Lace Bug Damage on Azaleas and Rhododendrons
I have noticed a lot of lace bug damage recently on azaleas and rhododendrons. Azalea lace bug (Stephanitis pyrioides) is a relatively new insect pest in the Pacific Northwest. According to Washington State University Hortsence web site (http://pep.wsu.edu/hortsense/), “azalea lace bug attacks both azaleas and rhododendrons and may cause significant damage on both. Both adults and nymphs feed on the underside of leaves. Symptoms of damage are stippling, bleaching, or a silvery or yellowish (chlorotic) appearance of the leaves. The underside of the leaf will appear dirty due to the presence of insects (eggs, nymphs, and adults) and brownish or tar-like fecal spots, particularly along the leaf veins.
Heavily damaged leaves may drop from the plant. Adults are about 1/10 inch long with lacy, net-like, transparent wings. The azalea lace bug has smoky, brown markings on the wings, which distinguish it from the pale whitish-tan rhododendron lace bug. The young nymph is colorless to black and spiny depending on age.”
Several insecticides will control lace bugs. The problem is getting the bottoms of all the leaves thoroughly covered. Because of this, systemic insecticides which are translocated through the plant’s circulation system are most effective. Imidacloprid is a systemic pesticide which can be applied to the soil and is taken up by the roots. It is available in several brands including Monterey Once A Year Insect Control and Bonide Systemic Insect Control granules. Acephate (Orthene) is another systemic available in both spray and granular form. Spinosad is a new systemic organic pesticide which is effective on a wide range of insects. Neem oil is another organic pesticide which will control lace bugs.
Three spray applications at 2 to 3 week intervals are necessary to control the multiple generations of this pest. One application of granules is sufficient.
Allen Wilson
Allen has been writing about gardening for over 30 years. He is a retired professor of Horticulture.