Creeping thistle (Cirsium arvense) and spear thistle (Cirsium vulgare) are two of just five weeds labelled “injurious” under The Weeds Act 1959.
Both are strong spreaders and competitors which invade a wide spectrum of environments in the agricultural, horticultural forestry and amenity sectors. They pose particular problems for pasture by establishing and spreading quickly to smother grass plants.
Creeping thistle and spear thistle carry leaf spines and those on spear thistle are especially sharp and unpleasant. Both are avoided by grazing livestock, giving individual plants even more scope to develop and spread.
All grassland is at risk and, once established, these weeds are notoriously difficult to shift. Farm pasture and non-agricultural environmentally-sensitive grassland and heathland are the two most important areas affected, although increasing use of livestock to maintain the latter makes the distinction less obvious.
The copious quantities of seed produced by creeping thistle are mostly non-viable but creeping thistle more than compensates with its highly efficient vegetative propagation system. Creeping underground stems (rhizomes) spread quickly to form huge patches and any soil disturbance, including attempts at mechanical control, generally makes matters worse because new plants will grow from even small pieces of rhizome.
Spear thistle seed is viable and carried far and wide by wind inside the hairy pappus (parachute type) fruits.
Creeping thistle and spear thistle are robust perennials with underground food storage organs (rhizomes and tap roots, respectively) for successful overwintering with a quick “getaway” in spring. Early spring is the ideal time to hit thistles while they are still relatively small and vulnerable, but easy to identify in turf, grassland and on bare ground in their vegetative leaf rosette stage.
Thistles generally grow in isolated patches so blanket-spraying with boom sprayers or knapsack sprayers is wasteful, as well as causing an unnecessarily high risk for the environment. Spot treatment is a targeted and environmentally friendly solution.
The handheld Microwipe from Micron Sprayers, developed for specific and selective spot application of systemically acting herbicides to potentially stubborn weeds, is the thistle wiping weapon of choice. Microwipe offers distinct advantages in accuracy, economy and safety over conventional application methods such as boom or knapsack sprayers, especially in environmentally sensitive areas.
Operators simply walk through the field moving the Microwipe over the target plants to directly deliver a lethal dose by direct contact of the herbicide-containing rope wick and the target weed. This will deliver a lethal dose of herbicide onto and into target weed leaves but nowhere else, making Microwipe ideal for safe despatch of “outstanding” weeds in clumps, groups or growing individually in grassland. Micron also offer a vehicle mounted Weedswiper for rapid treatment of large areas.
Spear thistle’s classic leaf rosette display means it may also be controlled using the Micron Weedstick which delivers discrete doses of herbicide directly onto the ground hugging rosette of leaves. Like the Microwipe, the Weedstick is a hand-held applicator which can control weeds without impacting on grass and other valued plants.
Wildlife trusts acknowledge the weed status of creeping and spear thistles. However, creeping thistle and spear thistle are food sources and breeding sites for many non-pest insects, including butterflies and moths, and one of the major food sources for birds like the goldfinch which feeds on the seed heads and uses ‘thistle down’ for nest building. By using the Microwipe or the Weedstick operators can leave some thistle plants in the sward as food if they so wish.
Ideal timing for treatment with the Microwipe or the Weedstick is during early spring – from March onwards – when thistles are still relatively small plants and most vulnerable to herbicides. Plants ‘stand out’ in the sward and therefore make easy targets because the grass is only just starting to grow. Moreover, if livestock are already out and/or rabbits are present their reluctance to graze thistles makes plants even more obvious targets for spot application.
• Cereals 2010 exhibitor information as supplied by Micron Sprayers