"Anonny Moose" wrote:

There is dark speckling on the underside of the leaves but it looks more
like physiological leaf spot - or maybe both types of spotting. I'm just too
inexperienced to tell the difference. I did find a couple of tiny
light-colored insects on the underside of each leaf I brought in for
inspection that might well be lacebugs (if they are tiny enough to be hardly
able to make out with a 10X loupe).
A few rhododendron leaves are showing a loss of color this winter.
They look white with green speckling. Anyone know what this is and
what I can do for it?

Could be either thrips or lace bugs.

Thrips are characterized by a silvery white discoloration on the leaf's
upper surface and silvery on the bottom with small black frass specks.
The damage is similar to that from lace bugs. Thrips are a problem in
warm and dry climates like California and New Zealand. Most of the
standard insecticides and insecticidal soaps can be used. Control for
thrips whether an insecticide or insecticidal soap is a contact control
and must be applied on the adults. This is most likely done in May when
they are visible. Locally, biological controls may also be available. It
is best to remove infected flowers.

Whitish specks on the upper surface of leaves and dark spots
varnish-like on the bottom are symptoms of rhododendron lace bugs . They
are more prevalent on certain varieties and on plants grown in sunny
areas. When damage first appears, it may be controlled by any of a
number of contact insecticides. Care must be taken to spray the lower
surfaces of the leaves where the lace bugs live.

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