Summary
This report presents general pointers to the kinds of weeds likely to become increasingly important in future, especially in hill country pastures. It is less precise in describing which species will become future problems, although our survey shows a few new weeds may be emerging in some regions. It highlights the difficulty of trying to predict future weeds. Few people in the field are in a position to know, much less measure, which weeds are beginning to be troublesome. Twenty years ago 120 noxious plant officers, partly funded by central government, advised farmers on weed control on pastoral land and kept a watch for newly emerging pest plants. Today about 60 biosecurity officers are dedicated to helping land-owners control pest plants in both amenity areas and on agricultural land. They are employed by Regional Councils and although they visit most farm properties, they devote less time to observing emerging problems on pastoral land.
Fewer sheep on hill country, higher cattle to sheep ratios and lower fertiliser application in the 1980s and 1990s have led to increases in scrub weeds and in the incidence of weeds like ragwort. Many of the respondents to our survey reported on increases in the importance of gorse, broom and ragwort.
The southward spread of warm zone plants in New Zealand will continue. Warm-zone grasses still move southwards, as do weeds like Bathurst bur. Accelerating climate change will hasten this movement and will increase the importance of warm-zone plants in areas where they already occur. Higher carbon dioxide levels may promote the growth of herbs at the expense of grasses. Climate change will cause more floods and droughts, which will allow more opportunities for invasion by short-lived species like thistles, but also allow greater invasion of scrub weeds. Rainfall, increasing in the west and lessening in the east, means that scrub weeds will benefit in the west and annual weeds like thistles and barley grass in the east.
Greater diversity of land use - more forestry and more non-traditional crops like grapevines, tree crops and hemp - makes aerial spraying of pastoral weeds more difficult. Differentiation between weeds of pasture, forestry, conservation areas and permanent or semi-permanent crops will become more blurred. Lifestyle blocks are sometimes blamed for spread of weeds and 'organic' farmers on such blocks may refuse to use herbicides to control new weed problems.
Predicting future weeds can reduce future expense and heartache. Improved border security is important for stopping new potential weeds entering the country legally or illegally. Regional councils appear to be doing an excellent job, but fewer biosecurity officers and fewer people on farms make early detection of new and spreading weeds difficult. Farmers or contractors, and perhaps schoolchildren, should be encouraged to provide information to Regional Councils. Improved co-operation is needed between the agencies involved in weed control - Department of Conservation (DoC), Ministry of Agriculture and Forestry (MAF) and Regional Councils. Better national co-ordination between Regional Councils would help in tracking of and advising on weed control. Research work should be better co-ordinated between the funding and delivery agencies concerned.
Contact for Enquiries
MAF Information Services
Pastoral House
25 The Terrace
PO Box 2526
Wellington, NEW ZEALAND
Fax: +64 4 894 0721
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