Soybean Seedling Diseases

 

Seed and seedling diseases reduce stands in the spring, with severity varying from year to year. Click on image to view a larger version. Photo credit: S.S. Navi, Iowa State Univ

Seedling health can be compromised by plant pathogenic fungi that cause seed rot, seedling death, and root decay. Seedling-infecting fungi are common in soybean fields.

Poor stands may be the first indication of a pathogen problem. Damping-off, or seedling blight, is a general name for infections that occur underground or at the soil surface, toppling the seedlings at the base.

Seedling problems are usually associated with wet soil conditions, although problems might not be noticed until some time after the wet conditions occurred. Slow germination, slow growth of soybean seedlings, poor quality seed, and plant stress all create favorable conditions for seed and seedling diseases of soybean.

Causal pathogens

Phytophthora sojae, several species of Pythium fungi, and Rhizoctonia solani are the most important seedling pathogens in the north-central states. Plant pathologists at Iowa State University have found that Pythium, Phytophthora, and Rhizoctonia account for nearly 90% of disease-related stand reduction problems in Iowa.

Other plant pathogens actively invade plants from growth stages VE to V4 as well, including Fusarium solani, Mycoleptodiscus terrestris, Macrophomina phaseolina (charcoal rot), Fusarium verguliforme (sudden death syndrome), and Phialophora gregata (brown stem rot). Seedling infection by these pathogens may cause chronic symptoms, or the infection can remain latent and cause premature decline of foliage and stems later in the growing season.

Seedborne fungi

Seedborne pathogens can also affect germination. Seed infected with Phomopsis longicola, Cercospora spp. or Fusarium spp. may rot during the germination or emergence phase.

Plant health assessment is important in the seedling stage

Frequently, seedling health is ignored because plant populations are acceptable and stem and leaves do not express symptoms during early vegetative growth. However, notes taken about plant health in the seedling phase can be used to make adjustments in crop management in subsequent years, and may explain symptoms or less-than-anticipated yield later in the season.

 

Resources

Soybean Seed Health - Iowa State University (pdf)
Soybean Seedling Health - University of Wisconsin
Fungi associated with soybean seedling disease in Iowa. Rizvi, S.S. A and X.B. Yang. 1996. Plant Disease  80 (1): 57-60 (pdf)