Divisi
Cercospora leaf spot
Cercospora beticola · Fungal
Photo: Howard F. Schwartz, Colorado State University, United States · CC BY 3.0
Cercospora leaf spot is the most damaging leaf disease of beet-family crops — beetroot, sugar beet, Swiss chard and spinach. It is caused by a fungus (Cercospora beticola) that survives from season to season on old infected leaves and seed, then spreads by airborne spores whenever the weather turns warm and humid and the leaves stay wet from dew, rain or overhead watering. Round tan-and-red spots peppering the older leaves multiply into a scorched, dying canopy, forcing the plant to waste its strength regrowing leaves instead of filling the root or leaf you sell.
Ayman Esh · CC BY-SA 4.0 
Howard F. Schwartz, Colorado State University, United States · CC BY 3.0
Why it matters
Cercospora leaf spot is the worst leaf disease of beetroot, chard, spinach and sugar beet. Once it takes hold in warm, humid weather it multiplies fast from just the first few spots, scorching the leaves until the plant has to burn its energy regrowing them instead of filling the root or leaves you sell — a bad attack can cost you up to 40% of your crop (nearly half). No spray brings a dead leaf back, so the whole game is catching it at the very first spots and stopping it from spreading through the canopy.
When to act
Begin scouting at canopy closure; start fungicides when the first spots appear during warm, humid weather and repeat on disease pressure.
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 cercospora leaf spot field guide
- Identify it
- Scout for it
- Control it
12 field-guide sections in the app
The full guide to cercospora 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 cercospora leaf spot?
The first sign: small round spots freckle the older, outer (lower) leaves first, while the young centre leaves stay green. As the spots multiply the leaf yellows and scorches from the outside in, and a badly hit plant throws up a flush of small new leaves to replace the dying ones.
When should I take action against cercospora leaf spot?
Begin scouting at canopy closure; start fungicides when the first spots appear during warm, humid weather and repeat on disease pressure.
How do I control cercospora leaf spot?
Prevent — break the cycle: the fungus over-winters on old leaves and seed, so rotate away from beet-family crops (beetroot, chard, spinach, sugar beet) for 2–3 years, plough down or clear away infected leaf trash after harvest, plant clean, disease-free seed, and pull out volunteer beets (stray beet plants that sprout on their own from last season) and weedy relatives that carry the fungus over.
Which crops does cercospora leaf spot affect?
Among the crops covered here: Beetroot, Swiss chard.
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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