Plant Health Initiative

Soybean Seedling Diseases

Seed and seedling diseases reduce stands in the spring, with severity varying from year to year. Photo credit: X.B. Yang

Seedling health can be compromised by several plant pathogenic fungi that cause seed rot, seedling death, and root and stem decay. Damping-off, or seedling blight, is a collective name for fungal infection that occurs underground or at the soil surface, toppling the seedlings at the base. Poor stands may be the first indication of a pathogen problem.

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.

The pathogens

Seedling-infecting fungi are soil inhabitants common to soybean fields. Phytophthora sojae, several species of Pythium fungi, and Rhizoctonia solani are the most important seedling pathogens in the North Central states. Iowa State University researchers have found that Pythium, Phytophthora, and Rhizoctonia account for nearly 90 percent of disease-related stand reduction problems in Iowa.

However, 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 during the reproductive growth stages.

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.

 

Sources

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.