Avena fatua (wild oat)
- Taxonomic Tree
- Notes on Taxonomy and Nomenclature
- Plant Type
- Distribution Table
- History of Introduction and Spread
- Habitat List
- Host Plants and Other Plants Affected
- Biology and Ecology
- Rainfall Regime
- Soil Tolerances
- Means of Movement and Dispersal
- Pathway Vectors
- Plant Trade
- Wood Packaging
- Impact Summary
- Threatened Species
- Risk and Impact Factors
- Uses List
- Similarities to Other Species/Conditions
- Prevention and Control
- Distribution Maps
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PicturesTop of page
IdentityTop of page
Preferred Scientific Name
- Avena fatua L. (1753)
Preferred Common Name
- wild oat
International Common Names
- Spanish: avena loca; avena silvestre; avena silvestre comun; ballueca
- French: folle avoine
- Portuguese: balanco
Local Common Names
- Brazil: aveia-brava; aveia-fatua
- Germany: Flug-Hafer; Wind-Hafer
- Italy: avena matta; avena selvatica
- Japan: chahiki; karasumugi
- Netherlands: oot; wilde haver
- Poland: owies gluchy
- Sweden: fyghavre
- Turkey: yabani yulaf
- AVEFA (Avena fatua)
Taxonomic TreeTop of page
- Domain: Eukaryota
- Kingdom: Plantae
- Phylum: Spermatophyta
- Subphylum: Angiospermae
- Class: Monocotyledonae
- Order: Cyperales
- Family: Poaceae
- Genus: Avena
- Species: Avena fatua
Notes on Taxonomy and NomenclatureTop of page The taxonomy of Avena species is not uniform in all countries. The classification system and nomenclature has been discussed by Baum (1991) and Scholz (1991).
Many subspecies of A. fatua requiring different climatic and soil conditions have been identified. Maillet (1980) sampled six forms of A. fatua abundant in France and Yamaguchi (1982) divided the common form of A. fatua in Japan into four groups. Scholz (1991) also distinguished different varieties of A. fatua (ssp. fatua, septentrionalis, meridionalis and aemulans). In Germany, Siebert and Brix (1984) found the following subspecies: pilosissima, cinerea, pilosa, superba, glabrata and intermedia. Several subspecies of A. fatua are known to occur in the Netherlands: pilosissima, intermedia, hybrida and glabrata (Zonderwijk, 1974). The following subspecies have been sampled by Korniak (1985) in Poland: A. fatua ssp. fatua (pilosissima), intermedia, glabrata and vilis. Initial studies on wild oat varieties in Jiangsu, China, indicated two varieties of A. fatua (A. fatua var. glabrescens and A. fatua var. glabrata) and four ecotypes, which have different coloured husks (Zhang et al., 1999).
Avena fatua and other Avena species are universally referred to as 'wild oats'. Other species of Avena are not as widespread as A. fatua, but are also troublesome in some countries. They include A. sterilis or A. sterilis ssp. sterilis (syn. A. macrocarpa) (wild red oat), A. ludoviciana or A. sterilis ssp. ludoviciana (winter wild oat), A. strigosa (bristle pointed oat) and A. barbata (syn. A. wiestii) (slender oat).
Species which are very seldom listed in the literature are A. nodipilosa, A. magna, A. byzantina, A. pilosa, A. ventricosa, A. clauda, A. longiglumis, A. alba, A. carophylla, A. flavescens, A. nuda, A. pratensis and A. pubescens.
DescriptionTop of page A. fatua is an annual tufted grass with erect culms (Häfliger and Scholz, 1981). Plant height varies from 25 to 120 cm (Holm et al., 1977; Yamaguchi and Sasaki, 1985). Blades are dark green, grow up to 40 cm and show a membranous ligule, which is 1 to 6 mm long and often irregularly toothed. Rooney (1990) found upright and prostrate forms; the former are mostly taller than the crop stand. Sheaths are smooth or slightly hairy, especially in younger plants.
The inflorescence of A. fatua is a loose, open panicle with 2 to 3-flowered pedicelled spikelets. As a specific trait of Avena species, lemmas have 2 to 3 awns arising from the back, which are mostly dark-coloured, bent and 3 to 4 cm long (Holm et al., 1977). Each of the 2 to 3 florets has an oval abscission scar at its base, causing them to fall separately.
Grains are 6 to 8 mm long and usually of mass 11 to 18 mg, but grains of mass 25 mg may also be found. Increasing seed mass enhances competitiveness and seed production (Peters, 1985). Without interference A. fatua can produce more than 20 tillers and 1500 seeds per plant (Morrow and Gealy, 1982), but in crop stands only 1 to 5 tillers and 200 (50 to 1000) seeds per plant are reached (Hanf, 1990).
The height of wild oat lines is related to climate and the number of tillers is correlated with the USA state of origin (Somody et al., 1980a). Morphological characteristics of A. fatua selections can also vary within relatively narrow geographical limits (Somody et al., 1981a).
In a study by Yang et al. (1999) that looked at the genomic structure of A. fatua, a translocation not previously observed in reports on other hexaploid Avena species was found. If this translocation is found to be unique to A. fatua, then this information, combined with more traditional morphological data, will add support to the view that A. fatua is genetically distinct from other hexaploid Avena species.
Plant TypeTop of page Annual
Grass / sedge
DistributionTop of page A. fatua and its subspecies are well adapted to the life cycle and growth of spring cereals, but are also abundant in winter cereals. It is believed to have originated in Central Asia and has been associated with the cultivation of oats and other cereals since the early Iron Age (Jones, 1976; Holm et al., 1977). The plant has been used for bread making and flavouring alcoholic drinks and was considered a good animal feed (Fogelfors, 1984).
In addition to the countries shown on the distribution map, A. fatua has been noted as present in all European regions except Faroes, Spitzbergen and Crete (Rocha Afonso, 1980), and present in all USA states except Arkansas, Florida, Georgia, North and South Carolina, Mississippi, Rhode Island and Tennessee (USDA, 2003). It has become a real problem in the grain growing regions of Australia and the distribution and infestation of A. fatua has been described as parallel to those in China (Tang and Lamerle, 1996).
Distribution TableTop of page
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.
|Continent/Country/Region||Distribution||Last Reported||Origin||First Reported||Invasive||Reference||Notes|
|Afghanistan||Present||Holm et al., 1977|
|Armenia||Present||Holm et al., 1977|
|Azerbaijan||Present||Holm et al., 1977|
|China||Widespread||Hafliger and Scholz, 1981; Tu, 1983|
|-Heilongjiang||Widespread||Chen and Lin, 1989|
|-Hong Kong||Present||Holm et al., 1979|
|India||Present||Sabale, 1985; Mustafee, 1989; Saraswat and Rabha, 1993|
|-Indian Punjab||Widespread||Bir and Sidhu, 1979|
|-Maharashtra||Restricted distribution||Sabale, 1985|
|-Manipur||Present||Devi et al., 2016|
|Indonesia||Present||Hafliger and Scholz, 1981|
|Iran||Widespread||Holm et al., 1979|
|Iraq||Present||Holm et al., 1977|
|Israel||Present||Holm et al., 1977|
|Japan||Present||Hafliger and Scholz, 1981|
|Jordan||Present||Holm et al., 1977|
|Korea, DPR||Present||Hafliger and Scholz, 1981; Yamaguchi, 1982|
|Korea, Republic of||Present||Hafliger and Scholz, 1981; Yamaguchi, 1982|
|Kuwait||Present||Holm et al., 1977|
|Lebanon||Widespread||Holm et al., 1979|
|Pakistan||Widespread||Hussain and Rashid, 1989|
|Philippines||Present||Holm et al., 1977|
|Syria||Present||Holm et al., 1977|
|Taiwan||Present||Taiwan Sugar Research Institute, undated|
|Turkey||Widespread||Holm et al., 1979; Uzun, 1979|
|Turkmenistan||Present||Holm et al., 1977|
|Uzbekistan||Present||Holm et al., 1977|
|Algeria||Present||Holm et al., 1977|
|Egypt||Present||Holm et al., 1977|
|Ethiopia||Present||Holm et al., 1977|
|Kenya||Widespread||Holm et al., 1979|
|Libya||Present||Holm et al., 1977|
|Morocco||Present||Holm et al., 1977|
|South Africa||Widespread||Holm et al., 1979|
|Tanzania||Present||Holm et al., 1977|
|Tunisia||Present||Holm et al., 1977|
|Zimbabwe||Present||Thomas and Schwerzel, 1981|
|Canada||Widespread||Chow, 1980; Hafliger and Scholz, 1981|
|-Alberta||Present||Darwent and Smith, 1985|
|-Manitoba||Widespread||Thomas and Wise, 1988a|
|-Saskatchewan||Widespread||Thomas and Wise, 1989b|
|-Yukon Territory||Present||Introduced||Bennett et al., 2010|
|Mexico||Widespread||Holm et al., 1979; Hafliger and Scholz, 1981|
|USA||Widespread||Holm et al., 1979|
|-Alaska||Present||Introduced||Holm et al., 1977; USDA, 2003|
|-Arizona||Present||Introduced||Watkins and Hargrave, 1984; USDA, 2003|
|-California||Present||Introduced||Hull and Mooney, 1990; USDA, 2003|
|-Colorado||Present||Introduced||Zorner et al., 1984; USDA, 2003|
|-Hawaii||Present||Introduced||Holm et al., 1977; USDA, 2003|
|-Idaho||Present||Introduced||Lish et al., 1986; USDA, 2003|
|-Missouri||Present||Introduced||Blank, 1980; USDA, 2003|
|-Montana||Present||Introduced||Schweitzer et al., 1988; USDA, 2003|
|-New Hampshire||Present||Introduced||USDA, 2003|
|-New Jersey||Present||Introduced||USDA, 2003|
|-New Mexico||Present||Introduced||USDA, 2003|
|-New York||Present||Introduced||USDA, 2003|
|-North Carolina||Present||Introduced||USDA, 2003|
|-North Dakota||Present||Introduced||Miller and Nalewaja, 1990; USDA, 2003|
|-Oklahoma||Present||Introduced||McNeil and Peeper, 1979; USDA, 2003|
|-Rhode Island||Present||Introduced||USDA, 2003|
|-South Carolina||Present||Introduced||USDA, 2003|
|-South Dakota||Present||Introduced||USDA, 2003|
|-Texas||Present||McCully and Wiese, 1984|
|-Washington||Present||Curran et al., 1987|
|-West Virginia||Present||Introduced||USDA, 2003|
|Argentina||Widespread||Holm et al., 1979; Hafliger and Scholz, 1981|
|Bolivia||Present||Hafliger and Scholz, 1981|
|Chile||Widespread||Holm et al., 1979; Madariaga and Scharen, 1985|
|Colombia||Widespread||Holm et al., 1979; Hafliger and Scholz, 1981|
|Peru||Present||Hafliger and Scholz, 1981|
|Uruguay||Present||Holm et al., 1977|
|Venezuela||Present||Hafliger and Scholz, 1981|
|Belgium||Widespread||Holm et al., 1979; Belien et al., 1983|
|Croatia||Present||Lozanovski et al., 1980|
|Czech Republic||Widespread||Koblihova, 1989|
|Czechoslovakia (former)||Widespread||Kropac, 1980; Koblihova, 1989|
|Denmark||Present||Thorup, 1984; Nortoft, 1985|
|Finland||Restricted distribution||Ervoie, 1984; Ulvinen Nordestgaard, 1982|
|Former USSR-in-Europe||Present||Holm et al., 1977|
|France||Widespread||Holm et al., 1979; Hafliger and Scholz, 1981|
|Germany||Widespread||Tienhoven et al., 1984; Holm et al., 1979|
|Greece||Widespread||Holm et al., 1979|
|Hungary||Widespread||Lorinczy, 1988; Toth et al., 1989|
|Iceland||Present||Holm et al., 1977|
|Ireland||Widespread||Holm et al., 1979|
|Italy||Widespread||Hafliger and Scholz, 1981; Speranza et al., 1990|
|Macedonia||Restricted distribution||Lozanovski et al., 1980|
|Netherlands||Present||Jones and, 1976; Naber, 1977|
|Norway||Widespread||Bylterud, 1984; Fykse, 1984|
|Poland||Widespread||Warcholinska, 1986; Rola, 1990|
|Portugal||Restricted distribution||Costa, 1988|
|Romania||Present||Slonovschi, 1982; Naoy and Sarpe, 1987|
|Russian Federation||Present||Present based on regional distribution.|
|-Central Russia||Restricted distribution||Jones and, 1976|
|-Siberia||Present||Nesterova and Chukanova, 1981|
|Spain||Restricted distribution||Aibar et al., 1988; Recasens et al., 1990|
|Sweden||Widespread||Granstrom, 1984; Gummesson, 1985|
|Switzerland||Present||Holm et al., 1979|
|Yugoslavia (former)||Widespread||Lozanovski et al., 1980; Shala, 1987|
|Australia||Present||Hafliger and Scholz, 1981|
|-Australian Northern Territory||Present||Holm et al., 1977|
|-New South Wales||Widespread||Martin and McMillan, 1984|
|-Queensland||Present||Holm et al., 1977|
|-South Australia||Present||Holm et al., 1977|
|-Victoria||Present||Holm et al., 1977|
|-Western Australia||Widespread||Milroy et al., 1990|
|New Zealand||Widespread||Hafliger and Scholz, 1981; Bourdot and Saville, 1988|
History of Introduction and SpreadTop of page As a cosmopolitan grass species, A. fatua is known almost everywhere, especially where cereals are grown. It is believed to have originated in Central Asia and has been associated with the cultivation of oats and other cereals since the early Iron Age (Jones, 1976; Holm et al., 1977). There are two hypotheses about the origin of A. fatua. The first, most widely accepted hypothesis states that A. fatua originated from the cultivated A. sativa, which is derived from A. sterilis. The reverse (diphyletic versus the monophyletic) hypothesis suggests that A. sterilis and A. fatua are ancestors of A. sativa (Scholz, 1991).
In recent times, A. fatua has become one of the most important weeds in the USA, Canada and the UK (Sharma, 1979). Since the 1960s this species has spread widely, e.g. in Finland (Erviö, 1984), Norway (Synnes, 1984), Germany (Kulp and Cordes, 1986; Petzoldt, 1986), Poland (Korniak, 1985), Italy (Speranza et al., 1990), former Yugoslavia (Shala, 1987), the former Czechoslovakia (Koblihova, 1989) and India (Mustafee, 1989). Increasing infestation may be caused by seed importation (Erviö, 1984), prolonged cereal cropping or new production technology (Bachthaler, 1985). Milijic (1980) pointed out that growing wheat in rotation with other annual field crops, as opposed to monoculture, and high fertilization result in an increase in abundance of A. fatua. In contrast to these findings, A. fatua declined in the Netherlands because the area of spring cereals planted decreased and control of A. fatua was encouraged by the government (Naber, 1977).
HabitatTop of page A. fatua is a cosmopolitan grass weed growing on nearly all soil types. The plant tolerates soil pH as low as 4.5 (Holm et al., 1977), but calciphilous subspecies are also found (Korniak, 1985; Hanf, 1990). It is mainly associated with heavy and fertile soils and spring cereals (Naber, 1977; Korniak, 1985; Pallutt, 1991). It does not require good quality soil, but seed production is higher on richer soils. However, soil conditions have a large effect on the longevity and therefore the control of A. fatua (Streibig, 1984). Siebert and Brix (1984) found some subspecies of A. fatua with different soil requirements: subspecies pilosissima occurred mainly on alluvial soils and subspecies cinerea on loess loams. The subspecies pilosa, superba, glabrata and intermedia occur less frequently and are not associated with any particular soil type.
Growth and viability are not restricted by low temperatures, although A. fatua has its origin in the relatively arid climate of Asia. The species seems to be troublesome wherever cereals are grown in locations with an annual rainfall of 375 to 750 mm (Holm et al., 1977). Avena fatua is also common in other rotation crops, on pasture, in vineyards and on wasteland (Häfliger and Scholz, 1981). It is especially common in the following crops: wheat, barley, rye, oats, rice, maize, potatoes, oilseed rape, sugarbeet, sugarcane, sorghum, cotton, tea, peas, lentils, alfalfa, soyabeans, flax and sunflowers.
Yamaguchi (1982) divided the common forms of A. fatua into four groups according to habitat: accessions from high latitude (Canada, German Federal Republic and Hokkaido, Japan); those from the urban waste land of southern Japan comprising relatively tall plants; those from cultivated fields and the rural waste land of southern Japan, Korea, Australia and Mexico; those with relatively short culms from cereal fields in Japan. In Spain evaluation of the occurrence of A. fatua has suggested that it is prevalent in areas with cooler, wetter climates (Recasens et al., 1996). In former Yugoslavia and Spain, it is noted that, in contrast to other Avena species, A. fatua prefers higher altitudes and is only occasionally present near the coast (Lozanovski et al., 1980; Recasens et al., 1990).
Habitat ListTop of page
|Terrestrial – Managed||Cultivated / agricultural land||Present, no further details||Harmful (pest or invasive)|
|Protected agriculture (e.g. glasshouse production)||Present, no further details||Harmful (pest or invasive)|
|Managed forests, plantations and orchards||Present, no further details||Harmful (pest or invasive)|
|Managed grasslands (grazing systems)||Present, no further details||Harmful (pest or invasive)|
|Disturbed areas||Present, no further details||Harmful (pest or invasive)|
|Rail / roadsides||Present, no further details||Harmful (pest or invasive)|
|Urban / peri-urban areas||Present, no further details||Harmful (pest or invasive)|
|Terrestrial ‑ Natural / Semi-natural||Natural forests||Present, no further details||Harmful (pest or invasive)|
|Natural grasslands||Present, no further details||Harmful (pest or invasive)|
Host Plants and Other Plants AffectedTop of page
|Arachis hypogaea (groundnut)||Fabaceae||Other|
|Avena sativa (oats)||Poaceae||Main|
|Beta vulgaris var. saccharifera (sugarbeet)||Chenopodiaceae||Other|
|Brassica napus var. napus (rape)||Brassicaceae||Other|
|Camellia sinensis (tea)||Theaceae||Other|
|Cicer arietinum (chickpea)||Fabaceae||Other|
|Cynara cardunculus var. scolymus (globe artichoke)||Asteraceae||Other|
|Glycine max (soyabean)||Fabaceae||Other|
|Helianthus annuus (sunflower)||Asteraceae||Other|
|Hordeum vulgare (barley)||Poaceae||Main|
|Lens culinaris subsp. culinaris (lentil)||Fabaceae||Other|
|Linum usitatissimum (flax)||Other|
|Medicago sativa (lucerne)||Fabaceae||Other|
|Oryza sativa (rice)||Poaceae||Main|
|Pisum sativum (pea)||Fabaceae||Other|
|Saccharum officinarum (sugarcane)||Poaceae||Other|
|Secale cereale (rye)||Poaceae||Main|
|Solanum tuberosum (potato)||Solanaceae||Other|
|Sorghum bicolor (sorghum)||Poaceae||Other|
|Triticum aestivum (wheat)||Poaceae||Main|
|Zea mays (maize)||Poaceae||Main|
Biology and EcologyTop of page A. fatua has an annual life cycle and produces up to 1000 seeds per plant (Rauber, 1977). It is an obligate inbreeding species.
Germination and Dormancy
In the northern hemisphere, A. fatua germinates mainly in spring and to a lesser extent in autumn (Jones, 1976; Davies, 1985; Wilson, 1985). It has been reported to germinate over a wide range of temperatures (5-30°C), with optimum germination around 15°C (Koch and Hurle, 1978; Fernandez-Quintanilla et al., 1990) and 20°C (Hassanein et al., 1996). The rate of germination was greatest at 20°C while greatest plumule length and seedling dry weights were achieved at 25°C (Hassanein et al., 1996). However, Murdoch (1983) indicated an optimum soil temperature for germination of only 4-8°C and a maximum temperature of 17°C. These differences in germination requirements are most likely the result of variability between locally adapted ecotypes.
It is known that the awn of the A. fatua seed twists into a helix on drying and untwists when wet, thereby drilling the seed into the soil (Stinson and Peterson, 1979). The geniculate awn is necessary for self-burial. Rain was not required for self-burial and self-burial was not impeded by the presence of straw on the soil surface (Somody et al., 1985). Germination is inhibited by direct or diffused light (Froud-Williams, 1985; Sawhney et al., 1986) but is enhanced by ethylene (Adkins and Ross, 1981), nitrate (Adkins et al., 1984; Saini et al., 1986) and ammonium (Agenbag et al., 1989). Seeds of the summer annual species generally have long, strong primary dormancy, whereas seeds of species that can over-winter have short, weak primary dormancy (Fykse, 1984). Primary dormancy may be broken after a few days or several months (Symons et al., 1987). The duration of dormancy also depends on the temperature at the time of ripening (Sawhney et al., 1985; Adkins and Simpson, 1988), on day length and on genotype (Somody et al., 1980a; Armstrong and Adkins, 1998). Even the grain location in relation to the panicle and, therefore, time of maturity are known to be factors influencing dormancy (Kojic and Canak, 1980). Murdoch et al. (1996) found that dormancy was induced in late spring as a result of soil temperatures being greater than 20°C and water potentials being between -10 and -100 kPa, whereas the dormancy was relieved during autumn and winter (temperatures below 20°C and soil at field capacity). Hou et al. (1997) examined the water uptake patterns in dormant and non-dormant seeds of A. fatua and found that non-dormant seeds absorbed water much more rapidly during imbibition than dormant seeds. Significant differences were also found in the sensitivity of water distribution in A. fatua seeds to the phytochrome germination effect (Hou et al., 1997). The rate and sequence of embryo/scutellum hydration were the important factors in initiating dormancy release. Seed dormancy may be broken by wounding (Foley, 1987) or by treating the air-dry seed with ammonia (Cairns and Villiers, 1986). Seeds can enter into weak secondary dormancy but viability is often lost (Parasher and Singh, 1985).
It is difficult to generalize the dormancy behaviour of A. fatua because of the many interacting environmental factors, high genetic variability and ecotypic variation (Holm et al., 1977). Fennimore et al. (1998) found that backcrossed generations of A. fatua with high and low dormancy displayed a generation-by-germination-temperature interaction. At the lower temperatures the more dormant generations were favoured but as the temperature increased, the generation with lower dormancy displayed higher germination. This, it was concluded, may play an adaptive role allowing the wild oat to persist in diverse ecosystems. Martinez-Ghersa et al. (2000) reported changes in dormancy and germination traits in seeds of A. fatua in different agricultural systems, suggesting an adaptive value for invasion of plants into specific human disturbed habitats. A recent paper by Foley and Fennimore (1998), in which the current knowledge on seed dormancy is summarized, includes information on A. fatua. Several models to help explain the presence of competition and dormancy in A. fatua have also been created (Damgaard, 1998; Fennimore et al., 1999; Foley et al., 1999).
Gibberellic acid is not the primary regulator of seed dormancy in A. fatua but rather it is the after-ripening that is crucial for dormancy release (Fennimore and Foley, 1998). Previously, Foley and Lang (1996) found that after-ripening removes the restriction of germination whereas fructose circumvents it. Gibberellic acid and fructose were tried to see if germination of excised embryos was apparent (Myers et al., 1997). They found that fructose and gibberellic acid both had little effect on the germination and early development in after-ripened embryos but induced germination in dormant seeds. Seedlings resulting from after-ripened seed treated with both fructose and gibberellic acid also grew larger than untreated seedlings. Johnson et al. (1996) found that the expression of cDNAs of dormant and non-dormant A. fatua seeds was modulated by gibberellic acid.
Phosphorous has been found to influence the dormancy and germination of A. fatua (Quick et al., 1997). As phosphorous levels decrease, nutrients accumulate, the water content decreases and dormancy is onset. As the phosphorous levels rise, dormancy is relieved and germination occurs. Other chemicals for relieving dormancy have been examined. Cranston et al. (1996) found that A. fatua germinates after exposure to ethylene. Carmona and Murdoch (1998) found that sodium azide damaged and often killed seeds of A. fatua at pH 4, but actually increased germination at pH 6.2. Carmona and Murdoch (1996) investigated the response of A. fatua to different temperatures and germination-stimulating substances. They found that A. fatua did not respond to thiourea, ethephon and hydrogen potassium, potassium nitrate or sodium azide when subjected to constant or alternating temperatures greater than 10°C. However, they found that when the temperature was reduced to 3-10°C, sodium azide and potassium nitrate relieved dormancy. McIntyre et al. (1996) found germination of A. fatua to be promoted by 50 or 100 mM KNO3 if the adaxial surface of the caryopsis was pierced. They suggested this was due to the KNO3 acting osmotically to increase water uptake.
Cranston et al. (1999) used differential display of mRNAs from embryos of A. fatua caryopses to isolate an mRNA more abundant in non-dormant than dormant caryopses during early imbibition. Increased abundance of this mRNA during early germination and in actively growing tissues indicates that the respective protein is associated with rapid cell elongation, cell division and growth.
Murdoch et al. (1998) further discussed the annual dormancy cycle and germinability of buried seeds of A. fatua.
Barralis and Chadoeuf (1987) recognized that A. fatua belonged to a group of weed species with a high annual rate of seed bank decline (about 80% per year) but that on average successful germination and seedling emergence accounted for only 15% of the annual seed bank losses. Koch and Hurle (1978) reported seed viability of between 3 and 8 years. In field experiments Miller and Nalewaja (1983) found that seed viability declined by 80% shortly after burial but 1-7% of the seed was still viable after 9 years of burial. Miller and Nalewaja (1990) found some viable seeds after 14 years, but 20% were non-viable after 7 months. Conn (1990) reported that less than 1% of seeds were viable after 5 years. Demo (1999a) concluded that viability was related to soil conditions, and that seeds were viable longer in the soil than under laboratory conditions. In field trials in Western Australia, Peltzer and Matson (2002), showed an 80% seed bank decline after 1 year.
Attempts to characterize the influence of soil burial depth on A. fatua viability and longevity have produced unclear and confounding results. Conn and Farris (1987) found that viability was higher for seeds buried at 15 cm than at 2 cm. Hsiao et al. (1983) showed that mortality of seeds on the soil surface is very high, particularly when they are exposed to freezing temperatures. In contrast to these findings, Miller and Nalewaja (1990) indicated a higher seed loss with increasing depth of burial. At depths of 6 cm, Pickering and Raju (1996) reported greater mortality than at 1-2 cms, with seedling emergence being poor and delayed. They attributed this mortality to parasitization of seeds by the soil microbes. Murdoch (1983) found similar germination totals at depths of 2.5-23 cm after 19 months in the soil. However, less than 2% of seeds which germinated at 23 cm were able to emerge. The depth from which seed will germinate is greatest with large seeds, with A. fatua germinating from up to 25 cm below the surface (Fykse, 1984). Seed size affects not only emergence rate, but also growth rate and therefore the competitiveness of the plant (Peters, 1985). A. fatua plants produce fewer panicles when established from seed emerging from 2 cm depth than from seed emerging from 10 cm depth (Somody et al., 1981b).
Growth and Crop Competition
A. fatua forms a large root system with a high uptake of phosphorus and nitrogen (Haynes et al., 1991). Nitrogen and root competition are therefore very important determinants of yield impact in cereals (Satorre and Snaydon, 1992). The timing of fertilizer application may also result in the promotion of A. fatua amongst crops (Kirkland and Beckie, 1998; Dastgheib et al., 1998, 1999). The addition of fertilizer to a wheat crop in New Zealand resulted in increased densities of A. fatua (Dastgheib et al., 1998, 1999) but vigour decreased (Dastgheib et al., 1998). In glasshouse trials, Freedom et al. (1998) explored the influence of fertilization and atmospheric carbon dioxide enrichment on ecosystem carbon dioxide and H2O exchanges in single and multiple-species grassland microcosms. In further studies, O'Donnell and Adkins (2001) examined the influence of carbon dioxide enrichment, temperature increase and soil moisture level on A. fatua and wheat.
The competition of A. fatua with winter cereal crops has been assessed in China. Results (Qian, 1996) indicated that the cereal crops were generally more competitive than the wild oats with the competition beginning at the tillering stage, increasing during growth with the maximum occurring at the shooting and heading stages. For the crops it was intraspecific competition that was the most significant whereas for wild oats it was the interspecific competition that was the more significant (Qian, 1996). In Cundinmarca (Columbia) the competitive effect of eight successive cohorts of wild oats in wheat was assessed and the earliest emerging cohorts were shown to be the strongest competitors (Marquez et al., 1996).
Competition was also studied by Lanning et al. (1997) who investigated the suppression of wild oats by wheat and barley growth by lowering the amount of light available to the A. fatua plants. They found that barley was a much better competitor with wild oats than wheat as one half of the wild oat biomass and seed were produced. High positive correlations were evident between light penetration and wild oat growth. In China, an analysis of the interactions of three weeds on wheat was examined (Li, 1996). It was seen that A. fatua had the greatest impact of the three weed species on wheat. Increasing the density of A. fatua by one plant/m² decreased the wheat yield by 2.92 kg/667 m² (see additional notes on crop competitiveness under Economic Impact).
See additional notes under Habitat.
RainfallTop of page
|Parameter||Lower limit||Upper limit||Description|
|Mean annual rainfall||250||1000||mm; lower/upper limits|
Rainfall RegimeTop of page Summer
Soil TolerancesTop of page
Special soil tolerances
Means of Movement and DispersalTop of page Natural Dispersal
A. fatua has relatively large seeds, the majority of which fall close to the parent plant. There are no reports of natural dispersal by wind or water, though this must occur to some extent. Movement by animals is similarly not discussed in the literature.
The dispersal and spread of A. fatua is closely associated with the cultivation of cereal crops around the world. In a study examining weed dispersal within fields, patches of A. fatua typically advanced by 1-3 m in a single year with some movement of up to 30 m noted (Wheeler et al., 2001). Movement was in the direction of cultivation and harvesting. Movement over longer distances is most likely the result of importation of contaminated grain.
Plant TradeTop of page
|Plant parts liable to carry the pest in trade/transport||Pest stages||Borne internally||Borne externally||Visibility of pest or symptoms|
|Growing medium accompanying plants||seeds||Yes||Pest or symptoms usually invisible|
|True seeds (inc. grain)||seeds||Yes||Pest or symptoms usually visible to the naked eye|
|Plant parts not known to carry the pest in trade/transport|
|Fruits (inc. pods)|
|Stems (above ground)/Shoots/Trunks/Branches|
Wood PackagingTop of page
|Wood Packaging not known to carry the pest in trade/transport|
|Loose wood packing material|
|Processed or treated wood|
|Solid wood packing material with bark|
|Solid wood packing material without bark|
Impact SummaryTop of page
|Fisheries / aquaculture||None|
ImpactTop of page A. fatua is considered to be among the world's worst agricultural weeds and is still increasing in importance (Holm et al., 1977; van der Puy, 1986). Daugovish et al. (2003) estimated that A. fatua infests 11 million ha of cropland in the US. Mortimer (1985) called A. fatua an intractable weed, because its life cycle is synchronized with the growth of the crop. A computer package has been developed for assessing the economics of A. fatua control in cereal and oilseed crops (O'Donovan, 1996).
A. fatua shows a high competitive ability and is often more competitive than Alopecurus myosuroides (Farahbakhsh et al., 1987), Galium aparine (Wilson and Wright, 1990) or wheat (Martin and Field, 1988). Shoot biomass and competitiveness are enhanced by ploughing and high levels of fertilization with nitrogen (Bozic, 1986) and phosphorus (Konesky et al., 1989). Competition between cereals and A. fatua occurs predominantly below ground (Satorre and Snaydon, 1992). Crop yield response depends on time of emergence and density (Farahbakhsh and Murphy, 1986). In cereals, competition starts mainly at the two-node stage and reduces the number of crop tillers (Morishita and Thill, 1988). However, a study by Dhaliwal (1998) found that when mixed with A. fatua, all barley cultivars being tested displayed improved growth characteristics. O'Donovan et al. (1999b) also found that each year wild oat seed yield and shoot dry weight decreased as barley plant density increased.
Many damage threshold levels have been estimated for various crops. For cereals the following have been reported: eight A. fatua plants/m² caused 14% yield reduction and 5.5% less protein content in wheat (Wimschneider et al., 1990); 100 panicles/m² reduced the yield of winter wheat by 34% and of spring wheat by 40% (Rola, 1987); 60 plants/m² caused an average yield loss of 0.5 t/ha in about 100 wheat trials (Meinert, 1983); wheat yield loss was below 1% up to 3 plants of A. fatua/m², reached 2.2% at 5 plants and was 50-60% at 100 plants (Walia et al., 1998); infestations ranging from 8 to 662 seedlings/m² in the spring resulted in yield reductions varying from 0 to 72% in spring barley (Wilson and Peters, 1982; Weaver and Ivany, 1998); 10 culms diminished spring barley yield by 0.08-0.15 t/ha (Korolova et al., 2000); 17-30% reduction in winter wheat yields was caused by 8-16 A. fatua plants/m², although with fewer than 8 plants/m² yield reductions were not significant (Pardo and Encina, 1977); 1% yield loss was measured in cereals for each A. fatua plant/m² (Wilson and Wright, 1990); the damage threshold in spring barley is around 10 A. fatua plants/m² (Murdoch et al., 1988); no yield loss was observed with 4 A. fatua plants/m² in wheat and with 15 plants/m² in cultivated oats (Mondragon et al., 1989). In contrast to the majority of reports, Kiec (1997) found that planting densities of 0, 4, 8, 16 and 32 pcs/m² in crops of spring wheat had no effect on crop yield or other triticale variables. In the case of sugarbeet, Mesbah et al. (1995) found that one A. fatua plant/m of row reduced yield by 14%, but in mixed density with 0.8 Sinapis arvensis, yield (plants/m of row) was reduced by 29%. For maize, 9 or 27 A. fatua plants/m of row reduced maize grain yield by 14 or 25%, respectively, whereas 3 plants/m of row caused no significant yield reduction (Castillo and Ahrens, 1986). In field trials using peas, A. fatua was shown to cause significant reductions in total yield and also a reduction in seeds per pod (Wright and Baloch, 1999).
Variations in the yield reduction potential of A. fatua as evidenced above are inevitable and are the result of site to site, climatic and genetic variation. An analysis of the economic benefits of integrated weed management approaches for the control of A. fatua in northern New South Wales, Australia, reinforced the idea that strategies that directly reduce seed production and seed bank populations yield the greatest economic benefit (Jones and Medd, 1997). Crop competition and bioeconomic decision support models have been developed for A. fatua control. A decision model of Cousens et al. (1986) predicts that the highest long-term benefits will be obtained when A. fatua is controlled at a density of 2-3 seedlings/m². Jones and Medd (2000) convincingly identify the shortcomings of A. fatua control strategies that simply attempt to minimise yield impacts in a single year and advocate population based management that attempts to reduce the soil seed bank over a longer term.
The continuous and widespread use of herbicides for the control of A. fatua has frequently resulted in the evolution of herbicide resistance and A. fatua is listed as the second most herbicide resistance prone weed in the world (Heap, 2003). Herbicide resistant populations of A. fatua have been reported in Australia, Canada, Belgium, Chile, France, South Africa, the UK and USA (Heap, 2003) and resistance to at least five herbicide modes of action has been documented. In Canada, where the problem is most severe, upwards of 2 million acres of cropland are infested with herbicide resistant A. fatua. In a recent survey in Saskatchewan, Canada, over one half of fields had populations of A. fatua resistant to either ACC'ase or ALS-inhibiting herbicides (Beckie et al., 2002).
Only a few data are available concerning the long-term effect of A. fatua as a host for cereal pests and diseases. Rauber (1977) and Sharma and van den Born (1978) found no obvious differences in susceptibility between A. fatua and A. sativa. Nevertheless, Madariaga and Scharen (1985) reported that Septoria tritici [Mycosphaerella graminicola] on A. fatua was not pathogenic to wheat. In a study by Barlow et al. (1999) results indicated that A. fatua was a poor host for the tarnished plant bug (Lygus hesperus).
Threatened SpeciesTop of page
|Threatened Species||Conservation Status||Where Threatened||Mechanism||References||Notes|
|Amaranthus pumilus (seabeach amaranth)||NatureServe NatureServe; USA ESA listing as threatened species USA ESA listing as threatened species||California||Competition - monopolizing resources||US Fish and Wildlife Service, 2008|
|Streptanthus glandulosus subsp. niger (Tiburon jewelflower)||USA ESA listing as endangered species USA ESA listing as endangered species||California||Competition - strangling||US Fish and Wildlife Service, 2010a|
|Verbesina dissita (big-leaved crownbeard)||National list(s) National list(s); USA ESA listing as threatened species USA ESA listing as threatened species||California||Competition - monopolizing resources||US Fish and Wildlife Service, 2010b|
Risk and Impact FactorsTop of page Invasiveness
- Invasive in its native range
- Proved invasive outside its native range
- Highly adaptable to different environments
- Tolerates, or benefits from, cultivation, browsing pressure, mutilation, fire etc
- Highly mobile locally
- Has high reproductive potential
- Has propagules that can remain viable for more than one year
- Negatively impacts agriculture
- Negatively impacts tourism
- Reduced amenity values
- Reduced native biodiversity
- Competition - monopolizing resources
- Competition - strangling
- Pest and disease transmission
- Highly likely to be transported internationally accidentally
- Difficult/costly to control
UsesTop of page A. fatua has been used to develop resistant traits in wheat (Tang et al., 1997). Resistance of a tetrageneic hybrid of triticum, Avena and Elymus conferred resistance in wheat to leaf rust (Puccinia recondita), stem rust (P.graminis) stripe rust (P. striiformis), powdery mildew (Erysiphe graminis) and root rot (Alternaria alternata).
Uses ListTop of page
Animal feed, fodder, forage
- Fodder/animal feed
- Gene source for disease resistance
- Gene source for drought resistance
- Poisonous to mammals
Similarities to Other Species/ConditionsTop of page A. fatua has to be distinguished from many other species of Avena. The characters most useful for this are (i) the florets/lemmas of A. fatua are always to some degree hairy; (ii) the individual florets of A. fatua all separate from the spikelet and from each other; (iii) there are awns on the backs of at least two of the florets in each spikelet; and (iv) the lemmas end in two small teeth.
Because of its vigour, growth habit and large spikelets, A. fatua looks similar to cultivated oat (A. sativa). However, A. sativa has a denser panicle, the spikelets have only 0 to 1 awn and the florets do not readily separate and shed (Hanf, 1990). The most common of the other wild oat species is A. sterilis, which differs in the florets not separating from each other but falling as a cluster of 2 to 5 florets. Avena ludoviciana is very similar to A. sterilis and is sometimes treated as a sub-species, differing in size with spikelets mostly below 30 mm, while those of a typical A. sterilis plant are over 30 mm. Of other species occurring as weeds, A. strigosa has spikelets that are glabrous and do not separate, while A. barbata has lemmas ending in two distinct bristles, 3 to 7 mm long. In Ethiopia the most common wild oat species, A. vaviloviana, is distinguished by having bristles 1 to 3 mm long on the lemmas and the spikelets are more slender with very narrow abscission scars at the base of each floret (Stroud and Parker, 1989).
For separation of these and other species, additional characters including the abscission scars at the base of each floret, details of the lemma, awn and caryopses etc. are described by e.g. Edgar (1980), Lyshede (1987) and Scholz (1991). Detailed identification keys are provided by Raju (1990) and Scholz (1991).
Prevention and ControlTop of page Physical and Cultural Control
There are some effective non-chemical methods for controlling A. fatua. These are mainly soil cultivation and crop rotation. The most effective non-chemical control was achieved by the shallowest cultivation possible, carried out as late as possible (Zorner et al., 1984). Tine cultivation, besides favouring increase of an uncontrolled population, results in a faster population decline than ploughing (Wilson and Cussans, 1983).
Depth of burial and crop rotation influence the seed bank (Froud-Williams, 1987). Peters (1991) found no viable seeds after 3 years of intensive soil tillage. Under zero tillage the numbers of A. fatua are generally reduced, but the control of surviving plants with herbicides can be less effective (Bowren, 1983). Summer treatment of soil after cereal harvest (stubble ploughing, summer deep tillage and spring seed-bed preparation), which buries A. fatua seeds, can create good conditions for weed seed germination and help to markedly reduce weed seed banks (Demo, 1999). Palys et al. (1999) reported that direct sowing and no ploughing caused the greatest increases in the densities of A. fatua in a faba bean/winter wheat/spring barley rotation prior to harvest. Post-harvest soil cultivation can promote weed seed germination and emerged weeds can be controlled with glyphosate prior to drilling. This treatment combined with a pre- or post-emergence herbicide programme resulted in reduced numbers and a decline in A. fatua over a 4-year period (Hutcheon et al., 1998).
Straw burning kills many seeds and reduces the dormancy of survivors (Ivens, 1978; Moss, 1985). In contrast, stubble cultivations have a smaller effect on the germination of A. fatua (Cussans et al., 1987). Delayed sowing results in a consistently high degree of A. fatua control but can also result in significant losses in grain yield and quality (Hunter, 1983).
In many cases farmers have had to seek alternative methods in their control of A. fatua. In a study on the LIFE pilot farm in the UK, the presence of the wild oats in such abundance caused a switch to spring cropping of oilseed rape and peas in addition to a ley period of 1 year grass-clover mix (Davies et al., 1997). In cereal crops, reducing the seed bank of weed seeds is the optimum control method. This can be done through changes in the crop sequences (Malik et al., 1996).
Schoofs and Entz (2000) reported forage systems (e.g. triticale) were at least as effective as the sprayed wheat control in suppressing wild oat.
In contrast to these indirect control methods there are only a few non-chemical measures for direct control of A. fatua. Mechanical methods are mostly less successful because of the large seed and dense root system (Koch and Hurle, 1978). Nevertheless, harrowing or hoeing may break dormancy and therefore increase late emergence (Raju et al., 1988). A. fatua and other grasses are not susceptible to thermal control methods (Ascard, 1995). However, a flame weeder used in an onion crop resulted in 31-93% control of A. fatua (Mojzis, 2002). Tsuruuchi (1986) reported that emergence of A. fatua in wheat and barley can be reduced by flooding. Soil solarization is used in Israel, the USA, Italy and India (Arora and Yaduraju, 1998) to control A. fatua as well as other weeds and pests (Cartia, 1985).
Composting has been found to kill weed seeds (Tompkins et al., 1998). In an experiment conducted using feedlot manure containing 12 weed species of which A. fatua was one, composting reduced the viability drastically within two weeks and killed all seeds within four weeks (Tompkins et al., 1998).
Olson et al. (1999) found that shoot extracts and living tissue extracts from wheat (Triticum aestivum) resulted in a significant decrease in total biomass, pigment, carbohydrate and protein content of A. fatua. In a field trial in Pakistan, sorghum water extract reduced the density and biomass of A. fatua by 22-27% (Cheema et al., 2002). Parthenin, a natural extract from Parthenuim hysterophorus reduced germination of A. fatua and inhibited shoot and root growth (Batish et al., 2002). In a study on the allelopathic effects of Triticum speltoides (a wild relative of wheat), one out of 17 accessions were found to reduce the radicle length of A. fatua by 50% (Hashem and Adkins, 1998).
Enhanced crop competition can also reduce the growth and yield reduction effect of A. fatua. Increasing the sowing rate of five varieties of barley improved the competitiveness of all varieties as evidenced by reduced wild oat shoot dry matter and seed production and, in some cases, improved barley yields (O'Donovan et al., 2000a). In field trials in Canada, hybrid rape varieties were twice as competitive against A. fatua as open-pollinated varieties (Zand and Beckie, 2002). Xue and Stougaard (2002) showed that the combined effects of large seed size and increased wheat sowing rate could decrease A. fatua biomass and seed production by 20%.
A commercially available smoke-water solution has also been shown to stimulate the germination of A. fatua (Adkins and Peters, 2001).
Few papers have been published concerning biological approaches for controlling A. fatua. They are resultant of fungal infections such as those by Erysiphe graminis f.sp. avenae (Sabri and Clark, 1996; Sabri et al., 1997), Puccinia coronata (Chong and Seaman, 1996, 1997; Salmeron-Zamora et al., 1996; Johnston et al., 2000), P. coronata f.sp. avenae (Carsten et al., 2000), P. graminis (Harder and Anema, 1993), P. recondita (Pfleeger et al., 1999), Pyrenophora (Kastanias and Chrysayi Tokousbalides, 2000), nematodes (Riley and McKay, 1991) or hydroxamic acids that have allelopathic effects (Perez, 1990). A. fatua is generally susceptible to the same range of parasites as cultivated oats (Sharma and van den Born, 1978). Research into fungal pathogens for the biological control of A. fatua is occurring in many countries including Vietnam (Hetherington et al., 1996), Australia, USA, Netherlands, Japan and South Africa (McRae, 1998).
A. fatua has been confirmed, via virological analysis, to be a natural host plant for the Oat blue dwarf virus (Vacke, 1998). The majority of host plants identified in this study exhibited characteristic symptoms of the infection. Another pathogen, Drechslera avenacea, was identified and isolated and found to be specific to A. fatua over wheat (Zhang and Li, 1996) and has been investigated as a potential bioherbicidal organism for A. fatua (Hetherington et al., 2002). Chong and Seaman (1997) isolated 101 virulence phenotypes from 189 isolates from A. fatua and commercial field oats in Manitoba and Ontario, Canada. Hot dry weather was seen to slow the infection of the fungus.
The effect of Erysiphe graminis f.sp. avenae on the photosynthesis and respiration of A. fatua was studied by Sabri et al. (1997). It was evident from these studies that E. graminis [Blumeria graminis] reduced levels of photosynthesis and chlorophyll. In a comparison of wild oats with cultivated crops in their tolerance to B. graminis it was seen that the wild oats were significantly more tolerant, due to the lower sensitivity of their metabolism to B. graminis (Sabri and Clarke, 1996).
The ant species Messor barbarus has been shown to preferentially predate A. fatua seeds (Detrain and Pasteels, 2000).
Herbicide weed control of A. fatua has been found to be more effective than cultural control (Stevenson et al., 2000a) and many herbicides have been successfully used (Milne, 1997). Good levels of control are given by herbicides belonging to the urea family (e.g. isoproturon or chlorotoluron) and phenoxypropionates (e. g. diclofop-methyl). In a review by Fisher and May (2000), advice is given for the chemical control of A. fatua, along with a list of new herbicide registrations for 2000. Zahradnicek and Kohout (1996) also examined various graminicides for use against wild oats in sugarbeet crops.
Many selective herbicides sprayed alone, in mixtures or sequences are known for their high efficacy against A. fatua. These include the following: atrazine (Stork, 1998), benzoylprop-ethyl, chlorsulfuron, chlorotoluron, clethodim (Szilvasi, 1996), clodinafop, cycloxydim, diclofop-methyl (Balyan and Malik, 1996; Koscelny and Peeper, 1997; Troccoli et al., 1997; Fayed et al., 1998), difenzoquat, diflufenican, dimethenamid + trifluralin (Soliman et al., 1998), fenoxaprop-ethyl (Koscelny and Peeper, 1997; Fayed et al., 1998; Mathiassen and Kudsk, 1998), flamprop-isopropyl (Fayed et al., 1998), fluazifop-P-butyl, fluoroglycofen (Lueschen et al., 1997; Hutchinson et al., 1999), flucarbazone sodium (Kirkland et al., 2001), haloxyfop-P-ethoxyethyl, imazamox (Lueschen et al., 1997; Hutchinson et al., 1999), imazamethabenz (Hsiao et al., 1996; Koscelny and Peeper, 1997; Wille et al., 1998), isoproturon (Angiras and Vinod Sharma, 1996; Balyan and Malik, 1996; Pandey et al., 1996), linuron, linuron + monolinuron + fluazifop-butyl (Soliman et al., 1998), methabenzthiazuron, oxyfluorfen (Arnold et al., 1998), pendimethalin (Pandey et al., 1996), pirifenop-N-butyl, propaquizafop (Gimenez-Espinosa et al., 1997; Gimenez Espinosa et al., 1999), pyridate (Gimenez Espinosa et al., 1999), quizalofop-ethyl, rimsulfuron, sethoxydim, sulfometuron (Arnold et al., 1998), sulfonylaminocarbonyl, triazolinone (Santel et al., 1999; Scoggan et al., 1999), terbutryn (Balyan and Malik, 1996; Fayed et al., 1998), tralkoxydim (Balyan and Malik, 1996; Fayed et al., 1998; Belles et al., 2000; Stevenson et al., 2000b), tri-allate and tria-allate sulfoxide (Kern et al., 1996) and trifluralin (Lueschen et al., 1997; Scursoni and Satorre, 1997).
Several herbicides derivatives have been examined for potential use in wild oat control. A herbicide called CGA184927 (2-proponyl(R)-2-(4-(5-chloro-3-fluoro-2-pyridinyloxy)-phenoxy)-propionate/5-chloro-8-quinolinoxyacetic acid-1-methylhexylester) was evaluated in its efficacy of A. fatua control (Blackshaw and Harker, 1996). It was evident that CGA184927 is sensitive to environmental conditions as the application rate needed to produce >90% control over several years varied from 22 to 90 g/ha. This herbicide was also compatible in tank mixes with bromoxynil, clopyralid and 2,4-D ester, whereas tank mixing with metsulfuron or dicamba reduced the effectiveness in controlling wild oats. Examination of other derivatives found that derivatives of 2-[4-(3,5-dichloro-2-pyridyloxy) phenoxy] propionamidoxyacetic acid to show selectivity between oats and wheat and N-ethyl-2-[4-(3,5-dichloro-2-pyridyloxy) phenoxy] propionamidoxyacetamide to have a higher herbicidal action than diclofop-methyl while retaining similar selectivity (Matsumoto et al., 1996).
A new cyclohexanedione herbicide, tepraloxydim, provided effective control of A. fatua in broadleaf crops in Poland (Stachecki and Krawczyk, 2002). A new additive, consisting of the pyrimidine allopurinol and molybdenum trioxide, formulated in 50% monolaurate, was found to boost the activity of sulfosulfuron used mainly for the control of wild oats (A. fatua). This increased activity led to the effective control of wild oat populations which are not normally controlled by the herbicide (Cairns et al., 2001)
Chao et al. (1997) examined whether the efficacy of imazamethabenz could be improved when applied to the tillers of wild oats plants. They found that the presence of tillers neither improved nor decreased the efficacy of imazamethabenz. Hsiao et al. (1996) found that when imazamethabenz was tank mixed with 1 and 2% ammonium sulphate, the phytotoxicity of the herbicide was increased when applied to A. fatua at the 2 to 3 or 3 to 4 leaf stage. If ammonium sulphate was applied at 10%, the phytotoxicity of the herbicide was reduced. There was also a difference in effects of ammonium sulphate on the herbicide toxicity according to application method (Hsiao et al., 1996).
The uptake of some herbicides is also influenced by temperature and moisture levels, which may be important for the successful control of A. fatua (Olson et al., 1999). Control of A. fatua was greater when the temperature after application of MON 37500 (1-(2-ethylsulfonylimidazo[1,2-a]pyridin-3-ylsulfonyl)-3-(4,6-dimethoxypyrimidin-2-yl)urea) was 25/23°C or soil moisture was at full pot capacity compared to when the temperature was at 5/3°C or soil moisture was at one-third pot capacity (Olson et al., 2000). Holm et al. (2000) found the optimal graminicide rate depended on the level of A. fatua infestation and the best time to control A. fatua depended upon the type of graminicide. Xie et al. (1996) found that water stress influenced the phytotoxicity of herbicides. Adkins et al. (1998) examined the efficacy of glyphosate on wild oats in relation to soil moisture content, irradiance, temperature and relative humidity and found that the efficacy was greatest under well-watered, warm (30/25°C) and humid (>92/90%) conditions and was not altered by irradiance. Xie et al. (1996) also found that in A. fatua, fenoxaprop-ethyl and imazamethabenz-methyl absorption is affected by temperature and irradiance. There was an increase in absorption with higher temperatures of 30/20°C and under 70% shading, the phytotoxicity of both the herbicides was enhanced. Sharma et al. (1996) also examined herbicide application and found that the distribution of the herbicides was dependent on the content and concentration of the surfactant and the surface characteristics of the herbicide droplets.
The uptake of diclofop-methyl in A. fatua was higher after root application compared to foliar application, whereas the uptake of fenoxaprop-p-ethyl after foliar application was lower than that for diclofop but greater if applied to the roots (Dahroug, 1996). The translocation of these herbicides was faster from roots to shoots.
Stevenson et al. (2000b) found that the efficiency of tralkoxydim in controlling A. fatua in Canada was affected by the rate of herbicide application, water volume, spray mixture pH, diurnal application time and sodium bicarbonate concentration of the water source. At Scott, the negative effects of tralkoxydim rates lower than 200 g/ha applied with 50 or 1000 L of water per hectare on wild oat fresh weight were most apparent when applications were made in the morning, especially with an unbuffered spray mixture. However, at Saskatoon, spray mixture pH or time of application did not modify the effects of tralkoxydim rate and water volume on wild oat fresh weight.
When plants are stressed the phytotoxic effects of herbicides are often diminished. A study in Canada (Xie et al., 1997a) demonstrated that when A. fatua was subjected to drought conditions or drought and high temperatures, the reduction in phytotoxicity was most evident following fenoxaprop and diclofop applications. Flamprop and imazamethabenz also had reduced phytotoxicity but to a lesser degree. It appeared that imazamethabenz was mostly affected by high temperatures, whereas fenoxaprop was mostly affected by drought. However, the combination of both drought and high temperatures was sufficient to markedly reduce the efficacy of all herbicides examined.
The phytotoxicity of herbicides can be increased by the addition of surfactants (Xie et al., 1997b); ammonium sulphate ([NH4]2SO4) in the case of fenoxaprop; sodium bisulphate (NaHSO4) for imazamethabenz (Xie et al., 1997b); methylated seed oil and urea ammonium nitrate with quizalofop (Stougaard, 1997) and specific temperatures (Xie et al., 1997a, b). The combination of methylated seed oil and urea ammonium nitrate with quizalofop enabled greater than 90% control when the quizalofop was applied at the lowest level of 20 g/ha (Stougaard, 1997).
Alternative methods to broadscale spraying to control weeds have been examined. In the UK patch spraying to control wild oats in wheat crops have been developed (Lutman et al., 1998).
Herbicide resistance has evolved in response to intense selection pressure (a result of high herbicide application frequencies and efficacy) (Morrison et al., 1996). O'Donovan et al. (2000a) found that the evolution of resistance was positively correlated with the number of triallate or difenzoquat applications over a 9 year period. To delay the onset of herbicide resistance, repeated usage of the same herbicide or group (mode of action) should be avoided and wherever possible, integrated use of alternative control strategies is recommended (Morrison et al., 1996).
Herbicide resistance has been reported in A. fatua to the following active ingredients: tri-allate in Canada (Thai et al., 1985; Morrison and Devine, 1994; Blackshaw et al., 1996; Kern et al., 1996; Beckie and Jana, 2000; O'Donovan et al., 1996, 2000b) and the USA (O'Donovan et al., 1994; Davidson et al., 1996; Kern et al., 1997), diclofop-methyl in America (Seefeldt et al., 1996b, 1998), Australia (Powles and Holtum, 1990; Mansooji et al., 1992), Canada (Devine et al., 1993) and in South Africa (Malik et al., 1996), difenzoquat in Canada (O'Donovan et al., 2000b), sethoxydim in Canada (Maurice and Billett, 1991), fluazifop in Australia (Mansooji et al., 1992), fenoxaprop-ethyl (Devine et al., 1993; Cavan and Moss, 1997), and imazamethabenz in Canada (Heap, 1997; Friesen et al, 2000) and America (El-Antri and Nalewaja, 1997), flamprop and fenoxaprop-P in Canada (Friesen et al., 2000), imazamethabenz-methyl (Nandula and Messersmith, 2000), and difenzoquat (O'Donovan et al., 1994; Kern et al., 1996; Rashid et al., 1997), diallate (Kern et al., 1996), tralkoxydim (Marshall et al., 1996; El-Antri and Nalewaja, 1997; Cocker et al., 2000) in the USA and EPTC (Rashid et al., 1997). Up-to-date records of the extent of herbicide resistant A. fatua populations are given by Heap (2003).
Several surveys have been conducted across Canada to assess the distribution of herbicide resistant A. fatua (Beckie et al., 1998, 1999b; Beckie and Juras, 1998). Resistance to aryloxyphenoxypropionic acids has been reported in France (Letouze et al., 1997) and the UK (Cocker et al., 2000) and resistance to phenylureas has also been reported in France (Letouze et al., 1997) with some resistant populations surviving more than 100 times the normally lethal dose. Murray et al. (1996) tried to elucidate the inheritance of aryloxypenoxypropionate resistance in different populations exhibiting different cross-resistance patterns and found that the resistance in both populations is encoded at the same gene locus.
In Montana, USA, triallate resistance was surveyed and found to constitute 94% of all patches/areas in 1993 but this declined to 77% in 1995 (Davidson et al., 1996). Management strategies were said to have an important role in the pattern of dispersal. Blackshaw et al. (1996) examined triallate resistant populations in Alberta, Canada, and found that they could be controlled by atrazine, ethalfluralin, fenoxaprop-p, flamprop, imazamethabenz and tralkoxydim but that integrated weed management practices should also be implemented. Kern et al. (1997) examined several triallate resistant lines of A. fatua to determine the effects on wax and lipid biosynthesis. They found that by greenhouse application of tri-allate, the epicuticular waxes were dramatically reduced as were the elongated fatty acid fractions in susceptible varieties (also reported in Rashid et al., 1997) but not resistant varieties. However, treatment with tri-allate sulfoxide reduced the in vivo concentrations of elongated fatty acids equally in the resistant and susceptible lines. This infers that tri-allate sulfoxide is more inhibitory towards fatty acid elongases than tri-allate. This is turn suggests that in vivo tri-allate sulfoxidation is necessary for herbicidal action and so reduced rates of tri-allate sulfoxidation can confer resistance. Rashid et al. (1997) also examined the effect of tri-allate and difenzoquat on the fatty acid chains. They found results similar to those by Kern et al. (1997) for tri-allate whereas the difenzoquat did not cause any change in the fatty acid composition of susceptible or resistant lines, hence suggesting that fatty acid biosynthesis is not involved in cross-resistance to this herbicide.
Having fallow in the crop rotations slowed the rate of evolution of tri-allate resistance in wild oat (Beckie and Jana, 2000). Resistance was not detected in herbicide untreated continuous spring wheat cultivar Neepawa and wheat-fallow plots and herbicide treated wheat-fallow plots. While resistance was not detected in herbicide treated continuous spring wheat cultivar Neepawa plots in 1996, 3% of the seeds screened in 1997 and 14% of the seeds in 1998 were resistant. In 1996, 53.9 and 98.7% of wild oat plants had dormant seeds in the Neepawa and wheat-fallow rotations, respectively. The enhanced dormancy of seed selected by fallow treatment may also have contributed to delaying the evolution of resistance in wheat-fallow.
Mechanisms of resistance in A. fatua for diclofop were examined (Seefeldt et al., 1996b). It was evident that resistance could not be attributed to differential absorption, translocation or metabolism of diclofop, nor membrane plasmalemma repolarisation. Cross-resistance to fenoxaprop was also more likely in diclofop-resistant biotypes (Seefeldt et al., 1996b). Baerg et al. (1996) found that tribenuron antagonized diclofop control, which was attributed to a reduction by tribenuron in the basipetal translocation of diclofop to meristematic regions of A. fatua.
Multiple herbicide resistance in A. fatua is not rare. Friesen et al. (2000) reported resistance to imazamethabenz, flamprop and fenoxaprop-P in three Avena populations in the north-west agricultural region of Manitoba, Canada. The evolution of herbicide resistance in the absence of direct selection (cross resistance) is a very serious development as producers with resistance to multiple herbicides in A. fatua are left with a very limited number of herbicide options for selective control in crops commonly grown in western Canada (Friesen et al., 2000).
Cavan et al. (2001) utilised a model to predict the time required to develop field resistance of A. fatua to aryloxyphenoxypropionate (AOPP) and cyclohexanedione (CHD) herbicides in a number of field situations. The model predicts that plough cultivation could delay the development of resistance relative to tine cultivation and that herbicide rotation can dramatically increase the times required for field resistance to develop in a tine cultivation system. Resistance can be delayed for at least 66 years if three herbicides, each with a different mode of action, are rotated and each herbicide causes 90% mortality in a tine cultivation system.
Tri-allate and tri-allate sulfoxide pytotoxicity have been evaluated by comparing the metabolism occurring during growth. Tri-allate metabolised 12 times slower than the resistant populations tested, although the end result was the same. However, tri-allate sulfoxide was metabolised rapidly in both the susceptible and resistant lines (Kern et al., 1996). It was therefore concluded that resistance to tri-allate is the result of reduced rate of formation of the sulfoxide from tri-allate. O'Donovan et al. (1996) developed a bioassay for determining triallate resistance in A. fatua where routine samples suspected of resistance are collected.
Modes of resistance to herbicides are largely unknown. In A. fatua the mechanism to the pre-emergent thiocarbamate herbicide tri-allate was examined (Kern et al., 1998). It was found that the metabolism of tri-allate was more than 12-fold slower in the resistant than the susceptible seedlings, suggesting there is a slower rate of tri-allate activation (and slower accumulation) in resistant plants. From this study it was also found that resistance occurs prior to the conversion of tri-allate sulfoxidation to metabolites and that tri-allate sulfoxidation requires two enzymes, both of which need mutations to confer this resistance. Studies to determine the application timing on the efficiency of herbicides on wild oats populations suggested that efficacy was governed by growth stage, weed demographics and environmental considerations (Stougaard et al., 1997).
Diclofop can infer differences in the membrane transport and the plasma membrane potential of resistant and susceptible biotypes (Renault et al., 1997). Further evaluation of this showed no differences between herbicide resistant and susceptible biotypes in plasma membrane lipid structure or lipoxygenase (LOX) activity (Renault et al., 1997).
The resistance of A. fatua to herbicides is likely to spread rapidly and become a serious problem if farmers do not quickly adopt measures to check its development (Davis, 1992). A study by Greenwood et al. (1999) found that several populations of A. fatua exhibited resistance to different herbicides and at different rates. Investigations into the evolution of herbicide resistance among several populations of A. fatua and A. sterilis ssp. ludoviciana in England, UK, concluded that hybridization had occurred between the species and that resistance had spread from one population to another (Cavan et al., 1998). Rotational strategies for weed control are also likely to be effective in delaying or minimizing the development of herbicide resistance (Martin and Felton, 1993). A survey across northern New South Wales, Australia, identified A. fatua resistance to aryloxyphenoxypropionate herbicides and methods were given to manage herbicide resistant wild oats (Storrie and Edwards, 1998).
The widespread evolution of resistance to herbicides for the selective control of A. fatua highlights the need for integrated weed management strategies that do not rely on herbicides alone. Beckie et al. (2001) discuss proactive and reactive strategies for the management and containment of herbicide-resistant weeds. They suggest greater awareness and consideration of the relative risks of different modes of action to select for resistance, effective herbicide mixtures and the incorporation of management practices that reduce weed seed production and spread. Jones and Medd (1997) estimate the economic benefit associated with an integrated weed management approach for wild oats (A. fatua and A. ludoviciana) in Australia, involving fallow, herbicide and crop rotational options and suggest a population based approach to the control of A. fatua which goes beyond efforts to minimise the effect of A. fatua in any single year. This study and those by Scursoni et al. (1999) and O' Donovan et al. (1999b), confirm the importance of strategies which prevent seed production and deplete the seed bank.
In a Russian study by Dudkin (1999), it was concluded that mechanical soil treatments and crop rotations resulted in reduction of A. fatua by depleting the seed bank. Watson et al. (1999) found that the seed bank of A. fatua in the UK was reduced in integrated and conventional wheat after beans during a 7 year rotation. The occurrence of A. fatua in Canada was also effectively suppressed in cereal fields that had previously contained Medicago sativa in crop rotations (Ominski et al., 1999). Inclusion of 75% or more cereals in a crop rotation study by Derylo (1997) resulted in decreased barley yields and increased weed infestation, both in numbers and dry weight of A. fatua. Catch crops reduced weed infestation in spring barley but could not completely compensate for the effect of less desirable crop rotations. Young et al. (1996) writes one of the more thorough reviews on integrated weed management that examines control strategies for A. fatua.
Within a barley crop, A. fatua was controlled by a combination of applying trifluralin herbicide (there was no effect of time of application) and conventional planting rather than deep planting pattern (Scursoni and Satorre, 1997). Experiments conducted into the control of A. fatua in rape crops in Canada showed that if high density plantings were used, low rates of quizalofop were required to reduce A. fatua seed production (O'Donovan et al., 1996). Angiras and Vinod Sharma (1996) also examined combinations of bi-directional sowing, row orientation and row spacing in combination with isoproturon for weed control in wheat.
Extracts from the residues of crops were trialed to determine whether they had any influence on the control of weed species. Although they were found to control other species, A. fatua was not affected (Moyer and Huang, 1997).
Analysis of the various control strategies for the management of wild oats for economic evaluation has determined that out of all the control strategies examined, the most economically beneficial ones are those which involve the removal of the weed seed and the reduction of seed in the soil seed bank (Jones and Medd, 1997). In the UK an ECO-tillage project involving soil preparation to encourage weed germination followed by application of glyphosate prior to drilling has resulted in >50% reduction of the use of herbicides compared to conventional systems with a decline in the numbers and levels of A. fatua over a 4 year period (Hutcheon et al., 1998).
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