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Triadimenol insensitivity in Pyrenophora teres
Notes and brief articles Table 4 summarizes results from dosage-response tests, in which hyphal tip isolates from 'sensitive' Rothamsted sites were supplemented with some from' resistant' field sites to help make comparisons. Although there was some variation, no overlap was observed in carbendazim sensitivity between the 'resistant' and 'sensitive' isolates. The limited data available provide no evidence to link resistance with a particular growth type. Cross-resistance was demonstrated to other MBC-generating fungicides (data not shown) but not to prochloraz, which confirms the results of Brown et al. (1984). Carbendazim-resistant isolates were more sensitive to MDPC than carbendazim-sensitive isolates, suggesting that this, or a similar compound, may be of some value in alleviating the problem of field resistance in eyespot. This is being further investigated. The establishment of appropriate methods for monitoring fungicide resistance in eyespot populations and for characterizing and comparing individual isolates was the first stage in a field study of the development and dispersal of resistance. The suitability of the sites, with low background resistance level, for this study was confirmed. REFERENCES
BROWN, M. C., TAYLOR, G. S. & EPTON, H. A. S. (1984). Carbendazim resistance in the eyespot pathogen Pseudocercosporella herpotrichuitks. Plant Pathology 33, 101-111.
FEHRMANN, H., HORSTEN, J. & SIEBRASSE, G. (1982). Five years' results from a long-term field experiment on carbendazim resistance of Pseudocercosporella herpotrichoides (Fron) Deighton. Crop Protection 1, 165-168. GRIFFIN, M. & YARHAM, D. (1983). Fungicide resistanceMBC resistance in the eyespot fungus. Agrospray. FBC Ltd. Technical Information no. 6,2-5. HORSTEN, J. & FEHRMANN, H. (1980). Fungicide resistance of Septoria nodorum and Pseudocercosporella herpotrichoides. 1. Effect offungicide application on the frequency of resistant spores in the field. Zeitschrift fur Pjlanzenkrankheiten und Pjlanzenschutz 87, 43~453. KATO, T., SUZUKI, K., TAKAHASHI, J. & KAMOSHITA, K. (1983). Negative cross resistance between benzimidazoles and methyl N-(3,5-dichloropheny1)-carbamate. Abstracts of Papers. Fourth International Congress of Plant Pathology, abstract no. 66. OLVANG, H. (1983). Sensitivity of Pseudocercosporella herpotrichoides to benomyl. Zeitschrift fur Pjlanzenkrankheiten und Pjlanzenschutz 90, 515-520. RASHID, T. & SCHLOSSER, E. (1975). Resistenz von Cercosporella herpotrichoides gegenuber Benomyl. Zeitschrift fur Pjlanzenkrankheiten und Pjlanzenschutz 82, 765-766. SCOTT, P. R. (1971). The effect of temperature on eyespot (Cercosporella herpotrichoides) in wheat seedlings. Annals of Applied Biology 68, 16~175. SCOTT, P. R, HOLLINS, T. W. & MUIR, P. (t"975). Pathogenicity of Cercosporella herpotrichoides to wheat, barley, oats and rye. Transactions of the British Mycological Society 65, 52~538. ZADOKS, J. C., CHANG, T. T. & KONZAK, C. F. (1974). A decimal code for the growth stages of cereals. Weed Research 14,415-421.
TRIADIMENOL INSENSITIVITY IN PYRENOPHORA TERES BY
J. EDMUND SHERIDAN, NICK GRBAVAC* AND MARY H. SHERIDAN Botany Department, Victoria University of Wellington, New Zealand
The occurrence of triadimenol-sensitive and -insensitive isolates of Pyrenophora teres in New Zealand is reported. The latter are now widespread in barley crops. Cross resistance to imazalil and nuarimol was found in some triadimenol-insensitive isolates. Pyrenophora teres Drechsler (anamorph Drechslera teres (Sacc.) Shoemaker) causes net blotch of barley. Good control was initially obtained with the seed treatment 'Baytan F 17', containing 15 % triadimenol and 2 % fuberidazole, registered with the New Zealand Pesticides Board in 1979 (Sheridan & Grbavac, 1979). In the spring of 1981-2 infection from seed-borne inoculum was observed in commercially treated crops and an epidemic of net blotch occurred in the following
* Present address: Plant Health and Diagnostic Station, Ministry of Agriculture and Fisheries, Private Bag, Levin, New Zealand. Trans. Br. mycol. Soc. 85 (2), (1985)
season in the southern half of the North Island. The problem was associated with newly introduced barley cultivars, particularly Mata and Triumph. Trials showed that 'Baytan F 17' treatment gave little or no control of net blotch on all of the recently introduced cultivars tested but continued to give good control on cv. Zephyr (Sheridan & Grbavac, 1983). In the spring of 1984 it failed on cv. Zephyr also and the Ministry of Agriculture and Fisheries withdrew recommendations for 'Baytan F17' in net blotch control (Hampton & Liew, 1984). The reason for failure was believed to be due to the introduction of a triadimenol insensitive strain of P. teres on seed from overseas (Sheridan
Printed in Great Britain
Notes and brief articles
339
Fig. 1. Isolates of triadimenol sensitive (bottom) and insensitive (top) P. teres on malt extract agar after 14 days. Left - without triadimenol. Right - with 10 #g ml-\ triadimenol.
Table
1.
Growth of P. teres on malt extract agar amended with triadimenol Isolate
Code S10 SII
SI S3 Tl T2 R3 GPI GP2 ANT 8
Triadimcnol conen CJLg ml- 1 )
Source NZ Zephyr 1981 NZ Zephyr 1981 NZ Zephyr 1982 NZ Zephyr 1982 NZ Triumph 1984 NZ Triumph 1984 NZ Zephyr 1984 NZt Golden Promise 1984 NZt Golden Promise 1984 Denmark Unnamed 1984
53* 54 52 50 53 52 55 55 55
5 10 8 13 15 15 17 40 43 33
60
so
0
10 0 0 0 0 0 0 30 35 30 40
25 0 0 0 0 0 0 15 20 15 25
50 0 0
0 0 0 0 13 15 5 23
* Mean colony diam (2 replicates) measured to the nearest mm, less 5 mm for the plug of inoculum, after 7 days. t ex U.K. and grown for one season in New Zealand.
& Grbavac, 1985). This note presents further evidence for the existence of triadimenol-sensitive and -insensitive strains of P. teres and the overseas origin of the insensitive strain. Isolations of P. teres were made by plating barley seeds from the 1981 to 1984 harvests on to malt extract agar containing 10 pg ml- 1 benomyl to Trans. Br. mycol. Soc. 85 (2), (1985)
suppress saprobes. Pure cultures were established on the same medium. These were then screened for sensitivity to triadimenol by inoculating plates containing to pg ml- 1 triadimenol (added to the medium after autoclaving) centrally with 5 mm plugs of the fungus. None of the isolates made from seeds harvested before 1984 (all of cv. Zephyr)
Primed in Great Britain
Notes and brief articles
340 Table
2.
Growth of P. teres on malt extract agar amended with imazalil or nuarimol Concn (pg ml- 1 ) Imazalil
o
Isolate
70 + * 70+ 70+ 70+ 70+
S10 T1 GP1 ANT 8 Coriolus versicolor
*
Mean colony diam (2 replicates) measured
Fig.
2.
to
5 0 0 0 16 50
10
0 0 0 15 36
Nuarimol 5 0 0 18 31 0
10
0 0 13 25 0
the nearest mm, less 5 mm for the plug of inoculum after 9 days.
Triadimenol-insensitive isolates of P. teres on malt extract agar after 14 days. Top Bottom 50 f.Lg ml- 1 •
grew on the triadimenol amended medium. Most from the 1984 harvested seed (Zephyr and other cultivars) grew well on the amended medium (Fig. 1). Six sensitive and 4 insensitive isolates were selected for further testing. Plates were incubated on the laboratory bench at 15-22 °C. The results shown in table 1 revealed a tolerance of 50 JLg ml-' triadimenol for the insensitive isolates. Best growth at 50 JLg ml-' was given by an isolate from Golden Promise of U.K. origin and a coded seed line of Danish origin (Fig. 2). Both of these were able to Trans. Br. mycol. Soc. 85 (2), (1985)
10 f.Lg
ml- 1 .
grow on malt extract agar amended with 10 JLg ml-' nuarimol (Table 2). The isolate of Danish origin grew with 10 JLg ml-' imazalil in the medium. Coriolus versicolor (L. :Fr.) Quelet was included for comparison because of its high sensitivity to triadimenol and usefulness in detecting triadimenol in cereal leaf tissue (Williamson & Gilmour, 1984). Triadimenol sensitivity and insensitivity in P. teres has been demonstrated in laboratory media. Some isolates tolerated 50 JLg ml-' while others failed to grow on 10 JLg ml-'. One triadimenol-
Printed in Great Britain
Notes and brief articles
34 1
Mrs Maureen Cooper and Mrs Olga Vincent for typing the manuscript.
insensitive isolate from seed of Danish origin also tolerated 10 pg ml- 1 imazalil and nuarimol while another from seed of Golden Promise tolerated 10 pg ml- 1 nuarimol but not imazalil. A search has REFERENCES revealed a few triadimenol-insensitive isolates in New Zealand grown seed of cv. Zephyr harvested FUCHS, A. & DRANDAREVSKI, C. A. (1976). The likelihood of development of resistance to systemic fungicides in 1981 and 1982 which had never come in contact which inhibit ergosterol biosynthesis. Netherland with triadimenol or the newer cultivars. This Journal of Plant Pathology 82,85-87. indicates that the insensitive strain is present in the GASZTONYI, MAYA & JOSEPOVITS, GYULA (1984). Metanatural population of the pathogen. Two of bolism of some sterol inhibitors in fungi and higher these triadimenol-insensitive isolates also tolerated plants, with special reference to the selectivity of 1 1 10 pg ml- nuarimol. None tolerated 10 pg mlfungicidal action. Pesticide Science 15,48-55. imazalil. HAMPTON, J. G. & LIEW, R. S. S. (1984). Barley cultivar response to seed treatments for net blotch control - a Further investigations are needed because most note. New Zealand Journal of Experimental Agriculture of the currently registered seed treatments for net 12,265-267. blotch control in use in New Zealand contain imazalil. It is generally considered that tl!e SHERIDAN, J. E. & GRBAVAC, N. (1979). Healthy barley crops demand constant surveillance. New Zealand development of insensitivity or resistance to sterol Journal of Agriculture 139,25-29. inhibitors is unlikely under practical conditions SHERIDAN, J. E. & GRBAVAC, N. (1983). Seed treatments because of reduced fitness (Fuchs & Drandarevski, for control of net blotch of barley. Proceedings 36th New 1976; Gasztonyi & Josepovits, 1984). This is Zealand Weed and Pest Control Conference 237-241. believed to be the first case of field resistance to an SHERIDAN, J. E. & GRBAVAC, N. (1985). Cultivar differences in response to triadimenol seed treatments EBI where the resistant strain has become for control of barley net blotch caused by Pyrenophora widespread. We are grateful to Mr Max Moore of Bayer (NZ) Ltd, Mr Hilary Kearney of The Canterbury (NZ) Malting Co. Ltd, and Mrs Linda Ballard of The N .Z. Farmers Fenilizer Co. for supplying chemicals and showing an interest in our work. We thank
teres. Plant Disease ", 77-80. WILLIAMSON, M. B. R. & GILMOUR, J. (1984). A bioassay procedure for detecting triadimenol and its degradation products in cerealleaftissue. Tests ofAgrochemicals and Cultivars no. 5 (Annals of Applied Biology 104, Supplement), pp. 50-51.
CONTROL OF ERGOT BY A SELECTIVE HERBICIDE AND STUBBLE BURNING BY T. W. BRETAG
Department of Agriculture, Victorian Crops Research Institute, P.R. 260, Horsham, Victoria 3400, Australia Control of ryegrass in wheat fields prevented contamination of grain by ryegrass ergot. Burning of ergot-infected wheat stubbles considerably reduced the number of viable sclerotia. Grain contaminated with ergot, Claviceps purpurea (Fr.) Tul., is either rejected or heavily discounted because of its toxicity to animals and man (Wiese, 1977). In Australia, the sclerotia most commonly detected in wheat samples are from ryegrass and only rarely are the much larger wheat ergots present (Brown, 1975; Kuiper & Murray, 1978; Walker & Evans, 1976). Previous studies (Bretag & Merriman, 1981 a) have shown that ryegrass ergot is common and that cross infection of cereals may occur. Control of ryegrass within wheat fields should therefore reduce the risk of ergot contamination of grain. Current data on herbicides (Anon., 1979) indicate there are several chemicals available Trans. Br. mycol. Soc. 85 (2), (1985)
for the control of ryegrass in wheat crops but studies should be undenaken to establish whether this is sufficient to prevent ergot contamination of grain. In the Pacific northwest region of the United States, ergot in perennial ryegrass has been controlled by stubble burning following harvest (Hardison, 1974) and it has been suggested (Hardison, 1976) that this technique may assist in the control of wheat ergot also. The fires destroy ergot sclerotia thereby removing the source of primary inoculum. To establish whether or not ryegrass control in wheat crops was likely to prevent ergot contami-
Printed in Great Britain
BROWN, M. C., TAYLOR, G. S. & EPTON, H. A. S. (1984). Carbendazim resistance in the eyespot pathogen Pseudocercosporella herpotrichuitks. Plant Pathology 33, 101-111.
FEHRMANN, H., HORSTEN, J. & SIEBRASSE, G. (1982). Five years' results from a long-term field experiment on carbendazim resistance of Pseudocercosporella herpotrichoides (Fron) Deighton. Crop Protection 1, 165-168. GRIFFIN, M. & YARHAM, D. (1983). Fungicide resistanceMBC resistance in the eyespot fungus. Agrospray. FBC Ltd. Technical Information no. 6,2-5. HORSTEN, J. & FEHRMANN, H. (1980). Fungicide resistance of Septoria nodorum and Pseudocercosporella herpotrichoides. 1. Effect offungicide application on the frequency of resistant spores in the field. Zeitschrift fur Pjlanzenkrankheiten und Pjlanzenschutz 87, 43~453. KATO, T., SUZUKI, K., TAKAHASHI, J. & KAMOSHITA, K. (1983). Negative cross resistance between benzimidazoles and methyl N-(3,5-dichloropheny1)-carbamate. Abstracts of Papers. Fourth International Congress of Plant Pathology, abstract no. 66. OLVANG, H. (1983). Sensitivity of Pseudocercosporella herpotrichoides to benomyl. Zeitschrift fur Pjlanzenkrankheiten und Pjlanzenschutz 90, 515-520. RASHID, T. & SCHLOSSER, E. (1975). Resistenz von Cercosporella herpotrichoides gegenuber Benomyl. Zeitschrift fur Pjlanzenkrankheiten und Pjlanzenschutz 82, 765-766. SCOTT, P. R. (1971). The effect of temperature on eyespot (Cercosporella herpotrichoides) in wheat seedlings. Annals of Applied Biology 68, 16~175. SCOTT, P. R, HOLLINS, T. W. & MUIR, P. (t"975). Pathogenicity of Cercosporella herpotrichoides to wheat, barley, oats and rye. Transactions of the British Mycological Society 65, 52~538. ZADOKS, J. C., CHANG, T. T. & KONZAK, C. F. (1974). A decimal code for the growth stages of cereals. Weed Research 14,415-421.
TRIADIMENOL INSENSITIVITY IN PYRENOPHORA TERES BY
J. EDMUND SHERIDAN, NICK GRBAVAC* AND MARY H. SHERIDAN Botany Department, Victoria University of Wellington, New Zealand
The occurrence of triadimenol-sensitive and -insensitive isolates of Pyrenophora teres in New Zealand is reported. The latter are now widespread in barley crops. Cross resistance to imazalil and nuarimol was found in some triadimenol-insensitive isolates. Pyrenophora teres Drechsler (anamorph Drechslera teres (Sacc.) Shoemaker) causes net blotch of barley. Good control was initially obtained with the seed treatment 'Baytan F 17', containing 15 % triadimenol and 2 % fuberidazole, registered with the New Zealand Pesticides Board in 1979 (Sheridan & Grbavac, 1979). In the spring of 1981-2 infection from seed-borne inoculum was observed in commercially treated crops and an epidemic of net blotch occurred in the following
* Present address: Plant Health and Diagnostic Station, Ministry of Agriculture and Fisheries, Private Bag, Levin, New Zealand. Trans. Br. mycol. Soc. 85 (2), (1985)
season in the southern half of the North Island. The problem was associated with newly introduced barley cultivars, particularly Mata and Triumph. Trials showed that 'Baytan F 17' treatment gave little or no control of net blotch on all of the recently introduced cultivars tested but continued to give good control on cv. Zephyr (Sheridan & Grbavac, 1983). In the spring of 1984 it failed on cv. Zephyr also and the Ministry of Agriculture and Fisheries withdrew recommendations for 'Baytan F17' in net blotch control (Hampton & Liew, 1984). The reason for failure was believed to be due to the introduction of a triadimenol insensitive strain of P. teres on seed from overseas (Sheridan
Printed in Great Britain
Notes and brief articles
339
Fig. 1. Isolates of triadimenol sensitive (bottom) and insensitive (top) P. teres on malt extract agar after 14 days. Left - without triadimenol. Right - with 10 #g ml-\ triadimenol.
Table
1.
Growth of P. teres on malt extract agar amended with triadimenol Isolate
Code S10 SII
SI S3 Tl T2 R3 GPI GP2 ANT 8
Triadimcnol conen CJLg ml- 1 )
Source NZ Zephyr 1981 NZ Zephyr 1981 NZ Zephyr 1982 NZ Zephyr 1982 NZ Triumph 1984 NZ Triumph 1984 NZ Zephyr 1984 NZt Golden Promise 1984 NZt Golden Promise 1984 Denmark Unnamed 1984
53* 54 52 50 53 52 55 55 55
5 10 8 13 15 15 17 40 43 33
60
so
0
10 0 0 0 0 0 0 30 35 30 40
25 0 0 0 0 0 0 15 20 15 25
50 0 0
0 0 0 0 13 15 5 23
* Mean colony diam (2 replicates) measured to the nearest mm, less 5 mm for the plug of inoculum, after 7 days. t ex U.K. and grown for one season in New Zealand.
& Grbavac, 1985). This note presents further evidence for the existence of triadimenol-sensitive and -insensitive strains of P. teres and the overseas origin of the insensitive strain. Isolations of P. teres were made by plating barley seeds from the 1981 to 1984 harvests on to malt extract agar containing 10 pg ml- 1 benomyl to Trans. Br. mycol. Soc. 85 (2), (1985)
suppress saprobes. Pure cultures were established on the same medium. These were then screened for sensitivity to triadimenol by inoculating plates containing to pg ml- 1 triadimenol (added to the medium after autoclaving) centrally with 5 mm plugs of the fungus. None of the isolates made from seeds harvested before 1984 (all of cv. Zephyr)
Primed in Great Britain
Notes and brief articles
340 Table
2.
Growth of P. teres on malt extract agar amended with imazalil or nuarimol Concn (pg ml- 1 ) Imazalil
o
Isolate
70 + * 70+ 70+ 70+ 70+
S10 T1 GP1 ANT 8 Coriolus versicolor
*
Mean colony diam (2 replicates) measured
Fig.
2.
to
5 0 0 0 16 50
10
0 0 0 15 36
Nuarimol 5 0 0 18 31 0
10
0 0 13 25 0
the nearest mm, less 5 mm for the plug of inoculum after 9 days.
Triadimenol-insensitive isolates of P. teres on malt extract agar after 14 days. Top Bottom 50 f.Lg ml- 1 •
grew on the triadimenol amended medium. Most from the 1984 harvested seed (Zephyr and other cultivars) grew well on the amended medium (Fig. 1). Six sensitive and 4 insensitive isolates were selected for further testing. Plates were incubated on the laboratory bench at 15-22 °C. The results shown in table 1 revealed a tolerance of 50 JLg ml-' triadimenol for the insensitive isolates. Best growth at 50 JLg ml-' was given by an isolate from Golden Promise of U.K. origin and a coded seed line of Danish origin (Fig. 2). Both of these were able to Trans. Br. mycol. Soc. 85 (2), (1985)
10 f.Lg
ml- 1 .
grow on malt extract agar amended with 10 JLg ml-' nuarimol (Table 2). The isolate of Danish origin grew with 10 JLg ml-' imazalil in the medium. Coriolus versicolor (L. :Fr.) Quelet was included for comparison because of its high sensitivity to triadimenol and usefulness in detecting triadimenol in cereal leaf tissue (Williamson & Gilmour, 1984). Triadimenol sensitivity and insensitivity in P. teres has been demonstrated in laboratory media. Some isolates tolerated 50 JLg ml-' while others failed to grow on 10 JLg ml-'. One triadimenol-
Printed in Great Britain
Notes and brief articles
34 1
Mrs Maureen Cooper and Mrs Olga Vincent for typing the manuscript.
insensitive isolate from seed of Danish origin also tolerated 10 pg ml- 1 imazalil and nuarimol while another from seed of Golden Promise tolerated 10 pg ml- 1 nuarimol but not imazalil. A search has REFERENCES revealed a few triadimenol-insensitive isolates in New Zealand grown seed of cv. Zephyr harvested FUCHS, A. & DRANDAREVSKI, C. A. (1976). The likelihood of development of resistance to systemic fungicides in 1981 and 1982 which had never come in contact which inhibit ergosterol biosynthesis. Netherland with triadimenol or the newer cultivars. This Journal of Plant Pathology 82,85-87. indicates that the insensitive strain is present in the GASZTONYI, MAYA & JOSEPOVITS, GYULA (1984). Metanatural population of the pathogen. Two of bolism of some sterol inhibitors in fungi and higher these triadimenol-insensitive isolates also tolerated plants, with special reference to the selectivity of 1 1 10 pg ml- nuarimol. None tolerated 10 pg mlfungicidal action. Pesticide Science 15,48-55. imazalil. HAMPTON, J. G. & LIEW, R. S. S. (1984). Barley cultivar response to seed treatments for net blotch control - a Further investigations are needed because most note. New Zealand Journal of Experimental Agriculture of the currently registered seed treatments for net 12,265-267. blotch control in use in New Zealand contain imazalil. It is generally considered that tl!e SHERIDAN, J. E. & GRBAVAC, N. (1979). Healthy barley crops demand constant surveillance. New Zealand development of insensitivity or resistance to sterol Journal of Agriculture 139,25-29. inhibitors is unlikely under practical conditions SHERIDAN, J. E. & GRBAVAC, N. (1983). Seed treatments because of reduced fitness (Fuchs & Drandarevski, for control of net blotch of barley. Proceedings 36th New 1976; Gasztonyi & Josepovits, 1984). This is Zealand Weed and Pest Control Conference 237-241. believed to be the first case of field resistance to an SHERIDAN, J. E. & GRBAVAC, N. (1985). Cultivar differences in response to triadimenol seed treatments EBI where the resistant strain has become for control of barley net blotch caused by Pyrenophora widespread. We are grateful to Mr Max Moore of Bayer (NZ) Ltd, Mr Hilary Kearney of The Canterbury (NZ) Malting Co. Ltd, and Mrs Linda Ballard of The N .Z. Farmers Fenilizer Co. for supplying chemicals and showing an interest in our work. We thank
teres. Plant Disease ", 77-80. WILLIAMSON, M. B. R. & GILMOUR, J. (1984). A bioassay procedure for detecting triadimenol and its degradation products in cerealleaftissue. Tests ofAgrochemicals and Cultivars no. 5 (Annals of Applied Biology 104, Supplement), pp. 50-51.
CONTROL OF ERGOT BY A SELECTIVE HERBICIDE AND STUBBLE BURNING BY T. W. BRETAG
Department of Agriculture, Victorian Crops Research Institute, P.R. 260, Horsham, Victoria 3400, Australia Control of ryegrass in wheat fields prevented contamination of grain by ryegrass ergot. Burning of ergot-infected wheat stubbles considerably reduced the number of viable sclerotia. Grain contaminated with ergot, Claviceps purpurea (Fr.) Tul., is either rejected or heavily discounted because of its toxicity to animals and man (Wiese, 1977). In Australia, the sclerotia most commonly detected in wheat samples are from ryegrass and only rarely are the much larger wheat ergots present (Brown, 1975; Kuiper & Murray, 1978; Walker & Evans, 1976). Previous studies (Bretag & Merriman, 1981 a) have shown that ryegrass ergot is common and that cross infection of cereals may occur. Control of ryegrass within wheat fields should therefore reduce the risk of ergot contamination of grain. Current data on herbicides (Anon., 1979) indicate there are several chemicals available Trans. Br. mycol. Soc. 85 (2), (1985)
for the control of ryegrass in wheat crops but studies should be undenaken to establish whether this is sufficient to prevent ergot contamination of grain. In the Pacific northwest region of the United States, ergot in perennial ryegrass has been controlled by stubble burning following harvest (Hardison, 1974) and it has been suggested (Hardison, 1976) that this technique may assist in the control of wheat ergot also. The fires destroy ergot sclerotia thereby removing the source of primary inoculum. To establish whether or not ryegrass control in wheat crops was likely to prevent ergot contami-
Printed in Great Britain