C.O.R.N. Newsletter 2013-25

Dates Covered: 
August 6, 2013 - August 13, 2013
Rory Lewandowski

How Late is too Late to Apply Foliar Fungicide in Corn?

We have seen positive results in terms of disease control and yield for foliar fungicide applications made before tassel, at tassel, and even as late as R3. However, from year to year, the most consistent results and the greatest benefits are seen when applications are make at tassel or silking (VT/R1). The diseases we are most concerned about in Ohio such as gray leaf spot and eye spot usually develop from the lower to the upper leaves of the plant. Fungicides are applied to prevent these diseases from moving up and reaching the ear leaf and the leaves above the ear leaf before grain fill is complete. Some diseases like rust and northern corn leaf blight may show up first on the upper leaves, but in most years this usually occurs too late (after R3) to significantly affect grain yield. By the time we get to brown silk (R2), the number of rows of kernel per ear and the number of kernels per row are already made. Therefore, applying a fungicide at or after R2 will not change these numbers, even if disease lesions develop on the upper leaves. However, severe blighting of the upper leaves after R2 may affect the size of the kernels, and as such, we may see a benefit form applying a fungicide between R2 and R3.

Based on reports coming in from across the state, most of the corn in Ohio is at the R2-R3 growth stage, with very little or no disease on the upper leaves. However, gray leaf spot, eye spot and southern corn leaf spot have been reported on the leaves below the ear in some fields planted with susceptible hybrids. Before making a decision to apply a fungicide, walk the field and look for disease lesions and determine the growth stage of your crop. If your crop is at R1 or early R2, and you have a susceptible hybrid, and there are disease lesions on the leaves below the ear, you may see a benefit from a fungicide application. However, if your hybrid is resistant or moderately resistant, your crop is past brown silk (R2), and lesions are restricted to the leaves below the ear, you are less likely to see a benefit from applying a fungicide. In addition to not always being as effective as VT/R1 applications, late applications may be off label. Some fungicides cannot be applied after R3 or R4. Before making an application, please read product labels carefully.             

Bean Leaf Beetle Pod Feeding

We received a report from central Ohio on pod feeding occurring in an early planted soybean field, which is extremely early.  Pods were large enough to indicate that the plants were well into the R4 growth stage.  The culprit is probably bean leaf beetles, which at this time of year would most likely be from the first generation.  Other possible insects feeding on the pods at this time might be grasshoppers.  Whatever the case, growers might want to check their fields, perhaps concentrating on early planted fields which would have the highest populations of first generation bean leaf beetle.  If pod feeding is occurring and has reached 10-15%, an insecticide treatment would be warranted.  If checking fields, make sure to walk 100 feet into the field to take away the field edge effect.  We will further address pod feeding in future C.O.R.N. issues.

Estimating Corn Yields Prior to Harvest

Two procedures that are widely used for estimating corn grain yields prior to harvest are the YIELD COMPONENT METHOD (also referred to as the "slide rule" or corn yield calculator) and the EAR WEIGHT METHOD. Each method will often produce yield estimates that are within 20 bu/ac of actual yield. Such estimates can be helpful for general planning purposes.

THE YIELD COMPONENT METHOD was developed by the Agricultural Engineering Department at the University of Illinois. The principle advantage to this method is that it can be used as early as the milk stage of kernel development, a stage many Ohio corn fields have probably achieved. The yield component method involves use of a numerical constant for kernel weight which is figured into an equation in order to calculate grain yield. This numerical constant is sometimes referred to as a "fudge‑factor" since it is based on a predetermined average kernel weight. Since weight per kernel will vary depending on hybrid and environment, the yield component method should be used only to estimate relative grain yields, i.e. "ballpark" grain yields. When below normal rainfall occurs during grain fill (resulting in low kernel weights), the yield component method will OVERESTIMATE yields. In a year with good grain fill conditions (resulting in high kernel weights) the method will underestimate grain yields.

In the past, the YIELD COMPONENT METHOD equation used a "fudge factor" of 90 (as the average value for kernel weight, expressed as 90,000 kernels per 56 lb bushel), but kernel size has increased as hybrids have improved over the years. Dr. Bob Nielsen at Purdue University suggests that a "fudge factor" of 80 to 85 (85,000 kernels per 56 lb bushel) is a more realistic value to use in the yield estimation equation today: http://www.agry.purdue.edu/ext/corn/news/timeless/YldEstMethod.html

Step 1. Count the number of harvestable ears in a length of row equivalent to 1/1000th acre. For 30‑inch rows, this would be 17 ft. 5 in.

Step 2. On every fifth ear, count the number of kernel rows per ear and determine the average.

Step 3. On each of these ears count the number of kernels per row and determine the average. (Do not count kernels on either the butt or tip of the ear that are less than half the size of normal size kernels.)

Step 4. Yield (bushels per acre) equals (ear #) x (avg. row #) x (avg. kernel #) divided by 85.

Step 5. Repeat the procedure for at least four additional sites across the field. Keep in mind that uniformity of plant development affects the accuracy of the estimation technique.

The more variable crop development is across a field, the greater the number of samples that should be taken to estimate yield for the field.

Example: You are evaluating a field with 30‑inch rows. You counted 29 ears (per 17' 5" = row section). Sampling every fifth ear resulted in an average row number of 16 and an average number of kernels per row of 33. The estimated yield for that site in the field would be (29 x 16 x 33) divided by 85, which equals 180 bu/acre.

THE EAR WEIGHT METHOD can only be used after the grain is physiologically mature (black layer), which occurs at about 30‑35% grain moisture. Since this method is based on actual ear weight, it should be somewhat more accurate than the yield component method above. However, there still is a fudge factor in the formula to account for average shellout percentage.

Sample several sites in the field. At each site, measure off a length of row equal to 1/1000th acre. Count the number of harvestable ears in the 1/1000th acre. Weigh every fifth ear and calculate the average ear weight (pounds) for the site. Hand shell the same ears, mix the grain well, and determine an average percent grain moisture with a portable moisture tester.

Calculate estimated grain yield as follows:

Step A) Multiply ear number by average ear weight.

Step B) Multiply average grain moisture by 1.411.

Step C) Add 46.2 to the result from step B.

Step D) Divide the result from step A by the result from step C.

Step E) Multiply the result from step D by 1,000.

Example: You are evaluating a field with 30‑inch rows. You counted 24 ears (per 17 ft. 5 in. section). Sampling every fifth ear resulted in an average ear weight of 1/2 pound. The average grain moisture was 30 percent. Estimated yield would be [(24 x 0.5) / ((1.411 x 30) + 46.2)] x 1,000, which equals 135 bu/acre.

Because it can be used at a relatively early stage of kernel development, the Yield Component Method may be of greater assistance to farmers trying to make a decision about whether to harvest their corn for grain or silage.


 Nielsen, RL. 2011.  Estimating Corn Grain Yield Prior to Harvest. Corny News Network, Purdue University. http://www.agry.purdue.edu/ext/corn/news/timeless/YldEstMethod.html

(URL checked August 5, 2013).

Foliar diseases are common this year

Frogeye leaf spot and brown spot are very common this year.  This is especially surprising for frogeye.  There is resistance in northern varieties, so this is a great year to assess the resistance levels in those varieties.

Soybean rust (SBR) has made it to northern Alabama (http://sbr.ipmpipe.org/cgi-bin/sbr/public.cgi ).  My colleague Dr. Ed Sikora found soybean rust in DeKalb County in the northeast corner of the state.  He stated “less than 1% of the plants had visible symptoms.  The plot consisted of a group III variety at the R5 growth stage with 80% canopy coverage.  This is the earliest SBR has been detected in DeKalb County by approximately 4 weeks.”

Soybean rust is found in the lower to mid canopy of the crop.  The rust lesions are found on the underside of the leaf and look like small craters filled with light colored spores.  If you have questions and want to be sure that your fields are free of rust to date, send leaves, 50 to 100, in a plastic bag to the:

Soybean Pathology Lab, OARDC, 1680 Madison Ave., Wooster, OH  44691

Phone:  330-202-3560 or to:

 C. Wayne Ellett Plant and Pest Diagnostic Clinic
The Ohio State University
8995 E. Main Street, Bldg. 23
Reynoldsburg, OH 43068-3399

Phone: 614-292-5006

(If SBR is suspected, ship samples using overnight services and not over the weekend; leaves can deteriorate rapidly if in the bag too long.  Or hand deliver to either location.)

Note:  Soybean rust has not been documented in the state, so we still are required to go through the first find procedures.  We have been scouting southern Ohio and to date have not found soybean rust.  We will increase our efforts over the next week.

Soybeans that were planted during May/early June are not at risk from soybean rust.  However, there are several fields in the very southern counties that were not planted until early July.  These may be at some risk. This will be dependent if rain storms come up from the south.  We will be monitoring developments and finding of soybean rust in Tennessee and Kentucky.

2013 Ohio Wheat Performance Results Available

The purpose of the Ohio Wheat Performance Test is to evaluate wheat varieties, blends, brands, and breeding lines for yield, grain quality and other important performance characteristics. This information gives wheat producers comparative information for selecting the varieties best suited for their production system and market. Varieties differ in yield potential, winter hardiness, maturity, standability, disease and insect resistance, and other agronomic characteristics. Depending on variety and test site, yields varied between 37.7 and 107.2 bushels per acre, and test weight ranged from 55.6 to 59.4 pounds per bushel. Selection should be based on performance from multiple test sites and years. Results of the 2013 wheat performance evaluation are available at:  http://hostedweb.cfaes.ohio-state.edu/perf  and https://agcrops.osu.edu/specialists/wheat

Weather Outlook

As a state, this summer has seen about normal temperatures with rainfall slightly wetter than normal.

For Ohio, May was the 19th driest, June was the 111th wettest out of 119 years. July data was not in yet but it was wetter than normal. It is shaping up to be slightly wetter than normal for the summer as a whole in Ohio. Some places have been a bit drier, some wetter. Overall, it is about as good as it gets from weather issues in Ohio for summer growing conditions though.

Going forward, the trend looks to remain your friend. Expect temperatures to remain at or below normal for much of August. Temperatures for the week of August 5 will be near normal, the week of August 12 will be below normal. Daytime high will generally be below normal while overnight lows will be all over the place from normal to above normal this week and below next week.

Rainfall will be near normal for the state the week of August 5, but the north will be normal or slightly below while southern and eastern sections are above. Rainfall will be 0.5 to 1.0 inches in the north and 1-2 inches in the south and east sections. Normal is 0.75 to 1.0 inches.

Looking into autumn, early indications in June and July was near normal for temperatures and precipitation. However, our climate models are trending toward the pattern of this summer lingering into fall of slightly cooler and wetter conditions. Confidence is low right now but it does not look to be a real warm fall or dry based on current indications. We will try to get a better handle on this in the coming weeks. It still could turn out to be a real nice fall around here, hopefully we will know in the next few weeks.

The latest climate model run is here:



In early 2012, we called for a warmer and drier summer with negative impacts to crops and that happened. In late 2012 we called for a good growing year for 2013 with less risk and we have gotten it. We will keep you posed on what we think for 2014 in the coming months. Early indications are risk increases again in 2014, but how much is the question!

Machine Systems Engineer Search

The Ohio State University seeks qualified candidates for a 9 or 12-month, tenure-track faculty position for Machine Systems Engineering in the Department of Food, Agricultural and Biological Engineering, at the Assistant or Associate Professor available in Columbus starting January 1, 2014.  The search is open until September 1. Outstanding candidates at the Associate Professor level may be recommended for an endowed appointment. The successful candidate will:

  • Provide statewide leadership to outreach education in precision agriculture, as well as providing educational programs in traditional areas such as: conservation tillage practices; soil compaction; controlled traffic; cover crops; management strategies to reduce off-site sediment and nutrient movement from agricultural fields; and selection, proper operation and management of agricultural machinery.
  • Conduct engineering research addressing clientele needs such as field machinery automation, precision agriculture technologies, logistics of moving agricultural commodities from the field to market or storage, sustainable practices for the production of agricultural commodities, and environmental impacts of machinery systems.
  • Teach one course in machine systems.
  • Obtain funding to support research and outreach programs.
  • Advise graduate and undergraduate students.

Qualifications: An earned Ph.D. in agricultural engineering, biological engineering or closely allied program; and registration as a Professional Engineer or demonstrated eligibility.

For a full job description for this position, please visit http://fabe.osu.edu/sites/fabe/files/imce/files/Machinery%20Systems%20PD-5-21.pdf

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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.