Understanding myrtle rust in New Zealand

Myrtle rust - it's been in the news a lot since it was first found in New Zealand in 2017 and could have a major effect on some of our native trees. So what actually is it, how far has it spread and what native trees are most at risk? Blue Plunkett talks to Dr Robert Beresford, a pathologist and specialist on rusts who has been working on understanding the spread of the disease in New Zealand.