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Agronomic Crops Network

Ohio State University Extension


C.O.R.N. Newsletter 2005-08

Dates Covered: 
April 11, 2005 - April 19, 2005
Steve Prochaska

Proven Practices for Getting Your Corn Crop off to a Good Start

Authors: Peter Thomison

The record corn yields of 2003 and 2004 owed much to timely planting and good seedbed conditions. Last year, corn growers had 52 percent of their crop planted by May 2 compared to 31 percent for the five-year average, and in 2003, 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 rainfall throughout much of the state was near normal to below average with temperatures normal or 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.

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 (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.

2. 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.

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 (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.

Weed Management Issues for Early-Planted Corn

Authors: Mark Loux

Weed scientists know, from weed-crop interference studies conducted over the past 40 years or so, that weeds emerging at the same time as the corn have the most potential to reduce corn yield. These same studies generally show that early-emerging weeds have little impact on yield if managed in one of the following two ways: 1) preemergence herbicides applied at the time of corn planting keep the field free of weeds for approximately four weeks after planting; or 2) weeds that emerge with the crop are controlled with herbicides within 3 to 4 weeks after planting. Later-emerging weeds can reduce yield if present in high enough numbers and/or if the crop has not developed to the point that it is competitive with the weeds, but usually are much less deleterious than early emergers.

These principles are based on research where corn was planted primarily in early May or later. Planting corn in early to mid-April changes the situation somewhat, with regard to weed and crop emergence and growth. The following factors have to be taken into consideration in early-planted corn:

- corn emerges and grows more slowly when planted early, so additional time may be required for it to become competitive with weeds. For example, if we consider corn to be competitive with weeds once it reaches the V4 stage, early-planted corn may take longer to reach the V4 stage than later-planted corn.
- the primary period of summer annual weed emergence is approximately late April through early June. Consequently, planting earlier results in a need for a longer period of weed control, to account for most of the weed emergence. In other words, corn planted in early May would need four weeks of weed control to account for weed emergence through early June, while corn planted in mid April would require six weeks of weed control.

The bottom line – corn herbicide programs may need to provide several additional weeks of weed control when corn is planted early, to account for a longer period of weed emergence and to allow more time for a competitive crop to develop. It is possible for atrazine premix products (Bicep, Guardsman, etc) or similar combinations to control weeds through early June when applied in Mid-April, especially if weather and soil conditions favor rapid development of a competitive crop. However, there is an increased likelihood of late weed escapes that can still interfere with corn growth. Some strategies that can extend the length of weed control from an herbicide program follow:

- extend the activity of preemergence herbicides applied at the time of corn planting, by increasing rates or adding another herbicide to the treatment (Balance, Callisto, Hornet, etc). This may be less effective than the next two strategies, especially on weeds that have a tendency to emerge late, such as giant ragweed and fall panicum.
- delay application of preemergence herbicides until the corn and weeds have emerged. Weed emerge and grow more slowly in April, compared to May, and most atrazine-containing treatments can be applied after corn and weeds have emerged. This type of application (spike or early postemergence) can effectively control the first flush of weeds, and result in more herbicide availability in late May or early June, since it is applied later. Increasing atrazine rates to 2.0 lbs ai/A or applying a broader spectrum product such as Lumax/Lexar can result in the most effective control of emerged weeds.
- use a combination of preemergence and postemergence herbicides. This is the best of both worlds, really, since the preemergence herbicides applied at planting prevent weeds from competing with corn for several weeks, and the postemergence herbicides control late-emerging weeds that escape the preemergence herbicides. Rates of preemergence herbicides can be reduced in this program, when followed by a broad-spectrum postemergence program (examples: Harness Xtra followed by glyphosate in Roundup Ready corn; Cinch ATZ followed by Steadfast ATZ; Guardsman followed by Lightning in Clearfield corn; Define + atrazine followed by Equip)

Stage Wheat to Avoid Injury from Dicamba

Authors: Mark Loux

Herbicide treatments for wheat that contain dicamba should be applied prior to jointing, or prior to the appearance of the first node. Application of dicamba after jointing can result in sterile heads without grain and loss of yield. All other wheat herbicides can still be applied after jointing.

Alfalfa Weevil in Alfalfa

Authors: Ron Hammond, Bruce Eisley

The warmer temperatures the past few days and those that will occur over this coming week means that we will need to begin scouting alfalfa for alfalfa weevil (AW), especially in southern counties, although those fields in central OH should begin being watched. Fields that have a south facing slope tend to warm up sooner and need to be checked for weevil earlier. 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. See the OSU Alfalfa Weevil FactSheet for more on alfalfa weevil scouting and thresholds. Remember that it is still too early to scout for potato leafhopper since they do not move into Ohio until May.

Pelletized Lime, Can I Get Away with Lower Rates?

Authors: Robert Mullen

This question comes up every year – can I put down a lower rate of pelletized lime and achieve the same result as typical ag-lime at a higher rate? Maybe, but a fraction of the recommended rate (say a fourth or a third) will likely not achieve the desired result. It is not that pelletized lime is a poor lime source. It is one of the better lime sources because it is very fine material. It simply can not neutralize soil acidity any better (or faster) than conventional lime sources. Ohio uses a term – effective neutralizing power (ENP) – to compare the neutralizing power of different liming materials. The ENP of a given liming material is a function of three things – total neutralizing power (TNP-depends upon purity of the source and the ratio of calcium to magnesium), fineness (how smaller are the particle sizes), and moisture (how much water does the liming material contain). Pelletized lime is typically finer than ag-lime, so its ENP value may be higher meaning that it takes less pelletized lime to neutralize the same level of soil acidity. If the lime recommendation from the Tri-State Fertilizer Recommendations is 3 ton per acre, and you had a pelletized lime with an ENP of 2000 (which is what most pelletized liming materials approach) you would need 3 ton of that liming material per acre to achieve the desired neutralization. Let’s take that same 3 ton per acre recommendation and use an ag-lime with an ENP of 1000. It would require 6 ton of ag-lime to achieve the desired change in soil pH. Applying only 300 to 500 lb of pelletized lime per acre would not result in the desired change in soil pH because we have not even approached the rate necessary (3 ton per acre). Just because you needed twice as much ag-lime as pelletized lime does not necessarily make pelletized lime the best choice based on cost. Price comparison is the best way to evaluate liming materials. Select the one that will give you the necessary results at the best price.

Check Wheat Growth Stage Before Applying Herbicides

Authors: Patrick Lipps

Warmer weather throughout the state over the past week or so has favored rapid growth of the wheat crop. As usual, wheat growth in southern Ohio is ahead of wheat in northern Ohio due to the accumulation of more heat units in southern areas. Wheat growth stage can vary considerably from location to location in the state and from field to field, depending on planting date, fall growing conditions, soil moisture levels earlier this spring, fertility and accumulated heat units. Therefore, never rely on a calendar date or plant height to estimate growth stage, especially when deciding to make herbicide applications. Certain herbicides are labeled to be applied before the wheat plant enters the stem elongation growth stage. The reason for this is to avoid injury to the wheat crop. In the past some herbicides (Banvel and some 2, 4-D products) have been mistakenly applied too late causing markedly reduced yield. To avoid any problems with injuring the crop refer to product labels to determine what growth stage the herbicide should be applied.

Growers should learn to identify several of the critical growth stages of wheat to help better manage the crop. All spring topdressing of nitrogen should be applied by stem elongation so the wheat can take full advantage of the nitrogen. Additionally, several herbicide products known to be injurious to wheat if applied after stem elongation should be on the field by beginning stem elongation (jointing). The Feekes' growth stage scale is a commonly used system to describe various growth stages in the US. Feekes' growth stage 6 is the stage when the stems of the wheat plant begin to elongate and the first node is detected at the base of the stems. Feekes' growth stage 6 is also call the 'first node visible' stage. You can identify growth stage 6 by digging up a few plants and examining their largest tillers. Separate a larger tiller from each of the plants and strip down the several layers of bottom leaves and leaf sheaths to expose the lower stem. A plant is considered to be at growth stage 6 when the first node is detected on the lower stem above the roots. This node may be from a half inch to several inches above the crown of the plant. In southern Ohio growth stage 6 generally occurs by mid-April and in northern Ohio this growth stage usually occurs during the last week of April. However, temperature and day length play a significant role in overall developmental growth stage of wheat.

Delayed Application of Anhydrous Ammonia

Authors: Robert Mullen, Peter Thomison

Due to wet field conditions, some producers have not been able to apply their anhydrous ammonia yet. So the question is, what should I be worried about first -getting my anhydrous down or -getting my corn planted?

If it appears that intermittent rains may delay field work this spring, growers should focus on establishing their corn crop, and then turn their attention to N fertilizer application. The loss in yield from planting delays cannot be recouped; but delayed applications of N fertilizer should not translate into lower yields. In central Ohio, yields decline approximately 1 to 1.5 bu/day for planting delayed beyond the first week of May. Growers have seen the benefits of early planting during the past two years when record corn yields were associated with earlier than normal planting dates. Many growers may also recall years like 2002 when protracted wet weather delayed planting until late May and early to mid June, and remember the impact of planting delays on crop performance.

Producers accustomed to preplant applications of N should not be too concerned with delaying applications till after plant emergence. In fact, it can result in a yield benefit (if early season environmental conditions are conducive to N loss). Applications of N can be delayed up to V4 to V5 with little to no yield impact (again with possible improvement). Physiologically this makes sense because corn does not take up a large quantity of N prior to V6 to V8. When delaying application of N try to keep anhydrous ammonia away from the corn plant as severe injury can occur (make sure you get a good seal behind the knife). This does not necessarily translate into yield loss, but you may want to stay away from the field for a week or so.

There may be some concern of anhydrous ammonia injuring germinating seeds. The reaction of anhydrous ammonia and soil is primarily a function of depth of application, soil moisture, and spacing of injection points. If anhydrous is applied at a depth of six inches there should be little problem with seeding shortly after application (unless the soil is coarse textured and extremely dry – under these conditions wait a few days). Planting after shallow anhydrous ammonia applications (4 inches or less) should be delayed several days to allow the ammonia saturation zone to dissipate. Soils that are fairly wet (not too wet or the pack wheel will not properly seal the soil behind the shank) when anhydrous ammonia is applied should be ready to plant immediately after fertilization if applied well below the seeding depth (at least three inches). Try to keep at least three inches between the seed and the ammonia band. The other thing to consider is injection spacing. Wide injection spacing means that ammonia bands will have a higher ammonia concentration and increase what is referred to as the ammonia saturation zone. This is the zone surrounding the band that represents an area that contains high concentrations of ammonia. To minimize the risk of anhydrous ammonia injury, apply the ammonia in a diagonal pattern to the direction of planting. This will ensure that entire rows of corn are not injured.

Early Planting and Poorly Drained Fields – Seed treatments Are Needed

Authors: Anne Dorrance

Cool wet soils favor many early season pathogens including Pythium and Rhizoctonia. Seed treatments which contain metalaxyl or mefenoxam are essential to control Pythium, while Captan, PCNB, TBZ, thiram, azoxystrobin all have good activity against Rhizoctonia. Early spring planting, on fields that are typically poorly drained usually have the greatest return on seed treatment investments. General efficacy ratings of many common seed treatment fungicides can be found at the website:

Phytophthora sojae, one of the most common soybean pathogens in Ohio, requires warmer soil temperatures (>60 F) and also requires the highest rates of metalaxyl and mefenoxam which are on the label. Again, poorly drained soils and planting soybean cultivars with Rps genes that may no longer be effective in many fields (Rps1a, Rps1c and Rps1k) will see the biggest return on seed treatments. For season long control of Phytophthora root and stem rot, planting a cultivar with a Rps gene combined with high levels of partial resistance (field resistance) is required. Seed treatments are not silver bullets. If conditions occur where fields are totally saturated for longer than 3 to 4 days (ie: flooded) or rains do not occur at all – these environmental conditions can overwhelm even the best seed treatment.

Seedcorn Maggot in Field Crops

Authors: Ron Hammond, Bruce Eisley

Seedcorn maggots, larvae of small flies, are capable of causing significant stand reductions in corn and soybeans under the suitable conditions. Seedcorn maggot populations are significantly enhanced when living, green plant growth is plowed or tilled into the soil. This growth could include alfalfa, wheat, or rye, and can even be extremely heavy weed growth. There is a possibility that heavily manured fields that are tilled might also result in the problem. Although seedcorn maggots are often found feeding on seeds in no-till situations, economic problems are rarely seen. Growers should consider an insecticide seed treatment in fields where green plant material is tilled into the soil in the spring. There are a number of commercially-applied, insecticide seed treatments for both crops and studies have shown them to be very effective in preventing stand reduction from seedcorn maggots. If the seed is not treated when purchased, growers should check with their dealers for available hopper-box treatments. If seed treatment is not an option, waiting at least 3-4 weeks after tilling will usually help to reduce seedcorn maggot injury.

Monitoring for Corn Insects in Ohio

Authors: Bruce Eisley, Ron Hammond

We have begun trapping for some of the agronomic insects that can cause problems in Ohio. At the present time we have pheromone traps in the field at two 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:

Archive Issue Contributors: 

State Specialists: Mark Loux and Jeff Stachler (Weed Science), Pat Lipps, Anne Dorrance and Dennis Mills (Plant Pathology), Peter Thomison (Corn Production), Robert Mullen (Soil Fertility), Ron Hammond and Bruce Eisley (Entomology), Extension Agents and Associates: Roger Bender (Shelby), Todd Mangen (Mercer), Alan Sundermeier (Wood), Tammy Dobbels (Logan), Steve Bartels (Butler), Ed Lentz (Seneca), Steve Foster (Darke), Gary Wilson (Hancock), Dusty Sonnenberg (Henry), Mark Koenig (Sandusky), Harold Watters (Miami), Greg Labarge (Fulton), Howard Siegrist (Licking), Glenn Arnold (Putnam) and Steve Prochaska (Crawford)

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.