Powdery Mildew of Wheat

Powdery Mildew of Wheat

Powdery mildew has been recognized as a disease problem on wheat as well as other cereals and grasses for centuries. It is common in wheat growing areas with a humid or semi-arid environment. Powdery mildew can be found in all wheat growing areas of the United States but tends to be most severe in the east and southeast. Recent literature lists the causal organism as Blumeria graminis (DC.)E.O. Speer f. sp. tritici Em. Marchal. The official listing by the American Phytopathological Society is: Erysiphe graminis DC. F. sp. tritici Em. Marchal Erysiphe graminis DC. = Blumeria graminis (DC.)E.O. Speer (anamorph: Oidium monilioides (Nees)Link). Blumeria graminis f. sp. tritici is specific to wheat. Multiple races of the fungus exist and new ones continue to be formed as a result of genetic recombination. The fungus overwinters as cleistothecia on plant debris. In warmer climates it can also survive as conidia or mycelium on infected plants. Survival on volunteer wheat is important in areas where fall seeded wheat is grown. Ascospores and conidia serve as primary inoculum. Both spores are wind blown with ascospores dispersed in midsummer and conidia dispersed in spring. Both types of spores germinate when the relative humidity is between 85-100%. Free water on host tissue is not necessary for spore germination. Host tissue is invaded directly by the germ tube. Haustoria are formed inside invaded cells and mycelium is formed on the surface of these cells. Conidia are produced on the mycelium and serve as secondary inoculum. Conidia formation and host penetration require light but most other stages of the life cycle occur in the dark. Under favorable conditions the fungus can complete a repeating cycle in 7-10 days. Disease development is favored by cool, damp weather with temperatures between 60^oF - 70^oF being optimum. Development is arrested at temperatures above 77^oF. Other factors that favor powdery mildew development are; presence of susceptible cultivars, dense plantings, and high nitrogen fertilization.

Symptoms

Symptoms may be evident anytime after plant emergence. Signs of the powdery mildew are most common on leaves but they may develop on all aerial parts of the plant. White patches of mycelium and conidia develop on upper leaf surfaces. The patches turn gray with age and dark brown or black cleistothecia develop in the mycelial mat. The lower leaf surface corresponding to the mycelial mat is chlorotic. Symptoms progress from lower to upper leaves. Severe infection can result in premature death of leaves, failure to produce heads, reduced kernel weight and lodging. Yield losses associated with powdery mildew may be as high as 40% and are most severe when infection occurs prior to or at flowering and the flag leaf becomes infected. Plant vigor is reduced as a result of reduced photosynthesis. Plants become desiccated due to increases respiration and transpiration associated with the infection.

Plant Health Management

Resistant Cultivars:

Several types of resistance are available. Those that "hold up" the longest possess multiple-gene, durable or slow-mildewing resistance. Cultivars with these types of resistance become infected but disease development is retarded and losses are minimized. Resistance of this type may last 15 years or more. Single gene or race specific resistance is also available but only lasts until a new race develops. In some cases this may be only 1 or 2 years.

Crop Rotation.

This practice is most effective if adjacent fields do not contain wheat stubble (a source of inoculum).

Destroy Volunteer Wheat.

Fungicide Application.

Compounds labeled for control include the foliar fungicides benomyl (Benlate) and propiconazole (Tilt), and the seed treatment difenoconazole (Dividend) 1997.

Plant a mixture of varieties.

This practice has been recommended as a means of incorporating genetic diversity (and resistance to a number of individual races) into a single planting.

References

Cook, R. J. and Veseth, R.J. 1991. Wheat health management. APS Press, St. Paul, MN. 152 pp.

Lipps, P.E. 1986. Powdery mildew of wheat. Ohio Cooperative Extension Service, The Ohio State University, Clolumbus, OH. AC-10.

Shi, A.N, Leath, S., and Murphy, J.P. 1998. A Major Gene for Powdery Mildew Resistance Transferred to Common Wheat From Wild Einkorn Wheat. Phytopathology 88:144-147.

Wiese, M. V. ed. 1987. Compendium of wheat diseases, 2nd ed. APS Press, St. Paul, MN. 112 pp.

Willis, W. G. 1984. Wheat diseases. Cooperative Extension Service, Kansas State University, Manhattan, KS. Publication S-23, 31 pp.

Useful Links

Cornell University

Caveat

This description is presented for information only and no endorsement is intended for products listed, nor criticism meant for products not mentioned. Always consult the product label before purchasing and using any pesticide.

Material contained on the Links from the page are the responsibility of the linked page's author(s).

This page was researched and drafted by: Jane Christensen, Department of Plant Pathology, University of Nebraska-Lincoln

Disease images were provided by: Dr. David Wysong, Department of Plant Pathology, University of Nebraska-Lincoln

Questions, Comments, Complaints and Complements?

This page is authored and maintained by:
Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln

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