Wild Oat

Avena fatua L.

Synonyms - Avena sativa ssp. fatua

Family: Poaceae.

Names:

Wild Oat

Summary:

A tufted annual grass with hollow stems up to 1.7 m tall and a loose pyramidal shaped seed head. The loosely branched inflorescence has large drooping spikelets that are 2-2.5 cm long. Each spikelet has 2 or 3 florets. The outer segment of each floret (lemma) has a prominent bent and twisted awn. The hairs on the lemma are brownish and somewhat appressed to the lemma surface. The seeds are usually dark and may range from black to dark yellow. Native to southern Europe, it is a widespread weed in areas of agricultural cropping. It is a competitive weed in winter crops and produces large quantities of seed with a staggered germination pattern.

Description:

Cotyledons:

One. Does not emerge. Usually underground.

Leaves:

Emerging leaf rolled in the bud.
Blade - Flat. 100-300 x 3-15 mm. Hairless to hairy. Sometimes rough to touch. Anticlockwise twist. Rolled in the bud. They tend to be a blue green colour, especially when young. or stressed
Sheath - Rolled, hairless to hairy
Ligule - membranous and obvious.
Auricles - none

Stems:

Erect. Up to 1700 mm, but usually 300-1200 mm tall. Several from base. Tufted. More or less hairless.

Flower head:

Loose, pyramidal in outline. 200-350 mm long panicle. Toward ends of stems in umbrellas of 3-6 slender pendulous branchlets carrying 2-3 seeds each.

Flowers:

On both sides of stem. 18-30 mm. Loose. Awned.
Spikelets - Large and gaping. Drooping from fine stalks.
Florets - 2-3. All or the 2 lower ones are awned. Shorter than the glumes. Readily split apart, leaving 2 lower lemmas with an oblique hollow scar at the base.
Glumes - Two, 24-27 mm long. Almost equal length, becoming papery on maturity.
Lemma - 2 to 3 that are 18-20 mm long, hardened and covered with golden brown silky hairs in the lower half, and rough to touch above. Split in two near the tip. All lemmas or the lower 2 have awns.
Awn - Brown to black. Twisted. Arises from the lower half on the back and is more than twice as long as the its lemma.
Stamens -
Anthers -

Seeds:

Usually dark in colour ranging from black to grey or yellow. Oval. Gold or brown hairs on the lower half of the seed. The hairiness of the seed is variable. 2-5 mm wide, 12-20 mm long excluding the 25 mm long awn.

Roots:

Fibrous.

Key Characters:

Golden brown hairs on lemmas.
Splits between the glume and florets at maturity.
Twisted awns.
Pyramidal seed head.
Seeds shed as single units rather in sets of 2-3.
Membranous ligule.
No auricles.
Emerging leaf rolled in the bud.
Sheath rolled and overlapping.

Biology:

Life cycle:

Annual. Germinates from autumn to spring with a flush in autumn and is dependent on moisture, soil disturbance, temperature and short term dormancy. Flowers from August to December.

Reproduction:

Wild oats are self pollinated.

Flowering times:

Any time of year but most common from August to December.

Seed Biology and Germination:

Up to 225 seeds per plant and 20,000/m2 65.
Hard seeded, but few seeds survive for more than 3 years. The half-life of seed is around 6 months (Martin and Felton, 1993). 60-70% of the seed bank turns over each year.
It normally has a staggered germination pattern.
Little germination occurs when the temperature is above 27 degrees C. Maximum germination occurs when there is adequate moisture and temperatures are 10-26.5 degrees C
Simpson (1992) has reviewed dormancy and its relevance to control.
Deep burial induces dormancy due to lack of oxygen, cooler temperatures and a moist environment at depth. Seeds returned to the surface by tillage normally germinate if other conditions are suitable.
About 40% of seed germinates at the break of the season and a further 10-30% germinates later in the season.
Very few seeds survive more than 4 years on the surface or if regularly cultivated (S. Walker, GRDC, 2009)
Less seed emerges under pasture than cropped areas, so it takes longer to deplete seed banks in pasture.
Burning stubbles increased Wild Oat emergence by 43% in a South Australian study.
Wheat stubble in or on the soil appears to stimulate the emergence and early growth of Wild Oats. Conversely, Sorghum stubble appears to delay emergence and reduce early growth.

Vegetative Propagules:

None.

Hybrids:

Probably.

Allelopathy:

Wild Oat stubble is allelopathic.
Root exudates from Wild Oat reduce the root and leaf growth of wheat.
Sorghum root exudates reduce and delay Wild Oat emergence (Jones, 1992). Rye root exudates may do the same in some conditions.

Population Dynamics and Dispersal:

Spread by seed mainly as a contaminant of grain and produce or on machinery.
Mowing and grazing may cause spread of up to 14 m (Auld, 1988).
Most seed falls within 1 m of its parent (Thurston and Philipson, 1976).
Birds may spread some seed but those that are eaten don't survive.
Up to 60% of the seed bank may germinate to produce young plants each year. Germination patterns vary widely between years. Avena fatua tends to germinate in several waves from autumn to spring somewhat earlier than Avena sterilis ssp. ludoviciana.
At low densities (up to 40 plants/m2) each plant may produce 225 seeds. This falls to less than 50 seeds/plant at densities of more than 50 plants/m2. In untreated crops seed production ranges from 1000 to 20,000 seeds/m2. In herbicide treated crops, with more than 50 Wild Oats/m2 initially, seed production ranged from 300-5000 seeds/m2 (Medd et al, 1995).
Seed catching is more effective early in the season before seed is shed.
Seed production is reduced as cereal crop density increases (Radford,1980). With cereal densities above 75 plants/m2 wild oat seed production following treatment with herbicides rarely exceeds 200 seeds/m2 irrespective of the initial density of Wild Oats.
Wild Oats that germinate early and are not controlled usually produce more seed than later germinating plants.
Burning crop stubble destroys some Wild Oat seeds (Nietschke, 1996).
Fertilisers and their placement have had variable results on the effects of WIld Oats on crops. Banding fertiliser generally benefits the crop.
Swathing usually reduces the WIld Oat seed returned to the paddock but may result in extra grain cleaning costs or dockage.
Seed catching is only partially effective on Avena fatua. In early harvested crops, up to 75% of the seed may be taken in by the harvester whereas in late harvested crops very few Wild Oat seeds are harvested.
Harvesters may spread the seed up to 250 metres from the parent plant.
Persistence of Wild Oats is mainly due to new seed being produced each year rather than dormancy carrying seed from one season to the next.
The staggered emergence of Wild Oats over most of the cool growing season, its ability to mature rapidly and its propensity to shed seed make it a difficult weed to control.
Cultivation
Deep burial prevents seeds germinating but induces dormancy so that if they are brought to the surface in later years they will germinate.
Shallow cultivation encourages germination and recruitment.
Wild Oat seed banks decline more quickly under systems using tyned rather than disc implements for cultivation.
Delayed seeding allows greater control of Wild Oats before planting but in Victorian research Walsh (1995) found it uneconomic and not very effective alone.
Burning can destroy seed on the soil surface and reduce the dormancy of the remaining seed. It is most effective when conducted directly after harvest but in most cases this is not possible (Neitschke, 1996).
Rotations
Continuous cereal and cereal/pulse rotations tend to lead to a build up in Wild Oat numbers. Cereal pasture rotations tend to lead to a reduction in Wild Oat populations.

Origin and History:

Central Asia.

Distribution:

ACT, NSW, NT, QLD, SA, TAS, VIC, WA.
Tends to be the major wild oat species in cropping systems in Southern Australia. Avena ludoviciana tends to be the major species in subtropical areas.

Courtesy Australia's Virtual Herbarium.

Habitats:

Roadsides, cultivated crops and disturbed areas.

Climate:

Temperate

Soil:

Found on most soil types, but prefers the heavy grey clays and in particular the self mulching soils.
Grows on a wide range of soil acidities from pH 4.5-9.

Plant Associations:

Grasslands, woodlands and cotton bush country.

Significance:

Two thirds of cereal farms have wild oats and they are increasing on 40% of these farms (Medd, 1996). Around $23.5M of Wild Oat herbicides are applied to about 1 million ha each year in Australia. Another $5.2M is spent on application costs.

Beneficial:

Fodder as vegetative matter and grain.
Source of genes for plant breeding, and especially for disease resistance.

Detrimental:

Weed of crops causing yield reductions due to competition. They are estimated to cost the Australian grain industry $20M/year in lost yield (Medd, 1996) and $60M/year for herbicides and application (Nugent, Storrie and Medd, 1999).
They also contaminate the grain sample and the costs of cleaning are estimated at $1M/year (Medd, 1996).
Wild Oats is ranked as the most important weed of the northern grain region and second most important in the southern grain region of the eastern states. In W.A and most of S.A it ranked as the third most important weed and in the mallee areas of S.A. it is ranked fifth.
Weed of wastelands.
It is a major host of Cereal Cyst Nematode (Heterodera avenae) and Root Lesion Nematode (Pratylenchus neglectus). It carries Stem Nematode (Ditylenchus dispaci) and is a poor host of Root lesion Nematode (Pratylenchus thorneii) allowing some build up of numbers. It also carries other nematodes and the bacteria associated with annual ryegrass toxicity (Riley and McKay, 1991, Vanstone & Russ 2001).
It carries diseases such as rusts of cultivated oats, root diseases (Rovira, 1987) including Rhizoctonia (Rhizoctonia solani) and Crown Rot (Fusarium graminearum). Studies In southern NSW show it may carry Take-all (Gaeumannomyces graminis) but with little effect on subsequent wheat yields, whilst those in SA have shown it is not a host for Take-all.
Fire hazard. They burn with an intensity of 20,000 kW m-1 and a spread rate of 23 Km hr-1 (Noble, 1991).

Toxicity:

Not reported to be toxic in Australia.

Legislation:

None

Management and Control:

Most Wild Oat infestations occur because of our activities rather than natural spread. Plant clean seed. Clean tillage, harvesting machinery, vehicles and radiator grills when entering clean areas. Cover trucks transporting grain. Feed clean hay and grain to stock.
Control Wild Oats early to gain maximum yield benefits. The group A herbicides (fops and dims) usually provide the best control but repeated use may lead to resistance. Rotation with Flamprop (group K) and the use of pre emergence tri-allate plus trifluralin can help delay resistance.
In a survey of northern NSW crops, pre emergent herbicides had a mean control level of 70±16% and early post emergent herbicides a control level of 65±18% (Nietschke and Medd, 1996).
Flamprop-m-methyl (Mataven®), fenoxaprop-p-ethyl or mixtures of flamprop-m-methyl and fenoxaprop-p-ethyl are the herbicides that provide the best control of seed set when applied at tiller elongation stage and averaged up to 97% reduction in seed set. Applications at booting average around 70% seed set reduction (Nietschke and Medd, 1996). Clodinafop (e.g. Topik®) or pinoxaden (e.g. Axial®) are also effective.
Increase cereal seeding rate to achieve at least 100 plants/m2. Use minimum tillage. Use narrow row spacings. Band fertiliser. Catch Wild Oat seed at harvest. Use selective crop topping. Use spray topping, manipulation and heavy grazing in pastures.

Thresholds:

1 plant/m2 is sufficient to contaminate grain.
10-20 plants/m2 causes around 10% yield loss in cereals. Yield loss is roughly proportional to the relative density of Wild Oat compared to cereal.
For pre emergence herbicides maximum profit occurs when levels are reduced to < 20 plants/m2 and for early post emergent herbicides when levels are reduced to < 10 plants/m2. Pre emergent herbicides tended to be more profitable than post-emergent herbicides.
Early germinating Wild Oats are more competitive than those that germinate some time after the crop. A Wild Oat that germinates at the same time as the crop has about the same competitive ability as a wheat plant. Barley tends to be more competitive against Wild Oats than wheat.

Eradication strategies:

Eradication will be difficult because of a very small number of very dormant seeds, however reductions of populations to low levels should be achievable with an integrated weed management plan.
Strategies that target the control of seed set can reduce populations fairly quickly. Completely stopping seed set for 2 years has resulted in a drop in wild oat population of 99% (Philpotts, 1975)
Cutting crops for silage before Wild Oats sets seed can virtually eliminate Wild Oats in three years (Wilson and Phipps, 1985). Green manuring should be equally effective.
Aim to -
1) Increase germination and emergence with shallow early cultivations. Apply some nitrogen before planting to stimulate wild oat germination and make them more susceptible to herbicides.
2) Use a knockdown herbicide such as glyphosate followed 5-7 days later with Spray.Seed and minimum tillage. Avoid disk and mouldboard ploughs.
3) Use a pre emergent herbicide such as tri-allate plus trifluralin.
4) Decrease survivorship with increased crop density, narrow row spacings and good crop agronomy. Delay seeding to allow greater emergence and subsequent control by cultivation or knockdown herbicides before planting.
5) Use adequate fertiliser and band as much as possible near the crop seed. Plant crop seed as shallow as possible.
6) Apply top up nitrogen dressings before post emergence spraying.
7) Use an early post emergence herbicide in Wheat, Barley or Triticale such as diclofop, Achieve, Tristar Advance, flamprop(Wheat and Triticale only), Fenoxaprop(Wheat and Triticale only), Topik(Wheat only) or Monza(Wheat only).
8) Use a late post emergence herbicide (Mataven or fenoxaprop) at the tillering stage of Wheat or Triticale to reduce seed set of Wild Oats (i.e. Selective spray topping).
9) Use a selective post emergence herbicide on broad leaf crops.
10) Consider rotations that include silage (or early hay), pasture, sorghum, winter fallows and green manures
11) Reduce seed rain by seed catching and harvesting early.
12) Reduce seed carryover by burning stubbles as soon as possible after harvest.
13) If burning is undesirable then heavy grazing of stubbles will stimulate germination in the following season.
14) Improve hygiene - don't spread seed in grain, produce or on vehicles.
15) Manipulate pastures in winter with Paraquat plus Simazine.
16) Graze pastures heavily in late winter and spring.
17) Spray top or mechanically top pastures in spring.
18) Graze after topping to prevent survivors or regrowth setting seed.
19) Test for herbicide resistance.

In non agricultural situations
Prevent seed set for at least 3-5 years. This may be achieved by manual removal, regular mowing, grazing or spraying. Pay particular attention in spring when plants may produce seeds quickly.
Grass-selective herbicides are preferred for control in most situations. A mixture of 5 mL quizalofop(100g/L) or 8 mL Fusilade®Forte or 1 mL Verdict®520 plus 100 mL spray oil in 10 L water applied in winter before flowering will provide control of many grasses with little damage to broad-leaved species. In situations where control of all annual species is required use 40 mL glyphosate(450g/L) in 10 L water as a hand spray and spray until just wet any time the plant is actively growing before seed set, or use 2 L/ha glyphosate(450g/L) as an overall. For selective control of annual grass species apply 500 mL/ha quizalofop(100g/L) or 800 mL/ha Fusilade®Forte or 100 mL/ha Verdict®520 plus 1% spray oil when the plants are actively growing prior to flowering. Repeat as required.

Herbicide resistance:

Some populations are resistant to some herbicides. Resistance to group A herbicides has been reported at low levels in most cereal growing areas. Some populations are resistant to group B herbicides. Overseas, some populations are resistant to group E and K herbicides.

Biological Control:

Classical biological control is unlikely because it is closely related to oats. However, inundative biological control, where fungal pathogens are sprayed onto the Wild Oats, is being investigated.
Ants harvest wild oats and transport them to their nests.

Related plants:

Bearded Oat (Avena barbata) occurs mainly on roadsides and non agricultural land. The lemma has 2 fine 3-12 mm long bristles that extend beyond the bend in the awn and the spikelets droop to one side.
Ludo Wild Oat (Avena sterilis ssp. ludoviciana) has a larger seed with low lying hairs and the tail of the seed is not spread. The spikelets do not break up easily like other wild oats and the secondary seeds don't have an abscission scar. It is more prevalent in the northern grain belt of the eastern states but is also common at low levels in the southern grain belt. 85% of Wild Oat infestations in Victoria contained both Avena fatua and Avena ludoviciana. Ludo Wild Oat flowers and shatters about a week earlier than Wild Oat.
Oats (Avena sativa) is awnless or has awns that are not twisted and has plump golden seed.
Sand Oat (Avena strigosa) has black seed. Saia is a commonly grown cultivar.
Sterile Oat (Avena sterilis) tends to occur on roadsides.

Plants of similar appearance:

Wild Oats can be distinguished from Wheat and Barley in the vegetative phase because the leaf twists in the opposite direction (anticlockwise for Wild Oats), they have no auricles and the ligule is much larger. The ligule of wheat has a fringe of fine hairs.
Annual ryegrass, Barley grass, Brome grass, Darnel, Fountain grass, Guildford grass, Quaking grass, Sand fescue, Silver grass, Volunteer cereals, Wild oats, Toad rush, Winter grass.

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne). P37-38. Photo.

Auld, B.A. (1988). quoted in Medd (1996).

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P165. Diagram.

Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P38. Seed diagram.

Ciba Geigy 2.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P62-63. Photo.

Gilbey, D. (1989). Identification of weeds in cereal and legume crops. Bulletin 4107. (Western Australian Department of Agriculture , Perth). p59. Photo. Diagram.

Jones, C.E. (1992) Crop rotation for the control of wild oats in wheat. Proceeding of the 6th Australian Agronomy Conference, Armidale, p438-441.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).

Lazarides, M. and Hince, B. (1993). CSIRO handbook of economic plants of Australia. (CSIRO, Melbourne). #150.2.

Medd, R.W., Nicol, H.I. and Cook, A.S. (1995). Seed kill and its role in weed management: A case study of seed production, seed banks and population growth of Avena species (wild oats). Proceedings of the 9th European Weed Research Society Symposium. Volume 2 Budapest, Hungary, p627-632.

Medd, R.W. (1996) Wild oats - what is the problem? Plant Protection Quarterly 11: (sup 1) 183-184.

Medd, R.W. (1996) Ecology of WIld Oats. Plant Protection Quarterly 11: (sup 1) 185-187.

Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). p941.

Martin, RJ. and Felton, W.L. (1993). Effect of crop rotation, tillage practice and herbicides on the population dynamics of wild oats in wheat. Australian Journal of Experimental Agriculture 33:159-165.

Nietschke, B.S. (1996). Cultural weed management of wild oats. Plant Protection Quarterly 11:187-189.

Nietschke, B.S. and Medd, R.W. (1996). Chemical management of wild oats. Plant Protection Quarterly 11:190-191.

Noble, (1991). quoted in Medd (1996).

Paterson, J.G. (1977). Grasses in South Western Australia. (Western Australian Department of Agriculture Bulletin 4007). P27-28. Diagram.

Philpotts, H. (1975). The control of wild oats in wheat by winter fallowing and summer cropping. Weed Research 15:221-225.

Quail, P.H. and Carter, O.G. (1968). Survival and seasonal germination of seeds of Avena fatua and A. ludoviciana. Australian Journal of Agricultural Research 19, 721-9.

Riley and McKay, (1991). quoted in Medd (1996).

Rovira, (1987). quoted in Medd (1996).

Simpson, G.M. (1992). Understanding Dormancy in WIld Oats (Avena fatua) and its implications for control strategies. Proceedings of the 4th International Oat Conference 'WIld Oats in World Agriculture' Volume 2, Adelaide, p14-19.

Thurston and Philipson (1976). quoted in Medd (1996).

Walsh, M.J. Biology and control of wild oats. GRDC final report, DAV 54, p1-22.

Wilding, J.L. et al. (1987). Crop weeds. (Inkata Press, Melbourne). p19. Photos. Diagram.

Wilson, B.J. and Phipps, P.A. (1985). A long-term experiment on tillage, rotation and herbicide use for control of A. fatua in cereals. Proceedings of the British Crop Protection Conference, Brighton, England. p 693-700.

Acknowledgments:

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