SOC TRANG, Vietnam — When the rice shoots began to wither on Lam Thi Loi’s farm in the heart of the Mekong Delta, a usually verdant region of Vietnam, she faced a hard choice: Let them die in the parched earth, or pump salty water from the river to give them a chance.

Like many seasoned farmers here, she risked the saline water. The crop perished within days.

The Mekong Delta, Vietnam’s premier rice growing region, is suffering its worst drought since French colonial administrators began recording statistics in 1926. Giant cracks, some a foot deep, gouge the hard earth; brown stalks of dead rice litter the fields; and the dryness is so severe even the pests lie shriveled on the ground.

“I’ve been planting rice since I was 13, and I have never seen anything like this,” Ms. Loi, 38, said as she sat in her neat living room. “In February I got one bag of rice. Last year we harvested 1.4 tons.”