By Peter Hobson CANBERRA (Reuters) – An Australian court on Tuesday heard closing arguments in a class action lawsuit alleging that a weedkiller produced by Bayer caused cancer, the first such case in Australia to reach this stage. Bayer has already paid billions of dollars to settle claims that exposure to its glyphosate herbicide, Roundup, damaged health, in most cases by causing non-Hodgkin lymphoma, a blood cancer. The company faces more than 50,000 claims in the United States, with the latest ruling requiring it to pay $2.25 billion to a single Pennsylvania man and driving its share price…