Plant Protection Quarterly Vol.11 Supplement 1 1996 187 oats. Plant Protection Quarterly 11, Simpson, G.M. (1992). Understanding seed control wild oats (Avena ludoviciana Dur. 190-2. dormancy in wild oats (Avena fatua) and and A. fatua L.) in Queensland. Proceed- Pandey, S., Lindner, R.K. and Medd, R.W. its implications for control strategies. ings of the 6th Asian-Pacific Weed Sci- (1993). Towards an economic frame- Proceedings of the 4th International Oat ence Society Conference, Jakarta, Indo- work for evaluating potential benefits Conference ‘Wild Oats in World Agri- nesia, pp. 301-8. from research into weed control. Journal culture’, Volume 2, Adelaide, pp. 14-9. Wilson, B.J., Cousens, R. and Cussans, of Agricultural Economics 44, 322-34. Taylorson, R.B. (1987). Environmental and G.W. (1984). Exercises in modelling Paterson, J.G. (1977). Interactions between chemical manipulation of weed seed populations of Avena fatua L. to aid stra- herbicides, time of application and dormancy. Reviews of Weed Science 3, tegic planning for the long term control genotype of wild oats (Avena fatua L.). 135-54. of this weed in cereals. VIIe Colloque In- Australian Journal of Agricultural Research Thurston, J.M. (1961). The effect of depth ternational sur l’Ecologie la Biologie et la 28, 671-80. of burying and frequency of cultivation Systematique des Mauvaises Herbes, Philpotts, H. (1975). The control of wild oats on survival and germination of seeds of Paris, France, pp. 287-94. in wheat by winter fallowing and sum- wild oats (Avena fatua L. and A. Wilson, B.J., Cussans, G.W. and Ayres, P. mer cropping. Weed Research 15, 221-5. ludoviciana Dur.). Weed Research 1, 19-31. (1974). The effects of tri-allate and Quail, P.H. and Carter, O.G. (1968). Sur- Thurston, J.M. (1966). Survival of seeds of barban on the control of Avena fatua in vival and seasonal germination of seeds wild oats (Avena fatua L. and Avena spring barley, on the yield of barley. of Avena fatua and A. ludoviciana. Aus- ludoviciana Dur.) and charlock (Sinapis Proceedings of the 12th British Weed tralian Journal of Agricultural Research 19, arvensis L.) in soil under leys. Weed Re- Control Conference, Brighton, England, 721-9. search 6, 67-80. pp. 25-32. Radford, B.J., Wilson, B.J., Cartledge, O. Wilson, B.J. (1979). Post-emergence con- Wilson, B.J. and Peters, N.C.B. (1992). Bio- and Watkins, F.B. (1980). Effect of wheat trol of wild oats in Queensland with logical and agronomic reasons for the seeding rate on wild oat competition. difenzoquat, flamprop-methyl, dichlo- continuing importance of wild oats in Australian Journal of Experimental Agri- fop methyl and barban. Australian Jour- the United Kingdom. Proceedings of the culture and Animal Husbandry 20, 77-81. nal of Experimental Agriculture and Ani- 4th International Oat Conference ‘Wild Simpson, G.M. (1990). ‘Seed Dormancy in mal Husbandry 19, 108-17. Oats in World Agriculture’, Volume 2, Grasses’, 297 pp. (Cambridge University Wilson, B.J., Cartledge, O. and Watkins, Adelaide, pp. 9-13. Press, Cambridge). F.B. (1977). Managerial practices to

Crop competition Cultural weed management of wild oats Competitive interactions between wild oats and crops are a very complex issue. Several agronomic factors will influence B.S. Nietschke, Co-operative Research Centre for Weed Management Systems, the extent to which crop yield is reduced Department of Agronomy and Farming Systems, The University of Adelaide, by wild oats, and the amount of wild oat Roseworthy Campus, Roseworthy, South Australia 5371, Australia. seed returned to the soil (Thill et al. 1994). Crops and crop cultivars differ in their competitive ability with wild oats. In Introduction longevity. If brought to the surface by sub- Canada, barley is considered the most A range of cultural control techniques can sequent tillage, seeds are released from competitive grown crop species, followed be utilized for weed management in dormancy and become available for re- by canola, wheat and linseed (O’Donovan southern Australian cropping systems. cruitment (Medd in press). Consequently, and Sharma 1983). Increasing the seeding These include; sanitation, cultivation, de- wild oat populations tend to increase more rates of cereal crops generally reduces layed seeding, increased crop competition, under pre-sowing cultivations than prac- wild oat competition (O’Donovan and fertilizer use and placement, windrowing, tices which involve no or minimal soil dis- Sharma 1983), whilst planting high quality weed seed collection at harvest, crop stub- turbance such as direct drilling (Medd crop seed at a relatively shallow depth ble burning, crop rotation, allelopathy, 1990, Walsh 1995). Wilson (1978) found gives the crop maximum competitive ad- green manuring, hay making, silage, pas- that wild oat seed banks decline more rap- vantage in the early stages of growth ture slashing and livestock grazing. These idly using tyned compared with plough- (Cussans and Wilson 1976). Crops sown in strategies are reviewed as control meth- ing implements which inverted the seed. narrow row spacings, are equal to or more ods for wild oats (Avena spp.). competitive with wild oats than widely Delayed seeding spaced crop plants (Thill et al. 1994). Sanitation Delaying the date of seeding allows in- Immigration of most wild oats into a field creased wild oat seedling emergence Fertilizer use and placement can be prevented by planting clean seed, before sowing, thus reducing weed infes- Of the many studies of interference be- cleaning harvest and tillage equipment tation levels in the subsequent crop. Con- tween A. fatua and cereals, some have between fields, and covering grain trucks sequently, those fields with the worst wild shown that nitrogenous fertilizers in- used to transport grain (Thill et al. 1994). In oat populations are recommended to be crease yield loss, some show a decrease the United Kingdom wild oats were found planted last at seeding. Overseas research and others show no effect (Cousens and in 15% of cereal seed drills which were has shown that continuous late sowing can Mortimer 1995). Recently, Walsh (1995) sampled at sowing (Elliott and Attwood effectively control A. fatua L. populations determined that the addition of fertilizer 1970), whilst the transport of infested ce- (Whybrew 1964). Conversely, Walsh (nitrogen and phosphorus) to increase real straw bales has also been implicated (1995) in Victoria determined that delayed crop competition with wild oats, failed to as a source of wild oat seed spread (Wilson seeding of wheat did not affect wild oat achieve any reduction in growth and de- 1970). populations, due to the extended germi- velopment of the weed. Nitrogen ferti- nation pattern of the weed. Furthermore, lizer can stimulate wild oat emergence Cultivation the practice usually results in lower grain before sowing, but as a long term means Deeper burial of wild oat seed favours yield and or quality and is therefore con- of reducing wild oat infestations, has longer dormancy and thus increased sidered an uneconomic control method. little effect (Watkins 1971). Preliminary 188 Plant Protection Quarterly Vol.11 Supplement 1 1996 research conducted in Idaho, United States oat populations is clearly possible under farmers is a major worry. Conversely, he of America demonstrated that fertilizer winter lucerne ley crop rotations, al- suggests that some obvious cultural con- placement influences wild oat growth. In though the lack of soil disturbance in the trol tactics include; crop stubble burning, spring barley, 28–60% fewer wild oat till- pasture phase reduces recruitment some- adoption of appropriate crop rotations ers were measured when nitrogen ferti- what, and so seed banks are generally not (e.g. wheat/sorghum), preventing seed lizer was band-applied compared to depleted to the same extent as arable crop- burial by minimizing soil disturbance and broadcast-applied. Wild oat seed produc- ping situations. Philpotts (1975) and Mar- increasing crop competition. Maximizing tion was not recorded in this experiment. tin and Felton (1993) effectively reduced the competitiveness of the crop relative to Thill et al. (1994) concluded that banding wild oat seed reserves through winter wild oats may include; growing competi- nitrogen fertilizer near the crop seed gen- fallowing in association with a rotation of tive crops and cultivars, increased seeding erally favours the crop, while broadcast- wheat, and sorghum over summer. Con- rates, sowing high quality seed at a shal- ing fertilizer favours wild oat growth. versely, continuous winter cereals do not low depth, sowing with narrow row contain wild oat populations and probably spacings and placing fertilizer to favour Windrowing neither do winter cereal-chickpea rota- the crop. Windrowing crops prior to weed seed fall tions, due to the poor competitive ability Herbicides will continue to be the most may increase the amount of wild oat seed of chickpeas (Medd in press). potent component of any integrated man- retained during the harvest operation, but agement system for wild oats (Nietschke as the usual fate of wild oat seeds at har- Allelopathy and Medd 1996), however, the importance vest is to be carried with the cereal grains, Field research conducted by Jones (1992) of effective cultural techniques cannot be the cost of re-cleaning wild oat contami- found sorghum root exudates reduced disputed. Especially given the advent of nated grain must be evaluated against the and delayed wild oat plant emergence, by herbicide resistant wild oat biotypes, there potential benefits (Matthews 1994). exerting an inhibitory allelopathic effect will always be a need for the utilization of on buried wild oat seeds. Osvald (1950) control strategies which are less depend- Weed seed collection at harvest reported that root exudates of rye reduced ent on herbicides. Wild oats shed their seed before or during germination of A. fatua by 10%. However, grain harvest and only a small proportion Thurston (1962) disputed these findings, as Possible research emphasis is able to be caught at harvest (either in a her field results showed that rye had no In summer rainfall environments wild separate collection unit or grain bin). inhibitory effect on wild oat seed produc- oats can be contained by including a win- Therefore, seed collection is generally an tion. Alternatively, wild oats has the abil- ter fallow, followed by a summer crop. In ineffective wild oat control strategy. Con- ity to confer allelopathic effects on other most southern Australian cropping zones versely, overseas research by Thill et al. plants, including wheat. Root exudates this is not possible. Delayed sowing is gen- (1994) states that a chaff collector used at from A. fatua inhibited root and leaf erally considered a successful wild oat con- harvest will collect many wild oats seeds, growth of spring wheat, and thus Schu- trol method, but due to the yield penalty whilst Wilson (1970) was able to catch 84% macher et al. (1983) implicated allelopathy associated with late sowing is an uneco- (in the grain bin) of the total seed pro- in the reduction of crop yields. nomic option. Alternatively, crops such as duced in an early maturing winter barley safflower and early maturing barley suf- crop. These results do not seem particu- Prevention of wild oat seed return fer little yield loss when sown late. Data is larly relevant to Australian conditions, but Cutting crops infested with wild oats for lacking on the effect of incorporating late suggest harvest time, environment and hay or silage, before seed shed can greatly sown crops into a rotation and their subse- even wild oat species/biotypes may influ- reduce seed rain (Thill et al. 1994), which quent impact on wild oat seed bank dy- ence seed catching efficacy. makes them ideal rotational crops namics. (Cussans and Wilson 1976). In England, Little information is available on the Crop stubble burning continuous spring barley cut for silage re- competitive differences between crop Various studies have shown that wild oat duced wild oat emergence to nil after three cultivars and wild oats (the majority of seed can be destroyed on the soil surface years (Wilson and Phipps 1985). The green work has concentrated on annual by burning crop stubble (Nietschke et al. manuring of crops should be an equally ryegrass). Research is needed to deter- 1996, Wilson and Cussans 1975). Seed kill effective control method if wild oat re- mine competitive varieties which are lo- is maximized when burning is conducted growth and seed production is prevented. cally adapted to weedy situations. Future directly after harvest (Wilson and Cussans Intensive grazing by livestock (Jenkinson work at The University of Adelaidewill 1975). Additionally, burning can stimulate 1976) and mechanical slashing of leys also evaluate crop cultivars for their competi- surface seed emergence by modifying provides the opportunity to prevent wild tiveness with a variety of weeds, including seed dormancy in a proportion of seeds oat seed production in the pasture phase wild oats (G. Gill personal communica- that survive the burn (Nietschke et al. of a rotation. Prevention of A. ludoviciana tion). 1996, Whybrew 1964). Overseas studies Durieu seed production by Mansooji Little data from Australia exists on the conclude that the practice of stubble burn- (1993) reduced the wild oat seed bank of a seed bank decay of wild oats in the pasture ing by itself does not prevent a wild oat pasture by 97% in 3.5 years. phase of a rotation. Where seed produc- population increase (Whybrew 1964, tion is prevented, the rate of decline is per- Wilson and Cussans 1975). This is almost Conclusion ceived to be less rapid compared to condi- certainly the case for Australian agricul- A range of cultural techniques currently tions where soil has been disturbed. Ac- ture and , in any event, the practice is dis- exist in southern Australian cropping sys- cording to Medd (in press) this means re- couraged because of the recognised ben- tems for the control of wild oats. Practices sidual seed stocks may allow rapid efits of stubble retention. such as delayed seeding, winter fallow and reinfestation at the beginning of the crop- other strategies that prevent wild oat seed ping phase. Crop rotation production, significantly deplete the seed Preliminary research from overseas has Incorporating a pasture phase into a rota- bank, although few are economically at- demonstrated that banding nitrogen ferti- tion provides an ideal opportunity to pre- tractive to warrant significant adoption. lizer near the crop seed probably favours vent wild oat seed production before re- Combellack (1992) argues in view of the crop growth over wild oats. As the major- verting back to the cropping phase. Medd considerable research effort devoted to ity of weed seed resides in the top few (in press) claims the containment of wild wild oats, lack of clear control methods for centimetres of soil, and cereal crops are Plant Protection Quarterly Vol.11 Supplement 1 1996 189 recommended to be sown shallow, ferti- Nietschke, B.S., Reeves, T.G., Matthews, lizer placement may also benefit wild oat J.M. and Powles, S.B. (1996). Compo- growth. A variety of agronomic factors nents of an integrated weed manage- influence crop and wild oat competition, ment strategy to control herbicide re- and fertilizer placement may interact with; sistant Avena spp. – an Australian per- fertilizer type, fertilizer rate, crop row spective. Proceedings of the 2nd Inter- spacing, crop density and or wild oat den- national Weed Control Congress, Co- sity. penhagen, Denmark, pp. 493-8. O’Donovan, J.T. and Sharma, M.P. (1983). References Wild oats, competition and crop losses. Combellack, J.H. (1992). The importance Proceedings of the Wild Oat Sympo- of wild oats in world agriculture. Pro- sium, Regina, Canada, pp. 27-42. ceedings of the 4th International Oat Osvald, H. (1950). On antagonism be- Conference, ‘Wild oats in world agricul- tween plants. Proceedings of the 7th In- ture’, Volume 2, Adelaide, pp. 1-8. ternational Botanical Congress, Stock- Cousens, R. and Mortimer, M. (1995). ‘Dy- holm, Sweden, pp. 167-71. namics of weed populations’. (Cam- Philpotts, H. (1975). The control of wild bridge University Press, Cambridge). oats in wheat by winter fallowing and Cussans, G.W. and Wilson, B.J. (1976). Cul- summer cropping. Weed Research 15, tural control. In ‘Wild oats in world agri- 221-5. culture’, ed. D. Price Jones, pp. 127-42. Schumacher, W.J., Thill, D.C. and Lee, G.A. (Agricultural Research Council, London). (1983). Allelopathic potential of wild oat Elliott, J.G. and Attwood, P.J. (1970). Re- (A. fatua) on spring wheat growth. Jour- port on a joint survey of the presence of nal of Chemical Ecology 9, 1235-45. wild oat seeds in cereal seed drills in the Thill, D.C., O’Donovan, J.T. and Mallory- United Kingdom during spring 1970. Smith, C.A. (1994). Integrated weed Technical Report of Agriculture Re- management strategies for delaying search Council, Weed Research Organi- herbicide resistance in wild oats. zation, pp. 1-12. Phytoprotection 75 (Suppl.), 61-70. Jenkinson, R.H. (1976). A planned ap- Thurston, J.M. (1962). The effect of compe- proach to wild oat and grass weed con- tition from cereal crops on the germina- trol, integrating herbicides with cultural tion and growth of A. fatua L. in a natu- methods on a large cereal and grass rally infested field. Weed Research 2, farm. Proceedings of the British Crop 192-207. Protection Conference, Brighton, Eng- Walsh, M.J. (1995). Biology and control of land, pp. 857-64. herbicide resistant wild oats. GRDC Jones, C.E. (1992). Crop rotation for the Final Project Report DAV 54, pp. 1-22. control of wild oats in wheat. Proceed- Watkins, F.B. (1971). Effects of annual ings of the 6th Australian Agronomy dressings of nitrogen fertilizer on wild Conference, Armidale, pp. 438-41. oat infestations. Weed Research 11, Martin, R.J. and Felton, W.L. (1993). Effect 292-301. of crop rotation, tillage practice, and her- Whybrew, J.E. (1964). The survival of wild bicides on the population dynamics of oats (A. fatua) under continuous spring wild oats in wheat. Australian Journal of barley growing. Proceedings of the 7th Experimental Agriculture 33, 159-65. British Weed Control Conference, Mansooji, A.M. (1993). Herbicide resist- Brighton, England, pp. 614-20. ance in wild oats, Avena spp. Ph.D. The- Wilson, B.J. (1970). Studies of the shedding sis, The University of Adelaide. of seed of A. fatua in various cereal crops Matthews, J.M. (1994). Management of and the presence of this seed in the har- herbicide resistant weed populations. In vested material. Proceedings of the 10th ‘Herbicide resistance in plants-biology British Weed Control Conference, and biochemistry’, eds. S.B. Powles and Brighton, England, pp. 831-6. J.A.M. Holtum, pp. 317-35. (Lewis Pub- Wilson, B.J. (1978). The long term decline lishers, Boca Raton). of a population of A fatua L. with differ- Medd, R.W. (1990). Seed bank dynamics of ent cultivations associated with spring wild oat (A. fatua L.) populations in barley cropping. Weed Research 18, wheat. Proceedings of the 9th Austral- 25-31. ian Weeds Conference, Adelaide, pp. Wilson, B.J. and Cussans, G. . (1975). A 16-9. study of the population dynamics of A. Medd, R.W. (In press). Biological con- fatua L. as influenced by straw burning, straints: weeds. In ‘Sustainable Crop seed shedding and cultivations. Weed Re- Production in the Sub-tropics: an Aus- search 15, 249-58. tralian Perspective’, eds. A.L. Clarke and Wilson, B.J. and Phipps, P.A. (1985). A long P.B. Wylie. (Queensland Department of term experiment on tillage, rotation and Primary Industries, Brisbane). herbicide use for the control of A. fatua Nietschke, B.S. and Medd, R.W. (1996). in cereals. Proceedings of the British Chemical weed management of wild Crop Protection Conference, Brighton, oats. Plant Protection Quarterly 11, 190-2. England, pp. 693-700.