Why is there white powdery mould on my gooseberries?

Powdery mildews are the odd fungal diseases that are worse in dry conditions than wet ones, because the spores germinate in humid air but do not need free water — and the plants most affected are the ones under drought stress. That is why a gooseberry against a dry wall with a congested centre suffers badly and the same variety in an open, mulched, watered position often barely gets it.

Step by step

1. Identify which mildew you have.American gooseberry mildew starts as a white powdery coating on the shoot tips and young leaves, spreads to the fruit, then turns brown and felted. European gooseberry mildew stays as a white powder on the leaves and does not usually affect the fruit or turn brown.
2. Cut out infected shoot tips as soon as you see them.In summer, remove and bin affected tips. In winter, cut back any shoots showing brown felted growth into clean wood. This removes the overwintering source.
3. Prune to an open goblet on a clear leg.The whole point of the shape is airflow. A bush that dries quickly after rain and dew gets far less mildew than a congested one, and this is the most effective control available.
4. Summer prune the sideshoots to five leaves.In late June or July. It lets light and air onto the fruit at exactly the point in the season when mildew takes hold.
5. Keep them watered and mulched.Drought stress makes powdery mildew much worse. A mulched, evenly watered bush resists it considerably better.
6. Stop the heavy nitrogen.Soft sappy growth is far more susceptible. Use sulphate of potash in late winter rather than a nitrogen-led general feed.
7. Space bushes properly and clear around them.1.2–1.5m apart, with weeds and long grass kept off the base so air moves through.
8. Grow a resistant variety where it recurs.Invicta, Hinnonmaki Red, Greenfinch and Rokula all have useful resistance. In a garden that gets mildew every year this is the real answer.
9. Use the fruit anyway.Mildewed gooseberries are edible — the felted skin can be rubbed or peeled off, and the fruit is fine for cooking. It is a quality problem rather than a safety one.

Tips

• The same disease affects blackcurrants, where it shows on the shoot tips and young leaves rather than the fruit.
• Cordon-trained gooseberries have excellent airflow and get noticeably less mildew than bushes.
• Do not compost mildewed prunings in a cool heap. Bag them or hot-compost them.
• A gooseberry in the dry rain shadow at the foot of a wall is a mildew candidate. Move it or mulch and water it properly.

Common mistakes

• Leaving infected shoot tips on the bush over winter — That is where the fungus overwinters. Cutting them out in winter reduces next year's infection substantially.
• Feeding with a nitrogen-rich fertiliser to help it recover — Soft growth is exactly what mildew colonises. Potash, water and mulch are the right response.
• Assuming mildew means the bush is too wet — Powdery mildew is worse on drought-stressed plants in humid still air. Watering and mulching help; letting it dry out makes it worse.

Questions people ask