Why annual control mattersNassella tussock is a highly invasive pest grass that can spread rapidly if left unchecked. Thanks to that collective effort, controlling nassella tussock has become part of the annual routine for many rural properties. “Nassella tussock control is one of those jobs where every property matters. The progress made against nassella tussock over the years has been built on people doing their part. Landowners can complete their annual control work at any time of the year but must ensure the plants do not seed.