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Key Knowledge: strategies for prevention and control of the following weeds commonly affecting agricultural and/or horticultural production: flickweed; gorse; wild radish
Key Knowledge: strategies for prevention and control of the following weeds commonly affecting agricultural and/or horticultural production: flickweed; gorse; wild radish
This page covers three significant weeds that impact Victorian agricultural and horticultural systems. These weeds compete with crops for nutrients, water, and sunlight, and can significantly reduce the productivity and value of food and fibre products.
A weed is defined as any plant growing where it is not wanted. In a commercial setting, weeds are managed because they lower crop yields, contaminate harvests, and can provide a habitat for pests and diseases.
Flickweed (Hairy bittercress) Cardamine hirsuta
Flickweed (Hairy bittercress) Cardamine hirsuta
Flickweed is a common horticultural weed, particularly in nursery and greenhouse environments. It is a small, upright plant that belongs to the brassica family.
It competes with young plants for space and nutrients in potting media. Its primary impact is the speed at which it spreads. When the seed pods mature, they explode and flick seeds up to several metres away, allowing the weed to quickly infest an entire greenhouse.
Prevention: Maintaining clean pathways and using sterile potting mix are essential preventative measures.
Control: Hand weeding before the plant reaches the flowering stage is the most effective physical control. In a professional nursery, a pre-emergent herbicide may be applied to the soil surface to stop seeds from germinating
Gorse Ulex europaeus
Gorse Ulex europaeus
Photo by Annie Spratt on Unsplash
Gorse is a woody, thorny shrub that is classified as a weed of national significance. It is a major problem in Victorian grazing lands and along roadsides.
Gorse forms dense, prickly thickets that are impenetrable to livestock. This reduces the available grazing area and provides a perfect safe place for rabbits and foxes. Because the plant is high in oil, it also presents a significant bushfire risk.
Prevention: Strong biosecurity is required to ensure seeds are not moved between properties on machinery or in contaminated hay.
Control: Biological control can involve the release of the gorse spider mite, or grazing by goats. Physical control involves mechanical mulching or heavy machinery to pull out the shrubs. Chemical control usually requires a targeted woody weed herbicide applied directly to the cut stumps or as a foliar spray.
Wild Radish Raphanus raphanistrum
Wild Radish Raphanus raphanistrum
Photo: Weed Smart Wild Radish Fact Sheet
Wild radish is one of the most competitive and economically damaging weeds in the Australian grain industry. It is a robust annual plant with white, yellow, or purple flowers.
It competes heavily with wheat and barley crops for nitrogen and moisture. The seeds are a similar size to grain, making them difficult to clean out of a harvest. If wild radish seeds contaminate a grain delivery, the farmer receives a lower price for their crop. It also acts as a host for pests like aphids.
Prevention: Managing the green bridge by killing weeds in the fallow season ensures there are no plants to host pests or set seeds for the following year.
Control: Crop rotation is a key cultural control; planting a different type of crop allows farmers to use different chemical groups to kill the radish. Many populations of wild radish have developed biological resistance to common herbicides, so farmers must use an integrated approach including narrow windrow burning to destroy seeds at harvest time.
PRACTICE:
Q1: Why is the explosive seed dispersal of flickweed a particular challenge in a greenhouse environment?
Q2: Describe two ways that gorse reduces the productivity of a sheep farm.
Q3: Explain the concept of the green bridge in the context of wild radish and how managing it is necessary for a grain farmer.
Agricultural Weed Management and Control
Agricultural Weed Management and Control
PRACTICE:
NOTE: Make sure you have looked at the VCAA page on Pests, Diseases and Weeds (This link will direct you to the PDF to download)
Question 1: Horticultural Weed Spread (2 Marks)
Flickweed is a significant problem in nursery and greenhouse environments. Describe the biological mechanism that allows flickweed to spread rapidly within a confined space and explain why this makes physical control difficult.
Question 2: Economic Impact of Broadacre Weeds (3 Marks)
Wild radish is often cited as one of the most economically damaging weeds in the Victorian grain industry. Explain two different ways that a wild radish infestation can reduce the financial return a farmer receives for a wheat crop.
Question 3: Integrated Management of Woody Weeds (4 Marks)
Gorse is classified as a weed of national significance. A farmer decides to use an integrated pest management approach to clear a large infestation from a hillside. Discuss how the farmer could combine biological, physical, and chemical control methods to manage this weed effectively over the long term.
Summary of Management Principles
Summary of Management Principles
While the physical appearance and environments of these weeds differ, their management relies on the same core principles of integrated pest management.
Prevention: This involves ensuring that seeds are not introduced to a clean area. In horticulture, this means using clean potting media to avoid flickweed. In broadacre farming, it means cleaning machinery to prevent the spread of gorse or wild radish seeds.
Competition: A healthy, vigorous crop or pasture can often outcompete weeds. By ensuring crops have the right nutrients and water, they can grow faster than weeds like wild radish and shade them out.
Timing: The most effective time to control any of these weeds is before they set seed. For an annual like wild radish or flickweed, stopping the current generation from dropping seeds can significantly reduce the problem in the following year. An old saying is, "One year's seeds are seven year's weeds".
Diversity: Relying on a single method, such as one type of herbicide, often leads to biological resistance. Using a mix of physical, biological, and chemical control measures ensures a more resilient farming system.
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