Marcia McMullen

Extension Plant Pathologist

North Dakota State University

Fargo, ND 58105

Cereal diseases are a result of three components occurring in a field at the same time: 1) favorable weather for disease development; 2) a susceptible host crop; 3) and the disease organism being present in the field. Plant Pathologists call this the disease triangle. Without all three components, a disease will not occur. Cereal diseases are managed through an integration of strategies aimed at one or more of these three components. Reliance on a single strategy may lead to failure. Strategies that may be integrated include crop rotation, use of a resistant or tolerant variety, planting date, residue management, seed treatment, foliar fungicides, and disease forecasting. This paper provides a brief overview of how producers can direct their management strategies to control root rot, fungal leaf spots, and Fusarium head blight of wheat and barley.

In recent years, several diseases have had major impact on yield and quality of wheat, durum, and barley crops in North Dakota (McMullen 1997, 2001). Fusarium head blight (FHB = scab) has caused severe yield and quality losses in certain districts of North Dakota each year, while leaf spot diseases and root rot also have been common. Wheat and barley losses to FHB and its spread westward have been reported in Canada (Gilbert and Tekauz, 2000; Tekauz, et al. 2000; Clear and Patrick 2000). Growers who have experienced these diseases have several options for management. This paper will describe some management options directed at the pathogen, the host crop, or the environment, for control of root rot, fungal leaf spots, and FHB.

Common root rot, caused by Cochliobolus sativus, is a frequently observed disease in the northern US prairie states and in the prairie provinces of Canada (Ledingham, et al. 1973; Stack and McMullen 1999). The fungus infects when soil is wet and warm, but the most damage to the crop is done when the weather turns hot and dry at heading, at a time when water is needed for kernel fill, but the roots and crown are too infected or too sparse to transport adequate water. The causal fungus overwinters in soil, seed (black point), and debris. All wheats and barley are susceptible hosts, but differences in tolerance do exist among cultivars.

Management options to reduce the risk of common root rot include crop rotation, seed treatment, and variety choice. Chinn (1976) showed the effect of crop rotation on root rot, indicating that the longer a field was not planted to a cereal crop, the lesser amount of inoculum of the causal fungus was present. The benefits of incorporating non-host crops into crop sequences on root disease and other cereal disease management are summarized by Krupinsky et al. (2002). Wheat and durum cultivars with more tolerance to the disease also have been identified (Stack 2002,). Certain seed treatments also are effective in reducing root rot levels and increasing yields (Ashley et al. 2001). Tillage systems either have no effect on common root rot or no-till may actually reduce the severity of the disease (Ledingham, et al. 1960; Salas and Stack 1989; Windels and Wiersma, 1992). Recent studies with root rot and seed treatment in a wheat field in SW North Dakota has indicated that the predominant root rot fungus in that field was not Cochliobolus sativus, but Fusarium graminearum, which causes dryland root and crown rot (Ashley, R, O, personal communication). Methods of dryland root rot control would be similar as for common root rot.

Tan spot, caused by Pyrenophora tritici-repentis, and Septoria leaf blotch, caused by several Septoria species, including Septoria tritici or Stagnosopora (Septoria) nodorum, are frequently found on small grain crops, causing reduced yields and lighter weight kernels. These fungal leaf spot organisms require dew periods of 12 hours or longer for infection. The tan spot spores are wind dispersed while the Septoria spores are splash dispersed. The fungi overwinter in our region on infested wheat and/or barley residue, hence wheat or barley crops planted into same crop residue are at greater risk of these diseases if wet weather occurs during the growing season. Winter, spring and durum wheat are the hosts for the tan spot fungus and several Septoria species, while barley is host to several Septoria species, several of which may also infect wheat.

Management strategies integrated to control these fungal leaf spots include crop rotations with non-host broadleaf crops, variety choice, and early or late season fungicide use. Wheat varieties vary substantially in their response to the fungal leaf spots (Peel and Sorenson 2001). Barley varieties are all currently considered susceptible to Septoria leaf spot, although differences do exist among cultivars to other leaf spot fungi such as net blotch and spot blotch organisms (Peel 2001). Fungicides have been shown to control both early season and late season infections of tan spot and the post-boot stage infections of Septoria. Early season application of Tilt fungicide at the 2 fl oz rate, applied at the 4-5 leaf stage in a tank mix with herbicides, gave a 5.7 bu average yield increase in a study in SW ND in two wheat fields planted into wheat stubble, while no yield increase was observed with the same treatment when applied to wheat grown in sunflower stubble (Ashley et al. 2001). Applications of Folicur fungicide at the 4 fl oz/acre rate to the flowering stage of three spring wheat cultivars and three durum wheat cultivars reduced flag leaf disease severity by 45-90% in studies in ND in 2001.

Fusarium head blight (FHB) is caused primarily in by Fusarium graminearum in the US and Canada (Bai and Shaner 1994). The fungus overwinters on infested wheat, barley, or corn residue. Moisture is needed for spores to develop in the residue and then 15-48 hours of moisture on the grain head are required for infection to occur. Infection is most likely when rainy weather with long periods of dew coincide with the flowering and early grain fill period of the crops. All wheats, barley, corn, and other grasses are potential hosts.

Multiple strategies are required for effective management of FHB. Variety choice can have an important impact on the level of scab infection. Spring wheat cultivars such as Gunner, AC Barrie and Alsen have shown much more tolerance to the disease than some cultivars. Durum cultivars inherently are more susceptible than spring wheats, but some recent releases from ND, such as Belzer and Lebsock, are showing more tolerance than other cultivars. Among barleys, all malting cultivars are very susceptible, but 2-row barleys are less susceptible than 6 row cultivars. Crop rotation will reduce the disease potential in a field (Dill-Macky and Jones 2000), but under extremely favorable weather conditions, susceptible crops grown on fallow or broadleaf ground will still become infected. Crop rotation will minimize risk in a marginal environment for FHB infection. Early planting date or staggering of maturities may help a crop escape the most favorable weather for infection. Early planted grain in portions of ND in 2001 had kernels that developed prior to the period in July when rains began and favored FHB infection.

Fungicides have been tested extensively since the FHB 1993 epidemic in the Dakotas, Minnesota and Manitoba (McMullen et al. 1997). In addition to regional efforts in testing, a national effort in uniform testing has been in place for several years as part of the US Wheat and Barley Scab Initiative. Results have been mixed across locations and years and products, with reduction in FHB plot severity ranging from almost zero to 65%, and reduction in DON (vomitoxin) levels ranging from an increase in DON with some products, to a reduction of 60% with others ( Milus and McMullen 2000; McMullen 2001). Products tested have been registered, experimental or having special use registrations. Application of fungicides has been generally once, at early flowering of the main stem (Feekes growth stage 10.51). Application has been with flat fan nozzles oriented both forward and backwards toward the grain head at an angle 30⁰ from the horizontal. With ground equipment, angling the nozzles toward the grain head, instead of orienting them vertically, has given the best coverage (Halley et al. 1999).

Results in 2000 in ND indicated that the products reduced FHB severity by 54-84%, reduced DON by 20-70% and increased yield by 6-12 bushels. Tests in ND in 2001 (McMullen 2001) indicated that some experimental fungicides have great promise and did outperform available products in tests in ND. Data in ND also has indicated that Folicur fungicide applied with Lorsban insecticide at early flowering period has resulted in maximum increase in yield and reduction of disease and midge damage in areas of high risk to both FHB and wheat midge ( Jan Knodel, personal communication).

Integrated management strategies are necessary for effective reduction of root rots, fungal leaf spots, and FHB in small grain cereal crops. Reliance on a single method frequently fails. Producers need to assess which diseases are the most threat for their cropping location and system, seek information on crop cultivars best adapted for their area that have disease tolerance, and learn which seed treatment and foliar fungicide products are registered or have special registrations in their state or province.

Ashley, R.O., McMullen, M. P., Carr, P.M., Barondeau, D., and Martin, G. 2001. Seed treatment demonstration - Regent 2000. Http://www.ag.ndsu.nodak.edu/dickinso/research/2000/agron00k.htm.

Ashley, R. O., McMullen, M. P., Peterson, H., Barondeau, D., and Buckley, J. 2001. Early foliar application of tilt fungicide on hard red spring wheat in southwest North Dakota.

Http://www.ag.ndsu.nodak.edu/dickinso/research/2000/agron00o.htm.

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Clear, R.M. and Patrick, S.K. 2000. Fusarium head blight pathogens isolated from fusarium-damaged kernels of wheat in western Canada, 1993-1998. Can. J. Plant Pathol. 22:51-60.

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Gilbert, J. and Tekauz, A. 2000. Review: recent developments in research on Fusarium head blight of wheat in Canada. Can. J. Plant Pathol. 22:1-8.

Halley, S., Pederson, J., McMullen, M., and Lukach, J. 1999. Sprayer modifications for enhanced control of Fusarium head blight with fungicides. Pages 51-52 in: Proceedings of the National Fusarium head blight forum, Dec. 5-7, 1999, Sioux Falls, SD. US Wheat and Barley Scab Initiative, Michigan State Univ. (www.scabusa.org/)

Krupinsky, J., Bailey, K.L., McMullen, M. P., Gossen, B.D., and Turkington, T.K. 2002. Managing plant disease risk in diversified cropping systems. Agron. J. ( in press).

Ledingham, R. J., Sallans, B.J., and Wenhardt, A. 1960. Influence of cultural practices on incidence of common rootrot in wheat in Saskatchewan. Can. J. Plant Sci. 40:310-316.

Ledingham, R. J., Atkinson, T.G., Horricks, J.S., Mills, J.T., Piening, L. J., and Tinline, R.D. 1973. Wheat losses due to common root rot in the prairie provinces of Canada, 1969-71. Can. Plant Dis. Surv. 53: 113-122.

McMullen, M., Jones, R.K., and Gallenberg, D. 1997. Scab of wheat and barley: a re-emerging disease of devastating impact. Plant Dis. 81:1340-1348.

McMullen, M. 2001. Small grain disease survey, 2001. Pages 477-478 in: Crop Production Guide 2002. NDSU Extension Service Crop Production Guide 12. Fargo, ND.

McMullen, M. 2001. ND Uniform wheat fungicide trials, 2001. Pages 473-475 in: Crop Production Guide 2002. NDSU Extension Service Crop Production Guide 12. Fargo, ND.

Milus, G. and McMullen, M. 2000. Analysis of the 2000 Uniform wheat fungicide trials across locations. Pages 100-104 in: Proceedings of the 2000 National Fusarium Head Blight Forum, Dec. 8-10, 2000, Erlanger, KY. US Wheat and Barley Scab Initiative, Michigan State Univ.

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Peel, M. 2001. 2002 North Dakota barley, oat, rye and flax variety performance descriptions. NDSU Extension Service Circular 1-1049. 12p.

Peel, M. and Sorenson, B. 2001. 2002 North Dakota hard red spring wheat variety selection guide. NDSU Extension Service Circular A-574. 9p.

Salas, B., and Stack, R.W. 1989. Influence of tillage and crop rotation on soil populations of Cochiolbolus sativus (Abstr.) Phytopathoology 79:1005.

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Stack, R. W. and McMullen, M. 1999. Root and crown rots of small grains. NDSU Extension Circular PP-785. 8 p.

Tekauz, A., McCallum,B., and Gilbert, G. 2000. Review: Fusarium head blight of barley in western Canada. Can. J. Plant Pathol. 22:9-16.

Windels, C. E. and Wiersma, J. V. 1992. Incidence of Bipolaris and Fusarium on subcrown internodes of spring barley and wheat grown in continuous conservation tillage. Phytopathology 82:699-705.