Plant Protection Quarterly Vol.11 Supplement 1 1996 215 wheat and wild oats. In all cases, wild oat plants were severely damaged and wheat Biological control of annual grass weeds—progress unharmed. Optimization of environmen- and prospects tal conditions and increased inoculum den- sity may produce even more damage to wild oats. Other fungi found during sur- S.D. Hetherington and B.A. Auld, Co-operative Research Centre for Weed veys to be tested for pathogenicity to wild Management Systems, NSW Agriculture, Agricultural Research and Veterinary oats include Pyrenophora seminiperda Centre, Orange, New South Wales, 2800, Australia. (Brittlebank and Adam) Shoemaker, Septoria avenae Frank, Ascochyta spp. and Colletotrichum spp. Why biocontrol? Progress The advantages of biological control in re- Biological control of annual grasses in Pyrenophora seminiperda—possible ducing use of chemicals, non-target dam- wheat cultivation (Hetherington, Auld, bioherbicide for grass weed seeds (Medd age and environmental contamination are Priest and Smith) and Campbell) well known. Application of pathogenic or- An Australian Centre for International Pyrenophora seminiperda is a ubiquitous ganisms to grass weeds remains a scarcely Agricultural Research project is studying fungal pathogen infecting a wide range of investigated option for weed control potential fungal biocontrol agents of hosts causing a variety of symptoms in- (Evans 1991). In the early 1990s, five of the weeds in cultivation. Emphasis has been cluding seed sterilization, seedling blight, six recorded herbicide resistant weeds in placed upon Avena spp. and L. rigidum. leaf spotting and leaf striping (Medd 1992, Australia were grasses (Davis 1992). Her- Surveys of diseased weedy annual Medd and Jones 1992). bicide resistant populations of annual grasses commenced throughout wheat This pathogen may be used for biologi- ryegrass (Lolium rigidum Gaudin) (Holtum growing areas of southern Australia as cal control of a number of weedy annual and Powles 1991), wild oats (Avena spp.) well as several coastal locations (e.g. grasses, notably Avena fatua, Vulpia (Powles and Holtum 1990) and vulpia Grafton and Brisbane) in August 1995. The bromoides and Lolium rigidum. The pro- (Vulpia bromoides (L.) Gray) (Purba et al. samples are returned to the Agricultural posed strategy is based upon the patho- 1993) have been recorded in Australia. Research and Veterinary Centre for gens ability to infect seed and subse- Calls for augmentation of chemical con- processing. A collection of isolates has quently decrease germination, emergence trols and the diversification of control been established and a comprehensive and vigour ( Table 1). strategies have been made following the record of each isolate kept on a database. While the fungus infects wheat it does appearance of herbicide resistance (Howat Currently, approximately 700 fungal iso- not appear to affect milling quality. Levels 1987). lates have been isolated from Avena fatua of seed damage greater than 70% have and L. rigidum and stored. Representative been predicted as necessary to bring about Biocontrol and the biology of grasses isolates are identified by the fungal her- population decline in wild oats (Medd and Many grasses produce large numbers of barium at Biological and Chemical Re- Campbell in press). The only limitation seeds which may have high dormant search Institute, Rydalmere. placed upon the grower is that treated populations. Additionally, growth occurs Pathogenicity testing of these isolates seed cannot be used for grow-on. from intercalary meristems situated near has commenced. A simple bioassay of sus- or just below the soil surface and sheathed ceptibility to disease has been established. Prospects in leaves. This allows recovery from injury Leaf segments are floated on an agar me- Biological control of annual grasses in e.g. grazing or foliar diseases (Terry 1991). dium containing the antisenescent wheat cultivation (Hetherington, Auld, Biological control strategies should target benzimadazole. These segments are in- Priest and Smith) these aspects of grass biology and may oculated with potential fungal pathogens A listing of recorded pathogens compiled aim to: and if the interaction is compatible, lesions from the New South Wales host index (Ta- • reduce plant vigour, subsequently af- appear within days. Crop plants of inter- ble 2) gives an indication of the wide range fecting the competitive influence and fe- est can be included in this test (e.g. wheat is of fungi which might be available for use cundity of the weed population e.g. leaf included in wild oats tests). in biological control systems. It is hoped spots, root rots, Whole plant inoculations have also been that the survey will also find unrecorded • directly affect reproductive structures, conducted. Fifty isolates of the fungal pathogens which may be added to this e.g. smuts, false smuts, pathogen Drechslera avenae (Eidam) Sharif range. Leptosphearulina trifolii (Rostr.) Petr. • destroy meristems and kill plants e.g. have been tested at low inoculum concen- was previously unrecorded as a pathogen crown rots. tration (103–104 spores mL-1) against of wild oats in New South Wales, but has been found several times during this sur- vey and its pathogenicity confirmed. Table 1. The effect of field applications of a single isolate of P. seminiperda on Drechslera avenae has caused severe dam- caryopsis infection, germination and development of wheat and several age to wild oats in pathogenicity tests. annual grass weeds (Reproduced with permission from Medd and Campbell Optimization of the inoculation technique in press). should increase this severity. At present, it is possible to produce inoculation with Reduction in Reduction in Reduction in spore concentrations of only 103–104 Seed infected germination emergence vigour spores mL-1. It is likely that we will be able (%) (%) (%) (%) to increase this concentration using filter paper incubation techniques (Bournival et Triticum aestivum L. 21 2 55 34 al. 1994). Bromus diandrus Roth. 62 35 51 26 The wide geographical range from Avena fatua L. 8 2 11 10 which we are collecting pathogens may L. rigidum 18 12 12 22 help to avoid the high humidity require- Hordeum leporinum Link. 38 15 38 30 ments of some biological control systems. V. bromoides 59 16 70 54 It is hoped that, given the large number of 216 Plant Protection Quarterly Vol.11 Supplement 1 1996 Table 2. Listing of pathogens recorded on three grass weeds in New South Wales. Avena Lolium Vulpia fatua rigidum spp. Bipolaris sorokiniana (Sacc.) Shoemaker ✓ Cladosporium herbarum (Pers.) Link : Gray ✓ Claviceps phalardis ✓✓ Claviceps purpurea (Fr.) Tul. ✓ Cochliobolus sativusA (Ito & Kurib.) Drechslera : Dastur ✓ Colletotrichum graminicola (Ces.) Wilson ✓✓ Drechslera avenae (Eidam) Sharif. ✓ Drechslera sp. ✓ Gaumannomyces graminisA (Sacc.) von Arx & Oliv. ✓ Phoma sorghina (Sacc.) Boerema, Dorenbosch & van Kesteren ✓ Phytophthora macrospora (Sacarardo) Ito & Tanaka ✓✓ Phytophthora sorghina ✓ Pseudocercosporella herpetrichoides (Fron) Deighton ✓✓ Puccinia coronata Corda ✓✓ Puccinia graminisA Pers ✓✓✓ Puccinia reconditaA Roberge : Desm. ✓ Pyrenophora seminiperdaA (Brittlebank and Adam) Shoemaker ✓✓✓ Ramularia pusilla ✓✓ Sclerophthora graminis ✓ Selenophoma donacis (Pass.) Sprague & Johnson ✓ Septoria avenae Frank ✓ Septoria triticiA Roberge in Desm. ✓✓ Stomaticola spp. ✓ Tilletia fusca (Ellis & Everh.) ✓ Urocystis agropyriA (Preuss) Schrot. ✓ Urocystis occulta Rabenh ✓ Ustilago avenae (Pers.) Rostr. ✓ Ustilago bullata Burk. In Hook. f. ✓ Ustilago nudaA Kellerman & Swingle ✓ A recorded as infecting wheat. isolates of each pathogen which we have References stored, certain isolates will be able to infect Bournival, B.L., Ginoza, H.S., Schenck and annual grass weeds of arable lands us- under drier conditions. A new project, run Moore, P.H. (1994). Characterization of ing a non-specific fungal seed pathogen. in conjunction with this work will be ex- sugarcane response to Bipolaris sacchari: Proceedings of the IX International amining formulations to overcome dew Inoculations and host-specific HS-toxin. Symposium on Biological Control of requirements such as invert emulsions Phytopathology 84, 672-6. Weeds, Stellenbosch, South Africa. (Womack et al. 1996). Davis, R.C. (1992). Agrichemical initiatives Medd, R.W. and Jones, K.H. (1992). Host to combat development of herbicide re- range, distribution and importance of Pyrenophora seminiperda—possible sistance. Proceedings of the 1st Interna- the fungus Pyrenophora seminiperda bioherbicide for grass weed seeds (Medd tional Weed Congress, Melbourne, pp. (Brittlebank and Adam) Shoemaker and Campbell) 144-7. (Ascomycotina: Pyrenomycetes) in Aus- A provisional patent has been granted for Evans, H.C. (1991). Biological control of tralia. Proceedings of the Linnean Society, the novel use of P. seminiperda against tropical grassy weeds. In ‘Tropical NSW 113, 15-26. grass weeds. The concept is still largely un- Grassy Weeds’, eds. F.W.G. Baker, and Powles, S.B. and Holtum, J.A.M. (1990). explored and much remains to be done. P.J. Terry, pp. 52-72. (Redwood Press Herbicide resistant weeds in Australia. The results presented are from a single iso- Ltd., Wiltshire, England). Proceedings of the 9th Australian Weeds late. It is likely that more virulent isolates Holtum, J.A.M. and Powles, S.B. (1991). Conference, Adelaide, pp. 185-93. exist. Therefore, collection and screening Annual ryegrass: an abundance of re- Purba, E., Preston, C. and Powles, S.B. is a priority. Formulation and field deliv- sistance, a plethora of mechanisms. Pro- (1993). Paraquat resistance in a biotype ery systems must be explored and ceedings of the Brighton Crop Protec- of Vulpia bromoides (L.) S.F. Gray. Weed optimized. Because wheat is also a host of tion Conference, Brighton, pp. 1071-8. Research 33, 409-13. P. seminiperda, particular emphasis will Howat, P.D. (1987). Weeds resistant to Terry, P.J. (1991). Grassy weeds—a gen- need to be placed upon the toxicity of in- herbicides in Australia and contributing eral overview. In ‘Tropical Grassy fected grain since the agent could affect factors leading to their resistance. Plant Weeds’, eds F.W.G. Baker, and P.J. grain used for human consumption (Medd Protection Quarterly 2, 82-5. Terry, pp. 5-38. (Redwood Press Ltd., and Campbell in press). Medd, R.W. (1992). A review of the world Wiltshire, England). distribution and host range of Womack, J.G, Eccleston, G.M., and Burge, Pyrenophora seminiperda. Review of Plant M.N. (1996). A vegetable oil-based in- Pathology 71, 891-901. vert emulsion for mycoherbicide deliv- Medd, R.W. and Campbell, M.A. (In ery. Biological Control: Theory and Applica- press). A rationale for regulating some tions 6, 23-8.