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August 25 - September 1, 2003
C.O.R.N. 2003-28
In This Issue:
A) Corn Leaf Diseases Increasing
B) "Beer Can" Ears Appearing in Corn Fields
C) Estimating Corn Yields Prior to Harvest
D) Soybean Aphid Populations May be in Transition
E) Soil Compaction During Forage Harvesting
F) Farm Science Review, Something for Everyone
Common leaf rust, gray leaf spot and northern leaf blight are three common leaf diseases seen in corn this year. Rust was first detected in late June and can be recognized as small red pustules scattered over the leaf surfaces. Most hybrids have a fair level of resistance to common rust so yield losses are generally rare. Rust is usually more prevalent during cool growing seasons with moderate levels of rainfall. Generally it is much more important on popcorn and sweet corn that on field corn.
Gray leaf spot has been present in fields for about three weeks, but has shown little spread within most fields. Exceptions to this may be found in some fields in southern Ohio where the disease got an earlier start and the conditions for disease spread have been more favorable. Earlier this season, the wet weather probably limited the development of the disease because the spores are readily washed off the leaf surfaces thus preventing spread. Now that the continuous rains have stopped we will likely see gray leaf spot increase dramatically over the next few weeks. Gray leaf spot needs both a humid and a drying period each day to spread rapidly and cause significant disease levels. Fog or heavy due for 13 or more hours a day followed by dry afternoons with a light breeze promote spore development and spread to other corn plants. Additionally, as the corn develops beyond the dent stage, the leaf tissue becomes less resistant to infection. Thus, we generally see rapid increases in disease severity during the latter part of the corn growing season. Diagnose the disease by examining the older spots on the leaves for the characteristic rectangular shape. There is a lot of variability in lesion types among hybrids but in general the lesions begin as yellow spots and enlarge parallel with the veins and become more rectangular with age.
Northern leaf blight has been uncommon in Ohio over the past 20 years because most hybrids available for our growers have had a good level of resistance to the northern leaf blight fungus. The fungus produces long cigar shaped lesions on leaves. Some lesions can be 6 to 8 inches long and up to an inch and a half wide. The lesions are usually tan to brown and the older lesions generally have a dark green discoloration due to the spores present in the lesion center. Yield losses occur when the leaves above the ear become infected before the plants are in dent stage. Additionally, excessive leaf blighting can predispose plants to stalk rot diseases causing increased lodging by harvest. Growers should not grow hybrids with susceptibility to northern leaf blight. There are many good hybrids on the market with very good levels of resistance to this disease. Discuss this problem with your corn seed dealer and request seed of a resistant hybrid for planting next year.
You can obtain more information about common rust, gray leaf spot and northern leaf blight by visiting the Ohio Field Crop Disease web site at: http://www.oardc.ohio-state.edu/ohiofieldcropdisease.
The two key visual symptoms associated with ear stunting are ears that are much shorter than normal and a considerable section of the ear tip that has not produced kernels. This latter symptom appears to be related to poor pollination, perhaps the result of tight husks preventing and/or delaying normal silk emergence. These husks tightly cover stunted ears and may not provide adequate space for silks to emerge normally.
Corn plants with stunted ears have generally appeared healthy with normal husk formation and growth. However, husks appear somewhat pointed, probably because husks were more tightly wrapped around the much smaller ear enclosed. At harvest, plants with stunted ears often turn purple due to an accumulation of sugars in the leaf and stalk tissue. Ear stunting is often localized within fields (e.g. in head rows and border rows) with only a small percentage of plants (<5%) affected.
Little is known concerning possible causes of this abnormal ear development. The problem may be related to a low temperature stress or shock during ear development between the 5-leaf collar stage and 12-leaf collar stage. In 1992, a year during which corn ear stunting was widely observed across the Corn Belt, the only common factor shared by fields exhibiting ear stunting problems seemed to be low temperature (down to near freezing) in late June during ear size determination. No consistent relationships between soil fertility levels, herbicide programs or corn diseases were evident. Some have suggested micronutrient deficiencies associated with high pH effects may play a role. Hybrids also appear to differ in susceptibility to the problem.
If you are interested in learning more about this ear abnormality Dr. Bob Nielsen at Purdue University has written a more detailed article on this topic (what he refers to as blunt ear syndrome or BES) that includes some excellent pictures. The article is available online at: www.agry.purdue.edu/ext/corn/news/articles.03/BeerCanEars-0812.html
Dr. Nielsen is initiating research to learn more about the underlying causes
of BES and would welcome hearing about instances of BES that are discovered
this growing season: www.agry.purdue.edu/ext/corn/research/beercan/FieldInfoform.pdf
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 that 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 (watch out for plants with more than one ear). 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
(this will be particularly important in some fields given the likelihood of
uneven stands due to ponding early in the season).
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 have resulted in poorly filled small ears, there may be mechanical difficulties with sheller or picker efficiency, which needs 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.
Most soybeans have or are entering the R5-6 pod fill growth stages where the primary activity is seed growth. At this time, aphid populations would need to be very large before treatment would be warranted. The level needed would probably need to be in the 1000s per plant, perhaps over 2000. Growers should also be aware that many aphid populations are beginning to crash, either from mass migration of winged aphids, or aphid death from beneficial insects or insect pathogens.
Prior to making any treatment, growers should make sure that the aphid populations
in their fields have not crashed and that they are still active. Also, growers
should check to see if aphids have wing pads. At this time during high population
levels, many aphids will begin developing wings prior to migrating from the
field. These wing pads will appear as "shoulder pads" behind the head
of the aphid. If the majority of aphids have these pads, the population is perhaps
within a few days or so of a mass migration, and treatment may not be warranted.
As mentioned in other C.O.R.N. articles, treatment decisions should be on a
field-by-field basis. Although fields needing treatment might still exist, many
fields may no longer need treatment.
Frequent rains have kept the soil moisture high in many
fields. Machinery traffic for harvesting silage and hay may cause more compaction
problems than in a normal August and September.
Surface compaction is the main problem with this relatively light machinery.
At least it's light compared to most combines and grain carts.
- One solution is to minimize pressure on the soil by minimizing tire inflation pressure. Minimize" does not mean to go below the correct pressure for the load. But many farm tires are over inflated so checking the pressure can make a difference with no cost.
- On tractors remove any excess weights that are only needed for heavy tillage work.
- On forage wagons, consider a plan to stop with only a half or three-quarter load in fields where you know compaction can be a problem. If this applies to all fields, you could reduce tire inflation accordingly. Since tire inflation recommendations are for worst-case situations (full load, at highway speeds) reducing the maximum load, and perhaps keeping to a lower speed for road travel can allow a lower correct pressure. The lower pressure can also have a slight benefit with less rutting and lower rolling resistance.
- Switching to bigger tires or rubber tracks or adding duals are also aids for minimizing compaction.
All farmers, from large and small operations, can find their niche at Ohio State University's 2003 Farm Science Review. This year's three-day trade show, Sept. 16-18, features a mix of exhibits that appeal to visitors of all backgrounds.
The event takes place at OSU's Molly Caren Agricultural Center near London, Ohio. Farm Science Review is not just for the 5,000-acre farmer anymore, said Craig Fendrick, the Review's general manager. The three-day agricultural trade show has evolved over the past years, becoming an event for all farmers, large and small.
"For years the focus at the Review was corn and soybeans," Fendrick said. "A lot of niche things have come into being, making it a more well-rounded event."
Certain areas: the Gwynne Conservation area, the Center for Small Farms, and the Utzinger Memorial Garden, have begun to develop and assist with the Review. People now come just to see the niche-type areas, which have grown by leaps and bounds, Fendrick said.
This year, visitors will be greeted by a new Center for Small Farms building that will accommodate exhibits and seminars. Visitors also will find commercial exhibitors in the Gwynne area, another new addition. On top of that, about 575 commercial company lines will be scattered throughout the Review grounds, with everything from equipment to clothing to new technologies.
The event is estimated to draw 135,000-140,000 people, the 10-year average. Ticket sales thus far have been on track, attitudes are positive and it looks like it will be a good year, said Fendrick, who hopes to exceed last year's record-setting gate sales.
This year's ticket prices increased to $5 in advance and $8 at the gate. The price increase is the first in 12 years, but was needed to help pay for operating costs and luxuries, such as permanent bathrooms and the new Center for Small Farms building, Fendrick said.
Visitors should get every penny's worth with these highlights and more:
* Field demonstrations on yield monitors, auto steering equipment and other
GPS technologies.
* An Ohio State Horse Plowing Contest in the Review's drying area on September
16 from 10 a.m. to 3 p.m.
* Sessions on growing grapes and implementing ornamental grains into gardens
in the Utzinger Memorial Garden.
* Habitat highlights, wetland discussions and shooting/archery events in the
Gwynne Conservation Area.
* Sessions on consumer demands, new sources of employees and food markets during
"Question the Authorities."
* Hoop house demonstrations and sessions on hydroponics in the Center for Small
Farms.
* Volunteer sewing of weighted vests and blankets for autistic children in the
McCormick building.
For a complete listing of this year's presentations and events, log onto: http://fsr.osu.edu/sched.html.
Ohio State's College of Food, Agricultural, and Environmental Sciences sponsors the Farm Science Review. Tickets are available at any county office of OSU Extension and many agribusinesses. Children 5 and younger are admitted free.
Show hours are 8 a.m. to 5 p.m., September 16-17 and 8 a.m. to 4 p.m. Sept 18.
Readers can subscribe electronically to this newsletter by sending an e-mail message to: corn-out-on@postoffice.ag.ohio-state.edu. A successful subscription message will receive by an automatic reply from the listserv. Contact your local Ohio State University Extension Office or e-mail labarge.1@osu.edu if you have problems subscribing.
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.
State Specialists: Anne Dorrance & Dennis Mills (Plant Pathology), Peter Thomison (Corn Production), Jeff Stachler (Weed Science), Bruce Eisley (IPM) and Ron Hammond (Entomology); District Specialists: Ed Lentz (Agronomy); Extension Agents: Roger Bender (Shelby), Clark Hutson (Seneca), Greg La Barge (Fulton), Glen Arnold (Putnam), Dusty Sonnenberg (Henry), Steve Foster (Darke), Jim Lopshire (Paulding), Harold Watters (Miami) and Steve Prochaska (Crawford).Editor: Harold Watters Web Editor: Nathan Watermeier
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.
All educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, creed, religion, sexual orientation, national origin, gender, age, disability or Vietnam-era veteran status.
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.
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