The flower thrip’s (Frankliniella tritici and F. occidentalis) feeding habits cause the blossoms of the daylily to appear diseased and deformed. Flowers wilt and rarely open before falling from the plant.
Flower thrips are small brown insects. They measure less than one-sixteenth of an inch, according to the University of Illinois Extension Integrated Pest Management. Identifying thrip species is difficult without magnification due to their small size but all varieties feed and behave in the same manner. The difficulty in visually seeing the thrip is one reason why gardeners often think the flowers of their daylily are suffering from a disease instead of a pest.
The flower thrip uses its powerful mouthparts to scrape the cells of the flower bud. The action weakens the bud, destroys the flower’s surface and causes scarring to result. The scraping benefits the insect by causing the bud to weep sap but the wounds eventually cause the flower to perish.
Control the insects by applying an insecticidal systemic drench in the spring months. Insecticidal soaps also help control the flower thrips. The use of insecticidal sprays is often difficult because the insects hide within the petals of the flower where the spray cannot reach them, according to the Connecticut Agricultural Experiment Station.