Direct dissemination of expert knowledge to agricultural producers through computer programs will increase product quality as well as profit margin. The construction of an expert system to help farmers manage apple orchards is reported. The system provides advice regarding specific pest management, treatment of winter injuries, drought control and general pesticide selection. The knowledge structures employed in the construction of the system are explained, and some sample interactions are provided. A model of the apple scab disease cycle is incorporated into POMME to give the system a more fundamental reasoning capability than available from the use of infection tables. Extension experts who have run trial cases on the system have approved its release for use by commercial apple growers.