Tobacco already comes with nicotine. God put it in the DNA of that plant.
Can tell you have never been anywhere near a tobacco crop. Workers can get nicotine poisoning from wearing short sleeve shirts in the field.
Yep. Any time the plant is wet while topping, cutting, hoousing. Heavy dew, foggy, after a rain. Have friends who work tobacco from March to November/December every year. Always take a second change of clothes with them when the tobacco is wet. Change into dry clothes at lunch time to reduce the exposure. If it is bad, they will hop in the river or a pond with a bar of soap. Hauled a couple guys with "green tobacco poisoning" when I ran EMS. First they were afraid they were going to die... Then they were afraid they wouldn't...