I have a problem with my 30-plus daylilies. As they finish blooming, the leaves get brown streaks and spots and die. I have been told they have thrips. I need to know what to do to have healthy plants.
Thrips are so small that they are hard to spot with the naked eye. These insects cause brown streaks on the leaves and distorted, damaged flower buds. There are also foliage diseases that can disfigure daylilies. If you suspect diseases or pests, you should have an extension agent or master gardener give your daylilies a look.
But I think it’s more likely that they are simply displaying typical daylily behavior. Daylilies love lots of moisture when they are in bloom. They grow best in rich, porous soil that stays moist. If the soil dries out during hot weather, leaves will turn brown at the tips and start to shrivel, beginning with the oldest leaves. Sometimes by the time the clump is done blooming, more than half its leaves are brown. Some varieties of daylilies are more prone to shabby foliage than others. The repeat-blooming ‘Stella d’Oro’ is one of the worst offenders.
The solution is to give the soil a regular soaking while the daylilies are blooming. Avoid high-nitrogen fertilizers. Mulch the soil to maintain moisture. Healthy daylilies, by the way, are better able to fend off diseases and pests (like thrips). Even so, you may find it necessary to cut back the fans of foliage halfway in late summer, and to groom out the remaining brown stuff. This will prompt fresh leaf growth. —Doug Hall