February 28: Soil Fertility Seminar to offer continuing education

Soil fertility, crop production practices and environmental stewardship will be the foci of a Soil Fertility Seminar on February 28, 2017 in 18 different University of Illinois Extension county offices.

Presentations will be delivered through web conferencing from 9 a.m. to 2:30 p.m.

Topics and speakers will include:

  • Increasing importance of sulfur for field crops–Dr. John Sawyer, Iowa State University
  • Illinois NREC: What have we learned?–Dr. Robert Hoeft, Illinois Nutrient Research & Education Council
  • Managing Nitrogen to Improve Efficiency–Dr. Emerson Nafziger, University of Illinois
  • Tile Nitrate Loss: Effect of fertilizer N application method and cover crops–Lowell Gentry, University of Illinois
  • N and P retention as influenced by tillage and cover crops in a corn-soybean rotation–Dr. Maria Villamil, University of Illinois

Registration costs $50 per person, which includes lunch. Certified crop advisors may earn up to five nutrient management credits.

To view a list of participating counties, a detailed agenda and to register, please visit the Soil Fertility Seminar Webpage.

Please note that the registration deadline may vary by county.


Extension Bi-State Crops Conferences in and near Western Illinois

Newer and longer-term partnerships between personnel in Illinois and personnel in Missouri and Iowa have resulted in several bi-state crops conferences to be held during January 2017 in Western Illinois or Eastern Iowa.

 

Friday, January 6, 2017: Bi-State Crop Advantage Conference, Burlington, IA, 8:30 AM – 4:00 PM

Location: Comfort Suites, 1708 Stonegate Center Drive, Burlington, IA.

Hosts: Iowa State University and University of Illinois Extension

More Information: Click here to access the flier.

Online Registration: Click here to register

 

Friday, January 27, 2017: Bi-State Crop Advantage Conference, Davenport, IA, 8:30 AM – 4:00 PM

Location: Rhythm City Casino Resort, 7077 Elmore Ave., Davenport, IA

Hosts: Iowa State University and University of Illinois Extension

More Information: Click here to access the flier.

Online Registration: Click here to register.

 

Friday, January 27, 2017: Western Illinois-Northeastern Missouri No-till Crop Management Conference, Quincy, IL, 8:45 AM – 2:00 PM

Location: John Wood Community College, 1301 S. 48th St., Quincy, IL

Hosts: University of Illinois and University of Missouri Extension, Illinois and Missouri NRCS

More Information: Click here to access the flier.

Online Registration: Click here to register.


2016 SDS Commercial Variety Test Results Available

SDS Variety Report

This past growing season personnel from Southern Illinois University, Iowa State University and University of Illinois evaluated more than 580 soybean varieties from 22 seed companies in USB-sponsored sudden death syndrome (SDS) variety trials. The varieties that were evaluated ranged from the very early (MG 0) to late (MG V) maturity groups. Maturity groups were divided into early and late categories; for example, MG II was split into early (2.0 to 2.4) and late (2.5 to 2.9) categories in order to more easily monitor crop development and assess disease at the appropriate growth stage (Figure).

Figure. Aerial picture of the 2016 Commercial SDS Variety Trial at the Northwestern Illinois Ag R&D Center in Monmouth. The difference in variety maturity is evident in this picture. Moving left to right are varieties in Early MG II, Late MG II, Early MG III and Late MG III.

Figure. Aerial picture of the 2016 Commercial SDS Variety Trial at the Northwestern Illinois Ag R&D Center in Monmouth. The difference in variety maturity is evident in this picture. Moving left to right are varieties in Early MG II, Late MG II, Early MG III and Late MG III.

At one or more locations in Illinois and/or Iowa each variety within a maturity group category was randomly assigned to a two-row plot within a block (replication); each variety was planted in three replications. Production of the crop within these trials followed university Extension recommendations and was similar to soybeans produced in any Midwestern farm field with a couple of exceptions: 1) to provide a disease-favorable environment irrigation water (where available) supplemented rainfall, and 2) to increase the chance that germinating seedlings would be exposed to the pathogen, at planting time sorghum seed infested with Fusarium virguliforme, the fungus that causes SDS, was placed in-furrow.

Plots were monitored throughout the growing season for growth and development. At the R6 or full seed growth stage, disease incidence and severity ratings were collected for each plot. In each maturity group category, varieties known to have high levels of SDS resistance or susceptibility were included as ‘checks’. Sufficient disease in the susceptible check varieties was required in order for data from a particular trial to be included in the final report.

The final report is available for download here.

While the data may be of use to crop producers to use as a reference when making their 2017 seed selections or for crop advisors or seed company representatives to use when advising their clients, the final report is forthcoming with its limitations:

“Data presented here is from a single year at one or two locations. Varieties may perform differently in other environments.”

“Plots were not harvested for yield in this program because yield comparisons can be misleading from disease nurseries utilizing small plots. Accurate yield data for commercial varieties should be obtained from state variety trials.”


Registration is now open for the 2017 Regional Illinois Crop Management Conferences

Registration is open for the 2017 Crop Management Conferences. These regional conferences provide a forum for discussion and interaction between participants and university researchers and are designed to address a wide array of topics pertinent to crop production in Illinois: crop management, pest management, nutrient management, soil and water management.

Certified Crop Advisers can earn up to 8 hours of continuing education credit. Advance registration, no later than one week before each conference, is $100 per person. Late and on-site registration is $120. Dates and locations along with links to location-specific agendas and online registration are listed below.

Conference topics include:

  • Updating Grain P and K Removal Levels – Dr.  Emerson Nafziger, University of Illinois, Extension Agronomist, Department of Crop Sciences
  •  Crop Management Strategies for Leaner Times – Dr. Gary Schnitkey, University of Illinois, Extension Economist, Department of Agriculture and Consumer Economics
  •  Increasing the Odds of Success: Integrating Weed Management Strategies – Dr. Aaron Hager, Univ. of Illinois, Extension Weed Scientist, Department of Crop Sciences or Dr. Bob Hartzler, Iowa State Univ., Prof. Weed Science or Dr. Karla Gage, Southern Illinois Univ., Asst. Prof. Plant Biology
  •  Is record-setting weather the ‘new normal’? – Dr. Jim Angel, Illinois State Climatologist, Illinois State Water Survey
  •  Management Practices to Reduce Tile Nitrate Loading – Lowell Gentry, University of Illinois, Senior Research Specialist, Department of Natural Resources & Environmental Sciences
  •  The living soil: Crop management, organic matter and soil biology – Dr. Michelle Wander, University of Illinois, Prof. Soil Fertility & Ecology, Department of Natural Resources & Environmental Sciences
  •  Predicting Insect Pressure: Surveys and Web-based Tools – Kelly Estes, Cooperative Agricultural Pest Survey Coordinator, Prairie Research Institute
  •  New Bacteria to Perennial Fungi: Revisiting Crop Disease in 2016 – Angie Peltier, University of Illinois, Extension Educator

 

January 18: Mt. Vernon – Krieger/Holiday Inn Convention Center. Click here to view the Mt. Vernon agenda. Click here to register for the Mt. Vernon location. For more information, contact Angie Peltier: (309) 734-1098, apeltier@illinois.edu.

January 25: Springfield – Brookens Auditorium – University of Illinois-Springfield. Click here to view the Springfield agenda. Click here to register for the Springfield location. For more information, contact Angie Peltier: (309) 734-1098, apeltier@illinois.edu.

February 1:  Champaign – i-Hotel and Conference Center. Click here to view the Champaign agenda. Click here to register for the Champaign location. For more information, contact Dennis Bowman: (217) 244-0851, ndbowman@illinois.edu.

February 15: Malta – Kishwaukee College Conference Center. Click here to view the Malta agenda. Click here to register for the Malta location. For more information, contact Russ Higgins: (815) 274-1343, rahiggin@illinois.edu.

Mail-in registrations must arrive one week before each conference in order to take advantage of the advance registration discount. To download the mail-in registration form, click here.

 


Soil Nitrogen and N Management Following the 2016 Crop

The 2016 growing season has been a very good one for corn in Illinois, with the November yield estimate of 202 bushels per acre, slightly higher than our previous best of 200 bushels per acre in 2014.

In sharp contrast to the wet June of 2015, most of Illinois received below-normal rainfall in June 2016, with parts of western and southwestern Illinois receiving less than an inch for the month. With May rainfall close to normal across the state in 2016, the wet soils and N loss conditions that we saw over most of Illinois in 2015 never materialized in 2016.

2016 soil nitrogen and N response

In our N-tracking project funded by the fertilizer assessment (Nutrient Research & Education Council), we apply 200 lb. of nitrogen per acre as fall-applied ammonia, early spring-applied ammonia, fall ammonia plus spring-split UAN, or spring-split UAN. We then sample during the spring to see how much N remains in the top 2 feet of soil.

Averaged over three locations in 2015, sampling in mid-June and at tasseling recovered about 70 and 42 percent, respectively, of the amount of N applied as fertilizer. In 2016, we found a little more N than this –about 76 percent in mid-June and 47 percent at tasseling. Grain yield levels didn’t differ greatly between the two years, but more of the N needed by the crop was taken up by tasseling in 2016 compared to 2015. Yields were similar in both years, though, so having more N taken up by tasseling did not clearly lead to higher yields.

Warm soils and wet weather in December 2015 caused a lot of concern about loss of fall-applied N in 2016. We did not, however, find lower amounts of soil N following fall N applications than we found following spring applications in 2016. But there were some differences between the two years in how much of the N recovered was in the ammonium form (coming directly from ammonia application) and how much was nitrate. Nitrate can move in the soil and be lost.

In both 2015 and 2016, about 80 percent of the N recovered in early May following fall ammonia application was nitrate. Following spring ammonia application, 59 percent of the nitrogen was nitrate in early May in 2015, while in 2016 only 39 percent was nitrate. By early June, when N uptake by plants began, 80 to 90 percent of the recovered N was nitrate in both years, regardless of timing of application.

It’s clear from these numbers that applying ammonia in the fall versus spring did not have much effect on how well the nitrogen was protected by remaining in the ammonium form, at least by the time N uptake began. This suggests that N loss is tied more closely to conditions during N uptake (June) than to N fertilizer timing, although sidedressing ammonia, which we did not do in this study, would have increased the amount present as ammonium.

Most N rate trials are showing considerably less N needed in 2016 compared to 2015. This year, we’re often seeing yields leveling off at N rates of only 140 to 160 lb. N per acre, at yield levels between 200 and 250 bushels per acre. We think that this reflects both the large supply of N from mineralization of soil organic matter under the favorable conditions of May and June this year, and also the drier June weather this year that limited N loss and root damage. Another sign of a good supply of N from the soil was the delay in development of N deficiency symptoms in corn grown without fertilizer N. It was common in 2016 to see unfertilized corn in our trials remain dark green into mid-June, when the crop was 3 feet tall or taller.

Nitrogen in the soil this fall

One might expect that less N loss might lead to higher amounts of N left over at the end of the season. We aren’t seeing this in most cases. Dan Schaefer of IFCA took soil samples at the time of crop maturity at a number of on-farm sites, nearly all of these showed soil N levels of less than 6 or 7 ppm, which we consider to be baseline levels. We’re also finding low soil N levels in samples taken following harvest in our N-tracking trials. The only place we’re seeing elevated levels is at N rates considerably higher than those needed to maximize yield. Using too much N is never a good idea, and that was especially true in 2016.

Those who added N late in late vegetative stages this year in addition to normal rates applied earlier might well have ended up with more soil N than usual after harvest. A vigorous cover crop like cereal rye will take some of this up. But the low levels of soil N in fields with normal rates of fertilizer N may not have enough N to produce vigorous cover crop growth. Trying to “prime” cover crop growth by applying fertilizer N this fall will increase N uptake, but may not necessarily increase net uptake after subtracting the amount applied.

Despite slow cooling at the start of November this year, soil temperatures are now below 50 degrees over most of northern and central Illinois, and ammonia application is underway. Soils are mostly in good shape for this, but application should be delayed in fields with wet surface soils .

Nitrogen management for the 2017 crop

We can think of no good reason to adjust N rates, unless planned rates are substantially higher that the 175 (155 in northern Illinois) and 210 lb. N per acre or so calculated by the N rate calculator for corn following soybeans and corn following corn, respectively, in the region of Illinois where fall N is used. If planned rates are higher than this, a downward adjustment is in order. We never know what the spring will bring, but it makes more sense to react to loss conditions if they occur that to apply more N “just on case.”

If the plan is to apply some N in the spring after fall application, consider subtracting that amount from the fall application rate in order not to exceed the suggested rate. If 2017 is like 2016 with regard to N nutrition, using more than suggested rates will nothing to increase yields, but will increase both economic and environmental costs.

There’s been a lot of talk in recent years about how CEC “limits” the amount of N that should be applied to a given soil; the maximum amount commonly mentioned is 10 lb. N per unit of CEC. CEC is a measure of the concentration of negatively-charged exchange sites in a soil. Soils with more clay and more organic matter have higher CECs; silt loam or silty clay loam soils with 3 or so percent organic matter typically have CEC values between 20 and 40. That’s more than enough to “hold” the right amount of N.

There’s no sound basis for considering CEC a measure of “N-holding capacity,” any more than to consider it as potash- or calcium-holding capacity. One unit of CEC in the topsoil will hold 360 lb. of ammonium, so a soil with a CEC of 20 would have only 2.5% of its exchange sites occupied by ammonium if it were all on the exchange sites. Ammonia applied to soil dissolves instantly in soil water, then converts quickly to ammonium. Like any positively-charged ion (cation) in the soil solution, some ammonium ions quickly occupy exchange sites, and some stays in soil solution. Little if any ammonium does not move down in most soils, regardless of the amount applied (within reason.) A possible exception is light, sandy soils with very low CEC values. Nitrogen should not be applied in the fall in such soils.

So there’s no reason to be concerned about CEC values when it comes to applying N on the vast majority of Illinois soils. Instead, base N rates on the N rate calculator, which is based on research showing what rate can be expected to maximize profit. And then apply N responsibly in order to minimize N loss and to keep N for the crop.


Diplodia ear mold at harvest: What can be done now?

Producers in western and west-southwestern Illinois may have observed symptoms of Diplodia ear mold during harvest.

Figure. Healthy corn kernels (left) and kernels showing symptoms and signs of Diplodia ear mold have been found throughout the western and southwestern Illinois crop reporting districts and in corn harvested at the Northwestern Illinois Agricultural Research and Demonstration Center in Monmouth.

Figure. Healthy corn kernels (left) and kernels showing symptoms and signs of Diplodia ear mold have been found throughout the western and southwestern Illinois crop reporting districts and in corn harvested at the Northwestern Illinois Agricultural Research and Demonstration Center in Monmouth.

 

Diplodia Symptoms and Machinery Adjustments at Harvest. Diplodia ear mold can cause lightweight kernels with a dull grey to brownish color and sometimes small black structures call pycnidia (Figure). The infected kernels are prone to breakage and can result in poor test weights, poor grain quality and fine materials in the hopper or grain bin. Adjusting combine settings can help to maximize grain cleaning and minimize breakage.

Figure. Kernels on ears that have symptoms of Diplodia ear mold may appear dull and more greyish than healthy kernels. Breaking an ear in half may reveal small black fruiting structures call pycnidia that are produced by the fungus that causes Diplodia ear mold.

Figure. Kernels on ears that have symptoms of Diplodia ear mold may appear dull and more greyish than healthy kernels. Breaking an ear in half may reveal small black fruiting structures call pycnidia that are produced by the fungus that causes Diplodia ear mold.

 

How Much is Out There? An informal survey of several grain elevators and farmers in Western Illinois had reports of less than 2 to more than 50% kernel damage from Henry to Madison County, respectively. Factors such as planting date, the timing of rain events after fertilization and hybrid susceptibility can result in a range of damage within the larger region and even within a farming operation.

Dockage at the Elevator. Further conversations with elevator and ethanol facility personnel suggested that the threshold for accepting damaged grain can vary depending upon the local market and end-use. The price at which a farmer can market grain begins to decrease for every percentage point of damaged kernels above 5% and some grain elevators will set a damage threshold above which they will not accept the grain depending upon the end use and how quickly the grain will leave the elevator.

It is important for those producers that encounter Diplodia ear mold to be in communication with their crop insurance agent. While the high yields expected this year may offset lower grain prices overall, those farmers with low sale prices due to a lot of dockage may be able to recoup some of their losses.

Stenocarpella maydis, the fungus that causes Diplodia ear mold, metabolizes the starches in corn kernels leaving them lighter weight than non-infected kernels. The ethanol manufacturing process uses bacteria to turn corn starch into simple sugars, eventually fermenting them to yield ethanol. Diplodia-damaged kernels can yield less ethanol and may be why elevators that supply ethanol plants may have a lower threshold (one mentioned 10%) for damaged kernels than others.

One positive is that unlike Aspergillus, Fusarium or Gibberella ear molds, Diplodia ear mold is not associated with a mycotoxin. However, regardless of whether infected kernels are in the field, in the combine hopper, semi trailed or grain bin, unless the grain is cooled and dried to below 15% moisture, the fungus will continue to grow and metabolize starches, lowering test weights and grain quality. Additionally, unless properly dried, the fungus can colonize uninfected kernels that are damaged during harvest or storage operations.

Drying and Storing Moldy Grain. With on-farm storage, many crop producers have the option to hold onto their grain to market it at a later time. Storing diseased grain separately and for only short periods of time is recommended to reduce the chance of additional losses.

Agricultural engineers from Iowa State University have produced several tools that can help those interested in learning more about just how long air drying may take with a given fan and grain bin size and the crop moisture and air temperatures outside. For those that have the ability to add heat to the drying process, these experts have also produced tools that can help in factoring all of the costs associated with drying with or without heat.

Here are resources related to these topics produced by Iowa State University Agricultural Economists and Engineers:

Grain Storage – Quality Management​:
Dryeration
Aeration
Fan Performance

Grain Storage – Economics:
Grain Drying Economics
Grain Storage Economics

General information about Diplodia ear mold and practices to help reduce disease risk in future corn crops can be found here.


Corn Earworm, European Corn Borer, Fall Armyworm, or Western Bean Cutworm: Which One Is Causing the Injury I’m Finding on My Corn Ears?

Several questions about injury on corn ears has made it way to my desk the past week.


Insect injury to corn ear (photo courtesy of Duane Frederking).

Damaged ear tips, missing kernels, and fungal pathogens are all being reported. Several insect pests in Illinois could be the culprit. Corn earworm, fall armyworm, European corn borer, and western bean cutworm are pests of Illinois cornfields. Their larvae all feed on the ears of corn plants.

So how does one determine the cause of ear damage this late in the season? The answer is simple: You really can’t. At this time in the season, it is rare to find any larvae still feeding on corn ears. Without larvae, you can’t be positive if injury was caused by earworms, corn borers, fall armyworms, or bean cutworms, as they cause very similar injury. Let’s look at each insect individually.

Corn earworm. Two generations of corn earworm infest Illinois cornfields each year. Because earworms generally do not overwinter in Illinois, summer populations arise primarily from immigration of moths from southern states in late spring and early summer. Infestations of earworm larvae can cause injury to corn plants, including slight defoliation of leaves, damage to the tassel, and consumption of silks and kernels. The second corn earworm generation usually occurs during pollination. Larvae enter the ear primarily through the silk channel, unlike European corn borer and fall armyworm, which enter through the husks or cob. As silks dry, corn earworm begin feeding on kernels. Larvae feed at the tip and along the sides of the ear near the tip, continuing to feed until they mature. At that time the larvae drop to the ground to pupate. When leaving the ear, corn earworm may drop from the ear tip or create exit holes by chewing through the husk. These exit holes can be mistaken for entrance holes caused by other larvae.


Corn earworm larvae.


Corn earworm injury to corn ear.

European corn borer. Two to three generations of European corn borer occur in Illinois each year. Injury to corn ears is caused by the second and third generations. Loss of grain to larvae’s direct feeding on kernels has not recently been an issue in field corn, but in sweet corn and seed corn, losses can be significant. We’ve also received reports of corn borer feeding in non-GMO corn. Larvae feed on pollen and silks before entering the ear. Entry to the ear is also gained by tunneling through the shank and cob. Ear feeding by corn borer larvae is not focused on any one area. Injury can be found at both ends and along all sides of the ear. Larvae feed until mature; they overwinter as fifth-larval instars in stalks and plant debris.


European corn borer larva (photo courtesy of Marlin Rice, Iowa State University).


European corn borer injury to corn ear (photo courtesy of Marlin Rice, Iowa State University).

Fall armyworm. Like the corn earworm, fall armyworm moths migrate north into Illinois each year. Fall armyworms are a concern for cornfields from mid- to late summer. They cause serious leaf-feeding damage and feed directly on corn ears. Late-planted or later-maturing hybrids are more susceptible to fall armyworm injury. Most common is pretasseled corn. Larvae consume large amounts of leaf tissue, but as corn plants develop, larvae move to the ear. Unlike the corn earworm, the fall armyworm feeds by burrowing through the husk on the side of the ear. Larvae also enter at the base of the ear, feeding along the sides and even tunneling into the cob. They usually emerge at the base of the ear, leaving round holes in the husks.


Fall armyworm larva.


Fall armyworm injury to ear.

Western bean cutworm. A mid- to late-summer pest of corn, western bean cutworm moths begin to emerge in early July. Though some leaf feeding occurs, larvae feed primarily on silks, tassels, and developing kernels. Larvae of the western bean cutworm are not cannibalistic, and several larvae may infest one ear. Entry to ears is gained through silk channels or by chewing through husks, injuring the tip, base, and sides of the ear. Larvae feed on kernels until about mid-September, when they exit through husks. Reports of western bean cutworm injury have been very sporadic the past couple of years.


Western bean cutworm (photo courtesy of Marlin Rice, Iowa State University).


Western bean cutworm injury to corn ear (photo courtesy of Marlin Rice, Iowa State University).

Any one or combination of the aforementioned insects could be the cause of the injury being seen in cornfields. As much as we would like to be able to pinpoint the direct cause of injury, that is often impossible this late in the season. Summer scouting is the key to determining the potential insect culprits.

 

(Updated from 2005 article)


How can we improve your experience with the Pest Degree Day Calculator?

Insects require a certain amount of heat to develop from one stage in their life cycle to another (eggs to larvae to pupae to adults). Degree-days measure insect growth and development in response to daily temperatures. The accumulation of these degree-days can be measured over a period of time and used to estimate growth and predict insect development. Calculating degree-days allows us to predict when significant biological events such as the appearance of insect pests may occur or when they may reach a life stage that is damaging to a particular crop.

Fortunately, we have at our fingertips a calculator that can help us calculate degree-days for selected pests. The Pest Degree Day Calculator is a result of a collaborative scientific effort that combines daily weather data collected by the Water and Atmospheric Resources Monitoring (WARM) Program (Illinois State Water Survey, Prairie Research Institute, University of Illinois) and the Integrated Pest Management (IPM) Program (Department of Crop Sciences, University of Illinois) to provide daily, up-to-date information about pest and crop development in Illinois. Many of you may utilize the calculator to predict cutting dates in your area for black cutworm or to identify when rootworm hatch may be occurring.

We are working hard to improve our Degree Day Calculator. Let us know what you like, don’t like, or what you would like to see changed. Take our survey to share your thoughts: https://illinois.edu/sb/sec/1753389. Thanks in advance for your help!


Agronomy Day 2016

Agronomy Day is a collaborative field day hosted by the Department of Crop Sciences in partnership with several academic units in the College of Agricultural, Consumer and Environmental Sciences (ACES). From nitrogen management to drone demonstrations Agronomy Day shares cutting-edge research with practical implications for your farm or business. CEU and CCA credits are available during tour stops. Want to know more about Agronomy Day? Sign up now for the Agronomy Day mailing list!

For directions and a list of field tour presentations, please visit the Agronomy Day web site.


Soybean: crunch time to come

The 2016 Illinois soybean story is similar to the corn story; current (July 24) crop ratings for both crops are similar to those we saw in 2014, when we produced the highest-ever yields for both crops. Illinois producers matched the 2014 soybean yield (56 bushels per acre) in 2015, despite the crop’s getting off to a very rocky start last year. Few surprises in crop production have been greater than that of seeing fields that looked marginal in July 2015 go on to produce 60, 70, or even 80 bushels per acre.

Compared to the 2015 soybean crop, the 2016 crop took off well and has looked good the whole season in most Illinois fields. Stands are good, growth is generally uniform, and unlike most seasons, there are few drowned-out spots in many areas if the state. In some places where June was dry then heavy rains came in July, Phytophthora has developed. But overall, the 2016 soybean crop is the most visually appealing one we’ve seen in a long time.

While we appreciate the outstanding appearance of this year’s soybean crop, we saw last year that soybean appearance even in late July is a poor predictor of yield. In fact, it’s possible that the soybean crop might even look (and be) “too good” for this time of year. We don’t say that about the corn crop, so why is soybean different?

Corn is a highly efficient crop that makes enough leaf area to form a complete canopy but not much more than that. Corn also has a single ear attached to the stalk, and all leaves feed sugars into that same stalk, so every leaf contributes to both forming and filling the ear. Pollination takes place over the course of a few days, and high yields depend on the number of kernels, so it’s “all hands on deck” for corn leaves, and having too much canopy or plants too tall is not an issue.

Soybeans differ in that flowering takes place over a period of several weeks, and the success of flowering (that is, number of seeds/pods formed) is closely tied to the ability of the leaf at each flowering node to photosynthesize at a rapid rate while the flowers are forming. When leaves are large and plants are tall, not all leaves can compete successfully for light, and they can be partially shaded at critical times, resulting in fewer pods formed and less ability to fill the pods that form.

Petioles (stems that support leaflets) in soybean can be as long as 18 inches to help leaves get up into sunlight. But when stems get to be more than 40 inches tall (to the tip of the stem, not the top of the canopy), lower leaves will be shaded or partly shaded much of the time.

Shading of leaves attached to the lower stem nodes is a problem not only in terms of pod numbers that form at those nodes, but also in these leaves’ getting enough sunlight later in the season to fill those pods. Tall plants with a lot of leaf area in mid- to late August may have few pods forming on the lower stem, and while this might be partly offset by having more pods at mid- to upper nodes, total pod numbers per plant is often decreased.

This “overgrowth” phenomenon in soybean has been known for a long time, and has given rise to various attempts aimed at reducing plant height or leaf area to “help” the soybean plant get over this problem. Dinging leaves with herbicide or growth regulator, “topping” plants by hand or mechanically, and generally undoing what (large) plants spent time and effort building has been the common theme. I’ve seen this work in the subtropics where intact soybean plants turn into vines, but in the Corn Belt, such treatments have almost always done more harm than good. It’s just difficult to get consistently positive results by beating up soybean plants.

By this time of the season soybean plants have not yet reached their maximum height; that will happen by about the second week of August, and plants could add 25 or 30% more to their height by then. Warm temperatures and good soil moisture will keep them growing. There’s not a lot we can do about that.

There is one thing we might not do that will provide some help: application of in-season nitrogen. Application of N (and fungicides) tends to keep leaves a little greener and to increase growth rates a little. Neither of these would be a good thing for a soybean crop that is already approaching stem height of 30 to 36 inches. For those who might want photos showing how tall your soybean crop is, have the person standing in them bend his or her knees a little. Or just acknowledge that really tall soybean plants are not usually the highest-yielding and that they are no indicator of best management.

Heavy canopies tend to keep humidity higher in the canopy, which can lead to more disease development. I haven’t heard too much about white mold so far, but these are the type of conditions that favor its development if it has already infected flowers. There are some other foliar fungal diseases such as frogeye leafspot that may be favored if it stays damp.

While we’ve found a yield increase of 2 bushels per acre or more from applying foliar fungicide in about half of the trials we’ve done, we’re not able to find many clues about when it might work and when it might not. There is no correlation between response and yield level, so “making high yields higher” doesn’t work as a principle. While we can’t rule out a physiological effect, it makes sense that using fungicides to help control fungal diseases should provide the most consistent return.

What’s our best-case for the 2016 soybean crop? Some cooler, drier weather will help slow growth down a little, but that may not be enough to bring back really high yield potential. Although we are concerned about heavy canopies, we have had years when this seemed to have less effect; only by looking at pod numbers per node in mid-August will we really know. If many nodes have 4 or 5 pods like we saw in 2015, we can consider this a false alarm, or at least a case where possible negatives were canceled by some positives, even if we don’t understand how.