Dealing With Weather-Related Planting Delays in the Southern U.S.

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Planting Date Impact on Corn Yield

Although yields generally trend downward after April, good corn yields can be achieved well into May (Table 1).

Table 1. Influence of planting date on optimum corn yield for various regions of the U.S. assuming optimum plant populations. ^a,b

In the Mid-South for instance, nearly 90% yield potential can be achieved for corn planted as late as May 9. For areas with more Midwestern growing conditions, greater than 90% yield potential can be maintained through mid-May. Mid- to late-April is typically considered a normal corn planting window in Virginia; however, equal to slightly higher corn yields have been reported with May plantings (Figure 1). Based on a six-year study in Kentucky, yields from early- to mid-May plantings were only 8% lower than those achieved with April plantings (Figure 2).

**Figure 1.** Corn yields as influenced by planting date in Virginia. Yields were averaged over two tillage types and three planting depths. Data collected during 2004 and 2005 growing seasons.
Source: Thomason et al. Virginia Polytechnic Institute and State U.

**Figure 2.** Corn yields as influenced by planting date in Princeton, Ky. Yieldsaveraged over six growing seasons (2000 to 2005). Source: Herbek, University of Kentucky.

Corn Adjusts to Later Planting

A three-year study conducted by researchers at Purdue and Ohio State Universities documented that hybrids can adjust their growth and development, requiring fewer growing degree units (GDUs) to reach maturity when planted late (Table 2). Three hybrids were grown at two locations. GDUs to physiological maturity were measured. Early planting dates ranged from late April to early May, while late planting dates were from early- to mid-June.

Table 2. Reduction in GDUs required to reach 50% black layer with delayed planting in a three-year study.

Averaged over all hybrids, locations and years, 244 fewer GDUs were required when planting was delayed from late-April or early-May to early- or mid-June (approximately 40 days). This is an average reduction in hybrid GDU requirement of about six GDUs per day of planting delay.

Research conducted in Ark. demonstrated that corn reduces the number of days from planting to silking when planted late (Figure 3). Days from planting to silking were 74, 74, and 79 for commonly planted hybrids with 111, 114, and 116 CRM. In contrast, days from planting to silking ranged from 47 to 51 for the same hybrids planted in mid-May.

Wet Corn Field — Delayed planting due to wet spring weather can cause growers to consider switching to an earlier maturity hybrid.

Hybrid Relative Maturity - AR — **Figure 3.** Days from planting to silking for corn planted March 19, April 16, and May 13 near Mariana, Ark. in 2010. Source: Jason Kelley, Univ. of Arkansas.

Should I Switch to an Earlier Maturing Hybrid?

In the southern U.S., corn hybrids with longer relative maturities generally produce higher yields than shorter season hybrids (Table 3). Pioneer conducted on-farm strip trials at 528 locations between 2004 and 2007 across the southern U.S. to determine the effect of hybrid relative maturity on yield performance. Growing a 108 CRM hybrid was found to yield about 7 bu/acre less and generate $30 to $39/acre less income than growing an adapted 113 or 118 CRM hybrid based on a corn selling price of $4.25 per bushel.

Table 3. The influence of corn hybrid maturity (CRM) on yield and gross return for the southern U.S.

Influence of CRM on yield and gross return.

Data from the Ark. study mentioned previously also suggests that well-adapted fuller season hybrids can maintain this yield advantage over shorter season hybrids even with later planting dates (Figure 4).

**Figure 4.** Yield for corn hybrids of different relative maturity planted on 3 different dates near Mariana, Ark. in 2010. Source: Jason Kelley, Univ. of Arkansas.

Management Tips for Late-Planted Corn

Planting corn later than normal does pose some challenges and additional management may be required to prevent or minimize yield-limiting factors such as heat stress, insect pressure and disease pressure. A few tips for producing late-planted corn are:

If available, irrigate in a timely fashion especially during pollination. This will help ensure that the corn plant cools itself adequately during periods of intense heat that later-planted corn has to endure.
Consider a Bt hybrid and/or scout and treat for insects where needed. Budget at least one insecticide application for refuge acres.
Choose hybrids with solid disease resistance. Scout and apply foliar fungicides as needed. Incidence and severity of some diseases like southern rust are generally higher in late-planted corn. Consequently, economic yield responses to foliar fungicides are generally more likely with late-planted corn.
Harvest in a timely fashion. Corn plant height is generally maximized with May planting dates. High insect and disease pressure associated with late planting dates can weaken stalks.

References

Nielsen, R.L. (Bob). 2003. Estimating Yield and Dollar Returns From Corn Replanting (AY-264-W) [Online]. Purdue Univ. Coop. Ext. Service, W. Lafayette, IN 47907.

Thomason, W. W., Phillips, S. B., Alley, M. M., Davis, P. H., Lewis, M. A., and Johnson, S. M. In-row subsoil tillage and planting depth influence on corn population and yield on sandy textured Mid-Atlantic coastal plain soils.