We present Starburst, a routing-based protocol designed to efficiently disseminate data items to small subsets within a sensor network. Starburst constructs a routing hierarchy to enable fast, efficient and reliable dissemination to nodes in a sensor network that satisfy data-specific predicates. The protocol is based on the idea that when only a few nodes need an update, it is more efficient and much faster to route to those nodes directly. When every node needs an update, algorithms such as Trickle are more efficient. Starburst therefore dynamically determines what portion of nodes need an update and locally adapts its delivery policy accordingly. We also present dynamic beacon selection algorithms which enable scalability and fault tolerance in Starburst. We have implemented and evaluated Starburst on top of both the BVR and S4 routing protocols with promising results. Our simulations show that Starburst reduces both the transmission cost and latency of existing dissemination protocols by at least 50% for small subsets of nodes, and performs no worse than them for larger sets. Finally, tests on the Motelab testbed validate our simulation results.