Daylilies are nearly carefree, attract few pests and require little in the way of feeding. Each flower lasts only a day, but numerous buds on each stalk ensure weeks of continuous profuse blooming year after year. However, several species of thrips feed on daylilies, causing poor flower color, torn leaves and distorted, stunted blooms and buds. Thrips become more active during dry weather. Allowing beneficial predators to manage thrips invasions, is the most effective approach. But if natural predators aren't up to the job, initiate diligent low-toxicity organic application efforts.
Make sticky traps for thrips detection early in the growing season before thrips can develop into a large destructive population. Cut 3-by-5 inch pieces of cardboard. Paint one side bright yellow and the other side bright blue. These are colors known to attract thrips. Staple or glue the painted cards to garden stakes and cover their surfaces with liberal amounts of petroleum jelly. Stick a staked trap every several feet or so in your daylily bed. If you have adult thrips, you'll catch some with these traps within a day or two.
Check your thrips traps for the tiny, near microscopic captured adults every two to three days. Traps will also attract fungus gnats, winged aphids and whiteflies. If you've caught some thrips, examine your daylily plants for the presence of pirate bugs. If you find these guys, no further action on your part is necessary. Adults are about 1/20 inch long, brownish to black in color with grey-white faces. Each pirate bug consumes about 20 thrips larvae daily.
Apply insecticidal soap spray if you don't detect the presence of pirate bugs or visits by other beneficial predatory insects to your daylily plants. Insecticidal soaps are low-toxicity products and are highly effective for thrips control. Coat all surfaces of the plants generously with the solution at three- to four-day intervals to control all life stages of the thrips.
Repeat insecticidal soap applications until you no longer capture adult thrips with your traps.
Continue to monitor traps for re-appearances of thrips throughout the season, and respond aggressively with insecticidal soap applications as necessary.