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Factors that can contribute to less than ideal stands include: planting into a poorly prepared seedbed, improper planter adjustments, poor quality seed, soil crusting or compaction, inadequate or excessive soil moisture, seedling diseases and insect pests, herbicide damage, and numerous environmental issues.
Soil Crusting and Compaction. Soil crusting can delay or prevent seedling emergence. Soybean seedlings tend to have more difficulty than corn when trying to penetrate crusted soils. In soybean, soil crusting can cause hypocotyls to become swollen or break when trying to push through the crust. When the hypocotyl breaks, the seedling usually dies. In corn, soil crusting can result in the formation of a twisted mesocotyl during elongation, and cause leafing out underground. Fields with fine- textured soils, low organic matter, and little surface residue can be vulnerable to crusting, especially where excessive tillage has taken place.
Figure 1. Emergence problems in corn. (Top) Soil compaction. Photo courtesy of J. G. Davis, Colorado State University, Bugwood.org. (Right) Corn leafing out underground.
Tilling fields when the soil is too wet can cause soil compaction. Additionally, disk openers slicing through wet soil can create sidewall compaction in the seed zone. Any type of soil compaction can result in decreased seedling germination and restricted root growth and nutrient uptake (Figure 1). To test if a field is fit to plant, take soil from the top 3 to 4 inches; soil should break apart when pressed between fingers rather than forming a ribbon or ball.
Figure 2. Above ground damping-off symptoms in soybean. Photo courtesy of Daren Mueller, Iowa State University, Bugwood.org.
Chilling Injury. Early planted corn seeds and seedlings can be at risk for chilling injury if they are exposed to soil temperatures under 50 ºF for an extended period of time and/or experience large swings (25 to 30 ºF) in daily soil temperatures. Chilling injury can result in failed germination and/or hindered growth of the radical or coleoptile if it occurs within 24 to 36 hours after planting, and corkscrewed mesocotyls and/or leafing out below the soil surface if it occurs during the emergence process (Figure 1).
Figure 3. Seedcorn maggot larvae feeding on a corn seed.
Seedling Diseases. Wet and cool soil temperatures can delay germination and emergence and predispose seedlings to disease. Management options are generally the same for all seedling diseases. Plant high quality seed at the appropriate planting depth and soil conditions to promote rapid germination and emergence. Avoid planting too early in fields that have a history of seedling diseases. Broad spectrum seed treatments can provide a level of protection against seedling pathogens, but may not eliminate all threats under severe environmental conditions that favor infection.
Figure 4. Herbicide carryover injury from ALS herbicides. Bottom photo courtesy of Purdue University.
Insect Injury. Insects that feed on corn and soybean seeds and seedlings can cause stunting, delayed emergence, and stand loss. While rescue treatments are available for some early-season insects, timing is critical, making preventative treatments essential for some species. Soil insecticides and seed treatments can provide a good level of control for up to 30 days after planting.
Herbicide Carryover. Applications of soil-applied herbicides immediately before or after planting, coupled with stressful conditions such as dry or cold weather, may result in a high concentration of the herbicide near emerging seedlings and increase the potential for injury. Applications made several days or weeks prior to planting may allow the herbicides to be more evenly distributed in the soil profile. Good weed management planning and recordkeeping is necessary to help minimize potential carryover problems.
Nielsen, R.L. 2012. Early planted corn & cold weather. Purdue University Extension. http://www.agry.purdue.edu. Web sources verified 3/25/16. 160328090827