C.O.R.N. Newsletter 2008-08

Dates Covered: 
April 7, 2008 - April 15, 2008
Editor: 
Harold Watters

Nitrogen Concerns in Wheat

Authors: Edwin Lentz, Robert Mullen

Producers still have time to apply their spring topdress of nitrogen. Ohio State University research has shown that yields are not affected by delayed nitrogen until after early stem elongation (generally the end of April). Studies over the last five years have shown that yields were the same or slightly better when a single application occurred at Feekes 6 (first node visible of early stem elongation) compared to initial greenup. Yields dropped 10 – 15% when a single application was delayed to early boot stage. At this time, we would recommend producers to apply N as soon as field conditions allow application equipment and that there is no need for more expensive aerial applications. Since we are applying N between initial greenup and early stem elongation, any nitrogen source would be appropriate, so selection should be based on cost and availability.

Some producers who had applied N in February have asked whether there are any tests they may use to check the N status of their plants at this time (concerns that the N may have been lost). Unfortunately there are no definitive tests. Tissue analysis is a relative test and not a procedure used to make N recommendations. A producer may topdress a wheat strip in a field with extra N now and then later use a chlorophyll meter to compare to the rest of the field at early stem elongation. The meter will qualitatively detect differences and assist in a best guess look. However, even if a significant different green color is observed or detected, a producer will not be able to determine how much more to apply based on research information.

Alfalfa Weevil

Authors: Ron Hammond, Andy Michel, Bruce Eisley

As we enter the spring months where we hope to see some warmer temperatures, we need to remind alfalfa growers that the time for scouting for alfalfa weevil is close. The need for scouting is when heat unit accumulation beginning from January 1 reaches 250- 300 heat units (HU). This time period is when we begin to have weevil egg hatch and start to see feeding. Growers in southern Ohio will see this sooner than those growers in central and northern Ohio. Remember that fields that have a south facing slope tend to warm up sooner and need to be checked for weevil earlier. As of April 7, southern locations are around 235 HU, central and northern sites are near 125 and 100, respectively. Thus, we would recommend that growers in the southern third of Ohio begin sampling this week, while those in the central and northern thirds begin in the coming weeks. We will update heat unit accumulations in the coming weeks in this C.O.R.N. newsletter.

Alfalfa weevil scouting is accomplished by collecting a series of three 10-stem samples randomly selected from various locations in a field. Place the stem tip down in a bucket. After 10 stems have been collected, the stems should be vigorously shaken in the bucket and the number of larvae in the bucket counted. The shaking will dislodge the late 3rd and 4th instar larvae which cause most of the foliar injury. Close inspection of the stem tips may be needed to detect the early 1st and 2nd instar larvae. The height of the alfalfa should also be recorded at this time. Economic threshold is based on the number of larvae per stem, the size of the larvae and the height of the alfalfa. The detection of one or more large larvae per stem on alfalfa that is 12 inches or less in height indicates a need for rescue treatment. Where alfalfa is between 12 and 16 inches in height, the action threshold should be increased to 2 to 4 larvae per stem depending on the vigor of alfalfa growth. When alfalfa is 16 inches in height and there are more than 4 larvae per stem, early harvest is recommended. See the OSU Alfalfa Weevil FactSheet http://ohioline.osu.edu/ent-fact/0032.html for more on alfalfa weevil scouting and thresholds. For insecticides that are labeled for alfalfa weevil, see http://entomology.osu.edu/ag/545/aiaw.pdf. Remember that it is still too early to scout for potato leafhopper since they do not move into Ohio until May.

Preplant Herbicide Applications

Spring has sprung! Summer annual weeds such as giant ragweed, lambsquarters, Atriplex, and prostrate knotweed have started to emerge in central Ohio. The emergence of these weeds increases the need for appropriate preplant (burndown) herbicide mixtures in no-tillage crops. With few preplant herbicides applied to date due to cold and wet soil conditions, questions are being asked about the importance of 2,4-D in preplant herbicide applications. Because of the prevalence of dandelion and glyphosate-resistant weeds such as giant ragweed, marestail (horseweed), common ragweed, and lambsquarters in Ohio no-tillage fields, the addition of 2,4-D in preplant herbicide applications is very important in achieving effective weed control prior to planting. At this point in the season, it is more important to include 2,4-D in preplant herbicide applications and to delay planting of corn and soybean rather than planting the crops and controlling weeds after planting. We will continue to monitor weather conditions and weed populations and recommend appropriate preplant herbicide mixtures as the season progresses.

Consider Controlled Traffic for 2009

Authors: Randall Reeder

Farmers who have established a controlled traffic system have a huge advantage this spring. For the majority of farmers who don’t have controlled traffic, this may be the perfect year to make plans to transition into controlled traffic for 2009.

If a farmer already has, or is planning to invest in, a RTK autosteer system, then controlled traffic is a natural companion that can help maximize the return from the autosteer system.

Advantages include:
Firm tracks to drive on. The benefits for this spring would include timely N application on wheat and earlier corn planting by at least a day or two. Later in the year, consider the value of timely application of pesticides and harvest. Firm tracks give better traction and minimize the risk of getting stuck.

Minimized compaction. Driving on permanent lanes keeps heavy wheel traffic off most of the soil where roots are growing, including all corn rows. With compaction under control, continuous no-till will be more economical.

Reduced input costs. With precise autosteer and permanent lanes, benefits include reduced costs for fuel, labor, seed, pesticides and fertilizer.

Disadvantages:
Are mainly confined to upfront costs of getting all equipment to match the primary width and wheels to line up in the desired tracks. If the change is done immediately, the costs might be substantial. But if carried out over a few years as equipment is traded in, the extra cost will be minimal. Efficiency of small grain and soybean harvest may drop slightly.

Perhaps the most persuasive argument for controlled traffic is in the answer to this question: do you wish you already had it?

Fall Anhydrous Ammonia - Should You Be Concerned?

Authors: Robert Mullen, Edwin Lentz

Some producers are wondering how much, if any, of their fall applied nitrogen has been lost. Fortunately we have a rather cold winter, and if fall application was made to cool soils (<50 F) as anhydrous ammonia, then losses are most likely minimal up to this point. The real question is how much loss potential are we looking at this spring? This is difficult to foresee, but with soils warming and more rainfall in the forecast nitrogen loss may be something producers face.

If nitrogen was applied after November 1 with an inhibitor, losses are likely to be minimal. However, this inability to predict the potential loss is one of the reasons Ohio State University does not recommend fall applied nitrogen.

Now the question is how do you identify if additional nitrogen will be needed this spring? Presidedress soil nitrate test (PSNT) is one tool that could be used to assess soil nitrogen supply. Soil samples should be collected in mid to late-May to a depth of one foot. Fields with nitrate levels greater than 25 ppm are unlikely to respond to additional nitrogen, but fields with less than 25 ppm may require additional nitrogen input. The rate of nitrogen applied should not be greater than 70 pounds per acre (if PSNT is less than 25 ppm). Tissue testing can also be used to evaluate the crop during the growing season. The only thing to be cognizant of is the potential influence of the growing environment. If it is a cool and dry, or exceptionally wet spring, tissue testing may reveal a deficiency that is not related to soil nutrient availability. The presence of the deficiency is due to adverse growing conditions.

An alternative tool that may be useful to evaluate fall N programs is the establishment of a nitrogen rich test strip. Typically 100 pounds of N per acre are applied in a small strip (applicator’s width) to compare with the rest of the field. This visual comparison may help answer nitrogen availability questions throughout the growing season.

Keep an eye on your corn and be ready to act if necessary.

Transgenic Hybrid Traits Available in Corn and Export Approval Status

Authors: Peter Thomison

The National Corn Growers Association (NCGA) maintains a list of transgenic corn technologies available to US corn growers (http://www.ncga.com/biotechnology/Search_hybrids/know_where.asp). The list includes the trade names, characteristics/traits (e.g. insect and herbicide tolerance), and events associated with these products. The list also indicates the export approval status of these transgenic products. Certain transgenic events and combinations of these events have not yet been fully approved for export markets, especially the European Union. Given the tremendous demand for corn this year, it is unlikely growers will have much difficulty finding markets for grain from corn hybrids not yet approved for export. However, the NCGA recommends that growers planting such hybrids contact their grain handler before harvest and delivery.

The number of transgenic products is steadily increasing. In last year’s Ohio Corn Performance Test, 15 transgenic products associated with different events and combinations of events were evaluated. In the most recent NCGA chart of biotech corn hybrid traits, 23 transgenic products are listed.

Tips for Successful Corn Establishment

Authors: Peter Thomison

Mistakes made during the planting operation are usually irreversible, and can put a "ceiling" on the crop's yield potential before the plants have even emerged. The following are some proven practices that will help get a corn crop off to a good start.

Perform Tillage Operations Only When Necessary and Under the Proper Soil Conditions.
Avoid working wet soil and reduce secondary tillage passes. Perform secondary tillage operations only when necessary to prepare an adequate seedbed. Shallow compaction created by excessive secondary tillage can reduce crop yields. Deep tillage should only be used when a compacted zone has been identified and soil is relatively dry. Late summer and fall are the best times of year for deep tillage.

Complete Planting by Mid-May
The record corn yields of recent years owe much to timely planting and good seedbed conditions. If soil conditions are dry, begin planting before the optimum date. (The recommended time for planting corn in northern Ohio is April 15 to May 10 and in southern Ohio, April 10 to May 10). Avoid early planting on poorly drained soils or those prone to ponding. Yield reductions resulting from "mudding seed in" may be much greater than those resulting from a slight planting delay. If growers have the equipment capability to plant more than half of their corn acres prior to the optimum planting date, then this should allow planting all the corn acres prior to the calendar date when corn yields begin to decline quickly. During the two to three weeks of optimal corn planting time, there is, on average, about one out of three days when field work can occur. This narrow window of opportunity further emphasizes the need to begin planting as soon as field conditions will allow, even though the calendar date may be before the optimal date. As a guide, calendar date is more reliable than soil temperature for making the decision on when to begin to plant corn.

Adjust Seeding Depth According to Soil Conditions
Plant between 1-1/2 to 2 inches deep to provide for frost protection and adequate root development. In April, when the soil is usually moist and evaporation rate is low, seed should be planted no deeper than 1-1/2 inches. As the season progresses and evaporation rates increase, deeper planting may be advisable. When soils are warm and dry, corn may be seeded more deeply up to 2 inches on non-crusting soils. Consider seed-press wheels or seed firmers to ensure good seed-soil contact. One risk associated with shallower planting depths is the possibility of poor development of the permanent (also referred to as secondary or nodal) root system if the crown is at or near the soil surface. Permanent roots may not grow under hot, dry conditions (resulting in the "rootless" and "floppy" corn syndromes). Another potential risk from planting less than 1-1/2 inches is shoot uptake of soil-applied herbicides. Seeding depth should be monitored periodically during the planting operation and adjusted for varying soil conditions. Irregular planting depths contribute to uneven plant emergence, which can reduce yields.

Adjust Seeding Rates on a Field-by-Field Basis.
Adjust planting rates by using the yield potential of a site as a major criterion for determining the appropriate plant population. Higher seeding rates are recommended for sites with high-yield potential with high soil-fertility levels and water-holding capacity. On productive soils, with long term average yields of 160 bu/acre or more, final stands of 30,000 plants/acre or more may be required to maximize yields.

Lower seeding rates are preferable when droughty soils or late planting (after June 1) limit yield potential. On soils that average 120 bu/acre or less, final stands of 20,000 to 22,000 plants/acre are adequate for optimal yields. On soils that average about 150 bu/acre, a final stand of 28,000 plants per acre may be needed to optimize yields. Seeding rate can be cut to lower seed costs but this approach typically costs more than it saves. Most research suggests that planting a hybrid at suboptimal seeding rates is more likely to cause yield loss than planting above recommended rates (unless lodging becomes more severe at higher population levels and harvest delays occur). Under moderate drought stress, high plant populations usually do not cause significant yield reduction on most Ohio soils. When planting occurs in cold soils, usually early planting dates, the seeding rate should be 10-15% higher than the desired harvest population. Follow seed company recommendations to adjust plant population for specific hybrids.

Calculate Appropriate Seeding Rates
The number of plants/acre at harvest is always less than the number of seeds planted (unless you have a lot of volunteer corn!) Planting date, tillage practices, pest problems, chemical injury, planter performance, and seed quality can affect final corn populations obtained in the field. To compensate for these losses, a corn grower needs to plant more seed than the desired population at harvest.

To determine an appropriate seeding rate, use the following formula:
Seeding rate = Target plant population per acre at harvest/ (Seed germination x Expected survival)

Seed germination is the percent germination shown on the seed tag. Most seed corn has a germination rate of 95% or higher. Expected survival is the percentage of plants that you expect to survive to become harvestable plants in the fall. Keep in mind that survival rates for corn are often in the range of 85 to 95% but can vary considerably depending on planting conditions and other environmental factors. When early planting is likely to create stressful conditions for corn during emergence (e.g. no-till in early to mid April), consider seeding rates 10 to15% higher than the desired harvest population.

EXAMPLE: A grower wants to achieve a final stand of 28,000 plants/acre. The seed tag indicates a germination rate of 95% and the grower expects that 90% of the germinable seed will survive until harvest. Based on the formula above, divide the desired plant population at harvest, 28,000 plants/acre, by 0.95 x 0.90 (0.855) to obtain a seeding rate of 32,749 seeds/A. (Note that % germination and % survival are converted to decimal form for use in the formula.) If only 85% of the germinable seed were expected to survive (due to stressful environmental conditions during emergence), then dividing 28,000 by 0.95 x 0.85 (.8075) would give a higher seeding rate of 34,675 seeds/A.

Archive Issue Contributors: 

Anne Dorrance and Dennis Mills (Plant Pathology), Ron Hammond, Andy Michel and Bruce Eisley (Entomology), Peter Thomison (Corn Production), Robert Mullen (Soil Fertility), Ed Lentz (Agronomy) and Jeff Stachler (Weed Science). Extension Agents and Associates: Todd Mangen (Mercer), Roger Bender (Shelby), Howard Siegrist (Licking), Glen Arnold (Putnam), Alan Sundermeier (Wood), Greg LaBarge (Fulton), Steve Foster (Darke), Harold Watters (Champaign), Bruce Clevenger (Defiance), Wes Haun (Logan), Les Ober (Geauga), Mike Gastier (Huron) and Marissa Mullett (Coshocton).

About the C.O.R.N. Newsletter

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.