Temperature is an environmental factor which strongly affects wilt diseases since it has an influence on each of the three biotic components involved in the production of the syndrome of wilt diseases, i.e., the pathogen, the host plant and soil microorganisms. Surface temperatures vary with latitude and altitude and change cyclically each day and each year. Soil temperature is affected by the presence of vegetation, water content and depth (Griffin 1972) and therefore, may vary under natural conditions, and in extreme cases from far below freezing point to even above 60 C. Thus, temperature determines not only the relative prevalence of soil-borne diseases at different times of the year, and from one year to another, but also their geographical distribution (Garrett 1960). A better understanding of the effect of temperature on the three biotic components of wilt diseases may enable us to better predict disease development and also to develop means for disease control, such as by thermal eradication of the pathogen, plant thermotherapy, disease escape, and through thermal manipulation of biocontrol agents in the soil.