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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2007-06

Dates Covered: 
March 19, 2007 - April 3, 2007
Harold Watters

March Wheat Crop Update

Authors: Pierce Paul, Jim Beuerlein, Dennis Mills

Even before the wheat starts greening up and without having a chance to assess the status of the crop, some Ohio wheat growers are considering tearing up their wheat fields to plant corn. This is because all that could have possibly gone wrong with the establishment of a wheat crop seemingly went wrong with the crop in some locations; late planting, heavy rains and flooded fields shortly after planting, and atypical early-winter weather conditions. While all of these conditions have contributed to very poor-looking field in some parts of the state, growers who were able to plant at the recommended time and did not have problems with standing water in their fields have very decent-looking wheat fields. It is still too early to say whether some of the average looking fields will recover well enough to produce a profitable crop this will all depend on the weather. If we have another few warm days like we had last week (without excessive rain), wheat will start greening up and fields that appeared poor before the snow could improve their appearance greatly.

The next two to three weeks will be critical for development of the crop and this is the time for producers to look at their fields and get a good feel for what is there. Even if you decide to switch to corn or beans, it will be several weeks before anything can be done in terms of planting a different crop, so use this time to carefully evaluate your fields before making a final decision. Here is what to look for:

1 - If the stand is patchy, determine how widespread the patchiness is. Take a look at the field (probably from the pickup truck) and estimate what percentage of the field is bare and whether the patches are limited to a small section of the field or widespread throughout the field.

2 - Make a stand count. Pick about 10 to 15 spots in the field and count the number of plants per foot of row. It is still too early to count tillers per foot of row, but the number of plants/foot will provide a good early estimate of the stand. Once the weather warms, some tillering will occur (especially in fields which did not have a chance to tiller in the fall) and a stand with an average of about 12 plants per foot of row may still result in a good population of head-bearing tillers. Our studies have shown that under adequate weather conditions, tillering may compensate for relatively poor initial stand establishment. We have had crops in 15-inch rows and low stand counts (40% of a normal population) make 90 percent yields. It all depends on what happens in May and June.

Getting Your Corn Crop Off to a Good Start

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 crop off to a good start.

1) 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.

2) 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 in the seed" 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.

3) 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.

4) 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 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.

5) 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.

Soybean Insecticide Seed Treatments

Authors: Ron Hammond, Bruce Eisley

We recently attended a meeting of soybean entomologists that included researchers and extension specialists from most of the soybean growing states. Although not developing an official position on the subject, there was general agreement and consensus on how seed treatments could be used and what to expect from them.

Neonicotinoid seed treatments are recommended in fields with a history or expected incidence of economic damage from seed corn maggot, white grubs, and other early-season insects including bean leaf beetle and Mexican bean beetles. While able to reduce population numbers and feeding of overwintered bean leaf beetles, their ability to reduce bean pod mottle transmission below economic levels is questionable. Growers would be reminded if using seed treatments for this purpose, that a second treatment against first generation beetles in mid summer is necessary.

Seed treatments for prophylactic control of soybean aphid are not recommended. Laboratory and field studies indicate that soybean aphid begins to survive on seed-treated plants 35 to 40 days after planting, when aphids are beginning to colonize fields in many regions of the US and Canada. In outbreak years, populations in seed-treated fields can still reach the 250 aphid economic threshold, and require foliar insecticide sprays, at the same time as in untreated fields. Although there is some evidence that reaching threshold might be delayed a week or more, the fields nevertheless do reach it and require treatment. Replicated, statistically-analyzed university research trials across multiple states and years do not show a significant yield benefit of using seed treatments under no or low insect pressure.

During aphid outbreaks, using an IPM approach based on crop scouting and thresholds to optimally-time foliar sprays results in significantly greater yield compared to prophylactic seed treatments. An IPM approach to soybean aphid control also limits insecticide use to when and where it is needed, reduces pesticide exposure and selection for resistance, and helps to conserve natural enemies.

Setting Up the Sprayer to Apply 28%

Authors: Harold Watters

After we have evaluated our wheat crop the next step may be to apply our spring nitrogen. Do keep in mind that 28% nitrogen solution is considerably heavier than water. I checked with a couple of sources on how to best determine how to calibrate the boom sprayer to apply these nitrogen solutions. This first is from the folks who bring us TeeJet sprayer tips, the Spraying Systems Company:

Spraying Solutions Other Than Water
Since most of the tabulations in manufacturers' catalogs are based on spraying water, which weighs 8.34 lbs. per USA gallon, conversion factors must be used when spraying solutions which are heavier or lighter than water. To determine the proper size nozzle for the solution to be sprayed, first multiply the desired GPM or GPA of solution by the water rate conversion factor. Then use the new converted GPM or GPA rate to select the proper size nozzle.

Example: Desired application rate is 20 GPA of 28%N. Determine the correct nozzle size as follows:

GPA (solution) x Conversion factor (from table 1) = GPA (water)

20 GPA (28%) x 1.13 = 22.6 GPA (water)

The applicator should choose a nozzle size that will supply 22.6 GPA of water at the desired pressure.

Table 1. Liquid solution weights, specific gravity and conversion factors.

Weight of Solution Specific Gravity Conversion Factor
7.0 lbs. per gallon 0.84 0.92
8.0 lbs. per gallon 0.96 0.98
8.34 lbs per gallon - WATER 1.00 1.00
9.0 lbs. per gallon 1.08 1.04
10.0 lbs. per gallon 1.20 1.10
10.65 lbs. per gallon - 28% nitrogen 1.28 1.13
11.0 lbs per gallon 1.32 1.15
12.0 lbs. per gallon 1.44 1.20
14.0 lbs. per gallon 1.68 1.30

And from Erdal Ozkan’s Boom Sprayer Calibration Factsheet AEX-520-92:

Calibrating for Broadcast Application by the 1/128th method.

Follow these steps when calibrating boom sprayers for broadcast applications:
1. Fill the sprayer tank with water.
2. Run the sprayer, inspect it for leaks, and make sure all vital parts function properly.
3. Measure the distance in inches between the nozzles. Then measure an appropriate distance in the field based on this nozzle spacing, as shown in Table 2 below.
4. Drive through the measured distance in the field at your normal spraying speed, and record the travel time in seconds. Repeat this procedure and average the two measurements.
5. With the sprayer parked, run the sprayer at the same pressure level and catch the output from each nozzle in a measuring jar for the travel time required in Step 4.
6. Calculate the average nozzle output by adding the individual outputs and then dividing by the number of nozzles tested. If an individual sample collected is more than 10 percent higher or lower than the average nozzle output rate, check for clogs and clean the tip, or replace the nozzle.
7. Repeat steps 5 and 6 until the variation in discharge rate for all nozzles is within 10 percent of the average.
8. Then, the final average output in ounces is equal to the application rate in gallons per acre: Average output (ounces) = Application rate (GPA).
9. Compare the actual application rate with the recommended or intended rate. If the actual rate is more than 5 percent higher or lower than the recommended or intended rate, you must make adjustments.
10. You can start the adjustments by changing the pressure. Lowering the spray pressure will reduce the spray delivered; higher pressure means more spray is delivered. Don't vary from the pressure range recommended for the nozzles that you use. (Look to "Useful Formulas" on the back page to determine the new pressure rate.)
11. You also can correct the application error by changing the actual travel speed. Slower speeds mean more spray is delivered; faster speeds mean less spray is delivered. (Look to "Useful Formulas" on the back page to determine the new pressure rate.)
12. If these changes don't bring the application rate to the desired rate, then you may have to select a new set of nozzles with smaller or larger orifices.
13. Recalibrate the sprayer (repeat steps 5 through 12) after any adjustment.

Table 2. Calibration distance for each nozzle to spray 1/128 acre.
Nozzle/row Travel Nozzle/row Travel
spacing (in.) distance (ft.) spacing (in.) distance (ft.)
18 227 30 136
20 204 32 127
22 185 34 120
24 170 36 113
26 157 38 107
28 146 40 102


Archive Issue Contributors: 

Peter Thomison (Corn Production), Anne Dorrance, Pierce Paul and Dennis Mills (Plant Pathology), Ron Hammond and Bruce Eisley (Entomology), Ed Lentz (Agronomy) and Jim Beuerlein (Soybean Production). Extension Agents and Associates: Woody Joslin (Shelby), Howard Siecrist (Licking), Glen Arnold (Putnam), Keith Diedrick (Wayne), Steve Prochaska (Crawford), Mark Koenig (Sandusky), Gary Wilson (Hancock), Wes Haun (Logan), Mike Gastier (Huron) and Harold Watters (Champaign).

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.