The early spring seedbed is a very unfavorable environment for corn seeds. Though dry seeds can be stored unharmed for many years at -20 °F (-29 °C) or below, corn planted very early is at risk to cold injury and even death once the seeds begin to imbibe water. Early planting often exposes seeds to hydration with cold water, which can cause direct physiological damage. In addition, prolonged exposure to low temperatures reduces seed and plant metabolism and vigor, increases sensitivity to herbicides and seedling blights and causes oxidation damage due to the effects of free radicals in the cell. Free radicals are unstable molecules that damage cells and organs. This damage is similar to damage that occurs in mammalian cells during aging and sun exposure.
When the dry seed imbibes cold water as a result of a cold rain or melting snow, imbibitional chilling injury may result. The cell membranes of the seed lack fluidity at low temperatures, and under these conditions, the hydration process can result in rupture of the membranes. Cell contents then leak through this rupture and provide a food source for invading pathogens. Cold water can similarly affect seedling structures as they begin to emerge.
Corteva Agriscience routinely conducts research studies on corn germination and emergence in stressful environments, in fields where soil temperatures are at or below the minimum recommended threshold for planting corn. Results of these studies have shown that temperatures at or below 50 °F (10 °C) are often detrimental to the germination and emergence process, especially if they persist long after planting (Table 1).
Table 1. Planting dates, average soil temperature the week after planting, cumulative precipitation the week after planting, days to emergence, and final stand in Corteva Agriscience research plots in 2018.
* Values reflect averages of multiple hybrids planted at each location.
** Locations characterized as high stress environments for germination and emergence.
In Corteva research studies conducted in 2018, days to emergence and percent final stand varied considerably depending on the average soil temperature and rainfall during the week following planting. Three research locations experienced average soil temperatures below 50 °F (10 °C) with greater than 1 inch (2.5 cm) of rainfall the week following planting. These locations had substantially longer time to emergence and lower stand establishment than locations with soil temperatures above 50 °F (10 °C) and less rainfall. These data show that cold, wet soils after planting can have serious consequences for stand establishment. However, the degree of damage will vary with soil type and is generally greater in heavier or poorly drained soils.
For decades, Pioneer plant breeders have selected within the natural variation expressed by corn genotypes to develop hybrids with strong emergence and vigor characteristics under cool soil conditions. In the late 2000’s, Pioneer introduced a new rating for Pioneer® brand corn products called stress emergence. Stress emergence is a measure of the genetic ability or potential to emerge in the stressful environmental conditions of cold, wet soils or short periods of severe low temperatures, relative to other Pioneer brand products. Ratings of 7 to 9 indicate very good potential to establish normal stands under such conditions; a rating of 5 or 6 indicates average potential to establish normal stands under moderate stress conditions; and ratings of 1 to 4 indicate the product has below-average potential to establish normal stands under stress and should not be used if severe cold conditions are expected immediately after planting. Stress emergence is not a rating for seedling disease susceptibility, early growth, or speed of emergence.
Corteva research scientists are continuing to work to improve early season corn performance through conventional and molecular breeding, as well as through rigorous testing of research and commercial hybrids. By identifying molecular markers and pathways associated with superior cold germination, Corteva researchers are beginning to develop an understanding of the genetic basis of stress emergence. This knowledge should eventually lead to even stronger early-season performance in elite Pioneer brand corn products.
Table 2. Corn seedling symptoms and likely causes.
Figure 3. Fused coleoptile / bursting on the side caused by cold injury.
Figure 4. Corn seedlings with necrotic tissue resulting from flooding.
Figure 5. Corn seedings showing both brown root tissue and bursting on the side due to cold and flooded soil conditions.
The foregoing is provided for informational use only. Please contact your Pioneer sales professional for information and suggestions specific to your operation. Product performance is variable and depends on many factors such as moisture and heat stress, soil type, management practices and environmental stress as well as disease and pest pressures. Individual results may vary. Pioneer® brand products are provided subject to the terms and conditions of purchase which are part of the labeling and purchase documents.