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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter: 2014-15

  1. Corn Emergence Problems: “Corkscrewed” Mesocotyl Development

    Author(s): Peter Thomison

    Last week I received several reports of abnormal corn emergence. Often the problems were associated with corn seedlings leafing out underground and it’s likely weather and seedbed conditions were responsible for the occurrence of the abnormal growth. Seedlings exhibiting abnormal emergence (see figures) may have a twisted appearance because internal leaves start expanding before the seeding has elongated. “Corkscrewed” mesocotyl/coleoptile development may occur when the coleoptile encounters resistance (like soil crusting or a dense soil surface) as the mesocotyl elongates. Several factors (or combination of factors) may be responsible for this abnormal growth. These factors may be characterized as environmental, chemical, or mechanical. Environmental conditions associated with underground leafing include light penetration, cold soils, or heavy rains soon after planting. When plants unfurl below the soil surface, they usually turn yellow and die.

    In a cloddy field where soil coverage of seed is poor and irregular, sunlight can reach the germinating seedling and induce leaf emergence beneath the soil surface. Also, heavy rains after planting can cause a hard crust, which makes emergence of small seedlings very difficult (this seemed to be the most likely factor causing problems this year). As a result, bending and twisting of the seedling below the crusted layer often occurs. Planting the seed too deep has also been associated with premature unfurling of the corn.

    Certain herbicides, such as cell growth inhibitors like acetochlor, and various premixes that contain their active ingredients can show similar symptoms (i.e. twisting, abnormal growth) when excessive rates are applied pre-emergence. Besides excessive rates, improperly closed seed furrows can allow the pre-emergence herbicide to come in direct contact with the seed.

    In a 2012 article concerning corn emergence problems (, Dr. Bob Nielsen at Purdue University notes that cold soils and/or wide fluctuations in soil temperatures throughout the day during the emergence process may be a major contributing factor for the development of corkscrewed mesocotyl. We have also encountered some swings in soil temperatures during emergence in areas where problems occurred.

    Corn seedlings that exhibit abnormal unfurling symptoms during emergence will be unable to penetrate any but the loosest soil even if the crust is broken mechanically or softened by rain. Prompt treatment with a rotary hoe, weeder, spiketooth harrow or cultipacker may help break the crust and improve emergence. However, even when used carefully, these salvage operations can cause some damage to seedlings, which are emerging normally. To minimize poor seedling emergence due to unfurling below the soil surface, watch for cloddy seedbeds, open seed furrows, and crusting surface soils after rains.


    Nielsen, R.L. 2012. Corkscrewed Mesocotyls & Failed Corn Emergence
    Corny News Network, Purdue Univ. Online at [URL accessed May 27, 2014]

  2. Should seeding rates be adjusted for delayed corn plantings?

    Author(s): Peter Thomison

    Past university research indicates that optimal plant populations for early (mid to late April) and late planted (late May to early June) corn are similar. Based on results of these studies, most extension agronomists recommend that final plant populations should not be changed as planting date is delayed. If planting is delayed until early June, some Ohio data suggests that certain hybrids are more susceptible to stalk lodging at high populations. In delayed planting situations, use the optimal seeding rates for the yield potential of each field. Recommended seeding rates for early planting dates are often 10% higher than the desired harvest population. However, soil temperatures are usually warmer in late planted fields, and as a result germination and emergence should be more rapid and uniform. So, as planting is delayed, seeding rates may be lowered (decreased to 3 to 5% higher than the desired harvest population) in anticipation of a higher percentage of seed emerging. 

  3. Corn Replant Issues

    Author(s): Peter Thomison

    Localized ponding and protracted saturated soil conditions have adversely affected corn in many fields across Ohio. Heavy rains have also resulted in soil crusting which is contributing to reduced emergence. Producers confronted with poor stands due to these problems may be considering replanting their fields.

    Replant decisions in corn should be based on strong evidence that the returns to replanting will not only cover replant costs but also net enough to make it worth the effort. Don’t make a final assessment on the extent of damage and stand loss too quickly. The following are some guidelines to consider when making a replant decision.

    If the crop damage assessment indicates that a replant decision is called for, some specific information will be needed, including:

    • Original target plant population/Intended plant stand
    • Plant stand after damage
    • Uniformity of plant stand after damage
    • Original planting date
    • Possible replanting date
    • Likely replanting pest control and seed costs

    To estimate after‑damage plant population per acre, count the number of viable plants in a length of row that equals 1/1000 of an acre and multiply by 1000. Make several counts in different rows in different parts of the field. Six to eight counts per 20 acres should be sufficient. Table 4-12 in the OSU Agronomy Guide shows row lengths required to equal 1/1000 acre when corn is planted at various row widths.

    A major consideration in making a replant decision is the potential yield at the new planting date and possibly different planting rate; this can vary depending on the hybrid used, soil fertility and moisture availability. Table 4-15 in the OSU Agronomy Guide is a chart developed by Dr. Emerson Nafziger at the University of Illinois that show effects of planting date and plant population on final grain yield for the central Corn Belt. Dr. Bob Nielsen has modified this table to provide estimates of potential yield losses for planting dates in early June (on-line at

    Grain yields for varying dates and populations in both tables are expressed as a percentage of the yield obtained at the optimum planting date and population.

    Here’s how these tables might be used to arrive at a replant decision (Table 4-15 from the OSU Agronomy Guide will be used in this example). Let’s assume that a farmer planted on May 9 at a seeding rate sufficient to attain a harvest population of 30,000 plants per acre. The farmer determined on May 28 that his stand was reduced to 15,000 plants per acre as a result of saturated soil conditions and ponding. According to Table 4-15, the expected yield for the existing stand would be 79% of the optimum. If the corn crop was planted the next day on May 29 and produced a full stand of 30,000 plants per acre, the expected yield would be 81% of the optimum. The difference expected from replanting is 81 minus 79, or 2 percentage points. At a yield level of 175 bushels per acre, this increase would amount to a gain of about 3.5 bu per acre.

    It’s also important to note plant distribution within the row. Remember that values in replant charts like Table 4-15 from the OSU Agronomy Guide are based on a uniform distribution of plants within the row. Add a 5% yield loss penalty if the field assessment reveals several gaps of 4‑6 feet within rows and a 2% penalty for gaps of 1‑3 feet. Yield loss due to stand reduction results not only from the outright loss of plants but also from an uneven distribution of the remaining ones. The more numerous and longer the gaps between plants within the row, the greater the yield reduction. It’s also important to consider the condition of the existing corn.

    When making the replant decision, seed and pest control costs must not be overlooked. Depending on the seed company and the cause of stand loss, expense for seed can range from none to full cost. As for the correct hybrid maturity to use in a late planting situation, continue to use adapted hybrids switching to early/mid maturities, if necessary, depending on your location in Ohio.

    You also need to review herbicide and insecticide programs under late‑planting conditions. For instance, it may be necessary to reapply herbicides, especially if deep tillage is used. However, try to avoid such tillage depending instead on postemergence chemicals or cultivation for weed control. Concerning insect control, if soil insecticides were applied in the row at initial planting, check insecticide label restrictions before re‑application. Also remember that later May and June planting dates generally increase the possibility of damage from European corn borer (ECB) so planting ECB Bt hybrids is often beneficial.

    The cost of replanting will differ depending on the need for tillage and chemical application. The cost and availability of acceptable seed will also be considerations. These factors must be weighed against expected replanting yield gains. If after considering all the factors there is still doubt as to whether or not a field should be replanted, you will perhaps be correct more often if the field is left as is. 

  4. Scab Risk Continues to be Low, but Rain is in the Forecast

    Ohio Scab Risk Prediction Center
    Author(s): Pierce Paul

    For wheat flowering today, May 27, the risk of scab is low, according to the prediction took. Several fields across south-central Ohio reached anthesis over the weekend, and since conditions were fairly dry in most of those areas, the risk tool also predicted low scab risk for those fields. However, things may change for fields in the Northern half of the state that are likely to reach anthesis later this week. The weather forecast is for wetter condition, with between 40 and 60% chance of precipitation on two of the next five days in some locations. Moreover, conditions have been humid; both rainfall and high humidity favor scab development and vomitoxin contamination of the grain.

    Continue to use the prediction tool to assess the risk for scab over the next 7 to 10 days, and be prepared to apply Prosaro or Caramba, if moderate to high risk is predicted at the time the crop reaches the flowering growth stage. Remember, these fungicides are most effective against scab and vomitoxin when applied at flowering. However, if you are unable to treat your field at the flowering stage, you can still get good scab and vomotoxin control if you apply the fungicide up to six days after flowering. Later applications may be less effective, and most importantly, may be off label, since the pre-harvest interval for both Caramba and Prosaro is 30 days. On average, wheat in Ohio is usually harvested between 40 and 45 days after anthesis.    

  5. Early Season Soybean Damage- Frost, PPO, or Disease?

    Symptoms on soybean seedlings hit with a “trifecta”: cold, saturated soils; potential freeze injury; and closely timed planting to herbicide applications.

    Spring 2014 has been quite challenging with wet soil and cold temperatures.  We’ve received several calls and e-mails regarding soybean seedling damage (from those who have actually been able to plant).  It appears that some soybean fields were hit with a “trifecta” of stress issues. What should we be looking for in terms of frost, PPO herbicide injury, and disease?

    Frost.  Frost can occur at air temperatures between 32-36°F while a freeze requires temperatures less than 32°F.  From the weather records I have looked over, air temperature dropped as low as 34°F in northern Ohio on May 16.  Soybean plants should be assessed for frost damage at least five days after suspected injury to inspect for regrowth.  If damage occurs above the cotyledons, the plant will likely recover.  If damage occurs below the cotyledons, the plant will not recover.  Look for a discolored hypocotyl (the “crook” of the soybean that first emerges from the ground) which indicates that damage occurred below the cotyledons.  If soybeans were not yet emerged at the time of the frost, they should be fine.  I did observe some frost damage last week in west central Ohio; however, just the tips of the cotyledons were damaged, so a full recovery is expected.

    Herbicide.  Many of the situations we were made aware of involved the use of flumioxazin (Valor) products, which are widely used in the state, along with sulfentrazone (Authority) products.  Both of these PPO-inhibiting (group 14) active ingredients can injure soybeans, but primarily when applied after planting.  Injury is most likely when the herbicide is applied closer to the time of soybean emergence and rain occurs during this period also.  This is the reason for the statement on flumioxazin product labels specifying that the herbicide can be applied only up to two days after planting.  Even this restriction does not completely prevent injury, since we have observed it in our research plots from applications on the day of planting.  Most of the residual soybean herbicides used in Ohio are applied a week or more before planting with burndown herbicides, which greatly reduces the risk of injury.

    Symptoms of soybean injury from soil-applied group 14 herbicides include necrosis of cotyledons and early leaves, distorted leaf growth, and reduced rate of growth (stunting).  The severe injury and death of plants that has been observed in some fields would be atypical of this type of herbicide injury.  However, the herbicides were applied after planting in these fields followed by substantial rain and cold, so herbicides could be a contributing factor.  This situation has been observed in other soybean-growing areas, and addressed in university newsletters and blogs.  Two examples:

    “Soybean Injury from Soil-applied Herbicides” U of Illinois,

    Soybean Seedling Emergence Issues:  Environmental Stress Compounding Factors, Mississippi State

    Disease.  Heavy rains on poorly drained soils will provide the perfect environment forPythium spp.  Add to this situation injured soybeans, several other types of fungi will move in and take advantage as well.  We were able to receive plants from several of the affected fields, and the pathogens are present.  Pythium as well as Fusarium are the two that we recovered from affected seedlings.  Seedlings with soft brown to dark tissue will not recover.  The lesions will continue to grow.  Seedlings with some small lesions will recover but may not perform to the fullest potential through the season. 

    Optimum Soybean Stand.  During the past ten years, the AgCrops Team has conducted several seeding rate trials which are summarized below.  Generally, soybean yield is maximized when there is at least 116,000 plants/acre at harvest when planting in May.  When planting in June, generally at least 155,000 plants/acre is necessary at harvest to maximize yield.  To quickly estimate stand, count the number of plants in 69’8” of row for 7.5 inch row spacing, 34’10” for 15 inch row spacing, or 17’5” of row for 30 inch row spacing.  These counts represent 1/1000th of an acre (i.e., 120 plants in 69’8” of row in 7.5 inch row spacing = 120,000 plants/acre).  Also, keep in mind soybean yield is decreased by approximately half a bushel per acre every day when planting later than mid-May.  When considering replanting soybean, make sure to take into account existing stand, yield loss due to late planting, and the cost of additional seed (we recommend higher seeding rates when planting in June).  

Crop Observation and Recommendation Network

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.


Bruce Clevenger, CCA (Field Specialist, Farm Management)
Eric Richer, CCA (Field Specialist, Farm Management)
Glen Arnold, CCA (Field Specialist, Manure Nutrient Management )
Les Ober, CCA (Educator, Agriculture and Natural Resources)
Mark Badertscher (Educator, Agriculture and Natural Resources)
Mike Gastier, CCA (Educator, Agriculture and Natural Resources)
Nathan Douridas, CCA (Farm Science Review Farm Manager)
Sam Custer (Educator, Agriculture and Natural Resources)
Sarah Noggle (Educator, Agriculture and Natural Resources)
Tony Nye (Educator, Agriculture and Natural Resources)


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