Cynodon dactylon
(Bermuda grass)

C. dactylon is a stoloniferous grass widely naturalized in tropical and subtropical regions of the world. This species is a C₄ grass included in the Global Compendium of Weeds (Randall, 2012) and it is listed as one of the most “serious” agricultural and environmental weeds in the world (Holm et al., 1977). It is a fast-growing grass that spreads by seeds and stolons and rapidly colonizes new areas and grows forming dense mats. As with many other African grasses, this species has the potential to alter ecosystem functions by altering fire regimes, hydrological cycles, biophysical dynamics, nutrients cycles, and community composition (D’Antonio and Vitousek, 1992). C. dactylon is very drought tolerant by virtue of rhizome survival through drought-induced dormancy over periods of up to 7 months. After dormancy, it has the ability to easily re-sprout from stolons and rooted runners. Plants also recover quickly after fire and can tolerate at least several weeks of deep flooding (Cook et al., 2005). Currently, C. dactylon is listed as invasive in many countries including Australia, Indonesia, Singapore, Cambodia, Vietnam, USA, Mexico, Costa Rica, Puerto Rico, Chile, Colombia, Uruguay, Argentina, Brazil and many islands in the Pacific Ocean such as Hawaii, Fiji, and French Polynesia among others (see distribution table for details). 

C. dactylon is thought to have originated in Africa but now occurs worldwide in both tropical and subtropical regions including Asia, North, Central and South America, the Caribbean, and islands in the Pacific Ocean (see distribution table for details). It also spreads into temperate areas of Europe and North America but is limited by sensitivity to prolonged frost.

C. dactylon invades almost all kinds of crops and modified ecosystems, including urban areas and circulation paths (road and railroad tracks) in many regions. 

C. dactylon has high potential for further spread in those areas where it is still absent. Ecophysiological and genetic traits coupled with both forms of propagation give this species a high score for success in almost any ecosystem.

C. dactylon requires moderate warmth. It is tolerant of extremely high temperatures but is susceptible to hard or prolonged frost. It is especially predominant in subtropical conditions as a weed in both annual and perennial crops and in pastures, fallows and waste areas. It occurs under semi-arid and irrigated conditions on a wide range of soil types of varying pH and salinity.

C. dactylon is treated by Holm et al. (1977) as the second most important weed in the world (after Cyperus rotundus), a status justified by its occurrence in virtually every tropical and subtropical country and in virtually every crop in those countries. In Holm et al. (1979) it is listed as a 'serious' or 'principal' weed in no less than 57 countries. A list of crops in which C. dactylon is, or could be, a problem weed would include virtually every crop of the tropics and subtropics and most temperate crops. The crops in which it is most commonly a major problem are those of the subtropics that are planted in wide rows, for example, cotton, sugarcane, tobacco, citrus, olive, deciduous fruit, forestry and ornamental species and many vegetables, but also some closer-planted but less competitive crops such as rice, lucerne, mixed lucerne and grass pastures, onion and jute (Labrada, 1994).

Genetics

The chromosome number reported for C. dactylon varies from 2n = 18 to 2n = 36 with diploid and polyploid populations (Cook et al., 2005).

Ramakrishan and Singh (1966) and Sarandon (1991) have found differences in total biomass and biomass partition according to the origin of the population. Sarandon (1991) points out that characters are highly heritable, which means that high genetic variability for biomass production and variable architecture allows an ample base for selection, which in most cases is induced by herbicides, mechanical control or forage production.

Reproductive Biology

C. dactylon is wind-pollinated and generally self-incompatible, suffering from inbreeding depression when genotypes are self-pollinated. Quantitative traits such as seed yield and forage yield can be dramatically negatively affected by inbreeding depression (Cook et al., 2005). In diploid populations, caryopses are formed after zygote formation. In polyploids, which are sterile, caryopses may be apomictic.

Physiology

This C4 plant (Kissmann, 1991) has high rates of accumulation under adequate irradiance, water and nutrient supply and may consume 75 kg of N, 20 kg of P and more than 1,500,000 litres of water for 5000 kg/ha of biomass dry matter (Fernandez , 1991). In the south of Santa Fe province, Argentina, a maximum biomass of 8000 kg/ha may be generated under a summer crop of maize or sunflower with >75 % located in the first 10 cm of the soil profile (Lombardo, 1973), whereas in Balcarce (Argentina) about 5000 kg/ha is commonly found in maize or sunflower stubble.

Phenology

A photoperiod of 13 hours induces flowering. Low night temperatures coupled with high diurnal temperatures induces blooming (Nir and Koller, 1976). A reduction in irradiance drastically decreases inflorescence production (Moreira, 1975). In North America, annual plants reproduce during spring and perennial plants reproduce all year long (USDA-NRCS, 2014).

Longevity

C. dactylon grows as both an annual and perennial grass. The annual growth-form becomes dormant and turns brown when nighttime temperatures fall below freezing or average daytime temperatures are below 10° C (Cook et al., 2005).

Activity Patterns

Seeds may be the route of invasion in weed-free fields through the faeces of cows (Rodriguez, personal communication). Rhizome biomass exhibits an annual cyclic pattern and, as with any perennial weed, low temperatures reduce biomass and viability is lost as a consequence of the consumption of materials due to respiration and maintenance. The digestibility of stocked material is severely decreased, implying a loss in forage quality (Vaz Martins, 1989). This is a character that has largely improved in cultivated varieties. Each node has a physiological self-governing structure in relation to the apex, but is highly dependent on substances from other plant parts. The mother plant determines the runner growth pattern on the soil surface according to the sugar-gibberellin balance (Montaldi 1970). Node disconnection may be caused by natural decay and cultivation and produces damage in the breakdown zone and changes in hormone and nutrient relationships. It is widely demonstrated that rhizome or runner fragmentation induces the activation of buds. The proportion of activated buds increases as the number of buds per segment decreases (Moreira, 1980; Kigel and Koller, 1985; Fernandez and Bedmar, 1992). The cultivation method is mainly responsible for vegetative propagation fragmentation. The higher the cultivation intensity, the smaller the segments produced (Kigel and Koller, 1985).

Population Size and Structure

This weed produces an enormous number of small seeds (0.25-0.30 mg), the viability and dormancy of which are highly variable according to genotype and the conditions when formed. The seed is important because it confers high genetic variability on the population.

Perez et al. (1995) recorded a very low germination rate. Uygur et al. (1985) obtained up to 15% germination at constant temperatures of 35-40°C, and 50% at temperatures alternating between 20 and 30°C. Moreira (1975) obtained up to 80% germination with the help of nitrate, chilling and alternating temperatures, and Elias (1986) recorded up to 96% germination from heavier samples of seed. Seeds remain viable in the soil for at least 2 years (Caixinhas et al., 1988). As a rule, cultivars have relatively high viability. Osmo-conditioning of Bermuda grass seeds with PEG followed by immediate sowing improved seed germination and seedling growth under saline conditions (Al-Humaid 2002).

The probability of emergence and successful establishment of C. dactylon decreases with the depth of the fragment, but increases with the weight of the node and internode (Perez et al., 1998). Growth from plants originated from a runner may exhibit a different biomass partition than that from plants originated from a rhizome (Fernandez, 1986). From sprouting onwards, weed growth is controlled mainly by temperature (optimum 25-30°C) and radiation, but also by humidity and soil fertility. The efficiency of carbohydrate reserve usage during sprout growth is highly dependent on temperature and the type of vegetative structure; it is maximum at 20°C and is higher for rhizomes than for stolons (Satorre et al., 1996). Runners and rhizome growth begins 30 days after growth but only if soil temperature is >15°C. Rates of 15 g/g/day have been recorded in Argentina (Lescano de Ríos, 1982).

Environmental Requirements

The annual cycle of the weed starts with bud reactivation by the end of winter. There is no innate dormancy and buds can activate if adequate temperature and humidity is available at any time of the year. Base temperature for bud sprouting ranging from 7.7°C, to 10°C (Bedmar 1991; Satorre 1996). New rhizomes are generated when temperatures exceed 15-20°C (Horowitz 1972). Aerial fractions have maximum dry matter content during the autumn and old rhizomes may have higher dry matter content than new rhizomes. C. dactylon tolerates a wide range of temperatures, especially very high temperatures in near-desert conditions. There is variation in tolerance to low temperatures and interactions between the time of exposure and relative humidity. Freezing point ranges from -2 to -3°C (Thomas 1969). Extreme temperatures were lethal to bud survival, but from 0 to 30°C, the rate of sprouting increased with increasing temperature.

Growth is favoured by medium-to-heavy, moist, well-drained soils but C. dactylon will also grow on acid and quite highly alkaline soils and the undisturbed rhizome system can survive flood conditions and drought (Holm et al., 1977). Runners allow C. dactylon to expand the exploration for new resources; avoid interference from other species; and propagate the most adapted genotype.

A wide range of natural enemies of C. dactylon have been recorded, including many that cause undesirable damage or disfigurement of C. dactylon lawns. They include a mycoplasma-like organism, which causes pale foliage and commonly occurs in weedy populations. Damage from natural enemies is rarely sufficient to provide useful control. Many of the species listed as natural enemies are better known as polyphagous pests of poaceous and other crops, while others such as Sipha maydis require evaluation before being considered as potential biological control agents attacking inflorescences and leaves in India (Labrada, 1994).

Animal feed, fodder, forage

• Fodder/animal feed
• Forage

Environmental

• Erosion control or dune stabilization

General

• Ornamental

Materials

• Poisonous to mammals

Medicinal, pharmaceutical

• Traditional/folklore

Outside Africa, there is rarely confusion between C. dactylon and related species. However, in eastern Africa there is frequent confusion with C. nlemfuensis. This species is similar to C. dactylon in almost all respects but lacks below-ground rhizomes. Two larger, more vigorous species, which are also without rhizomes and can occur as weeds, are C. plectostachyus and C. aethiopicus. C. plectostachyus, which is often cultivated as giant star grass, is distinguished by the upper glume being very short, less than one-quarter the length of the spikelet; and C. aethiopicus differs mainly in being very robust and woody with multiple whorls of coloured racemes. For further details, descriptions and keys, see Clayton and Harlan (1970) and Clayton et al. (1974).

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.

Cultural Control

Legumes or other cover crops are sometimes used for smothering C. dactylon since the weed does not tolerate deep shade. Vigorous crops and higher crop density may be important in reducing weed competition.

Mechanical Control

Traditional techniques of controlling C. dactylon rely very little on manual methods, as it easily survives shallow hoeing and positively thrives on mowing. However, the benefits of deep cultivation have been confirmed in Botswana and Zimbabwe where double ploughing, either after crop harvest or before the onset of the next season's rains, provided a high degree of control and was beneficial to crop yields (Phillips, 1993; Phillips and Moaisi, 1993; Mabasa et al., 1995). In these studies, conditions were dry and the rhizome systems not too deep, and standard ploughing depths of 10-15 cm were adequate to cause desiccation of the rhizomes. In contrast, Egamberdiev and Suleimanov (1985) found that double ploughing to 60 cm was needed, perhaps because wetter or cooler conditions meant that control had to be achieved by burial rather than desiccation. The main non-chemical approaches to control are deep tillage and shading/smothering crops.

Solarization

Solarization, using plastic sheets to raise soil temperatures, has proved highly effective in the control of C. dactylon in Egypt (Satour et al., 1991) and India (Nasr Esfahani, 1993; Anju-Kamra and Gaur, 1998). This technique has been also been recently tested in tomato orchards by Kumar et al (2003).

Chemical Control

EPTC may be used as a pre-plant incorporated treatment in soyabean and Phaseolus beans and, in combination with an herbicide such as dichlormid, in maize and sugarcane (Labrada, 1994). In each case a follow-up treatment with a post-emergent herbicide may be needed. In sugarcane, banana and plantain, glyphosate can be used successfully as a directed spray but care is needed to avoid contact with crop foliage. In sugarcane, dalapon may be a less hazardous choice for directed spraying, while an alternative for citrus and pineapple is the older soil-acting herbicide bromacil (Labrada, 1994).

Sulfometuron applied pre-emerge reduced C. dactylon ground cover from 73 to 93% in a succession-planted sugarcane crop in Louisiana, USA (Miller et al., 1998). Richard (1998) reported similar results with sulfometuron and also with thiazopyr. Richard et al. (2000) recently found that at-planting applications of clomazone mixed with either atrazine or sulfentrazone or imazapyr with atrazine were the only treatments evaluated that increased cane (7%) and sugar (9%) yields over the control of a weed community where C. dactylon was included.

Glufosinate-ammonium at maximum rate mixed with paraquat effectively controlled the weed under zero tillage in mustard and controlled C. dactylon under a non-crop situation (Das and Yaduraju, 2002.

Fluchloralin sprayed pre-sowing along with hand weeding gave effective control of C. dactylon in Cicer arietinum (Sesharee et al., 1996).

In other annual broad-leaved crops such as soyabeans, sunflower and potatoes, graminicides are selective and generally effective, with haloxyfop-methyl and quizalofop-ethyl having perhaps the highest activity, followed by fluazifop-butyl, and sethoxydim somewhat less effective (Kempen, 1983; Johnson and Talbert, 1985; Bedmar, 1997). Repeated applications may be needed for season-long control. The effects of different herbicidal combinations on weed management in soyabeans have been investigated by Jadhav et al. (2003).

The effects of addition of urea on herbicides have been tested by El-Quesni et al. (2000) in Egypt. Results suggest that glyphosate or fluazifop applied with urea gave an effective level of control of C. dactylon in July and August. Glyphosate formulations may have different behaviour, and have been studied by Martini et al. (2002): best results were obtained with 2.50 kg a.i./ha of potash glyphosate.

Imazapyr has proved selective in Pinus taeda and in Eucalyptus viminalis (Rivoir et al., 1987).

In tree and orchard crops, control of the actively growing weed before or after annual crops may be achieved using glyphosate (or the related sulphosate), which is effective at standard rates. The activity of glyphosate on C. dactylon is improved by a lower spray volume rate (Chivinge and Mare, 1991) and by various additives. However, a single application is unlikely to give permanent control and best results may be obtained by integration with tillage (Mabasa et al., 1995), smothering crops or ground covers: paraquat and glufosinate cause only temporary damage to the foliage.

The effects of most herbicides tend to vary according to the clone (biotype) or the population of C. dactylon being treated. Several studies have attempted to relate this to polyploidy level but little or no correlation has been detected for the activity of dalapon (Rochecouste, 1962b; Thomas and Murray, 1978) or sethoxydim (De Silva and Froud-Williams, 1992).

Biological Control

Drechslera cynodontis, Ustilago cynodontis, Puccinia cynodontis, and Fusarium poae as fungal pathogens and a specimen of Thripidae family were identified on C. dactylon and studied for potential use in biological control (Uygur, 2000).

Integrated Control

A single ploughing followed by glyphosate after a regrowth of C. dactylon may provide an effective and affordable control method to small-scale farmers (Abdullahi 2002).

Integrated weed management practices in spring planted sugarcane of coastal Orissa have been studied by Mishra et al. (2003). The effects of combined management techniques were studied in Italy by Caruso et al. (1997) who measured the effects of herbicides, and transplanting date of onions in the weed community structure. They found that crop growth rate increased during the first phases of the crop cycle, that the Shannon-Wiener diversity index showed a decreasing trend from the first to the third planting time for the herbicide treatment, and that the greatest mean influence on the diversity index was given by Amaranthus retroflexus, C. dactylon, Cyperus esculentus and Portulaca oleracea.

When designing a weed management program the following should be taken into account:

-The depletion of carbohydrates accumulated in the vegetative structures of the weed (sprouting promotion) coupled with the exposition of rhizomes and stolons to the soil surface in winter when low temperatures may kill buds to a greater extent.
-The design of a crop sequence, in which the initial crop must be highly competitive (such as sunflower or soyabean), to be sown early in the spring. The main target should be to avoid irradiance reaching this C₄ creeping weed.
-The use of herbicides such as glyphosate. These chemicals should be applied when the aerial/subterranean biomass ratio is at its highest value (at the end of favourable season), after the crop harvest in early autumn.

20/05/14 Updated by:

Julissa Rojas-Sandoval, Department of Botany-Smithsonian NMNH, Washington DC, USA

Pedro Acevedo-Rodríguez, Department of Botany-Smithsonian NMNH, Washington DC, USA