Security is an important phenomena for energy conservation in wireless sensor networks (WSN). Moreover, the management of trust in the WSN is a challenging task since trust is used when collaboration is critical to achieve reliable communication. In a military application using WSN, it is often necessary to communicate secret information such as military operation urgently. However, the existing routing algorithms do not consider security in the routing process. Moreover, since security is an important aspect in WSN, it is necessary to consider the security aspects in routing algorithms. Different approaches for providing security are trust management, intrusion detection, firewalls and key management are considered in the literature. Among them, trust management can provide enhanced security when it is compared with other security methods. Therefore, a new secure routing algorithm called energy aware trust based secure routing algorithm is proposed in this paper where the trust score evaluation is used to detect the malicious users effectively in WSN and spatio-temporal constraints are used with decision tree algorithm for selecting the best route. From the experiments conducted, it is proved that the proposed trust based routing algorithm achieves significant performance improvement over the existing schemes in terms of security, energy efficiency and packet delivery ratio.