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April 2014 Archive for Ask an Agronomist

RSS By: Farm Journal Agronomists, Farm Journal

Have your agronomic questions answered by a Farm Journal agronomist. E-mail us directly at, and we’ll respond on this blog to provide an interactive dialogue.

When it comes to weed control diversify, diversify, diversify

Apr 29, 2014

Everyone is pretty much in planting mode at this point, understandably so.  But, in the process of getting your corn and soybeans in the ground, keep in mind your options to tackle weed problems early before they can take a bite out of crop yield potential. Mark Loux, Ohio State University weed scientist, has placed several resources on his website to help with understanding diversification requirements in herbicide selection. The videos are each about 10 minutes long and will keep you entertained in the process of providing some solid information and recommendations.

What type of phosphate application in soybeans is best?

Apr 24, 2014

Question: We plant soybeans on 15 inches.  Our soil samples call for phosphate only. Which is better for the plant and higher yields, side-dressed liquid phosphate or broadcast phosphate?  It would seem the plant would use the side-dressed liquid before the broadcast version.

Answer: The best return-on-investment strategy to alleviate low P would be a broadcast application paired with a 2 x 2 starter.

This answer was provided courtesy of Shawn Conley, University of Wisconsin Soybean Extension Specialist.

Do Soybeans Need Nitrogen Fertilizer?

Here's what to know if you are weighing a nitrogen fertilizer application to your 2014 soybean crop. By Stephanie Henry, University of Illinois crop sciences researcher.


Which nitrogen source should I use for sidedressing

Apr 22, 2014

Question: What type of nitrogen do you recommend for sidedress applications in corn?

Answer: For a sidedress application, farmers have a choice in what nitrogen product to apply. Many are asking if there is an agronomic difference between 28% and anhydrous ammonia. At sidedress, as far as the plant’s uptake of the nitrogen, these products will both convert to nitrate for its uptake. The difference between these two is their timing for availability. If you have yellow corn, and you were to sidedress the corn to make it green, the 28% has nitrate, and that turns corn back green faster. With anhydrous ammonia, you create a core and it could be 14 days for the nitrogen to be released from that core. If you are sidedressing green corn, it’ll mineralize back slower and be more stable.  Beyond that, if you have enough nitrogen to keep corn green at sidedress, it won’t make a difference which product you use.

What Are the Nitrogen Requirements for Corn Early in the Season?

Agronomist Ken Ferrie explains why fertility is the foundation for the Systems Approach pyramid and key to increasing corn yields


When Is The Best Time To Apply Phosphorus?

Here's how to differentiate between phosphorus loss from fall-applied fertilizer and loss from spring-applied fertilizer.

When is N available to corn from soybeans or a cover crop of rye?

Apr 17, 2014

Question: When is the nitrogen in soybean nodules available to another plant? If it isn't available immediately; when in the following year is it?  When would the nitrogen stored in a cover crop of rye that is killed at the 6" to 8" range in the spring be available to that year’s corn crop?  

Answer:   There really isn’t that much nitrogen (N) available in the soybean nodule. The nodule is where N is made for the soybean plant but then it’s sent throughout the plant. When we talk about N coming from the soybean plants, it’s actually from the whole plant decomposing. You harvest most of the N and take it away in the soybean. In other words, the soybean you haul out of the field has a lot of N in it.  The nodule itself is no diff from the root, the stem, the leaves, and the pod as far as that whole plant breaking down.  Farmers mistakenly think that N is in the nodules only.  Farmers also often think if they leave the nodules in the ground they can still take an N credit, but that’s not really the case. The reality is the N is in the plant residue. Think of it like a cover crop, you have to decompose the entire cover crop to get that N back. In the recycling of a bean crop, that recycling is temperature sensitive depending on when harvest takes place.  As we try to track that here in central Illinois, it looks like it’s somewhere in that five- to seven-week range, once soil temperatures are above 60 degrees F. There’s actually more N left in a cornstalk field than there is in a bean field, but the cornstalk field is so much slower in breaking down the N. As for the cover crop of rye, the bigger the rye gets the longer it takes for it to be available for a corn crop. With a cover crop of rye at the 6- to 8-inch range, again it depends on temperature and some other factors, but typically you’re in that 40- to 50-day range before the N will be available to the corn crop.

What Are the Nitrogen Requirements for Corn Early in the Season?

Here's how to maintain healthy nitrogen levels, starting with emergence.


What Factors Help Determine Nitrogen Rates?

There are multiple factors that are in play as you determine your nitrogen rate--are you dealing with a high-yield or low-yield environment (both of which can be in a single field)?

Can I expect a corn yield boost if I use Y drop attachments to apply N prior to tassel?

Apr 15, 2014

Question: I am an agronomist in northeast Ohio and have a customer that is interested in exploring an avenue to apply nitrogen (N) late in his corn crop.  He is currently applying 40 lbs. of N at planting in a 2X2 through the planter.  At spike he applies 100 lbs. of AMS.  Then he side dresses 220 lbs. of anhydrous ammonia around V-4.  He is looking to set his sprayer up with the Y drop fertilizer attachments and apply up to 45 lbs. of N prior to tassel.  He asked me to ask you if you had any experience with Y drop or any suggestions.   

Answer:  We used the Y drop for the first time last year here in Illinois. We compared it to side dressing versus direct dribbling, and the Y drop did as well as the side dressing with the coulter. It did better than just the dribble. In your customer’s case, an additional application of N is only going to help him if he’s running out of N later in the season. You need to monitor that with visual inspections of the field and tissue testing. If he’s not having an N deficiency, it may not be worth doing as it won’t improve yield any.  If he pulls his side-rate application down and loses that N later, he might be able to make some money by being more efficient.  Breaking up his applications into a number of applications—but not applying more N—might help him make some yield headway. Adding N applications will only improve yields if he’s losing N late in the season.  The last window of opportunity where you can really make a difference is making an N application about the week before tassel.  Going later than that probably won’t be beneficial as you’re not likely to get the N up into the plant quickly enough to impact yield.

What Are the Nitrogen Requirements for Corn Early in the Season?

Here's how to maintain healthy nitrogen levels, starting with emergence.

Saturated Soils Put Pressure on Nitrogen Applications

Record snowfall this winter is causing farmers to evaluate the potential impact excess moisture may have on the nitrogen applications they made last fall.


Nitrogen Advice

Shifting nitrogen fertilizer applications to later in the growing season pays off in higher yield.



Put A Stop to Palmer Amaranth Pigweed

Apr 09, 2014

Palmer amaranth is a weed species that must be thoughtfully and carefully managed. Simply attempting to control Palmer amaranth often leads to ineffective herbicide applications, substantial crop yield loss, and increased weed infestations, says a University of Illinois Extension weed scientist.

"If ignored or otherwise not effectively managed, Palmer amaranth can reduce corn and soybean yield to nearly zero," says Aaron Hager. "The threat of Palmer amaranth during the 2014 growing season is very real across a large portion of Illinois."

The U of I weed science program has developed recommendations for management of Palmer amaranth in agronomic crops. These recommendations were developed in accordance with the unique growth characteristics of this weed species. The goals of the recommendations are twofold: to reduce the potential for Palmer amaranth to negatively impact crop yield, and to reduce Palmer amaranth seed production, which ultimately augments the soil seed bank and perpetuates the species. 

Three general principles of Palmer amaranth management include:

  • Prevention is preferable to eradication. Prevention refers to utilizing tactics that prevent weed seed introduction and weed seed production.  "Palmer amaranth is not native to Illinois so any population discovered in the state originated from seed that somehow was moved into the state," Hager says. "The myriad of ways in which Palmer amaranth seeds can be transported, however, makes preventing seed introduction extremely challenging. Once Palmer amaranth populations become established, utilizing any and all tactics to prevent seed production becomes of paramount importance."
  • Expect treatment to be costly. It is not uncommon for annual herbicide costs to at least double once Palmer amaranth becomes established. There are simply no soil- or foliar-applied herbicides that will provide sufficient control of Palmer amaranth throughout the entire growing season. 
  • Control of Palmer amaranth should not be less than 100 percent. "In other words, the threshold for this invasive and extremely competitive species is zero," the researcher says. "Female Palmer amaranth plants produce tremendous amounts of seed, and in less than five years a few surviving plants can produce enough seed to completely shift the weed spectrum in any particular field."


Recommendations based on Palmer amaranth germination and emergence characteristics include:

  • Be certain to control all emerged Palmer amaranth plants before planting corn or soybean. Burn-down herbicides or thorough tillage are effective tactics to control emerged Palmer amaranth plants before planting. Keep in mind, however, that glyphosate will not control glyphosate-resistant Palmer amaranth and that growth regulator herbicides (such as 2,4-D or dicamba) are most effective on Palmer amaranth plants less than 4 inches tall.  If pre-plant scouting (which is especially important prior to planting soybean) reveals Palmer amaranth plants taller than 4 inches, consider using tillage instead of herbicides to control the plants.


  • Apply a full rate (based on label recommendations for soil texture and organic matter content) of an effective soil residual herbicide no sooner than seven days prior to planting and no more than three days after planting. Many soil residual herbicides that are effective for controlling waterhemp are also effective for controlling Palmer amaranth. In soybeans, products containing sulfentrazone (Authority) or flumioxazin (Valor) have provided effective control of Palmer amaranth. Application rates of products containing these active ingredients should provide a minimum of 0.25 lb ai/acre sulfentrazone or 0.063–0.095 lb ai/acre flumioxazin.

Hager says growers should not rely solely on glyphosate to control Palmer amaranth. "Molecular assays have indicated that resistance to glyphosate appears to be relatively common among recently identified Palmer amaranth populations in Illinois," he explained.

Recommendations based on Palmer amaranth growth rate include:

  • Begin scouting fields within 14 to 21 days after crop emergence. "We recommend this interval even for fields previously treated with a soil residual herbicide applied close to planting," he explained.
  • Foliar-applied herbicides must be applied before Palmer amaranth plants exceed 4 inches in height. The effectiveness of most foliar-applied herbicides dramatically decreases when Palmer amaranth plants are taller than 4 inches.  Postemergence herbicides that demonstrate control or suppression of Palmer amaranth include synthetic auxin herbicides (dicamba, 2,4-D), diphenylethers (acifluorfen, lactofen, fomesafen), glufosinate, glyphosate, and HPPD inhibitors (mesotrione, tembotrione, topramezone). 
  • Consider including a soil residual herbicide during the application of the foliar-applied herbicide. A soil residual herbicide applied with the foliar-applied herbicide can help control additional Palmer amaranth emergence and allow the crop to gain a competitive advantage over later-emerging weeds.
  • Fields should be scouted 7 to 14 days after application of the foliar-applied herbicide to determine herbicide effectiveness; if the soil residual herbicide included with the post application is providing effective control; and if additional Palmer amaranth plants have emerged. 

"If scouting reveals additional Palmer amaranth plants have emerged, make a second application of a foliar-applied herbicide before Palmer amaranth plants are 4 inches tall," Hager says.

In regard to Palmer amaranth seed production, Hager says research has demonstrated that female Palmer amaranth plants are capable of producing numbers of seed comparable to that of waterhemp (several hundred thousand to over one million). "Physically remove any remaining Palmer amaranth plants before the plants reach the reproductive growth stage," he advises. "Plants should be severed at or below the soil surface and carried out of the field. Severed plants can root at the stem if left on the soil surface, and plants can regenerate from stems severed above the soil surface."


Calibrate equipment to adjust for variable soybean seed size

Apr 08, 2014

Reports of larger-than-normal soybean seed are fueling some concerns about planting this spring. While smooth planting with larger soybean seed may not be a snap, it shouldn’t be a problem, either, according to Seth Naeve, University of Minnesota Extension soybean specialist.

"It's not nearly as big of a deal as in years past because seed is now generally sold by the number (140,000 seeds) instead of by the weight," says Naeve.  "Farmers will just need to be aware that they will have larger volumes (and weight) in seed if seed size is large."

He adds: "Some producers even prefer larger seed. A larger seed does have more stored energy and mineral recourses for the emerging soybean plant.  However, the larger cotyledons can be more difficult to force up through the soil.  So, soil type does impact whether large or small seeded soybeans emerge better, but overall it's a wash."

Seed size is greatly affected by the environment, but there is little interaction with variety, he notes.  So, when seed size increases, it’s usually across soybean lines (of the same maturity).  

He adds that very large seed is usually the result of poor conditions during seed-set, paired with much better conditions during late seed-fill.

While there are reports of larger-than-normal seed size in some parts of the country, Naeve points out that the 2013 U.S. Soybean Export Council survey indicates that last year Iowa farmers produced average to below-average sized seed except in the northwest corner of the state, where seed size was much larger than normal.

As in any year, the important thing is to calibrate your soybean planter or drill as you head to the field, and remember to recalibrate between varieties to make sure you plant the intended amount of seed. If you have any concerns, contact your seed supplier and equipment dealer about setting your equipment to handle this year’s seed sizes.


Four Tips to Give Soybeans a Good Start

The time you spend monitoring soil moisture, planting depth, seed-to-soil contact and planting equipment calibration will be rewarded with uniform and rapid soybean emergence.




Four States Confirm Western Corn Rootworm Resistance Problems

Apr 03, 2014

University entomologists report that field-based western corn rootworm (CRW) resistance to the Bt toxin Cry3Bb1 is now found in four states, with confirmation recently announced in Nebraska. Resistance has been confirmed by researchers previously in Illinois, Iowa and Minnesota. Scientists in Colorado, Kansas, Missouri, New York, South Dakota and Wisconsin also are reporting significant damage in fields planted to corn hybrids containing the single Bt toxin. However, researchers in those states have not made a final determination that resistance is there. While Cry3Bb1 has been suspect in most of the CRW resistance cases, the practice of continuous corn and the repeated use of a single toxin are putting increased stress on all of the Bt toxins currently available. In 2013, Aaron Gassmann, an entomologist at Iowa State University, confirmed some cases of western corn rootworm resistance to the mCry3A toxin in that state. Ken Ostlie, University of Minnesota Extension entomologist, is finding similar problems in that state. "We continue to receive reports of Cry3Bb1 performance problem fields, although with VT Triple and VT Triple Pro being phased out, the issue will be masked by Cry34/35Ab1 in SmartStax," he notes. "We've also verified cross resistance with mCry3A at several locations.  We also have had some troubling reports the last two years of performance problems with SmartStax and even Herculex Xtra, but don't have confirmed resistance to Cry34/35Ab1 yet." Most scientists are concerned the resistance issue will continue to worsen if farmers don’t adopt a more comprehensive integrated pest management (IPM) program. Consider these recommendations to reduce your risk in 2014:

1.      Rotate your crops. If you must plant continuous corn, make it a point to rotate fields on a schedule every three to four years.  

2.      If you must grow continuous corn, rotate modes of action, just as you would with herbicides.  Avoid using the same Bt year after year by planting a hybrid with a different Bt trait or multiple Bt traits for rootworm. Alternatively, plant a conventional hybrid with a soil insecticide. The use of a soil insecticide on top of a Bt hybrid is not recommended by most corn entomologists.

"We have shown in our field trials that insecticide on top of a single trait only improves relative root protection if the single trait is starting to fail in the field (i.e. due to resistance evolution)," explains Lance Meinke, University of Nebraska-Lincoln entomologist.   "In this case, root protection improves but selection for resistance to the trait continues, so this is not a good long-term solution to the problem.

"Root protection from single traits that work well does not increase when insecticide is added on top of the trait," he adds.  "Also, we have not seen an increase in root protection when an insecticide is added on top of a pyramid containing Cry34/35Ab1.  So in most cases, we do not recommend using a soil insecticide on top of a pyramid that contains Cry34/35Ab1."    

3.      Scout cornfields for damage this summer and report any problems identified to your state Extension entomologist.

Western Corn Rootworm Bt Resistance Now Includes mCry3A Toxin

The problem has been confirmed in some continuous cornfields in Iowa and likely extends to other Midwest states, an Iowa State University entomologist says.


Be on the Lookout for Corn Rootworm Beetles

In appearance, adult western corn rootworms are about 1⁄4"-long with yellow bodies and three black vertical stripes across their backs.


Resistance Reality

Western corn rootworm breaks through Bt control.




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