Purple Leaf Plum Dieback: Armored Scale Infestation and Pruning

Purple leaf plum branches dying after blooming in Illinois suggest armored scale infestation. Check branches for small, circular bumps (1-2 mm) that scrape off with a fingernail—these are scale covers protecting feeding insects underneath. Heavy infestations kill branches by sucking sap.

Treatment: spray horticultural oil in late March (before bud break) at dormant rate, coating all bark thoroughly. Repeat in 2-3 weeks. For active crawlers (late May), use insecticidal soap or systemic insecticide (imidacloprid). Prune out dead wood, reshaping the tree naturally—remove crossing branches, open the center, maintain the vase form.

Scale often attacks stressed trees. Ensure proper watering, mulch, and avoid lawn herbicides near the root zone. Monitor annually—scale returns if predators (lady beetles, parasitic wasps) are absent.