Hello Ruth,

Thank you for contacting Ask Extension about your rhododendrons. Would it be possible for you to send us some photos? One photo of the entire plant, and closeups of the rust colored powder, the black dots on the underside, and the winged insects.

Also, it would be helpful if you can find out whether the black dots are actually pests (do they move at all?) Have you used anything on the rhodies (fertilizers, pesticides, etc.) this season?

I'll be glad to try to advise you if we can determine what problem(s) you are dealing with.

Dear Ruth,

You should be able to reply directly to this email and attach your digital photos.

Dear Ruth,

Thank you for all your efforts to send photos and information about the pests on your rhododendron. My apologies for the delay in getting back to you, but as you will see, the pest you are dealing with is quite new in Oregon. 

The crawling, spiny bugs are the nymphs of the azalea lace bug (Stephanitis pyrioides), a pest that originated in Japan and has been found primarily in the eastern states before now. The flying insects are the adult form of the same bug. 

Two or three generations per year are expected in the Northwest. They have piercing/sucking mouthparts that cause the yellow stippling on the leaves of your rhododendron. As you noticed, this often resembles chlorosis. The dark specks are frass (poop) and there may be skin casts also. 

Plants that are stressed by drought are especially susceptible to lace bug attack. Proper watering (slowly and deeply rather than frequent shallow "sprinkling") and regular fertilizing (composting or a slow-release fertilizer) will help reduce stress and damage potential to the plant. Damage may also be reduced when plants are located in a shadier area.

A number of beneficial insects are proving to be effective in helping to eliminate this pest, including the azalea plant bug, tree crickets, earwigs, green lacewings, minute pirate bugs, and spiders. Therefore, is very important not to harm these in the process of controlling the azalea lace bug. 

While systemic pesticides may be an option, they are extremely detrimental to bees and beneficial insects. So I strongly suggest you use insecticidal soap, horticultural oil, or neem oil instead. All of these must be applied exactly as instructed on their respective labels. It is important to spray the undersides of the leaves as well as the top surface. The packages will specify how and when to spray, as well as the precautions for you, your plants, and the environment. Repeated applications may be needed to destroy all generations of the pest. A good garden supply store or nursery should be able to help you select an appropriate product. 

Since azalea lace bug over-winters as eggs on leaves, thoroughly rake up all fallen leaves and destroy them (do not compost) or put them in a sealed trash bag. Keep the soil around your plants mulched at all times with about 3 inches of wood chips.

You mentioned that you have been pruning your plants. After you have removed any dead or dying wood, remove some of the branches with leaves back to their origination point. This will thin out the foliage to allow better airflow into the shrubs. 

Here is some additional information about the azalea lace bug:
https://entnemdept.ufl.edu/creatures/orn/shrubs/azalea_lace_bug.htm  

The brown and rust-colored spots may be areas that the pests have been feeding. I suggest you watch the situation after you begin your control regimen to see if it persists or gets worse. 

I hope this information is helpful, and wish you luck with your rhododendrons. Please write again if you have any other questions.