Rushes
Other names
Latin names
Juncus spp.
Weed Type
Miscellaneous Weeds
Occurrence
Rushes occur mainly but not solely on poorly drained soils of low pH. Infestations often arise in disturbed areas of pasture or where the sward is weak. Rushes are a particular problem when poor pasture is ploughed for cropping as happened during World Wars 1 and 2. Some species have a spreading habit others are tuft forming. Only a few of the British species are of importance as weeds and in many other situations rushes are valuable constituents of the natural vegetation. Rushes provide cover for wildlife especially wading birds.
Biology
Soft rush (J. effusus L.) (Syn. common rush, J. communis var. effusus)
Soft rush, the main weedy species, is widespread and forms tussocks that extend by means of the short creeping rhizomes from which new shoots and ultimately new plants arise. Undisturbed plants grow into clumps over 1 m tall but mowing or heavy trampling alters this to a uniform spread of shoots. It is native in marshes, ditches, bogs, wet meadows, damp woods and by water, mostly on acid soils. Soft rush is abundant throughout the British Isles and is ubiquitous in moist situations and regions of high humidity. It prefers an open situation but can grow in partial shade. At one time, the soft rush and the compact rush were treated as a single species.
Soft rush flowers from June to July in the south and July to August in the north. The flowers are wind or more rarely insect pollinated. Capsules contain an average of 82 seeds and a plant may produce 700,000 or more seeds. The seeds are not ready to germinate until the April after shedding. Light and moisture are required for germination. Initially, seedlings are susceptible to drying-out, shading and mechanical damage but once established they become more resistant. The rhizomes that develop form a dense horizontal mat 6 to 50 mm below the soil surface. Stout roots penetrate vertically downwards to 25 cm. Shoots commence vigorous growth in March.
Hard rush (J. inflexus L.) (Syn. wire rush, J. glaucus)
Hard rush, the other main weedy species, is native in marshes, dune slacks, wet meadows or by water on neutral or base rich soils. It is common through most of the British Isles. The hard rush is a tuft forming species with the shoots borne on an extensive rhizome system. It flowers from June to August. The average seed number per capsule is 67 and there may be over 200,000 seeds per plant. The seeds require light for germination. The shoots, if grazed, are said to cause poisoning in sheep and cattle. Cattle that acquire a taste for it may suffer blindness and death.
Compact rush J. conglomeratus L. (Syn. J. communis var conglomeratus )
The compact rush is a rhizomatous, tuft forming rush with the shoots borne on underground stems. This perennial rush is native in marshes, dune slacks, wet meadows or by water. It occurs throughout Britain on neutral, base rich and acid soils, although the impression is sometimes given that compact rush is restricted to the latter. It occurs in wet meadows and pastures on less heavy soils poor in nutrients. Compact rush flowers from early May to July and a plant may produce 500,000 seeds. The seeds germinate in April-May following soil disturbance.
Jointed rush (J. articulatus L.) (Syn. shining-fruited rush, J. lampocarpus)
The jointed rush is widespread in waterlogged areas in hilly districts. It is a perennial with an extensive rhizome system and forms a sward rather than tussocks but is very variable in habit. The prostrate growth form may root at the nodes and form clonal patches. It is common throughout Britain and is native in damp grassland, heaths, moors, marshes and dune slacks. It is absent from dry habitats. Jointed rush flowers from June to September. The flowers are wind pollinated and jointed rush may hybridise with other species. Seed is set from September to October. The seeds require high light levels for germination.
Heath rush (J. squarrosus L.)
The heath rush is a tough, wiry, sward forming plant with a compact, slow-spreading rhizome. It has a distinctive appearance and shows little variation. It is found on acid soils throughout Britain but is common only in the north and west. It is confined to wet heaths and upland moors where it is sought out by grazing animals early in the season, so it is a useful plant rather than a weed. The leaves are tough and fibrous but are eaten by cattle, horses and sheep in winter and spring when other food is scarce. Sheep eat the developing inflorescences. Heath rush is favoured by grazing, without grazing, the grasses increase and suppress the less competitive rush. Heath rush can grow on a range of soils but cannot withstand competition from the fast growing species in base-rich habitats and is usually confined to acidic or peat soils. Heath rush is intolerant of shade both at the seedling stage and when mature. It can withstand water logging but not submergence. It is absent or stunted on dry soils. Plants may not flower until 5 years old. Flowering occurs in late June and July. The seed capsules contain around 50 seeds that ripen from August to October. Seed germination occurs in May and June but a bare area is needed for successful seedling establishment. In closed communities regeneration is mainly by rhizome growth. New shoots begin to grow in March and growth increases through April and May.
Blunt-flowered rush (Juncus subnodulosus Schrank) (Syn. J. obtusifolius)
The blunt-flowered rush is a rhizomatous perennial native in fens, marshes and dune slacks. It is locally frequent in England and Wales especially in unreclaimed areas where the groundwater is alkaline. The horizontal rhizome is far creeping. The blunt-flowered rush flowers in July-August and seed is shed in September-October. The seeds require light for germination.
Sharp-flowered rush (J. acutiflorus Ehrh. Ex Hoffm.) (Syn. J. sylvaticus)
The sharp-flowered rush has a spreading habit and is common in wet pastures. It is native in bogs, marshes, damp grassland and on the margins of rivers and ponds throughout Britain. It has a stout, far-creeping rhizome. Sharp-flowered rush flowers from July to September and is the last of the common rushes to flower. There are 12 seeds per capsule.
Slender rush (J. tenuis) (Syn. North American rush, J. macer)
The slender rush is a perennial from North America that was first seen in Britain in 1883, although earlier dates have been given. Within 60 years of introduction it had spread to 50% of British counties. It occurs on damp barish ground on roadsides, tracks and pathways. It is locally frequent throughout Britain. Slender rush flowers from June to September. The seeds become slimy when wet and adhere to boots and tyres, hence the distribution along trackways. The average number of seeds per plant is 33,000.
Toad rush (J. bufonius L.) (Syn. frog grass, saltweed, J. minutulus)
The toad rush is the most important annual species of rush and is common throughout the UK. It is native in all kinds of damp habitats both natural and artificial. Toad rush is found on tracks liable to temporary flooding. It flowers from May to September and fruits from July to October. The flowers are cleistogamous and there are around 100 seeds per dehiscent capsule. Seed numbers per plant range from 5,300 to 34,000. Toad rush seed germinates from April to December with peaks in spring and autumn. Light is required for germination.
Persistence and Spread
Once established, the perennial rushes spread vegetatively and by the small seeds that are produced in vast numbers. The seeds can remain viable in soil for 20 years or more and have been recorded in enormous numbers in the soil beneath pastures. In a study of the annual percent decline of toad rush seeds in cultivated soil there was no measurable loss of viability with time.
In soft rush, vegetative spread is the primary method of reproduction and spread. The strongly rhizomatous rush may form extensive clonal patches. The wind-dispersed seeds are blown a short distance away from the parent plant. Few are blown more than 2.5 m. The seeds become mucilaginous and stick together when wet. Soft rush seeds are reported to remain viable in soil for 60 years.
In heath rush, the seed capsules open in dry weather and many seeds are dispersed by the wind. However, some seed may not be dispersed until the flower stem decays and falls to the ground in spring, leading to small clumps of seedlings. The production of numerous seeds with high viability and extensive dispersal give heath rush an advantage in colonising recently disturbed areas. Once established, buds at the shoot bases of the developing plants give rise to new shoots on the edge of the rosette and large patches can be formed some of which are over 100 years old.
Seeds of hard rush are dispersed by wind and rain splash, also on the feet of birds and on shoes. Seeds of the soft and slender rush become mucilaginous and sticky when wet and this may aid dispersal in wet conditions. In dry conditions wind dispersal is more likely but few seeds are blown more than 2.5 m. Toad rush seeds have been found in cattle and horse droppings. Where rushes are used as animal bedding the seeds are spread with any farmyard manure that is produced.
Management
Control is limited to cutting, grazing cultivating and drainage. Cutting before flowering may help to stop the spread by preventing further seed shed but there may be many seeds present already in the soil seedbank. Grazing may also help but is unlikely to be effective alone. Topping in early August followed by grazing with hardy breeds of cattle or ponies over 2 years is said to give good control in uplands. In lowlands, cutting followed by grazing is effective. In lowland areas that flood naturally, topping followed by flooding is effective on wet grassland. Pulling of clumped rushes is another method of control. In an established sward, regular annual mowing for hay reduces compact rush. Goats will eat soft rush in grassland. Neither cattle nor sheep grazing alone has much effect on hard and soft rush. Jointed rush can withstand mowing and grazing.
All rushes are controlled by ploughing or rotary cultivations but this may stimulate seed germination and the establishment of new infestations unless the new sward develops rapidly. Where an uncut field of rushes is ploughed the rushes may reappear between the furrow slices. The vegetative tillers grow out into the light and become re-established. A preliminary rotary cultivation may be needed to break up the tussocks before ploughing. Plants left on the soil surface exposed to sun and wind are susceptible to drying out. Fourteen days exposure is usually fatal. Sowing to a short-term crop followed by further surface cultivations may be best before establishing a long-term sward. However, it may not be possible to plough on shallow soils upland soils.
Rush seeds require light for germination and seedlings are only likely to emerge in open areas left bare due to poaching etc. Rushes do best on wet soils so improved drainage will help with any control measure. Seedlings are sensitive to competition and to moisture deficit but become tougher once established. The application of lime has been suggested as a control measure in the past. Burning and treading have little effect on the heath rush.
A variety of insects feed on rushes and a number of pathogens attack them too.