INTRODUCTION
Importance of the Study
Plant diseases need to be controlled to maintain the quality and abundance of food, feed, and fiber produced by growers around the world. Different approaches may be used to prevent, mitigate or control plant diseases. Beyond good agronomic and horticultural practices, growers often rely heavily on chemical fertilizers and pesticides. Such input to agriculture have contributed significantly to the spectacular improvements in crop productivity and quality over the past 100 years. however, the environmental pollution caused by excessive use and misuse of agrochemicals, as well as fear- mongering by some opponents of pesticides, has led to considerable changes in people’s attitudes towards the use of pesticides in agriculture. Today, there are strict regulations on chemical pesticide use, and there is political pressure to remove the most hazardous chemicals from the market. Additionally, the spread of plant diseases in natural ecosystems may preclude successful application of chemicals, because of the scale to which such application might have to be applied. Consequently, some pest management researchers have focus their efforts on developing alternative inputs to synthetic chemicals for controlling pest and diseases. Among these alternatives are those referred to as biological control.
According to Cook and Baker (1983)‘‘Biological control is the reduction of the amount of inoculum or disease producing activityof a pathogen accomplished by or through one or more organisms other than man’’. Biological pest control (such as Cosmos 'Sensation White', lantana, African marigolds, and Bacillus thuringiensis) are the most efficient and responsible control to maintain pesticide free crop. We also control harmful insects (pests) by introducing insects that are their natural enemies. In this way, pests are kept at low levels without damaging the crop.