Septoria Blotch of Wheat
Septoria Blotch of Wheat
Septoria blotch is one of the most common diseases of wheat grown in climates with cool
conditions is spring and fall. The disease has a world wide distribution and causes an annual
yield loss of about 2% to the global wheat crop. Many names have been associated with this
disease including Septoria Leaf Blotch, Septoria Leaf Spot, Speckled Leaf Blotch, Septoria tritici
Blotch and the Septoria complex. The causal organism is Septoria tritici Roberge in
Desmaz. (teleomorph: Mycosphaerella graminicola (Fuckel) J. Schrot. In Cohn). The
fungus has been subdivided into physiological races by some researchers but others merely
state that isolates show variability in pathogenicity. Two other fungi, Septoria nodorum and
Septoria avenae f. sp. triticea have also been associated with this disease in
the past but are now separated out as the causal organisms of Stagonospora Blotch. Wheat
is the primary host of Septoria tritici, however, barley, rye and other grasses including Poa and
Agrostis spp. are also susceptible hosts. The fungus overwinters as mycelium or
pycnidia on leaves of cultivated or volunteer wheat. Oversummer survival occurs as pycnidia
on plant debris and volunteer wheat. The fungus also survives for long periods of time (up to
3 years) on wheat stubble. Primary inoculum consists of conidia (pycniospores). Ascospores
, produced in pseudothecia, also serve as primary inoculum for late summer and fall
infections. Infection may occur at any stage of plant development and disease development is
favored by cool wet weather. Spores are exuded from pycnidia in a sticky mass and are
splashed or windblown. Conidia germinate and invade host tissue by direct penetration
through stomata. A six-hour period of leaf wetness is required for infection to occur. The
optimum temperature range for disease development is 60 - 70oF. Pycnidia are formed at
infection sites and secondary conidia serve as inoculum for repeated cycles of Septoria Blotch.
Disease development is arrested by hot, dry weather in late spring and early summer and
by temperatures that remain consistently below 40oF in late fall.
Symptoms
All aerial parts of the plant as well as the roots may be affected by infection by Septoria tritici,
however leaf infections are most common. Chlorotic spots on leaves characterize initial
infection. Spots enlarge longitudinally and are vein limited with parallel sides. Leaf spots are
initially water-soaked then dry and change in color from yellow to reddish brown. They are
often surrounded by a yellow margin. Centers of spots become light brown to gray and
develop small black fruiting bodies (pycnidia). The pycnidia often appear in rows since they
form in substomatal cavities. Leaf infection usually occurs first on lower leaves in contact
with the soil. Heavily infected leaves become yellow, wither and die. Leaves may also die
prematurely when lesions are formed near the base of the blade. Leaf sheaths and stems
(primarily nodes) may become infected. Infected nodes may be dark and sunken and may
also contain pycnidia. Infection also occurs occasionally on the tips of glumes. Heavy
infection in the fall results in reduced root development that may contribute to higher stand
loss due to root and crown rot.
Plant Health Management
Residue management.
Septoria leaf blotch is one of many diseases that increase in incidence and
severity with conservation tillage. However, removal of residue may not be feasible
where conservation tillage is commonly used as a means of controlling erosion and
retaining soil moisture.
Crop rotation.
Rotate every third or fourth year to oats, row crops or alfalfa.
Destroy volunteer wheat.
Delay planting winter wheat until Hessian fly-free date.
Fungicide application.
Compounds labeled for control of Septoria blotch include benomyl (Benlate),
mancozeb ( Dithane, Manzate 200 and Penncozeb), propiconazole (Tilt), and
triadimefon (Bayleton) 1997. The label may list the disease by other names such as
Speckled Leaf Blotch or Septoria Leaf Spot.
Resistant Cultivars.
Intermediate or moderate resistance is available is some cultivars.
References
Leath, S., Scharen, A.L., Lund. R.E., and Dietz-Holmes, M.E. 1993. Factors associated with
global occurrences of Septoria nodorum blotch and Septoria tritici blotch of wheat. Plant Dis.
77:1266-1270.
Nyvall, R.F. 1989. Field crop diseases handbook, 2nd ed. Van Nostrand Reinhold, New York,
NY. 817 pp.
Watkins, J.E. 1984. Septoria leaf blotch of wheat. Cooperative Extension Service, Institute of
Agriculture and Natural Resources, University of Nebraska - Lincoln. NebGuide G84-701.
Wiese, M.V., ed. 1987. Compendium of wheat diseases, 2nd ed. APS Press, St. Paul, MN.
112 pp.
Zelikovitch, N., and Eyal, Z. 1991. Reduction in pycnidial coverage after inoculation of wheat
with mixtures of isolates of Septoria tritici. Plant Dis. 75:907-910.
Useful Links
Highlighted Area
Septoria blotch or Stagonospora blotch?
These two diseases are very similar. They have the same hosts and similar symptoms.
The two "blotches" may coexist in some of the same geographic areas and they may both be
present on an individual plant. So, what's a Plant Pathologist to do when it comes to
identifying which disease is present on a given plant? The answer lies in the morphology of
the pycnidiospores. Septoria tritici (Septoria blotch) has the longer spores measuring
1.7-3.1 x 39-86 micrometers with 3 to 7 septations. They are threadlike in shape.
Septoria nodorum's pycnidiospores are 2-4 x 15-32 micrometers in size, have 1, 2, or
3 septations and rounded ends. Septoria avenae f. sp. triticea pycnidiospores are
intermediate between the other two. They are 2.5-4.5 x 21-45 micrometers in size, are
straight with rounded ends and have 3 or 4 septations. As you can see some spores from
the different species may overlap in size so it may be necessary to measure a number of
spores in order to get an accurate identification. The three fungi also differ somewhat in the
type of colonies they produce on artificial media so culturing may also be necessary to
correctly identify the pathogen.
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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Copyright (C) 2003 J.E. Partridge, University of Nebraska-Lincoln. All Rights Reserved.
