Stephanitis pyrioides
These infuriating little insects hide on the underside of azalea (and rhododendron) leaves. There they suck the sap from the plant and leave dark dots of excrement, leading to the silvery leafed appearance of affected plants from the top view, and dark dots underneath. Even more annoying, the juvenile forms excrete honeydew (which can attract ants – often a clue that you have a problem), the honeydew can lead to sooty mould. So now you have silvery leaves and sooty mould, and your azalea is becoming seriously compromised, as photosynthesis is difficult.
What to do:
Melbourne has relatively mild winters, so the Lace Bugs can overwinter fairly easily on your azaleas and explode in numbers in spring, but they also overwinter in the litter underneath the plants. If your infestation is bad, and you are prepared to pull out all stops for a year or two to get it under control, remove all the leaf litter/mulch underneath your plants for winter. Re-apply fresh clean mulch next spring.
Insecticides
We do not recommend the use of residual systemic insecticides. However, judicious use of contact, non-residual insecticides (see below) applied directly to the Lacebugs will be effective in the short term. Unfortunately the Lace Bugs are almost exclusively on the underside of the leaves which makes spraying difficult, but it is a waste of time to spray the topside of the leaf, these insecticides need to land on the Lace Bug to work.
• Neem Oil
• White/horticultural Oil
• Insecticidal Soap
• Pyrethrum (Pyrethrin) sprays
Predator Insect release
Azalea Lace Bug can be predated on by a range of generalist predators including ladybugs, lacewings, and mites. These can be ordered over the internet from Bugs for Bugs and posted to you.
These are a good long term solution, and they will also predate on annoying aphids and other pests. If you go this route you need to be very careful if / when you use any insecticides. We have more information on: https://www.baag.com.au/garden-pest-control/