Sorghum Downy Mildew
Sorghum Downy Mildew
This disease is caused by the fungus Peronosclerospora
sorghi (Weston & Uppal) C.G. Shaw = Sclerospora sorghi
W. Weston & Uppal. Hosts of the fungus include grain sorghum
and other Sorghum spp., corn, teosinte, millet and Panicum
spp., many of which are common weeds of Nebraska. The fungus
overwinters as oospores in the soil, both free and contained in
plant debris. It can also survive in perennial grasses. Mycelium
can be found in seed embryos, but looses its viability when seed
moisture drops below 20%. Plants can be systemically or locally
infected. Systemic infection occurs when oospores germinate and
invade the roots. Infections occurs under conditions of low soil
moisture and temperature. Mycelium grows internally from roots
to meristematic leaf tissue. Conidia produced on leaves as a
result of systemic infection are windblown to nearby plants and
provide the inoculum for secondary (local) infection. Infection
occurs when conidia germinate and enter leaf tissue via stomata.
If new leaves are infected before they are fully developed the
mycelium from a local infection may enter meristematic tissue
in the shoot and produce a systemic infection.
Symptoms
Systemically infected seedlings are chlorotic
and stunted. The chlorosis may be more noticeable on the lower
half of the leaf. Young plants may die prematurely. Infected
plants that survive the seedling stage produce a mixture of interesting
symptoms. Under cool, humid conditions a white downy growth is
produced on the lower leaf surface. This growth is a combination
of conidia and conidiophores. Conidia are only produced at night
and require a layer of moisture on the leaf for spore production
to occur. As the plant matures, leaf symptoms become more striking.
Older leaves may exhibit alternating parallel stripes of green
and yellowish-green to white tissue. The tissue in the lighter
stripes eventually dies and leaves become shredded, resembling
hail injury. Oospores are produce in these leaves and are released
when shredding occur. Heads produced on these plants are fully
or partially sterile. Symptoms of local infections are a little
less dramatic. Short necrotic streaks (stipples) are produced
on leaf blades. Downy conidial growth on leaves is also associated
with these infections.
Plant Health Management
Crop Rotation.
Tillage practices associate with crop rotation serve to bury inoculum in the soil and
decrease its viability.
Chemical seed treatment.
Seed treatment fungicides containing metalaxyl are labeled for use on sorghum for control
of sorghum downy mildew (1997).
References
Frederiksen, R.A. 1980. Sorghum downy mildew
in the United States: overview and outlook. Plant Disease
64:903-908.
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 Univ. System, Texas Agricultural
Extension Serv. 25M--4-80. 16 pp.
Nyvall, R.F. 1989. Field crop diseases handbook,
2nd. ed. Van Nostrand Reinhold, New York. 817 pp.
Partridge, J.E. and B.L. Doupnik. 1979. Occurrence of sorghum downy mildew on
shattercane and sorghum in Nebraska. Plant Dis. Reptr. 63:154-155.
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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 buying and using any fungicide.
Material contained on the Links from the page are the responsibility of the linked page's author(s).
Questions, Comments, Complaints and Complements?
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
This page is maintained by:
Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln
jpartridge1@unl.edu
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Copyright (C) 2003 J.E. Partridge, University of Nebraska-Lincoln. All Rights Reserved.
