Plant Doctor Archive

Zucchini fruit rotting

We have a problem with our zucchinis. We have two plants — one green and the other yellow fruiting. When the fruit is about say 3 inches long, the flowers are dying and the fruit is rotting. We planted them on a mound to help with drainage, havn't watered them that much due to the rain — so are mystified as to why our fruit is just rotting. Can you help?

I asked our resident vegetable expert, Ingrid Ennis, what she thought of your problem. She suggested that the problem could be with inadequate pollination. Pollination is usually done by bees, but wet weather and the Varroa bee mite can have a drastic effect on bee numbers around your plants.

If the fruit is failing to set, then you might like to try hand-pollinating. Zucchinis have male and female flowers, so you will need to dust the pollen from the male flowers into the female flowers when they open. Male flowers have obvious little pollen sacs, female flowers have single pistils inside.

Another possibility is that you have a fungus called Botrytis rotting the remains of the flower and then the fruit. This would be more common during periods of wet weather. You could make sure that there is plenty of air flow around your plants, try not to water the leaves and remove the remains of the petals after fruit set.

Another common fungal disease, powdery mildew, does not directly attack the fruit, but debilitates the whole plant, which will reduce overall yield. You can control this as with Botrytis and with commercially available sprays.

Advice by Dr Dan Blanchon from Unitec's Diploma in Sustainable Horticulture and Bachelor of Resource Management.

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