Wasps aren't my area of expertise, but we do frequently find large leaf, mature rhododendrons to be favorite nesting sites for (black and white) bald faced hornets here. It's happened often enough that we inspect reqularly for the nests, which can grow to rather amazing sizes in just a few days but are still easy to miss if not diligently looking for them.

So, what I've found about paper wasps...they will feed on nectar as adults - your early blooms shouldn't be attracting them in large numbers. They eat insects - have you noticed an infestation of anything at all on your rhododendrons? Could there possibly have been nest (s) you couldn't see in the interior of a large shrub like you describe? That seems like a more logical explanation for large numbers of paper wasps.

They are actually beneficial to your garden, which isn't to say I would leave them alone in a traffic area and risk anyone being stung, although paper wasps don't appear to be especially aggressive towards people.

The good news is, they don't inhabit the same nest twice, there may be nothing at all for you to do this season. You might begin by keeping an eye on your plants early this year and if you notice wasps in the area, try to find out what may be attracting them.

Morz8,
I looked for the nest, the exterminator looked for the nest, just couldn't find one. We've got bald faced hornets here, luckily they haven't nested on the property. The wasps are brown and yellow paper wasps, not hornets or yellow jackets and not particulary aggresive but there were alot of them! I also have some brown paper wasps that are pretty aggresive and I will not let them nest near the house at all. I will also have to really check to be sure they are not ground nesting, I did find a nest in a pot of iris under the rhizomes, pretty scarey when transplanting and holding a nest of 5-10 wasps in front of your face, although not one attacked? Back to the rhodo...when sprayed with the hose, most flew away from the bush not protective at all, just a few went for the stream of water. I did notice a black soot like covering on the stems, I'll check for scale or some other insect this spring. They (wasps) really only were a problem in the summer after the blooms faded. I generally tend to leave nests alone if they are not in a traffic area, I really am petrified of them but have learned to live with them, just not that close!

Maybe you already know - that black soot is a secondary fungus growing on surface of leaf or stem - honeydew sap left by insects (aphids, scale, whitefly, sometimes lace bug) as they feed on plant. If that does happen to be the case and you find the insects, treat those and the wasps will leave - but treat only if the wasps are not controlling them, and/or you are not able to safely control or co-exist the wasps :)

(I do not co-exist with bald faced hornets well, the last time I was stung I was pruning a rhododendron for a neighbor and hadn't realized there was a nest in it. I'm not allergic, but a sting below my ear left me feeling 'sickish' with headache for two days)

The black soot was only on the main trunks as I recall. I will be sure to check again this spring. I've been stung once or thrice and the reaction I get is a delayed allergic reaction, I get flu like symptoms about 3 days after the sting (not bad enough that they hurt like heck!) As petrified as I am I am really interested in them and did quite a bit of research this past summer. I was actually able to sit in a patch of spearmint and trim the flowers with hundreds of them flying around me, not aggressive at all! Of course after 15 minutes I completely freaked out and had to stop. LOL, my fear with the wasps around the rhodos is that the lawm mower or other activity will cause them to attack. Thanks for the info about the bugs, I will check for sure.

Sooty mold growth on stems and petioles is a symptom of Azalea Bark Scale, Eriococcus azalea, and Cottony Azalea Scale, Pulvinaria floccifera. These small sucking insects feed on the bark and exude a sticky substance that turns the stems black. A scale infestation is indicated by sooty mold on leaves, yellowing of leaves, and twig dieback. This scale is most obvious from May through June when white egg sacs may be found in twig forks. Heavy infestations over several seasons may kill plants.

Overwintering immature scales (nymphs) are about 2 mm long, gray, and are usually found in twig forks. This scale primarily attacks azalea and rhododendron, but has also been found on andromeda, maple, arborvitae, willow, poplar, and hackberry. Azaleas can tolerate low populations of this scale without injury, and if there are no yellowing leaves, no treatment is necessary.

Beneficial predators and parasites will usually provide adequate control of light scale infestations. Examine egg sacs for holes which indicates control by parasites, and look for predators such as ladybird beetles. To control heavy infestations, spray dormant plants with a late oil spray to kill developing nymphs on twigs. If necessary a 2% summer rate of horticultural oil may be applied in July after all of the eggs have hatched.

Here is a link that might be useful: How to grow rhododendrons and azaleas.

rhodyman
Thanks for the information. My rhodos have not lost leaves or branches other than what has gotten wind burned above a fence that shelters them. The taller one is a bit thin on top but still flowers and has buds and leaves. I will spray with the oil once the weather warms up a bit, even if they are kept under control by the natural preditors, the wasps that are attracted are quite a problem for me. I rarely use chemicals for control unless its wasp/hornet problems, I really fear them I know they are beneficial but wow they hurt when annoyed!

Your paper wasps are almost certainly taking advantage of that sugary residue excreted by the scale (or what ever) insects. These wasps are valuable in their control of caterpillars and the larvae of beetles, making them a little bit of a bad guy in the butterflyer's garden! ;-)

I'd suspect that if you gain control of your pest problem (and the black sooty mold is a certain indication of one of those sucking insects) that the paper wasps will find some other source of sweetness.

rhizo,
I've actually watched some of the wasps carry caterpillars away, dragging them across the patio because they were to large to fly with! I hate to kill any insect, and I know the wasps are beneficial, I just don't want that many around! I'll be sure to reduce if not get rid of any scale mealy population I have and see if that works. I enjoy watching the activity of the wasps from a distance in other areas of the garden, and most seem pretty docile when they're not annoyed. The problem is the same as in my mint patch and on a rubylimerock correopsis, hundreds of them. Thats just to many for me! I've moved the coreopsis and try to keep the flowers trimmed on the mint. Now to tackel the Rhodos!

very informative , Thank you all .I have learnt a lot from all the comments..I noticed wasps on my Rhodies last week Had it for about 5 years , and not seen this before...I have a small tray of water nearby and they use that avidly. Have not detected what is attracting them..May leave that to my husband ...