Effects of Early Planting on Potential for Corn Diseases

  • Seed and seedling diseases can reduce viable plant populations.
  • Early season disease development potential increases when soils are cold and wet.
  • Insect feeding damage can mimic seedling disease symptoms.

 

The potential for corn seeds and seedling plants to become infected with a disease is greatly determined by environmental conditions, use of fungicidal seed treatments, time of planting, residue from a previous crop, and the presence of causal agents (fungal or bacterial pathogens, viral vectors, and nematodes). Genetic improvements in germination and seedling growth characteristics under cool conditions has allowed for earlier and earlier corn planting. However, early planting increases the opportunity for seeds to be affected by unfavorable environmental and agronomic conditions.  

Newly planted seeds are immediately subjected to pathogenic fungi, bacteria, and soil-inhabiting insects that can infect or feed on seeds, seedling tissue, or both. In general, disease pathogens have a greater potential for causing damage when soils are wet and cold; however, some pathogens prefer warm conditions. Infected seedlings may show signs of damping-off or rotting, stunting, leaf discoloration, and deformities. If the causal pathogen is a fungus, fungicidal seed treatments can help protect the seeds from infection. If a systemic fungicide is used, the treatment can help protect the seedlings as well. Fungicidal seed treatments generally do not protect against bacterial diseases. 

Soil insect injury can mimic disease symptoms because injured plants can be stunted, wilted, or discolored (Figure 1). Therefore, it is important to dig up seedling plants to closely examine the roots and other below ground seedling tissue for evidence of insect feeding. Insects that may be a threat to seeds and/or seedlings include seed corn maggot, seed corn beetle, garden symphylan, wireworm, billbug, true white grub, stink bugs, cutworm, grape colaspis grub, and corn flea beetle. While feeding, corn flea beetles can transmit the bacterium that causes Stewart’s bacterial wilt, which has a seedling phase and a later-season phase. Should insects be the cause for seedling death, insect activity may need to be addressed depending on the life cycle and threshold for each insect if the field will be replanted. For additional information on seedling corn insects, please see  Managing Seed and Seedling Insect Pest in Corn. 

image Figure 1. Wireworm “deadheart” is caused by wireworms boring into the stem below ground. Without digging around the seedling, the insect damage could be mistaken for seedling disease.

Depending on environmental conditions and crop residue, infection by some foliar diseases may occur during the seedling stage; however, symptoms may not appear until later in the growing season. Foliar diseases that may infect seedling corn include anthracnose, holcus spot, and Goss’s bacterial wilt.  

Early season scouting is important to identify emergence issues and determine a course of action. Randomized population counts across the field should be made to determine the population levels of healthy plants. These counts, compared to projected potential yield based on planting date, can help a grower determine if replanting corn is necessary and profitable. For additional replant information, please see  Corn Replantng Decisions.

Considerations to help reduce the potential for seedling disease development include: 

  • Rotate crops to reduce crop specific disease pathogens living on crop residue. 

  • Improve soil drainage through compaction alleviation, subsurface drainage, and where practical, conservation minded surface drainage. 

  • Select seed products with high scores for emergence and rapid seed growth. 

  • Invest in fungicidal and insecticidal seed treatments. 

  • Plant when the forecast calls for a period of warm weather without cold rain. 

For more information on Seed and Seedling Diseases click on a tab.
Sources: 

Robertson, A. and Munkvold. G. 2000. Check general root and mesocotyl health when assessing corn stands. Iowa State University Extension. https://crops.extension.iastate.edu/

Jackson-Ziems, T. and Korus, K. 2013. Seedling diseases appearing in corn. University of Nebraska. https://cropwatch.unl.edu

Corn, Stewart’s wilt. The Center for Agriculture, Food and the Environment. University of Massachusetts, Amherst. https://ag.umass.edu/.

Thomas-Murphy, J. Stewart’s bacterial leaf blight. Cornell University. https://fieldcrops.cals.cornell.edu/

Malvick, D. 2018. Holcus spot on corn. University of Minnesota Extension. https://extension.umn.edu/.

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