In a nutshell...
- Weeds are plants that grow in the wrong place.
- They have a big negative visual image of 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 for land owners.
- Landowners also risk prosecution for having certain weeds on their farms.
- 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 spreading leaf form of many weeds (eg catsear, broad-leafed plantain, and hyracium) smother and prevent upright plants from 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 the wind across properties and in waterways on farms downstream.
- These often lead to legal problems and illustrate that weed control must often be a combined effort between properties.
- Weeds are often encouraged by the 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 no 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 flower 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, and 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 are caused by weeds - eg twin cress, wart cress, and wild garlic.
- On windy days, weed seeds blow across the property and from neighbours.
- Weed seeds in sheep's wool and in the hair of 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 grow and reproduce.
- Examine management practices that encourage the 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 your 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 onto 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.
Written by: Dr Clive Dalton