the app
The full guide to algal leaf spot — every symptom to check, how and when to walk your field looking for it, and the controls that actually work, ranked. Built into your crop plan, so you are told to look before it costs you a harvest.
Crops it affects
Frequently asked questions
How do I identify algal leaf spot?
The spots (what you see first): on the older leaves, look for round, slightly raised patches from the size of a match-head to a small coin (3–10 mm across) that feel velvety or felty, like a little pad of fine carpet stuck to the leaf. They start out grey-green and sit mostly on the upper side of the leaf.
When should I take action against algal leaf spot?
Treat when orange-green velvety spots appear on more than a few leaves of stressed or shaded trees.
How do I control algal leaf spot?
Prevent first — open up the tree: your biggest non-chemical lever is airflow and light. Prune and thin the canopy so sun and wind get right in and the leaves dry fast after rain — the alga can only swim and spread while the leaf stays wet, so a dry leaf starves it. Space your trees and don't let them crowd into one another.
Which crops does algal leaf spot affect?
Among the crops covered here: Avocado, Guava, Mango, Tea.
Catch it before it costs you a harvest
Divisi builds scouting into your crop plan — it tells you when to walk your field, what to look for at that stage, and what to do when you find it. Free for farmers, works offline.
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