Stunted growth, yellowing soft and limp leaves with a soggy centre.
A sign of over-watering. Some plants may present this with water-soaked spots or blisters known as oedema.
Take the plant out of its plant pot and place on a saucer to allow for air circulation and a chance for the plant to dry out. Take this opportunity to investigate any damage to the roots. Healthy roots are turgid and white.
If the stems near the soil are soggy and show signs of rot, that damage has gone quiet far.
Grey fine mould on the leaves and stems.
This is known as Botrytis Cinerea, which is a necrotrophic fungus caused by too much humidity. It is unlikely that the plant will suffer with this in a home setting, however, should this happen, ensure there is good air circulation around the plant, which will allow for the excess moisture to evaporate.
White, powdery patches across the leaves and stems.
This is a fungal disease called Powdery Mildew caused by too much moisture and poor air circulation around the plant. Remove any infected leaves and flowers. Prune out any infected shoots to reduce the risk of new infection in spring. Allow good air circulation around the plant especially during hot days.
Black, water-soaked stems at the base of the plant.
Blackleg is caused by a fungus called Pythium. The fungi are borne in the soil or the original seed. It can also be spread by rain and wind. The best conditions for the spread of the fungus is cool temperatures, moisture and poor ventilation.
Unfortunately, there is no effective treatment for this problem. It is best to remove the plant and its soil, avoid adding it to your compost, and wash the plant pot thoroughly before re-using it.