Divisi
Guava rust
Austropuccinia psidii · Fungal
Photo: John Tann from Mullumbimby, Australia · CC BY 2.0
Guava rust (also called myrtle or eucalyptus rust) is a wind-borne fungus that attacks the young, soft, actively growing parts of guava — new leaf flush, shoots, buds and small fruit. Powdery yellow spores land on tender growth in warm, wet, humid weather and infect it within hours. Repeated attacks twist and kill the growing tips, strip the tree of leaves, and scar the fruit, so a susceptible tree keeps getting hit every time it pushes new growth.
Peter de Lange · CC0 
David Eickhoff from Pearl City, Hawaii, USA · CC BY 2.0
Why it matters
Guava rust hits the soft new growth your tree needs to make fruit — and on a badly-hit, susceptible tree it can wipe out up to 70% of your crop. It kills the growing tips and strips the leaves, so the tree keeps re-infecting itself every time it flushes, weakening year after year. Once the fungus is loose in a warm, humid orchard, no spray fully clears it — the only real win is protecting each new flush before the spores get in, so catching it early matters more than curing it late.
When to act
Bright yellow rust pustules found on young flushing leaves, shoots or fruit, especially during warm humid weather and new flush.
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 guava rust field guide
- Identify it
- Scout for it
- Control it
13 field-guide sections in the app
The full guide to guava rust — 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 guava rust?
What you see first: on the newest soft leaves and shoot tips, tiny raised spots that quickly turn into bright yellow to orange, powdery dust — like someone flicked turmeric or yellow chalk powder onto the young growth. Rub a spot and the yellow powder (the spores) comes off on your finger.
When should I take action against guava rust?
Bright yellow rust pustules found on young flushing leaves, shoots or fruit, especially during warm humid weather and new flush.
How do I control guava rust?
Prevent first — plant tough trees and keep the canopy open (cultural and variety, the safest layers): where you can, plant less-susceptible guava selections — some types shrug off rust far better than others in humid zones. Then prune to open up the canopy so air and sun move through and the leaves dry faster (the fungus needs long wet, still, humid hours to infect), and do not carry infected shoots, prunings or seedlings to a clean tree or a neighbour's orchard — that is how it travels between farms.
Which crops does guava rust affect?
Among the crops covered here: Guava.
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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