What's Eating Your Peppermint?

Specks barely larger than a pinhead, in tan, red, or pale yellow, clustered on the underside of peppermint's opposite leaves. Fine webbing collects between the leaf pairs along the square stem. Tap a stem over white paper and the mites scatter as moving dots.

Leaves fade to a dull silvery-yellow then turn brown and drop from the bottom of the plant upward. Indoor peppermint near heat vents can lose half its foliage in 2 to 3 weeks. The oil glands on the leaves release a weak menthol smell where mites have been feeding because the cells are damaged.

Soft pear-shaped insects 2 to 3 mm long, in green, black, or grey, packed on the soft new shoot tips and along the underside of the topmost leaves. They concentrate where peppermint's growing points push new sets of paired leaves above the oldest growth.

New tips curl and twist, often with a sticky honeydew coating that draws sooty black mold. Heavy infestations stunt the season's runners and dilute the menthol oil content of the leaves, leaving harvested sprigs flat-tasting and weak.

Tiny shiny black or bronze beetles, 2 to 3 mm long, that hop away like fleas when you approach. The mint flea beetle is a specialist on mint family plants and shows up in established mint patches in late spring and summer. Larvae feed underground on the roots.

Leaves develop a peppered shotgun pattern of tiny round holes, sometimes hundreds per leaf, that gives the patch a lacy or scorched look. Heavy beetle pressure can yellow whole runners, and the underground larvae weaken the rhizome system that lets mint spread.

Soft-bodied brown or grey mollusks, 1 to 4 inches long, active overnight and on cool damp mornings. They hide under leaf litter, the dense ground-level layer of mint runners, and beneath mulch by day. Silvery dried slime trails on the lower leaves are the giveaway at dawn.

Large ragged holes appear in the soft lower leaves overnight, often eaten from the leaf edge inward. Heavy slug pressure on a wet spring shreds the bottom third of a mint patch and creates entry points for fungal disease on the damaged tissue. Outdoor mint planted in shade is most vulnerable.

Small soft insects covered in a white waxy fluff that looks like cotton or lint. They tuck deep into the leaf-node joints of peppermint's square stems and along the runners just below the soil. Slow-moving and easy to miss until colonies coat the lower stem.

Stems weaken and snap easily, and the leaves above the colony yellow and curl. Sticky honeydew coats the lower foliage and draws sooty mold. Indoor potted peppermint is the most vulnerable, especially plants overwintered in heated rooms with stagnant air.