Wild Oats in W.A

Journal of the Department of Agriculture, Western Australia, Series 4

Volume 17 Number 3 1976 Article 7

1-1-1976

Wild oats in W.A

J G. Paterson

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Recommended Citation Paterson, J G. (1976) "Wild oats in W.A," Journal of the Department of Agriculture, Western Australia, Series 4: Vol. 17 : No. 3 , Article 7. Available at: https://researchlibrary.agric.wa.gov.au/journal_agriculture4/vol17/iss3/7

This article is brought to you for free and open access by Research Library. It has been accepted for inclusion in Journal of the Department of Agriculture, Western Australia, Series 4 by an authorized administrator of Research Library. For more information, please contact [email protected], [email protected], [email protected]. Wild oats in W.A.

A summary of background in as one of the recommended herbi relationship between the various formation, recent research findings cides (barban) must be applied soon types of cultivated and wild oats has and current recommendations for after seedling emergence. allowed classification into several the control of wild oats in Western The differences are shown in Fig. 1. major sub-groups or species. These Australia. Wild oat seedlings are easily are distinguished by the way their seed identified by the anti-clockwise twist is shed at maturity, on the external in the first leaf. In contrast, wheat characteristics of their seed, and on seedlings have a clockwise twist in the cellular characteristics which con the first leaf. trol their breeding habits. Wheat seedlings also have two auricles (ear-like projections) and a Life cycle of wild oats rim of fine hairs at the base of each Germination leaf-blade, where it joins the leaf- Different oat types germinate under sheath surrounding the stem. The different specific conditions. This auricles and hairs are not present on may give one type an advantage over oat plants. Barley seedlings have others, leading to the predominance auricles but no hairs at the base of of one or other species, depending on each leaf-blade. their suitability to each environment. Seed germination can therefore be Plants important in controlling the relative Wild oats belong to the same group distribution of various species. of plants as cultivated oats, the genus 'Avena1. This classification was first Vegetative growth established in the 1700's. Recent Differences between and within more detailed investigation of the species are also important during the

The author, Research Officer Dr. John WILD OATS Paterson, shows the contrast in growth habit and maturity of the southern form of Avena barbata (left) with the southern form of A. fatua.

L sof blade usual ly Wild oats have been agricultural develops with an weeds for at least 4 000 years. They anti-clockwise twist are thought to have originated in the Mediterranean region, spreading to England and then to Tasmania in wheat and barley seed. It is thought that they entered Western Australia in seed wheat from Launceston in the early 1830's. In some countries wild oats are an immense problem; for example, in Canada more than half of the area sown to cereals is infested. They are now a problem in all Australian Leaf sheaf pu States. sway to expos Identification Seedlings It is often difficult to distinguish be tween wild oat and wheat seedlings. Suspected plants should be ex Fig. I—The difference between wild oats and wheat seedlings, Wild oats have no amined a few days after they emerge, auricles and a hairless ligule. 90 Journal of Agriculture Vol 17 No 3, 1976 vegetative stage of growth, as they The wild oat problem can give an advantage to the best In the 1960's it became obvious that suited type in the prevailing environ the density of wild oats increased mental conditions, such as tempera rapidly with multiple cereal cropping. ture and daylength. Multiple cropping gave little oppor Most wild oat seedlings, like some tunity for control by grazing, which cereals, require a period of cold reduces seed setting considerably. winter temperatures (vernalization) The problem was accentuated by before they can begin to flower. The widespread use of "hormone-like" amount of cold treatment required herbicides—which control broad- can differ between and within species, leafed weeds and allow grass weeds and types with a large vernalization to grow with reduced competition— requirement are likely to be restricted and the greater use of header-har to cold districts. vesters, which work better in a fully Varying daylength requirement be mature crop after the wild oats have comes important once the vernaliza shed. tion requirement has been satisfied. At this time little was known of the Types which flower late in the season actual species of wild oats present. do not do so until a critical day-light This situation led to a detailed period each day has been reached in study of wild oats in Western Aust spring. ralia.

o o

90% A.fatuo

75% A. fatua

E sperance

Avena steri lis Kilometres 0 50 100 150 I •—

Fig. 2—Seed characteristics of the three wild oat species found in Western Aus tralia. Fig. 3—Distribution of Avena fatua and Avena barbata in W.A. 91 Journal of Agriculture Vol 17 No 3, 1976 Wild oat survey Table I.—Frequency of occurrence (per warmer and shorter growing season centage of all plants examined) of Avena northern and inland areas. Little information was available on fatua and Avena borbata on various soil the natural variation within Western types in Western Australia. A. fatua and A. barbata were found Australian wild oats and for this on a wide range of soil types, but A. fatua was most common on heavy reason a study was undertaken to Soil type A. barbata A. fatua define the species present, their soils and A. barbata on light soils, distribution, and the conditions pre especially gravels (Table 1). ferred for their survival and growth. Gravel* 18.6 7.9 A. fatua was the most common The species present were surveyed Sand* 20.7 18.7 species in cereal crops and A. barbata Loamy sand* 20.5 16.7 on roadsides (Table 2). to determine their local preferences. Loamf 20.5 32.4 The information gained was used to Silt loamf 12.8 15.2 plan experiments concerned with Clay loamf 6.9 9.1 Seed type and colour plant development, seed survival, Totals— Differences in the seed colour or seed Light* 59.9 43.3 characteristics, such as hairiness or nutritional requirements and soil Heavyf 40.1 56.7 moisture preferences. size of wild oats, could not be re lated to any particular district. There was no reason to believe that such Western Australian species * Light soils with more than 50% by weight particles greater than 0.2 mm. characteristics were related to part Two wild species of A vena were f Heavy soils with less than 50% by weight icular types of wild oat. found to predominate: Arena barb- particles greater than 0.2 mm. ata, comprising 50 per cent, and Adaptive features Arena fatua, 47 per cent of the popu Table 2.—Frequency of occurrence lation. The remaining 3 per cent (percentage of all plants examined) of Plant derelopment was A rena sterilis. Avena fatua and Avena barbata in three dif Both A. fatua and A. barbata ap ferent habitats in Western Australia. parently became well established with The differences between the seed early agricultural development in characteristics of these species are Habitat A. barbata A. fatua Western Australia more than 140 shown in Figure 2. years ago. Since then, a close as The very low incidence of A. sterilis sociation has developed between the may seem surprising in view of its Crop II.1 53.2 environmental requirements of these Pasture 13.9 8.8 widespread distribution in eastern Roadside 75.0 38.0 species and climatic features. Australia. A. barbata has become well adap However, it is likely that A. sterilis ted to the climate of the South-West. is poorly adapted to local conditions. The later-maturing types found with This species is reported to have a in this species give it an advantage in lower temperature requirement for Distribution the South-West where cooler, wetter, germination than A. fatua, so would The geographic distribution of the and longer days are experienced in germinate later in Western Australia. major wild oats in Western Australia the spring. This would place it at a disadvantage. is shown in Figure 3. A. fatua was found to have a The evidence available suggests A. barbata predominates in the poorly developed association with its that A. sterilis is unlikely to become South-West, in areas of high rainfall environment; there was little evidence a serious weed in south western and long growing season. A. fatua of any mechanism, such as a vernali Australia. is most common in the lower rainfall, zation requirement, which could de-

Per cent germination kg ho 100 Crop yield

90- 1000 80

7 0 60-

50- 40-

20-

Apr 100 200 300 Wild oat plants per s q. metre Fig. A—Seasonal differences in the potential germination of A. fatua, which predominates in crop infestations, and A. bar Fig. 5—The reduction in yield of three wheat crops, caused bata, which is destroyed by pre-cropping cultivation. by different densities of wild oats. 92 Journal of Agriculture Vol 17 No 3, 1976 lay flowering to make this species ditions would be advantageous to uced by an increase in the wild oat more suitable for a long growing both species, A. fatua could suffer density. season. A. fatua is the wild oat apparent nutrient deficiency on low The illustration also shows the found in cereal crops, where such a fertility light soils because of its more large reduction in wheat yield in a restraint would be a disadvantage. rapid development. 1 000 kg crop caused by a relatively Also, in the drier, warmer north-east This could account for the observed low infestation of wild oats compared of the agricultural areas, where predominance of A. fatua on heavy with its negligible effect in a 400 kg A. fatua predominates, the growing soils (which are usually fertile); highly crop. Therefore a reliable estima season is relatively short and a rapid fertile light soils often carried a high tion of the effect of wild oats cannot rate of development is an advantage. population of both species. be made without an estimation of Thus, A. fatua is unlikely to be a wheat yield. problem in the far south-west of Importance as weeds In addition to the reduction of Western Australia. More import Wild oats can produce a large num cereal yields caused by plant com antly, the life-cycle of this species is ber of seeds, between 250 and 500 per petition, wild oats are considered a well adapted to the climate of the plant. At this rate an infestation of contaminant in harvested grain and cereal growing districts, causing it to 50 plants per square metre could pro are subject to dockage by grain hand be a major weed problem there. vide a population of 15 000 seeds per ling authorities. square metre. This is at least 50 times the number of cereal seeds sown Frost resistance CONTROL OF WILD OATS Frosts are more frequent and more in an average crop. The greatest benefit to be gained The control of wild oats depends on intense inland than near the coast. the identification of problem areas A. barbata seedlings are more sus from the removal of wild oats occurs in high yielding cereal crops. This is and on the correct application of ceptible to frosting than those of control techniques. A. fatua, which restricts the north illustrated in Figure 5. eastern migration of A. barbata. For example, in a wheat crop with a potential yield of 1 000 kg/ha a Cultural control Germination wild oat infestation as low as 50 A. barbata is easily controlled with a A large proportion of A. fatua seed plants per square metre reduces the single cultivation and is rarely a weed will not germinate with the opening yield by about 200 kg/ha. Where in cereal crops. In contrast, A. fatua rains, in April or May. In contrast, there are more than 400 wild oat is difficult to control by cultivation, A. barbata seed germinates at the plants per square metre the yield of due to its highly dormant seed. It is break of the season. These seedlings wheat is unlikely to be further red unlikely that this species could be are easily killed by cultivation and few live seeds remain to germinate in er cent emergence the sown crop. 100' For this reason A. barbata is rare WMMffl in Western Australian cereal crops, 90' T?K^HW 1 but is common on roadsides. Research has also shown that seed 80- of wild oats from the northern, inter 70- mediate, and southern parts of the agricultural areas differ in their 60' germination characteristics. On the south coast up to 30 per cent of A. 50- barbata seed could survive the open ing rains without germinating, so 4 0- making it potentially difficult to control in cereal crops; however, 30' cereals are not grown in this area. 20'

Soils and nutrition 10' To determine the effect of rainfall patterns on the growth of wild oats 0' both A. fatua and A. barbata were 05 cm 2-5-12-5 cm 150 cm 17-5 tested under experimentally-imposed Depth of planting restricted and excess moisture, on a Viable after three years range of soil types. Both species reacted similarly, suggesting that | Natural losses high rainfall is not responsible for the predominance of A. barbata in the Emerged in third year south-west. Other trials revealed no difference Emerged in second year in the response of the two species to Fig. 6—The emergence of seedlings Emerged in first year from seed of A. fatua planted at a range applied fertiliser. While fertile con of depths. 93 Journal of Agriculture Vol 17 No 3, 1976 controlled by cultural practices with such as in a first crop, this ploughing Where this is not done the chemical out complete suppression of fresh should be deeper than usual. Sub rapidly disperses into the atmosphere seed formation for at least three sequent cultivations should be much and is lost. For this reason the seed years. shallower. bed should not be cloddy, nor too The reason for this can be seen in Where the break of the season wet or dry. Figure 6. permits, some delay in seeding-time The herbicide should be sprayed on When seed of A. fatua was buried can be used to give additional weed- to the soil surface at the rate of 2 • 1 at depths between 0.5 and 17.5 cm it killing cultivations. litres in 80 to 110 litres of water per was found that seedlings emerged End-of-season crop vigour and hectare and immediately incorpor best from depths between 2.5 and potential yield can be improved by ated with five or six-row harrows, 12.5 cm deep, in each of the three sowing early-maturing varieties at a dragged behind the boom. This years they were observed. At the shallower depth and at a higher rate could be followed by cross-harrowing end of this period only 3 per cent of of seeding than normal. This will to complete the incorporation before the original seed remained alive and lessen the stress caused by retarded seeding at least 5 cm deep. only one third of this was germin- growth resulting from weed competi Triallate is equally effective if able in the following year. tion. A seeding rate of at least 60 applied either two days before or kg of wheat per hectare is suggested two days after seeding; no toxic In Western Australia stubble-soil effects on wheat can be expected. populations of live A. fatua seed can where the wild oat problem is likely to be severe. Triallate cannot be applied effectively be as high as 1 500 per square from an aircraft. metre. The above result suggests Chemical control that less than 15 seedlings per square BARBAN is a post-emergent mat metre would be expected after three Two herbicides are available for the erial, sold as Neobanf, and is closely years of control-grazed pasture. This control of wild oats in wheat and related to CarbyneJ which has been number of plants would be unlikely barley crops. Other materials are available for a number of years. to cause an economical yield reduc continually under test but at present It can be applied after a wild oat tion in a cereal crop. cannot be recommended. infestation becomes obvious. Barban Within each species it has been Where cereal cropping is planned, stops the growth of wild oats, allow a minimum of three prior years pas shown that many types of wild oats ing the crop to outgrow the weed and ture, with regulated grazing to stop occur. These ranged from rapid smother it. Thus, competition from seed formation is therefore suggested. growing A. fatua to slow growing the wheat or barley is essential for A. barbata. The effect that these successful control of wild oats with Seed near the surface was more differences could have in their sus barban. viable and therefore, before pas ceptibility to herbicides requires Barban must be applied when the ture establishment, shallow culti further investigation. Current her vation to bury surface seed would wild oat plants have from one to 2\ bicide recommendations are based leaves (Figure 7). This period only improve the chance of germination on field experience. and weed control. lasts for about seven days and occurs between 2J and five weeks after TRIALLATE is a pre-emergent material Pre-crop cultural treatments should planting. Spraying outside this be designed to kill as many weeds as and is sold as Avadex BW*. It acts on the germinating seed and must be growth stage will give poor results, possible and to suppress those re except in southern districts where maining in the crop. The initial placed as close to this as possible, necessitating incorporation into the recent research has indicated that ploughing should be delayed as long later spraying may be effective. as possible to allow emergence of the soil immediately after application. wild oats. Where most of the wild t Neoban: Registered trade name of Fisons Pty. Ltd. * Avadex BW: Registered trade name of Monsanto + Carbyne: Registered trade name of Fisons Pty. oat seeds are near the soil surface, Australia Ltd. Ltd.

Seed ling 1 leaf stage 2 leaf stage 2'2 leaf stage 3 leaf stage

Toio earl y Spray Spray Spray Too late Fig. 7—The best stage of spraying with barban in most districts can be judged by the number of leaves on most of the wild oat plants. 94 Journal of Agriculture Vol 17 No 3, 1976 Barban can be applied either by ively safe to apply to all recom In each year grazing pressure in ground boom spray at the rate of 550 mended wheat varieties even if there spring should be increased to stop all ml per hectare or from an aircraft at is a slight error in application tech wild oat seed production. In this 500 ml per hectare. niques. Similarly Beecher and Dam- way the likelihood of wild oats in a With ground equipment a relat pier barley can be treated with safety. following cereal crop will be mini ively high pressure of 350 kPa will Barban can damage Prior and mised. increase the effectiveness and an Atlas 57 barley if the application The ability of the crop to compete efficient boom with nozzles giving a techniques are not correct. Clipper with wild oats which survive the pre- fine spray will give the best results. and Proctor barley are easily dam sowing cultural treatments is import Aerial treatment is generally more aged and should not be treated. ant. If it is anticipated that the crop effective than application from the will be vigorous and high yielding, ground; the rate can be slightly Wild oat recommendations—in herbicide treatment with triallate or reduced when this method is used. brief barban should be considered. Where wild oats are a problem, a Herbicide treatment is unlikely to Crop tolerance three-year pre-cropping plan should give an economical return in low- Both triallate and barban arc relat be developed. yielding crop.

The two main species of wild oats in Western Australia: Avena fatua (left) and A. barbata, characterised by the drooping habit of its seed head. 95 Journal of Agriculture Vol 17 No 3, 1976