State agriculture officials plan to release about 1,000 fireweed moths from Madagascar on Hawaii island Wednesday to try to control the fireweed plant, which is damaging large tracts of pastureland.

Entomologists from the state Department of Agriculture will release the moths, Secusio extensa, at Kahua Ranch in Waimea, the department announced.

Since the late 1980s, fireweed has become a growing problem for ranchers, especially on Maui and Hawaii island. The plant contains alkaloids that are toxic to cattle and horses.

The state’s exploratory entomologist, Mohsen Ramadan, went to South Africa and Madagascar to search for a natural enemy of the fireweed that would be appropriate to release in Hawaii, the department said.

The department said the caterpillar stage of the moth will eat the fireweed and control its spread, though it may not eliminate it.