Round-Up?

NPR reports that Columbia is giving up on the Bush Administration's program for fumigating coca plants. As reported on NPR:

Coca hasn't been cut back, and cocaine trafficking continues unabated. The punitive approach also has driven poor farmers to grow more coca and to help the guerrillas.

The government says manual eradication is far less venomous, and it is moving in that direction, quietly.

"Manual eradication" means that Columbia has crews going through the countryside pulling up the coca plants using hoes and hands. Columbia says this method is more effective than aerial spraying of herbicides and prevents the herbicides from drifting onto farms and causing damage to crops.

I'm wondering why manual eradication is preferable to spraying herbicides at ground level. It seems a bunch of guys with sprayers strapped to their back would be able to quickly handle the coca plants. We in the south know how well Round-Up works.