(Adds comments from critics)

By Carey Gillam

Jan 15 (Reuters) - Monsanto Co. received final U.S. approval on Thursday for herbicide-tolerant crops to be used with a new herbicide the company says will fight problematic weed resistance on farm fields, but critics say will only worsen the problems.

The U.S. Department of Agriculture's Animal and Plant Health Inspection Service (APHIS) said the genetically modified cotton and soybean plants are granted "non-regulated" status. Monsanto is still waiting for final approval from the Environmental Protection Agency for the herbicide it designed to be used with the crops.

The company also is still awaiting approval from Chinese regulators to allow imports of the new soybeans. China is a key buyer of U.S. soybeans, but the country has shown reluctance to approve imports of new GMO crops recently.

Last week, Monsanto Chief Technology Officer Robb Fraley told analysts the company expects to have Chinese approval in time for a commercial launch in 2016.

Monsanto developed the new soybeans and cotton to resist a new herbicide that combines dicamba and glyphosate and which Monsanto is branding as components of the "Roundup Ready Xtend crop system." The new products are aimed at combating the millions of acres of weeds that have grown resistant to Monsanto's glyphosate-based Roundup, which has been used extensively on the company's biotech corn, soybeans and cotton.

Monsanto's Xtend system drew intense opposition from many consumer, environmental and farmer groups who say using more herbicides on weeds will only increase weed resistance over the long term. Increased herbicide use also brings increased risks of health problems and environmental pollution, they say.

"The pesticide treadmill spins on, and that's great news for Monsanto," said Gary Ruskin, executive director of U.S. Right to Know, a food issue research group. "This is just the latest in a endless string of favors from our federal government to Monsanto."

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Projections made both by the USDA and Monsanto, indicate that the new Xtend system will lead to an increase in dicamba use in cotton by 14 times current levels. Use in soybeans is expected to surge by up to 500 times current levels, a factor that will increase pesticide exposure risk to farm families, the Pesticide Action Network said in a statement Thursday.

As well, fruit, nut and vegetable growers who argued against approval say dicamba drifts easily and will damage their farm fields.

Monsanto has said it is teaching growers about proper herbicide use to reduce drift.

(Reporting by Carey Gillam in Kansas City; Editing by David Gregorio)