Divisi
Stem rust
Puccinia graminis · Fungal
Stem rust (Puccinia graminis) is a wind-blown fungus of wheat and barley that erupts in brick-red, powdery blisters (pustules) breaking straight through the stem and leaf-sheath surface. Its rusty spores blow long distances and, in warm weather with dew or rain, multiply so fast that a clean field can be badly hit in a week or two. Bad infection ruptures the stem, chokes the flow of water and food to the grain, shrivels the seed and topples the crop. Aggressive new races such as Ug99 can attack varieties that were once resistant.
Brauna55 · CC BY-SA 4.0 
bjoerns (iNaturalist) · CC BY-SA 4.0
Why it matters
Stem rust is the most explosive of the cereal rusts on wheat and barley. In a warm, wet season a severe attack can take up to 70% of your grain — more than half your crop gone — because it bursts the stem, starves the head, shrivels the seed and knocks the plants flat so you cannot even harvest what is left. It is hard to stop once it takes hold: it spreads on the wind, doubles fast in warm damp weather, and by the time the whole field is rusty there is little left to save. Catching the very first pustules is everything.
When to act
First pustules found on stems or leaf sheaths, especially between stem elongation and heading; act quickly because stem rust can explode in warm wet weather.
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 stem rust field guide
- Identify it
- Scout for it
- Control it
15 field-guide sections in the app
The full guide to stem 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 stem rust?
The first sign you notice: a rusty, reddish-brown powder on the stems and leaf sheaths that rubs off orange-brown on your fingers, clothes and hands as you walk through the crop — like brick dust or paprika.
When should I take action against stem rust?
First pustules found on stems or leaf sheaths, especially between stem elongation and heading; act quickly because stem rust can explode in warm wet weather.
How do I control stem rust?
Prevent it first (your strongest tool) — plant a resistant variety: grow a rust-resistant wheat or barley variety, and choose one bred to resist the locally dangerous races such as Ug99 if they are in your area. Ask your extension officer or seed dealer which resistant variety is recommended for your district — this is the single most effective defence.
Which crops does stem rust affect?
Among the crops covered here: Wheat.
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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