CORN
Crop Observation and Recommendation Network

May 13 - 20, 2002
C.O.R.N. 2002-13

In This Issue:

A) Management Considerations For Late Planted Corn
B) Nitrogen Loss In Ohio In 2002
C) Late Planted Corn & Seeding Rates
D) Considering A Change From Corn To Soybeans - Remember To Scn Fields In A Rotation
E) Wet Soils Favor Soil-Borne Pathogens

A) Management Considerations For Late Planted Corn - Peter Thomison CORN Questions

Persistent wet weather across Ohio has kept farmers out of fields for most of April and probably for the first three weeks of May. According to the Ohio Agricultural Statistics Service, only 17% of the state's corn crop and 6 % of the soybean crop was planted as of May 12 (compared with past five year averages of 70% and 44%, respectively, for corn and soybeans). Planting delays may require some adjustments in hybrid selection and other management practices.Most of the hybrid maturities commonly grown in Ohio will mature safely when planted as late as the end of May. However, growers in the northern third of Ohio should consider switching from adapted full season hybrids to adapted early and mid season hybrids by the last week of May. Growers in central Ohio should consider switching to earlier adapted hybrids during the first week of June, and in southern Ohio, where the growing season is longer, growers can probably wait until June 1015 before switching hybrid maturities. Corn planted for silage may be planted until June 1015 if not later and still produce yields of high quality feed. When selecting hybrids for delayed planting (through early June), DON'T switch to early maturity (90-95 day or earlier) hybrids which are not adapted to Ohio. In some areas of southern Ohio, switching to unadapted earlier hybrids may limit disease control. In fields where virus and foliar diseases like Maize Dwarf Mosaic and gray leaf spot are a problem, early season hybrids generally do not have the same level of resistance found in late maturity hybrids. Similarly, the grain quality and stress tolerance of these early hybrids are often inferior to adapted hybrids. Therefore, producers should not switch to earlier maturing hybrids any sooner than necessary. Contact your seed company representative for specifics on GDD requirements of late planted hybrids and the availability of earlier maturing adapted hybrids. When corn planting (for grain) production is delayed beyond mid-June growers should consider switching to crops other than corn except in far southern counties.

Corn seeding rates should not be changed much as planting is delayed. Since soils should be warmer in late May and early June, we can generally reduce seeding rates slightly in anticipation of a higher percentage of emergence and faster growth. See the article "Late-Planted Corn & Seeding Rates" in this issue of C.O.R.N. (5-13-02) for more information on this topic.

If soil test P and K levels are relatively high, eliminate starter fertilizer application. This will help save time and money with little risk of yield loss.

Reduced tillage and no-tillage are recommended to reduce compaction and speed the planting operation. No-till planter speed should not exceed 4 mph for best stands. Nitrogen applications should be delayed until after corn planting to allow planting to progress as rapidly as possible. The rate of nitrogen application should be reduced in accordance with the corn yield potential in Table 1.

TABLE 1. Expected Corn and Soybean Grain Yields for Various Planting Dates. _________________________________________________________________

Planting Date ------Percent Yield------
Corn Soybeans
(drilled)
------
May 17 100 100
May 814 93 100
May 2128 86 95
May 29June 4 79 88
June 510 70 80
--------------------------------------------------------

A recent OSU study indicated that when planted on or about May 1 a corn crop generally required 100 to 150 lb N/acre to achieve optimum yield for the individual growing season. There was no significant effect of application method; split applications of N produced yields comparable to those produced by at planting applications. Corn planted on or about June 1, however, showed different responses with little or no benefit accrued
from applying more than 100 lb N/acre. At the 100 lb N/acre rate, yield was optimized to the point where costs of further fertilizer addition would not be recovered in additional yield except at very low fertilizer prices.

Depending on current corn and soybean costs of production, yield response to date of planting (Table 1), and expected fall prices, soybeans may be more profitable than corn after June 1. The decision to plant soybeans in the place of corn will be determined by the need for corn as feed, government program restrictions, crop rotation benefits, and whether either nitrogen or herbicides have been applied to unplanted fields. Corn planting
delays may result in higher grain drying costs if the crop dries slower than normal in late September and October.

B) Nitrogen Loss In Ohio In 2002 - Peter Thomison CORN Questions

Excessive rains across Ohio during the spring of 2002 have raised some concerns about the amount of nitrogen that may have been lost. The following is an article by Dr. Bob Hoeft, Extension Soil Scientist at the University of Illinois (from the May 3, 2002 Univ. of Illinois Pest and Crop Bulletin that assesses this potential loss.

The warmer-than-normal winter, coupled with a wet spring, has many wondering whether nitrogen loss is or will be greater than normal for the 2002 crop year. Fortunately, research conducted at the University of Illinois over a number of years has provided a data base on which to make an informed decision about the amount of N loss that has occurred or that might occur in the next few weeks. Nitrogen loss associated with excessively wet soils will occur only from that portion of the fertilizer that is in the nitrate form when soils become saturated. Because most fertilizers are applied as ammonium or a form that quickly converts to ammonium, you must first determine how much of the applied nitrogen has been converted to nitrate. This rate of conversion of ammonium to nitrate--a process called nitrification--is primarily dependent on soil temperature. Nitrification does not occur when soils are frozen, but it does occur at temperatures above freezing and is faster the warmer soils are. Equations that define the relationship between soil temperature and nitrification have been developed for two Illinois soils, a Drummer silty clay loam and a Cisne silt loam. These equations, using daily soil temperature data provided by the Illinois State Water Survey for the Drummer at DeKalb and Bondville and the Cisne at Brownstown were used to estimate the amount of fall-applied nitrogen that had been converted to nitrate during the winter and spring of 2001-2002. As expected, there were significant differences in the rate of nitrification, dependent on location, with higher values the farther south in the state. Addition of a nitrification inhibitor, N-Serve, substantially reduced the rate of conversion of ammonium to nitrate. The conversion of ammonium to nitrate does not mean that it has been lost from the soil system but rather that it is susceptible to loss in fields that have been or may become saturated with water for several days. When soils are excessively wet, nitrogen will
be lost through the process of denitrification or leaching. As of April 1, the amount of nitrate-nitrogen lost from tile lines was less than 6% of the equivalent of the total fertilizer nitrogen applied without a nitrification inhibitor in a central Illinois experiment. Denitrification is the major nitrogen loss mechanism in most Illinois soils, particularly in medium to heavy textured soils. Illinois research has shown that 4 to 5% of the amount of nitrate-nitrogen present (note that this is not 4 to 5% of the total nitrogen applied) will be lost via denitrification for each day that soils are saturated when soil temperature is above 65 to 70 deg F. At temperatures less than 55 deg F, it is estimated that denitrification will be closer to 1 to 2% of the nitrogen that is in the nitrate form. Prior to April 25, soil temperatures were less than 55 deg F all but 8 days in central and northern Illinois and 15 days in southern Illinois. Assuming 7 days of saturated soils in late April and 160 pounds of nitrogen applied without a nitrification inhibitor on November 1, 2001, the loss potential would be 160 lb N/acre x 59% [.59] (nitrification rate) x 19% [.19] (7 days saturated at 2% denitrification per day + 5% leaching) = 18 lb N/acre loss for a central Illinois location. If a nitrification inhibitor had been used, the loss potential would be reduced to 160 x .23 x .19 = 7 lb N/acre. For a southern Illinois location, the comparable situation would be 160 x 100% x .19 = 30 lb N/acre without an inhibitor, or 20 lb N/acre with an inhibitor. The bottom line of this analysis is that most producers need not worry about N loss up to this time. They can save that worry for later in the season if soils become saturated. This information will be updated as the season progresses. Additional nitrogen is not being recommended at this time to compensate for loss. Producers should wait until late May when additional information will be available to better predict the need for additional nitrogen.

C) Late Planted Corn & Seeding Rates - Bob Nielsen and Peter Thomison* CORN Questions

• Do you know what is normally optimum?
  
• General advice: Don't change from optimum rates.
  
• Certain exceptions may call for increasing or decreasing rates.

Among the many questions raised by Indiana & Ohio corn growers as the rain-delayed planting season continues is whether delayed planting should influence their seeding rate decisions for corn. As might be expected, several factors need to be considered.

First of all, what defines 'optimum' final population for corn in our two states? For most of our production areas, the answer is a range of final stands from 28-32,000 plants per acre. Some exceptions exist for that rule of thumb. Marginally yielding soils (consistently less than about 120 bu/ac) probably respond best to final populations nearer to 24,000 plants per acre, while exceptionally high yielding environments (greater than 180 bu/ac) probably respond better at final stands approaching 34-36,000 plants per acre. So, the first step for Indiana & Ohio corn growers when considering late planting consequences for seeding rates is to determine whether they are normally seeding at rates that will achieve the optimum final stands for the productivity level of each field in their operation. Typically, seeding rates are calculated based on an assumed 90 percent success of germination, emergence, and seedling survival. For example, to achieve a targeted final stand of 30,000 plants per acre at harvest, one would seed at a rate equal to about 33,300 seeds per acre (30,000 divided by 0.90). If you are already following these seeding rate guidelines, then delayed planting should not alter those seeding rates because the range of optimum final plant populations is similar for early and late planted corn. Table 1 illustrates the similarity of yield responses to population for corn planted at varying planting dates in research conducted by the Univ. of Illinois. Regardless of planting date, optimum grain yield occurs for most situations within a similar range of final populations.

Caveats: Choose What Fits Your Situation.
That said, it is important to recognize that no two farming situations are the same. Caveats and exceptions abound and should be considered when making a decision about seeding rates for late plantings.

• Scenario #1: Soil temperatures for corn planted in late May or early June will be quite warm relative to that of usual late April or early May plantings. Couple that with the likely ample availability of soil moisture and the odds are that germination and emergence success will be greater than normal. Consequently, you may elect to reduce your seeding rate accordingly. Instead of planting 33,300 seeds to achieve 30,000 plants (90% success rate), you may elect to plant only 30,600 seeds per acre (98% success rate).
  
  
• Scenario #2: If you eventually switch from your normal hybrid maturity to a much earlier maturity hybrid, you may actually want to increase your seeding rates by several thousand. Hybrid maturities of 100-day comparative relative maturity or less often respond better to higher final stands than later maturity hybrids. Instead of aiming for final stands from 28-30,000 plants per acre, these very short season hybrids may respond better to final stands of 34-36,000 plants per acre. Consult your seed company sales representative for specific hybrid planting rate information.
  
  
• Scenario #3: Later planted corn will be taller than early planted corn because its stalk elongation phase occurs during a time period that is relatively warmer (later in the season) than when early planted corn goes through the same phase. Not only will the plants themselves be taller, but ear placement will also be higher (same stalk node, but higher off the ground due to stalk elongation). Consequently, a hybrid that is on the tall side to begin with will be even taller and its ears placed higher when planted unusually late. Such a combination of a tall hybrid and delayed planting will result in an increased risk of stalk lodging this fall if strong windstorms occur before harvest (anyone remember last October?). One strategy to minimize this risk is to seed such a hybrid at rates closer to the low end of the optimum range in order to minimize the plant-to-plant competition that can cause etiolation (elongation under shade conditions) and thinner diameter stalks. Another strategy is to simply switch to a physically shorter hybrid.
  
  
• Scenario #4: Later planting of corn, in and of itself, does not increase the risk of stalk rot development later in the season. However, taller, high-eared, late-planted corn will be more susceptible to the stalk lodging consequences of stalk rot IF stalk rot develops. One of the primary factors that contributes to stalk rot development is severe stress (heat, dry soils, disease, hail, insects, cloudy weather, soil compaction) occurring early in the grain filling period that severely limits photosynthesis. The timing of that stress relative to grain filling is the critical determinant to whether stalk rots develop in corn of any planting date (anyone remember two years ago?). Planting strategies to minimize this risk would be similar to those of Scenario #3 above, as well as to avoid wet fieldwork (compaction) yet this spring.
  
  
• Scenario #5: There will undoubtedly be a few fields tilled and planted on the wet side once field conditions get even close to being suitable for field work over the next few weeks. One consequence of doing so is a cloddy seedbed that does NOT promote good seed-to-soil contact for rapid and uniform germination.
  IF the weather should suddenly switch from frequent rains to total dryness after such fields were worked and planted, germination would be extremely variable, if not disappointing. Along with the cloddy seedbed preparation, tilling and planting wet fields creates various forms of soil compaction that are not conducive for successful root development.
  IF you are forced into this wet fieldwork scenario, you may want to increase your seeding rate beyond what you normally use, in anticipation of unsuccessful stand establishment. Similarly, IF you decide to forgo some tillage in fields where seedbed conditions are marginal (characterized by a cloddy surface, ruts, uneven residue distribution) and plant no-till, you may want to increase seeding rates to compensate for the higher probability
  of greater seedling mortality.

* R.L. (Bob) Nielsen, Agronomy Dept., Purdue Univ., West Lafayette, IN P.R. Thomison, Hort. & Crop Sci. Dept, The Ohio State Univ., Columbus, OH

D) Considering A Change From Corn To Soybeans - Remember To Scn Fields In A Rotation - Anne Dorrance & Dennis Mills CORN Questions

Soybean cyst nematode has been found in close to 30 to 40% of the production fields in Ohio. SCN is best managed through crop rotation. SCN can increase 8 to 10 fold in population when a susceptible soybean variety is planted and can decrease by 50% in years when a non-host such as corn is planted. For those fields in which SCN has been identified, be sure to keep them in the rotation. Once SCN is identified in a field, it becomes a "life-long" commitment to manage those SCN populations and keep them at levels well below where economic damage can occur.

E) Wet Soils Favor Soil-Borne Pathogens - Anne Dorrance CORN Questions

Let me describe the scenario that we use in the laboratory to favor isolation and baiting of Phytophthora and Pythium out of soils. We dry the soil in the greenhouse, place it in pots, saturate it for 24 hours, drain slightly and incubate it wet for 2 weeks. Seeds are planted in the soil and allowed to germinate. We then flood the soil again for 24 hours and begin to count the number of seedlings that die over the next 5 to 7 days. Sound familiar? Fields have been saturated for the past month - allowing for incubation and priming of oospores of both Pythium and Phytophthora. It will be critical this year to apply seed treatments. Pythium spp. are excellent seed rotters and typically effects soybeans in the early part of the year. Phytophthora sojae can cause seed rot, root rot and stem rot thus can attack plant season long. The challenge we now face is that the Phytophthora sojae has changed or adapted and can now cause disease on many varieties which carry the resistance genes (Rps1a, Rps1c, Rps1k). Partial resistance (also called field resistance or general resistance) is not effective or able to limit infections to an economic level until that plant is up and photosynthesizing. Seed treatments can potentially provide protection to soybeans against Phytophthora until that plant is up and out of the ground. Seed treatment products with metalaxyl or mefenoxam sold as Allegiance or Apron XL are the only products that can provide protection against these two pathogens. For hytophthora only the high rates are effective. If you have had stand problems in 1997, 2000 or 2001, if your fields are poorly drained, if you have seen an increase in the amount of late season Phytophthora - these are the fields to shoot for the 1.5 fl oz rate of Allegiance or 0.64 fl oz of Apron XL.

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C.O.R.N. is a summary of crop observations, related information, and appropriate recommendations for Ohio Crop Producers and Industry. C.O.R.N. is produced by the Ohio State University Extension Agronomy Team, State Specialists at The Ohio State University and Ohio Agricultural Research and Development Center. C.O.R.N. Questions are directed to State Specialists, Extension Associates, and Agents associated with Ohio State University Extension and the Ohio Agricultural Research and Development Center at The Ohio State University.

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