Bok choy

Club root

What you will see

Thickened and distorted roots; plants lag behind and wilt.

The source says: in brassicas it causes swollen roots and severely stunted growth.

How to protect

1. Prevention

   • Buy plants only from a source guaranteed free of clubroot; be careful even with plants from friends.
   • Do not carry soil on tools, wheelbarrows and footwear.
   • On acid soil, lime (1.64 oz/sq ft, then 0.88 oz/sq ft in following years) and improve drainage; this reduces the disease but does not rule it out.
   • Grow young plants on for longer in healthy soil (pots at least 3½ in) and plant them out larger; consider varieties with partial resistance.
2. By hand as soon as it appearsDig up affected plants, roots included, and dispose of them (do not compost). There is no chemical product for gardeners against clubroot.

Cabbage caterpillars (cabbage white butterflies, cabbage moth, diamond-back moth)

What you will see

Holes in leaves and caterpillars on them.

How to protect

1. Prevention

   • Cover brassicas with mesh that does not touch the leaves (otherwise butterflies lay eggs through the mesh).
   • Tolerate some caterpillars: they are food for birds and parasitic wasps.
2. By hand every week from springRegularly pick pale yellow butterfly eggs, round white moth eggs and caterpillars off the leaves.
3. Biological when caterpillars are presentA mixture of pathogenic nematodes sprayed onto the leaves, ideally in cool, damp weather.
4. Chemical — only when nothing else helps according to the product labelLast resort only: a product authorized in your country against caterpillars on brassicas. Try non-chemical methods first.

Flea beetles (Phyllotreta, Psylliodes)

What you will see

Small round holes in leaves, mainly on seedlings; tiny beetles jump away when you touch the plant.

How to protect

1. Prevention

   • Cover seedlings and young plants with fine mesh.
2. By hand from sowingCover brassica seedlings with fine mesh.

Slugs and snails

What you will see

Irregular holes in soft leaves and young shoots and slime trails; they feed at night.

How to protect

1. Prevention

   • Plant sturdy potted plants, not delicate young seedlings.
   • Water in the morning, not the evening (evening watering helps them move around).
   • Encourage their natural enemies: birds, hedgehogs, toads, ground beetles.
2. By hand evening, after rainPick them off by hand on damp evenings and take them far away. Traps: hollowed-out citrus halves placed cut side down, or sunken containers of beer; check in the morning.
3. Biological when the soil is warm and moistSlug-specific nematodes (from a biological control supplier) are watered into the soil.
4. Chemical — only when nothing else helps according to the product labelLast resort only: a product authorized in your country against slugs and snails. Try non-chemical methods first.

Pigeons (wood pigeon, feral pigeon)

What you will see

Torn leaves, often only the stalks are left; brassicas are among the worst affected.

How to protect

1. Prevention

   • The only sure protection is to grow under netting or in a cage; scarers and repellents protect only briefly at best.
2. By hand after plantingStretch netting over the crop (keep it taut and free of holes so birds do not get caught) or use a cage.

Aphids

What you will see

Colonies of tiny insects on young shoots and under leaves, stunted and distorted growth, sticky honeydew and black sooty mold on it.

How to protect

1. Prevention

   • Tolerate a small number: aphids are food for beneficial insects.
   • Check plants often so you can act in time.
   • Encourage ladybirds, hoverflies, lacewings and parasitic wasps.
2. By hand as soon as you spot themSquash colonies with your fingers or remove affected shoot tips.
3. Biological before a heavy infestationIn a greenhouse you can buy in hoverfly larvae, lacewings and parasitic wasps.
4. Chemical — only when nothing else helps according to the product labelLast resort only: a product authorized in your country against aphids. Try non-chemical methods first.