A mobile robot was developed to directly apply chemical to individual weed, plant specific direct chemical application. The robot has a mobile platform equipped with a laptop, a robotic arm with the direct application end effector and a machine vision. The laptop computer and the arm were connected to the robot's microcontroller via a serial interface, and the machine vision was controlled by the computer via IEEE 1394 interface: the machine vision detects weeds and the arm with the end effector eliminates weeds. A C++ program was written to control the robot and its components: the program included an image processing algorithm for the machine vision to detect weeds under variable outdoor illumination, and a robotic arm motion control algorithm to eliminate detected weeds. Detected weeds were eliminated by the end effector via cutting a stem and sweeping chemical on its surface. As a result, the developed robot showed the fully automated processes of plant specific direct chemical application: detecting and eliminating weeds, examining the application results, and executing the re-application. While the robot was testing in the field, the robot was able to detect the plants despite outdoor illumination changes. The robot controlled 63.6 % of the weeds in the field. Developed robot may enlighten the potential to reduce the chemical use, to improve chemical efficiency and to reduce environmental contamination from agrochemical.