Hello Gary,

Are you able to send photos of the azalea's symptoms? Yellowing and paling of the leaves in azaleas can be caused by several different factors (examples below), some of which may be overlapping.

• ailing roots - roots that are dying due to drought stress or (more commonly) overwatering or poorly-drained soil won't be able to absorb all the nutrients the plant needs, resulting in deficiency symptoms (iron, nitrogen, etc.) in foliage even though a soil deficiency does not exist; root rot in azaleas often results in foliage taking on a sickly, olive/yellow-green color
• pH is too high - as you mention, if the soil acidity isn't strong enough, the iron in the soil won't be available to the roots; aim for a pH of 4.5 to 5.5 for azaleas
• lace bugs - sap-sucking insects common on azaleas which create pale stippling damage on the leaves; when heavy, this stippling covers most of the leaf and results in a yellowing or silvery color change
• autumn leaf drop - some varieties turn yellow while others turn more orange-red, but all evergreen azaleas shed some of their older foliage in autumn; inner and lower leaves tend to be the ones dropped, especially if the plant is routinely sheared

If iron supplementation is needed, you can apply it any time, though how long it takes to be available to the plant for uptake may vary with soil temperature and moisture. The package should include instructions about dosage, either in oz/gal dilution or perhaps in pounds per 1,000 square feet (mainly referenced for lawn applications). There is no standard dosage since iron is formulated in different ways between different brands/products. If the pH is too high, then that will have to be adjusted first, since iron levels may already be sufficient. pH adjustments also take weeks or months to complete, which is beneficial so that roots aren't stressed by more rapid changes.

Miri

Not a problem, and yes, this is classic lace bug damage and not malnourishment. Here is our other information page on lace bug damage and control, though it will largely overlap with the content on the azalea page: https://extension.umd.edu/resource/lace-bugs-trees-and-shrubs

Miri

You could do either, but it's probably best to wait as few adults are likely still present at this time. If spraying now, you'll mostly be coating eggs, as this is the stage that overwinters. However, they are inserted into leaf tissue and often covered in frass (insect poop) so this may render the effort unsuccessful. Using horticultural oil in spring - only once new feeding damage or the bugs themselves are seen - should be sufficient, though as with most contact insecticides, multiple treatments may be needed.

If you opt for a systemic spray, that should be applied after spring bloom to avoid harming pollinators. The active ingredient acephate is absorbed by foliage, but only where the spray contacts the leaf, so thorough coverage is needed for good control. Systemic options that are instead soil-absorbed need to be applied by a certified pesticide applicator since those chemicals are not available for homeowners to acquire or apply legally in Maryland.

Miri