I have five fuscia midget azalea plants facing a northern exposure- partial...

Asked June 6, 2013, 3:49 PM EDT

I have five fuscia midget azalea plants facing a northern exposure- partial shade. Last year I noticed a white blight growing on the stems of one of my plants. It looks like crystallized salt. I tried treating it with a liquid detergent solution with no success. This year that plant did not flower and the blight is still on it. The plant next to it has the same blight this year. Is there a remedy? Should I remove the two plants? They are approximately ten years old.

Montgomery County Maryland insect identification

1 Response

It looks like your azalea has an infestation of scale insects. Scale insects suck plant sap and then some types (soft scales, but not armored) secrete a sweet 'honeydew', which then can cause a black 'sooty mold' to grow on it.
This is probably Azalea bark scale. When populations are low, they tend to be found in the forks of the twig branches, and are generally tolerated by the plants. Continuous heavy infestations over years may kill the plants. Often beneficial insects keep this scale in check. Lots of plant diversity and avoiding the use of broad spectrum pesticides (which often kill all insects, including the good ones that help us) encourages beneficials.
You can attempt control in July, which is when the crawler stage of the scale is out and most vulnerable. You can use a summer rate of hort oil, a labelled insecticidal soap or contact insecticidal spray (pyrethrin). As a last resort, there are also soil drench systemic products containing imidicloprid that can also help. (Follow all label instructions, including temperatures at spraying time, carefully)
We are not sure you can save the azalea in the foreground. You should cut back the dead branches and dispose of them, and wait and see if it re-sprouts.