We want to alert you to an insect that may be feeding on your rhododendrons and azaleas. Originally from Japan and first spotted in Washington in 2008, the Azalea Lace Bug (Stephanitis pyrioides) has now become widespread in our area. In addition to your prized azaleas and rhododendrons, it can also feed on other landscape ornamentals such as mountain laurels and pieris.
Despite their delicate appearance and minute size (⅛” - ¼”), their feeding habits can cause severe damage to plants. They’re often hiding out on the underside of the foliage where they insert their needle-like mouth parts into the leaf, secrete saliva, and suck out a chlorophyll rich smoothie. You may notice stippling on the leaves, and over time the whole leaf may bleach out. Severely damaged leaves brown out and die, which can defoliate the plant over time. For affected Evergreen varieties, the foliage retains injury and could be less functional for more than a year.
Visuals of the types of damage left behind by ALBs and their various life stages. Photo: Oregon State University
Prevention is key - keep your plants hydrated! This bug is most active during our spring and summer months. Plants that are dehydrated send out distress signals that attract destructive insects like lace bugs. We encourage watering less frequently, but more deeply, and adding a thick layer of mulch to reduce your watering needs. Since rhododendrons and azaleas have a shallow root system, they may be suffering while surrounding plants with deeper roots show no signs of drought stress. See our blog here for our full tips on watering. Another important step is ensuring that your plants get the right nutrients, like those found in our FertileTea. Keeping your plants well-fed and hydrated is a great first defense against all pests and diseases.
Try choosing cultivars that have shown resistance to Azalea Lace Bugs such as ‘Dram,’ ‘Marilee’, ‘Seigei,’ ‘Macrantha,’ ‘Salmon Pink,’ ‘Elsie Lee,’ ‘Red Wing,’ and ‘Sunglow’.
If possible, move your plant to a shadier location, or create shade with taller canopy plants. Bonus if you include other flowering plants nearby to increase the complexity of your landscape and the variety of tiny predators hanging around. Lace bugs are the prey of green lacewings, assassin bugs, pirate bugs, mirid plant bugs, earwigs, lady beetles, spiders, and more. You can attract these beneficial insects by incorporating a wild area, herb garden, or flowers into your landscape.
Understanding the life cycle of lace bugs is important to controlling the population. They overwinter as eggs that have been deposited inside the leaf and then covered with frass that creates a varnish-like shield. This double layer of protection makes treating the egg stage very difficult. In some areas, there’s a parasitic wasp that lays its larvae inside the egg, controlling up to 1⁄3 of the population. Without the help of these wasps, most organic insecticides with the exception of specific horticultural oils would not be effective at treating the egg stage.
ALB adults and nymphs feeding on the underside of leaves Photo: Gardener's Path
It’s best to treat during the nymph stage in spring after their first hatch, typically around May to early June. They have a long hatching period, and climate has a direct impact on how fast they go from nymph to adult. In warmer temperatures, it could take a short 22 days, in cooler areas it may take up to 97 days. Check once a week for nymphs. When populations are low, the nymphs can be knocked off with a strong stream of water from the hose. They’re first born clear, turning brown and spiky over time. In the clear stage they can be hard to detect, but they tend to cluster. By holding foliage to the sun, you can see the silhouettes of these clusters. Treating at the nymph stage is the best way to prevent damage to the plant. This will reduce the number of adults, who do 12 times more damage than nymphs, and will prevent the laying of future generations.
Azalea lace bugs are considered more destructive than other lace bugs, such as their cousin Stephanitis rhododendri, because they lay multiple generations in one year. Catching this first generation is key, but there is a second one around late June - July, and if warm weather continues there could be a third generation around late August - September. If knocking them down with water doesn’t seem strong enough or they’ve reached the adult stage, there are various organic methods using insecticidal soaps and horticultural oils for control. We do not recommend the use of chemical insecticides which have harsher effects on pollinators, beneficials, and the environment. It’s important to consider when using any insecticide, organic or otherwise, the possible damage they can cause to beneficials, the environment, and yourself. Always follow the label and wear the recommended protective equipment. Don’t apply to flowers in bloom, and try to spray during the early or late hours of the day when pollinators are resting. Organic and naturally occurring insecticides must have direct contact with insects to be effective and may take multiple applications to be completely effective.
Ideally, there would be enough diversity and natural predators that resorting to insecticides would not be necessary. For some, it may be a line they won’t cross. If the Azalea Lace bug has become unmanageable, it may be better to switch to a different flowering shrub altogether like camellias or daphnes.
There are many ways to create a beautiful, robust, and varied landscape. As plants and bugs get moved all around the world, it’s crucial to be aware of the changes happening in our yards. Our landscapes are part of a patchwork that make up the urban ecosystem. By choosing to plant the right plants in the right place, increasing biodiversity, and using organic management methods, it's possible to have your own low-maintenance outdoor sanctuary.
Want to learn more about organic pest management? Give us a call! We’d love to help.