Crazy Top Downy Mildew

Crazy Top Downy Mildew

This disease is caused by the fungus Sclerophthora macrospora (Sacc.)Thirumalachar et al. = Sclerospora macrospora Sacc. Crazy top is most commonly seen on sorghum and corn in Nebraska but it has a wide range of hosts including wheat, oats, rice, crabgrass, witchgrass, green foxtail, barnyard grass and many other grasses. The fungus overwinters as oospores in buried crop debris and grassy hosts. Oospores germinate and produce zoospores when soils are saturated for 24-48 hrs. Zoospores move through the soil on a film of water and infect roots of seedling plants at the zone of elongation. Coenocytic intercellular mycelium is produced in the host. It is prevalent in meristematic tissue and spreads throughout the entire plant. Sporangiophores are formed in stomata and produce sporangia. Zoospores released from these structures provide secondary inoculum. As the season progresses, oospores are formed in infected leafy tissue, including leaf blades, leaf sheaths, ear husks and foliar portions of the tassel, and remain in debris between crops. Oospores are formed in association with vascular tissue. Xylem cells in close proximity to oospores enlarge and become distorted . When the fungus overwinters in perennial grasses, the source of primary inoculum is

Symptoms

The first symptoms of crazy top on young sorghum plants is mottled chlorosis of the leaves. As disease development progresses, leaves become stiff, twisted or curled and yellow. Affected leaves may exhibit more than one symptoms such as twisting together and curling downward. Leaves commonly have a bumpy texture in addition to the other symptoms. Heads may be absent or contain few or no seeds and an abundance of leafy shoots (phyllody). Plants may also exhibit excessive tillering. Symptoms on corn are the same as on sorghum with the additions of phyllody in the ears.<

Plant Health Management

Currently, the only known means of controlling crazy top is to avoid planting susceptible hosts in areas of the field with a known history of poor drainage or to take steps to improve drainage in these areas.

References

Frederiksen, R.A. 1986. Compendium of sorghum diseases. American Phytopathological Society. St. Paul, MN. 82 pp.

Horne, C.W. and R. W. Berry. 1980. Sorghum diseases atlas. The Texas A&M University System, Texas Agricultural Experiment Station 25M-4-80.

Nyvall, R.F. 1989. Field crop disease handbook, 2nd. ed. Van Nostrand Reinhold, New York. 817 pp.

Schurtleff, M.C. ed. 1980. Compendium of corn diseases, 2nd. ed. American Phytopathological Society. St. Paul, MN. 105 pp.

Whitehead, M.D. 1958. Pathology and pathological histology of downy mildew Sclerophthora macrospora, on six graminicolous hosts. Phytopathology 48:485- 493.

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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 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

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

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