See:
Fungicide Effectiveness as Seed Treatments for Cereal Diseases
Cause Pythium spp. (syn. Globisporangium spp.) are fungus-like microorganisms that live for years in soil and on old root debris, parasitizing the roots of wheat and many other plant species. The disease can be important in all wheat-producing areas.
Recently the genus Pythium Pringsheim (nom. cons.) sensu lato (s.l.) was reorganized into three genera based on DNA sequencing and molecular phylogenetics: Pythium, Elongisporangium, and Globisporangium. Wheat can develop root rot in addition to seed rot and damping-off in the PNW and other regions due to a range of Pythium and Globisporangium spp., including P. abappressorium, P. aristosporum, P. arrhenomanes, P. debaryanum, P. heterothallicum, G. irregulare (formerly P. irregulare), P. sylvaticum, P. torulosum, and G. ultimum (formerly P. ultimum). Research conducted at Washington State University showed that P. abappressorium, G. irregulare, and G. ultimum decreased wheat emergence while P. abappressorium, P. debaryanum, P. heterothallicum, G. irregulare, and G. ultimum caused significant reductions in root growth with the latter species causing the most severe disease.
Symptoms Mild infections may reduce stand numbers and tillering, and delay maturation. Adult plants may be stunted and/or chlorotic, as if nitrogen deficient. Root length may be reduced. Heads may contain shriveled grain. Symptoms are often uniform across the field and are difficult to recognize and diagnose. Severe infections cause a general root rot.
Cultural control
- Plant when soil temperature (about 50°F) allows seeds to germinate and establish quickly.
- Use high-quality seed and supplemental phosphorus.
Chemical control Seed treatment reduces seedling infection.
- Acquire (Group 4) at 0.75 fl oz/100 lb seed plus a dye. See label for reentry restrictions.
- Allegiance-FL (Group 4) at 0.75 fl oz/100 lb seed plus a dye. See label for reentry restrictions.
- Apron XL (Group 4) at 0.32 to 0.64 fl oz/100 lb seed plus a dye. See label for reentry restrictions.
- Intego Solo Fungicide Seed Treatment (Group 22) at 0.2 to 0.3 fl oz/100 lb of seeds. 12-hr reentry.
References Chamswarng, C., and Cook, R.J. 1985. Identification and comparative pathogenicity of Pythium species from wheat roots and wheat-field soils in the Pacific Northwest. Phytopathology 75:821-827.
Ingram, D.M., and Cook, R.J. 1990. Pathogenicity of four Pythium species to wheat, barley, peas and lentils. Plant Pathol. 39:110-117.
Nguyen, H.D.T., Dodge, A., Dadej, K., Rintoul, T.L., Ponomareva, E., Martin, F.N., de Cock, A.W.M., Lévesque, C.A., Redhead, S.A., and Spies, C.F.J. 2022. Whole genome sequencing and phylogenomic analysis show support for the splitting of genus Pythium. Mycologia 114(3):501-515. https://doi.org/10.1080/00275514.2022.2045116.
Paulitz, T.C., and Adams, K. 2003. Composition and distribution of Pythium communities in wheat fields in eastern Washington state. Phytopathology 93:867-873.
Paulitz, T.C., Adams, K., and Mazzola, M. 2003. Pythium abappressorium - a new species from eastern Washington. Mycologia 95:80-86.