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Azalea
Lace Bugs were first reported in Oregon in 2009. I first noticed it in 2011 when I saw some azalea leaves that were bleached out until
they were a dirty white. Rhododendron leaves were yellow. The tiny spots on the leaves looked like Rhododendron Lace Bug damage, but it was
many times worse than I had ever seen before. This was because Azalea Lace Bugs have three or four generations each year so they multiply faster
and feed longer than Rhododendron Lace Bugs, which have only one generation each year.
Azalea Lace Bugs are very similar to Rhododendron Lace Bugs, which have been here a long time. They both have flat, overlapping wings which are mostly transparent with dark markings. The nymphs hatch from eggs in the spring and begin to feed on the underside of the leaves. The dark spots on the leaves are varnish-like droppings. Most azaleas and many rhododendrons are seriously damaged by these lace bugs. I also saw lace bug damage on Japanese holly.
A single
spray in June with imidacloprid will quickly kill the lace bugs and protect the plants for the rest of the summer. It is also systemic which means it will
absorb into the plant and move around to protect the undersides of leaves which did not get sprayed. It is most effective if sprayed when lace bugs
first appear in late May or early June. However, it is toxic to bees, so it cannot be sprayed until plants are finished blooming. Sometimes I pull
the last of the flowers off of the late blooming rhododendrons so I can spray all the rhododendrons and azaleas at the same time.
Unfortunately, imidacloprid is also toxic to beneficial insects which are natural predators of lace bugs: assassin bugs, lacewing larvae, ladybird beetles, pirate bugs and predaceous mites. These help limit the numbers of lace bugs, but they will not eliminate them.
Instead of spraying the leaves, another option is to drench the soil around the base of the azaleas and rhododendrons with a stronger mixture of imidacloprid such as Monterey Once a Year Insect Control. This soil drench has to be applied in early May because it takes several weeks to absorb into the plants. The big advantage of soil drenching is that all of the plant is protected from harmful insects but there is much less effect on bees and beneficial insects.
Another insecticide which can be used is Captain Jack's Deadbug Brew, which contains Spinosad, an organic insecticide. It is very effective on lace bugs, but has minimal effect on many of the natural predators and beneficial insects. However, it is poisonous to bees, so it cannot be sprayed on plants while they are blooming. Other insecticides which are not as effective on lace bugs but are much safer for bees are horticultural oil, insecticidal soap and neem oil. However, they have to be sprayed directly onto the insects so thoroughly spray the undersides of the leaves until they just start to drip.
The ideal solution for lace bug damage is to remove heavily damaged plants and replace them with azaleas and rhododendrons which are resistant to lace bugs. Unfortunately, I found lace bug damage on every variety of azalea and rhododendron, but some varieties were much less likely to have damage than others. The worst damage on rhododendrons I found was on Chinoides, Cilipinense, PJM, Scarlet Wonder, Unique and Vulcan. The least damage was on Anah Kruschke, Daphnoides, Jean Marie and Ramapo. I had some in my yard which had never been treated and the damage was light and acceptable. Of the azaleas, Delaware Valley, Flame Creeper, Hahn's Red, Hino Crimson, Macrantha and Rosebud had the least damage. There were other varieties with little damage, but I could not positively identify them.
Yaku hybrid rhododendrons and other varieties with thick fuzz (indumentum) under the leaves are likely to have less damage. Azaleas reported to have less damage are Cavalier, Dawn, Elise Lee, Red Wing and Salmon Pink. Some of the Encore Azaleas varieties are reported to be more resistant: Autumn Amethyst, Autumn Cheer, Autumn Rouge, Autumn Royalty, Autumn Sangria and Autumn Twist.
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