Nassella Tussock

October 2005
Nassella tussock is a very invasive perennial grass that is unpalatable to stock and difficult to control. It is widespread in Canterbury, Marlborough, and present in many other regions of both Islands. The grubbing out of plants is the main control method. Current levels of control are only holding the infestation in heavily infested areas, and it has the potential to spread more widely and inhabit very large tracts of land. Regional councils are anxious to reduce current infestation and prevent further spread.

Nassella tussock is a perennial tussock native to South America, which can form a dense mat throughout pastures. It is unpalatable to sheep and cattle. It produces numerous seeds on feathery wind-dispersed panicles (branched clusters) and thrives in drought-prone grassland. Viable seeds are present on plants from early November, peaking in number around the New Year.

Fortunately, seeds do not survive in the soil for ever in some soils most are dead within five years. Also seeds do not continue ripening once a plant is grubbed out. Research has shown that population growth depends more on year-to-year seeding than on survival of seeds in the soil. This means that any control program designed to prevent all seeding will be the most effective in reducing re-infestation to low levels.

The majority of new seedlings emerge in the autumn. The grubbing or spraying prior to flower panicle emergence in November prevents the production of viable seed.

Nassella tussock is well established in Marlborough, North Canterbury, and to a lesser extent in the rest of Canterbury, Otago, Wellington/Wairarapa and Hawkes Bay. Small pockets exist elsewhere throughout the country. Recent AgResearch work has shown that it could grow readily in many other areas and has the potential to spread. Vast tracts of land, particularly in the Canterbury, Otago, Hawkes Bay and Wellington regions are climatically ideal for invasion. Graeme Bourdot from AgResearch says that Nassella occupies only 50% of the potential area it could invade. Surveillance and early action in these regions will help prevent further spread.

Nassella tussock populations in North Canterbury and Marlborough appear to be stable although there are fears that younger farmers are not as aware of the problem as they should be, and may reduce control measures for economic reasons. This would be a big mistake, and programme is under way to encourage farmers to take greater action, which will be necessary if the population density is to be reduced.

Nassella tussock has been in NZ at least since the 1920s and possibly arrived in the late 1800s. It probably arrived in Marlborough in the Boards 1930s as a contaminant in lucerne seed. It was spread by the prevailing wind and quickly became widespread. Experiments with mob stocking to control its growth were unsuccessful -- although horses actually thrived on it cattle lost condition quickly and sheep all died. So a dense Nassella tussock infestation renders pastoral land useless for most forms of livestock farming.

It is now quite widespread in Marlborough and while it really thrives in dry pastoral country it also grows in Marlborough Sounds where rainfall is much higher.

A number of landowners in the Marlborough area spend about $20,000 a year on containing it, but at that level of expenditure they are not reducing infestation levels.

Farmers and contractors use a standard grubber from a hardware store and carry it with them as they go over the hills. All roots must come out when plants are grubbed so they do not regrow. When there are just a few plants here and there, grubbing is the ideal way to get rid of them, but some farmers use glyphosate in a knapsack or boom sprayer when the plants are fairly dense.

With current technology eradication is not possible, but some research into biological control is being carried out be Landcare Research.

Many years ago a Tussock Control board was formed and there was a government subsidy for Nassella control, but both have now gone and it's up to farmers to cover the costs. Harry Neal, pest monitoring officer, says that farmers will generally do just enough to hold the tussock at bay. In some areas the tussock is under control, and in others farmers are losing the battle.

Control work is carried out by gangs, and there are several in the Marlborough area which farmers can employ, and they generally get them back every year. Spraying is advisable when there is a larger area that can be covered with a knapsack sprayer, otherwise grubbing is the best method. Getting labour to do the grubbing is becoming a problem many young people are not too interested in that type of work, but they can make good money and keep fit.

The Marlborough District Council encourages control programmes. Farmers are legally obliged under the regional pest management strategy to destroy all plants before they produce seed, and Council officers carry out inspections to make sure the control work is up to standard. They work with farmers to keep the control program going, and enforce the regulations when necessary. The Councils view is that they have a responsibility to the community, and it is the community and the land that will suffer if Nassella gets away.

Harry Neal was involved with grubbing Nassella for about 25 years, and for the past nine years has been a pest monitoring officer with the Council. His main message is that farmers should not underestimate Nassella. There is no doubt that the perception of a lot of landowners is changing the father may have handed the property down to his sons and they don't realise what an issue Nassella can be, and that is scary because the control work needs to carry on otherwise Nassella will take the hold on the country again, says Harry.

They have to keep the pressure on it because it has the potential to render a huge amount of pastoral country useless for farming.

Further information available to farmers from:

Shona Lamoureaux or Dr Graeme Bourdot, AgResearch, Lincoln 03-325 9900

Laurence Smith, Environment Canterbury, Amberley, 03-314 8014

Alan Johnson or Ben Minehan, Marlborough District Council, Blenheim 03-578 5249