"The estimates are nothing more than estimates," Vigil, author of "Metal Coffins: The Blood Alliance Cartel," told Business Insider."And it is very, very difficult to come up with an accurate figure, simply because many times the Mexican government over exaggerates how many hectares they have sprayed in the eradication program," he added.The visit could put Mexico on the same footing as anti-drug operations in places like Colombia and Afghanistan.
But if the US and Mexico are about to make the opium-poppy eradication a joint effort, they may find their progress stymied by conditions on the ground and the nature of their foe.
A US official told Reuters that the area of poppies under cultivation in 2016 was estimated at 32,000 hectares in 2016.
The Mexican defense secretariat also said it destroyed 22,235 hectares of opium poppies in 2016 and 26,249 hectares in 2015.
(Through the end of April 2017, the Mexican government says it eradicated 15,179 hectares of poppies.) What effect this eradication has on the overall crop level is not clear.
At the beginning of April, the Mexican army took US military officials, UN personnel, and officials from the US embassy on a tour of a half-dozen sites in the Golden Triangle - the heart of Mexico's heroin country - to witness the destruction of opium poppies.
The trip marked the first time in at least 10 years that the Mexican army had allowed US and UN officials to observe poppy eradication, and, according to Reuters, more trips were being arranged.
One official told Excelsior the chemical used was only harmful to poppy plants, not to other crops or underground water systems.
(The Mexican defense secretariat has in the past classified the exact chemicals used in aerial fumigation, calling it a matter of national security.) According to Vigil, Mexican authorities tasked with aerial fumigation in the past have tried to mask the true amount of poppies destroyed, often to bolster their totals.
The most recent US efforts to support Mexican eradication are at least a year old, dating to when Brownfield told Congress more work needed to be done to destroy poppies.
Since then, despite turmoil introduced to the relationship by Donald Trump rise to the presidency, bilateral anti-drug efforts have gone smoothly.
"We don't know with any level of precision how heroin production has evolved in recent years," Mexican security analyst Alejandro Hope wrote in February 2016.