Septoria Leaf and
Glume Blotch

Washington State University Bulletin

SP0004 -- 1993

Diseases of Washington Crops.

Otis c. Maloy and Debra Ann Inglis

 

Small Grains Home * Wheat Diseases * Barley Diseases

Cause

Hosts

Symptoms and Signs

Disease Cycle

Control

1997 PNW Pesticide

Recommendations

Another Picture

Other interesting Septoria Leaf and Glume Blotch sites

Septoria leaf and glume blotch are two diseases caused by different species of Septoria. Both diseases occur throughout the state but generally are not severe. Glume blotch has occasionally caused noticeable damage in more moist wheat growing areas in western Washington.

Cause
The two diseases are caused by the fungi, Septoria tritici and S. nodorum. The sexual stages, Mycosphaerella graminicola and Leptosphaeria nodorum, respectively, occur but are not commonly seen. S. tritici forms round, gray-brown pycnidia. Conidia are threadlike, 3- to 7septate, having often indistinct septations. The conidia are extruded from the pycnidia in milkwhite to buff-colored cirrhi. S. nodorum conidia are shorter and broader than those of S. tritici, having 1,2 or 3 septations and rounded ends. The cirrhi are pink. S. tritici is usually regarded as the cause of leaf blotch, while S. nodorum is the cause of glume blotch. Both species grow best at 68-79F with limits at 38 and 90F.

Hosts
Most smal1 grains and many grasses are affected, but wheat is the only important commercial host.

Symptoms and Signs
Septoria leaf spot first appears as small, light green to yellow spots between veins of the lower leaves. The spots elongate to form light brown to reddish brown, irregular lesions. Scattered, small, dark brown to black pycnidia, easily seen with a hand lens, are embedded in lesions, which sometimes have ashen centers.

Glume blotch develops mainly in areas where the weather is warm and moist. It appears as small, irregular gray to brown spots or blotches on the glumes, although infections may also occur at the nodes. When the lesions enlarge, a sprinkling of pycnidia develop.

Disease Cycle
The fungi survive on seed, straw or stubble. Conidia can remain viable for several months between 34 and 50F in the slime in which they are exuded. S. nodorum tolerates even warmer temperatures. At least 6 hours of wetness and temperatures between 41 and 95F are needed for infection. Prolonged wet, windy weather favors Septoria diseases.

Ascospores or conidia germinate to infect directly through the epidermis or through stomata. Eventually pycnidia develop. Secondary disease cycles occur as long as weather conditions are favorable and host tissue is available.

Control
Chemical. Protective foliar sprays are used in areas where losses are severe. Seed treatments with appropriate fungicides can also reduce disease severity.

Cultural. Plant Septoria free seed. Early seeding of winter wheat promotes good growth in the fall and increases both the over-wintering vigor of the plants and their ability to withstand damage. Rotating crops out of cereals and grasses for 3-4 years, deep plowing wheat stubble, and destroying volunteer hosts reduce the amount of inoculum. Minimum tillage practices may increase disease risk. Septoria diseases are especially prevalent when wheat has dense foliage and is heavily fertilized.

References
Eyal, Z., A.L. Scharen, J.M. Prescott, and M. van Ginkel. 1987. The septoria diseases of wheat: Concepts and methods of disease management. Mexico, D.F. CIMMYT.

Luke, H.H., R.D. Barnett, and P.L. Pfahler. 1986. Development of Septoria nodorum blotch on wheat from infected and treated seed. Plant Disease 70:252-254.

Other Interesting Septoria sites:
Alberta Agriculture, Food and Rural Development -- description and pictures.

University of Nebraska NebGuide -- description and pictures.