An important group of seed-borne fungal diseases of soybean are collectively known as the Diaporthe/Phomopsis complex. This group of diseases includes Phomopsis Seed Decay, Pod and Stem Blight, and Stem Canker. All three diseases are caused by Phomopsis or Diaporthe species.

Symptoms
Phomopsis Seed Decay causes soybean seed to become cracked, shriveled, and white in appearance. Seed may be infected and not show any symptoms. Planting infected seed provides a source of the fungus for field infection. Soybean pods can become infected and later infect seed.

Pod and Stem Blight can be difficult to detect in the field as symptoms do not always develop on leaves or stems. The fungus can be found on dry stems and pods and is spread by plant residue as well as infected seed.

Stem Canker produces lesions on stems and leaves. This disease can cause seedlings to die in the field thus reducing overall stand. This disease is again spread by plant residue and infected seed.

Control
These fungal diseases can be controlled by:

• planting disease-free seed
• resistant varieties

Testing
The Seed Department conducts an agar test for Diaporthe/Phomopsis using a minimum sample size of 500 seed. This test is typically completed in seven days and results are reported as a percentage of infected seed.