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Plantwise Technical Factsheet

wild oat (Avena fatua)

Host plants / species affected
Arachis hypogaea (groundnut)
Avena sativa (oats)
Beta vulgaris var. saccharifera (sugarbeet)
Brassica napus var. napus (rape)
Camellia sinensis (tea)
Cicer arietinum (chickpea)
Cynara cardunculus var. scolymus (globe artichoke)
Glycine max (soyabean)
Gossypium (cotton)
Helianthus annuus (sunflower)
Hordeum vulgare (barley)
Lens culinaris subsp. culinaris (lentil)
Linum usitatissimum (flax)
Lolium (ryegrasses)
Medicago sativa (lucerne)
Oryza sativa (rice)
Pisum sativum (pea)
Saccharum officinarum (sugarcane)
Secale cereale (rye)
Solanum tuberosum (potato)
Sorghum bicolor (sorghum)
Triticum (wheat)
Triticum aestivum (wheat)
Zea mays (maize)
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.
Prevention and control
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).

Biological Control

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).

Chemical Control

Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:

Integrated Control

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).
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).
Related treatment support
Plantwise Factsheets for Farmers
Faizi, Z.; Fahim, A.; CABI, 2012, English language
Faizi, Z.; Fahim, A.; CABI, 2012, Dari language
Pest Management Decision Guides
Etagegnehu, G.; Tamado, T.; Desalegne, G.; Negussie, E.; CABI, 2016, English language
External factsheets
BioNET-EAFRINET Invasive Plant Factsheets, BioNET-EAFRINET, 2011, English language
Bayer CropScience Crop Compendium, Bayer CropScience, English language
University of California IPM Pest Management Guidelines, University of California, 2009, English language
Plant Health Australia Factsheets, Plant Health Australia, English language
Department of Agriculture Western Australia Factsheets, Government of Western Australia, 2004, English language
Video factsheets
Agropedia ICRISAT PPT-Videos, IIT, Kanpur, 2014, English language
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