Divisi
Bunch rot (grey mould)
Botrytis cinerea · Fungal
Photo: Rasbak · CC BY-SA 3.0
Bunch rot, also called grey mould (Botrytis cinerea), is a fungal rot of ripening fruit — grapes, tomatoes and strawberries. The fungus sneaks in early through wounds, insect holes, cracks and dying flower petals, then explodes as the fruit sweetens in cool, wet, humid weather. One infected fruit grows a fuzzy grey coat and rots its neighbours where they touch, so a tight bunch can collapse in days right at harvest.
davitydave (Flickr) · CC BY 2.0 
davitydave (Flickr) · CC BY 2.0
Why it matters
Grey mould strikes at the worst possible moment — on ripe fruit right before you pick, after a whole season of work. In cool, wet weather it can rot up to half your fruit (50%), and it spreads fast: one mouldy berry rots the whole bunch where the fruit touch. Worse, it often creeps in silently back at flowering and hides inside the fruit, so by the time you see the grey fuzz it is already inside and established. Once a bunch is rotting in damp weather you cannot spray it clean — you can only slow it and save what is still sound, which is why preventing it and catching the very first berry beats trying to cure it.
When to act
first rotting berries in a bunch as fruit ripens, especially after rain near harvest
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 bunch rot (grey mould) field guide
- Identify it
- Scout for it
- Control it
16 field-guide sections in the app
The full guide to bunch rot (grey mould) — 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 bunch rot (grey mould)?
The first sign: a single berry or fruit turns soft and brown, usually where two fruits press together, at a split or crack, or at an insect hole. Press it gently and it is watery and gives way — not firm like healthy fruit.
When should I take action against bunch rot (grey mould)?
first rotting berries in a bunch as fruit ripens, especially after rain near harvest
How do I control bunch rot (grey mould)?
Prevent it first — open up for air and sun (your strongest tool): grey mould dies in sun and moving air. Remove the leaves shading the bunches so fruit dries fast after rain and dew, space and train your plants so air moves through, and avoid very dense, tight bunches. Keep fruit off wet soil with mulch or supports, and do not over-water as the fruit ripens.
Which crops does bunch rot (grey mould) affect?
Among the crops covered here: Tomato.
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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