What's eating my zinnia?

Zinnias are most damaged by Japanese beetles eating flowers and foliage (US), aphids on new growth, thrips inside flowers, and caterpillars. In wet seasons, powdery mildew and Alternaria blight devastate foliage. Japanese beetles are the single biggest direct pest threat in the eastern US, often skeletonising plants by midsummer.

Adult beetles skeletonise leaves (leaving lace-like veining) and devour flower petals from June through August, congregating in groups and working rapidly through entire beds. Hand-pick beetles into soapy water each morning; do not use pheromone bag traps near plants; apply pyrethrin or neem oil spray; treat surrounding lawn with Heterorhabditis nematodes for grub control.

Colonies on soft stem tips and buds cause stunted, curled growth; honeydew attracts ants and promotes sooty mould on leaves and flowers. Strong water jet to dislodge; insecticidal soap spray; encourage ladybirds and parasitic wasps; remove heavily infested tips by hand.

Petals develop silvery streaks and brown-edged damage; flowers are distorted and short-lived; thrips hide deep inside flower heads making them difficult to see. Remove spent flowers frequently; apply spinosad spray at dusk; use blue sticky traps to monitor populations; avoid overhead irrigation which worsens flower damage.

Zinnia leaf tie caterpillars roll or fold leaves together with silk and feed inside the shelter; other caterpillars eat flower petals and leaves, leaving ragged holes and frass. Unroll tied leaves by hand and destroy larvae; apply Bt (Bacillus thuringiensis) spray for soft-bodied caterpillars; inspect plants every few days.