The rise in sea level, which causes an increase in salinity in both surface and ground water systems, is among the resultant effects of global climate change. Soil salinity is one of the notable environmental factors contributing to infectious plant diseases. Stress due to soil salinity affects plant tolerance to biotic stress by attenuating their immunity to pathogens leading to prevention of defence genes expression, reduced antioxidant activity and weakening of defence signalling proteins. The pathogen virulence and pathogenicity as well as an enhancement of pathogen development and multiplication are all influenced by soil salinity. Restriction of water absorption, toxic ion build up in plant tissues, nutrient deficiency, hormonal and metabolic imbalance, oxidative stress as physiological effects of salt stress, significantly affect the degree and occurrence of plant diseases. Thus, level of soil salinity is directly proportional to the severity and incidence of plant diseases. Controlling the effect of salinity by improving salinity tolerance in plants and deployment of salinity control measures will provide a long lasting solution on its effect on plant diseases. This will also serve as an approach to plant economic disease control.

An epidemy of a disease usually occurs when there is an interaction of the three (3) major factors of disease development popularly called disease triangle. The disease triangle consists of a susceptible host, virulent pathogen, and a suitable environment that favors the growth of the pathogen. When the two other factors interact with the pathogen, disease can reach epidemic condition referred to as epiphytotic stage. However, apart from these factors, many activities of human have a direct or indirect effect on plant disease epidemics, some of them favors and some reducing the frequency and the rate of epidemics. It has been established that some on-farm cultural practices such as selection of planting site, tillage, continues mono cropping and monoculture, inter cropping, spacing between plants/ plant density, weeding, crop rotation, fertilizer application and many others when misused or used carelessly may tend to allow or favor the development of epidemy by creating a suitable environment optimum for pathogen growth and development and sometimes making the host plant vulnerable to some peculiar diseases. This when human cultural practices are considered appropriately together with the disease triangle, could change the triangle shaped factors to a tetrahedral structure necessary for disease development. In this paper, major on-farm cultural practices that contribute to the epidemy of disease and the need to incorporate these factors as the fourth item in the disease factors are discussed.