C.O.R.N. Newsletter 2009-09

Dates Covered: 
April 14, 2009 - April 21, 2009
Editor: 
Steve Prochaska

Pelletized Lime, Can I Get Away with Lower Rates?

Authors: Robert Mullen, Keith Diedrick

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? Perhaps, but using 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 an effective lime source because it is very fine material as well as easy to handle and apply using broadcast fertilizer spreaders; however, it simply cannot neutralize soil acidity any better (or faster) than conventional ag lime materials. Ohio uses a term – effective neutralizing power (ENP) – to compare the strength 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 (size of the particles), and moisture content.

Lime recommendations can be found in an OSU Extension Factsheet titled “Soil Acidity and Liming for Agronomic Production” https://agcrops.osu.edu/fertility/documents/AGF505.pdf . Pelletized lime is typically finer than ag-lime, so its ENP value may be higher. Higher ENP means that it will take fewer pounds of pelletized lime than ag lime to neutralize the same amount of soil acidity. If the soil test lime recommendation for a field is 3 tons per acre, and you have pelletized lime with an ENP of 2000 (which is what most pelletized materials approach) you would need 3 tons of pelletized lime per acre to achieve the desired neutralization. Let’s consider that same 3 ton recommendation for ag-lime with an ENP of 1000. It would require 6 tons of ag-lime to achieve the desired change in soil pH. Though it is more effective on a pound-per-pound basis than ag lime, applying 300 to 500 lb of pelletized lime per acre would not result in the desired change in soil pH because the required amount is 3 tons 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, especially when pelletized lime can cost 5-7 times more per ton than ag lime. Price comparison using ENP is the best way to evaluate liming materials (unless a soil has a low magnesium level in which case you should utilize dolomitic lime). Select the product that will give you the desired results for the best price.

Another question we get: “is the use of lime in a starter band useful?” First of all we must realize one thing about lime – we are not supplying a nutrient like a typical fertilizer, we are amending the soil with an additive. The reason for banding nutrients is to improve their positional availability and/or to decrease soil interactions that affect plant availability. This is not a benefit to a lime addition, in fact, it would be a detriment because you will not be altering soil pH, but are incurring a considerable cost. Lime is quite insoluble and that is why we recommend lime to be incorporated with soil by tillage whenever possible. This increases the volume of soil that will react with the lime and achieve the desired neutralization. Applying lime in a band will only neutralize a small volume of soil, and will not achieve the desired results of raising soil pH.

An additional note: urea and liming compounds do not mix when surface-applied; substantial nitrogen losses can occur when urea is deposited on a high pH area. Also, remember that gypsum (calcium sulfate) does not have the capacity to change soil pH, and thus is not a liming compound.

Reminders on Preplant Burndown Treatments, Including Marestail and Dandelion

Authors: Mark Loux

Mid to late April is an ideal time to apply burndown and residual herbicides in much of Ohio, before marestail are very large and far enough in advance of planting to allow safe use of 2,4-D ester (see last weeks C.O.R.N. for more information on 2,4-D use). Burndown applications in April control weeds before winter annuals have produced seed, which helps prevent future infestations.

While it is possible to control small weeds in some no-till fields in late March or early April with mixtures of 2,4-D ester plus a residual herbicide, from this point on most soybean fields will require use of a mixture of glyphosate and 2,4-D ester, or paraquat, 2,4-D ester and metribuzin. Including products that contain chlorimuron (Canopy DF/EX, Valor XLT, and Envive) can substantially improve the activity of these treatments on many broadleaf weeds. Where the interval between herbicide application and soybean planting is too short to allow use of 2,4-D, a mixture of glyphosate plus a chlorimuron-containing herbicide is likely to provide the most effective control of a typical no-till weed population. Products that contain cloransulam (FirstRate, Gangster, Authority First, and Sonic) provide additional help primarily on ragweeds and marestail that are not ALS-resistant, and to a lesser extent, on dandelion.

The use of 2,4-D ester is not necessarily as essential in corn burndown programs, compared with soybeans, due to the effectiveness of atrazine, Basis, and Lumax/Lexar, among other herbicides. Based on OSU research, the most effective burndown treatments for corn include (broadleaf weeds): Lexar or Lumax; glyphosate + atrazine; Basis or Resolve + atrazine; dicamba + atrazine; paraquat + atrazine + 2,4-D ester; and atrazine + glyphosate + Balance or Radius. 2,4-D ester can be added to any of these for improved control of dandelion and other tough weeds. Lexar and Lumax have generally provided the most rapid and effective dandelion control, and the addition of 2,4-D to either of these can result in a greater reduction in population.

In both corn and soybeans, dandelions that regrow following a preplant burndown treatment, and are evident in the crop a month or so later, should be treated with postemergence herbicides for maximum reduction in population. It is possible to apply burndown herbicides too early in the spring for dandelion control, since herbicides will be most effective when the dandelions are actively growing with a few healthy leaves. Most of the state should be at this point, but dandelion in more northern areas may still be too small for most effective control. Application of herbicides during periods of cold weather (several days in a row with near freezing temperatures at night) will reduce their activity on dandelion.

An effective marestail management program ensures that the field is free of marestail at the time of soybean planting, and includes herbicides with residual activity to prevent marestail emergence for a month or so after crop emergence. It also helps to plan for the worst – that the population has resistance to glyphosate and ALS inhibitors, and will be impossible to control after soybean emergence. In OSU research, the most effective control of marestail has occurred from a combination of 2,4-D ester, residual herbicides and either glyphosate or paraquat applied in April, when the marestail is still in the rosette stage or has only an inch or two of stem elongation. The residual herbicide component can consist of primarily ALS inhibitors, but this will less consistently effective than a combination of ALS inhibitor plus an effective rate of Valor, Authority, or metribuzin. So, products such as Valor XLT, Envive, Gangster, or Authority First/Sonic often provide more effective residual control than Canopy, unless the Canopy is supplemented with additional metribuzin. Even when applied in spring, the most effective residual herbicides can fail to completely prevent emergence of marestail after soybean emergence.

Now is the time to scout soybean fields where residual herbicides were applied in the fall, in order to determine whether the fall treatment is still controlling marestail. Where scouting turns up small marestail plants in the field, our conclusion would be that the fall-applied residual herbicide is failing to adequately control marestail, and won’t control marestail that emerge later this spring either. Failure to take corrective action prior to soybean planting is likely to result in a marestail mess sometime after soybeans have emerged. The corrective action needed is a preplant application of 2,4-D ester and more residual herbicide (and glyphosate if the marestail are past the rosette stage), to make sure the crop gets off to a weedfree start and that later—emerging marestail are controlled. Marestail escaping a fall residual herbicide are likely to be ALS-resistant, and the residual applied now should include Valor, metribuzin, or Authority to ensure adequate control.

We have received a few questions about Star of Bethlehem control in no-till fields. This weed is not controlled by glyphosate or 2,4-D, but paraquat has substantial activity on it. Weed scientists at Southern Illinois University published a fact sheet on their research into herbicide activity on star of Bethlehem. This fact sheet is posted on the OSU Weed Science website, https://agcrops.osu.edu/weeds .
 

Alfalfa Weevil

Authors: Ron Hammond, Andy Michel, Bruce Eisley

This is the time that alfalfa growers should be beginning, or at least thinking about monitoring for alfalfa weevil. Scouting should begin when heat unit accumulations, beginning from January 1, reach between 250- 300 heat units (HU). This time period is when we begin to have weevil egg hatch and start to see feeding. These levels have been reached in southern Ohio, and thus, growers in that region should begin scouting. Central and northern Ohio will reach these levels in the coming weeks. Remember that fields that have a south facing slope tend to warm up sooner and need to be checked for weevil earlier. As of April 10, southern locations in Ohio are around 350 HU, central and northwest sites near 225, and northeast around 125. We will update heat unit accumulations in the coming weeks in this C.O.R.N. newsletter.

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. When alfalfa is 16 inches in height and there are more than 4 larvae per stem, early harvest is recommended. See the OSU Alfalfa Weevil FactSheet http://ohioline.osu.edu/ent-fact/0032.html for more on alfalfa weevil scouting and thresholds. For insecticides that are labeled for alfalfa weevil, see http://entomology.osu.edu/ag/545/aiaw.pdf . Remember that it is still too early to worry about potato leafhoppers because they do not move into Ohio until May.

Compaction and No-till

Authors: Randall Reeder

When compaction with big equipment is a concern, continuous no-till may give better yields than with annual sub soiling. According to results from our six-year compaction study at the OARDC Northwest Agricultural Research Station near Hoytville, land in continuous no-till showed less effect from intentional compaction than soil that was deep tilled each fall. Corn/soybean rotation plots were compacted in the fall of 2002 and 2005 using a 600-bushel grain cart with a load of 20 ton/axle. Averaged over six years, corn yields were reduced by 15 percent on sub soiled plots, as opposed to a 9 percent reduction in no-till fields. For soybeans, yields on sub soiled plots were down 24 percent, compared to a 13 percent yield drop under no-till. Continuous no-till has a better soil structure. Tillage tends to destroy soil structure.

You may remember that previous compaction research at the same site gave results more favorable to sub soiling, but there was a key difference. The plots were compacted 3 years in a row, but once annual sub soiling began in 1991, there was no additional intentional compaction for 12 years. In that situation, sub soiling gave consistently higher corn and soybean yields, compared to shallow chisel plowing. When the research practices were changed in 2002 to include intentional compaction every 3 years, and continuous no-till replacing chisel plowing, the benefit of deep tillage disappeared. The current research is much closer to what happens on farms with heavy machinery.

Soil moisture plays a big role in compaction. Wet soil compacts deeper than dry soil. This spring has been drier than usual for most of Ohio, so spring tillage and planting operations may do less compaction than normal. A heavy rain could quickly change that.
 

Thickening Alfalfa Stands

Authors: Mark Sulc

We have been getting questions about filling in thin areas in alfalfa seeded last summer that did not establish well because of the dry weather. Can one thicken up young alfalfa stands? The short answer is, “Yes”. However, there is a little more to it than that.

Older, established alfalfa plants release water soluble compounds into the soil that inhibit seedling development of new alfalfa plants. This is referred to as “autotoxicity”. The autotoxicity effect is considered to be a serious problem in older stands, especially in heavy textured soils. In stands less than a year old, the autotoxic inhibition of younger seedlings is not considered to be a problem, as it takes time for the autotoxic effect to accumulate. So there is potential to establish new alfalfa plants through interseeding within an alfalfa stand that was first established last summer. The interseeding should be done this spring. Use 12 to 16 pounds per acre, especially where the stand is very thin.

Successful interseeding to thicken young alfalfa stands depends in large measure on how much competition the new seedlings will encounter, whether it be from the existing alfalfa plants or weeds. Thin spots in the stand were probably invaded by winter annual weeds, which are very competitive against newly establishing seedlings. There are no herbicide options for controlling winter annual weeds that won’t harm seedling germination and emergence of interseeded alfalfa. Spot spraying with glyphosate or paraquat for burndown prior to interseeding may be the best option in areas where weed competition is severe. The judgment to be made is whether the stand is good enough to salvage, or whether it would be better to kill the stand and start over this spring with a completely new seeding.

Grasses can be interseeded into alfalfa stands, regardless of the age of the alfalfa stand. The primary limitation to successful grass establishment is moisture supply and competition during establishment. Perennial grasses can be interseeded in the spring, but late summer is also considered a good time because the existing alfalfa plants are not as competitive in the autumn as they are in the spring. However, moisture supply for grass seedling development can be a problem in late summer and autumn. Orchardgrass at 5 to 10 pounds per acre is probably one of the best choices for interseeding into alfalfa. Perennial ryegrass or festulolium at 10 to 15 pounds per acre are good options for the northern half of the state, and they have the best seedling vigor of any of the perennial grasses adapted to Ohio. Studies in Wisconsin have shown success when interseeding smooth bromegrass into a thin alfalfa stand, but it took over a year to become a contributor to yield. Several annual species, such as Italian ryegrass, oats, rye, or wheat can also work for a short term boost in forage yield.

When interseeding into existing alfalfa stands, use a no-till drill for best results. There is always the concern that a no-till drill will damage existing crowns of alfalfa, but broadcasting seed on the soil surface of an existing stand will almost certainly fail, unless it is accomplished as a frost-seeding, and we are well past that time-frame now.

The following resources provide excellent discussions of what is known about autotoxicity in older alfalfa stands and the potential for establishing alfalfa after alfalfa:

Managing Alfalfa Autoxicity, Purdue Univ. Ext. Bulletin AY-324-W
http://www.ces.purdue.edu/extmedia/AY/AY-324-W.pdf
Autotoxicity in Alfalfa: Implications for Crop Production, by Dennis Hancock, Univ. of Kentucky.

http://www.bae.uky.edu/precag/SDI/alfalfa%20autotoxicity%20paper%20-%20agents.pdf

Nitrification Inhibitors

Authors: Keith Diedrick, Robert Mullen

In order to maximize nitrogen (N) availability during the growing season and minimize N losses prior to plant uptake, nitrification inhibitor products may reduce agronomic risk. The purpose of these additives is to slow down the bacterial conversion of ammonium-N (which can stick to the soil CEC) into nitrate-N (which has the risk of loss by leaching or denitrification). The most common nitrification inhibitor on the market is nitrapyrin (N-Serve).

Anhydrous ammonia has been called the most efficient N source because of its ability to fumigate the microbes in the application band, thus reducing the population of the ammonium-converting bacteria for a couple of weeks. If the microbes are not there, they cannot convert ammonium-N into nitrate-N. Using nitrapyrin can extend the time of ammonium conversion another 4 to 10 weeks, depending on soil temperature and pH. Reducing the rates of nitrapyrin adds a level of risk if the anhydrous application is going to be in the soil for a time before the crop, since this is a biological issue with the microbes re-entering the application band.

Applying anhydrous with nitrapyrin in the fall (which is not our recommendation for summer crops in Ohio) may realize a benefit of the nitrapyrin (as it is out in the field for a long time), but for most of us who apply anhydrous ammonia in the spring soon before planting and as a sidedress treatment, the utility of a nitrification inhibitor is difficult to justify (from a summary of Ohio data from 1978 to 1997). No-till situations are more likely to show positive yield results than conventional till systems for spring applied anhydrous.

Nitrification inhibitors are less likely to show an economic benefit when high N rates are used in the field. Nitrogen losses at high N application rates are not likely to affect yield as much if lower N rates are applied (fewer bushels per acre are gained with each additional level of N at the high levels).

The overall bottom line is that the shorter the time span that the anhydrous is applied to when the crop is in the ground, the less of a chance that N will be lost from the field. We know it is not always possible, but applying N in the same window of time as the crop is the most beneficial situation.

For more information and background on nitrification inhibitors, see our previous article in C.O.R.N. at http://corn.osu.edu/story.php?setissueID=33&storyID=120

Is There a Benefit to Fungicides Application at Wheat Green-up?

Authors: Pierce Paul, Dennis Mills

Cool conditions across the state over the last week have prevented rapid growth and development of the wheat crop. Most fields have not yet reached Feekes GS 5 and spring fertilizer applications have not yet been made in some locations. However, once conditions become warmer as is forecasted for the end of this week, the crop will resume normal growth, possibly reaching Feekes GS 5/6 during next week. Questions are already being asked about Feekes 4 to 5 fungicide applications. This is a practice that is becoming increasing popular in wheat production in some parts of the state. Some producers are applying foliar fungicides at the time of spring nitrogen application. This early application will then be followed by a second application at half rate at flag leaf emergence (Feekes 8 or 9) or at boot (Feekes 10). However, some growers are questioning the value of such an early application. Our data suggest that the greatest yield responses to foliar fungicides in wheat are observed when applications are made to susceptible varieties with high yield potential, under high disease pressure. However, these observations are based on applications made between Feeke’s GS 8 and GS 10.5.1, the commonly recommended time for fungicide application for wheat disease management. There is very little Ohio-based data to support or reject early fungicide applications.

Based on reports from other states, early applications tend to be beneficial when wheat is planted after wheat. Wheat-on-wheat is not a very common practice in Ohio. For those growers who planted wheat after wheat, it is still important to scout fields to determine if you have a disease problem before applying a fungicide. Remember, there is a cost to applying a fungicide and that cost becomes much higher if multiple applications have to be made. In addition, multiple applications at half rate of the same active ingredient increase the risk of fungicide resistance.

One of the arguments used for early fungicide application in wheat is suppression of powdery mildew and Septoria leaf spot. It is not very common for us to see high levels of foliar diseases in Ohio at green-up. However, if powdery mildew and Septoria leaf spot are present on the leaves between GS 3 and GS 5, a fungicide application will certainly contribute to reducing the level of these diseases. However, of what value is such an early application, especially if conditions are favorable for disease development between GS 8 and GS 10? Remember, the goal of fungicide application is to protect the flag leaf, the leaf just below the flag leaf, and the spike during grain fill. For instance, let us consider leaf rust. The leaf rust fungus usually blows in from southern states and the level of disease occurring in Ohio’s fields depends on the amount of spores coming in from the south. If the spore load is high during flag leaf emergence, weather conditions are favorable, and the variety is susceptible, then rust may reach very high (yield-reducing) levels before grain fill is complete. In such a situation, there is no benefit to applying a fungicide at GS 3 or 5 (well before spores are present). Similarly, for other foliar diseases (Septoria, Stagonospora and powdery mildew), controlling these diseases at GS 3 or 5 on lower leaves that contribute little (relative to the flag leaf) to grain fill may be of questionable benefit.

When considering fungicide application for head scab and vomitoxin suppression, the value of early fungicide application becomes even more questionable. The head scab fungus infects and causes the greatest damage when conditions are wet and humid at flowering. A GS 3 or GS 5 fungicide treatment will not protect against leaf and spike infection at or after flag leaf emergence. Results from other wheat-growing states show that there is no benefit to an early application at half rate over the full rate at Feeke’s 8 (flag leaf emergence), 10 (boot) or 10.5.1 (flowering) when conditions are favorable for late foliar disease and head scab development.
Growth stage 6 to 8 marks the beginning of the period during which we recommend that fields be scouted to determine which disease is present and at what level. So far, no significant disease problems have been reported in the state. It has been too cold. However, as it warms up, leaf diseases may soon begin to show up on susceptible varieties, especially if rainy conditions continue. It would be wise to begin to visit fields at flag leaf emergence (growth stage 8) to check for the presence of diseases like powdery mildew. Fungicides are available to control foliar diseases in Ohio; however the decision to use these fungicides should be based on the susceptibility of the variety planted, the level of disease in the field, weather conditions, the yield potential of the field, and the market price of wheat. So, as you scout the fields, make a note of the level of disease and return to the field in the next week or so to see if disease is progressing. If disease continues to progress up the plants a fungicide application may be warranted. This is extremely important if you are growing one of the more susceptible varieties currently available.

Archive Issue Contributors: 

State Specialists: Pierce Paul and Dennis Mills (Plant Pathology), Ron Hammond and Andy Michel (Entomology), Mark Loux (Weed Science), Robert Mullen and Keith Diedtick, (Soil Fertility). County Extension professionals: Roger Bender (Shelby), Harold Watters (Champaign), Les Ober (Geauga), Steve Foster (Darke), Greg LaBarge (Fulton), Tim Fine (Miami), Wesley Haun (Logan), Bruce Clevenger (Defiance), Howard Siegrist (Licking), Ed Lentz (Seneca), Glen Arnold (Putnam) and Steve Prochaska (Crawford)

About the C.O.R.N. Newsletter

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.