Q Why did some of the buds on my hemerocallis swell but fail to open?
A They were attacked by the hemerocallis gall midge, which lays its eggs inside the buds. The larvae then hatch inside and cause the buds to become swollen and distorted and unable to open properly.
Caption: Hemerocallis gall midge causes the flower buds to swell and fail to open
Q What can I do to control hemerocallis gall midge?
A As the larvae are inside the buds, they can't be controlled by a contact insecticide, so the easiest way to control this pest is to pick off affected buds and burn them. Don't compost them or the adults will emerge and the cycle will go on. Early-flowering varieties of hemerocallis tend to be worst affected, while later ones produce buds after most of the gall midges have laid their eggs.