CHICAGO (Reuters) - China's approval of imports of a DowDuPont Inc DWDP.N genetically modified soybean puts rival Bayer AG BAYGn.DE on the defensive, investors and analysts said, as U.S. farmers will have a new choice when planting their most valuable agricultural export.

FILE PHOTO: The logo of Bayer AG, February 24, 2014. REUTERS/Ina Fassbender/File Photo

Bayer-owned Monsanto has long dominated the $40 billion U.S. soybean market. The market has opened up, though, as Monsanto’s Roundup Ready line of seeds - engineered to tolerate the weed killer glyphosate - has lost effectiveness as weeds develop tolerance to the chemical.

China cleared the way for U.S. farmers to eventually plant DowDuPont’s Enlist E3 soybeans, which can resist three herbicides, by approving imports of the crop on Tuesday.

For years, the company had postponed launching the seeds while waiting for the nod from Beijing. China bought about 60 percent of U.S. soy exports, worth about $12 billion, prior to the ongoing U.S.-China trade war and could reject shipments of unapproved varieties.

Farmers have struggled since China imposed a tariff on imports of U.S. soy in July as part of the trade war, in which the world’s two biggest economies have slapped billions of dollars of retaliatory duties on each other’s products.

Michael Underhill, chief investment officer of Capital Innovations, which owns shares of DowDuPont, said China’s approval of Enlist E3 soy will eventually lead to big orders for the company.

“When I think about how big of a deal this is, I think about the Led Zeppelin song ‘When the Levee Breaks,’” Underhill said. “Competition is going to get fierce. It forces everyone to get sharp and up their game.”

Enlist E3 soybeans are bred to resist the herbicides glyphosate, glufosinate and 2,4-D.

The seeds will challenge Roundup Ready 2 Xtend soybeans developed by Monsanto, which can resist glyphosate and a newer version of a chemical called dicamba.

Corteva Agriscience, the agriculture unit of DowDuPont, said it was happy the regulatory approval of its seed traits was progressing in China. A spokesman did not respond to requests for more information.

Bayer spokesman Darren Wallis said in an e-mailed statement that Roundup Ready 2 Xtend soybeans were the number one trait platform in the market. The company complained of China’s slow regulatory approvals process in an earlier statement.

U.S. farmers planted Xtend soybeans on about 45 percent of soy acres in 2018. Bayer, which bought Monsanto for about $63 billion last year, says dicamba and Xtend seeds work well to control weeds.

But Cleveland Research Company said last month in a report seen by Reuters that within a few years of launching, the Enlist platform of herbicides and chemical resistant seeds could win a comparable market share to Bayer’s Xtend platform.

“We envision Xtend’s U.S. soybean market share eroding several years out as Corteva pushes its own Enlist platform,” the report said.

DowDuPont developed Enlist E3 soybeans with a smaller seed company called MS Technologies, said Harry Stine, the chief executive of Stine Seed who is affiliated with MS Technologies.

Enlist E3 soy will probably not be fully launched in the United States this year because it is still missing approval from another market, the Philippines, Stine said. However, he expects substantial U.S. plantings of the seed in 2020.

Enlist E3 soy may find an opening with farmers unhappy with Bayer’s dicamba-resistant Xtend soybeans. Monsanto has been sued by farmers who say dicamba drifts away from where it is sprayed and damages nearby fruits, vegetables and other crops that cannot tolerate the chemical.

Enlist E3 soybeans can be sprayed with an herbicide based on the chemical 2,4-D.

“It does not drift at all,” Stine said about the Enlist herbicide. “That’s what sets it apart from other things.”

Richard Wilkins, a Delaware farmer who grows about 400 acres of soybeans and a former chairman of the American Soybean Association, has not planted Xtend soybeans because of the risk of dicamba damaging nearby vegetables.

He said he would ask his seed supplier whether Enlist E3 soy is available and may plant it to control marestail, a weed that has developed some resistance to glyphosate

“If there are some varieties that will work on any of my farm, then I probably will give it a try,” he said about Enlist E3 soy.

Missouri farmer Milas Mainord said he, too, would consider planting Enlist E3 soy but wanted more information. He is planning to plant soybeans from Bayer and rival BASF BASFn.DE on some of his 5,500 acres this spring.

“The main thing we would want before we open ourselves up to Enlist is some history with it and what kind of yield to expect out of it,” Mainord said.