Leaf Tier Control on Hydrangea

Leaf Tier Moths

• Their brown and pale-gray coloration disguises tiny leaf tier moths as bits of bark or decaying leaves. After pupating in the soil around hydrangeas over the winter, the moths emerge from mid spring to midsummer. After mating, the female moths lay their eggs on the shrubs' new, green branch tips.

Caterpillars

• Black-headed, greenish-yellow leaf tier caterpillars attach silken strands along the edges of two unfolding hydrangea leaves. They weave the leaves shut, sealing themselves and unopened flower buds inside. Seen from the outside, these leaf shelters look like tiny cabbages perched on the ends of the branches. A single hydrangea may shelter as many as 20 caterpillars. The tied leaves darken and crumble as the pests consume their inner tissues along with the flower buds. The caterpillars drop to the soil in summer to pupate and overwinter. Leaf tier infestations rarely harm hydrangeas, but the cosmetic damage they do may warrant control.

Insecticidal Soap

• An insecticidal soap solution suffocates garden pests. The traditional method of spraying the solution may not work on a leaf tier caterpillar nestled in its shelter. A better approach is to prepare an open container of solution and soak each pair of tied leaves, caterpillar and all, in it. The Colorado State University Extension recommends a mix of 5 tablespoons of liquid dish detergent or hand soap in 1 gallon of soft water. Rinsing the hydrangeas a few hours after treating them reduces the risk of sun damage.

Bacillus Thuringiensis

• Treating a hydrangea with Bacillus thuringiensis when leaf tier eggs begin hatching kills any caterpillars unlucky enough to ingest it. Spray the branch ends with 4 teaspoons -- or the label's specified amount -- of Bt concentrate mixed in 1 gallon of water. The bacteria disrupt the caterpillars' digestive processes so they eventually starve. Timing is critical; spraying when the pests have taken shelter inside the leaves is too late. On a cloudy or early evening, saturate the leaves on both sides with the spray. Repeat weekly until all the caterpillars have hatched.

Manual Control

• Pruning a few pairs of infested branch tips doesn't leave noticeable gaps on larger hydrangeas. If yours are still small and you don't want to spray with soap or Bt, a less appealing alternative is to open the tied leaves and crush the caterpillars. If you're squeamish, crush them by mashing the leaves together.