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Sustainable farming - weeds

In a nutshell...
  • Weeds are plants that grow in the wrong place.
  • They have a big negative visual image for the property.
  • People make assumptions that weeds mean poor management.
  • Getting rid of weeds can easily become an obsession and create a lot of stress to land owners.
  • Land owners also risk prosecution for having certain weeds on your farm.
  • Weeds use nutrients that could be used by productive grasses and clovers.
  • They reduce the amount of pasture that can be eaten by stock.
  • There is a very long list of weeds that grow on New Zealand farms - some of them are associated with high fertility and some with low fertility.
  • High fertility weeds (eg. chickweed, dandelion, plantain) respond to fertiliser applications and become more of a problem.
  • The speading leaf form of many weeds (eg catsear, broad-leafed plantain, and hyracium) smother and prevent upright plants growing.
  • Livestock will eat most weeds if stocked densely enough.
  • Unpalatable weeds that after cutting and wilting become more palatable to stock.  Thistles are a good example.  This can be a hazard if the weeds are poisonous eg ragwort.
  • Weeds are spread by stock - they pass through in the dung, and their rhizomes (long roots) are carried in cloven hooves.
  • Weed seeds are also transported by wind across properties and in waterways on to farms down stream. 
  • These often lead to legal problems and illustrate that weed control must often be a combined effort between properties.
  • Weeds are often encouraged by grazing habits of stock.  Horses are the best example where horses encourage overgrazed areas next to dunging areas covered in docks.
  • Organic farmers have a totally different attitude to weeds as they argue that deep rooted weeds like docks can bring up nutrients from the lower soil layers. 
  • There is now documented evidence of weeds that have developed a resistance to chemicals used to control them.
How can you tell if you have a problem?
  • Specific weeds flowering at certain times of the year. 
  • The vegetative stages of weeds may not be very obvious, and the farmer has no weed identification knowledge.
  • Areas of a paddock where stock cannot penetrate to graze.  Examples of such weeds are Californian thistle, Bathurst burr, gorse, blackberry.
  • Areas of the paddock where upright grasses and clovers have been shut out by weeds with spreading and overlapping rosette type leaves on the soil surface.
  • Poor stock performance due to the low nutrient value of the eaten weeds.
  • Taint's in cow's milk caused by weeds - eg twin cress, wart cress, wild garlic.
  • On windy days, weed seeds blowing across the property and from neighbours.
  • Weed seeds in sheeps' wool and in the hair on cattle and horses.
  • Weed seeds that penetrate the eyes of animals - eg. barley grass.
  • Weeds that appear after feeding out bough-in hay, balage or silage.
How can you tell if you're doing well?
  • A property free from weeds all year round.
  • Productive pastures that grow well all year round.
  • Healthy productive stock.
  • No weed seeds in fleece wool of sheep or on the hides or eyes of cattle.
  • A very low weed control account for the farm.
What can you do to improve things?
  • Accurately identify the weeds on the farm and understand how they grown and reproduce.
  • Examine management practices that encourage growth of these weeds.
  • Find out where any introduced weeds are coming from and discuss this with the Pest Officer of the Regional Council.
  • If you have a spray programme - make sure you are using the correct spray for the target weeds.
  • Check if there is a risk of chemical damage to non-target species.
  • Communicate with neighbours and discuss you weed eradication programme before you start.
  • Read the instructions on all chemicals to be used, and make sure you take the recommended safety measures (eg. protective clothing).
  • Spray when the weather is appropriate to prevent spray drift.
  • Look at management practices of weed control without chemicals - eg. weakening the weed plant's root reserves by frequent grazing and cutting.
  • Keeping a good pasture cover all year round will prevent bare ground on which weeds germinate.
  • Avoid pugging pastures, as weeds are the first plants to grow on the resulting bare soil.
  • Be vigilant when earth removing equipment comes on to the farm (eg. drain diggers) as they can transfer weeds from other properties.
  • Be aware that new stock can also bring weed seeds from previous properties.  Let them empty out in a restricted bare yard on arrival for half a day.
  • Be extremely careful when buying in hay, balage and silage as they may include weeds with viable seeds that will establish on the farm.
Where can you go for help?
  • Regional Councils
  • County Councils
  • Federated Farmers of NZ
  • Ministry of Agriculture and Forestry
  • Department of Conservation
  • Upritchard, E, A. (1997).  A guide to the identification of New Zealand common weeds in colour.  NZ Plant protection Society (Inc).
  • Craw, C, J. (1995). Poisonous plants and fungi in New Zealand.  Northland Regional Council.  ISBN 0-909006-27-X.
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