Likely from honeydew. So look for insects on the undersides of overhanging branches.

The most likely critters are aphids. Other possibilities are mealybugs, whiteflies and soft scale.

dpgrows, you should contact your local municipality for this information. With a couple of phone calls, you should be able to find out if and when any abatement trucks or planes have been out.

Please note that the honey dew from large trees can be carried in the wind, however odd that may sound.

dp:

The only time I've seen that is honeydew from aphids on large pecan trees. Any of those around? It can blow a ways from the tree. This is a common complaint about pecan trees but it seems early for a heavy aphid infestation.

If it is honeydew, rinse the lettuce and it will be fine to eat.

We have four large oak trees in the back yard, no pecans. Aphids are only a few here and there on any of the vegetable plants, so I wouldn't think they'd be overabundant in the trees. The trees dropped all their flowers quite awhile back along with thousands of tiny white maggot looking larvae of some sort. But if honeydew can travel a distance, maybe it is something from the tree. Thanks.

When an aphid creates honeydew it forms in a "bubble" on it's rear and it uses it's hind legs to kick the bubble off itself. If it's falling from a high area it can travel a bit of a distance/angle before it lands.

They love the red oaks in my front yard.

fruitnut, I cannot think of ANY tree that couldn't be the aphid provider in such a situation! Maples are big offenders, for example. Almost any hardwood and conifer alike can harbor the insects that will produce copious amounts of honeydew.

Is it sweet?

Some people cultivate aphids/honeydew for bees to feed off. It produces a very rich/dark honey. Go figure.

ltilton...LOL I have no idea and I wasn't about to taste it to find out. That rain that came through washed everything clean. But all of you have given me an interesting schooling on honeydew. I had no idea.