C.O.R.N. Newsletter 2004-08

Wheat In Condition Good; Normal Development

Authors: Patrick Lipps

After the colder weather in late March and the first week of April, the wheat crop appears to still be in fairly good condition. It is likely that the worst conditions are now past and we can expect rapid growth of the crop over the next couple of weeks. The recent colder weather has held the crop back somewhat, but there is no need to be concerned at this time. This will give growers a few more days to make the needed nitrogen applications and apply herbicides before Growth Stage 6 when the first node can be detected at the base of the stems. Crop development is on schedule with some early planted fields in extreme southern Ohio approaching this critical growth stage. In northern Ohio little growth has occurred to date. If weather conditions remain normal we can likely expect stem elongation to occur in two to three weeks in northern Ohio.

Winter damage to the wheat crop appears to be confined to sections in fields where water accumulated and froze into ice sheets in January. Therefore, expect few plants to recover or survive in these areas. Few diseases are usually detected in wheat before the flag leaf emergence stage, but in some areas we may see evidence of one or more virus diseases.

Wheat spindle streak mosaic and soilborne wheat mosaic virus can be detected during early phases of wheat growth in the spring. Symptoms of these two wheat virus diseases are sometimes very similar, except that wheat spindle streak is more uniform throughout a field and soilborne wheat mosaic affects plants in low areas or in pockets. Most modern wheat varieties have resistance to these two viruses, but there are still some out there that are susceptible to one, or less frequently, both diseases. Some varieties highly susceptible to soilborne wheat mosaic virus remain stunted in the spring and produce only a few tillers.

As temperatures warm in May plants generally recover and the yellowing symptoms tend to disappear. If plants recover soon enough there is little yield loss. If either of these virus diseases appear in your fields, do not plant that variety again in that field, but choose a variety resistant to soil-borne virus diseases in the future.

Getting Your Corn Crop off to a Good Start

Authors: Peter Thomison

The record corn yields of 2003 owed much to timely planting and good seedbed conditions. Last year, 83 percent of the corn crop was planted by May 4 – nearly three weeks ahead of the five-year average. However, keep in mind that 2003 rainfall was near normal to below average with temperatures generally warmer than normal in the 2 to 3 weeks preceding planting. Dry soil conditions allowed timely field operations and minimized soil compaction.

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.

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 (remember 2002 when we were hit with drought stress after the cold wet spring). 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
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 the seed in" may be much greater than those resulting from a slight planting delay. In 2003 many growers who prudently delayed planting wet fields until late May still ended up with some very decent yields.

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 (or secondary) root system if the crown is at or near the soil surface, some of the 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. 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 usually more likely to cause yield loss than planting above recommended rates (unless lodging becomes more severe at higher population levels). Under drought stress conditions, 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.

Calculating Seeding Rates for Corn

Authors: Peter Thomison

If the recommended plant population for a corn hybrid is 28,000 plants/acre based on various factors including site yield and potential hybrid characteristics, what should the seeding rate be? Remember a recommended plant population refers to final plant stand or the number of plants/A at harvest not seeding rate.

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 = 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.

Current Weed Control Reminders

- Alfalfa in most of the state is beyond 2 inches, therefore Velpar can no longer be used in alfalfa. The only options at this time are Pursuit and Raptor.

- If you are targeting winter annual weeds in wheat, those applications need to be going on now. If targeting Canada thistle or summer annual weeds, then wait a little longer. Watch wheat development stages and herbicide labels to prevent injury.

- Now is the time to begin early preplant burndown applications, especially in no-tillage soybeans. For excellent control of dandelion, marestail/horseweed, and lambsquarters that may be emerged be sure to include 2,4-D in the burndown mixture. Weedone 650 and E-99 can be applied at 1.3 pt/A (1.0 lb ai/A) 15 days before planting of soybeans.

- Do not apply herbicides when the morning lows are below 35 degrees.

CORN Can Be Downloaded to Your PDA

Authors: Greg LaBarge

The website for the CORN Newsletter http://corn.osu.edu/handheld.php gives instructions for downloading the CORN Newsletter into various PDA systems that are becoming increasingly popular on the farm. The system can be setup so each time you synchronize the PDA with your desktop computer; the latest CORN is added to your PDA web browser. Pictures and tables appear as they do on the web version. This is an exciting and useful new way to access the newsletter on the road and in the field.

Black Cutworm Moths Flying in Ohio

Authors: Ron Hammond, Bruce Eisley

We have begun trapping for some of the agronomic insects that can cause problems in Ohio. At the present time we will have pheromone traps in the field at three sites for black cutworm and common armyworm. Other traps will be added later in the season for European corn borer and southwestern corn borer. Pheromone traps will not tell us if a particular insect is going to be a problem or in which field(s) the problem is going to occur but the traps can be used to track insect emergence, movements and when peak populations occur. Information from the traps will be reported in future newsletters and on the web at: http://entomology.osu.edu/ag/04traps.htm