MSF600 (metsulfuron-methyl) is NZ’s favourite and most proven chemical for controlling gorse, especially heaps of big gorse.

It has a couple of quirks that are the key to understanding why it works like it does.

MSF600 suppresses production in the plant of an enzyme called acetolactate synthase (ALS). That enzyme is required to support new growth, both in the roots and the foliage. Without ALS, no new growth is possible. Most plants can tolerate not being able to produce new growth for a while, but eventually they must have some new growth to survive, otherwise they die.

That’s why it takes a long time for some species to die. Gorse is a tough one; it can manage without new growth for several months. So you can spray it with MSF600, and for some weeks you may notice no effect visible. And you wonder … is this stuff doing any good? Then, when the gorse finally surrenders, it starts to go yellow-brown at the tips, and its demise progresses from there to full desiccation and it eventually falls to bits. Dead.