Greenhouse crop stress management

Greenhouse crops are susceptible to a number of types of environmental stress. Stress in greenhouse crops can result from air pollutants such as sulfur dioxide, ozone and ethylene. For a particular crop, temperature, light, water supply and humidity may be too high or too low for optimum production. In addition, within a crop, certain processes, such as fruitset, may have a different optimum than growth and photosynthesis. Quality factors, such as flower size and number are also affected by temperature and light. For example, in many potted crops, quality is a function of compact growth habit which is influenced by day/night temperature differentials (DIF). In this review, temperature, daylength; irradiance, humidity and water supply requirements of selected greenhouse vegetable and floricultural crops are summarized. To manage stress in the greenhouse, growers are advised to: 1) determine the specific requirements of the crop and crop process of interest: 2) if using control programs that factor in energy conservation and IPM strategies, keep crop requirements paramount; 3) monitor the greenhouse carefully for 'trouble spots' where plants may be exposed to unfavorable conditions. Examples of disorders resulting from temperature and water stress are given for selected vegetable crops, with an emphasis on tomato. As an example of the complexity of stress-related plant responses, recent research results from tomatoes on the effects on fruitset of high temperatures pre-and post pollen release are discussed.