The challenge in the agricultural domain is how to use the has the power of Information Communication and Technology to build an advisory system which farmers can used to improved the farming exercises hence increase cotton crop production. A large quantity of agricultural information such as soil health information, different cropping pattern, crop disease at specific location and different pests were retrieved from various types of resource such as satellites remotely located, services and sensor connected in network. Cotton crop advisory system for cotton crop explained in this paper which eliminates the gap among agricultural domain experts and cotton crop farmers. The system has mainly three main components: Cotton crop pest Ontology, the web services to communicate between components .We have created ontology which contains information related to soil, crop, disease, pest, cultivation process and other relevant information .We have used Protégé tool for developing this ontology development .The web services were developed for interacting with various sources of data. The Java programming language supports RESTful web services. We have used Eclipse EE IDE and JAX-RS/Jersey API for building RESTful web services. A user interface is provided to Cotton crop farmers to submit their query regarding pest, observed symptoms, disease for cotton crop. Our system generates relevant recommendation of pesticide, insecticide which needs to be used for prevention of disease to cotton crop.