Downy mildew

Downy mildew shows itself through discoloration or yellowing of parts of the leaf, with fluffy grey or purplish growth beneath the patch. The disease is caused by a fungus and attacks young plants and those growing in damp conditions.
Control: Take off all infected leaves to prevent spread of spores. Improve drainage of your container

DownyMildew

Botrytis

A fungal disease evidenced by fluffy, off-white or grey-brown growth on infected areas. Lives off dead or living plant material, spreading by spores and invading plants through wounds or open flowers.
Control: Remove all dead material from and around plants. Cut out all infected material and dispose of.

Botrytis

Chlorosis

This appears as a yellowing of leaves, either across the whole leaf or in the veins. The symptoms may be caused by a variety of reasons: The main reasons may be because the leaf is not receiving sufficient light, the plant is not receiving enough nutrients, virus, or because of sudden low temperatures.
Control: Improve soil by mulching with garden compost and remove all affected leaves.

Powdery mildew

White fungal growth appears on the top of the plant leaves and may spread to the underside. Without control, the disease can spread and cause dieback, pitting of fruit and even death of the plant.
Control: Keep plants adequately watered, but avoid splashing the foliage. Mulch around the plant base. Resistant varieties of some plants are also available.

powdery_mildew
chlorosis

Virus

There are many different types of virus, but most show symptoms as stunting, mottling or distortion of foliage. Virused plants usually crop poorly if at all and may die prematurely.
Control: Ensure good hygiene of your tools, dispose of affected plants, change the soil in your windowbox if considering replanting with related plants.

Clubroot

This affects the Brassica family, including cabbage, radish, swede and turnip and involves a distortion of the root system and yellowing of the foliage. Plants also wilt easily and may even die off altogether. Clubroot is caused by a slime mould that thrives in poorly drained, acidic soils.
Control: Improve the drainage of your container and change the soil. Add lime if you have a particularly acidic soil. Burn all infected material and grow from shop-bought seed or buy in plants from a trusted source

clubroot
virus