Asked January 06, 2015, 2:12 PM EST
Clackamas County Oregon
Azalea lace bugs have been the scourge of local azaleas and some rhododendrons during recent years. It’s worth knowing that even though the azaleas may look nasty, those given a modicum of care will bloom year after year.
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; and if the plants are in excess sun, consider rigging temporary shade or transplanting to a different site in the fall.
- The best bet to decreasing the population for the coming year is to kill new hatchlings. To accurately time the first spray, monitor the undersides of the leaves regularly, beginning in April. To do so, check the undersides of the leaves every several days as you look for the small dark colored nymphs (the youngsters). The most effective time to spray is right after the hatch, when the nymphs are in a rather tight cluster on the undersides of the leaves and before they disperse. If you prefer to avoid pesticides, a harsh water spray to the undersides of the leaves can be very effective at this early stage. Adults are challenging to kill. If you use insecticides, they must also be applied to the undersides of the leaves. (See the list below.)
- Repeat sprays are required during the growing season because the lace bugs have multiple generations. Again, monitor to determine appropriate timing. (New generations tend to hatch in mid-May, June, July, August, with perhaps another in September.) A harsh water spray can be very effective against each new hatch.
- Don’t spray any pesticide if the temperature is, or will be, above 80F.
These contact insecticides will temporarily control lace bugs if the product thoroughly covers the underside of leaves where lace bugs live and feed. Repeat according to label directions:
- 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
The options among systemic pesticides are the active ingredients acephate and imidacloprid.
If the azaleas will be replaced, I suggest consulting with a nearby large independent garden center for shrubs that will thrive in our region. Encore azaleas have proved themselves elsewhere but haven’t been evaluated in the northwest.
Also see “Azalea Lace Bug” http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/40424/em9066.pdf