Undentified bumps on tree limbs
See picture below. This is a picture of sprigs that fell from a tree in my backyard. What are the little bumps on the limbs? What should I do to treat it? I also had a nearby oak die that was growi g easier this spring. See picture #2. Any thoughts or suggestions? It looks like a branch of a tree behind it is now dieing as well.
Anne Arundel County Maryland
The lumps on the oak stems are a type of Lecanium scale, an insect that feeds on plant sap through the stems and foliage. Juveniles, called crawlers, may be out now (or very soon) and are the most vulnerable stage in their life cycle. Predators seek them out and can provide control, but heavy infestations with insufficient beneficial insect activity may need control with insecticides. Horticultural oil sprays applied during the crawler period help, along with dormant oil (a more concentrated formulation specifically made for use when foliage isn't present) in winter. If the tree is too large to spray, a certified pesticide applicator (from a landscape company, for instance) can apply a systemic insecticide instead.
Death of older trees often occurs slowly as a gradual decline, though sometimes the symptoms are subtle until a final stress factor pushes them over the edge and leaf damage or dieback becomes more prominent or rapid. Urban and suburban growing conditions are hard on shade trees, and often they are subjected to compacted soils, insufficient (or excessive) moisture, reflected heat, and air pollution. Stress creates greater susceptibilities to insect and opportunistic fungal attack, which in turn makes trees less resilient to environmental stresses, and the feedback loops spirals into decline. We cannot determine what killed the trees in the photo; it can be quite difficult to discern the initial trigger for decline once dieback is severe or complete.
For oaks, here is information on common causes of drastic decline, though it is not exhaustive:
In the future, for trees with suspected issues or symptoms of decline or lackluster canopies, consulting a certified arborist is useful. They are trained to evaluate tree health, hazards and risks to safety, and can investigate symptoms and growing conditions more thoroughly than photographs can show.