According to Atlas Obscura, the problem stemmed from ragwort, a nuisance weed of European origin that began popping up in New Zealand in the late 1800s. Ragwort, or Jacobaea vulgaris, looks not unlike a dandelion but is far more harmful: Horses and cows react to it as a poison. With the rise of dairy farming in the country and a concurrent rise in grazing cows who knew better than to eat it, ragwort started proliferating.
Liars apparently aren’t the only ones who should be concerned with having their pants catch fire. In 1930s New Zealand, a series of events conspired to threaten farmers’ trousers with spontaneous and lethal combustion.
To respond to the invasive species, farmers took up the Department of Agriculture’s suggestion to use sodium chlorate as an herbicide. It worked, but what the farmers failed to understand was that sodium chlorate was extremely flammable. With a fine mist of the stuff drying on pants and overalls, they were prone to bursting into flames when exposed to heat—like a fireplace where pants might be hung to dry. Among the victims was Richard Buckley, who described just such an incident and witnessed, as one research journal put it, “a string of detonations in his pants.”
Friction could apparently do the trick, too, with farmers on horseback finding that all that jostling could lead to a fiery result. Lighting a match to smoke or just to see in the dark could also be calamitous. A handful of deaths were reported, as these poor laborers were essentially turning themselves into unwitting Molotov cocktails.
Word eventually spread of sodium chlorate’s hazards and it fell out of favor. Ragwort continues to annoy the population of New Zealand.