Blossom end rot on zucchini
A physiological disorder caused by calcium running short in the growing fruit, usually because of uneven watering. The tip of the fruit browns and sinks in, and secondary rot then moves in.
Symptom photos
Symptoms
- Browning and sinking at the blossom end of the fruit
- Tissue at the patch dry, leathery and darkened
- Growth of the affected fruit stopping
- Symptoms on the fruit only — the leaves stay healthy
- Secondary wet rot breaking down the tip
What it does to the crop
- Unmarketable fruit that will not keep
- The first, earliest pickings lost
- Secondary fungal and bacterial infection in the damage
- Symptoms recurring until watering is evened out
What encourages it
- Drought alternating with heavy flooding of the plants
- High temperature and rapid evaporation
- Too much nitrogen and potassium, blocking calcium uptake
- Acid soils low in calcium
Prevention
- Water evenly and regularly, ideally by drip
- Mulch to even out soil moisture
- Lime the soil to pH 6.0-6.8 before planting
- Keep nitrogen feeding moderate
- Foliar feed with calcium while the fruit is setting
⚠️ Before you reach for a spray
This atlas is informational and still growing — different diseases can look almost identical. Confirm the diagnosis and read the product label before applying any plant protection product. If you are unsure, ask your local extension or advisory service.
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