What's eating my big bluestem?

Big Bluestem, the tallest North American prairie grass, faces more pest pressure than most ornamentals. Rust fungus is the most common problem, causing orange pustules on the distinctive blue-green blades. Aphids colonise new growth, grasshoppers chew blades in dry summers, and armyworm caterpillars can cause heavy defoliation. Deer may browse young plants in late spring.

Orange or reddish-brown pustules across leaf blades and stems; heavy infection turns foliage prematurely brown and weakens the plant before fall color develops. Hard cutback in late winter removes overwintered spores; improve spacing for air circulation; sulfur or myclobutanil fungicide if infection is severe and recurring.

Dense colonies on young shoots produce honeydew, attract ants, and cause minor leaf curl on emerging growth in spring. Water jet to dislodge; insecticidal soap spray; rely on natural enemies (ladybugs, parasitic wasps, lacewings) for season-long control.

Caterpillars rapidly defoliate blades overnight, leaving ragged stubs — outbreaks are most severe in late summer in the south-central US. Bt or spinosad applied at first sign of feeding, ideally in the evening; scout after periods of warm humid weather.

Chew long strips along blade edges and consume seed heads during hot dry summers, reducing ornamental value significantly. Nolo Bait (Nosema locustae) applied early in the season; encourage bird predators; chemical control with carbaryl for severe outbreaks in large plantings.