A herbaceous perennial, the daylily (Hemerocallis spp.) grows in a clump form with straplike foliage. It produces a non-stop flowering display from spring to fall. Numerous cultivars exist that offer a wide array of flower colors. Easy to grow and relatively pest-free, the daylily often suffers from spider mite infestations. The spider mite, a member of the arachnid group, looks like a tiny spider when magnified.
Numerous species of spider mites exist, but the two-spotted spider mite (Tetranychus urticae) regularly occurs on the daylily. The mites appear greenish, yellow-orange or red. The small insects congregate on the underside of the leaf’s surface. They feed on the plant’s sap by piercing the leaf with a strong mouth and sucking the nutrients. Due to the spider mite’s small size, the pest often goes undetected by the gardener until widespread damage occurs.
The pests suck the chlorophyll from the plant’s leaves while feeding. The lack of chlorophyll causes the leaf to become yellow and have a mottled appearance. As the feeding on the leaf continues, the leaf turns completely yellow. The leaf rapidly turns brown, dries up and falls from the plant. Spider mites occur in great abundance during hot, dry weather. The gardener often mistakes the leaf’s discoloration for inadequate irrigation.
If a spider mite infestation is suspected, look closely at the underside of the leaf. The small insects are often hard to detect with the naked eye and a magnifying glass may be needed to see them. The gardener may also notice tiny, round eggs attached to the underside of the leaf. The spider mite also produces a fine, silken webbing on the plant’s foliage. The webbing provides protection to the eggs and the young spider mites.
A wide array of miticides and insecticidal soaps exist that offer control of the spider mite. Care should be taken when using an insecticide because it can also damage beneficial insects. Numerous beneficial garden insects feed on the spider mite, such as the lady beetle. Consider hosing the plant’s foliage off every few days with a strong stream of water to dislodge the spider mites and their eggs.