Latin: Cirsium spp. and Carduus spp.

Other names: Spear thistle, creeping thistle, milk thistle

Family: Asteraceae

Thistle is a common weed found in the UK and Ireland that belongs to the aster family (Asteraceae). There are several species of thistle, including spear thistle, creeping thistle, and milk thistle. Thistles are biennial or perennial plants known for their spiky leaves, prickly stems, and distinctive flowering heads.

Thistle at the ‘just right’ stage for spraying

Identifying Thistle

Thistles possess several distinct features that help distinguish them from other plants. They typically have deeply lobed or pinnately divided leaves with sharp spines along the edges. The stems of thistles are usually rigid and branched, and they can reach varying heights depending on the species.

The flowering heads of thistles are composed of numerous small flowers surrounded by protective spiky bracts. The colors of the flowers can range from pink and purple to white, depending on the species.

The Impact of Thistle on Grassland Yield

Thistles can have a significant impact on grassland productivity and yield. They compete with desirable grasses and other plants for essential resources such as nutrients, water, and sunlight. The aggressive growth and vigorous nature of thistles allow them to outcompete grasses, leading to a decline in grassland quality and productivity.

Creeping thistle in cereals

Wheat crop with creeping thistle before harvest. Without glyphosate this would be very common

Thistles have extensive root systems that enable them to extract nutrients and moisture from the soil, depriving neighboring plants of these resources. This can result in reduced grass growth, sparse grass cover, and the formation of patches dominated by thistles.

Furthermore, the presence of thistles can interfere with agricultural practices, such as mowing or grazing. The prickly nature of thistles makes them unpalatable to livestock, reducing the grazing potential of affected areas. Additionally, thistles can become entangled in machinery during mowing, leading to operational challenges and potential damage.

Managing Thistle in Grassland

Managing thistles in grassland requires a comprehensive approach to minimize their negative impact on yield. Here are some strategies commonly employed:

  1. Herbicide Use: Selective herbicides specifically designed for thistle control may be used in larger infestations or areas where manual methods are not feasible. It is crucial to follow the instructions provided by the herbicide manufacturer, considering the impact on non-target species.
  2. Cultural Practices: Implementing appropriate grassland management practices can help suppress thistle growth. Regular mowing or grazing can prevent thistles from reaching the flowering stage and reduce their seed production. Proper fertilization and soil management can promote healthy grass growth, making it more competitive against thistles.
  3. Mechanical Control: For small infestations, hand-pulling or digging out thistle plants can be effective. It is essential to remove the entire plant, including the roots, to prevent regrowth. Cutting or mowing thistles before they flower can help reduce seed production.
  4. Preventing Seed Spread: Thistles produce a large number of seeds that can be dispersed by wind or attach to clothing and animals. Regular monitoring and timely removal of flowering heads can help prevent seed spread and the establishment of new thistle plants.

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