Soybean Seedling Diseases

Key Points

 

  • Fungal pathogens can cause seedling diseases as well as slow germination and plant growth..
  • Air temperatures below 68° F, wet, and poorly drained soils increase the chance of occurrence of soil borne fungal pathogens.
  • Factors that delay germination such as inadequate seedbed preparation, compaction, planting too deep, nematode infestations, and high rates of some herbicides can enhance disease incidence.
  • Seed treatments and in furrow fungicide treatments such as Acceleron® Seed Treatment Products may help reduce the damage.

Seedling diseases of soybean may decrease plant stand resulting in production losses or the need to replant. The most prevalent seedling diseases of soybean include damping off and leaf blight. The pathogens that can cause these diseases are RhizoctoniaPhytophthora, and Pythium. In springs where soybean planting is delayed, growers may be planting into warmer soil temperatures (above 60°F), which are more optimal conditions for Phytophthora and Rhizoctonia.

Damping Off in Cool Soils

 

Pre-and post-emergence damping off in cool soils or early planted fields is generally caused by the soil borne pathogen Pythium. If seedlings emerge, leaves will first appear gray-green and then turn brown. Stems or hypocotyls become soft and brownish colored, appearing water-soaked. Plants wilt and finally die. Because of its preference to cooler temperatures of 50 to 60°F, Pythium damping off is often the first seedling disease to occur.

Red lesions characteristic of Rhizoctonia. Photo courtesy of Daren Mueller, Iowa State University, Bugwood.org. Figure 1. Red lesions characteristic of Rhizoctonia. Photo courtesy of Daren Mueller, Iowa State University, Bugwood.org.

Damping Off in Warm Soils

 

Post-emergence damping off that occurs in warmer soils can be caused by several different soil borne pathogens. 1) Rhizoctonia damping off characteristically causes a firm, brown to reddish-brown sunken lesion on the root or on the lower stem. Infected stems remain firm and dry. 2) Phytophthora produces similar symptoms as described for Pythium but does not typically cause pre-emergence damping off. Phytophthora prefers warmer soils with temperatures between 75 and 80 °F being optimal for disease.

Damping off symptoms in soybean. Photo courtesy of Daren Mueller, Iowa State University, Bugwood.org. Figure 2. Damping off symptoms in soybean. Photo courtesy of Daren Mueller, Iowa State University, Bugwood.org.

Management Options

 

It is very important to determine what pathogen is present to manage it effectively. More than one pathogen may occur at the same time in the field, and the correct diagnosis is needed as different pathogens require different management approaches. Also, symptoms from seedling diseases can also be confused with herbicide injury. Seedling diseases usually tend to occur in irregular patterns compared to herbicide injury which is equipment related and uniform throughout the field.

Measures that can be taken before planting: Planting good quality seed in well drained soils can reduce disease severity. Avoid low areas of fields, if a field has a history of seedling disease problems. If the field has had a history of Phytophthora, consider planting resistant or tolerant soybean products. Finally, a fungicide seed treatment such as Acceleron® Seed Treatment Products for Soybeans can be used to protect against the damage caused by seedling diseases. Usually seed treatments with two or more active ingredients are recommended to control different pathogens.

What you can do now: If the stand reduction does not cause economic damage, then do not do anything this year. However, do take preventive measures such as seed treatment for your next soybean crop in this field as pathogens may live in the soil for several years. If there is a severe stand reduction, work with your seedsman to determine if replanting is necessary and make sure to treat the seed with the Acceleron® Seed Treatment Products.

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