Nutrition plays an important role in the development of diseases in plants and can be managed to assist in disease control. Pathogens can limit the capacity of plants to take nutrients up and to distribute and utilise them. For example, the fungal root pathogens Pythium and Phytophthora in leafy vegetables damage the fine feeder roots inhibiting root uptake. Other pathogens, such as the fungi Fusarium and Verticillium which cause wilt diseases on a range of crops (including tomatoes, cucumbers and lettuce), and bacterial canker and bacterial wilt in tomatoes, move into the vascular system of the plant. The subsequent breakdown of internal tissues leads to the plugging of vessels, preventing the distribution and utilisation of nutrients. In approaching the management of diseases through nutrition, susceptibility to pathogens is generally minimised by providing optimum nutrition. An example of the risk of ignoring this is in the oversupply of nitrate fertiliser to lettuce. The associated accumulation of nitrate in the lettuce has been shown to increase susceptibility to the fungi Botrytis. Nutrients can also be supplemented to the growing system to boost resistance to diseases. For example, silicon (Si) can be supplied as a foliar spray or in a hydroponic solution and it is an effective preventative treatment for powdery mildew in greenhouse cucumbers. The Si provides protection by increasing the physical strength of epidermal cells so that they resist penetration by germinating fungal spores. A disease can therefore be viewed as a complex interaction between a plant, its nutrition and the pathogen. Knowledge of this relationship provides an appreciation of the importance of good crop management in disease prevention.