WHEATFIELD, Ind. — The Terminator — that relentless, seemingly indestructible villain of the 1980s action movie — is back. And he is living amid the soybeans at Harper Brothers Farms.

About 100 miles northwest of Indianapolis, amid 8,000 lush acres farmed by Dave Harper, his brother Mike and their sons, the Arnold Schwarzenegger of weeds refuses to die. Three growing seasons after surfacing in a single field, it is a daily presence in a quarter of the Harper spread and has a foothold in a third more. Its oval leaves and spindly seed heads blanket roadsides and jut above orderly soybean rows like skyscrapers poking through cloud banks. It shrugs off extreme drought and heat. At up to six inches in diameter, its stalk is thick enough to damage farm equipment.

“You swear that you killed it,” said Scott Harper, Dave Harper’s son and the farm’s 28-year-old resident weed expert. “And then it gets a little green on it, and it comes right back.”

Botanists call the weed palmer amaranth. But perhaps the most fitting, if less known, name is carelessweed. In barely a decade, it has devastated Southern cotton farms and is poised to wreak havoc in the Midwest — all because farmers got careless.