The noxious smell from a flowering weed prompted the closing of Waimea Canyon School for one day yesterday and the plowing of the field where the weed proliferated.

Earlier during the week, students complained of a bad smell and conditions that caused headaches and nausea. Health and agriculture officials traced the smell to the wild spider flower, Cleome gynandra, in an adjacent 12-acre fallow field that is farmed by Syngenta Seeds.

In a newsletter to students' parents, Waimea Canyon principal Glenda Miyazaki said that research suggests there are no long-term effects on health from exposure to the weed.

"According to research gathered by the Department of Health, Department of Agriculture and the National Tropical Botanical Garden, the spider flower" has oil sacs that release a pungent odor.

"Unfortunately, the combination of two days of Kona and variable winds caused the odor to drift onto campus from Tuesday morning," she wrote.

Miyazaki said Syngenta plowed the weeds under and then plowed the field a second time. She commended the company for its action and its concern about students.

She said students and teachers are to return to the school Monday. There will be an early morning assessment to determine whether it is appropriate to continue classroom instruction, she said.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.