LAZARO CARDENAS, Mexico (AP) – Thousands of soldiers sent to seize control of one of Mexico’s top drug-producing regions have discovered widespread cultivation of a hybrid marijuana plant that is easy to grow and difficult to kill, officials said Tuesday.

The plants can only be killed by having their roots pulled, a slow and tedious task, Army Gen. Manuel Garcia told The Associated Press, one of four media outlets allowed to accompany soldiers on the daylong raid.

“Before we could cut the plant and destroy it, but this plant will come back to life unless it’s taken out by the roots,” Garcia said.

The hybrid first appeared in Mexico two years ago but has become the plant of choice for drug traffickers in western Michoacan state, a remote mountainous region that lends to itself to drug production.

The plants resist chemicals that only burn the top leaves without hurting the root, making aerial fumigation impossible, Garcia said.

On Tuesday, dozens of soldiers wielding assault rifles swarmed 38 marijuana plantations, ripping plants out of the ground. As they flew back to their base, they spotted 32 new fields.

“For each 100 that you spot from the air, there are 300 to 500 more than you discover once you get on the ground,” Garcia said.

Last week, President Felipe Calderon sent 7,000 soldiers and federal officers to restore order in his home state and deal a blow to drug trafficking in the region.

The state has seen months of bloodshed from warring drug cartels that have carried out gruesome killings, including dumping five heads on a dance floor.

Calderon, who took office Dec. 1 after being elected on a law-and-order platform, has vowed to battle drug violence that has claimed more than 2,000 lives nationwide this year.

After a meeting with Navy Secretary Francisco Saynez, Calderon said the operation “is being carried out with success.”

Officials have so far arrested 45 people, including several suspected leading members of the feuding drug cartels in the state. They also seized three yachts, 2.2 pounds of gold, bulletproof vests, military equipment and shirts with federal and municipal police logos.

Mexico’s armed forces have also searched more than 18,000 people, 8,000 vehicles and numerous foreign and national boats.

“We are determined to shut down delinquency and stop crime in Mexico because it is endangering the lives of all Mexicans, of our families,” Calderon said.

In the past week, soldiers and federal police in Michoacan state have found 1,795 marijuana fields covering 585 acres, security officials said.

Officials estimate the raids could cost the cartels as much as $626 million, counting the value of the destroyed plants as well as the drugs that could have been produced with opium poppies and marijuana seeds seized in the raids, the army said.

Officials blame the violence in Michoacan on a battle between the Valencia and Gulf cartels over lucrative marijuana plantations and smuggling routes for cocaine and methamphetamine to the United States.

On Sunday, federal authorities said they had captured suspected drug lord Elias Valencia, the most significant arrest since the operation began.

Former President Vicente Fox also started strongly in the war against drugs – or at least was enthusiastically applauded in the United States, where top U.S. drug officials called the arrests of drug bosses unprecedented early in his six-year-term.

He boasted that his administration had destroyed 43,904 acres of marijuana and poppy plantations in its first six months in office and more than tripled drug seizures.

Drug violence, however, has spiked across the country in recent years. Authorities blame gangs fighting to take over the routes after the arrests of longtime druglords.

Meanwhile, Mexico has continued to struggle with corruption among its law enforcement ranks. Garcia said authorities did not tell soldiers where they were being sent on raids and banned the use of cell phones and radios.

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