http://www.ag.ohio-state.edu/~corn/

CORN
Crop Observation and Recommendation Network

September 4 to September 9, 2001
C.O.R.N. 2001-29

In This Issue:

A) Estimating Grain Yields in Corn Prior to Harvest
B) Determining the Proper Time to Harvest Corn for Silage
C) Variable Crop Conditions Warrant Some Special Harvest Considerations
D) Top Dieback From Anthracnose is Common in Some Locations
E) Grain Bin Clean-Up

A) Grain Yields in Corn Prior to Harvest - Peter Thomison CORN Questions

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. 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.

Calculate estimated grain yield using the Yield Component Method as follows:

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 using the Ear Weight Method 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. If stress conditions, such as drought, have resulted in poorly filled small ears, there may be mechanical difficulties with sheller or picker efficiency which need to be considered. Since it will probably be cheaper to buy corn for grain than to buy hay for roughage (because of the likely forage deficit), there will be greater benefit in harvesting fields with marginal corn grain yield potential for silage.

B) Determining the Proper Time to Harvest Corn for Silage - Peter Thomison and Mark Sulc CORN Questions

Despite relatively cool conditions recently, much of the early planted corn in SW Ohio and parts of West Central Ohio is rapidly maturing. Corn growers planning to ensile corn should be monitoring corn fields closely because their corn may be near or at the optimal stage for silage harvest.

Determining the proper time to harvest corn for silage is critical because whole plant dry matter (DM) content varies with maturity and it influences fermentation. Ensiling corn silage that is too wet produces poor fermentation, seepage losses, and lowered animal intake. Ensiling excessively dry corn increases the risk of heat damage and molding. Corn silage preserved between 30 and 40% DM generally provides good fermentation and animal performance, but different storage structures require different DM concentrations for optimal fermentation. Table 1 shows the recommended target DM content for corn silage in different types of structures:

Table 1. Recommended Dry Matter Content for Corn Silage Stored in Different Structures.

Structure	%DM
Upright, Top Unloading Upright, Bottom Unloading Horizontal	30 - 40 40 - 45 30 - 35

The recommended DM content for upright, bottom unloading silos is higher to ensure easier unloading. Horizontal silos require a lower DM content (higher moisture content) to ensure adequate packing to eliminate oxygen and prevent heating.

Observing the development of the corn kernel milkline has been suggested as an easy way to estimate when corn is at the proper dry matter content for ensiling. Generally, recommendations have been to harvest corn for silage when the milkline is 1/2 to 2/3 of the way down the kernel. However, Ohio research has indicated that there is a lot of variability in the relationship between the kernel milkline and whole plant DM content. The milkline is not a very accurate or reliable guide to gauge whole plant DM content. Hybrid, planting date, and growing season can affect the relationship between kernel milkline position and whole plant DM content. However, the appearance of the milkline in the upper 1/4 of the kernel indicates that the crop is very near the optimal time to harvest. A sample should be taken at this time and DM content determined with a commercial forage moisture tester or microwave oven.

A limited sampling of plots last week at the Waterman Farm in Columbus indicated that early planted (late April) corn was at the full dent stage of kernel development, with some corn as far along as 1/4 milkline. I've received similar reports from several seed company agronomists in SW and West Central Ohio.

Using a commercial forage moisture tester or microwave oven to determine the DM content is the best way to accurately determine the optimal time to harvest corn silage according to the storage structure to be used. Keep in mind that waiting until blacklayer will almost always result in corn being too dry for proper packing and fermentation, especially in horizontal and upright, top unloading silos.

For more information on handing corn silage, consult "Harvesting Drought-Stressed Corn for Silage" (Bill Weiss)in the C.O.R.N. (2001-26) newsletter for August 20 to August 26, 2001. On the internet at:
http://www.ag.ohio-state.edu/~corn/archive/2001/aug/01-27.html

C) Variable Crop Conditions Warrant Some Special Harvest Considerations - Peter Thomison CORN Questions

Dry weather in parts of Ohio (especially the NE) plus uneven crop development due to the protracted wet cold conditions in May and June, have has resulted in smaller than normal ears, and a greater percentage of "nubbin" ears in some fields. In addition, plants are shorter than normal with reduced ear heights. As a result of these conditions, some combine and harvesting adjustments may be necessary. The following are management suggestions from ag engineers and equipment specialists on harvesting drought-damaged crops.

Review the operator's manual for suggestions on harvesting a "light crop".
With short or lodged corn, run the gathering snouts and chains low. Watch for stones, and be sure stone protective devises are working.
Drive carefully and at normal speeds to avoid excessive harvest loss and machine damage from stones.
For small ears, set stalk rolls and snapping plates closer than normal to snap off a higher percentage of ears. Do not attempt to snap off barren cobs. clearance. Avoid excessive damage to kernels from good ears.
If cleaning losses are high, open the chaffer and chaffer extension slightly.
Initially decrease the amount of air from the cleaning fan. If cleaning becomes a problem, increase the fan blast, and close the lower sieve slightly.
Be alert to changes in weather and crop conditions, and make adjustments as necessary.

D) Dieback From Anthracnose is Common in Some Locations - Pat Lipps CORN Questions

The potential for corn stalk rots and lodging appears to be relatively high this year in different parts of the state. Weather conditions have varied greatly across the state during the growing season with some locations receiving adequate to surplus moisture and others being quite dry. The potential for stalk rot will vary according to several factors including weather and other stresses. Severe leaf damage due to leaf diseases like gray leaf spot blight will predispose plants to higher levels of stalk rots. Other stresses can include high plant populations and nitrogen deficiency. This may be especially prevalent in areas of the state where early rains resulted in loss of nitrogen. Regardless of the stalk rot disease affecting the field, the relative damage is the same: premature death of plants and weakened stalks prone to lodging.

So far this year we have seen damage from Anthracnose stalk rot. Anthracnose causes premature death of the plants and frequently causes top dieback on certain susceptible hybrids. Anthracnose stalk rot is more common in continuous corn fields, especially those in reduced tillage. The anthracnose fungus survives in old corn residues and infects the leaves of the plants. Spores are rain splashed onto stalk surfaces where the fungus infects the stalks. Shiny black streaks or spots on the surface of the stalks is characteristic of anthracnose stalk rot.

As corn growers prepare for harvest, scouting fields is just as important as getting the combine ready. Plants that die prematurely are most prone to lodging. Look for plants with stalks that loose their green color before other plants in the field. Tear off the lower leaf sheaths to examine the stalk surface and squeeze stalks above the brace roots to see how rotted they may be. Fields should be assessed for stalk rot by examining a hundred or so plants throughout the field. Randomly select plants, bend over and squeeze one of the lower internodes on each stalk. Record the number of soft stalks and plan to harvest those fields with the highest percentage of soft stalks before they lodge. Management of stalk rot diseases is achieved through selecting hybrids resistant to the disease or to lodging, crop rotation, destroying old corn residues, avoiding stress through water and fertility management, and planting proper plant populations for the available fertility.

E) Grain Bin Clean-Up - Linda Mason and John Obermeyer, Purdue University CORN Questions

Stored grain insect infestations usually begin from poor sanitation
Procedures are given to prevent infestations
Now is the time to carry out bin clean-up procedures

While driving Indiana's county roads, it is very apparent that harvest is fast approaching. Yields are expected to be good and storage facilities should be readied for corn that will likely carryover to next spring or summer. Preparing bins for storage now goes a long way toward preventing insect infestations. Several species of insects may infest grain in storage. The principal insects that cause damage are the adult and larval stages of beetles, and the larval stage of moths. Damage by these insects includes reducing grain weight and nutritional value, and by causing contamination (as live or dead insects), odor, mold, and heat damage that reduce the quality of grain.

Newly harvested corn may become infested with insects when it comes in contact with previously infested grain in combines, truck beds, wagons, other grain-handling equipment, augers, bucket lifts, grain dumps, or grain already in the bin. Insects may also crawl or fly into grain bins from nearby accumulations of old contaminated grain, livestock feeds, bags, litter, other cereal products, or rodent burrows.

Insect infestations can be prevented by employing good management practices. Now that many grain bins are empty, the following guidelines should be used before the 2001 grain is placed in bins:

Brush, sweep out and/or vacuum the combine, truck beds, transport wagons, grain dumps, augers, and elevator buckets to remove insect-infested grain and debris.
In empty bins, thoroughly sweep or brush down walls, ceilings, ledges, rafters, braces, and handling equipment and remove debris from bins.
Inside cleaned bins, spray wall surfaces, ledges, braces, rafters, and floors with an approved insecticide (Chlorpyrifos-methyl, methoxychlor, cyfluthrin, or diatomaceous earth) to create a perimeter barrier. Outside, complete this barrier by treating the bases and walls up to 15 feet high, plus the soil around the bins.
Remove all debris from fans, exhausts, and aeration ducts (also from beneath slotted floors, when possible). Fumigate the false floor area if the bin has a history of insect infestation or you have not cleaned the false floor area recently. Only certified fumigation applicators may purchase and apply these.
Remove all debris from the storage site and dispose of it properly according to area, state, and/or federal guidelines (the debris usually contains insect eggs, larvae, pupae, and/or adults, ready to infest the newly harvested grain).
Remove all vegetation growing within ten feet of the bins (preferably the whole storage area). Then spray the cleaned area around bins with a residual herbicide to remove all undesirable weedy plants.
Repair and seal all damaged areas to the grain storage structure. This is not only to prevent insect migration into the bin, but also to prevent water leakage, which leads to mold growth.
Do not store newly harvested grain on old grain already in storage.
Whenever fans are not operated, they should be covered and sealed. This reduces the opportunity for insects and vertebrates to enter the bin through the aeration system.

Source: Pest and Crop No. 24, page 2, August 31, 2001; Purdue Cooperative Extension Service

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Past versions of C.O.R.N. can be found on the World Wide Web at: http:/www.ag.ohio-state.edu/~corn/archive/

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.

Contributors to C.O.R.N. this week include: State Specialists: Pat Lipps & Anne Dorrance (Plant Pathology), Peter Thomison (Corn Production), Bruce Eisley (IPM), Extension Agents: Woody Joslin (Shelby), Clark Hutson (Seneca), Barry Ward (Champaign), Howard Siegrist (Licking), Glen Arnold (Putnam) and Andy Kleinschmidt (Van Wert)

Editor: Andy Kleinschmidt Web Editor: Tom Rosati

Information presented above and where trade names are used, they are supplied with the understanding that no discrimination is intended and no endorsement 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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Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Keith L. Smith, Director, Ohio State University Extension.