In this paper, we discuss the implementation of a rule based expert system for diagnosing diseases in paddy, wheat and maize. The proposed system is implemented as a rule based expert system in a MVC framework of PHP Laravel for the diagnosis of diseases in crops. In the system, the user is presented with a list of questionnaires about the symptoms seen in the crops and system identifies which is the most likely disease.In the system the users can access the application through the browser. They can choose to view the table that contains information about the disease and symptoms seen in leaf, steam and roots. User can also choose the view where they get to select one crop from paddy, wheat and maize that they want to diagnose. Then the users will be redirected to a view where they can select the symptoms that they have seen in their crops. When the users press submit button the result will be shown to them. Symptoms of disease that were known in priori was given to the system. The system correctly identified what disease the plant was suffering from in most of the cases. The system gave unable to identify for new disease that was not in the knowledge base.