Evergreen Azalea Insect Pest

Asked October 28, 2013, 11:09 PM EDT

What are the scale like insects on the underside of my evergreen azaleas and some rhododendrons leaves? Their stippeling can be seen on the tops of the leaves as well, similar in appearance to red spider. Treatment options?

Multnomah County Oregon insect issues insect management azaleas

1 Response

We’ve been receiving numerous questions about azaleas and rhododendrons recently. The problem is usually azalea lace bug. But to confirm that, please review this publication: “Azalea Lace Bug” -- http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/40424/em9066.pdf

If the information and images don’t match with your azaleas and rhododendrons, please let me know, and include at least 3 digital images: one of the shrubs and their surroundings, another of a damaged branch, and the final one of a close-up of several affected leaves side-by-side, some turned over to reveal the underside.

Among the keys to successfully battling lace bugs are these:
- Stressed plants appear to be the most common victims. To relieve stress, thin out individual plants to increase aeration, and ease of applying sprays; irrigate every two weeks through our dry months for good health.

- The most effective time for the first spray of the season is right after the insects hatch, usually late April to mid-May, at which time the dark-colored nymphs (youngsters) are clustered on the undersides of the leaves. (See photo in the above publication.)
- Most of the insecticides must thoroughly cover the undersides of the leaves. (See the list below.)
- Repeat spray applications are required during the growing season: June, July, August, with perhaps another in September.
- Don’t spray if the temperature is, or will be, above 80F.

Narrow-range horticultural oil can be applied in Nov/Dec to coat the undersides of the leaves where the eggs are laid alongside the midrib.

During the growing season, these contact insecticides will temporarily control lace bugs if the product thoroughly coats the insects on the undersides of the leaves. Choose one, then repeat the spray according to label directions: Azadirachtin; insecticidal soap; neem oil, spinosad

Acephate and imidacloprid are several options among systemic pesticides. Follow label directions.

If you decide to replace your azaleas, Encore azaleas have proved themselves to be among those tolerant of lace bugs in other regions but their value in the northwest remains to be seen.

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