CORN
Crop Observation and Recommendation Network

September 8-14, 2003
C.O.R.N. 2003-30

In This Issue:

A) Northern Leaf Blight Continues to Spread in Corn Fields
B) Corn Maturation Update
C) Lime Considerations
D) Grain Bin Clean-Up
E) New Technologies Demonstrated at Farm Science Review

A) Northern Leaf Blight Continues to Spread in Corn Fields - Patrick Lipps CORN Questions

Northern corn leaf blight has caused significant disease problems in certain corn fields in south and central Ohio over the past three to four weeks and continues to spread. Yield losses from northern leaf blight can be quite high if disease attacks the upper leaves of the corn plant by 3 to 4 weeks after tasseling, however if the leaves above the ear are not significantly damaged by beginning dent stage yield losses are usually less than 10%. Thus, the extent of the yield loss is dependent on when the disease becomes prevalent in the field, the growth stage of the crop when disease spreads to the upper leaves and the relative susceptibility of the hybrid. The disease can be readily identified by the large cigar shaped lesions on the leaves, which are tan to brown and may have a dark olive-green color due to the development of spores in the center of the lesions. Since the lesions can get quite large (up to 8 to 10 inches long and an inch to an inch and a half wide), it takes only a few lesions to kill a leaf (see photo at http://ohioline.osu.edu/ac-fact/0020.html). The extensive rainy weather and relatively cool average daily temperatures have promoted the development of the disease.

Although there is nothing that a grower can do at this point to limit northern leaf blight development, they should prepare for next year. The single most important thing to do for managing this disease is to grow hybrids with resistance to northern leaf blight. Now is a good time to visit seed company field trials in your area to look at the various hybrids they have for sale. Examine each hybrid for northern leaf blight and keep notes. Also get information from the seed companies and request hybrids with good levels of resistance. Hybrids may have either partial resistance (called polygenic resistance) or race specific resistance (called single gene or Ht resistance), or both. Hybrids with high levels of partial resistance will provide good levels of resistance and good control although, you may see some disease develop on the leaves. Ht resistance is effective against certain races of the fungus and probably should be 'backed up' in the hybrid with good levels of partial resistance. Be sure your seed dealer understands that you want a high level of resistance, especially if you have disease in your fields this year. The fungus will survive over winter on corn residues left on the soil surface. Tillage and crop rotation will also be important to manage this disease. For more detailed information on management see the OSU Extension Fact Sheet at http://ohioline.osu.edu/ac-fact/0020.html.

Northern Corn Leaf Blight

B) Corn Maturation Update - Peter Thomison and Allen Geyer CORN Questions

According to the Ohio Agricultural Statistics Service, as of Sept. 7, 2003, nearly half the corn crop had reached the dent stage, which is the same as last year but seven days behind the five year average. This later than normal maturation of the corn crop has led to questions about the likelihood for frost damage and whether more fuel will be needed to dry corn.

Physiological maturity (when kernels have obtained maximum dry weight and black layer has formed) occurs 7 to 8 weeks after silking. At physiological maturity (kernel moisture approximately 30-35%), frosts have little or no effect on the yield potential of the corn crop.

Table 1 shows the average number of calendar days and growing degree days (GDD) required to reach physiological maturity at different kernel development stages following silking. With average daily high and low temperatures of 80 and 60 degrees F, 20 GDD accumulate each day. At these temperatures, 65 days from silking to maturity are required (1300 divided by 20).

Table 1. Relationship between kernel growth stage and development. Source: National Corn Handbook. Chapter 40. Growing Season Characteristics and Requirements in the Corn Belt. R.E. Nield and J.E. Newman, 1986.

*Based on average daily high and low temperatures of 80 and 60 degrees F, respectively, during grainfill.

How many GDD can be expected from now until an average date of a killing frost? To answer this question, estimate the expected GDD accumulation from Sept. 9 until the average frost date (50% probability) for different regions of the state (Table 2). These GDD expectations are based on 30-year historical normals reported by the Ohio Agricultural Statistics Service. The growing degree day 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 GDD requirement to reach black layer at various stages of grain fill. Compare "GDD remaining" for the site with the GDD required to achieve black layer depending on the corn's developmental stage.

Table 2. Estimated GDDs remaining from Sept. 9 to the first fall frost for Ohio.

If your corn is in the "fully dented" stage as of Sept. 9, will it be safe from frost? Table 1 indicates that corn needs about 250 GDD to reach black layer from the "full dented" stage and Table 2 indicates that nearly all regions of the state will accumulate sufficient GDD to escape frost injury.

However, if your corn is in the "early dent" stage as of Sept. 9, it might be a different story. According to the kernel development - GDD accumulation relationships indicated in Table 1, corn needs about 500 GDD to reach black layer. Table 2 indicates that only one region of the state (south central Ohio) comes close to accumulating that number of GDDs before the 50% frost date. Does this mean frost damage is inevitable? No, late planted corn has shown the ability to adjust its maturity requirements, and most of this adjustment occurs during the late kernel development stages. Corn planted in early June compared to early May requires 200 to 300 fewer GDDs to achieve physiological maturity. Also, in previous growing seasons when GDD accumulation was markedly less than normal, the corn crop achieved physiological maturity before the first frost occurred. This means that for corn in early dent, most parts of the state, with the possible exception of areas in eastern (especially northeastern) Ohio, stand a good chance of accumulating sufficient GDDs to reach black layer before a killing frost.

C) Lime Considerations - Ed Lentz CORN Questions

Fall is the time of year that many of us test our soil pH and determine whether any lime needs to be applied for future crops. Proper soil pH is important for nutrient availability, herbicide activity, and crop development. For most soils, additional lime is not needed every year. Consider these points before liming your fields:

1. Do I need lime? Each year we hear stories of people adding lime to their fields without a soil test. The grower has a source of free waste-product lime that they pick up and apply to their fields. In many cases their soil pH was fine, but they did not want to pass up a "good deal". Without knowing the soil pH, a grower may inadvertently raise their soil pH to the high 7's. At this elevated pH, certain nutrients may become limited and the productivity of their crop may be reduced and require special management practices. Northwest Ohio has the greatest risk of elevating soil pH from careless applications of lime. A soil analysis is the best step to determine if a field needs lime.

2. What is the pH of my subsoil? Generally a laboratory recommends lime when the soil pH drops two to three units below the desired value. The desired value depends upon the crop and the pH of the subsoil. In parts of Ohio where the subsoil pH is less than 6.0 for mineral soils (eastern Ohio), additional lime is recommended after the soil pH drops to 6.2 for corn and soybean, and 6.5 for alfalfa. In other parts of the state (generally western Ohio), the subsoil pH for mineral soils is greater than 6.0 and lime is not needed until the soil pH drops below 6.0 for corn and soybeans, and 6.2 for alfalfa. Private laboratories may not take in account the subsoil pH and use recommendations based on a subsoil pH less than 6.0 for all parts of the state, possibly recommending lime applications several years earlier than needed for some areas.

3. Do I need magnesium (Mg)? Several parts of the state are historically low in soil magnesium (eastern and extreme southern Ohio). Adequate soil magnesium is important to reduce the risk of such problems as grass tetany for grazing animals. Soil test magnesium levels need to be greater than 50 ppm (100 lb) for optimal corn, soybean, wheat, and alfalfa production. Often areas low in magnesium also need lime, which has made the application of dolomitic lime an economic solution for both concerns. Unfortunately, some producers have been led to believe that magnesium levels in dolomitic lime may be undesirable. The Ohio State University has shown that crops yield the same over a wide range of calcium to magnesium ratios. As long as the soil test calcium to magnesium ratio is not less than one for a given field, select a lime source for its neutralizing ability and not its calcium content.

4. What is the Effective Neutralizing Power of my lime? An important item from a lime analysis report is the Effective Neutralizing Power (ENP) value, which is required for material sold as lime for agricultural purposes in Ohio. This value allows a producer to compare the quality among lime sources because ENP considers the purity, neutralizing power (including fineness) and moisture content. In other words, the ENP tells you how much of that ton of lime actually neutralizes soil acidity. The unit for ENP is pounds/ton (be careful not to use %ENP, which may also be on a lime analysis report). The ENP allows a producer to compare different lime sources because they can now determine price per pound or ton of actual neutralizing material.

In summary, make sure you take a soil test, determine if lime is needed, determine if magnesium is needed, know the historic pH of your subsoil, and then use the ENP to select the most cost effective lime material. A soil test every three to four years will determine the lime requirements for your fields. For additional information, refer to the Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat & Alfalfa (E-2567; available at http://ohioline.osu.edu/e2567/) and the Ohio Agronomy Guide (available at http://ohioline.osu.edu/b472/).

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

Many grain bins have recently been emptied and preparation should begin for this year's harvest. 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, any 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 2003-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 for empty bin use (New this year - Storcide (a mixture of chlorpyrifos-methyl and cyfluthrin), Reldan (chlorpyrifos methyl), Tempo SC Ultra perimeter spray (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.
  

E) New Technologies Demonstrated at Farm Science Review - Erik Bussa, FSR Media Services CORN Questions

New advances in mobile data collection and GPS navigation in agriculture will be showcased at the upcoming Farm Science Review, Sept. 16-18.

"Wireless data communications systems are very common in commercial business today and some of the newest technologies will be on hand," said Nathan Watermeier, Ohio State University Extension Program Leader Technology. Producers can collect and send data from anywhere on a farm with wireless data systems, including weather gauges, yield maps, voice and text communication, records, and the direction a tractor is headed.

"The collection of data has been happening for the past 10 years, but the problem is getting it sent quicker and not losing data from equipment malfunctions," said Watermeier. Farm-wide wireless systems can be costly but should become more affordable with time. Visitors can learn more about what wireless communications can do for agriculture at the Alumni Park.

An interactive exhibit at the Gwynne Conservation Area will show the latest in remote sensing, mobile GPS data collection systems, and digital geographic data available to land/water resource planners. "New this year will be mobile data collection systems with wireless GPS receivers that allow persons to take readings from a distance with no reliance on cables," said Watermeier. "A benefit of this technology is taking readings in geographic areas that are hard to reach or too hazardous for human contact."

Attendees also will be able to see hands-on how the mobile data collection systems, wireless GPS receivers, and guidance systems can work on their farm. Demonstrations will take place from 2-4 p.m. on Tuesday and Wednesday and from 2-3:30 p.m. on Thursday.

"The vehicle guidance system demonstrations continue to be one of the largest and most diverse in the Midwest," said Matthew Sullivan, Ohio State University Extension Program Specialist. Differential Global Positioning System (DGPS) guidance, DGPS auto-guidance, and Real-time Kenematic auto-guidance will be demonstrated. "All the different systems will be lined up for farmers at the Review - you won't be able to see that any other place," said Sullivan. "It's a great evaluation tool for farmers to grab hold and actually be able to sit behind the steering wheel."

These systems improve accuracy to within 4-6 inches, resulting in fewer overlaps or gaps with pesticides, fertilizer or seeds. The systems are also easier on the driver, reducing fatigue, and make it easier to implement controlled traffic in which farmers driver over the same place every time, reducing field compaction. Light bar technology will also be demonstrated. These guidance systems reduce overspray, make it easier to work at night and mean less reliance on foam markers.

At least eight brands of guidance systems will be set-up on utility vehicles at the Review for visitors to operate and evaluate. Equipment manufacturers will be on hand during the demonstrations to answer questions.

The Farm Science Review is sponsored by Ohio State's College of Food, Agricultural, and Environmental Sciences and takes place Sept. 16-18 at the Molly Caren Agricultural Center near London, Ohio. Tickets are $8 at the gate or $5 in advance when purchased at your local county office of OSU Extension. Children five and younger are admitted free.

Hours are 8 a.m. to 5 p.m., Sept. 16-17 and 8 a.m. to 4 p.m. Sept. 18. For more information, please visit http://fsr.osu.edu.

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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.

Editor: Andy Kleinschmidt        Web Editor: Nathan Watermeier

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