Iowa Corn, Soybeans: Cold, Wet Conditions Increase Risk of Soil-Borne Diseases

    Soybean seedlings, one rotten and one slow to emerge, from a soybean field with extensive stand loss due to seedling disease. Photo: University of Missouri

    Brrrrrrrrr.  Is summer ever going to come?  It’s cold.  It’s wet.  Planting progress is behind and everyone is starting to get antsy. When we finally get our seed in the ground, as Emily Unglesbee so eloquently wrote, “a dark, damp basement, teeming with unknown horrors” awaits.

    Those unknown horrors include soilborne pathogens, particularly Pythium and the SDS pathogen, Fusarium virguliforme, that thrive in cold wet soils.  Other Fusarium and Rhizoctonia species may also infect seedlings. Infection results in seed rot, root rot (Figure 1) and seedling death, and consequently stand loss.  Seedlings that survive infection are often less vigorous; for corn, this may mean uneven stands in which infected seedlings grow slower than their neighbors and fail to produce an ear.

    Rotted radicles of corn seedlings

    Figure1. Radicle root rot of corn caused by Pythium species.  Although these seedlings are likely to survive infection, they may be less vigorous than neighboring non-infected seedlings. Click Image to Enlarge

    What can you do to ensure your crop gets off to the best start?

    1. Wait for good planting conditions.

    Be patient.  Easier said than done right!

    2. Use seed treatments.

    This is the year to be using a seed treatment.  Soilborne pathogens are attracted to germinating seedlings by the exudates the seedlings leak.  The longer the seeds take to emerge, the more time they are susceptible to infection.  Seed treatments contain a mix of fungicides that protect the seed from these pathogens.  As you might expect, the efficacy of seed treatments varies among various pathogens.  The Crop Protection Network has a useful publication that compares the efficacy of commercially available fungicides against various seedling pathogens.

    3. Scout.

    Scouting your fields soon after emergence will be important. You’ll want to do stand counts and examine your seedlings for symptoms of seedling disease: rotted seed, root rot, mesocotyl rot (corn), and yellowed, wilted seedlings.  Remember, stand issues can be caused by planter issues or insects (see this article from Erin Hodgson and Ashley Dean).  Understanding what caused your stand problem is important, and can help with crop management in future years

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