My hydrangeas are over seven years old and they have always been healthy and blooming until this year. One lacecap hydrangea was developing leaves, but they were small and curled. The stalks from this past year on the other hydrangeas were not developing any leaves even though they had buds on them when I checked a few weeks prior to this. It appears something is boring a hole into the center of the stalks and leaving “sawdust” on the new leaves. All the hydrangeas have this same problem. On the lacecap, I cut away more and more, until I reached the base of the plant and thus had to destroy the plant altogether. The bugs look like ants with wings. They are not termites, as their bodies have a shape to them. I know that the plants will not bloom this year and I don’t know if they will live. This appears to have happened in less than three weeks. Any ideas?
Although hydrangeas can be susceptible to leaf spots, blights, wilts and powdery mildew, it is rare that insects plague them. The hollow stems you are finding may be the natural growth of your hydrangeas. Some have hollow stems, while some have hollow stems filled with white to brown pith, depending on the age of the particular stem. The presence of pests may actually be a sign of another problem that is causing your plants stress. Insects that may trouble the hydrangea include aphids, leaf tiers, rose chafers, oystershell scale and four-lined plant bugs.
Aphids distort the new growth and coat the leaves with sticky honeydew. These insects can be dislodged with a high-pressure water spray from your garden hose.
A leaf tier is evidenced by webs on the leaves and over the tips of the branches. Pick these insects off by hand.
Rose chafers are light tan beetles with red, spindly legs. They occur in large numbers where the soils are sandy. Chemicals are ineffective because more rose chafers quickly move into the treated area to replace those killed by pesticides.
Oystershell scale infests the upper stems of the hydrangea and often goes unnoticed. Sprays of dormant oil should control the overwintering stages and are less harmful to beneficial predators that help to control scale.
Four-lined plant bug causes round, brown, sunken spots on the leaves. The injury is often thought to be disease. Sprays are rarely needed for this.
Your local garden center will have pesticide sprays that you can use to control the crawlers. Ask their experts to help you choose the right product and, as always, read the labels carefully before using. Your keen observations and quick actions are the key to healthy plants.