You may find from time to time that a plant appears to have been affected by pest or disease damage; however, before treating, you should always make sure that the symptoms are not due to some nutritional deficiency or a physiological disorder.

Unsuitable growing conditions such as too much (or too little) water or an inappropriate temperature range can cause plants to display a range of symptoms including yellowing of foliage and wilting stems. Plants receiving unsatisfactory amounts of water, food, light or minerals will not only look unhealthy, but will be far less able to resist attack from pests or diseases caused by bacteria, fungi or viruses.