Successful corn emergence is a combination of three key factors – environment, genetics and seed quality (Figure 1). Hybrid genetics provide the basis for tolerance to cold stress. High seed quality helps ensure that the seed will perform up to its genetic ability. Pioneer brand corn products are selected to provide the best genetics for consistent performance of across a wide range of environments, and seed production practices are optimized for maximum quality. However, even with the best genetics and highest seed quality, environmental factors can still influence stand establishment. A combination of field- and lab-based research on the effects of stressful conditions on corn germination and emergence provides valuable insights which can help farmers make informed decisions and better manage their field operations to maximize stands.
This Crop Insights will discuss how the level and timing of cold stress affects seed germination and emergence and how farmers can mitigate these stresses when planting in challenging environments.
Spring soil temperatures can vary greatly year to year. Soil temperatures at planting in combination with near- to moderate-term weather trends have profound effects on the probability of establishing optimal stands and achieving maximum yields. Researchers recorded average soil temperatures at planting depth at several stress emergence research locations in 2018 (Figure 3).
At three research locations, soil temperature dropped well-below 50°F for a week or more after planting. Figure 4 illustrates the general relationship between soil temperature and stand establishment observed at these locations in 2018.
Early planting often exposes seeds to hydration with cold water, which can cause direct physical damage. 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. The degree of damage ranges from seed death to abnormalities such as corkscrews or fused coleoptiles (Figure 6).
To help understand the importance of the timing of cold stress, two hybrids with stress emergence scores of 4 (below average) and 7 (above average) were allowed to germinate in rolled towels for 0, 24, or 48 hours at 77°F (25°C). The hybrids were then subjected to a stress of melting ice for three days and allowed to recover for four days at 77°F (25°C). Hybrids were evaluated for the number of normal seedlings reported as percent germination (Figure 7).
Both hybrids showed significant stand loss when the cold stress was imposed immediately (0 hours). However, the hybrid with a higher stress emergence score had a higher percent germination than the hybrid with a low stress emergence score. Germination rates for both hybrids were greatly improved if allowed to uptake water and germinate at warmer temperatures for at least 24 hours before the ice was added.
Planting just before a stress event such as a cold rain or snow can cause significant stand loss. The chances of establishing a good stand are greatly improved if seeds are able to germinate at least one day in warmer, moist conditions before a cold-stress event. Also, choosing a hybrid with a higher stress emergence score can help moderate stand losses due to cold stress.
One reason why temperature during imbibition is critical to corn emergence is the fact that seed imbibes most of the water needed for germination very rapidly. To illustrate the rapid timing of water uptake, seed was submerged in 50°F water for 3 hours and weighed at intervals of 30, 60, 120 and 180 minutes to determine water uptake (Figure 8).
The data show that seed imbibes the most water within the first 30 minutes after exposure to saturated conditions. If this early imbibition occurs at cold temperatures, it could kill the seed or result in abnormal seedlings. Growers should not only consider soil temperature at planting, but also the expected temperature when seed begins rapidly soaking up water. Seed planted in warmer, dry soils can still be injured if the dry period is followed by a cold, wet event.
In 2015, soil temperatures were recorded at a 2-inch depth at a research location with sandy soils near Eau Claire, WI. Daytime soil temperatures reached acceptable levels for corn development (over 50°F) for the first week after planting. However, the early morning soil temperatures dipped to as low as 38°F, and on some days the soil temperature difference between 6 AM and 6 PM was over 20°F (Figure 9). An average 16% stand loss was observed at this location, suggesting that day-night temperature fluctuation after planting can cause added stress to germinating corn. Farmers should be aware of expected night temperatures when choosing a planting date.
Stress emergence is an agronomic trait intended to reflect genetic variability for tolerance to abiotic stress in the early season. It is not a rating for disease resistance. Early season stress can promote seedling disease if certain conditions are met, including inoculum presence and prolonged cool, wet conditions. Injury to emerging seedlings will also promote seedling disease. Injury can be caused by chilling, such as imbibitional damage, or by feeding of insects such as seedcorn maggots, white grubs, and wireworms.
In environments with heavy inoculum pressure, disease progression is often in a race with seedling growth. Conditions that promote rapid soil warming will generally favor seedling growth and reduce disease incidence. On the other hand, extended cool, wet conditions will generally favor disease progression.
Many soil pathogens, including some Pythium species, are most active at temperatures in the 40s and 50s (ºF). Low temperatures such as these can injure emerging seedlings and facilitate infection. Low temperatures also impede stand establishment and increase the window of vulnerability to infection. Fungicide seed treatments generally provide good efficacy against target organisms for 10 to 14 days after planting. However, protection will be diminished if emergence and stand establishment are delayed beyond this period.
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.
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