Poison Ivy Seeds!
 

Poison ivy is plentiful here. Do you realize its effect is delayed and
varies from person to person. Some people are not bothered by poison ivy at
all. If it would grow in your climate most people would not recognize it.
When a rash appears the next day they probably would not realize what caused
it or where they came in contact with it. So it probably would be of little
help with trespassers and might limit your ability to use your own yard if
you react strongly to it.