The pollen is wind-blown and can be carried 100km or more, though the vast majority only blows a very much shorter distance. If the tree had just a small number of acorns (from a small amount of pollen arriving from a distance), would your in-laws spot them, or would it need a heavy crop for them to notice? Resin

Meantime on land that you have control over, plant what you like, rip out what you don't Such a narrow view. There are choices that some people make on their own land that affect others. That is what invasives are all about. Similar to pollution - people that create it (on their own property) eventually share it with others. Was it right that they did what they wanted on their own land? What about if you dump pollution in a stream on your own land but it flows downstream to others? Just like streams, private properties are not isolated, they connect together. To me, and others, invasive plants affect all of us at some point. And yes, bad diseases and pests have been brought in on imported plants by people that thought they could do what they wanted. And now Elms, Chestnuts and Hemlocks are dead and dying. True, it was an accident, no one did this this on purpose; but this is one of the risks that come with "doing what you want". And it affected LOTS of people and even wildlife. I don't know if that was the source of the dogwood issues, btw. I'd like to encourage everyone to think beyond yourself and consider that your actions can have impacts on other people and the environment. When you're considering new plants, research them and find out what they're about. Make an informed decision.

I have seen the white leaves on volunteer ash and walnuts in my shed.

I want to know too! Fwiw, before Google, a botanist at Pearl City at extension service told me it was gumi or goumi, a Japanese ornamental. Now that I search on that name, gumi looks nothing like this plant. Good thing I cut it down and yanked the root from my garden back then!