Many people have asked about the need to make a fungicide application for frogeye leaf spot on soybeans this season. I have posted a new article on the Illinois Field Crop Disease Blog which reviews this pathogen, how it works, and some new tools that may help you with these important decisions. Find the article by clicking here.
If the appearance of the soybean crop going into late July predicts how it will yield, the 2018 crop in Illinois is going to be a high-yielding one. The crop in Illinois was rated at 78% good + excellent (G+E) as of July 22. Conditions across the US soybean growing regions are somewhat variable, but the 2018 crop is in good condition overall.
As I did with corn in the Bulletin on July 6, I examined Illinois soybean crop ratings in the second half of July over the past decade to see how well they predict yield. The drought year 2012 was in a category by itself, with a G+E rating of less than 10% by late July. Ratings were only about 50% G+E in 2015, but in six of the past ten years—2008-2011, 2013, and 2017—ratings were around 60% G+E in late July. In 2014, 2016, and now in 2018, ratings were high, at 75 to 80% G+E.
With a few exceptions, soybean crop ratings have tended either not to change much after mid-July or to drift up slowly. Exceptions included 2008, when crop conditions rose by about 20 points from late July to mid-August, and 2011, when ratings dropped about 20 points during the same period. In 2017, ratings drifted down after June, from 70% G+E in early July to less than 60% by late August.
Illinois soybean yields were 50 bushels per acre or less in years with late July crop ratings of 60% G+E or less, with the exception of 2010, when the crop yielded 51.5 bushels. In both 2015 and 2017, mediocre late-July ratings failed to predict high yields, of 56 in 2015 and 58 in 2017. In 2014 and 2016, high ratings did predict high yields, of 56 and 59, respectively. Overall, high soybean crop ratings by late July tend to predict high yields, while low to medium ratings can sometimes be offset by August weather, resulting in average or even above-average yields. Because high crop ratings in late July predict high yields, we expect high soybean yields in 2018.
Another factor favoring soybean crop prospects this year is the rapid pace of crop development. Planting did not start early this year but it was finished early, and with May and June warmer than average, the crop was off to the races, with 44% of the crop flowering by the end of June. This continued into July, with 44% setting pods by July 15 and 66% setting pods by July 22. The 5-year average shows 24% of the crop setting pods by July 22, and about 50% by August 1. So the 2018 crop reached 50% podsetting about two weeks earlier than normal.
An early start to podsetting should be favorable, as long as there’s enough water to keep the crop in good shape. The amount of time between podsetting and loss of green leaf color (both recorded by NASS) estimates the duration of the seedfilling period, which is well-correlated with yield. On average, the Illinois reaches 50% leaf color change by about September 15, or about 45 days after 50% podsetting. The 2018 crop needs only to fill seed through the end of August to reach 45 days. With somewhat higher temperatures and longer days in August than in September, having seedfilling begin and end two weeks early should be favorable for seedfilling rate and yield.
We don’t very well understand what signals the end of seedfilling, but both temperature and daylength have some influence. The number of pods that are filling, maturity rating of the variety, and other factors have some effect as well. If temperatures remain normal and the crop has enough water, the need to have days shorten to a certain length before seedfilling stops should mean a somewhat longer filling period this year; this should add yield. But with the early start, seedfilling should be adequate for good yields this year even if it ends by early September.
Other positive signs for the soybean crop this year are the excellent plant stands in most fields, the excellent condition and color of the canopy, and the large number of pods already formed and still forming. The canopy is outstanding in most fields now, and we expect it to take on a darker green color as podfilling gets up to full speed over the next two weeks. I have not heard much about fertilizer nitrogen application this year, but with the canopy in such good shape, it seems unlikely that the crop will need extra N. A fair number of fields have received fungicide, and probably insecticide as well, though we can probably call the “race” between canopy development and insect feeding in favor of the crop this year.
Soybean plants have grown tall due to warm temperatures and adequate water in most fields. Plants are at or close to their final height in fields where seedfilling has gotten underway. Periods of drier weather and warm temperatures have provided enough competition for water to keep the canopy in most fields from getting heavy enough to cause internal shading that can limit pod formation or seedfilling rates. We can probably expect some lodging, especially in 30-inch rows where plants are already tall. Moderate lodging as pods fill is a signal that pods are heavy, so is not a concern, especially if plants just “lean” without affecting light interception.
Counting pods and seeds on plants in mid-season is neither a lot of fun nor an overly accurate way to estimate soybean yield potential. But with pods setting early this year, it’s a little easier to see how yield potential is shaping up. Pod numbers and number of seeds per pod appear to be very good in most fields. We’d like to see 4-5 pods filling at each middle node, and 30 to 50 pods per plant. A field with 130,000 plants per acre, 40 pods per plant, 2.8 seeds per pod, and 2,700 seeds per pound at harvest projects a yield of 90 bushels per acre. While we don’t expect such yields in most fields, we have seen yields this high or higher in some fields in each of the past four years. Based on what we see now, we expect to see this in some fields in 2018 as well.
The University of Illinois Extension will host the Ewing Demonstration Center Agronomy Field Day on Thursday, July 26, 2018 at 9 a.m. Every growing season presents challenges to production, and this year is no exception! We are happy to host this summer field day to share with local growers current, ongoing agronomy research in southern Illinois, including cover crop trials on corn and soybeans, nitrogen management in corn, weed management in soybean, and our continuous no-till field, now in its 50th year of continuous no-till production.
We are highlighting our 50th year of continuous no-till production in our field day this year. This no-till trial area was established in 1969 by George McKibben, the “Father of No-Till”, long-time agronomist and researcher at the Dixon Springs Ag Center in southern Illinois. This plot has been cropped utilizing no-till production of corn and soybeans ever since. The “zero-till” system as it was first called, was researched to “save the soil” that was lost over the many years of intensive tillage required to raise grain crops on the sloping hills of southern Illinois with the planting equipment available at the time.
In honor of this milestone, we will have the original “zero-till planter” on display. This planter was modified and built in the early 1960s at the Dixon Springs Ag Center and used there and also at the Ewing Demonstration Center and other research sites. The demonstrated success of this zero-till planter and production system was one of the inspirations that led companies like Allis-Chalmers and John Deere to start engineering and producing no-till planting equipment. Also, joining us for the field day will be Donnie Morris, retired farm mechanic and engineer who built this planter, along with other retired Extension advisors and educators that worked at the Ewing Demonstration Center over the years.
The topics to be discussed at Field Day include:
Looking Back at 50 Years of Continuous No-till
- Current and Retired Staff, University of Illinois
Insect Management in Corn and Soybean
- Nick Seiter, Research Assistant Professor, University of Illinois
What We Have Learned After 48 Years of Continuous No-till
- Ron Krausz, Manager SIU Belleville Research Center
- Sarah Dintelmann, Undergraduate Assistant ,Weed Science, SIU
Managing Cover Crops in Corn and Soybean
- Nathan Johanning, Extension Educator, University of Illinois
Intro to Corn Genetics: Why is Sweet Corn Sweet?
- Talon Becker, Extension Educator, University of Illinois
Please join us for Agronomy Field Day to help celebrate this milestone in crop production! The field day is free and open to anyone interested, and lunch will be provided. Certified Crop Advisor CEUs will also be offered (Soil & Water – 2.0; IPM – 0.5, Crop Management – 0.5). The Ewing Demonstration Center is about 20 minutes south of Mt. Vernon located at 16132 N. Ewing Rd; Ewing, IL 62836, on the north edge of the village of Ewing, north of the Ewing Grade School on north Ewing Road. Watch for signs.
To help us provide adequate lunch and materials, please RSVP to the University of Illinois Extension Office in Franklin County at 618-439-3178 by Tuesday, July 24. For additional information on the field day, contact Marc Lamczyk at the Franklin County office or firstname.lastname@example.org.
We are at that time in the season where many people will be making final decisions regarding fungicide applications in soybeans and corn. I wrote an article with tips and other items to consider when making fungicide decisions and on farm trials on the Illinois Field Crop Disease Blog, which can be found by clicking HERE.
Authors: Talon Becker and Nathan Kleczewski
Among the various soybean pests, Heterodera glycines Ichinohe, known by most as soybean cyst nematode (SCN), continues to be a persistent cause of yield loss for soybean producers1. SCN has been found in every county in Illinois, as well as much of the eastern United States, Puerto Rico, and parts of Hawaii and Canada2 (Figure 1).
Map of the known distribution of the soybean cyst nematode, Heterodera glycines, in the United States and Canada from 1954 to 2017. Known infested counties are indicated in red. Map © C. C. Marett and G. L. Tylka, Iowa State University, 2017.
It is widely understood that the recommended control measures for this pest include rotation to non-host crops, often corn in this part of the country, and use of resistant varieties. However, what is not generally understood is the importance of rotating the source of the resistance genes introgressed into those resistant varieties. If a given field is planted year after year with soybeans that derive their SCN resistance from the same source (i.e. PI 88788), even if it is in a rotation with a non-host crop, a “race shift” in the SCN population may occur. The term “race shift” is derived from the terminology used to describe and differentiate SCN populations. Diagnostic tests were developed in the 1970s3, and updated in the late 1980s4, which classified SCN populations into “races” based on their ability to reproduce on a specified set of resistant soybean cultivars, called “indicator lines”. This classification system was updated again in the early 2000s5 with the use of HG Types, instead of races, for SCN resistance classification. The updated system also included an updated list of indicator lines (Table 1). HG Type is still determined by a given SCN population’s ability to reproduce on the indicator lines at a threshold of 10% compared to the standard susceptible check variety. For example, an SCN population with the HG Type of 1.2.4 would be able to reproduce on PI 548402 (Peking), PI 88788, and PI 437654 with at least 10% efficiency compared to the susceptible check.
|1||PI 548402 (Peking)|
|7||PI 548316 (Cloud)|
|Indicator lines for HG Type classification of genetically diverse populations of Heterodera glycines. Niblack et al., 2002|
By exposing the SCN population in a given field to the same resistance or control mechanism, one imposes a selective pressure on that population. What must be understood is that in any population, genetic diversity exists. In a given SCN population, there is likely genetic diversity associated with the nematode’s ability to feed/reproduce on a given SCN resistant cultivar. Even if the genetic advantage is marginal and only present in a small proportion of the population, over several generations, the gene or genes responsible for the nematode’s ability to overcome the soybean’s resistance mechanism become enriched in the population. For example, if a population of SCN is made up of individuals from HG Types 1, 2, and 4, in equal proportion, but only individuals from HG Type 2 can reproduce well on PI 88788 soybeans, several seasons of using soybeans with PI 88788-derived resistance, even in a corn/soy rotation, would likely result in an increase in the proportion of the population that would be characterized as HG Type 2 (Figure 2).
A. First season growing soybean variety with PI 88788-derived SCN resistance. B. Second consecutive soybean crop, following rotation to corn, using a variety with PI 88788-derived SCN resistance. C. Third consecutive soybean crop, following rotation to corn, using a variety with PI 88788-derived SCN resistance. SCN population has shifted to be a majority HG Type 2. This figure is meant to illustrate the concept of “race shift” and is not derived from actual data.
In addition to rotating sources of SCN resistance, other management practices for this pest may include the use of certain cover crop species grown during the fall and winter months. While data on the efficacy of certain cover crop species for suppressing SCN populations in the field is often inconsistent, there have been some studies exploring this subject. One such study was conducted by Nathan Johanning and Marc Lamczyk at the University of Illinois Ewing Demonstration Center in 2014-2017. This research investigated the effect of three grass cover crops on yield and SCN egg counts (performed by the Illinois Plant Clinic) taken at harvest using full-season soybean under a no-till system. Treatments included cereal rye (70 lbs/A), triticale (70 lbs/A), annual ryegrass (15 lbs/A), and no cover crop. Each treatment was replicated four times in a given year using strip plots measuring approximately 10’ x 270’. The experimental plot was rotated each year so that plots could remain in their corn, soy, wheat rotation. Results show no significant effect of cover crop on yield in the first three years of the experiment, but a significant yield decrease was seen in annual ryegrass plots in 2017. This result is also seen when yield data from all years are combined, as well as when data from 2014-2016 are combined, indicating this effect is persistent although not statistically apparent in every growing season alone (Table 2). The negative yield effect associated with this cover crop in 2017 was likely due to increased vole activity (possibly because of mild winter) and subsequent stand losses (observational, no data available), as this grass appears to be a preferred habitat for this rodent. This may also explain the significant yield reduction following annual ryegrass seen in the 2014-2016 combined analysis. Although the stand losses were not as noticeable in those years, localized stand loss in the center of plots would not be as apparent but would likely still affect plot yield.
|Mean Separation of Yields (bu/A)|
|Conducted using SAS University Edition: PROC MIXED; Type 3 SS; Year, Year(Rep), and Year*Treatment = RANDOM; Treatment = FIXED. Main effects and interactions containing ‘Year’ were not included in individual year analyses. Different letters within a column indicate significant differences (α=0.1) based on a Tukey’s multiple comparison test.|
As mentioned above, SCN egg counts were also performed on soil samples taken at soybean harvest. These data were highly variable, making it difficult to draw any conclusions in which we have high confidence pertaining to the effect of these cover crops on SCN populations. A significant effect was only observed in 2014, wherein plots that had contained any of the three grass cover crops the previous fall showed significantly lower SCN egg counts at soybean harvest (Table 3).
|Mean Separation of SCN_Harvest (SCN eggs/100 cc soil)|
|Conducted using SAS University Edition: PROC MIXED; Type 3 SS; Year, Year(Rep), and Year*Treatment = RANDOM; Treatment = FIXED. Main effects and interactions containing ‘Year’ were not included in individual year analyses. Different letters within a column indicate significant differences (α=0.1) based on a Tukey’s multiple comparison test.|
It is worth noticing that this is also the only year where the ‘No Cover’ treatment showed substantial SCN egg counts, although that did not translate into a significant decrease in yield (Table 2). In years where SCN pressure was relatively low, such as 2015 and 2016, egg counts were more or less unaffected by the grass cover crops. Egg counts in 2017 were in the “low to moderate” range, according to the University of Illinois Report on Plant Disease titled “The Soybean Cyst Nematode Problem” (RPD No. 501). And in this year, cereal rye plots showed a relatively low egg count compared to the other treatments, but this was not statistically significant due to the large variation in egg counts between replicates. This variation also contributed to the lack of statistically different means across all years of the study. Despite this, comparison of the four year average egg counts show triticale, annual ryegrass, and cereal rye plots to have had 46.1%, 26.3%, and 13.1% SCN eggs/100 cc soil, respectively, compared to the no cover (Figure 3). The results of this study suggest that cereal rye would be a preferred cover crop to control SCN before soybean, with repeatedly low egg count averages and no negative yield effect.
There is no standardized threshold for SCN egg counts after which damage is likely to occur, but 2,000 eggs per 100 cc of soil is considered “moderate to high”, according to RPD No. 501, and counts above this have been called “cause for concern” by the Illinois Soybean Association (ISA). This statement came in a press release announcing an ISA checkoff-funded study, led by Dr. Jason Bond of Southern Illinois University, that will further explore the relationship between grass cover crops, including wheat, and SCN. Larger studies like these are necessary for better understanding how cover crops may interact with SCN under a wide range of soil types, weather conditions, etc., particularly when dealing with a highly variable indicator of potential damage, such as SCN egg counts. Hopefully, from continued research into alternative control methods of SCN, such as cover crops, we will be able to add more tools for combating this pest to our proverbial toolbox, thereby reducing the farmers’ dependence on non-host rotation and host plant resistance.
If you would like to test your field(s) for SCN egg counts or HG Type, samples can be submitted to the University of Illinois Plant Clinic. Samples should be taken from a field following harvest, the season before soybeans are to be planted in that field to allow time for the development of a control strategy. More information on sampling methods and service fees can be found on the Plant Clinic’s website.
University of Illinois personnel will also be conducting an SCN survey this summer in concert with several other pest surveys. If you are a landowner and are interested in allowing traps to be placed on your land and/or soil samples to be taken from your fields, please contact Kelly Estes at email@example.com.
- Allen, T. W. et al. Soybean Yield Loss Estimates Due to Diseases in the United States and Ontario, Canada, from 2010 to 2014. Plant Health Prog. (2017). doi:10.1094/PHP-RS-16-0066
- Tylka, G. L. & Marett, C. C. Known Distribution of the Soybean Cyst Nematode, Heterodera glycines, in the United States and Canada, 1954 to 2017. Plant Health Prog. (2017). doi:10.1094/PHP-05-17-0031-BR
- Golden, A. M. & Al, E. Terminology and identity of infraspecific forms of the soybean cyst nematode (Heterodera glyecines’). Plant Dis. Report. 54, 544–546 (1970).
- Riggs, R. D. & Schmitt, D. P. Complete Characterization of the Race Scheme for Heterodera glycines. J. Nematol. 20, 392–395 (1988).
- Niblack, T. L. et al. A Revised Classification Scheme for Genetically Diverse Populations of Heterodera glycines. J. Nematol. 34, 279–288 (2002).
Well, it is that time of year where we start to see issues developing in the field. Questions such as, “What happened?” and “Why me?” will become more common. The key to managing diseases is proper diagnosis, and this starts in the field. In my recent post on the Field Crop Disease Blog, I provide several tips for diagnosing issues in the field, and distinguishing disease related problems from abiotic issues. Check out the post, and sign up for updates!
This past week we spent a few days surveying wheat fields throughout the state in order to see how the crop is progressing as well as better understand what disease related issues we may be experiencing. Most of the crop was near flag leaf emergence (Feekes growth stage 8/9) with a few fields near boot in locations further south. The good news is that of the 26 fields we looked at, none had any stripe rust, nor have I received any additional reports of this disease in the state. In general, diseases were minimal. In southwest portions of the state Septoria leaf blotch (aka speckled leaf blotch) was fairly common.
This is a residue-borne disease that is favored by cool, wet conditions and can grow and persist on small grain residues. The disease is often located deep within the lower canopy, and causes irregular brown lesions on the foliage. At the center of the lesions you will often see black structures that may resemble tiny peppercorns. These structures are why the disease has the extremely creative common name speckled leaf blotch. The disease spreads upwards predominantly via rain splash, and seldom causes significant yield impacts. This typically is due to increased temperatures that do not favor disease development as the crop develops and the flag leaf is produced. Remember, the flag leaf and green tissues above contribute the majority of carbohydrates for grain fill (over 70% from the flag leaf alone). Foliar diseases that do not reach these tissues are typically not a major concern.
Similarly, I came across a few fields with light powdery mildew. Unlike Septoria leaf blotch, powdery mildew is an obligate pathogen and requires a living host to grow and reproduce. Cool, humid (not wet) conditions favor powdery mildew development. In general, production practices that favor rapid plant growth and lush, full canopies early in the season favor this disease. For example, high nitrogen rates or manure use can result in rank growth early in the season. Powdery mildew can reproduce more quickly than Septoria, and therefore can occasionally impact early season growth or tillering in some instances. Although I did not see anything that would be of concerns and have not had any reports of severe powdery mildew, management is best achieved through selection of a resistant variety and avoiding excessive nitrogen application. Early season fungicide applications with nitrogen applications can have some benefit when a field is at high risk for disease (i.e. susceptible variety, heavy N use, disease present early, cool weather forecast for several days/weeks) but are not recommended if disease is low. Anything in the triazole (FRAC group 3), SDHI (FRAC group 7) or Strobilurin (FRAC group 11) fungicide classes will help control powdery mildew in high risk situations.
As we approach boot and heading you should keep an eye on the Fusarium Head Blight Prediction Center for updates on disease risk. I will follow up with a post on how to best use this tool on my blog in the next few days. Forecasts are calling for e moderate and potentially rainy conditions over the next 7-10 days depending on your location. In the meantime, keep an eye on your fields, and enjoy the weather!
Nathan Kleczewski Extension Field Crop Plant Pathologist University of Illinois email: firstname.lastname@example.org
Authors: Nick Seiter, Talon Becker, and Nathan Johanning
Slugs can be a difficult pest to manage when conditions are favorable for them, which has been the case often (particularly in southern Illinois) over the last couple of years. These mollusks can damage both corn and soybean early in the season, along with a variety of other crops; however, they have the potential to be especially problematic in soybean, where they can kill the cotyledons and ultimately reduce stands. There are a few management points to consider for slugs in field crops:
- Monitor slugs before planting to estimate the severity of the problem. Slugs can be monitored by inspecting residue, or by creating artificial shelters (made from shingles or other flat materials placed in the field to create a dark, damp environment) and inspecting them periodically before planting and during early stand establishment.1
- Cool, wet weather during stand establishment results in greater slug problems. Slugs require a moist environment to survive, and they perform best when conditions are wet. Cooler temperatures extend soil drying time and delay plant development, leaving seedlings vulnerable to slug feeding damage for a longer period of time. Discussions with several CCAs in southern Illinois highlighted the fact that, while slug damage is a fairly normal occurrence on a small scale in most years, particularly in no-till fields, the mild winter of 2017 followed by wet and cool conditions in the spring after many acres had already been planted likely contributed to the greater incidence of slug damage last season. It appears that soybeans were most affected last season in southern Illinois, with several thousand acres of replanting reported.
- Reduced tillage and/or certain cover crop systems can lead to larger slug populations. Higher levels of residue retain water and provide harborage for slugs, resulting in an increased probability of slugs reaching damaging levels. Reports from southern Illinois indicate that most problem fields last spring had a cereal rye cover crop that had not been terminated before producing excessive growth, creating a favorable environment for slugs. It is important to manage residue in cover cropped fields, particularly if they are no-till. If you had a problem with slugs last year, or have found concerning levels under your “shingle traps” in the field, make it a priority to terminate the cover crop before too much above ground biomass has accumulated (generally less than 1 ft. of growth). Cover croppers may also consider decreasing their seeding rate or planting a cover crop mix which includes species that winter-kill along with their favorite over-wintering species.
- Avoid open seed furrows. When planter closing wheels fail to seal the furrow, the resulting trench provides an ideal environment for slugs and allows them to consume developing cotyledons as the seed germinates.
- Chemical control options are limited. Slugs are not insects, and insecticides do not provide effective control. There are slug-specific baits available, but they tend to be expensive. Note that several formulations of the active ingredient metaldehyde (e.g., Deadline®) are labeled for use in corn, but this molluscicide is not currently labeled for soybean in Illinois.
Ultimately, the most reliable management tactic for slugs is to plant into a warm, dry seed bed, which is not always an option. However, by understanding conditions which are likely to lead to slug problems, you can be better prepared to address them when and where they occur.
Nick Seiter: email@example.com – Research Assistant Professor, Field Crop Entomologist, University of Illinois Department of Crop Sciences
Talon Becker: firstname.lastname@example.org – Extension Educator, Agriculture and Natural Resources, Illinois Extension
Nathan Johanning: email@example.com – Extension Educator, Agriculture and Natural Resources, Illinois Extension
1 Douglas, M. R. and Tooker, J. F. 2012. Journal of Integrated Pest Management 3(1) DOI: http://dx.doi.org/10.1603/IPM11023
A number of times over the past 30 months I’ve asked Illinois soybean producers for help in gathering field-level information on soybean fields to feed into a study, led by the University of Nebraska and funded by the North Central Soybean Research Program, looking at weather, soil, and management effects soybean yield over the Corn Belt.
The last growing season from which we are collecting information is 2017, so this is probably the last time I’ll ask. As we have done for the last year, we are offering a $50 gift card for those who fill out and return forms from 2016 and 2017.
We are not asking for detailed information – only the location of each field, yield level, and a little production information such as planting date, seeding rate, etc. We’d like information on four fields from each of the past two season from each producer if possible.
If you can help us in this effort, please download the PDF forms at http://go.illinois.edu/soy-survey – there are four pages, one an example with a little explanation, one is the gift card request form, and there is one page each for 2016 and 2017, with space on each for information from four fields. If it’s easier, you can email me and I’ll email the forms . We can send also forms by mail if anyone needs that.
Forms can be filled on the computer or printed and filled out by hand, then scanned and returned as email attachments or sent by mail.
We have fallen short of the number of fields in this project each of the first three years, and I’d really appreciate everyone’s help to get to reach goal this time. We’d like information from fields all over Illinois. Students (who might have special interest in the gift card), vo-ag classes, farmers, company agronomists, sales people – all can help with this effort.
Thanks in advance for your help on this. Let me know if you have questions.
It is looking like at least some harvest surprises may be positive after an up-and-down 2017 season in Illinois. The September 1 yield predictions released by the USDA this week are for Illinois corn yield to average 189 bushels per acre, up a bushel from the August 1 estimate. The soybean yield estimate is unchanged at 58 bushels per acre. Both would be outstanding after the tough start to the year and dry weather at times over much of the state.
Many soybean fields in east central Illinois are dropping their leaves, and harvest is getting underway. While we don’t expect as many 80+ bushel yields this year as we had in 2016, pod numbers look better than many had expected after dry weather in August and September. Rain now might boost yields by a little, but only in fields planted late or with late-maturing varieties where plants are still green. Cool temperatures in recent weeks have lowered water use rates, though, and we aren’t seeing the premature leaf drop that sometimes signals an early end to seedfilling due to lack of water.
With high temperatures in the 80s now and expected for the next week or more, the process of shedding leaves and drying down will accelerate, and it will be important to try to harvest soybeans at seed moisture above 10 percent. While some rain would help lawns and still-green crops, it would be better for the pod integrity if it stayed dry until after harvest, especially if temperatures stay high.
With high temperatures, seeds and pods following maturity will dry within hours instead of days, and we need to be alert and ready to harvest as soon as plants can be cut and seed moisture is at 12 or 13 percent. If moisture drops to 10 percent or less during harvest, it might be worth stopping until pods and seeds take on some moisture in the evening or overnight. Breeding and the use of improved combine headers have reduced pod shatter, but seeds less than 10 to 11 percent moisture can crack more easily. This might be one of those years with frequent switching between soybeans and corn harvest.
The corn crop in many fields is also looking a little better than expected as the leaves dry down and ears start to drop. As of September 10, two percent of the state’s corn crop had been harvested, mostly in southern Illinois. Yield reported so far range from low to high, reflecting differences in planting (or replanting) time, ability of soil to hold water for the crop, and whether rain fell or didn’t fall at critical times.
Nearly all of Illinois had below-normal rainfall in August, and little or no rain has fallen over most of Illinois during the first half of September. Dry soils during grainfill can decrease leaf photosynthesis, and when that happens, sugars are pulled out of the stalk into the ear to fill the grain. This leaves the stalks more susceptible to stalk-rotting fungi, and so more subject to lodging. So fields – especially those where leaves dried up earlier than expected – should be checked for stalk strength. Good growing conditions in July can increase the deposition of stalk-strengthening lignin, however, making stalks less likely to break even if sugars are pulled out. So as long as winds stay relatively calm, lodging is not expected to be much of a threat, especially in those parts of the state that received more rainfall in July and August.
Below-normal temperatures in recent weeks – most of central and northern Illinois are now about 150 GDD behind normal since May 1 – have slowed grainfilling rates and delayed maturity of the corn crop. The cooler temperatures have probably been positive for yields, by extending the water supply into mid-September. But the mid-August predictions that early-planted fields would mature by late August or early September didn’t happen. With GDD accumulation rates now above normal, a lot of fields will reach physiological maturity quickly, and grain will start to dry down. High temperatures mean rapid grain moisture loss; we’ve seen moisture loss as high one percent per day under high temperatures, especially if it’s breezy.
Dry conditions over the past month have limited the spread of ear rots. Most kernels now have the bright yellow color we like to see at harvest, and if the grain reaches maturity and can be harvested without an extended period of wet weather, we can expect grain quality to be good. Harvesting at high moisture and drying at high temperatures, or storing grain without proper care, can all compromise quality, however, and can mean getting a lower price for the crop.
One issue that often comes up for discussion during corn harvest is that of corn test weight. If test weight turns out to be lower than the standard of 56 pounds per bushel, many people consider that a sign that something went wrong during grainfill, leaving yield less than it could have been. And, test weights in the high 50s or above are often taken as a sign that kernels filled extraordinarily well, and that yield was maximized. Neither of these is very accurate –high yields often have test weights less than 56 pounds, and grain from lower-yielding fields can have high test weights.
Test weight is bulk density – it measures the weight of grain in 1.24 cubic feet, which is the volume of a bushel. Kernel density is the weight of a kernel divided by its volume, so does not include air like bulk density does. Kernel density is a more useful measure of soundness and quality than is test weight, but is harder to measure. A typical kernel density might be 91 pounds per 1.24 cubic feet of actual kernel volume. So a bushel of corn grain is about 56/91 = 62 percent kernel weight; the other 38 percent of the volume is air. Kernels with higher density tend to produce higher test weights, but only if they fit together without a lot of air space. Popcorn, as an example, has small, high-density kernels that fit together well, and a typical test weight of 65 pounds per bushel.
Hybrid genetics, growing conditions, and grain moisture at which test weight is measured can all affect test weight. If kernels appear to be well-filled, without a shrunken base that can signal that grainfill ended prematurely, it’s likely that they filled to their capacity and that yield was not compromised even if test weight is less than 56 pounds per bushel. For reasons that go back to an earlier time, though, corn needs to have a test weight of at least 54 pounds per bushel in order to be sold as U.S. No. 2 corn, which is the most common market class. Corn with a test weight of 52 or 53 might not be docked in price if it can be blended with higher test weight corn to reach the minimum. That’s much easier to do in a year when test weights are generally good. We expect that 2017 might be such a year.