C.O.R.N. Newsletter 2007-09

Dates Covered: 
April 17, 2007 - April 23, 2007
Editor: 
Steve Prochaska

Killing Failed Wheat Stands to Plant Corn or Soybeans

Authors: Mark Loux

Growers needing to kill a failed wheat stand in order to plant corn or soybeans have two options - glyphosate or a mixture of Gramoxone with a photosynthetic inhibitor (atrazine or metribuzin). Glyphosate should be applied at a rate of 1.5 lb ae/A. Many no-till fields will require the addition of 2,4-D ester (0.5 to 1 lb/A) to ensure control of emerged glyphosate-resistant marestail and giant ragweed, and generally improve control of lambsquarters and most other broadleaf weeds. Apply in a spray volume of 10 to 15 gpa and include AMS if applying in hard water.

Glyphosate is the less expensive option, but not necessarily the better choice where rapid death and drydown of the wheat is important. Where the intent is to plant corn as soon as possible, consider the use of Gramoxone Inteon (2 to 3 pt/A) plus atrazine at a rate of at least 1.5 lb ai/A (plus 2,4-D ester if necessary). This mixture is more expensive than glyphosate/2,4-D, but could result in more rapid burndown of the wheat, which will minimize the early-season competition between the remaining wheat and corn. Combinations of Gramoxone with metribuzin will be less effective for controlling wheat than Gramoxone plus atrazine, and may not be any better option than glyphosate. Gramoxone treatments should be applied with crop oil concentrate and 28%, and are most effective when 28% is used as the spray carrier. Use a spray volume of 15 to 20 gpa.

It’s likely that neither glyphosate nor Gramoxone will be consistently effective for control of wheat. We would suggest the planting of a Roundup Ready crop in these fields, because it allows the use of glyphosate after crop emergence to complete control of the wheat.

Control of Annual Ryegrass

Authors: Mark Loux

We have been hearing for the past year about problems associated with the control of annual ryegrass cover crops in the spring. It seems that the cart might be in front of the horse here, with the use of annual ryegrass promoted before there was sufficient research on how to effectively control it in order to establish corn or soybeans. We had the opportunity this spring to conduct research on the control of annual ryegrass. In this research, we are comparing several rates of glyphosate alone and with atrazine, and two rates of Gramoxone applied with atrazine. These treatments were applied on March 30 and will be applied again later this week, to determine how timing of application affects control. We also have several treatments where the initial glyphosate application is followed with another application of glyphosate, atrazine, or Gramoxone plus atrazine.

We have an incomplete story at this time since the study is in progress, but results from the first application timing support the comments by many growers that annual ryegrass can be difficult to control with glyphosate. At 12 days after application, control from glyphosate at 1.1, 1.5, and 3.0 lb ae/A ranged from 43 to 53%. The inclusion of atrazine with glyphosate did not affect control. Gramoxone/atrazine combinations resulted in more rapid and more effective control, compared with glyphosate. The combination of atrazine (1.5 lb ai/A) plus Gramoxone Inteon at 2 and 3 pints/A resulted in 93 and 99% control, respectively, at 12 days after application.

One of the concerns voiced by growers and our counterparts in surrounding states is that while glyphosate may eventually control the ryegrass, control can require a long period of time. Preliminary results of our research appear to validate these concerns. We are observing poor control with glyphosate at about 2 weeks after application. The goal of a spring burndown treatment is to control existing vegetation rapidly enough that the crop is planted into a weedfree seedbed. Failure to completely control a dense cover such as annual ryegrass could result in problems with crop establishment and early-season growth. While it’s a preliminary conclusion, our research indicates that a combination of Gramoxone plus atrazine may be the most effective treatment for control of annual ryegrass in the spring. We’ll update this story as our research progresses.

Spring Nitrogen Applications to Winter Wheat and Tissue Burn

Authors: Robert Mullen, Edwin Lentz

Top-dress applications of nitrogen to winter wheat are traditionally made this time of year and occasionally tissue burn can occur. The question is what impact will this burn have on winter wheat yield potential?

First, what causes the leaf tissue to show the burn injury? Application of a salty material (any salt formulation of fertilizer) to growing leaf tissue alters the water balance of the leaf causing water to be pulled from the tissue structures resulting in a burning or scorching of the tissue. The level of injury is a function of several factors including nitrogen application rate, air temperature (the higher the temperature the worse the injury), and humidity level (the lower the humidity the worse the injury).

So does this burning or scorching affect yield potential? It depends primarily on the timing of application. Applications of foliar nitrogen made prior to flag leaf emergence are unlikely to negatively affect yield potential, and the burn injury typically dissipates over a few days especially if a rainfall event follows the appearance of the injury. Applications made after flag leaf emergence may negatively affect yield potential if the flag leaf or the leaf below it are damaged. Bottom line, do not apply foliar nitrogen after flag leaf emergence, and if you do keep the rate of application low.

Top-dress applications of winter wheat can be managed to decrease the potential of leaf burn. The best tool available is stream bars or stream jet nozzles. This technology decreases the amount of plant tissue exposed to the salty fertilizer solution. Flat fan nozzles cover the entire plant with the nitrogen fertilizer solution and subsequently cause the highest level of burn. Also avoid mixing topdress nitrogen applications with some herbicide formulations (see the Herbicide Handbook to see compatibility). Cutting the nitrogen solution with water can help alleviate burn, but it will not likely completely remove the injury.


Frost Injury to Alfalfa: Issues and Concerns

Authors: Mark Sulc

The early alfalfa growth from late March has been killed back by the frigid early April temperatures across most of the state. Some fields still show green leaf material in the lower canopy, but the taller stems have collapsed from the cold injury.

I really don’t expect that we will see permanent damage to established, healthy alfalfa stands from this late freeze. Back in 1992 we had similar conditions of alfalfa breaking dormancy early in March, followed by cold temperatures that killed the shoots back to the crown. Alfalfa re-initiated growth that year and first-cutting yields were near normal, although the first harvest was delayed by 7 to 15 days.

Established stands of adapted varieties will initiate new growth with the warming temperatures, especially if the fields have good drainage and adequate fertility. If fertility is below optimum, make corrective applications as soon as soils are firm and dry enough to support traffic.

For late summer 2006 seedings, the frost injury may cause more significant problems depending on extent of seedling establishment and growth achieved last fall. Plantings made in late July to early August 2006 will likely have less long-term damage than those made in late August to September. Plant roots should be observed later this week. If the inner root tissue is soft, spongy, and possibly discolored, then severe injury has occurred. Those plants will or already have died. In contrast, healthy root tissue will be firm and white.

Weak stands, especially those under water logging stress, will likely have a more difficult recovery this spring and yield levels will be lower than normal. Keep a close eye on fields in that condition during the next two weeks.

My best guess is that we will have to delay our first harvest by 7 to 15 days this spring. We will know more as the crop recovers and develops. A delayed first harvest will give the crop time to recover and produce near normal yields. Forage quality should follow the normal changes in relation to crop maturity.

The delay in first harvest this year will mean that only three cuttings will be possible for stands where four cuttings are normally taken. Delayed first cutting will help restore plant vigor and achieve normal yield levels. In addition, allowing the alfalfa to mature to 30 to 50% bloom stage sometime this summer will help the stand regain full vigor.

Despite the potential for one less cutting (3 rather than 4 cuts) this year, overall yields could still be near normal provided weather conditions favor good alfalfa growth the rest of the growing season. Research has shown that alfalfa cut three times is often higher yielding than when four cuts are made. Forage quality is usually lower with three cuttings as compared with four; however, it is usually acceptable for dairy animals, provided the stand is pure alfalfa and not mixed with grass.

For mixed grass-alfalfa stands, I think yield loss will be very negligible, as the grass has been less affected by the frost. The tricky management issue will be that grass will grow rapidly and be ready for harvest much sooner than the alfalfa coming back from the frost injury.

Finally, I’ve also been asked three related questions: Should the frosted alfalfa growth be cut? Will the dead alfalfa stems interfere with new shoot development? Will forage quality at the first cutting be harmed by the dead alfalfa stems?

For pure alfalfa stands, my answer to all three questions is “No”. The dead stems should not be cut because they will have negligible or no effect on the growth of new shoots. I think the dead stems will have negligible effect on forage quality at first cutting because they probably won’t even be picked up during harvesting operations, and will be decomposing by that time. Because most of the frosted material has already collapsed to the ground, I doubt a cutter bar would even do much good at this point in time. Furthermore, soils are wet and soft, and the risk of crown damage from traffic is high. So I think we should save the fuel and be patient for the recovery to occur.

Finally, should grass-alfalfa mixtures be clipped to slow down the grass growth? I am less certain about answering “no” to that question, but I’m still concerned about cutting those stands. By the time one could get on the field to clip them, some young alfalfa shoots may be growing, especially those deep in the canopy that survived the frost. Cutting could remove those stems and potentially do more harm than good to the alfalfa recovery in the stand.

Stand Establishment Problems in Late Summer Seeded Alfalfa

Authors: Mark Sulc

I’ve heard reports of stand establishment problems in alfalfa planted last summer. This is particularly true in northwest Ohio where standing water reduced stands over the winter. The question is what can be done about it?

If the thin spots are not too numerous and are relatively weed free, alfalfa can be interseeded with a no-till drill to thicken up the stand as soon as soils are fit. Alfalfa planted just last summer (2006) will not yet be old enough to cause problems from autotoxicity.

Interseeding to thicken up the 2006 summer seedings will only be successful if the surviving plant density is very low and will provide minimal to no competition to new emerging seedlings. Use careful judgment before attempting to interseed where there is surviving alfalfa stand.

If winter annual weed populations are high in the areas with stand loss, a glyphosate treatment to eliminate that competition will be important before trying to interseed. Raptor and Pursuit are not an option where alfalfa is to be reseeded. The waiting period for alfalfa seeding is 3 months for Raptor and 4 months for Pursuit application.

If stand thinning is severe throughout the field, and especially if winter annual weeds are a concern, then it will be best to start over. Kill the entire stand (with glyphosate, and possibly tillage) and replant as if it were a completely new seeding.

I realize that precipitation has been well above normal during the past 6 to 8 months, but it will likely happen again in Ohio. So do your best to pick fields for alfalfa that have good internal and surface drainage to ensure a productive and persistent stand.

Boosting Forage Production After Winter Damaged Alfalfa

Authors: Mark Sulc

Interseeding alfalfa is an option to thicken up stands if the alfalfa was seeded last summer. In stands that are 2 years old or older, interseeding alfalfa into alfalfa to thicken up the stand usually does not work. New alfalfa seedlings may emerge and look good early on, but they often die out over the summer due to competition, diseases, and autotoxicity present in the existing alfalfa stand.

To extend the life of winter damaged alfalfa stands beyond this year, consider interseeding red clover or a grass species such as ryegrass or orchardgrass. The yield benefit from these perennial species may not be great until the second year, because they do require some time to establish. Perennial ryegrass would most likely provide an earlier yield boost because of its rapid establishment. The disadvantage of perennial ryegrass and red clover is that they are slower to dry, so curing times will be lengthened compared with orchardgrass-alfalfa mixtures.

If forage supplies are very critical for this year, consider interseeding with a cereal grain (oat, beardless barley, wheat, spring triticale) or annual ryegrass into alfalfa. All these annual grasses are quick to establish and will compete well in a thin alfalfa stand. The forage may need to be put up as silage or balage rather than as hay, but yields will be high and forage quality can be very good if cut in late boot to very early heading stage.

There are numerous annual species for boosting forage supplies for this year alone, corn silage being one of the best. The following are excellent sources of information on annual forages and managing alfalfa where winter injury is an issue:

The Ohio Agronomy Guide, Chapter 7 (section on Annual Forages)
http://ohioline.osu.edu/b472/0008.html

Articles on Univ. of Wisconsin Website:
http://www.uwex.edu/ces/forage/news/current/winterkill2005.htm

Wheat Scab Risk Prediction 2007

Authors: Pierce Paul, Dennis Mills

The 2007 wheat scab risk prediction tool is now up and running, and is available for use in 24 states. A few subtle, but very important, changes have been made to this tool in an effort to improve prediction accuracy and provide users with more information regarding the risk of head scab (Fusarium head blight) in their state. These changes include improved resolution of the risk maps (now at 5km), and risk predictions based on forecasted weather. In addition to risk predictions based on actual weather conditions (the default risk map), the 2007 risk tool will again provide predictions based on forecasted weather. Information from weather forecasts will be used to generate risk maps that estimate risk 24 and 48 hours ahead of time. You can find these forecasting tools in the upper left corner of the risk tool.

Another feature of the 2007 risk tool is the inclusion of commentaries provided by your state extension specialist. As the wheat growing season progresses, commentaries will be provided below the risk map and updated regularly to inform growers of the risk of scab occurring in their state. These comments will help users assess the risk of scab in their region based on the color patterns displayed on the risk map. The commentary will also provide information regarding observations of crop growth, weather patterns and other diseases of regional importance. To visit the scab prediction site go to: http://www.wheatscab.psu.edu/

Wheat Damage and Yield Potential

Authors: Jim Beuerlein, Pierce Paul

The loss of leaf area due to freezing temperatures and the application of liquid nitrogen will slow wheat development a bit, but the lost leaf area would have been lost in mid May anyway. For the most part the lost leaf area is what would have produced the carbohydrates the stems use to develop. The application of liquid nitrogen causes the loss of leaf area most years, but this year it is a bit worse than normal and we also have some leaf loss due to freezing. It is a setback that probably looks worst than the effect will be. Wheat is a very tough crop and it will recover with warmer weather and sunshine. Any yield reduction will be dictated by the weather we have between now and head emergence and also by the length of the grain fill period. With good wheat weather between now and the end of May all the damage to date could be nullified. If temperatures stay cool through June and into early July, then yields could be really good. It all depends on the weather.

Nitrogen moves a lot, so we don't need and don't want good coverage of the tissue. Applications of 28% should be made with very large flood jets and just enough pressure to produce a good application pattern, which produces a reduced number of very large droplets and reduced leaf damage. Stream bars for 28% application will also greatly reduce crop damage. Urea application usually doesn’t cause leaf damage except for the applicator tires.

Get CORN as a Podcast

Authors: Harold Watters

As we move from our desks and out into the field to tractors and trucks the ability to read the C.O.R.N. newsletter becomes more difficult. We think you would still like access to the information and have added a method to now hear the CORN newsletter. The Communications and Technology folks at OSU have created the CORN newsletter as a podcast. What is a podcast? From the Wikipedia website, http://en.wikipedia.org/wiki/Podcast : “A podcast is a digital media file, or a series of such files, that is distributed over the Internet using syndication feeds, for playback on portable media players and personal computers…. The term "podcast" is a portmanteau of the name of Apple's portable music player, the iPod, and broadcast; a pod refers to a container of some sort and the idea of broadcasting to a container or pod describes the process of podcasting.”

The CORN newsletter audio version is available in three places:
It is on an Ohio State University server: http://classcast.cfaes.ohio-state.edu/weblog/

Available on iTunes as a podcast. Apple iTunes is free downloaded software from http://www.apple.com/itunes/download/ that can be used on a Windows PC or a Macintosh computer. Once you have downloaded iTunes you may locate the CORN newsletter by searching for OSU CORN, and then subscribe to the newsletter. In the future the newsletter will be automatically retrieved as you log in to iTunes.
And as of this last week we have added a link on the Agronomic Crops Team website, https://agcrops.osu.edu It is located at the top of the center column, above the articles. Here you may select either the mp3 version of the newsletter, which may be played of any mp3 player or on most CD players. The m4a formatted newsletter may only be played through iTunes.

One note - due to the length of these spring newsletters the narrative is a little slow in getting done. CommTech will try to keep up but expect the audio version to follow the written newsletter by a day or two.

Please let us know if you appreciate having the newsletter available in this audio format.

Archive Issue Contributors: 

Mark Sulc (Forage Production), Jim Beuerlein (Soybean and Wheat Production), Pierce Paul and Dennis Mills (Plant Pathology), Robert Mullen (Agronomy) and Mark Loux (Weed Science). Extension Educators: Roger Bender (Shelby), Howard Siegrist (Licking), Glen Arnold (Putnam), Keith Diedrick (Wayne), Todd Mangen (Mercer), Steve Foster (Darke), Greg LaBarge (Fulton), Mike Gastier (Huron), Ed Lentz (Seneca), Harold Watters (Champaign), Steve Bartels (Butler), Wes Hahn ( Logan), Jim Lopshire (Paulding), Allen Sundermeier (Wood) 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.