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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2008-27

Dates Covered: 
August 18, 2008 - August 25, 2008
Andy Kleinschmidt

Estimating Yield Losses in Drought Stressed Corn Fields

Authors: Peter Thomison

Many Ohio counties have received only trace amounts of rain since early July and are extremely dry. Fields planted in late May and June are more likely to be impacted by this dry weather. In upcoming weeks, corn growers with drought stressed fields may want to predict grain yields prior to harvest in order to help with marketing and harvest plans. Moreover, while examining ears to determine potential grain yield, growers may encounter various ear development problems that may impact yield at harvest. Troubleshooting these corn ear disorders now rather than at harvest may give growers more time to diagnose likely causes of these problems.

Two procedures which 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.

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 90.

Step 5. Repeat the procedure for at least four additional sites across the field.

Example: You are evaluating a field with 30 inch rows. You counted 24 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 30. The estimated yield for that site in the field would be (24 x 16 x 30) divided by 90, which equals 128 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. Since drought stress conditions in some fields may result in poorly filled small ears, there may be mechanical difficulties with sheller or picker efficiency that need to be considered. When droughts occur, it’s often cheaper to buy corn for grain than to buy hay for roughage (because of likely forage deficits). Therefore, there may be greater benefit in harvesting fields with marginal corn grain yield potential for silage.

Abnormal Corn Ears

Authors: Allen Geyer, Peter Thomison

Corn growers may encounter a wide range of ear development and pollination problems during the growing season that affect grain yield and quality. This year is no exception and during past weeks, I’ve received reports and questions concerning blunt ears (“beer can ears”), “silk balling”, hail damaged ears, crazy top, smut, and barrenness. To help growers sort out various ear disorders and their possible causes, we’ve prepared a poster “Abnormal Corn Ears” and an accompanying web page “Troubleshooting Abnormal Corn Ears and Related Disorders”.

In the poster, ten abnormal corn ears with distinct symptoms and causes are highlighted. A reduced 11 x 14 inch version of the “Abnormal Corn Ears” poster is available online at

The webpage, “Troubleshooting Abnormal Corn Ears and Related Disorders” available online at provides more detailed diagnostic information on various corn ear disorders.

Our Communications & Technology section (contact information below) has 26 x 33 inch copies of the poster available for distribution. Ask for “Abnormal Corn Ears” poster” ACE-1. Poster cost is $10 plus shipping.

The Ohio State University
Communications and Technology
Media Distribution
216 Kottman Hall, 2021 Coffey Road
Columbus, OH 43210-1044
Phone 614-292-1607
Fax 614-292-1248

Ohio residents can contact their local county Extension office to place orders for the poster.

Twospotted Spider Mites on Soybean

Authors: Bruce Eisley, Andy Michel, Ron Hammond

We reported a few weeks ago that twospotted spider mite problems were beginning to occur in dry areas around Ohio. Most of this has been along field edges. The incidence of mites has increased in the state. We continue to think that they will not become whole field infestations, although growers should nevertheless check areas within their fields. Added to this concern is that in late August we begin to see higher nighttime humidity, which causes the plants to become very wet by early morning. These higher moisture levels will often cause a mite pathogen to become prevalent and help reduce the mite populations. Thus, before spraying for these mites, make sure that mites are still active and numerous on the lower leaf surfaces. It is a waste of money to be spraying mites that have already died.

If mites have built up sufficiently along the field borders, growers should make an edge spray, going at least one spray beyond where the see mite injury. This should give the soybeans enough time to continue to make good yields, especially if the normal rains in late August begin again. As mentioned in the earlier newsletter article, growers have a few choices in materials to spray: chlorpyrifos (Lorsban and various other formulations), dimethoate, Hero, and Cobalt.

Soybean Aphid Update

Authors: Ron Hammond, Andy Michel, Bruce Eisley

Reports are being received of aphids showing up in fields in northern and central Ohio. These populations are normal for late August in a “low” aphid year. These will be the aphids that give rise to the upcoming overwintering populations that we expect to find on buckthorn this fall. Except for very rare instances, these aphids on soybean should not build up to treatable levels, that being an average of 250 aphids per plant, with the population still rising. Most importantly, with most soybeans entering the full seed stage, growth stage R6, the thresholds are probably higher. However, at this time, we do not have good data to set a specific threshold at R6, but we know it takes more aphids than 250 per plant. We recommend growers monitor late planted soybean fields that are still in the R3-4 stages, but we do not expect much problems in them either. Stay tuned to the C.O.R.N. newsletter for information on what we find on buckthorn this fall, and for our prediction for 2009.

2008 FSR CCA College Set for September 18th

Authors: Harold Watters

Again this year we want to encourage you to attend the Farm Science Review. Plan also now to participate in a program targeting Certified Crop Advisors (CCA) and field agronomists.

The Ohio State University Agronomic Crops Team in cooperation with Purdue University will be presenting a Certified Crop Adviser program at the Review, the FSR CCA College.

Planned program:

• This is a soybean year for the demonstration area. We have field demonstrations at the training site with six fungicide treatments looking at Frogeye leafspot (and we expect to see other diseases too). This will feature OSU Plant Pathologist Dr. Anne Dorrance discussing diseases of the eastern cornbelt. We also expect to discuss Soybean cyst nematode, Sudden death syndrome as well as soybean insect issues.

• Also on the program will be Agricultural Econ-Agronomist Dr. Bruce Erickson from Purdue with a discussion on the Economics & Adoption of Precision Farm technology. Bruce runs the Top Farmer program at Purdue, has a great agronomic background and can pull this topic together for folks. Bruce will be aided in his discussion by members of the OSU Precision Ag Team.

• The third and final segment will center around fertility issues. We have had a lot of questions surrounding cover crops and nitrogen management. OSU Soil fertility specialist Dr. Robert Mullen will be discussing his work with N rates and cover crops. Robert will be joined by Purdue fertility specialists discussing other specific fertility management issues from this season.

The program will start at 8AM on Thursday of the Farm Science Review, September 18th, and end at noon followed by lunch. During the program and afterwards over lunch you will have time for interaction with other crop advisors and a chance to ask questions of the Ohio State University and Purdue University agronomic specialists.

For the CCA continuing education credits, meal, a parking pass, a ticket to the Farm Science Review and access to some of Indiana and Ohio’s best state specialists, we will charge $75. Registration is limited, please register now through September 5th; no registrations will be taken after that date.

To register this year you may download a registration form and the program details from:

We can also mail or fax a registration form if you wish; for more information call Harold Watters at the Champaign County Extension office 937 484-1526 or email

CORN as a Podcast

Authors: Jonah Johnson, Harold Watters

Would you like the ability to hear the C.O.R.N. newsletter? Perhaps you don’t always have time to read it but want the information anyway? One possible way to get the information is by listening to the newsletter as a podcast. The Communications and Technology folks at OSU last year helped us create the CORN newsletter as a podcast. After a lull and some adjustments we have brought the CORN newsletter back as a podcast again, with help from Jonah Johnson, Clark AgNR and Marissa Mullett, Coshocton AgNR.

The CORN newsletter audio version is available in three places:

• It is on an Ohio State University class server:

• And as a link on the Agronomic Crops Team website, It is located at the top of the center column, above the articles and under the C.O.R.N. To Go… Here you may select either the mp3 version of the newsletter, which may be played of any mp3 player or on most CD players. The m4a formatted newsletter may only be played through iTunes.

• Also available on iTunes as a podcast. Apple iTunes is free downloaded software from that can be used on a Windows PC or a Macintosh computer. Once you have downloaded iTunes you may locate the CORN newsletter by searching for OSU CORN, and then subscribe to the newsletter. In the future the newsletter will be automatically retrieved as you log in to iTunes.

One note - due to the length of the newsletters the narrative is a little slow in getting posted - Jonah, Marissa and CommTech will try to keep up but expect the audio version to follow the written newsletter by a day or two. Please let us know if you appreciate having the newsletter available in this audio format.

Weather Update

Authors: Jim Noel

No changes from last week. We are forecasting near normal temperatures into September and below normal rainfall.

Dry for most of this week followed by scattered rainfall this coming weekend into next week then a return to drier weather thereafter. We may see slightly above normal temperatures in the short term this week into next week but over the next 30-40 days it should be close to average for temperatures.

Another way to get CORN To Go: Regional Crop Reports Reminder

Authors: Harold Watters

With the variable conditions this summer, sometimes it helps to have a more localized report of conditions and pests in you region or county.

Many of the county Extension professionals and Agronomic Crops Team members include their local crop, insect, disease and weather scouting information on their county or regional websites. This information can be used to fill in the holes that can occur when a state specialist makes a report and recommendations to cover the entire state. Several new regional blogs have been added during this year to help with crop problems and pest issues during the growing season.

Blogs and websites with local Ohio crop progress, pest updates and weather information:

West Central Ohio – covering the counties of Darke, Auglaize, Miami. Mercer, Champaign, Clark, Logan and Shelby:
Northwest Ohio – from Fulton, Williams, Defiance and Paulding Counties:
Van Wert County:
Northeast Ohio, covering Geauga, Ashtabula and Trumbull Counties:
Coshocton County and east central Ohio:
South central Ohio – Fayette, Pickaway and Ross Counties:

Archive Issue Contributors: 

State Specialists: Ann Dorrance, Pierce Paul and Dennis Mills (Plant Pathology), Ron Hammond, Andy Michel and Bruce Eisley (Entomology), Peter Thomison (Corn Production), Mark Loux (Weed Science) and James Noel (NOAA/NWS/OHRFC). Extension Associates and Educators: Roger Bender (Shelby), Greg La Barge (Fulton), Steve Bartels (Butler), Wesley Haun (Logan), Harold Watters (Champaign), Glen Arnold (Putnam), Howard Siegrist (Licking), Mike Gastier (Huron), Tim Fine (Miami), Les Ober (Geauga), Jonah Johnson (Clark), and Suzanne Mills-Wasniak (Montgomery).

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.