Someone is stealing pumpkins off my vine. What can I put on the pumpkins as a deterrent... or that will cause a nasty rash?
where are the vines? if they are in your yard I would be a little more worries about trespassing. maybe put out a sign and say the area is under surevlance and you will be going to the police if it continues
If you spray pepper spray on them, when people grab them it will burn.
Get a motion camera and put some poison ivy around them pumpkins. Then after you have a pic of them grabbing your pumpkins they have a rash and a record.
get a dog guard