Corn Crop Damaged by Drought and Record High Temperatures (Field Facts)

Introduction

Drought combined with record high temperatures has severely damaged the corn crop over a historically wide area this year. The worst damage in Illinois and Indiana appears to be to corn that pollinated during a heat wave from June 28 to July 7. During this critical crop development period, sensitive silks, pollen and newly fertilized ovules were exposed to excessively high temperatures and severe water stress across much of the region (Figures 1 and 2). In many of these areas, drought began before or shortly after planting and has persisted into flowering and grain fill.

June to early July temperatures at Springfield, IL. Data from NOAA, National Weather Service, Central Illinois Weather Forecast Office (2012).

Figure 1. 2012 June to early July temperatures at Springfield, Ill. Data from NOAA, National Weather Service, Central Illinois Weather Forecast Office.

Impact of Drought and Heat Stress on Yield

Corn yield is most highly correlated to kernel number per acre (85%) and to a lesser degree kernel size (15%). Drought and excessive heat can negatively impact both parameters. Stress during pollination can greatly reduce kernel number. Some hybrids delay silk emergence much more than pollen shed. When silk emergence is delayed several days, pollen shed may be mostly complete before silks finally emerge. This can result in poor pollination and dramatically reduced yield.

One common characteristic of more drought-tolerant hybrids such as Pioneer's Optimum® AQUAmax® corn products is the ability to maintain strong silking in synchrony with pollen shed under stress conditions. Although a certain minimum amount of water is required for any hybrid to pollinate and produce a crop, hybrids that maintain silk and pollen synchrony have a higher likelihood of successful pollination under stress. A second characteristic that can be beneficial is early flowering. Hybrids that flower early for their maturity may escape severe stress during the hottest days of summer.

Drought stress during grain fill results in reduced kernel size. All areas in Indiana and Illinois have thus far received from 2 to 10 inches less rainfall than normal, creating a severe deficit leading into grain fill (Figure 2). Corn water demand exceeds 1.5 inches per week during early grain fill so the kernels that have set thus far will need timely rainfall to fill and mature.

Impact of High Night Temperatures on Yield

Prolonged drought has been exacerbated by record-breaking heat. Fortunately, recent night temperatures have been relatively cool. Under high night temperatures, corn plants utilize much of the carbohydrates made during the day for respiration at night, leaving fewer carbohydrates available for grain fill. High night temperatures also contribute to rapid GDU accumulation, accelerating crop development and reducing the number of days in which solar radiation is captured for photosynthesis and amassing crop yield.

Summary

No one can predict when stresses like extreme heat and drought occur. Yield results from 2012 may not accurately reflect the long-term stability of a hybrid. When selecting hybrids for next season, base decisions on multi-year and multi-location data. Other practices that reduce overall risk include utilizing a genetically diverse hybrid portfolio, and using a range of relative maturities and planting dates.

Accumulated Precipitation (inches) Departure from Mean

Accumulated precipitation departure from mean for the period of May 1 to July 13, 2012.

Figure 2. Accumulated precipitation departure from mean for the period of May 1 to July 13, 2012. Map from the Midwestern Regional Climate Center, University of Illinois.

Historical Comparisons of 2012 Drought

With persistent drought conditions across much of the U.S., many are making comparisons to past droughts, most notably, 1988, 1983 and the worst dust bowl years such as 1936. Below are maps for those years showing departure from the mean for rainfall and high temperatures for May 1 to July 13 (source: Midwestern Regional Climate Center, University of Illinois).

While 2012 conditions for this time period certainly appear drier and hotter than 1983, the droughts of 1988 and 1936 appear far worse based on these data. Nonetheless there are areas of the country that are currently experiencing historical levels of drought, certainly as severe as any in recent memory, in some cases leading to crop failure and in others leaving producers vigilantly watching the weather forecast for any sign of relief for their crops and nerves.

Precipitation Departure from Mean:                 High Temperature Departure from Mean:     
May 1 to July 13                                                  May 1 to July 13

U.S. rainfall deviation from the mean - May 1 - July 13, 2012.
U.S. rainfall deviation from the mean - May 1 - July 13, 1988.
U.S. rainfall deviation from the mean - May 1 - July 13, 1983.
U.S. rainfall deviation from the mean - May 1 - July 13, 1936.
U.S. temp. deviation from the mean - May 1 - July 13, 2012.
U.S. temp. deviation from the mean - May 1 - July 13, 1988.
U.S. temp. deviation from the mean - May 1 - July 13, 1983.
U.S. temp. deviation from the mean - May 1 - July 13, 1936.

In 223 on-farm comparisons, product advancement tests and research trials in 2008-2010 in water-limited environments concentrated in NE, CO, KS and TX and controlled stress evaluations in California and Chile, Optimum® AQUAmax® hybrids were tested against leading commercially available competitor and Pioneer hybrids. Optimum AQUAmax hybrids demonstrated a 5.0 percent average yield advantage over the leading commercial hybrids tested. Water-limited environments are those in which the water supply/demand ratio during flowering or grain fill was less than 0.66 on a 0-1 scale (1 = adequate moisture as determined by Pioneer) using Pioneer's proprietary EnClass® system and in which the average yield of the commercially available hybrids was less than 150 bu/acre. Moisture levels were measured either at trial location or the nearest weather station. Product performance in water-limited environments is variable and depends on many factors such as the severity and timing of moisture deficiency, heat stress, soil type, management practices and environmental stress as well as disease and pest pressures. All hybrids may exhibit reduced yield under water and heat stress. Individual results may vary.