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STRESS EMERGENCE AND FROST IMPACT ON CORN STAND ESTABLISHMENT AND GROWTH return to table of contents by Kelly Herbick, Technical Product Manager OVERVIEW • On May 14th and 15th, a widespread frost event impacted the Upper Midwest, causing significant crop damage to germinating corn and soybean fields. • Crop injury was documented by Pioneer sales professionals in a “Frost Survey App” to determine the scope and impact of the weather event. Over 100 fields were visited where leaf tissue damage ratings were made and stand counts were taken. • While limited replant was required, many emerged fields suffered severe damage and required 1 to 2 weeks to recover. • The results of this survey are shown below and highlight stress emergence, frost impact, recovery, and management considerations. STRESS EMERGENCE IMPACT • 2016 crop planting began early with a significant number of acres planted in mid to late April. • While daytime soil temperatures warmed to the mid 60s, soil conditions were volatile with temperatures dropping into the 40s as germination began. • Fluctuating soil temperatures stressed germinating seedlings, and a higher percentage of cold stressed seedlings were documented during this period. • The following soil temperature data were captured at the Eau Claire Research Station and provide an example of spring soil temperature fluctuations for the region (Figure 1). STRESS EMERGENCE TAKEAWAYS • Coarse textured soils have more porosity and are prone to fluctuation in air temperature; therefore, they were more likely to experience stressful emergence conditions from early planting. • Corn hybrid response to stress emergence varied by genetics. • Cold soil temperatures at planting, as well as large ( >20 ºF) temperature swings, impacted seedling germination and emergence. • When outliers were eliminated and stand count deviation was graphed, several planting dates appear to have been impacted by stress emergence as shown in Figure 2. Stand Loss (plants/acre) 8,000 7,000 6,000 5,000 4,000 3,000 2,000 1,000 0 Figure 2. Stand reduction (target stand – final stand) by planting date as reported in the frost survey (2016). 90 Max: Temp, ºF Min: Temp, ºF 80 70 60 50 40 30 4/13 4/15 4/17 4/19 4/21 4/23 4/25 4/27 4/29 5/1 5/3 5/5 5/7 5/9 5/11 5/13 5/15 5/17 4/13 4/15 4/17 4/19 4/21 4/23 4/25 4/27 4/29 5/1 5/3 5/5 5/7 5/9 5/11 5/13 5/15 5/17 Temperature (ºF) Figure 1. Maximum and minimum soil temperatures reported at the Eau Claire Research Station (2016). Corn seedlings exhibiting stress emergence symptoms from 2016 – corkscrewing and leafing out underground as a result of challenging soil conditions. 50

eturn to table of contents FROST IMPACT • A return to warmer temperatures aided crop recovery. • Because frosted plants are dependent on seed reserves and an immature root system for regrowth, health of plant structures was a good indicator of seedling survival. • Inspection of plants that were slow to recover or did not recover almost always revealed an additional stress factor. Some examples include: shallow seeding depth, seedling disease, insect damage, starter herbicide injury, or damage to the seedling mesocotyl. • Additional considerations for frost damaged corn fields are as follows: »» Frost damage may have thinned stands or resulted in uneven crop development as plants suffering most severe damage struggled to regrow. »» Plant staging following frost must account for initial leaf collars when determining V-stage. This is critical to follow herbicide label application guidelines. »» Herbicides applied immediately after frost (within 48 hours) may have enhanced plant stress and slowed recovery. »» Early season frost damage may cause delayed crop maturity and variability in crop development leading to higher moisture content at harvest. »» While it is difficult to predict the direct yield impact of frost damage, it is likely that fields impacted by severe frost injury may see a slight yield reduction from thinned stands and increased interplant variability. FROST RECOVERY Day 1 Day 3 Image 1 (left). Morning following overnight lows of 28 ºF. Note watersoaked leaf tissue. Image 2 (below, left). May 18, three days post-frost. Note regrowth pushing above soil line. Image 3 (below). June 7, three weeks post-frost. Note regrowth and interplant variability. Day 23 Figure 3 (below). Corn stand reduction in surveyed fields associated with stressful emergence conditions. Red: > 6,000 plants/ acre reduction from target stand, yellow: 2,000-6,000 plants/acre reduction, green: < 2,000 plants/acre reduction. Stand reduction at select locations east of St. Cloud, MN, may have been exacerbated by soil crusting. 51

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