Healthy Windowbox Plants... Dealing with disorders

There are many nasty plant diseases out there and lots of other disorders that you can do something about. Below are some of the most common, with ideas on how to combat them. For most, cutting out affected materials can do the trick, but in more extreme circumstances you may have to pull up plants altogether in order safeguard the other plants in your windowbox.
If in doubt, look up your disease on the very comprehensive RHS Website Pests & Diseases pages.

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

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

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, though usually because the plant is receiving too little light, tnot receiving enough of the right nutrients, virus, or through sudden low temperatures.
Control: Improve soil by mulching with garden compost and remove all affected leaves.

chlorosis

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

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

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: Keep your tools clean, dispose of affected plants, change the soil in your windowbox if considering replanting with related plants.

virus

Dieback

This may affect any bush fruit you are growing in your windowbox and may be caused by virus, but is also, more usually, a symptom of drought, waterlogging or poor watering.
Control: Prune out affected stems, mulch if soil is drying out quickly, ensure container has sufficient drainage and water more regularly if this could be the reason

Dieback