The Azalea lace bug, Stephanitis pyrioides, is a relatively new pest that home gardeners should be on the lookout for. First detected in Oregon in 2009, this bug has been causing significant damage on plants in the Ericaceae family, which includes rhododendrons, azaleas, and pieris. Because of our mild climate, this pest can survive the winter and breed multiple generations each year. The Azalea lace bug becomes active in mid- to late May and early June, when it starts laying eggs. So starting in mid-May, gardeners should keep an eye out for the eggs, which are partially embedded in the tissue underneath leaves. The azalea lace bug uses its mouth to pierce the underside of the leaves of the plants and eat small holes in the leaf tissue. This leaves a yellow dot-like pattern on the surface and black fecal spots underneath. Large populations can cause azalea leaves to turn white. On rhododendrons, severe damage may look like iron chlorosis with yellow leaves and green veins. Heavy feeding can kill plants.
The best defense against the Azalea lace bug is early detection. Examine the leaves of your plants if they appear stressed, turning them over to look for small pin holes and black dots of fecal material. You can apply insecticidal soaps, horticultural oils and neem-based products regularly to the bottom of the affected leaves to reduce or prevent further damage, but they will not restore the plant to its untouched appearance. Additionally, you can spray pesticides that kill insects on contact, such as pyrethroids or carbaryl. Coat the leaves well, including on the underside. Be sure to only spray the affected plant and be careful of spraying when other beneficial insects are out such as bees and butterflies.
Some azaleas are immune to the pest, including Indica alba, Flame Creeper, Hino crimson and the new Encore azaleas. Azalea lace bugs are more likely to damage plants in hot, sunny locations or in drought stressed conditions. So for new plants, choose a protected spot in your yard, out of direct coastal winds. Add lots of topsoil and compost when planting for a healthier plant. Water and fertilize regularly..