C.O.R.N. Newsletter 2011-06

Dates Covered: 
March 21, 2011 - April 1, 2011
Editor: 
John Yost

Plant Population Trends for Corn in Ohio

Corn response to population is continuously changing with seeding rates increasing about 280 plants/A/yr according to the National Agricultural Statistics Service (http://www.nass.usda.gov/) (2010). Plant populations in Ohio have increased 16% in the past 10 yrs (56% since the early 1970’s). According to NASS, plant population for corn in Ohio averaged 28,200 plants/A in 2010, which is lower than most Corn Belt states (e.g. Minnesota, 29,900 plants/A; Iowa – 29,950 plants/A; Illinois – 29,650; Indiana- 28,350 plants/A).

Research has demonstrated that the superiority of modern hybrids is fully expressed only at higher plant populations (Duvick, 2005). When hybrids of different eras (from the 1930’s through 2001) were planted at a very low population (4000 plant/A – a “low stress” environment), there was little to no difference in the yields of hybrids from different eras. However, when established at a higher plant population (32,000 plants /A) more typical of that required to maximize yields in recent years, hybrids exhibited progressively higher yields with each era of genetic improvement. The genetic improvements that have facilitated the positive interaction between hybrids and increasing seeding rates include increased yield stability across a range of environmental conditions, greater tolerance to drought (and higher plant populations), enhanced stalk and root strength, and  resistance to diseases and insects.

The distribution of corn acreage with varying plant populations at harvest indicates major differences in seeding rates used for corn production in Ohio and greater adoption of higher seeding rates by some corn growers in recent years. Final stands on nearly 40% of the state’s corn acreage was 30,000 plants/A or higher in 2010. Four years ago, final stands were 30,000 plants/A or higher on only 14% of the corn acreage.

Most corn agronomists recommend adjusting seeding rates by using the yield potential of a site as a major criterion for determining the appropriate plant population. Seed companies recommend final stands as high as 35,000 to 36,000 plants/A for some hybrids in high yield environments. Average seeding rates of hybrids entered in the Ohio Corn Performance Test have increased from about 25,000 seeds/ A in the early 1970’s to over 35,000 seed/A in 2010 (with final stands ranging from about 23,000 to 33,000 plants/A).  Ohio Corn Performance Test sites generally represent production environments with high yield potential.

Since 2006, we have conducted evaluations of corn response to plant population across a range of environments (primarily involving varying climatic conditions). Tests were established at up to nine locations each year in fields with high yield potential (200 bu/A + under favorable conditions). We considered final stands of 24, 30, 36, and 42,000 plants/A. Results have varied over the past five years, with yields averaging 191, 191, 177, 228, and 201 bu/A for 2006, 2007, 2008, 2009, and 2010 respectively. In 2006, 2009, and 2010, results suggested that final stands of 36,000/A or higher were required for optimal yields. In 2007 and 2008, there was no yield response to plant populations above 30,000 plants/A. Higher plant populations were usually associated with more stalk lodging (stalks broken below the ear). The most severe lodging occurred in 2008 when high winds associated with Hurricane Ike contributed to severe lodging (especially at 42,000 plants/A). Averaged across locations, lodging in 2008 was 52% at 42,000 plants/A and the extensive stalk damage may have accounted for the absence of yield increases above 30,000 plants/A. However, in 2007 stalk lodging was negligible at all populations yet there was no yield response above 30,000 plants/A.  On average, increasing plant population from 24,000 plant/A to 42,000 plants /A reduced grain moisture but effects were highly variable from year to year ranging from 0 in 2007 to 1.1% in 2009.

When yield potential is reduced due to stresses including to late planting, drought, root and stalk lodging, disease and insect injury, and harvest delays, yield response to plant population is often limited. Under severe drought conditions, yield may even decrease at higher plant population due to increased barrenness and greater stalk lodging but this is relatively rare in hybrids developed in recent years.

Based on OSU studies to date, a seeding rate of 31 - 33,000 seeds/A will be adequate for optimal yields in most production environments planted in late April and early May. For fields with low yield potential, seeding rates of 24 - 26,000 seeds/A will probably be sufficient. For fields with very productive soils and high yield (180 bu/A level and higher), seeding rates of 36 - 37,000 seeds/A may be necessary. (These seeding rate estimates are based on 10% mortality). Planting rate or population can be cut to lower seed costs but this approach typically costs more than it saves. In the absence of major environmental stresses, most research suggests that planting a hybrid at suboptimal seeding rates is more likely to cause yield loss than planting above recommended rates (unless lodging becomes more severe at higher population levels). Because of differences in genetic backgrounds for various traits, especially stalk quality, seed company recommendations should be followed to adjust seeding rates for specific hybrids.

References

Duvick, D.N.  2005. The contribution of breeding to yield advances in maize. Adv. Agron. 86:83-145.

New Insecticides Labeled on Field Crops

FMC Agriculture Products just received labeling for a new insecticide, Stallion, on multiple field crops, including alfalfa, corn, soybean, and wheat.  Stallion is a mixture of the pyrethroid zeta-cypermethrin which is the same active ingredient in Mustang Max and the organophosphate clorpyrifos, the active ingredient in Lorsban and numerous other generic brands.  In terms of control, it includes many if not most of the same insects that the two active ingredients control separately.  It is a restricted use pesticide.

There is another insecticide that should be mentioned that escaped our notice last year.  Dupont received labeling for Coragen on corn, an insecticide that is active against many caterpillars including European corn borer and western bean cutworm.  The active ingredient in Coragen is chlorantraniliprole.

Western Bean Cutworm Myth #1: We know the reason why Western Bean Cutworm has expanded across the Eastern Great Lakes

The spread of western bean cutworm (WBC) was quite rapid.  In about ten years, this pest of corn spread from western Iowa to Long Island, New York.  Although there are many possible reasons why this expansion occurred, there are no concrete reasons or data to support a single cause.  One possible reason suggests the use of transgenic corn against corn earworm (CEW) led to increases in western bean cutworm—a hypothesis known as “ecological replacement”.  This is because CEW will attack and consume WBC; therefore that killing CEW with Bt allows better survival for WBC.  While it is true that CEW eats WBC, we have to keep in mind that CEW does not infest every ear of corn, and that there were plenty of uninfested ears which WBC could have used.  A second possible reason suggests that reduced tillage leads to better WBC survival and therefore larger populations.  While we suspect that tillage does lead to mortality, no good experiments or data exist to let us know what the exact impact of tillage is.  Furthermore decreasing tillage is neither likely nor advisable given the scarcity of information available about the viability of this practice and the agronomic benefits of reduced tillage and soil conservation.  Other possible reasons implicate an overall trend of earlier planting dates, a sudden pathogen release, or climate change.  Additional research is needed to understand how each of these possible factors led to the expansion of WBC.  It is also likely that there is not a single reason, but many that have contributed to a shift in the Lepidopteran corn pest complex.

Nitrogen Recommendations for Wheat

Wheat is already at greenup in the southern two-thirds of the state and is beginning to greenup in the northern third. We would recommend applying nitrogen between greenup and Feekes Growth Stage 6 (early stem elongation), which is generally the latter part of April. The potential for nitrogen loss will decrease by waiting to apply closer to Feekes 6; however, since we are at greenup, a common sense approach would recommend applying as soon as field conditions allow application equipment, particularly since days available for field activities may be limited between now and Feekes 6.

We would still recommend the Tri-State guide for N rates in wheat. This system relies on yield potential of a field. As a producer, you can greatly increase or reduce your N rate by changing the value for yield potential. Thus, a realistic yield potential is needed to determine the optimum nitrogen rate. Once you have selected a value for yield potential, the recommendation may be based on the following equation for mineral soils, which have both 1 to 5% organic matter and adequate drainage:

N rate = 40 + [1.75 x (yield potential – 50)]

We do not give any credit for the previous soybean crop, since we do not know if that organic N source will be released soon enough for the wheat crop. The Tri-state recommends that you subtract from the total (spring N) any Fall applied N up to 20 lb/A, whether you deduct fall N depends how much risk you are willing to take and your anticipated return of investment from additional N. Based on the equation above and deducting 20 lb from a fall application, we would recommend a spring application of 110 lb N per acre for a yield potential of 100 bu, 90 for 90 bu potential; 70 for a 80 bu potential and 40 lb N per acre for a 60 bu potential.  Price and availability will probably be the main factors in selecting a N source. Volatilization losses should still be minimal for urea based fertilizers at this time but may occur if we get an extended hot and dry period. Potential loss of N from 28% solution may be furthered reduced by applying in a band (dribble bar).

NOAA Weather Outlook

The weather pattern looks to turn not quite as wet but cool over the next week. We expect some rain especially in the northern half of Ohio later Tuesday into Wednesday with average amounts of 0.5 to 1.0 inches especially in the north half. After that system we expect only minor systems into next week. Temperatures will be above average early this week except in the far north and then turn colder than average into early next week. The next major weather system after early to mid week will not likely occur until late next week.

Longer-range outlooks continue to show, as discussed last autumn, the trend for a cool spring with close to normal rainfall after the wet start. However, the frequency of rain will be quite active at least into the first half of April. It looks like the cooler than average temperatures will last into April with a gradual return to normal during later spring. We may move to above normal temperatures by sometime during summer. As for rainfall, after a wet early spring we will see a transition to normal and then likely drier than normal as we move into summer.

The result, with a cool/damp start and a warm/drier period by summer, this year will be another challenge on the weather front.

West Ohio Wheat Production Workshop

How do you top the beauty of wheat greening up this time of year?  By dedicating time to management practices that boost your chances of a profitable crop!  The 7pm, March 24th (this Thursday), West Ohio Wheat Production Workshop in Sidney should help farmers better care for the 2011 wheat crop.  Plan to bring wheat samples (both good and bad) from some of your fields to enhance the workshop discussion.  The Shelby County Agricultural Center, located about ¾ mile east of I-75 off Exit 90, at 820 Fair Road in Sidney is the location for the interactive meeting.

For the most part, wheat overwintered well, but there is still talk of ripping up fields for corn and soybean production. If that is what you are thinking, please hold on!  Granted, last year’s head scab debacle soured many growers on wheat, but planting of scab resistant varieties and availability of many production aids should help farmers harvest a bountiful crop and enjoy the rotational benefits of wheat as well.

Discussions will center on:

·         Wheat disease management including head scab…if fungicides are needed, how timely do you need to be?

·         Nitrogen Rates/fertilization timing

·         Weed control…when does it pay?

·         Insects to watch out for and best ways to control them (only if needed which is seldom)

·         Does wheat pay its own way?...or should you switch to another crop?

Plenty of time is slotted for your questions and looking at wheat plants brought to the meeting.

Let us know you are coming, and we can prepare for refreshments.  Email watters.35@cfaes.osu.edu, petrosino.3@cfaes.osu.edu, or bender.5@cfaes.osu.edu, or call 937.498.7239 or just show up!

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About the C.O.R.N. Newsletter

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.