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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2004-32

Dates Covered: 
September 21, 2004 - September 27, 2004
Andy Kleinschmidt

Corn Ear Rots: Diplodia and Gibberella

Authors: Patrick Lipps, Dennis Mills

We are receiving reports of Diplodia and Gibberella ear rots on corn from various locations in the state. Relatively cool and wet weather conditions have been favorable for ear rots this year.

Diplodia ear rot can be recognized as a thick white mold that usually starts at the base of the ear. Later the white mold changes to a grayish-brown growth over the husks and kernels. The entire ear may be shrunken, and the infected kernels appear glued to the husks. Infected ears are very lightweight and may be totally rotted. In some cases the mold may be detected at the tip end of the ear. Frequently, very small raised black fruiting bodies of the fungus can be detected on moldy husks or kernels. However, these black bodies usually form later in the season. Diplodia ear rot causes damage by causing lightweight kernels that reduce yield and by reducing the nutritional value of affected grain.

Diplodia ear rot is caused by a fungus that maintains itself in the field between corn crops on corn residue. Corn is the only known host for this fungus. Spores produced in raised black fungal bodies on corn residue are spread by splashing rain. Although the exact timing and point of infection is not entirely understood, it appears the fungus is capable of infecting through the ear shank or the base of the husks of the ear and through the silks. Spores splashed into the whorl prior to tasseling or those trapped in the leaf sheath covering the ear shank may initiate infection. Ear silks are also susceptible to infection. Wet weather in combination with mild temperatures from late whorl through early ear development favor disease development.

This fungus does not appear to produce mycotoxins in the grain under field conditions usually occurring in the United States. Thus, the toxic problems seen in other ear molds, like Gibberella ear rot, are not a problem with Diplodia ear rot. However, high levels of affected grain in feed may make the feed unpalatable or cause reduced weight gain in hogs. Under most conditions damage caused by Diplodia ear rot is limited to the field, but it can be a problem in storage if grain moisture is 20% or above.

Gibberella ear rot is recognized as a white to pink mold that usually develops at the tip of the ear and grows towards the ear base. In some cases, the color is too pale to be seen readily, so the mold appears white. Infected grain is generally light weight. The Gibberella fungus also causes Gibberella stalk rot of corn and head scab on wheat. It also causes seedling bights and root rots of corn and wheat during wet seasons.

Gibberella ear rot infections occur more commonly when the weather is cool and wet during the first five to nine days after silking. Continued development of the mold also depends on subsequent cool, wet weather. Optimum temperatures for disease development are 65-70°F. The spores of this fungus infect through silks; stalk infections are not believed to lead to Gibberella ear rot. Spores reach the silks by splashing rain or they may be carried by insects. Infections may originate at insect wounds rather than at the ear tip.

Gibberella ear rot is a serious problem because the Gibberella fungus produces several different mycotoxins that are harmful to livestock. Deoxynivalenol (DON or vomitoxin) and Zearalenone are the two most common mycotoxins found in associated with Gibberella infected kernels. Hogs are particularly sensitive to these toxins. DON can cause feed refusal at concentrations in grain at around 1 ppm. Therefore the FDA advisory level for DON in corn to be fed to hogs is 5 ppm and this is not to exceed 20% of the diet. Zearalenone is an estrogenic factor causing infertility and abortions in hogs and other animals. In general rations with over 0.5 ppm zearalenone should not be fed to swine.

If you see Gibberella ear rot at elevated levels and you are going to feed it to hogs, it is important that you have the grain checked for DON and Zearalenone. Although cattle are less sensitive to these mycotoxins than swine, it is important to protect breeding and milking stock as well. Laboratories are available to test for mycotoxins. Each has different methods to analyze samples and requirement for sending samples. It is best to phone the lab and determine costs, turn-around time and sampling procedures.

Fields with Diplodia or Gibberella ear rot should be harvested as soon as possible and the grain dried to below 15% moisture to prevent further mold growth and in the case of Gibberella ear rot, further mycotoxin accumulation. Make sure the grain stays dry during storage or the problem will get worse.

Next year you can plan to plant hybrids that have more resistance to ear molds. There are many hybrids available with good resistance to Diplodia ear rot and also hybrids with improved resistance to Gibberella ear rot. Talk to your seed dealer. Since both diseases are associated with corn residues, crop rotation and fall tillage can reduce the occurrence of the disease by reducing fungal levels in the field.

Visit the Ohio Field Crop Disease web site at for a list of laboratories that will conduct mycotoxin analysis. Additionally, you can get more information on mycotoxins and feeding problems as well as color pictures and general information about Diplodia ear rot and Gibberella ear rot by visiting the corn disease section of the web site. You might as well bookmark this web site because you will likely need field crop disease information sooner or later.

Tips for Evaluating Corn Hybrid Demonstration Plots

Authors: Peter Thomison

This is the time of year when corn growers visit and evaluate the numerous hybrid demonstration plots planted each year by seed companies and county Extension personnel, among others. When checking out these plots, it’s important to keep in mind their relative value and limitations. Such demonstration plots can be useful in providing information on certain hybrid traits, especially those that are usually not reported in state corn performance summaries. The following are some hybrid characteristics to consider while checking out hybrid demo plots.

PLANT/EAR HEIGHT. Corn reaches it maximum plant height soon after tasseling occurs. Remember that although a big tall hybrid may have a lot of "eye appeal," it may also be more prone to stalk lodging in the fall. Unless your interest is primarily silage production, increasing plant height should not be a major concern. Generally later maturity hybrids are taller than earlier maturity hybrids. Big ears placed head high on a plant translate to a high center of gravity, predisposing a plant to potential lodging. The negative effects of stalk rot on stalk lodging in the fall may be worsened by high ear placement.

STALK SIZE. Generally speaking, a thicker stalk is preferable to a thinner one in terms of overall stalk strength and resistance to stalk lodging. As you inspect a test plot, you will see distinct differences among hybrids for stalk diameter. However, also check that the hybrids are planted at similar populations. As population increases stalk diameter generally decreases.

LEAF DISEASES. During the grain fill period, leaf diseases can cause serious yield reductions and predispose corn to stalk rot and lodging problems at maturity. The onset of leaf death shortly after pollination can be devastating to potential yield, since maximum photosynthetic leaf surface is needed to optimize grain yield. Hybrids can vary considerably in their ability to resist infection by these diseases. Demonstration plots provide an excellent opportunity to compare differences among hybrids to disease problems that have only occurred on a localized basis. This year look for differences in resistance to northern corn leaf blight (NCLB). Some of our most popular hybrids are quite susceptible to NCLB.

STALK ROTS. Hybrids will likely differ widely when faced with strong stalk rot pressure. Begin checking plants in late August or about 6 weeks after pollination by pinching lower stalk internodes with your thumb and forefinger. Stalks that collapse easily are a sure indicator of stalk rot. Remember that hybrids with thicker stalks may be in plots having thin stands.

STALK LODGING/BREAKAGE. Perhaps as important as stalk rot resistance is the stalk strength characteristics of a hybrid. Sometimes, superior stalk strength will overcome the effects of stalk rot. If your variety plot is overcome with stalk rot in late August and early September, be certain to evaluate the stalk lodging resistance of the different hybrids. Demonstration plots also provide a good opportunity to evaluate another stalk related problem, green snap (a.k.a. brittle snap). Green snap damage in Ohio has usually been limited to localized areas where severe windstorms occur prior to pollination. Although green snap is not a major problem in Ohio, as it is in the western Corn Belt, there are differences in susceptibility among hybrids that growers may want to consider to avoid risks. Because damage from European corn borer (ECB) and western corn rootworm (WCRW) can be very localized, strip plot demonstrations may be one of the best ways to assess the advantages of Bt corns.

HUSK COVERAGE/EAR ANGLE. Hybrids will vary for completeness of husk coverage on the ear as well as tightness of the husk leaves around the ear. Ears that protrude from the husk leaves are susceptible to insect and bird feeding. Husks that remain tight around the ear delay field drydown of the grain. Hybrids with upright ears often associated with short shanks may be more prone to ear and kernel rots that those ears that point down after maturity. There have been a number of reports of Diplodia and Gibberella ear rot this year. Under certain environmental conditions, some hybrids are more prone to drop ears, a major problem if harvesting is delayed.

The following are some additional points to consider during your plot evaluations:

1. Field variability alone can easily account for differences of 10 to 50 bushels per acre. Be extremely wary of strip plots that are not replicated, or only have "check" or "tester" hybrids inserted between every 5 to 10 hybrids. The best test plots are replicated (with all hybrids replicated at least three times).

2. Don't put much stock in results from ONE LOCATION AND ONE YEAR, even if the trial is well run and reliable. Don't overemphasize results from ONE TYPE OF TRIAL. Use data and observations from university trials, local demonstration plots, and then your own on-farm trials to look for consistent trends.

3. Initial appearances can be deceiving, especially visual assessments! Use field days to make careful observations and ask questions, but reserve decisions concerning hybrid selection until you've seen performance results.

4. Walk into plots and check plant populations. Hybrids with large ears or two ears/plant may have thin stands.

5. Break ears in two to check relative kernel development of different hybrids. Use kernel milk line development to compare relative maturity of hybrids if hybrids have not yet reached black layer. Hybrids that look most healthy and green may be more immature than others. Don't confuse good late season plant health ("stay green") with late maturity.

6. Differences in standability will not show up until later in the season and/or until after a windstorm. Pinch or split the lower stalk to see whether the stalk pith is beginning to rot.

7. Visual observations of kernel set, ear-tip fill ("tip dieback"), ear length, number of kernel rows and kernel depth, etc. may provide some approximate basis for comparisons among hybrids but may not indicate much about actual yield potential.

Fall Plantings and Insects

Authors: Ron Hammond, Bruce Eisley

There are a number of potential pest problems that growers should be aware of in certain fall plantings of different crops. Although the incidence of them is likely to be low, they nevertheless can cause significant reductions in stand or yield loss.

Parts of Ohio had large populations of Mexican bean beetles in soybeans this past summer. Before adults go to wooded areas to overwinter, they go to late planted or double-cropped soybean fields and to other legumes to continue feeding. Of special concern is that we will observe beetles in fall-planted alfalfa fields. Although established fields are not a concern, beetles might cause severe feeding injury to newly planted alfalfa fields. Alfalfa growers in areas where Mexican bean beetles were common in soybean should check their new alfalfa plantings.

Another pest, which can cause problems in fall plantings, are slugs. Although most slug problems are from juvenile slugs occurring in the spring, we have observed in previous years significant feeding by adult slugs in fall plantings of alfalfa and winter wheat when either were no-till planted. Thus, no-till growers who have planted either crop should check their fields and take corrective action if slugs are active and reducing stands.

Fertilizing Established Alfalfa Stands This Fall

Authors: Robert Mullen, Mark Sulc

As final harvests of alfalfa are collected, fertilization of potassium should be considered if it is not a part of your program. Alfalfa that has adequate levels of potassium accumulates more carbohydrates in their root system which improves their over-wintering ability and vigor early the next spring. Application of K should be considered if soil test levels are less than 300 lb/acre. Potassium application rates can be determined by computing how much K next year’s crop will remove (base it this year’s yield or a known “average”). Generally, for every ton of alfalfa forage removed approximately 50 lb of K2O is removed. Thus a 6 ton/acre crop will remove 300 lb K2O/acre. If you wish to maintain current K levels, add 300 lb K2O/acre. Application can be split between this fall and after the first harvest in the spring (applying half in the fall and half in the spring will minimize luxurious uptake of K by the crop early next year). The earlier K is applied this fall the greater the opportunity for the crop to take it up and prepare for the winter. Soil test values well above 300 lb/acre probably do not warrant any application at all. Check soil test levels next fall to monitor K needs for the next year.

Phosphorus can also be applied in the fall after the final cutting. If soil test levels are below 100 lb P/acre, apply additional P. Crop removal can also be used to determine the rate of application (a ton of alfalfa removes approximately 13 lbs P2O5). If the soil test value is well above 100 then additional P is not necessary. Providing adequate nutrition for your alfalfa crop will pay dividends next year and extend the life of the stand.

Prepare Grain Storage Facilities for 2004 Grain Crop

Prior to storing new grain, producers should make every possible effort to prepare a pest-free environment in which to store the grain to reduce the risk of infestation by established pest populations, especially insects. Preparations include cleaning all equipment used in handling the grain (combines, trucks, wagons, augers, pits, legs, elevator buckets, and bins), cleaning the outsides of grain storage facilities, and application of insecticide treatments to eliminate established insect populations.

Most insect infestations of stored grain originate from immigration of insects into the bins from outside. These insects may be established around the grain storage facility in piles of old contaminated grain, cleanings from grain dryers and cleaners, spilled grain, livestock feeds, pet foods, wild bird seed, crop seed, bags, litter, weeds or any other cereal products.

Newly harvested grain may also become infested with insects when it comes in contact with infested grain in combines, truck beds, grain wagons, grain dumps, augers, bucket lifts or grain already in the grain bin from previous years. Insects may also be present in carryover grain in “empty” bins and from grain debris beneath perforated bin floors.

Sanitary practices include measures to thoroughly remove old grain, grain debris and weeds that may be supporting insect populations in and around the grain storage facility. At least two weeks before storing new grain, brush, sweep out and/or vacuum the combine, truck beds, grain wagons, grain dumps, augers and elevator buckets to remove insect-infested grain and grain debris. Remove all grain and debris from aeration fans, exhausts and ducts. Remove all grain and debris from the storage site. Dispose of the grain and debris removed from all areas by feeding it to livestock or destroying it. Remove all vegetation growing within ten feet of grain bins and preferably from the entire storage facility. Apply a residual herbicide around the grain bins to prevent new weeds from growing.

Inside empty bins, walls, ceilings, ledges, rafters, braces and grain handling equipment should be swept and/or vacuumed. Insects may remain in hard-to-clean areas such as cracks and crevices in bin walls and in the plenum beneath non-removable perforated floors. Therefore, once bins are thoroughly cleaned, an empty bin insecticide treatment should be applied. The empty bin insecticide treatment should help eliminate any remaining insect infestations and create a barrier for insects that may migrate into the bin from outside. Applying an insecticide in an empty bin supplements but does not replace sanitation measures.

Apply an insecticide to the walls, ceiling and floor of all bins that will be used to store grain for more than a few weeks during warm weather. The best time to apply the empty bin insecticide treatment is two to three weeks before loading new grain into the bin. Use one of the following products: Tempo SC Ultra (cyfluthrin), Tempo 20WP (cyfluthrin), Storcide (chlorpyrifos-methyl and cyfluthrin), Diacon II (s-methoprene), or diatomaceous earth. Most of these products may be applied to the outside of the bin as well to produce an additional barrier to outside insects. Unless the insecticide labels specify otherwise, spray all bin surfaces to the point of runoff and be sure to treat all cracks and crevices and around doors thoroughly. Whenever using insecticides, be sure to read the entire product label for proper application rates and use restrictions.

Malathion products were once widely used in stored grain protection both as an empty bin treatment and direct treatment of grain. Many malathion products now carry the statement "Do not apply directly to grain” and should only be used as a perimeter spray around the outside of bins (e.g., Malathion 5EC (57% malathion)). Some products may not be labeled for treating grain storage facilities at all. Products not labeled for application to stored grain facilities should not be used as empty bin sprays.

The insecticide, methoxychlor, had been registered for use in and around stored grain facilities for many years. As of June 30, 2004, the Environmental Protection Agency working under the guidelines of the Food Quality Protection Act has completed its reregistration eligibility decision for the methoxychlor, and has determined that methoxychlor is not eligible for reregistration. All registered technical sources of methoxychlor were canceled in 2003, and all tolerances have been revoked. Voluntary cancellation of remaining products is in process. The products remain suspended until the voluntary cancellations are effective. Thus, if you have any old stocks of this insecticide, DO NOT USE it.

Fumigating empty bins to control insects in the sub-floor plenum may be necessary if grain is to be stored in the bin for long periods of time (i.e., into next summer). Empty bin fumigation usually is not necessary if grain is to be treated with a grain protectant insecticide at the time of loading the bin. Be sure to check with your grain purchaser as to what insecticide residues are acceptable on the grain before treating grain with a grain protectant. The fumigant chloropicrin is labeled and effective for empty bin fumigations.

Chloropicrin is a restricted use pesticide that is extremely toxic. Chloropicrin forms a pungent, tear gas that is heavier than air and will settle into the bin’s sub-floor area. Approved respiratory protection and gas monitoring equipment are required when using chloropicrin. If you are uncertain about the safe use of chloropicrin, contact the manufacturer for detailed recommendations.

And one finial note, do not store newly harvested grain on top of old grain already in the bin.

Agricultural Lighting, Marking, and Towing Requirements

Authors: Wayne Dellinger

Certain measures should be taken to help enable a safe arrival to the desired destination. Proper lighting and reflective marking in addition to other safety procedures should be considered.

LIGHTING AND MARKING- During the period from sunrise to sunset and when visibility is good, Ohio law requires the following on tractors or implements in tow:

* SMV emblem. This emblem must be visible to 500 ft behind the vehicle, be mounted between 2 and 6 feet above the ground, and be as close to the center of the vehicle as possible. Remember, even if your vehicle or vehicle combination is capable of higher speeds, use of the SMV emblem requires speeds to remain at 25 mph or less. Amber flashers and turn indicators are also recommended for daytime transportation.

During the period of sunset to sunrise or when visibility is low (fog or rain), Ohio law requires the following for a tractor or implement in tow:

* SMV emblem visible 500 ft to the rear

* At lease one headlight visible to the front at a distance of 1000 ft or more

* Two red taillights visible to the rear at a distance of 1000 ft or more. As an alternative, one red taillight may be used visible to the rear at a distance of 1000 ft or more with the addition of two red reflectors visible to the rear at a distance of 600 ft or more. Amber flashers and turn indicators are also recommended for nighttime or low visibility transportation.

All tractors and equipment manufactured after 2001 will be equipped with the required lighting and marking. It is the operator’s responsibility to maintain these lights and reflectors. Additional requirements for dual-wheeled tractors manufactured prior to 2002:

* Flashing amber lights visible to the front and rear mounted within 16 inches of lateral extremities and between 3.3 and 12 feet above the ground

* Amber reflectors visible to the front

* Red reflectors visible to the rear

TOWING- Safety cables or chains should be used in any towing situation. Ohio law states that only one wagon/implement may be towed behind any vehicle with two exceptions:

* Towing with a tractor – More than one wagon/implement may be towed. While no maximum is indicated, common sense and safety should play a role in the decision.

* Towing with a pickup or straight truck – A truck designed by the manufacturer to carry a load of not less than 1/2 ton and not more than 2 tons may tow two wagons/implements.

Other Slow Moving Vehicle travel safety recommendations:

* Lock brakes together before traveling on public roadways

* Install Roll Over Protective Structures (ROPS) on tractors that do not yet have ROPS

* When possible, move equipment during off-peak hours of motor vehicle traffic

* Ensure all workers are familiar with equipment operation before traveling on roadways

* Wear seatbelts, use escort vehicles, and avoid fatigue

If you have questions or need more information regarding lighting and marking or roadway travel safety, call the OSU Extension Agricultural Safety Office at 614-292-1952, email at, or go to the website at:
Article reviewed by Staff Lieutenant Herb Homan, Ohio State Highway Patrol, Massillon District Headquarters.

Eyeing Ag. Technology at Farm Science Review

Authors: Candace Pollock

Agricultural technologies are becoming more varied and more affordable, and growers at Farm Science Review will have the opportunity to view equipment and techniques that best suit their farming needs. Ohio State University agricultural engineering and technology specialists will be on hand throughout the three-day event (Sept. 21-23) giving demonstrations and providing information on the latest in precision agriculture, wireless communications and other high-tech equipment.

One such demonstration will involve auto-steer GPS (Global Positioning System) guidance systems, which allow farmers to perform a variety of field functions with little or no guidance effort from the operator. There will be traditional auto-steer demonstrations, as well as two different levels of auto-steer this year: RTK (Real Time Kinematic) and DGPS (Differential Global Positioning System).

Another growing area in the world of high-tech agriculture is wireless communications. On display at Farm Science Review will be an updated version of the Field Monitoring Server (FMS) - the first technology of its kind to download real-time data directly to the Internet for a user's access. The technology was introduced at last year's Farm Science Review. The new prototype, developed by the National Agricultural Research Center in Japan and built by Panasonic, has been modified for easier use and with practical applications in agriculture.

An optical sensor and aerial/satellite sensors will be the focus of the remote sensing demonstrations. Field-based optical sensors are entering the crop production market, which can be used as hand-held devices or placed on farm equipment. They are designed to measure crop status, identify weeds and calculate nitrogen requirements for maximum plant health and yield. Remote sensing technology uses various electromagnetic spectrum wavelengths like the red and near infrared bands to measure plant health and vigor.

Look for such agricultural technology and precision agriculture demonstrations, along with other high-tech equipment at Farm Science Review. Farm Science Review is sponsored by Ohio State's College of Food, Agricultural, and Environmental Sciences, OSU Extension and the Ohio Agricultural Research and Development Center and takes place Sept. 21-23 at the Molly Caren Agricultural Center near London, Ohio. Tickets are $8 at the gate or $5 in advance when purchased from county offices of OSU Extension or agribusinesses. Children 5 and younger are admitted free. Hours are 8 a.m. to 5 p.m. Sept. 21-22 and 8 a.m. to 4 p.m. Sept. 23.

Archive Issue Contributors: 

State Specialists: Pat Lipps, Anne Dorrance and Dennis Mills (Plant Pathology), Robert Mullen (Fertility), Peter Thomison (Corn Production), Ron Hammond (Entomology), Mark Sulc (Forages), Mark Loux (Weed Science) Jeff Stachler (Weed Science), Bruce Eisley (IPM), Ed Lentz (Agronomy), Candace Pollock (Media), and Wayne Dellinger (Ag Safety and Health); Extension Educators: Steve Foster (Darke), Todd Mangen (Mercer), Glen Arnold (Putnam), Roger Bender (Shelby), Mark Koenig (Sandusky), Howard Siegrist (Licking), Greg La Barge (Fulton), Steve Prochaska (Crawford), Barry Ward (Champaign), Dusty Sonnenberg (Henry), and Harold Watters (Miami)

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.