Why Is My Lavender Covered in Frothy Cuckoo Spit?

The white, frothy blobs that appear on lavender stems in late spring and early summer are the work of froghopper nymphs (Philaenus spumarius), commonly known as cuckoo spit insects. The froth is produced by the nymph itself as a protective coating — it draws plant sap up through its body and expels it as a foam that keeps the soft-bodied larva moist and protects it from predators and desiccation. While the sight of multiple frothy blobs on a lavender plant can be alarming, the actual damage to established plants is usually minor.

What is inside the froth?

Parting the foam with a finger reveals a pale green, oval-bodied nymph — the larval stage of the common froghopper. The nymph feeds on the plant sap of the stem it occupies, slowly withdrawing nutrients from that specific point on the stem. After four to six weeks, the nymph completes its development, the froth dries, and the adult froghopper — a small, robust, brown or grey insect capable of jumping considerable distances — emerges and moves away.

The damage they cause

A single froghopper nymph on a lavender stem causes minimal damage — the stem at that point may show slightly stunted or distorted growth, but the overall plant is rarely affected. Heavy infestations involving dozens of nymphs on a single plant can weaken growth and distort developing flower spikes if feeding occurs on the stalks. Young or recently planted lavenders are more vulnerable than established plants with a robust root system.

Removing cuckoo spit without chemicals

The most effective and straightforward approach is to direct a firm jet of water from a hose or pump sprayer directly at each frothy mass. This dislodges the nymph from the stem and removes its protective foam. Exposed to open air and sun, the nymph usually cannot reattach and dies. Repeat after rain, as reinfestation can occur. Physical removal by hand — simply picking the nymph off the stem — is equally effective.

Chemical treatment — rarely warranted

Because froghopper feeding on established lavender causes relatively little lasting harm, and because lavender is heavily visited by pollinating insects including bumblebees, applying insecticides is not recommended as a routine measure. If an unusually severe infestation is distorting flower spikes on a young plant, a targeted soap-based spray to individual froth masses can help, but this is rarely necessary.

Preventing recurrence

Female froghoppers lay eggs in the stems and dead plant material at the base of the plant in autumn. Removing the previous year's dead flower stalks and old woody litter from around lavender plants in spring can reduce the number of overwintering eggs and modestly lower the following season's population.