C.O.R.N. Newsletter 2007-15

Dates Covered: 
May 30, 2007 - June 5, 2007
Editor: 
Keith Dietrick

Conditions Favorable for "Rootless, Floppy Corn"

Authors: Peter Thomison

The recent hot, dry weather combined with poor root development in early planted corn may be setting the stage for rootless corn problems in Ohio. Rootless corn (or "rootless corn syndrome") occurs when there is limited or no nodal root development. This is also a problem that’s currently receiving attention in other Corn Belt states including Indiana, Illinois, and Iowa (see list of “online sources of information” at end of article). Plants exhibiting rootless corn symptoms are often leaning or lodged, and may only be anchored in the soil by seminal roots or by a single nodal root. This condition is generally observed in plants from about the three leaf stage to the eight leaf stage of development. The problem often becomes evident when corn is subjected to strong winds, which result in plants falling over because there is a limited number or no nodal roots supporting them. The force of strong winds can also break off nodal roots and inhibit establishment of a permanent root system. Leaning and lodged plants (sometimes referred to as "floppy corn") may also be wilted with stubby, blunt, and unanchored nodal roots.

Rootless corn problems are usually caused by weather-related conditions that coincide with development of the permanent (or nodal) root system and various environmental factors. These include shallow plantings, hot, dry surface soils, compacted soils, and loose or cloddy soil conditions. Excessive rainfall and shallow plantings may cause erosion and soil removal around the crown region that can result in rootless corn. Nodal root development is inhibited by hot, dry compacted soils.

The nodal roots develop above the seed and comprise the permanent root system of corn. The nodal roots, not the seminal roots (associated with the seed), are important in providing the water and the mineral nutrients that the corn plant needs for normal growth and development. If corn seed is planted 11/2 to 2 inches deep, then the nodal (or crown) roots begin develop at about 3/4 inches below the soil surface. However, if seed are planted shallower (1 inch or less), then the nodal roots may form near or at the surface where they are more exposed to fluctuations in soil moisture and temperature. Nodal root growth is very sensitive to high temperatures (w/ root growth slowing or stopping at soil temperatures exceeding 86 degree F ). When unshaded surface soil temperatures reach the mid 90's or higher on hot days, the nodal root growth of shallow planted corn may stop. Plants are forced to rely on the seed root system or limited nodal root growth until more favorable temperatures and moisture conditions allow nodal root growth to resume.

Certain types of herbicide injury (e.g. 2,4-D, Banvel) and insect feeding (e.g. corn rootworm) may also cause lodging to occur in corn plants during vegetative development. Generally they are not the major causes of the rootless corn problems. However, there may be situations where insect feeding and/or herbicides may be a contributing factor.

Can rootless corn recover? Yes, after plants lodge, adequate rainfall will promote crown root development and plants can recover. Cultivation to throw soil around exposed roots may aid the corn's recovery. Of course, this is difficult to do in a no-till situation or when the soil is hard and dry. Since affected corn is likely to be vulnerable to potential lodging problems at maturity, it should be harvested as soon as grain moisture conditions permit.

The following are some additional on-line sources of information on rootless/floppy corn and other effects of dry soil conditions on early crop growth. If you have not seen floppy, rootless corn, check out Bob Nielsen’s article “Rootless Corn Syndrome” below for some excellent images.

Elmore, Roger and Lori Abendroth. 2007. Rootless Corn Syndrome. Integrated Crop Management Newsletter, Iowa State Univ. [On-Line]. Available at http://www.ipm.iastate.edu/ipm/icm/2007/5-21/rootless.html.


Nafziger, E. 2007. Seeds and plants in dry soils: Available at http://www.ipm.uiuc.edu/bulletin/article.php?id=740. From the Bulletin: Pest mgmt & crop developmt information for Illinois. Univ. of Illinois [On-Line]: http://www.ipm.uiuc.edu/bulletin/contents.php?id=85.

Nielsen, R.L. (Bob). 2007. Be on the Alert for Floppy, Rootless Corn. Corny News Articles, Purdue Univ. [On-Line]. Available at http://www.agry.purdue.edu/ext/corn/news/articles.07/Floppy-0523.html.


Nielsen, R.L. (Bob). 2007. Variable Emergence Due to Variable Seedbed Moisture. . Corny News Articles, Purdue Univ. [On-Line]. Available at http://www.agry.purdue.edu/ext/corn/news/articles.07/VariableEmergence-0520.html

Dry Weather and Postemergence Herbicide Activity

Authors: Mark Loux

Dry weather presents challenges for postemergence herbicide management for a number of reasons. Herbicide activity is often reduced on weeds that have been growing under droughty conditions. One of the more difficult decisions to make is whether to go ahead and apply postemergence herbicides before drought-stressed weeds get even larger and more difficult to control, or wait for a rain in the hope that replenishment of soil moisture will lead to more active weed growth and better herbicide activity. Weed emergence is also a factor in this decision, because prolonged dry conditions followed by rain can lead to additional weed emergence. So, there can be a tendency for growers to delay postemergence applications to ensure control late-emerging weeds.

Even though weeds grow more slowly under dry conditions, they do continue to grow and compete with the crop. Weed growth can be more variable than under adequate moisture, so that a few weeds may be reaching a height at which application should be made, but the rest are smaller. Our past experience indicates that, under dry conditions, postemergence herbicides will still be effective on relatively small weeds, but control of large weeds can be difficult. So while the natural tendency may be to delay postemergence application until all of the weeds reach a certain size, this can mean that control of the largest weeds will suffer.

Our best advice on this situation, as weeds approach the target size, relative to the chance of rain is: 1) if there appears to be a good chance of rain within several days, consider waiting until after the rain, which can improve control; otherwise 2) if rain is not likely in the foreseeable future, apply postemergence herbicides when weeds are small, and well within the maximum weed size allowed on the herbicide label. The weeds that emerge with the crop are the most competitive, presenting the greatest risk of yield loss. Obtaining effective control of early-emerging weeds should be a major goal, even if it means missing some of the later-emerging weeds.

Glyphosate Resistance in Giant Ragweed Part I: The Current Situation

Authors: Mark Loux

Giant ragweed remains one of the most difficult weeds to control in soybeans, due to its extended emergence period, rapid growth, and propensity to develop herbicide resistance. Giant ragweed control in Roundup Ready soybeans is generally maximized through the following steps:
1) using an effective preplant burndown that includes 2,4-D ester;
2) using residual herbicides to reduce the population and growth rate; and
3) making one to two postemergence glyphosate applications at rates appropriate for giant ragweed size and the history of control in the field.
Deviations from this approach, which usually involve over-reliance on glyphosate and application to weeds that are too large, have resulted in inadequate control in some fields and contributed to the development of glyphosate-resistant giant ragweed populations. Our experience has been that the glyphosate-only approach can work for several years for control of giant ragweed, but will eventually start to fail.

We were first aware of the possibility of glyphosate resistance in giant ragweed in 2004, based on poor control in a Licking County soybean field. Resistance in this field was confirmed by greenhouse and field research in 2005. The frequency of resistance has been increasing, and we are currently aware of at least 16 fields in 11 counties with glyphosate-resistant giant ragweed populations. These counties include Butler, Clinton, Darke, Fayette, Henry, Licking, Madison, Pickaway, Preble, Ross, and Union. We assume, based on our previous experiences with herbicide resistance, that resistant populations are most likely occurring in a number of other counties as well. Glyphosate resistance in giant ragweed has so far been relatively low level resistance, but field research we conducted in 2006 at four sites showed that resistance resulted in inadequate control with glyphosate programs that have historically provided effective control of sensitive populations. Specifically, control was still not acceptable when the field was weed-free at planting, and then treated with two postemergence glyphosate application, using a rate of 0.75 lb ae/A in each application.

It is essential to recognize that glyphosate resistance does not confer the complete immunity to herbicide applications that is typical of resistance to ALS inhibitors and triazines. Giant ragweed plants that are resistant to glyphosate almost always show some symptoms in response to treatment with glyphosate. Symptoms can include temporary yellowing or bleaching of leaves, some distortion in new leaf shape, and a “stacking” of the internodes that gives plants a sort of shrub appearance. However, we have also observed plants that just fail to increase in size for a while, without other symptoms, followed by a resumption of growth. What’s important here is that these plants may not be controlled by typical postemergence glyphosate rates and timings.

The good news from our research in 2006 – by starting weedfree at planting, increasing the glyphosate rate to 1.5 lb ae/A in the first postemergence application, and following with a second application three weeks later, we were able to control much of the resistant ragweed and prevent it from being competitive with the soybeans. We were not able to kill all of the giant ragweed plants or completely eliminate seed production. The bad news is that we expect that the level of resistance will continue to increase, so that even this approach is likely to eventually provide unacceptable control. It’s also possible that there are currently some giant ragweed populations with high enough resistance that this approach won’t work now. It appears inevitable that effective postemergence management of resistant ragweed in some fields is likely to require the integration of glyphosate with other postemergence herbicides. In our 2006 research, some of the most consistent giant ragweed control and lowest seed production resulted from an initial application of Flexstar, followed by an application of glyphosate three weeks later. We’ll have a better idea of exactly how other herbicides should be integrated with glyphosate upon the completion of our 2007 research.

The other piece of good news here is that not all giant ragweed populations have become more difficult to control with glyphosate. So far, resistant populations have been most likely to occur in continuous soybean fields treated with glyphosate exclusively. Populations in fields with a rotation of Roundup Ready soybeans and non-Roundup Ready corn, where other herbicides have been integrated with glyphosate, appear to be much less likely to develop resistant populations. Or, put another way, the rate of development of resistant populations appears to be far slower. The increase in use of Roundup Ready corn, and the corresponding transition to continuous Roundup Ready crops, will undoubtedly change this somewhat.

Glyphosate Resistance in Giant Ragweed Part II: Managing Postemergence Glyphosate Applications

Authors: Mark Loux

Because there is a range in the response of giant ragweed to glyphosate among fields, our recommendations for management of postemergence glyphosate applications are based on whether there is a history of control problems in the field. The guidelines listed below are based on the assumption that the field was weedfree at the time of planting, through use of tillage or an effective preplant burndown treatment. No-till fields where the crop was not started under weedfree conditions should be treated as soon as possible with the maximum allowable postemergence use rate, before giant ragweed become any larger.

Roundup Ready soybean fields without a history of giant ragweed control problems:
Apply glyphosate at a rate of 0.75 lb ae/A when the largest ragweed plants in the field are less than 10 inches tall. Increase the rate to 1.5 lbs ae/A where plants are larger than 10 inches. Follow with a second glyphosate application at 0.75 lb ae/A 3 to 4 weeks later as necessary, to control late emergers or plants that were not killed by the first application.

Roundup Ready soybean fields with a history of giant ragweed control problems:
Apply glyphosate at a rate of 1.5 lb ae/A when the largest ragweed plants in the field are less than 10 inches tall. Follow with a second application of glyphosate at 0.75 lb ae/A 3 to 4 weeks later. The second application is mandatory, not optional, in fields with a history of control problems.

Roundup Ready corn fields without a history of giant ragweed control problems:
Apply glyphosate at a rate of 0.75 lb ae/A when the largest ragweed plants in the field are less than 10 inches tall. Increase the rate to 1.1 lbs ae/A where plants are larger than 10 inches. Consider a mixture of glyphosate with dicamba, Distinct, Hornet, Status, Callisto or Impact to improve control of large plants and reduce selection for resistance. Where corn is less than about 12 inches tall at the time of the first postemergence glyphosate application, it is possible that a second application of 0.75 lb ae/A may be needed to control late-emerging plants.

Roundup Ready corn fields with a history of giant ragweed control problems:
Apply a mixture of glyphosate (1.1 lb ae/A) plus one of the following: dicamba, Status, Distinct, or Hornet. Giant ragweed plants should be less than 10 inches tall at the time of application. Where corn is less than about 12 inches tall at the time of the first postemergence glyphosate application, it is possible that a second application may be needed to control late-emerging plants.

Resources available on giant ragweed management include the following:

2007 Weed Control Guide for Ohio and Indiana, especially the section on giant ragweed in the “Problem Weeds” section (p 179).

The fact sheet, “Management of giant ragweed in Roundup Ready soybean fields with a history of poor control”, available at many OSU county extension offices and online at: https://agcrops.osu.edu/weeds/documents/girwfactfinal.pdf.

A new publication in the Glyphosate, Weeds, and Crops series, “Management of giant ragweed”, available online at https://agcrops.osu.edu/weeds/documents/GWC-12.pdf. We will eventually have a supply of these to distribute at no charge.

The Yellow Weed

Authors: Mark Loux

Cressleaf groundsel, the yellow-flowered plant found in many no-till fields, continues to spread into additional areas throughout Ohio. Cressleaf groundsel is a winter annual weed that emerges in the fall. It has an aster-type flower and a purplish and hollow stem with no hair, and reaches a height of 20 to 36 inches tall. Cressleaf groundsel is often confused with yellow rocket, which reaches a maximum height of about 24 inches. Yellow rocket is a mustard species, and the flowers have four petals and sepals.

Cressleaf groundsel can be seen in full flower at this time of the year primarily in no-till fields that were not treated with herbicides last fall or earlier this spring. These plants should be controlled as soon as possible to prevent seed production, which will occur imminently and will be the source of a new infestation this fall. Seeds of cressleaf groundsel are dispersed by wind, so that seed production can affect neighboring fields as well as the field where the infestation is currently found. This potential for seed production is the reason why we continue to stress the need for fall or spring preplant application of herbicides in no-till fields, before most of the winter annual weeds flower.

Use one of the following treatments to control cressleaf groundsel in no-till fields that have not been planted at this time: 1) glyphosate (1.1 lb ae/A) plus 2,4-D ester (0.5 lb ai/A); or, 2) where soybean planting cannot be delayed 7 days, apply glyphosate at 1.5 lbs ae/A. In fields with emerged soybeans and cressleaf groundsel still present, apply glyphosate (1.5 lb ae/A) immediately to reduce the amount and spread of cressleaf groundsel seeds.

Potato Leafhoppers Arriving in Alfalfa

Authors: Keith Diedrick, Bruce Eisley, Ron Hammond

As in every spring, potato leafhoppers have made their way north to Ohio. With alfalfa fields harvested for the first time, growers should plan on scouting for the leafhopper as the re-growth reaches sufficient height for sweep-net sampling. Growers in southern to central Ohio should begin sampling in the next week, and those in the north shortly after. Sampling is done using a sweep net and taking 10 samples throughout a field. Each sample should consist of 10 sweeps with the net. Count all potato leafhopper adults and nymphs, though mostly adults will be seen at this time. When the average number of leafhoppers in a single sample (10 pendulum sweeps) is equal or greater than the average height of the alfalfa stand, insecticide treatment is warranted for varieties not resistant to the potato leafhopper. For example, if the alfalfa is 6 inches tall and the average number of leafhoppers per 10-sweep sample is 6 or higher, insecticide treatment is warranted. If the average is lower, the grower should re-sample in a few days to check for populations above threshold. For potato leafhopper-resistant varieties of alfalfa, the economic threshold established from our research is three leafhoppers per inch of growth (30 leafhoppers for 10” tall alfalfa, for example). Pictures of potato leafhopper adults and nymphs can be found on the WEB at: http://ohioline.osu.edu/icm-fact/images/112.html, http://ohioline.osu.edu/icm-fact/images/113.html. This site lists those insecticides labeled for PLH on alfalfa: http://entomology.osu.edu/ag/545/aiplh.pdf.

Soybean Sentinel Report for May 29

Authors: Anne Dorrance

Soybeans are still coming through the ground in much of the state, and dry conditions prevail for the majority. Some areas received from a tenth to three-fourths of an inch of much needed rain. Rain totals are less than an inch for the month of May at some locations. Growth stages from the 16 reports this week were from just cracking the soil to V2 (two fully expanded trifoliates). No disease problems were identified. More locations with early bean leaf beetle feeding but only a few required treatment.

There were no additional finds of soybean rust in Louisiana or Florida last week and as of Tuesday afternoon, there were no additional reports. All is quiet in the south.

Interested in Becoming a Certified Crop Advisor?

Authors: Harold Watters

The American Society of Agronomy's Certified Crop Adviser Program (CCA) is the largest certification program in agriculture with over 14,000 certified throughout the USA and Canada.

There are four steps to Certification:
1) Pass two comprehensive exams
2) Have at least 2 years experience with at least a Bachelor of Science Degree in agriculture or 4 years with no degree
3) Document education and crop advising experience with transcripts and supporting references
4) Sign and agree to uphold the CCA Code of Ethics.

Once certified you must earn 40 hours of continuing education (CEUs) every two years and pay an annual maintenance fee. Any adviser/consultant that spends the majority of their time advising growers on agronomic practices should be certified.

The Certified Crop Adviser Program (CCA) is a voluntary program providing a base level of standard through testing and raising that standard through continuing education. The program is administered by 37 local boards throughout the United States and Canada.

Next CCA Exam Date: August 3, 2007
CCA Exam Registration deadline: June 15, 2007
For further information about the program and on how to register for the exam: https://www.agronomy.org/cca/.

Alfalfa Field Day – Defiance County, June 21st

Authors: Bruce Clevenger

OSU Extension is sponsoring an Alfalfa Field Day on Thursday, June 21, 2007 from 9:00 a.m. to 2:00 p.m. at the Andy Helmke Farm, 07730 Egler Road, Defiance, OH. The event will feature presentations by industry and educational representatives.

Greg LaBarge, OSU Extension Educator, Fulton County will discuss the fertility and pH requirements for establishing alfalfa. Gary Wilson, OSU Extension Educator, Hancock County will discuss creating the best stand with variety selection and cultural practices.

Dr. Mark Sulc, OSU Extension Forage Specialist, will share his research and experiences on “Why the Stand Declines.” It will include the cumulative stress load, insect and diseases, and evaluating winter injury risk. Alfalfa quality will also be discussed by Dr. Sulc, as will “Taking Forage Quality Samples and Field and Storage Factors that Will Influence Quality.”

A panel discussion of a farmer, industry reps and an extension educator will discuss marketing alfalfa as a cash crop to area forage markets – dehydration mills, livestock producers, horses, and others. Seventeen companies and organizations are sponsoring the event with equipment demo and displays on-site.

The cost for the Alfalfa Field Day is $10.00 which includes lunch. Pesticide applicator credits will also be available to private and commercial license holders. The program offers CCA continuing education credits in crop management, nutrient management and pest management. Please RSVP by June 18, 2007.

Agenda and registration material can be found at: http://defiance.osu.edu/. Questions and RSVP may be directed to the Defiance County OSU Extension office (419) 782-4771. The event is sponsored by the OSU Extension offices in Defiance, Fulton, Paulding, Williams and Henry Counties.

ALERT - Potato Leafhoppers in Seedling Alfalfa Stands

Authors: Mark Sulc

In this week's C.O.R.N. newsletter we mentioned the need to begin sampling alfalfa regrowth after first cutting for potato leafhoppers. In NEW SEEDINGS planted this spring, potato leafhoppers may already be very active and could be above action thresholds anywhere in Ohio this weekend. Yesterday I checked our alfalfa plots near Springfield, OH and found 32 leafhoppers in 10 sweeps in 6-inch tall seedling alfalfa that had been planted just this April. That is about 5 leafhoppers in 10 sweeps per inch of alfalfa height, or 5 times the normal threshold level. So we are applying an insecticide treatment to that alfalfa plot today, which is planted to standard susceptible alfalfa varieties. Slight yellowing and cupping of the leaves was just beginning to show.

In another field planted in April to a highly resistant alfalfa variety, we found 18 leafhopper in 10 sweeps on 6-inch alfalfa. That is 3 leafhopper in 10 sweeps per inch of alfalfa height, which is exactly the action threshold we have been recommending on established stands of resistant varieties. We will spray that field today as well. In fact, I encourage growers to use the normal threshold of 1 leafhopper in 10 sweeps per inch of alfalfa height on resistant alfalfa during the first growth of the seeding year. So we were well over that level!

With the dry and hot weather stress developing in these new seedling stands, the thresholds should be lowered below the normal level. If your soils are turning quite dry and you find from 0.5 to 1 or more leafhoppers in 10 sweeps per inch of alfalfa seedling height, it would be prudent to apply an insecticide treatment. On varieties with high resistance to potato leafhopper, consider using the normal threshold level of 1 leafhopper in 10 sweeps per inch of alfalfa height, especially during the very first growth from seeding. Resistance improves as the seedling stand develops, but on the very first growth of the stand I encourage you to use the normal threshold level. After the first cutting of the stand, the threshold for a highly resistant variety can likely be increased to 3 times the normal level for susceptible varieties.

To Sidedress or Not To Sidedress, That is the Question.

Authors: Robert Mullen, Peter Thomison, Edwin Lentz

Ohio’s dry late spring has caused many producers to re-consider their sidedress applications of nitrogen, so what should you do? There are a couple of things to consider when making your decision.

Nitrogen Source: Which source of nitrogen are you likely to apply? If you are planning to apply a urea-based fertilizer (either dry or liquid) proceed to the next section titled Application Methodology. If you are sidedressing your corn with anhydrous ammonia, you really need to assess your soil moisture situation. The primary concern with sidedress ammonia application is getting a good seal behind the knife so that we do not directly lose any nitrogen (it is way too expensive). Extremely dry soil that will not allow the furrow to be sealed properly will result in nitrogen loss and corn leaf tissue injury (that is unlikely to translate into yield loss - fortunately). Low soil moisture will also allow the nitrogen to diffuse a greater distance through the soil possibly reaching the soil surface where it can be lost. Remember the first reaction when ammonia is applied to the soil involves water, so if very little moisture is present the ammonia can move more readily and across a greater distance. Thus you many want to delay your application. Non-urea salt forms of nitrogen (ammonium sulfate, ammonium nitrate, potassium nitrate, etc.) can be applied with small chances of nitrogen loss (unless soil pH is extremely high ­ around 7.5 or higher). But realize that until a rainfall event those materials will simply set on the soil surface and provide very little nitrogen to the crop.

Application Methodology: How will the nitrogen be applied? Subsurface applications can be made using subsurface injection tools (knife applicators, coulter injectors, etc.) with little concern for nitrogen loss even when the soil is dry. If urea-based nitrogen is to be placed on the soil surface, proceed to the section titled Tillage.

Tillage: Just how much residue do you have laying on the soil surface? The greater the amount of residue on the soil surface the more critical it is to get the urea-based nitrogen materials below the soil surface (see Application Methodology). This is especially true when the long-term forecast for rain is not that great. Even if you are in a clean-till system, ammonia can volatilize from the soil surface under the right conditions. Unfortunately we have had the right conditions quite a bit here lately, high humidity in the morning causing dew events that can get the urea into solution, but it can not incorporate the material adequately. Under these conditions the chances of ammonia loss are greater. If you are going to surface apply urea-nitrogen a urease inhibitor may be used to decrease the chance of nitrogen loss by volatilization. Remember this though, in the absence of rain the nitrogen will not make its way into the soil and be usable by the plant, so you may want to wait until the probability of precipitation is better. The better the chance of rain the less likely you will need a urease inhibitor (but you do have to trust the weatherman).

Archive Issue Contributors: 

State Specialists: Anne Dorrance, Pierce Paul, and Dennis Mills (Plant Pathology), Ron Hammond and Bruce Eisley (Entomology), Peter Thomison (Corn Production), Mark Loux and Jeff Stachler (Weed Science). Extension Agents: Roger Bender (Shelby), Howard Siegrist (Licking), Glen Arnold (Putnam), Keith Diedrick (Wayne), Steve Prochaska (Crawford), Todd Mangen (Mercer), Mike Gastier (Huron), Alan Sundermeier (Wood), Gary Wilson (Hancock), Steve Bartels (Butler), Bruce Clevenger (Defiance), Mark Koenig (Sandusky), Harold Watters (Champaign), Greg LaBarge (Fulton), Steve Foster (Darke), and Jim Lopshire (Paulding).

 

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.