Problem species in grasslands and other habitats

Some naturally occurring native plant species can become problematic to farmers and other land managers.

These plant species, however, are native to the UK and provide very important resources for wildlife. Any management should therefore consider the impacts on other wildlife, and land managers should take a balanced approach to any control carried out.

What

Perennial species such as creeping thistle, broad-leaved dock, ragwort and nettle can become very abundant in some areas to the detriment of agricultural production, livestock and wildlife. Land managers have legal responsibilities for the management of some of these species. Any management should consider the impacts on other wildlife, and land managers should take a balanced approach to any control carried out.

Copyright 2004 Chris Hartfield. Permission granted to reproduce for personal and educational use only. Commercial copying, hiring, lending is prohibited.

Why

Thistles, ragwort, and nettles are part of our native flora and play an important role in many habitats. They support a range of other wildlife and are particularly important to our pollinating insects. Ragwort and thistles are two of the biggest suppliers of nectar and pollen in our countryside. Thirty species of insect are totally dependent on ragwort, including the cinnabar moth.

Thistles provide seed food for birds such as goldfinch, linnet, redpoll and twite and also provide nectar for butterflies such as the peacock and meadow brown. Thistle stems are also used for overwintering of many insect species and the larvae of the painted lady butterfly feed on thistle leaves.

Nettles and docks provide important habitats for insects such as ladybirds, beetles, spiders and weevils, and young nettles are the food plant for many moth and butterfly larvae, including the small tortoiseshell and comma.

In certain circumstances these species can multiply or spread rapidly causing problems for land managers. Creeping thistle, spear thistle, broad-leaved dock, curled dock, and ragwort are covered by the Weeds Act 1959, which places some obligations on land owners with regards to preventing their spread. The Ragwort Control Act and the Defra Code of Practice promotes a balanced approach to common ragwort control where it poses a threat to the welfare of grazing animals and the production of feed or forage, but does not seek to eradicate it from the countryside.

Control of all problem species should not be about total elimination but about achieving a level which does not impact unduly on farming management while allowing benefits to wildlife to continue. Control methods should be selected to have minimum impact on non-target plants and wildlife.

How

Good grassland management is key to preventing the spread of problem species.

Dominance by thistles, docks and ragwort isgenerally related to overgrazing and poaching which creates bare ground or gaps in the sward in which these species can develop. A well-managed perennial sward without gaps, and free from overgrazing and poaching will not provide opportunities for thistles, docks and ragwort to spread. Many problems can be avoided by keeping an eye on, and adjusting grazing levels particularly during droughts and in the winter, and by adjusting feeding or watering practices to avoid poaching.

Thistles

There are many species of thistle in the UK, but only creeping and spear thistles are likely to be a problem and are listed under the Weed Act. Creeping thistles generally spread via their extensive rhizome (root) systems and small fragments of root can quickly develop into large patches. Creeping thistles rarely propagate by seed however spear thistles depend on seed production, dispersed by wind.

Avoiding autumn/ winter poaching is key to preventing thistle populations building up. Grazing with cattle at a taller sward height (7cm+) through the spring/summer can help suppress thistles.

Cutting is an effective way of reducing concentrations of creeping and spear thistles. Cut just before the buds open and the flowers turn purple as this will reduce food reserves in the plants and prevent further seeding. Spear thistles can be dug out but this method should not be used for creeping thistles.

Herbicide treatment with a weed wiper is effective on large infestations. The grassland will need to be grazed as low as possible before weed wiping to ensure that the herbicide does not impact on other grassland species. Spot herbicide treatment with a knapsack sprayer is also effective but care is needed to prevent herbicide drift or leakage onto other plants. All herbicide treatments are best carried out in May and June.

Docks

Docks are most associated with soils containing high nitrogen levels, and fields mown to conserve grass. Repeated frequent cutting of docks combined with close grazing will reduce the weed burden over a period of a couple of years. Docks may also be dug out, although this can create bare soil which can provide niches for new docks to develop and/or new docks can develop from small pieces of root left in the ground. Both spot herbicide treatment and weed wiping can be effective, but will need to be repeated several times in one year, and potentially in subsequent years.

Ragwort

Ragwort is generally only a problem where it presents a poisoning risk to livestock, particularly when land is being used for hay or silage production and/or grazed by horses. The living plant is usually avoided by livestock, however, it becomes more of palatable or less detectable by livestock when dry. Livestock are particularly vulnerable when it has been incorporated into hay. There are several species of ragwort and also other plant species which look like ragwort, so ensure it is common ragwort that is causing the problem.

Good grassland management is the key to preventing ragwort establishment. Regular overgrazing tends to encourage ragwort growth and a well-managed sward provides little opportunity for ragwort to establish.

Ragwort pulling is the most common method of control. This is best taken forward when soils are wet (as this aids the operation) and before the flower heads mature. Try to remove as much of the root as possible as fragments of root can regenerate into new plants.

Cutting can be used as a last resort to prevent seeding of flowerheads, however cut plants will regrow and flower again later in the season or following years. All cut or pulled ragwort must be removed from the field and disposed of carefully.

Both spot herbicide treatment or weed wiping can be used, however all livestock should be removed from the grassland before treatment and excluded until all remnants of the ragwort have decomposed.