From our roots to our petals, we hydrangeas face constant challenges from tiny invaders. While we are resilient plants, a severe infestation can weaken us, dim our vibrant blooms, and even threaten our lives. Understanding these pests from our perspective is the first step toward a healthy, symbiotic relationship. Here is a detailed account of our most common adversaries and how you can help us combat them.
We often feel the first signs of an aphid attack on our tender new growth and the undersides of our leaves. These tiny, soft-bodied insects pierce our tissues with their needle-like mouths to suck out our vital sap. This feeding causes our leaves to curl, pucker, and turn yellow. Worse than the direct damage is the sticky, clear waste they excrete, known as honeydew. This substance attracts ants and encourages the growth of sooty mold, a black fungus that coats our leaves and blocks the sunlight we need for photosynthesis. A strong spray of water from a garden hose can often dislodge these fragile pests. For more persistent colonies, insecticidal soaps or neem oil applications are effective and gentle on our beneficial insect allies, like ladybugs and lacewings, who naturally prey on aphids.
Spider mites are a particular menace during hot, dry weather. They are so small they are difficult to see with the naked eye, but we feel their presence keenly. They live on the undersides of our leaves, piercing individual plant cells and draining their contents. The first symptom you might notice is a subtle stippling or speckling of yellow dots on the leaf surface. As the infestation grows, leaves may take on a bronzed, dusty appearance and we may produce fine, silken webbing between our leaves and stems. Increasing humidity around us by misting our leaves can deter them, as they thrive in arid conditions. Like with aphids, a strong spray of water can knock many mites off. Miticides or horticultural oils are often necessary for severe infestations, ensuring thorough coverage of the leaf undersides.
Scale insects are deceptive. In their juvenile "crawler" stage, they move about, but once they find a suitable spot on our stems or the veins of our leaves, they insert their mouthparts and become immobile, developing a hard, protective shell. They feed on our sap, weakening us over time and causing yellowing leaves and stunted growth. They also produce honeydew, leading to sooty mold. Their armor makes them resistant to many contact sprays. The best approach is to treat during the crawler stage with horticultural oil. For light infestations, you can carefully scrape them off our stems with a soft brush or your fingernail, or dab each scale with a cotton swab dipped in rubbing alcohol.
These mollusks are a primary concern for us, especially in shady, moist gardens. They emerge at night and on cloudy days to chew large, irregular holes in our leaves, often leaving a tell-tale silvery slime trail behind. Young, tender leaves are particularly vulnerable. To protect us, you can create barriers of diatomaceous earth or crushed eggshells around our base. Beer traps sunk into the soil near us will attract and drown them. The most effective method is often a nightly patrol with a flashlight to hand-pick these pests from our foliage.
Japanese beetles are a formidable foe. These metallic green-and-copper beetles descend on us in summer, and they do not merely nibble; they skeletonize our leaves. This means they eat the soft tissue between the leaf veins, leaving behind a lace-like skeleton of a leaf. This severely reduces our ability to produce energy. The most direct and immediate control is to physically pick them off our leaves early in the morning when they are sluggish and drop them into a bucket of soapy water. Neem oil can act as a repellent and disrupt their feeding. It is important to avoid Japanese beetle traps, as the pheromones they release can attract more beetles to your garden than they catch.
