Lace Leaf bugs
There is a big problem in Portland (Oregon) and specifically in my garden. All of my many rhodies and azaleas have been attacked for two years by these bugs. I've sprayed twice a year, but don't seem to be making progress. Last year everybody leafed out nicely but by mid-summer were in serious distress. I'm not even sure they will put out leaves this spring as they have lost so many leaves and are so yellow. Is there a systemic treatment?
Clackamas County Oregon
Invasive azalea lace bugs arrived in our region have become a scourge of azaleas and some rhododendrons in our region. It’s worth knowing that even though the shrubs look nasty, almost all will survive and will bloom again. If you decide to replace them, know that Encore azaleas have proved themselves tolerant of lace bugs in other regions but have *not* yet been evaluated in the northwest.
Among the keys to successfully battling lace bugs are these:
- Start by relieving stress on the shrubs: Thin out individual azaleas to increase aeration as well as make it easier to spray the undersides of the leaves; irrigate every two weeks through our dry months; and if the plants are in excess sun, either rig temporary shade or transplant in the fall.
- To make the biggest dent in the lace bug population, time the sprays shortly after each hatch, the first usually mid-May to April, with more in June, July, August, and possibly another in September. To verify a hatch, check the undersides of the leaves every several days to look for the nymphs (youngsters) which are smaller and darker than the adults. The newly hatched nymphs are an easy target because they cluster on the undersides of the leaves.
- Insecticide sprays must thoroughly cover the undersides of the leaves when the pests can be seen.
- Don’t spray if the temperature is, or will be, above 80F.
The contact insecticides azadirachtin and insecticidal soap are effective against azalea lace bugs if used in a timely manner (see above) and they thoroughly coat the underside of leaves when you can see the lace bugs. Repeat according to label directions.
You might also want to apply neem oil or other narrow-range horticultural oil in the fall; these materials must also to coat the undersides of the leaves where the eggs are inserted into the leaf alongside the midrib.
Systemic options are the active ingredients acephate and imidacloprid, with the latter long-lived within the plant.You might like to review “Azalea Lace Bug” http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/40424/em9066.pdf