Kohlrabi

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.

Mealy cabbage aphid

What you will see

Gray-white aphid colonies under leaves and on growing tips; leaves of young plants are curled and pale.

The source says: it is common on brassicas.

How to protect

1. Prevention

   • Check brassicas often from spring, especially young plants.
   • Dispose of old plants after harvest so it is not carried over into spring.
2. By hand as soon as it appearsSquash colonies with your fingers where possible.
3. Biological summerNatural enemies (ladybirds, hoverflies) usually reduce them in summer; in spring you often have to wait.

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.

Cabbage root fly

What you will see

Plants grow slowly and wilt because the larvae eat the roots.

How to protect

1. Prevention

   • Place a collar around the stem of each new transplant (3¼–6 in piece of carpet underlay, cardboard or roofing felt).
   • Cover plants with fine mesh or fleece and rotate crops (otherwise flies can emerge from pupae in the soil under the mesh).
2. By hand ongoingEncourage ground beetles and rove beetles, which eat the larvae.
3. Biological when eggs are laid and larvae hatchA mixture of pathogenic nematodes watered into the soil against the larvae (it also works on other insects in the soil).

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

   • On large brassicas whose outer leaves are discarded, tolerate them.
2. By hand from sowingCover brassica seedlings with fine mesh.
3. Chemical — only when nothing else helps according to the product labelLast resort only: a product authorized in your country against flea beetles. Try non-chemical methods first.