Corn Seed Survival: An update

After a corn seed is planted, it is a wonder that the seed can survive and return 400 to 600 fold or more. If Wisconsin's cool, wet spring soils do not kill the plant through imbibitional chilling, then seed rotting pathogens or hungry insects can attack and kill the seed. Once the plant emerges, it is subject to even more biotic and abiotic stresses that can often kill the plant. Even management operations like wheel traffic and cultivator blight can inflict significant harm. It is a wonder ...

I often get the question, "How much seed survives to produce grain yield?" The question is motivated by the fact that seed costs have risen dramatically in the bio-tech era of corn hybrid development (1996 to present). Some of the rising cost of seed is due to growers planting fields to higher plant densities. Between 1982 and 2017, growers in IA, IL, IN, MN, and WI have increased plant population at the rate of 261 to 309 plants/A*yr (USDA-NASS, click here). In our experiments, the corn plant density that produces maximum yield has been increasing over time at the rate of 260 plants/A*yr.

However, most of the rising seed cost is due to the use of bio-engineered traits in modern corn hybrids (USDA-ERS, click here). In the 1990s, a high performing adapted corn hybrid cost about $25 to $30/A ($80 to $125 per 80K bag or $1.00 to $1.56 per 1000 seeds). Today, typical retail seed prices are $100 to $150/A ($250 to $350 per 80K bag or $3.13 to $4.34 per 1000 seeds).

Since both seed cost and field plant density are increasing, growers are increasingly concerned about how much seed actually survives to emerge and grow into a plant that produces grain yield. In a previous article I summarized the effects of planting date and environment on corn seed survival (click here). This article adds more data to the discussion and looks at recent trends in corn seed survival.

Prior to 2008, we planted corn hybrids in UW trials by over-seeding and hand-thinning back to a uniform plant density. In 2008, we purchased a precision plot planter and dropped a uniform 34,100 seeds/A at every test site during the 2008 to 2015 planting seasons. In the winter of 2015, we had the planter refurbished and upgraded with new software set to drop 34,850 seeds/A since then. At harvest, plant population was measured on ~10% of the plots. All data collected since 2008 (N= 12,036 plots) were used in the analysis.

Seed survival in the traditional corn hybrid trials where chemical seed treatments are used, averaged 91% (Figure 1), and depended upon environment (year and location), cropping system, and seed company. Seed survival during 2012 (drought) was lowest at 82%, while seed survival was highest at 95% during 2009 (wet spring). In organic trials where conventional chemical seed treatments cannot be used, seed survival was lower averaging 83%. Seed survival was lowest at 68% during 2008, while seed survival was highest at 91% during 2009, 2014 and 2018.

Within the UW Corn Hybrid Evaluation program we have tested over 200 unique seed treatment combinations. However, there is no strong trend for seed survival improvement over time in the traditional trials, while there seems to be some improvement in the organic trials.

Figure 1. Corn seed survival across years in traditional and organic cropping systems. Data are derived from UW Corn Hybrid Performance Trials conducted between 2008 and 2018 (N= 12,036 plots).

Seed survival averaged 90% at test sites in northern Wisconsin, and 94% in southern Wisconsin (Table 1). Marshfield and Seymour had seed survival rates of 88 to 89%. Both Chippewa Falls and Hancock are sandy sites and had low seed survival (90%). Lancaster seed survival was lower due to tillage issues that caused crusting in many years. Arlington and Fond du Lac had the greatest seed survival at 96%.

Table 1. Corn seed survival in traditional trials across locations and production zones in Wisconsin. Data are derived from UW Corn Hybrid Performance Trials from 2007 to 2018 (N= 12,036 plots).

The choice of seed company also had a significant effect on seed survival. In the traditional trials, one company had a seed survival rate of 82%, while another company had a survival rate of 97% for a range of 15% (data not shown). In the organic trials, one organic seed company had a seed survival rate of 72%, while another averaged 86% for a range of 14% among companies. This range in company performance is likely due to choice of seed treatment and seed quality effects.

There are numerous factors that influence corn seed survival including hybrid, soil type, seed treatment, tillage system, cropping system, planting date, and environment. Traditionally, we have used a survival rate of 90%. More recent data indicates that 90 to 92% is a reasonable survival rate. However, seed survival at some locations and years can be as high as 95% and would need to be taken into account in order to achieve the target plant density.

The Corn Yield Gap in Wisconsin

Corn yields have been increasing in Wisconsin at the rate of 2 bu/A*yr (USDA-NASS) and there is no indication that corn yields are plateauing. The highest recorded state average yield occurred in 2016 at 178 bu/A. In 2012, Jeff Laskowski (Portage county) recorded the highest corn yield in Wisconsin at 327 bu/A. In the Wisconsin NCGA Corn Yield Contest yields above 300 bu/A have been recorded 21 times.

"Yield gaps" are the difference between potential crop yield and actual farmer yield. Potential yield is defined as the yield of a hybrid when grown in environments to which it is adapted; with nutrients and water not limiting; and with pests, diseases, weeds, lodging, and other stresses effectively controlled. Previous corn yield gap estimates from around the world have ranged from 11 to 84%. Lower yield gaps are typically seen under irrigated conditions. It is not clear if potential yield is determined by soil type or if eliminating water and nutrient stresses is more important. Political boundaries and technology availability also affect potential yield.

The challenge in understanding a yield gap is determining potential yield. The gap depends upon the method used to estimate yield potential. Some researchers use crop modeling techniques, others use yield maps from precision farming, or various statistical techniques, or yields from ag research station experiments, etc. Regardless, potential yield is location specific. The larger the geographical scale used to estimate potential yield and farmer yield, the more difficult it is to estimate a yield gap and to identify management practices that reduce or eliminate the yield gap.

The NCGA Corn Yield Contest consists of three categories: rain-fed, irrigated and conservation tillage. Overall winners of the contest over time regardless of category were used to set the potential yield for corn. Although most winners in the NCGA contest are from southern Wisconsin where farmers use longer-season hybrids with greater yield potential, the overall record and 8 of 21 yields above 300 bu/A are from north central Wisconsin. USDA-NASS average corn yields were used for farmer yields.

The regressions in Figure 1 show farmer and potential yield for Wisconsin. USDA-NASS yield (farmer yield) has increased from 96 bu/A in 1983 to 166 bu/A in 2018. The Wisconsin NCGA winners (potential yield) have increased yield from 184 to 320 bu/A. The yield gap in 1983 was 87 bu/A (47.6%), while the yield gap in 2018 was 155 bu/A (48.3%). The yield gap was widest in 2012 at 207 bu/A (63%) and narrowest in 1997 at 87 bu/A (40%). Clearly corn yields are increasing, however, the yield gap in 2018 is relatively the same as the yield gap in 1983 at about 48%. Surprisingly, the yield gap among NCGA categories is not statistically different (data not shown).

Figure 1. Corn yield gap between USDA average yield (farmer yield) and winners of the Wisconsin NCGA yield contest (potential yield). Data derived from USDA-NASS and NCGA corn yield contest winners.

Wisconsin corn production is a highly developed, sophisticated, high-yielding production system making it unlikely that variation exists in the availability of technology. Many farmers use the best technology available, however, some farmers choose not to employ the same level of technology as yield contest winners. At the farm level, yield gaps in many fields can be reduced by relatively simple changes in management practices. Yield maps are one way to identify yield gaps within a field and on your farm.

"One and Done" or a Disease Problem Here to Stay: Planning for Tar Spot in 2019

Map showing Midwest U.S. counties where tar spot infections were confirmed.
Figure credit: Kleezewski et al., 2019

In 2018, southwest Wisconsin was especially hard hit with a new disease called Tar Spot, Phyllachora maydis. I have talked to many growers this past winter about the disease and what might be done for the coming season. However, we have limited experience with the disease and it's implications for yield. At Montfort we had a significant tar spot infection in our hybrid trial plots. It was the only disease present. Dr. Damon Smith was able to rate each plot for the disease. Later we combine harvested each plot measuring yield, moisture, lodging and test weight. Dr. Smith rated ear leaf disease severity of 45 to 50% which correlated to yield impacts of 40 to 60 bu/A (18 to 27%). This is a disease that needs to be reckoned with in the future.

So how do we plan for 2019? Is tar spot a "one and done" disease, or is it here to stay? For any disease to be a problem, it needs a susceptible host, a virulent pathogen and favorable environmental conditions. All conditions have to be present. Since tar spot has affected yield during one growing season, the prudent thing to do is plan for the disease in the future.

To reduce tar spot development and severity, Kleezewski et al. (2019) recommends managing residue, crop rotation, using hybrid resistance, and using fungicide. Of these recommendations, crop rotation might be the easiest management tool to implement. Many fields in southwest Wisconsin are no-till planted so burying residue is problematic. Using hybrid resistance might be effective, but little public information is available about hybrid/family disease reaction of commercial hybrids sold to farmers. Some fungicides may reduce tar spot, but there is little data about application timing that provides an effective and economical response.

Further Reading

Kleezewski, N., M. Chilvers, D. Mueller, D. Plewa, A. Robertson, D. Smith, and D. Telenko. 2019. Tar Spot. Crop Protection Network. CPN-2012 – Corn – Tar Spot. https://cropprotectionnetwork.org/download/5830/ 

Smith, D., B. Mueller, J. Lauer, K. Kohn, and T. Diallo. 2018. The Effect of Tar Spot on Corn Hybrids in Wisconsin in 2018. see Badger CropDoc website https://badgercropdoc.com/category/corn/corn-disease/tar-spot/  (verified 2019Feb15)

Smith, D. 2019. Video: Tar Spot Management on Corn, A Wisconsin Perspective. Click here or click here (YouTube).