Lilacs and irises are longstanding low-maintenance performers in the Kansas landscape that bloom in spring. Sometimes they fail to produce flowers, though, and the gardeners who tend them wonder why. Insect borer infestations are the most likely culprit for bloom failure in established plantings of lilacs and irises, but the insects are difficult to detect without prior knowledge of their existence. To keep lilacs and irises blooming and healthy, gardeners must be diligent in watching for signs of borer presence and removing infested material.