Soybeans and corn seed rot – seedling blight and damping off
Editor’s note: This article is from the archives of the MSU Crop Advisory Team
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One of the most important management decisions in planning for a healthy crop is to use quality seed. Seed quality affects stand establishment and seedling rot in both corn and soybeans, particularly when seedlings are subjected to stress such as excessive moisture and low temperatures. In addition to quality seed, fungicide seed treatments are also highly recommended and often not optional. Fungicide seed treatments benefit stand establishment under adverse conditions such as cool, wet conditions and where pathogens are present. However, a fungicide seed treatment will not turn bad seed into good, and it will only provide a limited benefit under extreme weather and disease conditions.
A number of fungi, fungi-like organisms, bacteria and nematodes can contribute to seed and seedling rot in corn and soybeans, fungi and fungi-like organisms being the most significant. These fungi and fungi-like organisms can be divided into those that are seedborne and those that are present in the soil.
For soybeans, the soilborne pathogens Phytophthora sojae, several Pythium species and Rhizoctonia solani are considered to be the most important seedling pathogens in the North Central states. A study conducted in Iowa concluded that these three organisms compose 90 percent of soybean seedling diseases. Seedborne fungi such as Cercospora species, Phomopsis longicola or Fusarium species can also play a role in seed and seedling disease, particularly if conditions were poor for seed production in the preceding year. For more information, see the following websites:
In corn, the soilborne pathogens Pythium and Fusarium species, and Rhizoctonia are often recorded as causing seedling disease. Given the cool, wet harvest and high level of ear rot last year, we may see higher levels of corn seedborne diseases than normal. Seedborne fungi include Fusarium species, Stenocarpella maydis (Diplodia), Penicillium species and Aspergillus species. For more information, visit the following websites:
Corn and soybeans can also suffer from imbibitional chilling injury. Seeds imbibe water at temperatures above freezing and during seed imbibition (rehydration) cell membranes can rupture. At cooler temperatures (less than 50-55°F), seedling metabolism is slow, which delays membrane repair. Under warmer temperatures, injury through imbibition is repaired quickly so damage is limited. Imbibition chilling injury has the potential to kill seedlings, weaken them and slow development, even in the absence of pathogens. If pathogens are present, imbibitional chilling damage can predispose seedlings to infection. Distinguishing imbibitional chilling injury from pathogen damage can be difficult as the two are difficult to separate.