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.