Hydrangeas are highly valued garden shrubs, admired for their lush foliage and impressive floral displays. Identifying the specific cause of leaf damage is the initial step toward effective treatment and maintaining plant health. Pests attack hydrangea leaves in two primary ways: chewing and sap-sucking. The visible signs of their feeding offer clear clues about the culprit, helping distinguish between damage types and providing targeted solutions.
Pests That Chew Holes in Leaves
Physical holes and missing leaf tissue are the telltale signs of pests that use chewing mouthparts. The pattern of destruction helps narrow the list of suspects.
One recognizable form of damage is skeletonization, where the soft tissue is eaten away, leaving only the tough, lacy network of veins. This feeding pattern is characteristic of the adult Japanese Beetle, a metallic green pest active during the summer months. Japanese beetles often feed in groups, and their collective damage can rapidly defoliate a plant, leaving the leaves appearing scorched or netted.
Large, irregular holes, sometimes extending to the flowers, indicate the presence of Rose Chafers. These slender, tan-colored beetles are slightly smaller than Japanese Beetles and may also cause skeletonization on the edges of the leaves. Rose chafers are problematic in areas with sandy soil, and their grubs can also damage plant roots.
Slugs and snails are another common source of irregular holes, preferring the moist, shaded environment near the base of a hydrangea. These mollusks leave behind ragged-edged holes, typically on lower leaves. Their presence is confirmed by the silvery, dried mucus trails they leave on the foliage and surrounding surfaces. Inspecting the plant at night or after a rain shower is the best way to spot these primarily nocturnal pests.
Pests That Cause Leaf Discoloration
Sap-sucking insects damage hydrangeas by piercing the leaf tissue and extracting sap, causing discoloration or texture changes. This feeding method creates tiny injuries that disrupt the plant’s ability to photosynthesize effectively.
Spider Mites, which are tiny arachnids, cause a fine, speckled yellow or white pattern known as stippling on the leaves. These pests thrive in hot, dry conditions and feed primarily on the undersides of the foliage, often spinning fine silk webbing. Stippling occurs as the mites extract the contents of individual leaf cells, leaving small, discolored spots.
Aphids are small, soft-bodied insects that cluster on new growth and the undersides of leaves, sucking the sap from tender parts. Their feeding can cause leaves to curl, become distorted, or turn yellow. Aphids also excrete a sticky, sugary liquid called honeydew, which coats the leaves and can lead to the growth of sooty mold, a black fungus that blocks sunlight.
Scale Insects also feed by sucking sap, appearing as small, immobile, oval or dome-shaped bumps on the stems and leaf veins. An infestation of scale can cause leaves to yellow and drop prematurely. Like aphids, they excrete honeydew, which attracts sooty mold, and identifying adult scale requires close inspection due to their protective waxy covering.
Targeted Control and Prevention Methods
Effective management begins with the least toxic method. For chewing pests like Japanese Beetles, immediate manual removal is a practical first response. Adult beetles can be hand-picked from the foliage, especially in cooler morning hours when they are less active, and dropped into a container of soapy water.
Slugs and snails are controlled by reducing their habitat, which involves clearing leaf litter and debris from around the base of the plant to eliminate daytime hiding places. Barriers like copper tape or diatomaceous earth applied around the perimeter can deter their movement. Commercial baits containing iron phosphate are effective and safer for pets and wildlife than older chemical options.
For soft-bodied, sap-sucking pests, a strong jet of water from a garden hose can physically dislodge aphids and spider mites from the leaves, especially when directed at the undersides. This mechanical control is often sufficient for minor infestations and helps disrupt the fine webbing of spider mites.
If physical removal is not enough, horticultural products offer a targeted approach. Insecticidal soap is effective against aphids, mites, and scale nymphs, working on contact to penetrate the soft bodies of the insects. Neem oil, derived from the neem tree, acts as both an insecticide and a fungicide, effective against many chewing pests and early-stage sap-suckers by suffocating them and disrupting their feeding cycles.
When applying any spray, ensure complete coverage of the foliage, including the lower leaf surfaces and stems, and always follow the product label instructions carefully. Proper cultural care minimizes plant stress, making the shrub less susceptible to severe pest outbreaks. This includes ensuring the hydrangea is planted in appropriate soil and receives adequate, consistent watering.
For persistent or severe infestations of hard-to-control pests like Japanese Beetles, a targeted insecticide may be necessary. These should be used judiciously and preferably applied when the plant is not in bloom to protect pollinators.