Stevia

Aphids

What you will see

Colonies of tiny insects on young shoots and under leaves, stunted and distorted growth, sticky honeydew and black sooty mould 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 authorised in your country against aphids. Try non-chemical methods first.

Spider mites

What you will see

Speckled leaves and early leaf drop.

How to protect

1. Prevention

   • Plants in a hot, dry, overcrowded greenhouse suffer more: increase humidity and airflow.
   • In autumn, remove heavily infested plants and clear away debris, canes and ties; disinfect the greenhouse thoroughly.
   • Weed around the greenhouse; weeds are hosts.
2. Biological March to OctoberPredatory mites (from a biological control supplier) are the most common biological control against spider mites.
3. Chemical — only when nothing else helps according to the product labelLast resort only: a product authorised in your country against mites. Try non-chemical methods first.

Root and crown rot

What you will see

An overwatered plant rots at the roots and wilts.

How to protect

1. Prevention

   • Do not overwater and use a free-draining substrate.
2. By handReduce watering and discard the affected plant.

Septoria leaf spot

What you will see

Leaf spots (Septoria); in a trial it infected all plants in the field.

How to protect

1. Prevention

   • Buy healthy transplants: in the trial the disease spread on greenhouse-grown seedlings.

There is no proven protection protocol yet (new crop).