Nassella control continues

Press, 29 August 1986, Page 17

Nassella control continues

Controlling nassella tussock is a perpetual slog. Few plants can rival its sheer tenacity and alarming ability to spread rapidly. Although this noxious plant is now under control, there is a danger that farmers will become complacent. "Perhaps our biggest concern is that we do not know for sure where all the sites of nassella tussock are,” said Neil Harding, chairman of the interdepartmental committee on nassella tussock.

“Take the high country of the South Island, for instance. We are fairly sure there is no nassella there at present, but if these plants managed to get up as far as the headwaters, we would have lots of problems.”

Some also fear that once pine plantations planted in some areas to control the tussock are logged, millions of its seeds will spring to life again.

Nassella tussock probably arrived in New Zealand from South America early this century. By the 1940 s nassella was widespread in North Canterbury and Marlborough. As well as these sites, there are now scattered sites in the rest of Canterbury as well as isolated sites in Central Otago and from Napier to Kerikeri in the North Island.

It is a tough enemy, one that a Greta Valley farmer, Mr Geoff Maxwell, has been battling for most of his life. He is the longest serving member of the North Canterbury Nassella Tussock Board and was the board’s chairman in the 19605.

“Around Waipara, about 15,000 acres were just a solid mat of nassella. Nothing else could grow and animals would starve to death rather than eat it.

“The Government had to buy up some 20,000 acres in North Canterbury as well as a farm in Marlborough because the farmers couldn’t control the tussock,” Mr Maxwell said. The number of seed heads blown around was incredible. “I remember some people who went to Christchurch for the day in summer and left their garage doors open. When they got back the garage was filled with nassella seed heads and they had to fork them out.

“These seed heads piled up so thickly against fences that the weight pushed the fences over.” Now nassella is under control, thanks to an assault by herbicide and grubbing, along with oversowing and topdressing. But this enemy never sleeps. To make sure nassella tussock never again turns farms into barren wasteland, its weaknesses must be pinpointed and exploited so it can be controlled more effectively. Although much time has been devoted to controlling and • eradicating nassella, little is known about its biology and ecology — apart from a major study published in 1945 by Mr Arthur Healy of the D.S.I.R.’s Botany Division.

The Noxious Plants Council, through the interdepartmental committee on nassella tussock, has funded a three year con-

tract with the D.S.I.R.’s Botany Division.

The division has employed Mr Nigel Taylor to investigate aspects of the tussock’s biology and ecology.

As Mr Taylor explained, farmers need to be on guard constantly against nassella. Just one plant can produce 100,000 seeds per year. He is worried that nassella is still flourishing in some pine forests.

“It is a dilemma. Some of the worst affected land was taken over by the Forest Service for the Omihi State Forest.

“The pine trees have stopped the tussock flowering, although they haven’t stopped the plants from growing. “The intensive spraying programme is working effectively but huge seed banks have formed in the soil with something like 1200 nassella tussock seeds per square metre. “When logging starts the seeds could come to life even up to 10 years after being buried in the soil — and that is happening,” Mr Taylor said. He is putting every possible weakness of the plant under a magnifying glass — from germination to seed banks and the effect of grubbing. Mr Taylor also wants to find out how the tussock invades pasture and how well it competes for space with the other grasses. He has got study sites on several farms around Amberley as well as in the Omihi State Forest. Preventing nassella spreading has become a necessary obsession for him.

Mr Taylor had to promise to fence in his marked tussocks so the seeds cannot spread. When his experiments finish, he will grub out the tussock. And because nassella spreads so easily, he checks his clothing every time after visiting one of his study sites in case any seeds are caught on it and stalks the land around his study sites with a grubber. Given nassella’s remarkable list of survival attributes, prevention is most certainly better than cure, according to Mr Taylor. “Farmers in affected

areas must maintain a good ground cover in well managed pastures so nassella can’t get a foothold. This can be difficult es-

pecially as its deep roots mean it can tap any moisture and grow during summer when most grasses die,” he said.