Lace Bug infestation

Asked January 23, 2017, 2:33 PM EST

I have several 40 yr. old large azalea plants looking pretty bad. I broke off some branches & took them to a plant nursery. They said I had an infestation of Lace Bug. The backs of the leaves have tiny black spots on them. They said this is their dormant season & recommended I get some dormant insect spray, but weren't sure how I should use it or when & how often. The weather probably has a lot to do with it. They said to contact you. The branches are still green inside.

Washington County Oregon trees and shrubs insect issues horticulture

1 Response

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; and decide if the plants are in excess sun – if so, consider rigging temporary shade or moving the shrub in the fall.
- Start spraying the undersides of the leaves when the first generation hatches, usually mid-May. Monitor to determine the appropriate timing. To do so, check the undersides of the leaves every several days as you look for the small dark colored nymphs (youngsters). The most effective time to spray is right after the hatch, when the nymphs are in a rather tight cluster.
- Insecticide sprays must thoroughly cover the undersides of the leaves. (See the list below.)
- Repeat sprays of these materials are required during the growing season because the lace bugs have multiple generations. You have the best chance to decrease the population – and damage – when new generations hatch in mid-May and again in June, July, August, with perhaps another in September.
- Don’t spray if the temperature is, or will be, above 80F.

The following contact insecticides will temporarily control lace bugs if the product thoroughly covers the underside of leaves where lace bugs live and feed. Repeat the spray according to label directions:
- Azadirachtin
- Insecticidal soap
- Narrow-range horticultural oil. Use in the fall to coat the undersides of the leaves where the eggs are laid alongside the midrib.
- Neem oil
- Spinosad

You also have several options among systemic pesticides: acephate and imidacloprid.

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

You might like to review the recently published “Azalea Lace Bug” http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/40424/em9066.pdf

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