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Ohio State University Extension

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C.O.R.N. Newsletter 2011-10

Dates Covered: 
April 26, 2011 - May 2, 2011
Editor: 
Steve Prochaska

Although the penalty for late planting is important, care should be taken to avoid tillage and planting operations when soil is wet. Yield reductions resulting from "mudding the seed in" are usually much greater than those resulting from a slight planting delay. Yields may be reduced somewhat this year due to delayed planting, but effects of soil compaction can reduce yield for several years to come. (Keep in mind that we typically don’t see significant yield reductions due to late planting until mid-May or even later in some years).

If you originally planned to apply nitrogen pre-plant, consider alternatives so that planting is not further delayed when favorable planting conditions occur. Although application of anhydrous N is usually recommended prior to April 15 in order to minimize potential injury to emerging corn, anhydrous N may be applied as close as a week before planting (unless hot, dry weather is predicted). In late planting seasons associated with wet cool soil conditions, growers should consider side-dressing anhydrous N (or UAN liquid solutions) and applying a minimum of 30 lb/N broadcast or banded to stimulate early seedling growth. This latter approach will allow greater time for planting. Similarly, crop requirements for P and K can often be met with starter applications placed in bands two inches to the side and two inches below the seed. Application of P and K is only necessary with the starter if they are deficient in the soil, and the greatest probability of yield response from P and K starter is in a no-till situation.  Remember the longer our planting is delayed the less beneficial a starter with P and K will be (unless the soil test level is below the critical level).  The primary reason they are less beneficial is typically at later planting dates soil temperatures are higher (this is not necessarily true for no-till soils and that is why they are more likely to be responsive).

Keep time expended on tillage passes and other preparatory operations to a minimum.  The above work will provide minimal benefits if it results in further planting delays. No-till offers the best option for planting on time this year. Field seedbed preparation should be limited to leveling ruts that may have been left by the previous year’s harvest - disk or field cultivate very lightly to level. Most newer planters provide relatively good seed placement in "trashy" or crusted seedbeds.

Don't worry about switching hybrid maturities unless planting is delayed to late May. If planting is possible before May 20, plant full season hybrids first to allow them to exploit the growing season more fully. Research in Ohio and other Corn Belt states generally indicates that earlier maturity hybrids lose less yield potential with late plantings than the later maturing, full season hybrids.

In delayed planting situations, use the optimal seeding rates for the yield potential of each field. Recommended seeding rates for early planting dates are often 10% higher than the desired harvest population because of the potential for greater seedling mortality. However, soil temperatures are usually warmer in late planted fields, and as a result germination and emergence should be more rapid and uniform. So, as planting is delayed, seeding rates may be lowered (decreased to 3 to 5% higher than the desired harvest population) in anticipation of a higher percentage of seedlings emerging.

1.  One option is to just omit the 2,4-D ester and rely on glyphosate for the burndown.  This is probably the worst choice on this list, but it can work in some fields.  This is not an option in fields with marestail, or glyphosate-resistant ragweeds.  Use a glyphosate rate of 1.5 to 2.2 lbs ae/A.  We recommend applying with a residual herbicide that contains chlorimuron (Canopy/Cloak, Valor XLT, Envive, Authority XL) to improve control of dandelions and many summer and winter annual broadleaf weeds (but not ALS-resistant marestail or ragweeds).  The mixture of glyphosate and chlorimuron or cloransulam is likely to be variable for control of even ALS-sensitive marestail by the time we can get into fields.

2.  Keep 2,4-D ester in the mix with glyphosate and wait another 7 days to plant.  Plant the corn acres first and come back to soybeans to allow time for this.  Have the burndown custom-applied if labor or time is short. 

3.  Apply a combination of glyphosate, Sharpen (or other saflufenacil product), and MSO.  Major drawback to this is that saflufenacil cannot be used in combination with residual products that contain flumioxazin (Valor) or sulfentrazone (Authority/Spartan).   Best options for residual herbicide in this mixture, especially where marestail are present – metribuzin or Canopy/Cloak DF + metribuzin, making sure that the metribuzin rate is at least 0.38 lbs ai/A.  A spray volume of at least 15 gpa should be used and it is essential to use MSO as the adjuvant. 

4.  Use Ignite (32 to 36 oz/A) for burndown. One benefit of this compared with option 3 is that Ignite can be applied with any residual herbicide.  The addition of   metribuzin can improve control, especially under cloudy, cool conditions.  A spray volume of at least 15 gpa should be used.  Avoid use of nozzles that produce primarily large droplets.

5.  Substitute tillage for burndown herbicides. Make sure that the tillage is deep and thorough enough to completely uproot weeds.  Weeds that regrow after being “beat up” by tillage are often impossible to control for the rest of the season.

6.  Some things that probably will not work.  We have not had much success with combinations of glyphosate and 2,4-DB, although high rates of 2,4-DB can help control certain weeds.  Gramoxone usually works well only when combined with both 2,4-D ester and metribuzin, especially when weeds have much size.  Valor and Authority do not have enough foliar activity to help control emerged weeds, although they do cause contact herbicide symptomology on weed leaves.  Aim and Cadet also do not have enough activity on most weeds typically found in burndown situations, with the possible exception of small lambsquarters.  Metribuzin does help control emerged weeds, although this is expressed best in mixtures with Ignite or Gramoxone.

The cost of several of these options can be about twice the cost of a typical glyphosate/2,4-D mixture.  This is not really the situation to balk at spending a few extra dollars.  Failing to effectively control weeds at the time of no-till soybean planting creates problems for the rest of the growing season.

Our concern about N loss this spring from wheat is somewhat form specific.  Topdress applications of N from urea are unlikely to have experienced much in the way of loss.  The greatest concern would have been volatilization losses of N after application, but with our rainfall pattern this spring that should have been minimal.  Additionally, the cool soil temps have also limited biological activity meaning very little of the N has been converted to nitrate.  As you know, nitrate-N is the form we are concerned about losing.  The question that typically is asked is – should I have included an inhibitor (either urease or nitrification)?  The research that we have been doing over the last ten years, reveals that typically you do not need a urease or nitrification inhibitor.  This is due to cooler soil temperatures in the spring when these applications are taking place.

The story is a little different for urea-ammonium nitrate (UAN).  When you apply UAN, a quarter of what you apply is in the nitrate-N form the day it hits the ground.  This fraction of N is subject to loss, and there is really very little you can do to protect it.  Inhibitors will in no way shape or form protect the nitrate-N you supply.  So with all the wet weather some of that nitrate-N fraction may be lost via leaching.  The good news is that the greatest loss potential is for coarse textured soils, so those who farm clay soils have a lower loss potential.  Since soil temperatures have been so cool, denitification of nitrate-N has likely not occurred to any great extent (our greatest concern for heavy soils).

What about those fields that have yet to receive their topdress N?  Are you too late?  The one thing we want to point is calendar day late and crop growth stage late are two different things.  Just because your topdress N application is falling a little later than normal does not necessarily mean that your crop is missing an opportunity.  The fact is most of our wheat is a little behind schedule -- thanks to cool, wet conditions.  So much of the wheat is still at a period where timely applications of N can still be made.  For those who have wheat passed stem elongation (Feekes 7) and N has not yet been applied, you should still get out and apply N.  You might have lost some yield potential if the crop has been N stressed, but the crop will still respond to N applications.  In fact, most research shows that applications as late as Feekes 8 can see beneficial yield responses.  Let’s hope we do not have to wait that long. For the later N applications, if the weather forecast is for an extended drying period with windy and warm temperatures (>75°) and no rain for several days, you may want to consider a urease inhibitor with urea applications. However, these weather conditions appear to be unlikely the next several weeks.

We are typically concerned about nitrogen loss a little later into the year, but what about the present heavy rainfall.  The difference between last year (when concerns really became evident in mid-May) and this year are soil temperatures.  Weather monitoring stations located at OARDC research locations across the state are revealing that we have not reached soil temperatures above 53 F for any extended periods.  This is especially true for the northern half of the state.  Additionally, water logged soils that may be warming are not likely to experience much in the way of nitrification of the applied ammonia.  Remember, anhydrous applied during that very small window two weeks ago or even earlier has not really been subject to nitrification thanks to the cool, water logged soils.    

So, should you be concerned?  At this point, you should not be.  This is especially true if you used a nitrification inhibitor.

Something needs to be mentioned about this compressed time frame for corn planting this spring.  If you have yet to apply your N, and you were planning on using anhydrous ammonia, you must allow adequate time between application and planting and the anhydrous must be injected deep enough to prevent contact with the seed. Mismanagement of anhydrous ammonia applications close to planting can dramatically reduce stand and a thin stand is the easiest way to decrease yield potential.

We really want to caution growers in no-till systems that may be considering the use of the new anhydrous toolbars that apply ammonia shallower.  These toolbars do reduce surface disturbance, and they do require less draft power to make the applications, but they can cause issues on corn germination.  These toolbars are designed to apply N shallower in the soil, and planting to soon after application can cause some emergence issues.  We are not running down the toolbars themselves as they do what they are marketed to do quite effectively.  They allow no-till producers to supply anhydrous ammonia with minimal disturbance with less power.  Shallower applications of anhydrous are a greater risk for germinating plants, so if you are going to be using these toolbars be prepared to wait at least a week (maybe longer) to plant, or apply the N diagonal to the direction of planting.

Septoria blotch is usually one of the first to show up, and it already has been reported in some fields. This disease is favored by cool (50-68F), rainy conditions, and although it usually develops early in the season, it really does not cause yield loss unless it reaches and damages the flag leaf before grain fill is complete. Like many other foliar diseases such as Stagonospora, Septoria reduces grain fill and the size of the grain. It usually does not affect the number of spikelets per spike, an important yield component that is defined very early in the development of the plant. As a result, a foliar fungicide application at green-up or jointing is less likely to be as beneficial for Septoria and Stagonospiora control as an application made at or after flag leaf emergence. An early application will certainly control Septoria and powdery mildew, another disease that usually shows up early under cool conditions, but the residual effects of the fungicide will not adequately protect the flag leaf. If the weather conditions continue to be rainy and favorable for foliar disease develop, spores will continue to be produced or blown in from other areas, and new infections will occur, even after early applications have been made. In addition, frequent rainfall may also reduce the residual effects of the early fungicide applications, making them even less effective against mid- and late-season foliar disease development. Results from previous studies have shown that the greatest benefits from foliar fungicide applications were obtained when applications were made between Feekes 8 and 10. This is largely because most of our major foliar diseases usually develop and reach the flag leaf after Feekes 8-9.

During the 2010 growing season, we tested several early (before flag leaf emergence) foliar fungicide application programs in wheat to provide answers to question about the benefit of early applications. The month of May was wet and highly favorable for the development of diseases such as powdery mildew, Septoria and Stagonospora blotch, and head scab. It was an excellent year for testing fungicides. We evaluated the effects of single, split, and double applications of several triazole (Prosaro, Caramba and Folicur), strobilurin (Headline), and combination (Twinline, Quilt, and Stratego) fungicides on powdery mildew, Stagonospora, head scab, and grain yield. Applications were made at green-up, flag leaf emergence, boot, and flowering. Among the single application programs, applications made at flag leaf emergence or boot did better than green-up applications in terms of foliar disease control and yield. A single application of a triazole at flowering provided the best control of head scab. Among the programs with double or split applications, we observed the best results with those treatments that included an application at full rate at Feekes 8-9. A single full-rate application at flag leaf emergence did just as well or better than the green-up + flag leaf. Comparing a single application at flag leaf emergence with a single application at flowering, all of the tested fungicides resulted in better control of powdery mildew when applied at flag leaf emergence than when applied at flowering, and comparable levels of Stagonospora control were achieved with the two programs. This is largely because powdery develops early and as such applications made at flowering are generally too late to provide the best control of this disease. Stagonospora, on the other hand, usually develops later in the season, and in a wet growing season like 2010, foliar fungicides may still provide very good control when applied at flowering. In fact, because of the high levels of powdery mildew, Stagonospora, and head scab we had in 2010, the fungicide programs that provided the best overall control of all three diseases and resulted in the highest yield gain were those with a triazole applied at flag leaf emergence followed by a second application at flowering.

So, to answer questions regarding whether to apply a foliar fungicide, what to apply, when it should be applied, here are a few things to consider. SHOULD A FUNGICIDE BE APPLIED: Yes, if the variety is susceptible and weather conditions are favorable for disease development? WHEN SHOULD A FUNGICIDE BE APPLIED: It depends on the disease. Early (before flag leaf emergence) applications will not provide adequate protection against Stagonospora. Application at flag leaf emergence or at heading will control both Stagonospora and powdery mildew, but WILL NOT control head scab. Fungicides must be applied at flowering to achieve the best results against head scab. An application made at flowering will also control late-season Stagonospora development. WHICH FUNGICIDE TO APPLY: This also depends on the disease being controlled as we well as the cost of the fungicide. Choose the fungicide that is the cheapest and most effect against the disease being controlled. There are lots of excellent triazole (Prosaro, Caramba and Folicur), strobilurin (Headline, Quadris), and combination (Twinline, Quilt, and Stratego) fungicides labeled for use in wheat and they are all effective against foliar diseases. However, the triazoles provide the best results against head scab. In addition, the Strobilurins are usually not recommended for head scab management because they have been shown to result in vomitoxin increase in the grain. A fungicide efficacy chart can be found on our website:

http://www.oardc.ohio-state.edu/ohiofieldcropdisease/wheat/OFCDwheatfungicides.pdf                  

The scab forecasting system (www.wheatscab.psu.edu) is an excellent tool to help guide fungicide application decisions. Based on the flowering date of his/her crop and the weather conditions leading up to flowering, a producer can use this tool to estimate the risk of scab occurring and make a timely fungicide application to protect the crop. In addition, the commentary section of the scab forecasting website provides up-to-date information on the state of the crop and disease risk, along with disease management recommendations.

Producers can now gain access to the commentaries from the forecasting system directly on their cell phones or in their emails, without having to go to the website. As the wheat crop develops and we begin to approach flowering, the commentaries will be updated regularly and sent directly to the emails or phones of those who sign up to receive the alerts. Once there is cell phone coverage and email access, you will receive the alerts anywhere in the country. You can then visit the website to see whether your crop is at risk and contact your state specialist for more information.

To sign up, click on this link: http://scabusa.org/fhb_alert.php and complete the form with your name, email address, cell phone number and other requested information. You can choose whether you want to receive the scab alert via email, test message (on your cell phone), or both. You can also choose whether you want to receive alerts from all over the country or only from the Mid West / Mid South Soft Winter Wheat region.

Most folks are familiar with viruses that cause the common cold, influenza, and if you are a hog farmer, the virus that causes PRRS. There are a plethora of viruses that cause symptoms in our field crops. In soybeans there are viruses like bean pod mottle and maize dwarf mosaic in corn. Since wheat, for the most part, is currently the only actively growing grain crop in the state let’s discuss a few viruses of wheat.     

Whenever the Hessian fly free date is discussed barley yellow dwarf virus (BYDV), a disease caused by seven different species of virus, usually comes up. The fly and the viruses that cause BYDV are not related. However, by planting wheat after the fly free date we can usually avoid the vector of BYDV, hence the association between the two. A vector is another organism that introduces the virus into the plant it will infect. In the case of BYDV, more than 20 different species of aphids may serve as vectors. However, BYDV is not the only viral disease that affects wheat in Ohio. Other common diseases are wheat soilborne mosaic (WSBM) and wheat spindle streak mosaic (WSSMV). Unlike BYDV both of these are caused by soilborne viruses transmitted by Polymyxa graminis, a soilborne protist (a single celled relative of a fungus) that produces motile zoospores (the mobile single celled reproductive stage of a protist).

 Diagnosis of a viral infection can be difficult to make because visual symptoms may or may not be present. If visual symptoms are present they can be easily confused with nutrient deficiencies or physiological symptoms. In the case of BYDV symptoms appear as yellowing, purpling or reddening of the leaf, progressing from the tip down to the base of the leaf blade. This typically occurs on newer leafs (the flag leaf especially) but can easily be confused with normal senescence of lower leaves or deficiencies of nitrogen or phosphorus. As the name of the disease suggests, severe infection may result in dwarfed plants. Symptoms of wheat soilborne mosaic virus appear as a pale green to yellow mottling of leaves early in the spring with the possibility of stunted plants. Symptoms typically show up in wet areas of the field when temperatures are between 50 and 68 F. Symptoms can actually subside when temperatures warm up even though the virus is still present. For wheat spindle streak mosaic virus, symptoms usually appear in early spring as yellow-green mottling, dashes and streaks on the leaf. Streaks are parallel to the leaf veins and tapered at the ends to form spindles. Symptoms of both WSSMV and WSBM may be uniformly distributed in the field, but the distribution of WSSMV tends to be more uniform than WSBM. 

So how do we accurately diagnose a viral infection? The Wayne C. Ellet Plant and Pest Diagnostic Clinic at Ohio State can identify most common insects and diseases in Ohio for the great price of $20 (http://ppdc.osu.edu/). However, for viral infections of wheat a specialized lab is needed to complete the test. Labs like Agdia or plant pathology labs at land-grant universities in the Great Plains will perform tests for viruses for a fee. Samples submitted can be tested for a single strain of a virus or for multiple viruses with fees increasing with the number of strains and viruses tested.

The two main questions when a virus is diagnosed are: “will it impact yield?” and “how do I treat it?” Viruses can reduce yield but the severity of yield reduction depends on the strain of the virus, how susceptible the variety is, and how early in season the plants are infected. In terms of yield loss, fall infections are most important for all three of the viruses mentioned above. Fall infections of wheat by BYDV, WSSMV, and WSBM may reduce yield more severely than spring infections. Treatment is also virus specific. For BYDV, treating for the vector typically does not work. By the time aphids are found in the field and a control measure is applied, wheat has already been infected by BYDV. For WSSMV and WSBM, it is not economical to treat the soil to control Polymyxa graminis, neither is it effective. There are no products registered to control viruses. Fungicides control fungi, insecticides control insects, and herbicides control weeds. We can use cultural practices like planting after the fly free date to manage BYDV. Another and by far the best option is varietal resistance. Viruses are rarely detected in the field and also are very rare in variety performance testing, so it is hard to rate plants for resistance unless we are blessed with an infection during a performance test.  A quick search online using a site filter ‘site:edu wheat virus resistance’ (which filters out all the junk and leaves educational sites) can locate a few websites that will help with resistance ratings. Seed salesman may also have resistance ratings. Finally planting certified seed as opposed to bin run seed will help insure resistance traits are maintained in the seed stock.

So to answer the question in the title, no, wheat can’t get a cold, but it can get a viral infection. In the grand scheme of yield determination Mother Nature is still king, followed by soil fertility, insects, diseases, and weeds (in varying order). This spring wet weather is going to play an important role in yield determination. 

Kentucky is reporting seeing adult moth captures this spring similar to outbreak years of 2006 and 2008 (see http://www.uky.edu/Ag/IPMPrinceton/counts/taw/tawgraph.htm).  In their most recent newsletter from April 19, they are calling this to the attention of their growers.  If their higher numbers continue, we would also expect a large flight of adult moths in the coming weeks into Ohio.  

As pointed out in their article, this does not mean that any individual field will have an outbreak, let alone any area of Ohio.   However, it will mean that Ohio growers should be attentive to potential problems in both wheat and corn, especially when the latter is adjacent to wheat or planted into a rye cover crop, a preferred egg laying site.  See the following fact sheet for more information on this insect http://ohioline.osu.edu/ent-fact/pdf/0036.pdf.  We will keep you up-to-date on future happenings both in Ohio and surrounding states, and discuss the potential for economic problems with armyworms in the coming weeks.

Cereal Leaf Beetle:  We are beginning to see adult cereal leaf beetles along with eggs on wheat plants.  As wheat continues to grow and flag leaves emerge, and as spring-planted oats begin their growth, growers should keep an eye out for the presence of cereal leaf beetle larval feeding.  A big change this year with this pest is that we are reducing the threshold to 1 larva per stem or flag leaf.  Our colleagues on the east coast have done research suggesting that the thresholds that were being used were too high.  Thus, based on their research, we are dropping our thresholds in Ohio down to a single larva per flag leaf.  See the following fact sheet for more information on the cereal leaf beetle http://ohioline.osu.edu/ent-fact/pdf/0038.pdf .

Black Cutworm:  From reading newsletters from neighboring states and examining our own traps, it is obvious that black cutworm adults are now flying in the Midwest.  Black cutworms will begin cutting corn in May, especially in corn planted into weedy fields, with chickweed being a preferred weed species.  Of extra concern this coming spring is that much of the corn will be relatively small or just emerging when cutworm larvae become active.  A fact sheet on black cutworm is at http://ohioline.osu.edu/ent-fact/pdf/0035.pdf . 

Slugs:   We have been getting reports of slug eggs being found in numerous fields in Ohio, and expect egg hatch to begin soon in Ohio starting with the southern locations moving northwards.  For no-till growers or others that have had problems with slugs in previous years, they will need to begin to be watching for signs of slug feeding on emerging crops.  Because many fields will be planted relatively late because of the wet conditions, the conditions exist for significant problems if a field has a large populations of slugs.  For information on slugs, see http://ohioline.osu.edu/ent-fact/pdf/0020.pdf on our Agronomic Crops Insects web page.   In terms of molluscicides, the two metaldehyde materials, Deadline MPs and Orcal Snail and Slug bait, and an iron phosphate bait known as Sluggo, are available.  The most important thing for good slug control is even coverage with the bait when broadcasting.

It was very cold last winter in Florida with the result that rust and kudzu were knocked back.  According to Tom Isakeit (Texas A&M University), the drought has prevented infection in the southern tip of Texas and as well as adjacent parts of Mexico. 

Commercial soybeans are being planted in Mississippi (Tom Allen, MSU) and Alabama (Ed Sikora, Auburn University).  We will continue to monitor the initiation of infection and potential build-up of inoculums in the southern US throughout the season.  In reality for soybean rust to impact Ohio, inoculum will have to be very high in several southern states by early July to have any chance of impacting our soybeans.

 

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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.