Galium aparine is the universally accepted name for this common and widespread species. Moore (1975) recognizes two forms, G. aparine forma aparine and G. aparine forma intermedium and distinguishes between them on the basis of differences in the structure of the fruiting bodies. Chromosome numbers ranging from 2n = 22 to 2n = 88 have been reported, with 64 and 66 being the most common. The base number n = 11 (Malik and van den Born, 1988).
G. aparine is a slender, annual herb with branched roots. Cotyledons are petioled, ovate, usually notched at the apex, slightly rough above, 8-15 mm long and 6-9 mm broad.
The stems are green, soft, freely branched, numerous, weak, straggly and semiprostrate. They may be up to 120 cm long. G. aparine climbs or ascends by adhering to or lying on adjacent vegetation. Stems are quadrangular in cross-section, with prominent ribs, densely set with recurved thorn-like spines. They are jointed and branched at the first node. The nodes are usually densely tomentose, but sometimes only slightly so.
The leaves are sessile in whorls of 4-8 at the nodes. They are simple, narrow, oval-lanceolate, mucronate, single-veined, 30-60 mm long, 3-8 mm broad, usually dark green, thin, lax and mucronate. The leaf margins are weakly retrosely scabrous. The upper surface of the leaf is hairy and the lower surface has a row of forward directed spines along the midrib.
The flowers are 2 mm in diameter on peduncles in the axils of the leaf whorls. There are two to five flowers per peduncle (five to six bracts), in cymes. The corolla is white with four acute lobes. The flowers are bisexual, with four stamens and one pistil with two styles. The pollen grains are oval in equatorial view and the polar diameter (width) of the hexaploid plant is 25-31 µm.
The fruit is a schizocarp with two capsules per flower forming two globose mericarps. The fruits are grey or greyish-brown and oval in outline. They are 2-4 mm long, excluding the spines, with the scar somewhat oblong. The surfaces of the fruit are covered with hooked bristles, about 0.8 mm long, on tuberculate bases that are dilated and usually arise from a small tubercle formed by the elevation of the surface of the fruit. Fruits are sometimes sparsely spiny and very rarely smooth or tuberculate.
G. aparine is a common weed in temperate zones on all continents, but is restricted to higher altitudes in the tropics (Holm et al., 1977). In Europe, it occurs from Portugal in the west to Russia in the east, and from the UK in the north to Italy in the south. It occurs in Alaska, extending across the wheat belt of Canada and throughout the USA. It is a problem weed in Argentina, Chile and Uruguay and in Asia it extends from Pakistan to China and from Japan to New Zealand. It is less common in Africa where it is a weed of cereals in Tunisia and is found at higher altitudes in Ethiopia.
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
G. aparine is an annual herb that reproduces solely by seed. It behaves predominantly as a winter annual, and has been described as one of the most winter hardy weeds of winter-sown crops in Germany. In Japan, germination and emergence occurred between mid-November and February, with a peak in December, approximately 40 days after initial germination (Noda et al., 1965). In some years, a second flush of germination was observed in late February or March. This protracted germination periodicity helps G. aparine to escape herbicide treatments. In Canada, flowering begins in late May and is completed by mid-June, with mature fruits present from late June to mid-July (Moore, 1975). In some instances, flowering plants have been collected as late as August and September. In the UK, some emergence was observed in the field as late as April and May (Froud-Williams et al., 1984). Flowers are self-compatible and self-pollinated, each giving rise to two seeds. On average, one plant produces 300-400 seeds (Hanf, 1983).
Much research on the germination requirements for G. aparine is contradictory. Seed dormancy patterns vary greatly between populations, with hedgerow populations showing less dormancy than those in arable fields (Froud-Williams, 1985). In Sweden, freshly harvested seeds exhibited little innate dormancy, but germination occurred most readily in darkness (Sjostedt, 1959). Hirinda (1959) reported 50-76% germination in the dark, compared with 0-4% in light and 39-50% in intermediate conditions. Ueki and Shimizu (1970) showed that germination was enhanced by 5-10 minutes of light compared with continuous darkness. Various other techniques for breaking dormancy were tested (scarification, puncturing, soaking in enzymes, kinetin, thiourea or nitrate solutions), but soaking in 1000 p.p.m. gibberellic acid was the only treatment that resulted in an increase in germinability. Froud-Williams (1985) reported that seed germination was enhanced by nitrate, and that, in general, germination was promoted by light. He also found that hedgerow populations germinated over a wider range of temperatures (5-20°C) than field populations (5-15°C). Soil pH has little effect on germination (Holm et al., 1977).
Seeds of G. aparine buried in the soil display cyclical changes in dormancy, they lose dormancy in the autumn and re-acquire it in the spring so that seeds are dormant in the summer months. Dormancy was released again in the late summer to early autumn (Froud-Williams, 1985).
Numerous studies have examined the ability of G. aparine seeds to emerge from depth. Noda et al. (1965) reported that the maximum number of seeds emerged from a depth of 8-15 mm, and that the greatest depth was 33 mm. Hirinda (1959) reports the optimum depth of emergence as 2-5 cm. Other authors have reported the maximum depth from which seeds are capable of emerging as 4-20 cm (Kurth, 1967; Tsuruuchi, 1971). These variations probably depend on soil type. Holm et al. (1977) report that seeds are unable to emerge from 4 cm in a heavy, firm soil, but in light soils will emerge 7-12 days after being sown at a depth of 10 cm.
Brenchley and Warington (1930), in long-term field trials in the UK, indicated that the longevity of G. aparine seeds in the soil is usually less than 2 years. Holm et al. (1977) reported viability in soils in Germany as being limited to 2-3 years.
Seeds may be dispersed by wind, water, animals, farm machinery or as contaminants of crop seed. The hooked bristles on the fruits and seeds provide a mechanism for attachment to animal fur, feathers or human clothes and bags. The fruits also have a hollow space near to the point of attachment between the two halves, which enables them to float on water. In the Canadian prairie provinces, the planting of rapeseed contaminated with G. aparine seed is the principal means of spread (Malik and van den Born, 1988). G. aparine may also be spread with contaminated straw and manure and during the movement of harvesting machinery.
Batra (1984) surveyed the natural enemies of Galium spp. in North America and Eurasia. Schizomyia galiorum and Dasyneura aparines form galls on the flower buds of Galium spp. and prevent fruit formation. The gall-forming eriophyid mite Cecidophyes galii reduces seed production by 30-40%. Larvae of the tenthredinid, Halidamia affinis also feed on G. aparine.
A leaf spot disease caused by Cercospora galii, leaf and stem spots caused by Pseudopeziza rapanda and Septoria aparine, and stem spots caused by Rhabdospora galiorum have also been noted on G. aparine.
Holm et al. (1991) described G. aparine as a serious or principal weed in 10 countries. Worldwide it has been reported as a weed of 19 crops in 31 countries (Holm et al., 1977). Although the weed commonly occurs in vegetable crops, beets, pastures, vineyards and plantation crops, it is most troublesome in cereals, where it may cause large yield reductions, interfere with harvesting, cause lodging, and in some instances smother the entire crop.
In cereals, Rola (1969) reported potential yield reductions of 30-60%. From 1981 to 1989, Roder et al. (1990) found the yield decline caused by one G. aparine plant/m² was 0.24% in winter barley and 0.14% in winter wheat. Similar research, in the UK, found much higher reductions in wheat ranging from 0.7 to 2.9% per plant/m², total losses were 0.8-4.9 tonnes/ha (Wilson and Wright, 1987). Trials in Turkey estimated economic thresholds for the control of G. aparine as 0.7-2.1 plants/m² (Uygur and Mennan, 1996).
As well as severely reducing yield, G. aparine has other economically important effects. Water-soluble extracts of G. aparine contain substances that have allelopathic effects on oak seedlings (Mateev and Timoteev, 1965). Galium spp. also produce anthraquinones which are toxic to mammals and may cause skin irritation (Batra, 1984) and may have a diuretic effect when ingested by livestock (Long, 1960).
G. aparine also acts as an alternative host to a range of crop pathogens. These include the oat race of stem eelworm (Ditylenchus dispaci), stem and bulb eelworm (Anguillulina dispaci), Aphelenchoides fragariae, the potato aphid (Macrosiphum solanifolii) and Macrosiphum miscanthi (Malik and van den Born, 1988). Other authors have reported beet mosaic potyvirus (Katis et al., 1997), beet western yellows virus (Chod et al., 1997), petunia asteroid mosaic tombusvirus (Fuchs et al., 1994) and Mycocentrospora acerina (Hermansen, 1992). Turaev and Khurramov (1981) reported 10 species of parasitic nematodes infecting G. aparine in Russia.
The fruits of G. aparine may be used as a substitute for coffee and are used as such in Sweden (Long, 1960). The whole plant may be macerated and used either as an infusion to make a tea substitute or fed to poultry. The flowers serve as a food source for a number of beneficial insects. Extracts from adult plants may be used as a flavouring for food or wine (Batra, 1984).
G. aparine may be confused with G. spurium which is closely related to it. However, G. spurium may be distinguished by the following characteristics. Its cotyledons are smaller than those of G. aparine being 5-10 mm long and 2-4 mm broad. The leaves of G. spurium are linear, 12-62 mm long and 2.5-6 mm wide, always notched at the apex, a lighter green, stiff and more 'sticky' than the leaves of G. aparine. The stems of G. spurium reach up to 200 cm, and are stiffer, rougher and more branched than those of G. aparine. The base number of chromosomes in G. spurium is n = 10.
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
G. aparine is a severe weed of early sown winter cereals established under minimal or no tillage cultivation regimes. Buhr et al. (1977) reported that continuous bare ploughing for 6 years completely eradicated the weed. There is no evidence to suggest, however, that G. aparine is directly benefited by direct drilling (Froud-Williams, 1985). Field trials indicate that one-third more seeds may emerge following tine cultivation than after direct drilling (Schwerdtle, 1971), and it is believed that this is a result of greater soil aeration following harrowing.
Field trials in winter wheat in Germany demonstrated that tine harrowing following sowing and establishment of the crop successfully controlled G. aparine. Two cultivations, one at the tillering stage of wheat and a second at the end of shooting resulted in up to 79% control, and was equally effective as applying bromoxynil. Where only a single cultivation was applied, harrowing at the end of shooting was more effective than at the tillering stage (Steinmann and Gerowitt, 1994). In trials in the UK, cultivating with a flexible tine harrow in the autumn reduced the dry weight of G. aparine from 102 to 22-98 g/m². Despite a thinning in the wheat crop, yields were not affected (Wilson et al., 1993).
G. aparine is a vigorously competitive weed and its vegetative growth responds to increased nitrogen fertilization more effectively than does that of winter wheat (Wright and Wilson, 1992). In glasshouse trials, the effect of G. aparine on wheat yield increased as the nitrogen input increased (Baylis and Watkinson, 1991). Where it is permitted, straw burning can provide an effective means of control, by killing up to 90% of seeds on the soil surface (Froud-Williams, 1985).
For control of G. aparine in paddy fields, Ueki (1965) recommended flooding the fields, deep cultivation, use of a straw mulch, crop rotation or herbicide applications.
In UK trials, Lovegrove et al. (1985) assessed the efficacy of a range of pre- and post-emergence herbicides for the control of G. aparine. They found that pre-emergence applications of pendimethalin, trifluralin with linuron and bifenox with linuron gave inadequate control. Post-emergence applications of mecoprop in February or March resulted in 70% control of cleavers, but when mixed with ioxynil and bromoxynil, cyanazine or bifenox, control was greatly improved. They concluded that the most reliable control is achieved with post-emergent mixtures that include mecoprop.
A great deal of research has been conducted since the mid 1980s to establish herbicides and herbicide mixtures that will adequately and reliably control G. aparine.
In Germany, Snel and Scorer (1986) achieved adequate control of G. aparine with post-emergence applications of fluroxypyr. In trials in winter wheat, dichlorprop alone and mixed with bentazone gave excellent control of heavy infestations of G. aparine, resulting in 12-14% increases in 1000 grain weight (Hoffmann and Pallutt, 1989).
In Italy, Catizone and Viggiani (1990) achieved satisfactory levels of control with post-emergence mixtures of clopyralid plus MCPA plus mecoprop and ioxynil plus mecoprop. Cyanazine plus MCPA reduced seed germination but not weed biomass.
In the UK, applications of amidosulfuron made between the seedling stage in mid-February and the formation of flower buds in May gave excellent control of G. aparine (90-100%) (D'Souza et al., 1993). The same authors reported 83-100 and 86-90% control with fluroxypyr and macoprop-P, respectively.
In winter oilseed rape in Poland, applications of metazachlor plus quinmerac 3 days after sowing gave 90-100% control of weed populations which included G. aparine (Adamczewski and Stachecki, 1994).
Although efforts have been made to discover host-specific natural enemies of G. aparine, there is no reference in the literature to attempts to introduce these species in biological control programmes.
Studies have been conducted to establish potential biological control agents for Galium spp. Pavlinec (1992) searched for phytophages of G. aparine in areas around Berne, Switzerland. Only three oligophages were found. Larvae of the tenthredinid, Halidamia affinis were found at a number of sites, but their density and consumption rates were low. The chrysomelid, Sermylassa halensis occurred at four sites. S. halensis mainly attacks G. mollugo, but because of its tendency for complete defoliation it was thought to offer the best opportunities for biological control. The gall-forming eriophyid mite Cecidophyes galii was found in more than 50% of sites, and although it did not directly affect the viability of adult plants of G. aparine it did reduce seed production by 30-40%. Pavlinec suggested that the general paucity of insects feeding on G. aparine was a result of the production of insect-repellent chemicals.
Schizomyia galiorum forms galls on the flower buds of Galium spp. and prevents fruit formation. Dasyneura aparines also forms galls on G. aparine. Another European species that is relatively host-specific and demonstrates some potential for biocontrol is Aceria galiobia. Batra (1984) lists a number of pathogenic organisms that show some specificity towards Galium spp. including Puccinia punctata, P. punctata var. troglodytes and P. rubefaciens.
Adamczewski K, Stachecki S, 1994. Evaluation of a new herbicide Butisan Star for control of cleaver (Galium aparine L.) in winter oilseed rape. Oilseed crops. 16th Polish research conference, 15(2):115-118.
Bachthaler G, Dancau B, 1970. Influence of production technique on the weed flora in sugarbeet, with particular regard to chemical weed control. In: Proceedings of the 2nd International for Selective Weed Control in Beet Crops, Rotterdam, Netherlands, 1:221-233.
Noda K, Ibaraki D, Eguchi W, Ozawa K, 1965. Studies on ecological characteristics of the annual weed cleaver and its chemical control on drained paddy fields for wheat plants in temperate Japan. Bulletin of the Kushu Agricultural Experimental Station, 11:345-374.
Ueki K, 1965. Physiological and ecological studies on cleavers (G. aparine) control. PhD thesis. Kyoto, Japan: Kyoto University.
Ueki K, Shimizu N, 1970. Studies on the breaking of dormancy in barnyeard grass seeds. 1. The effects of some chemicals on the breaking of dormancy. Proceedings of the Crop Science Society of Japan, 38(2):261-272.