US aid against Farc
Alvaro Uribe, the Colombian president, receives millions of dollars in US aid to fight the illegal drugs trade and combat the Revolutionary Armed Forces of Columbia (Farc), the country's main left-wing guerrilla group.
Uribe said the crop spraying was necessary to fight drug trafficking that helps Farc to finance its resistance programme.
"In the end everyone will have to understand that Colombia cannot allow the Farc to keep growing drugs in the area," Uribe told reporters in Bogota.
Colombia, the world's main cocaine producer, halted herbicide spraying in a 10km zone near the border with Ecuador a year ago, after campaigners complained about the impact on local residents and legal crops.
"The planes pass to the Ecuadorian side of the border, and I insist they kill crops and sometimes Ecuadorian farmers"
However, Colombia renewed the spraying of herbicides on Monday and has denounced criticism of its actions by stating that the herbicide used is not toxic.
But Correa said: "Colombia's government has supposed studies, without much basis, that say it's not harmful, but ethics demand that as long as there is not certainty you should not use the product.
"The planes pass to the Ecuadorian side of the border, and I insist they kill crops and sometimes Ecuadorian farmers."
Correa said he would seek the backing of other South American governments to pressure Colombia to stop spraying coca, the raw ingredient for cocaine.