SAN FRANCISCO — A jury on Monday ordered agribusiness giant Monsanto Co. to pay a combined $2.055 billion to a couple claiming that the company’s popular weed killer Roundup Ready caused their cancers.The jury’s verdict is the third such courtroom loss for Monsanto in California since August, but a San Francisco law professor said it’s likely a trial judge or appellate court will significantly reduce the punitive damage award.The state court jury in Oakland concluded that Monsanto’s weed …