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You Are Here Growers > Diseases > Phoma Black Stem

Phoma Black Stem

Black stem from Phoma
Black stem from Phoma
Phoma is the most common sunflower disease. In the 2007 NSA Field Survey, field incidence ranged from 10% in Manitoba to 40% in Minnesota. This disease is the result of a soil borne fungus. The infection is characterized by large dark lesions on the stem. The infection usually starts on the leaf and follows the petiole to the stalk. The large patches on the stalk become most noticeable after petal drop.

Stalks with Phoma
Stalks with Phoma
Life Cycle: The fungus overwinters in plant debris and is spread by splashing rain. The disease is often spread by the stem weevils. The larvae can spread the fungus while tunneling in the stalk.

Damage: Losses are generally minimal. Infected plants may produce smaller heads and lighter seed. The stalk lesions are on the surface only and the inner pith is not destroyed. Thus, Phoma by itself may not be a lodging factor.

Economic Thresholds: This is not well defined since there is not a fungicide treatment available.

Scouting Method: Not available

Management: There is no fungicide treatment available for this fungus. A four-year crop rotation is a good tool. Controlling the stem weevil will reduce this disease as well. Tolerant hybrids are available and most seed companies have rated their hybrids for resistance/tolerance to Phoma.

Research: Good progress has been made in overall plant health in the public and private sectors. Expect more enhancements in the near future.

Photos: Visit the Photo Gallery.

Source: NDSU Extension Bulletin 25 Sunflower Production Handbook, NDSU Extension Service, September 2007 and High Plains Production Handbook June 2005

For further information, click on the links below. Another resource about Diseases can be found in the Archive section of The Sunflower magazine.

High Plains Sunflower Production Handbook (document) File Size: 1518 kb

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High Plains Sunflower Production Handbook

NDSU Extension Bulletin 25 - Revised 9/2007 (document) File Size: 5461 kb

Download Adobe Acrobat Reader
NDSU Extension Bulletin 25 - Revised 9/2007

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