Corn Newsletter : 2017-30

  1. Is Late Maturing Corn at Risk of Frost Injury?

    Author(s): Peter Thomison

    According to the National Agricultural Statistics Service ( as of Sept. 10, 69 percent of Ohio’s corn acreage was in the dent stage (R5) compared to 76 percent for the five-year average; 16 percent of the corn acreage was mature, slightly less than the five-year average, 18 percent. In some areas of the state, corn is considerably behind the five-year average because of late planting (the result of persistent rains and excessively wet soils that delayed planting in some localized areas) and cooler than normal temperatures in September. This later than normal maturation of the corn crop had led to questions concerning the potential for frost damage.

    In Ohio, physiological maturity (when kernels achieve maximum dry weight and black layer forms) typically occurs about 65 days after silking. At physiological maturity (kernel moisture approximately 30-35%), frosts have little or no effect on the yield potential of the corn crop.

    Dr. Bob Nielsen at Purdue University has summarized research findings from Indiana and Ohio that provide insight into both the calendar days and thermal time (growing degree days, GDDs) typically required for grain at various stages of development to achieve physiological maturity (kernel black layer, R6) and available on-line at The calendar days and thermal time from various grain fill stages to black layer for a 111-day hybrid maturity are shown in Table 1 (click here).

    This research indicated that corn planted in early June compared to early May requires 200 to 300 fewer GDDs to achieve physiological maturity.  Although slightly different responses among the four locations of the trial existed, there did not seem to be a consistent north / south relationship. Therefore, growers can use the results summarized in Table 1 to "guesstimate" the number of calendar days or heat units necessary for a late-planted field at the given grain fill stages to mature safely prior to that killing fall freeze.

    How many GDDs can be expected from now until an average date of a killing frost for an adapted 111-day hybrid planted in mid-June?  To answer this question, estimate the expected GDD accumulation from Sept. 2 until the average frost date (50% probability) for different regions of the state (click here for Table 2).  These GDD expectations are based on 30-year historical normals reported by the Ohio Agricultural Statistics Service. The GDD accumulation was calculated using the 86/50 cutoff, base 50 method.

    If you want to determine the "youngest stage of corn development" that can safely reach black layer before the average frost date at a given weather station, use the information in Table 2 on remaining GDD in conjunction with Table 1 which indicates GDDs needed to reach black layer at various stages of grain fill. Compare "GDDs remaining" for the site with the GDD required to achieve black layer depending on the corn's developmental stage.

    If your corn is in the dent stage (R5) as of Sept. 9, will it be safe from frost? Table 1 indicates that corn planted in mid - June required about 217 GDDs to reach black layer from R5 and Table 2 indicates that all regions of the state are likely to accumulate sufficient GDDs before the 50% frost date.

    However, if your corn is in the “milk” stage (R3) as of Sept. 9, it’s a different story. The kernel development - GDD accumulation relationships in Table 1 indicate that corn planted in mid-June that is at R3 needs about 681 GDDs to reach black layer. Table 2 indicates that no region of the state accumulates that number of GDDs before the 50% frost date. What if your corn is at the dough stage (R4) as of Sept. 9? According to Table 1 corn planted in late May that is at R4 requires about 489 GDDs to reach black layer and Table 2 indicates that only one region of the state (south central Ohio) come close to accumulating that number of GDDs before the 50% frost date.

    The research results in Table 1 demonstrate that late planted corn has the ability to adjust its maturity requirements, and most of this adjustment occurs during the late kernel development stages. In previous growing seasons when GDD accumulation was markedly less than normal, the corn crop has usually achieved physiological maturity before the first frost occurred.


    Nielsen, R.L. 2011. Predicting Corn Grain Maturity Dates for Delayed Plantings

    Corny News Network, Purdue Univ. [On-Line]. Available at

  2. Cool Weather and Corn Dry Down

    Author(s): Peter Thomison

    The recent cooler than normal temperatures may impact corn drydown. Once corn achieves physiological maturity (when kernels have obtained maximum dry weight and black layer has formed), it will normally dry approximately 3/4 to 1% per day during favorable drying weather (sunny and breezy) during the early warmer part of the harvest season from mid‑September through late September. By early to mid‑October, dry-down rates will usually drop to ½ to 3/4% per day. By late October to early November, field dry‑down rates will usually drop to 1/4 to 1/2% per day and by mid November, probably 0 to 1/4% per day. By late November, drying rates will be negligible.

    Estimating dry‑down rates can also be considered in terms of Growing Degree Days (GDDs). Generally, it takes about 30 GDDs to lower grain moisture each point from 30% down to 25%. Drying from 25 to 20 percent requires about 45 GDDs per point of moisture. In October, we accumulate about 5 to 10 GDDs per day. However, note that the above estimates are based on generalizations, and it is likely that some hybrids may vary from this pattern of drydown. Some seed companies indicate considerably lower GDDs for grain moisture loss, i.e. 15 to 20 GDDs to lower grain moisture each point from 30% down to 25% and 20 to 30 GDDs per point from 25% to 20%.

    Past Ohio research evaluating corn drydown provides insight on effects of weather conditions on grain drying. During a warm, dry fall, grain moisture loss per day ranged from 0.76 to 0.92%. During a cool, wet fall, grain moisture loss per day ranged from 0.32 to 0.35%. Grain moisture losses based on GDDs ranged from 24 to 29 GDDs per percentage point of moisture (i.e., a loss of one percentage point of grain moisture per 24 to 29 GDDs) under warm dry fall conditions, whereas under cool wet fall conditions, moisture loss ranged from 20 to 22 GDDs. The number of GDDs associated with grain moisture loss was lower under cool, wet conditions than under warm, dry conditions.

    Agronomists generally recommend that harvesting corn for dry grain storage should begin at about 24 to 25% grain moisture. Allowing corn to field dry below 20% risks yield losses from stalk lodging, ear drop, ear rots, insect feeding damage and wildlife damage.

    For more on grain drydown, check out the following article by Dr. Bob Nielsen at Purdue

    Nielsen, R.L. 2013. Field Drydown of Mature Corn Grain. Corny News Network, Purdue Univ.
    URL: [URL accessed Sept. 11, 2017].

  3. Cover Crop Seeding into Standing Soybeans

    As soybeans are maturing around Ohio, an opportunity to establish an early cover crop is available.   If a farmer waits until after soybean harvest, then many days of growth are being wasted.

    Soybeans should have dropped 10% of their leaves before seeding a cover crop.  Planting too early and the cover crop may have too much growth and interfere with combine operation and green material separation.  Waiting too late will place the seed on top of fallen leaves and not contact the soil properly.  The idea is to place the seed on the soil, then have soybean leaves cover and mulch the cover crop seed to enhance germination.

    Cover crops can be aerial seeded by plane or helicopter.  Use an experienced pilot who can calibrate the application and control seed drop location.  Also a high clearance sprayer can be used that is adapted for seed delivery.  Following tram lines will lessen the damage to soybeans from wheel tracks. 

    Germination success may be more difficult with broadcast seeding versus drilling or planting.  Therefore, seeding rates may need to be increased about 25% to result in a similar stand of cover crops compared to drilled.  Ideally, seeding before a rainfall will get the cover crops off to a quick start.

    Species like brassicas (radish), oats, buckwheat, and other frost sensitive cover crops need to be seeded before soybean harvest to ensure enough growing time before killing frost.  Frost tolerant species such as cereal rye (at 1-2 bushel per acre) can be seeded into late fall.    A mixture of cover crop seed such as ;  radish, crimson clover, and oats would do well seeded into standing soybeans.  A rate of 2 pounds radish, 15 pounds crimson clover, and 30 pounds oats per acre are minimum for soil coverage.

    Annual ryegrass (at 30-60 pounds per acre) will also do well seeded into standing soybeans.  Topgrowth is less than cereal rye yet root growth is deeper and more aggressive that cereal rye.  With any cover crop that overwinters, have a plan in place for termination next spring.

    Large seed size, such as Austrian Winter Pea, do not do well broadcast seeded.  Large seeded cover crops need to be incorporated into the soil for better seed/soil contact for germination.

    For more information refer to :

    Aerial Seeding of Cover Crops – NRCS Technical bulletin Agronomy #36

  4. Producing Wheat in 15-inch Rows

    Growers are interested in wide-row wheat production due to changes in equipment inventory (lack of grain drill and availability of air seeder) and to allow intercropping of soybean into wheat. Wheat row spacing work was conducted during the 2012-2013 and 2013-2014 growing seasons with funding from the Ohio Small Grains Marketing Program and Michigan Wheat Program. Overall, wheat grown in 15-inch row widths yielded 1 to 11% lower compared to wheat grown in 7.5-inch row widths.

    If you are planting wheat in 15-inch rows, consider the following:

    1.) Variety selection. Choose a variety that is high yielding and resistant to major diseases such as powdery mildew, leaf rust, Septoria and Stagonospora blotches, and head scab. See for the Ohio Wheat Performance Test Wide Row Evaluation.

    2.) Planting date. Plant wheat as soon as possible after the Hessian fly-safe date.

    3.) Seeding rate. A seeding rate of 25 to 29 seeds/foot of row (0.85 to 1.0 million seeds/acre) is recommended. In on-farm research trials conducted in Fulton County, there was no yield increase when wheat was seeded at 29 seeds/foot of row (1.0 million seeds/acre) compared to 43 seeds/foot of row (1.5 million seeds/acre).

    4.) Herbicide application. Spring herbicide application is very important to maximize yield.

    5.) Disease control. Changing row spacing will change the microclimate within the wheat canopy, and this could affect disease development. Scout fields for foliar diseases and use the scab forecasting system ( to determine whether disease risk is high enough to warrant a fungicide application.

  5. More on the Diagnosis of Southern Rust of Corn

    Author(s): Pierce Paul

    With corn now beyond the R4 growth state in most fields, there is really nothing you can do about southern rust in terms of fungicide application. However, correct diagnosis of this disease is still very important from the standpoint of identifying the hybrids that were most severely affected. Although our growing conditions generally do not favor this disease and we may go for another several years without seeing as much southern rust as we did in 2017, we still need to identify those highly susceptible hybrids. Late-season rust symptoms have some very characteristic features that are extremely useful for diagnosis.

    Late-season rust symptoms are somewhat different from those observed early in the season, adding to the confusion of trying to tell the difference between southern and common rusts. Figure 1, (click here) shows early southern rust pustules on the surface of a leaf. Notice the bright orange color that is considered typical of this disease. These look considerably different from the pale to almost yellowish-colored pustules in Figure 2 (click here). This latter picture also shows symptoms of southern rust, but these are older pustules on the leaf of an R5 plant. Southern rust symptoms often begin as bright reddish-orange pustules, but as the pustules and the leaf age, they take on the pale appearance seen in Figure 2.

    Taking a closer look at aging leaves with the pale pustules, you will also notice some very distinct black specks (insert in Figure 2). There are telia, a different stage of the same disease. Yes, we are still talking about southern rust. As the leaves age and begin to die, the fungus kicks into a type of “survival mode”, producing black instead of orange pustules. These black pustules may also develop on the stems and leaf sheaths as shown in Figure 3 (click here), and their arrangement relative to the orange or pale pustules is very important for the diagnosis of southern rust. As highlighted in Figure 3, the black pustules do not replace the orange pustules, but develop around them. This can be seen with the naked eyes by carefully examining the leaves, but are better detected with a hand lens or microscope as shown in Figure 4 (click here).        

    Common rust produces large cinnamon-brown pustules early-on, that also become pale and later dark, but the dark pustules usually replace the cinnamon-brown or pale-colored pustules instead of surrounding them.            

  6. Ag Crops Team at FSR

    The Farm Science Review will be held again this year at the London, Ohio location. Dates are September 19, 20 and 21. See for more information. Harvest has not quite stared yet so you should have the time to check in.

    The Agronomic Crops Team ( will once again be welcoming visitors on the east side of the grounds between the parking lot and the exhibit area.

    • Many farmers arrive early at Farm Science Review to beat the traffic. This year we will reward those early risers at 7:30 and 8 a.m. with coffee, a donut and pesticide credits at the Agronomy tent.
    • Other talks we will have at 9 a.m. and at 1 p.m. include Managing Manure for Crop Use, Soil Quality and Soil Health, Adaptive Nutrient Management and talks on Corn and Soybean management.
    • Sign in for the C.O.R.N. newsletter with your county, email and a text number so we can let you know to pick up your prize:
      • OSU Agronomy publications – the new Ohio Agronomy Guide or a Weed Control Guide
      • Or an AgCrops logoed seed corn digging tool
      • Or an AgCrops logoed Yeti products

    The Agronomic Crops Team also supports Certified Crop Advisers in the state. So, with many farmers and their advisers coming to Farm Science Review we will have several places across the grounds for CCA continuing education credits – all for the price of the FSR admission.

    • Areas to look for CEUs are in:
      • Agronomy plots at the east end of the exhibit area, at the
      • Small Farms Centers in the northwest corner of the grounds and up the road toward the grain bins is the
      • Gwynne Conservation area. The Gwynne has really increased their activities and the number of CCA CEUs there shows this.
    • Check the FSR program guide for CEU opportunities.

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.


Anne Dorrance (State Specialist, Soybean Diseases)
Chris Zoller (Tuscarawas County)
Clifton Martin, CCA (Muskingum County)
Dean Kreager (Licking County)
Debbie Brown, CCA (Shelby County)
Dennis Riethman (Mercer County)
Elizabeth Hawkins (Field Specialist, Agronomic Systems)
Garth Ruff (Henry County)
Glen Arnold, CCA (Field Specialist, Manure Nutrient Management )
Jeff Stachler (Auglaize County)
Ken Ford (Fayette County)
Les Ober, CCA (Geauga County)
Mark Badertscher (Hardin County)
Mark Loux (State Specialist, Weed Science)
Mary Griffith (Madison County)
Mike Estadt (Pickaway County)
Mike Gastier, CCA (Huron County)
Sam Custer (Darke County)
Wayne Dellinger (Union County)


The information presented here, along with any trade names used, is supplied with the understanding that no discrimination is intended and no endorsement is made by Ohio State University Extension is implied. Although every attempt is made to produce information that is complete, timely, and accurate, the pesticide user bears responsibility of consulting the pesticide label and adhering to those directions.

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