Anthracnose of Soybean

Anthracnose of Soybean

Anthracnose is common in soybean growing areas worldwide, especially where and when warm humid conditions exist. Several species of Colletotrichum have been associated with the diseases. The two most commonly cited fungi causing the disease are Colletotrichum truncatum (Schwein.)Andrus & W.D. Morre = C. dematium (Pers.) Grove f. truncatum (Schwein) Andrus & W.D. Moore and Glomerella glycines F.Lehm. & F.A. Wolf (anamorph: Colletotrichum destructivum O'Gara). These fungi have a broad host range that includes soybeans, alfalfa and numerous weedy hosts (see highlighted area). The fungi overwinter as mycelium in crop debris and in infected seed. The mycelium is the source of primary inoculum and infects plants during seedling development. Infection is most common during wet springs and plants show a range of symptoms. Seeds or seedlings may be killed or the fungus may remain latent in the plants until they start to bloom. The fungus becomes systemic at flowering and produces its characteristic fruiting structures on plant tissue (primarily stems) . Aceruvli containing long black "hairs" (setae) and conidia. When the Glomerella stage of C. detructivum is present, submerged perithercia containing ascospores are also produced on host tissue. Spores from these fruiting structures serve as the source of inoculum for secondary infection. Optimum weather conditions for disease development are warm temperatures (greater than 25^oC) with accompanying moisture (dew, fog, high humidity or rain). Anthracnose also tends to be more severe when the crop is planted with a narrow row spacing. Seed infection occurs when mycelium produced on infected pods penetrates the pod tissue and infects developing seed.

Symptoms

Host plants may become infected at any stage of development and as a result exhibit a wide range of symptoms. Early season symptoms are seed rot or pre- or post-emergent damping-off. Post-emergent damping off is characterized by the development of brown, sunken, water-soaked lesions on the cotyledons. The cotyledons eventual wither and are shed. The fungus grows from the cotyledons to the stem where sunken lesions (cankers) are also produced and eventually leading to the death of young seedlings. Infected seedlings which do not die early appear healthy until blossom. At this time symptoms begin to develop. The most common symptoms are brown, irregularly shaped spots on stem, pods and petioles. Girding of petioles by large lesions results in premature defoliation. When pod are infected mycelium may completely fill the cavity and no seeds are produced (pod blanking) or fewer and/or smaller seed form. Seed that does form may appear brown, moldy and shriveled or may look normal. Dark acervuli and/or perithia develop in lesions on all host tissues areas. Leaf infections, which generally develop as the result of secondary infection by conidia may exhibit, leaf rolling, necrosis of laminar veins, petiole cankers and premature defoliation. In general, infected plants appear stunted and may have significant yield reduction.

Plant Health Management

Plant disease free seed

Use fungicide treated seed.

Captan and thiram are labeled for control of seedling blights (1997).

Apply foliar fungicides during the growing season.

Fungicide application shouldbegin at bloom and follow manufacturer's recommendations for scheduling. Labeled compounds for anthracnose control include benomyl, chlorothalonil and thiophanate-methyl (1997).

Crop rotation.

Residue management

Destruction of residue may not be possible if conservation tillage has been implemented. In this case, crop rotation may be necessary to appropriately manage the residue.

References

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

Sinclair, J.B. 1988. Anthracnose of soybeans. Pages 92-95 in Soybean Diseases of the North Central Region. T.D. Wyllie and D.H. Scott, eds. American Phytopathological Society, St. Paul, MN.

Sinclair, J.B. and P.A. Backman, eds. 1989. Compendium of soybean diseases, 3^rd ed. American Phytopathological Society, St. Paul, MN.

Useful Links

Texas A&M University

Highlighted Area

C. trucatum

Caveat

This description is presented for information only and no endorsement is intented 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

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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