In This Issue:
- Illinois Soil Nitrogen Test and Its Potential in Ohio
- Why Are You Spending $15 on Herbicides in the Fall?
- Apply Herbicides Now to Stop the Yellow Weed Next Spring in Forages in Eastern Ohio
- Aflatoxin in Corn: Should Ohio Growers Be Concerned?
- Late Planted Wheat
- Should Tall Alfalfa Be Cut Before Winter?
- Tell CORN About Your Summer Experience With Aphids and Weed Control
Authors: Robert Mullen
The Holy Grail for soil fertility has long been the search for a method of determining nitrogen (N) mineralization (release of organic N to a plant available form) to make better N recommendations for cereal crop production. Researchers have spent careers attempting to understand and model this phenomenon. Estimating N mineralization and subsequent N responsiveness is the purpose of the Illinois Soil Nitrogen Test (ISNT) (Mulvaney et al., 2001). The ISNT is designed to quantify a particular fraction of soil organic matter that is easily mineralized – the amino sugar N fraction. This fraction of soil organic matter represents the form that has the potential to be mineralized and made plant available. Higher concentrations of amino-sugar N should mean less likelihood of N response, and initial data analysis revealed this to be true. Soils that contained less than 225 ppm amino-sugar N in Illinois were determined to be responsive to N fertilization, and soils with greater than 235 ppm amino-sugar N were considered non-responsive. The ISNT was not however calibrated to a specific N rate (i.e. an amino-sugar N value of 150 ppm could not be used to identify a specific N recommendation). It was developed to separate responsive sites from non-responsive sites. While work in Illinois shows the ISNT has promise, research conducted in other states is not as conclusive.
Iowa has evaluated the ISNT for use on their soils and could not identify a critical value for amino-sugar N that would differentiate responsive sites from non-responsive sites (Sawyer et al., 2003). The majority of soils evaluated in the Iowa study tested between 200 and 500 ppm amino-sugar N, but sites classified as non-responsive by the critical values established initially did respond to fertilizer N with as much as a 50% increase in yield. Wisconsin has also evaluated the ISNT for use in their production environment and found that they could not identify a critical value (http://ipcm.wisc.edu/wcm/pdfs/2005/BundySept22.pdf). The initial critical values (established in Illinois) were not appropriate for Iowa or Wisconsin soils and growing conditions. In fact, Iowa and Wisconsin could not establish correlations between the ISNT and crop responsiveness. It is unreasonable for Ohio producers to assume the critical values that have been established in Illinois would be appropriate for Ohio.
Fundamentally, the ISNT has a major hurdle to overcome. While the amino-sugar N fraction of soil organic matter may represent the most easily mineralized portion (potential mineralization), mineralization is not just controlled by the amount of easily mineralized N in the soil. It is also controlled by weather and the soil environment. As I make reference to in most of my discussions on N management, long-term weather predictions are not accurate enough to model N mineralization. Thus predictions of mineralization are not accurate enough to affect N recommendations (at least not yet). Another hurdle is that any fertilizer material recently applied that contributes significant ammoniacal N (ammonia/ammonium forms of N) such as animal waste or anhydrous ammonia can inflate the amino-sugar N value. This can be accounted for however by measuring the ammonium concentration of N in the soil (additional soil test information).
While the ISNT may be of value someday, it has not demonstrated itself to be robust enough to work across multiple environments. Ohio State University does not at present endorse its use for adjusting N recommendations.
Authors: Mark Loux, Anthony Dobbels
Over the past five years or so, we have investigated the effectiveness of many fall-applied herbicide treatments for control of problem winter weeds in no-till fields. Herbicides applied in the fall can be extremely effective for control of many winter annual and biennial weeds, and a first line of defense against dandelions. Many herbicides can be applied in the fall, but there is a core set of effective herbicide treatments that cost about $6 to $12 per acre, excluding application costs. We listed these treatments this fall in a previous C.O.R.N. article (“Fall herbicide treatments – how they fit into overall weed management plans: Part 1”, Sept 6 - http://corn.osu.edu/index.php?setissueID=102#C). It is not necessary to use more expensive treatments, and we really question the value of treatments where the cost of the herbicide is more than about $12 per acre. One of the reasons for this is that the use of a fall treatment, even one with residual activity, does not guarantee that only one herbicide treatment will be required in Roundup Ready soybeans the following year. Excess money spent on fall treatments results in less money available for weed control in the crop, where it usually is greatly needed.
Our experience has been that the primary benefit of fall treatments is control of weeds that are present at the time of treatment, not residual control of weeds the following year. The primary exception to this is CanopyEX, which provides a longer period of residual control of more weed species than other fall-applied herbicides. An effective fall treatment usually results in a field that is mostly free of weeds until about late April, and this goes for treatments without residual as well as those with residual. In other words, in late April we cannot usually discern much difference between a fall treatment of glyphosate plus 2,4-D versus CanopyEX plus 2,4-D, even though the CanopyEX provides residual activity into the spring. However, the effect of the residual herbicide becomes much more apparent by the end of May, when its activity on summer annual weeds comes into play.
The issue here is not really control at the time of soybean planting, since any effective fall treatment results in a relatively weed-free field at the end of April. The issue is how well the residual herbicide controls weeds after planting, in order to build more flexibility into the postemergence application window. This flexibility can result in less risk of early-season yield loss from weed interference and result in a better chance of getting the postemergence herbicides applied to the right size weeds. We also look to the residual herbicide to help control several weeds that glyphosate can be somewhat variable on, such as giant ragweed and lambsquarters. It is our opinion that, if glyphosate is being managed properly, it is typically going to be extremely difficult to get by with one postemergence glyphosate application unless the residual herbicide applied in the fall provides substantial weed control into late May.
Herbicides other than CanopyEX can provide residual control of certain weeds when applied in the fall, but they tend to control fewer weed species and/or be generally less effective than CanopyEX. For example, Valor provides residual control of lambsquarters into early June, but is less effective than CanopyEX and provides very little control of giant ragweed. Scepter provides very little control of lambsquarters or giant ragweed when applied in the fall, whereas it can provide substantial residual control of these weeds when applied in the spring. Gangster is labeled for fall application, and it may be fairly comparable to CanopyEX in its residual. Fall applications of Gangster would still require the addition of glyphosate plus 2,4-D, which would result in a high-priced treatment.
Some examples from our research follow – numbers reflect percent control compared to untreated plots (ratings in late April not shown since differences among treatments were not observed at that time):
Study 1 – herbicides applied Nov 9, 2004 – plots rated June 6, 2005
CanopyEX (1.5 oz)+2,4-D:
dandelion – 72%; chickweed&deadnettle – 100%; lambsquarter – 100%
dandelion – 73%, chickweed&deadnettle – 100%; lambsquarter – 0%
Glyphosate+2,4-D+Scepter (1.9 oz):
dandelion – 72%, chickweed&deadnettle – 100%; lambsquarter – 0%
Study 2 – herbicides applied Nov 9, 2004 – plots rated June 6, 2005
CanopyEX (1.5 oz)+2,4-D:
dandelion – 100%; chickweed – 100%, deadnettle – 100%; lambsquarter – 100%, giant ragweed – 93%
dandelion – 72%, chickweed – 53%, deadnettle – 100%; lambsquarter – 27%; giant ragweed – 0%
Scpeter (2.8 oz)+glyphosate+2,4-D:
dandelion – 70%, chickweed – 88%, deadnettle – 100%; lambsquarter – 10%, giant ragweed – 10%
FirstRate (0.4 oz)+glyphosate+2,4-D:
dandelion – 78%; chickweed – 85%, deadnettle – 100%; lambsquarter – 73%, giant ragweed – 97%
Study 3 – herbicides applied Nov 8, 2002 – plots rated May 28, 2003
CanopyXL (2.5 oz)+2,4-D:
chickweed – 96%, lambsquarter – 100%, giant ragweed – 78%
chickweed – 50%, lambsquarter – 7%; giant ragweed – 17%
Scpeter (2.1 oz)+glyphosate+2,4-D:
chickweed – 58%, lambsquarter – 23%, giant ragweed – 23%
FirstRate (0.3 oz)+glyphosate+2,4-D:
chickweed – 55%, lambsquarter – 50%, giant ragweed – 63%
Sencor (10 oz)+2,4-D:
chickweed – 60%; lambsquarter – 0%; giant ragweed – 0%
Python (1 oz)+glyphosate+2,4-D:
chickweed – 70%; lambsquarter – 20%; giant ragweed – 13%
Glyphosate+Valor (2 oz)+2,4-D:
chickweed – 59%; lambsquarter – 72%; giant ragweed – 5%
Study 4 – herbicides applied Oct 4, 2004 – plots rated June 6, 2005
CanopyEX (1.1 oz)+2,4-D:
dandelion – 90%; chickweed – 100%, deadnettle – 100%; lambsquarter – 100%
Valor (2 oz)+glyphosate+2,4-D:
dandelion – 85%; chickweed – 95%, deadnettle – 100%; lambsquarter – 43%.
Some suggestions for dealing with sales pitches on the use of residual herbicides in the fall and treatments where the herbicide costs more than about $12. First, ask to see weed control data from replicated field trials where two or more treatments are compared. The data should include: 1) a weed control rating sometime in mid to late April to show how effective the fall treatment was on winter annuals and dandelions, and 2) a rating sometime in mid to late May, prior to any postemergence herbicide application, to show how well the residual controlled summer annual weeds that emerge in May. This is one situation where the use of on-farm treatment comparisons can be beneficial. Since several companies promote the use of glyphosate and 2,4-D with their residual herbicide, the most logical comparison to see if the residual herbicide adds anything may be glyphosate plus 2,4-D versus the residual herbicide plus glyphosate plus 2,4-D. If the question is how the residual herbicide compares to CanopyEX, then the most logical comparison may be CanopyEX plus 2,4-D versus the other residual herbicide plus glyphosate plus 2,4-D.
Finally, regardless of what is used in the fall, be sure to manage herbicides properly the next year, and take advantage of industry performance programs. In non-GMO soybeans, we recommend the use of a preplant burndown even in fields treated with herbicides the prior fall. This burndown can be combined with a residual herbicide (See “Fall herbicide treatments – how they fit into overall weed management plans: Part II”, in Sept 13 C.O.R.N., http://corn.osu.edu/index.php?setissueID=103#C), and should be followed with postemergence herbicides when weeds are 4 to 6 inches tall. In Roundup Ready soybeans, be sure to make the first glyphosate application when weeds are less than 4 to 8 inches tall, regardless of the calendar date or status of the soybean canopy development. Make a second glyphosate application when the next flush of weeds is 4 to 8 inches tall, or to control regrowth of weeds following the first application. Use this approach and hold the manufacturer’s feet to the fire if they have promised to pay something toward the second glyphosate application. Our experience is that a combination of one fall and one in-crop treatment is not sufficient in many Roundup Ready fields. However, several companies promote this approach, and producers may be able to take advantage of industry programs to reduce their herbicide costs and maintain their most consistent weed control.
Authors: Mark Loux, Anthony Dobbels
The yellow flowering weed becoming more prevalent in forage fields in Eastern Ohio in April to May is most likely wild turnip. It may also be birdsrape mustard, however, because the two species appear identical and are so closely related, it is hard to separate them. Wild turnip is sometimes confused with yellow rocket in the spring. However, yellow rocket starts to flower later than wild turnip, and wild turnip will reach heights of up to 3 to 4 feet tall while yellow rocket usually gets no more than two feet tall.
There are limited research data on the control of wild turnip in forage production. However, based upon limited research conducted by The Ohio State University, Dr. Don Myers, and Melvin Lahmers, herbicides MUST be applied in the fall to achieve effective wild turnip control. For alfalfa production, apply 2,4-DB (2 qt/A), Pursuit 70 DF (1.08 to 1.44 oz/A) plus 2,4-DB (1 qt/A) plus crop oil concentrate plus AMS, or Raptor (6.0 oz/A) plus crop oil concentrate plus AMS. Raptor will control most grass species, 2,4-DB will not control any grass species, and Pursuit’s activity on grass species is intermediate between the other two products. Treatments containing 2,4-DB will provide some control of purple deadnettle, but almost no control of common chickweed unless applied with 2.16 oz/A of Pursuit.
In grass pastures, fall application of dicamba (1 pt/A) plus 2,4-D ester (1 pt/A), 2,4-D ester (1 qt/A), Cimarron (0.2 oz/A), Cimarron plus 2,4-D ester (1 pt/A) or dicamba (0.5 pt/A), or Crossbow (2 pt/A) effectively controls wild turnip. Tall fescue may be injured by the Cimarron application. Among these herbicides, dicamba plus 2,4-D ester, or Cimarron, provide the most broad-spectrum control of other weeds.
Authors: Dennis Mills, Pierce Paul
Some ear rot causing fungi produce secondary metabolites (by-products of their regular life functions) called mycotoxins. These compounds are called secondary not because they are not important, but because they are not necessary for the life of the fungi. Without the toxins, these fungi still live.
Aflatoxin is a naturally occurring toxin produced by several species of a fungus called Aspergillus (Aspergillus flavus and Aspergillus parasiticus). While Aspergillus is often considered a storage fungus, it can also occur in the field causing ear rots. It appears as a gray-green or yellow-green, powdery mold growing on the kernels. The infection of the ear with Aspergillus, however, does not necessarily mean that aflatoxin is being produced. Aflatoxin is only produced under certain environmental conditions. Corn that has suffered drought conditions and high temperatures is generally at risk for aflatoxin contamination. While drought conditions did occur in some parts of the state this season, drought is not the only requirement for aflatoxin production. Prolonged periods of nighttime and daytime temperatures at least in the 90oF range are also required. This year, the average daily air temperature for the period between July 1 and September 30 ranged from 53 to 84oF across the state. Daytime temperatures did exceed 90oF for a few hours in some locations in southern Ohio during the month of August, however, these temperatures did not occur for extended periods and nighttime temperatures were usually in the low 70oF range or lower. This indicates that even if Aspergillus did infect the ears, conditions for aflatoxin accumulation were very minimal.
Reports coming out of other states have had some Ohio growers concerned about possible aflatoxin contamination in their corn. But, should Ohio growers be concerned? Ohio growers should be concerned to the point of knowing and being able to identify this problem if it occurs. While the overall weather conditions have not been favorable, it is always possible for a disease problem to occur in small (restricted) areas where the on-farm weather conditions (especially in southern counties) may have been more favorable. If suspect samples are found, growers are encouraged to send these samples to the lab for testing and proper identification. Not all gray-green or yellow-green molds are caused my Aspergillus. As far as growers being concerned about having a major aflatoxin problem across the state this year, the weather conditions (temperatures) during the regular growing season have just not been favorable enough. However, growers are reminded that delayed harvest, late-season rainfall, and lodging observed in fields in some parts of the state are all conditions favorable for mold and ear rot development, including Aspergillus ear rot. To minimize the chances of mold growth and toxin accumulation in stored grain, please refer to the harvest and storage guidelines provided in the article “Corn ear rot problems in Ohio” by Pierce Paul, Peter Thomison, and Dennis Mills. C.O.R.N Newsletter 2005-34 (October 10, 2005 – October 18, 2005) available online at http://corn.osu.edu/story.php?setissueID=109&storyID=630.
For more on aflatoxin visit the OSUs "Ohio Field Crop Diseases” at http://www.oardc.ohio-state.edu/ohiofieldcropdisease/Mycotoxins/mycopageaflatoxin.htm.
Authors: Pierce Paul, Jim Beuerlein, Dennis Mills
For no-till wheat the recommended planting date in Ohio is within the first 10 days after the Hessian Fly Safe date for each county. The use of the Hessian Fly-Safe Date as a guide for wheat planting in Ohio serves two main purposes. First, delaying planting until this time helps to avoid serious insect and disease problems including Hessian Fly, aphids carrying Barley Yellow Dwarf Virus, and several foliar diseases. Second, planting at this time permits plants to develop 3 to 4 primary tillers prior to winter dormancy. This is necessary for winter survival. In some years, however, due to late harvest of the previous crop (soybean) and poor weather conditions, Ohio growers are forced to plant wheat after the recommended planting period. This has certainly been the case in some locations this year. Late planting (generally after October 20 in northern Ohio) can reduce the number of primary tillers that develop in the fall and increases the risk of cold temperature injury.
To compensate for fewer tiller development in late-planted wheat, when planting late (during the third and fourth week after the fly-safe date), growers are recommended to plant at a higher seeding rate than the regularly recommended seeding rate of 1.2 to 1.6 million seeds per acre for 7.5-inch rows (that is about 18 to 24 seeds per foot of row with normal sized seed). Plant at a rate of 1.6 to 2.0 million seed per acre instead. Remember, the number of seeds per pound and germination rate are important for determining the correct seeding rate and drill calibration. There are fewer seeds per pound of large seeds than per pound of small seeds. The number of seeds per pound can be found on the seed bag. Use this information along with the table provided in the C.O.R.N newsletter “Correct Wheat Seeding Rates Can Increase Profit” by Jim Beuerlein (2005-29: September 6, 2005, http://corn.osu.edu/story.php?setissueID=102&storyID=605) to determine the amount of seed needed to plant 1.6 to 2.0 million seeds per acre.
Late planting also affects the ability of wheat to compete with weeds. Poor stand establishment (fewer tiller per foot of row) and winter injury (likely to occur due to late planting) may increase weed problems. So, for dandelion control in no-till wheat, growers are recommended to apply glyphosate before the wheat emerges.
Authors: Mark Sulc
Earlier in this newsletter (September 6, 2005 - http://corn.osu.edu/index.php?setissueID=102#D) I wrote about the risks of fall cutting alfalfa, and how to minimize that risk. With the temperatures and good moisture this fall, alfalfa has grown exceptionally well. I have received many questions as to whether this amount of growth going into the winter can harm the stand. The fear is that the alfalfa will smother itself out this winter.
The excessive alfalfa growth will NOT harm the stand. I have let stands of alfalfa go into the winter with as much growth as we see this fall, and I have never experienced a problem or seen the crop “smother out”.
Think about this…75-80% of the alfalfa crop this time of year is water. In other words, the dry matter content is around 20-25%. So divide what you see out there by 4, and that will be how much residue remains after a couple of hard frosts. There will be much less residue left than it appears right now.
Perhaps if it were to snow early on warm soils covered with lush alfalfa, and the snow were to stay there all winter long, we just might see some snow mold on the alfalfa. But that would be a very rare occasion in Ohio, with the exception of the lakeside snowbelt. In southern Ohio, its possible that alfalfa weevils could lay eggs in the alfalfa stand, potentially increasing weevil populations early next spring. That could happen even with a lot less growth, and other factors influence weevil populations in the spring.
There really is no need to take a cutting now in order to remove the large amount of alfalfa growth. In fact, considering all factors, cutting this week probably holds more risk to the stand than not cutting. If we cut this week, we are likely to have enough good growing weather left for the alfalfa to regrow over the next 2-3 weeks. Regrowth will burn up precious root reserves that are needed for the winter and early spring. There won’t be enough time to replenish those root reserves if the alfalfa is cut now.
If the forage is really needed, a LATE fall harvest can be considered, IF the soil is well drained. By LATE, I mean as close as possible to a killing frost of alfalfa, which is 25 F for several hours. This often does not happen until sometime in November in Ohio. I know that the weather is usually lousy in November for cutting forage, but waiting another 2 weeks to get closer to the killing frost will prevent regrowth and loss of energy reserves, and will reduce the risk of less vigorous stands next spring.
A late fall harvest should only be considered if the soil is well drained and there is no history or risk of heaving on that particular soil. Without residue cover, the temperature of the soil will fluctuate much more and heaving is more likely. This happened in a study at Wooster, when a November 1 cutting resulted in heaving of up to 50% of the plants. Where no fall cutting was made, less than 10% of the plants heaved.
Fall management of alfalfa is one of the few controllable factors that will potentially influence the health of your alfalfa stand next spring. If you don’t need the forage, walk away from it and let it insulate your stand this winter. It won’t smother out because of excessive alfalfa growth.
If you need the forage, then take a cutting the last week of October or early November, and only on well-drained soils. Also leave a 6-inch stubble. If you do cut this fall, leave some strips or areas that you do not cut within the same field. You might learn something interesting next spring about fall cutting on your farm by having those side-by-side comparisons!
Authors: Greg LaBarge
CORN readers please let us know what your experience was this past summer with soybean aphid and weed control issues. A survey that asks some questions related to these two summer problems and a few other issues can be found at the following link: http://www.zoomerang.com/survey.zgi?p=WEB224LWXVCMXN.
If you have already responded to the survey, we thank you. If you haven’t responded to the survey, please take time to reply. The survey will only take a few minutes but provide us with valuable information on the extent of spraying for soybean aphids in Ohio and some weed control issues. The results of the survey will be used to direct research and educational activities. We will share the results in a future newsletter. We hope you can take time today or in the near future to share your experiences with us!
Dennis Mills and Pierce Paul (Plant Pathology), Robert Mullen (Soil Fertility), Jim Beuerlein (Soybean & Small Grain Production), Mark Sulc (Forage Production) and Mark Loux, Jeff Stachler and Tony Dobbels (Weed Science). Extension Agents: Ed Lentz (Seneca), Steve Foster (Darke), Roger Bender (Shelby), Dusty Sonnenberg (Henry), Gary Wilson (Hancock), Howard Siegrist (Licking), Harold Watters (Champaign) and Greg LaBarge (Fulton).