Too wet to sample for SCN?

Soybean Cyst Nematode is an extremely important, yield limiting pathogen of soybeans in Illinois, reducing yields an average of 1-3% across the state.  As I have written in earlier posts, sampling your fields every 3-5 years to assess SCN levels and HG types is the first step in managing this issue.  The best time to sample for SCN is after harvest in the Fall, and this can easily be added onto any samples you gather for soil nutrient testing.  However, wet weather across portions of the state have made it difficult to sample many fields, and in some areas, it may not be possible to obtain samples before the ground freezes.  The nice thing about SCN is that it will survive the winter in your soil, and still be present prior to planting in the spring.  Fall testing is more practical, and allows you more  time to obtain results and make management decisions, but spring sampling still will provide you with valuable information on SCN levels in your fields.  The take home message here is that you can expect similar data from fall and spring samples, and that it is better to sample in the spring than not at all.    #TheSCNCoalition

Notes on fall fertilization

With harvest winding down in most of Illinois after another year with high to very high yields, it’s time to review some basics of fall fertilization. Neither fertilizer nor grain prices are historically high, so there’s reason to be aware of costs while making sure to cover the nutrient basics.


In a webinar on October 19 organized by the Illinois Fertilizer & Chemical Association, we looked at some of the nitrogen response data that have come in so far this fall and considered what this might mean in terms of fall N management. In some of the trials, modest N rates produced high yields, much like we’ve been seeing routinely in recent years. But in a few other trials, we found that the crop needed more N than we have seen most recent trials on productive soils. It’s too soon to call this a phenomenon for 2018. Even if this turns out to be more common this year, using previous research results to determine best N rates, which is what the N rate calculator does, means that unusual results get “diluted” by normal results from this and previous years. So adding data from this year will not move the MRTN (best) N rates by very much. We have no way to predict what next year will bring, and so using all of the data from recent years really is the best guess at what N rates we should use for 2019. We really can’t react to unusual responses in any trial in any year by making wholesale changes in how we manage N fertilizer.

The need for high N rates in some in some trials this year may be partly related to high yields, though yields are not much higher in most trials than we had in 2017, when moderate N rates were usually enough. One unusual feature of the 2018 growing season was the cool, wet April followed by unusually warm weather in May. This might have caused a delay in the start of mineralization of soil N, which, coupled with rapid early crop growth. might have meant that more of the N for the 2018 crop needed to be supplied with fertilizer. As more results come in we’ll be able to get a better handle on this, perhaps including some possible ways to improve N management if we see similar developments another year.

Soil temperatures dropped quickly in mid-October this year, and in central and northern by now they are at or a little below the 50 degrees F that we consider to be the maximum soil temperature at which to safely apply anhydrous ammonia fertilizer in the fall. The forecast calls for cool and cloudy weather most of the next week, and it appears likely that soil temperatures will stay below 50 degrees into November. Low temperatures lower microbial activity that converts ammonium to nitrate, which helps keep N mostly in the ammonium form; this is the form we hope to have present as soils freeze up this fall. Soil temperatures (we suggest 4 inches deep under bare soil) can be tracked at the WARM website maintained by the Illinois State Water Survey. Data are available there either as maps of Illinois or as soil temperatures at one of the individual weather-recording sites. Map options include daily maximum, daily minimum, or “average hourly” values, which has a default of 10 AM. I suggest changing 10 AM to 12 PM (noon) on that map; soil temperature at noon is usually a little higher than at 10 AM, so is a little more conservative. Nitrification inhibitors such as nitrapyrin (N-Serve® from Dow/Corteva) and pronitridine (CenturoTM, new from Koch) inhibit microbial activity responsible for conversion of ammonium to nitrate in the soil, and so have the same effect as do cool soil temperatures. Both an inhibitor and waiting for cool soils are suggested as ways to minimize nitrification activity following application of fall-applied ammonia.

If we enter the NH3 price as $525 per ton ($0.32 per pound of N) and the corn price of $3.50 per bushel into the N rate calculator, it calculates MRTN rates of 161 and 178 lb. N per acre for corn that follows soybeans, and 205 and 203 lb. N for corn that follows corn, in northern and central Illinois, respectively. The “profitable range” given by the calculator includes about 15 lb. N on either side of the MRTN. This range is based on our finding that the return to N stays near its maximum over a range of N rates when we combine a lot of N rate trial data. This provides some leeway for those who want to adjust the rates based on experience. But producers and advisers should have a good reason to move N rates above the upper end of the range. We are not seeing this year, nor have we seen in previous good years (like 2017), that high corn yields consistently require higher rates of N than do lower corn yields.

Conditions not conducive to fall N (as ammonia) application to a field include having soils warm or wet, very poorly-drained soils, and light-textured soils through which water moves quickly. The latter two—poorly-drained and light-textured soils—should not have fall-applied ammonia even if they are cool and dry enough, given the potential for loss before crop uptake begins next spring. Higher loss potential due to warmer fall and spring weather also makes it too risky to apply fall ammonia south of the terminal moraine that roughly follows IL Route 16. Applying NH3 to wet soils restricts the spread of NH3—ammonia moves away from its release point in the soil only until it’s dissolved in soil water, which in wet soils may only be an inch or two. Such a small band means less dispersion in the soil before next spring, which can limit root access to the N. Having the N so concentrated in the band can also increase the chances for NH3 to move up and out of the soil if the soil happens to dry out after application. Ammonia knives should be run deep enough to release NH3 about 6 inches deep on most soils, and perhaps a little deeper on loam soils or dry soils, where we expect NH3 to move farther from where it’s released. The old rule of thumb—if you can smell ammonia during application you need to check its placement—remains useful.

We have compared fall- versus spring-applied ammonia in a variety of experiments over the past five years in Illinois, and have generally found that both produce similar yields at similar N rates. We have found modestly higher yields, in some cases with less N, for spring-applied N, but we have also found, more rarely, fall N producing slightly more yield than spring N. Most measurements of tile-line N loss report loss of a little more nitrate-N from fall-applied compared to spring-applied N. In our soil N studies, we have found that spring-applied NH3 takes several weeks longer to convert from ammonium to nitrate compared to other forms and times of N. So when the spring weather is wet, more nitrate in the soil from fall-applied ammonia can mean more loss of N. In relatively dry springs, water doesn’t move through the soil or stand in parts of the field to cause denitrification, so there is little or no N loss even if all of the N is present as nitrate. If carefully applied, both fall- and spring-applied NH3 are very good sources of N. Wet soils in the spring typically make it more difficult to apply NH3 properly, and without a lot of soil compaction. In general, applying NH3 in the fall as long as conditions are good (soils cool and not wet), then waiting until spring to apply the rest (as NH3 or some other form or combination of forms and times) constitutes sound N management.

We just completed a three-year study designed to measure how much of the N in the common phosphorus fertilizer diammonium phosphate (DAP, which is 18% N and 46% P2O5) is available to the corn crop the following year. We did this by applying rates of N ranging from 0 to 80 lb. N per acre, as either fall-applied DAP, spring-applied DAP, or UAN (no P) applied at planting. These rates were in addition to a base rate of 100 lb. N applied as UAN, and we used triple-super-phosphate (TSP) fertilizer (which has no N) to make sure all plots got the same amount of P. The trial was run at both Monmouth and Urbana over the 2016-2018 seasons, for a total of six site-years. We found that the corn crop responded the same to N from all three sources (Figure 1.) While that’s a little surprising given that the N in fall-applied DAP is likely to be nitrate (and so subject to loss) earlier in the spring than spring-applied DAP or UAN, it tells us that we can count all of the N applied as MAP or DAP as part of the total fertilizer N rate we plan to use. One caution: we applied fall DAP in this study between mid-October and early November; applying it earlier in October when soils are warmer will increase the rate of conversion of the N to nitrate, thereby increasing the potential for loss.

Figure 1. Corn yield response to N applied as fall-applied DAP, spring-applied DAP, or UAN at planting, averaged over six site-years in Illinois, 2016-18.

It is important to include in the N rate to be applied for next year’s corn crop all of the N we apply— “main” applications in fall or early spring, fall or spring DAP, N applied with the planter, N used as herbicide carrier after planting, N applied as manure, and any sidedressed amounts. We sometimes tend not to count “minor” amounts, but unless we have some way to know that some N was lost, we can’t justify leaving any of the N out of the total we record as the rate we will apply.

P and K

Fall application of the dry fertilizer materials to supply P and K to the next year’s (or next two years’) crops is normal practice, although there has been some moving of P and K applications to the spring. That’s not a problem with timing—even though P and K are relatively immobile in the soil, applying them as surface broadcast well in advance of crop emergence tends to work well. But fall soil conditions are often better for driving application equipment over fields, and many producers don’t want to add fertilizer application to the list of spring tasks. Most P and K fertilizers are broadcast, but some now apply these materials as bands placed into the soil, in some cases beneath where rows will be planted. Research has shown limited if any yield response to banding P and K compared to broadcasting, especially on productive soils with adequate P and K test levels already present. An advantage to placing P into the soil is that it is less prone to running off with rainfall. But this requires special equipment, and application of dry fertilizer in bands is substantially slower and more costly than broadcast application.

While most P and K fertilizer is applied to soybean stubble in preparation for corn the next year and then soybean the year after that, we have seen some claims recently that soybean “needs its own P and K” and that it shouldn’t have to “settle” for the P and K “left over” from the corn crop. In all but very low-testing soils, where crop roots can have trouble reaching enough P and K as they grow into the soil, research has failed to show a benefit to annual applications of P and K, at least in soils such as those in Illinois. We know for certain that it costs more to apply nutrients every year than only once in two years. There have also been claims that soils tie up P and K over time after they are applied, such that “freshly-applied” nutrients are more available to plants. But applying amounts of P and K that crops remove tends to keep soil test levels fairly constant, suggesting that any tieup of P and K is not a permanent “loss” of these nutrients; as long as soil test levels are adequate, both crops get enough even if their roots don’t encounter fertilizer granules as they grow.

A sound approach to determining rates for P and K is to add up the amount removed over the last two years (assuming a biennial application) and to apply that amount in preparation for the next two years. A year ago in a Bulletin article I reported the results from a recent NREC-funded grain nutrient sampling project in Illinois. We set grain removal levels as the values below which 75% of sample values fell, so a little higher than the average amounts of nutrients we found in the grain samples. In some 2,100 grain samples of both corn and soybeans, we found removal levels of 0.37 lb. P2O5 and 0.24 lb. K2O per bushel of corn grain, and 0.75 lb. P2O5 and 1.17 lb. K2O per bushel of soybean grain. These are 10 to 15% lower than previous “book values” used in Illinois and many other states, and are in line with levels reported within recent years by Iowa State University scientists.

Even with slightly lower P and K removal levels than we have used in the past, high yields mean removal of a lot of nutrients from fields. In a field that produced 240 bushels of corn in 2017 and 75 bushels of soybean in 2018, we calculate that harvested grain over the last two years removed 0.37 x 240 + 0.75 x 75 = 145 lb. P2O5 and 0.28 x 240 + 1.17 x 75 = 155 lb. K2O per acre. At current estimated retail prices of $520 per ton for DAP and $370 per ton for potash, the fertilizer to replace these amounts would cost about $123 per acre, not including the application cost.

The still-used “200-200” application (200 lb. DAP, or 92 lb. P2O5 and 200 lb. potash, or 120 lb. K2O) every other year was enough to keep soil test levels moving up when using such rates was common. That’s because yield levels were much lower than in recent years; Illinois corn and soybean yields from 1961 through 1979 averaged 96 and 31 bushels per acre, respectively. Having applied rates in many fields exceed removal for decades is why soil test levels are as high as they are in such fields today. But using that amount of fertilizer at today’s yield levels will mean a steady drop in soil test values as more nutrients are removed than are replaced.

Low crop prices often have some people wondering if they might cut back some on P and K in order to save money, presumably until crop prices are higher (or fertilizer prices are lower) in a year or two. Despite imaginative claims of “hidden hunger” and some overwrought interpretations of tissue testing levels, P and K deficiency symptoms are very rare in Illinois; we tend to see such symptoms when soils dry out after planting and roots have trouble growing into soils enough to take up adequate P and K, even when soil test levels are high. Such symptoms are more common in compacted soils and in no-till fields, but we hardly ever see such symptoms with spring rainfall is normal.

With adequate soil test levels of P and K in most fields and with crops that are good at extracting these nutrients, delaying the application of some or even all of the P or K for a year or even two years is likely to have little or no effect on the yield of the next crop(s). Still, nutrients removed by the most recent crops do need to be replaced, if not before the next crop or two then after that; higher soil test levels now provide more leeway. The real risk comes from allowing removal to exceed replacement over years, to the point where even good root systems can’t take up enough nutrients, and yields suffer. Reaching that point in most Illinois fields would take more than a year or two, but Illinois soils cannot generate enough P and K to meet the needs of high-yielding crops, so getting to that point is inevitable if the neglect continues. We can “kick the can” of nutrient replacement “down the road” for now, but that will mean having to replace ever-growing amounts of nutrients later, as grain, along with its nutrients, continues to come off the field every year.

Will the August 1 crop yield predictions hold up?

Illinois corn and soybean yields in 2018 were predicted in the August 1 NASS report (released on August 10) to be 205 and 65 bushels per acre, respectively, both an all-time record for this great state. Corn yields in the U.S. were predicted at 178.4 bushels per acre, a new all-time high, and for U.S. soybean the August 1 prediction was 51.6 bushels, which is very slightly below the 2016 U.S. yield.

Trying to guess which way and how far the yield numbers will move from predicted levels is a popular pastime, with a success rate probably similar to the success rate of amateur gamblers in Las Vegas. The August 1 estimate a year ago, in 2017, was for a corn yield of 188 and a soybean yield of 58 in Illinois. Neither crop had a great crop rating in 2017—both were around 60% good + excellent—and the August 1 estimates were widely considered at the time to be too high. Final yields were 201 bushels per acre for corn and 58 bushels for soybeans. This demonstrates that kernel and seed counts matter, and also that mediocre crop ratings can be neutralized by favorable conditions at the end of the season.

The high yield estimates in 2018 reflect high corn kernel and soybean seed counts, which were made on crops that were far ahead of normal development in many areas, including in Illinois. This should have resulted in more accurate counts this year compared to those made in years when seed numbers aren’t fixed until early August. That’s commonly the case in soybean, and less common in corn, though how many corn kernels will be retained can still be an issue in late July and early August.

So well actual yields (and the yield forecast for September) come in following the high levels forecast in August will depend on how grain filled under August conditions. There’s not much good news for those who would like yields to be lower. August rainfall was at or above normal over much of Illinois, with the exception of an area roughly east of I-39 from Bloomington to north of I-80, where rainfall was an inch or so less than normal. In this area, much of the rainfall came late in the month, and there was some damage (premature plant death) due to dry weather. Across the central and eastern Corn Belt, more areas received above-normal rainfall than below-normal rainfall, and in places the rainfall has been high to cause damage. In much of Minnesota and the Dakotas, though, less rain fell than normal, and this could lower yields.

August temperatures ranged from a degree or two above normal in the eastern Corn Belt, to a degree or two less than normal in the western Corn Belt; much of Illinois and Iowa had normal temperatures. Normal and below-normal temperatures helped extend the water supply in drier areas. But growing degree day accumulations remain far ahead of normal as the crop reaches or approaches maturity. Throughout Illinois, GDD accumulations from May 1 through September 2 were 300 to 400 ahead of normal, and hybrids of normal maturity planted in late April or early May accumulated enough GDD by the end of August to have reached black layer (physiological maturity.)

There was some corn planted late in states to the east, west, and north of Illinois, so there is still a small chance that kernels might not fill completely in parts of the Corn Belt. But there aren’t many ways to lose yield this late; even lodging (which does not appear to be an issue so far) does not increase harvest losses to a large extent, although it does slow harvesting. And even in areas where the crop was planted late, September is starting with good temperatures and adequate moisture in most areas–these should help the crop reach maturity without much problem. If this were late September, we would worry if the crop still needed a few hundred GDD to reach maturity; at the beginning of September, that’s not a big concern.

As of September 2, 36% of the Illinois corn crop was listed as mature. With temperatures high during the first week of September, this percentage could easily double by September 9. We can expect that those who wait the normal two weeks or so after maturity to begin harvest may find grain below 20% moisture. That could increase harvest losses some due to shelling at the header, but it will lower drying costs.

Soybeans are also “made” to a large extent in Illinois. By September 2, 49% of Illinois soybeans were listed as turning color, and 16% were dropping leaves. While there was no corn or soybean listed as harvested in the September 2 report, some combines were running in soybean fields on September 3 in Indiana just east of Danville, and I’ve had a few reports of both corn and soybean being harvested in parts of Illinois.

As is the case with corn, it’s hard to conjure up anything that represents a real threat to soybean yields now, at least in those fields that are already beginning to lose their green color. I have not heard any yields yet, but pod numbers once leaves drop are visibly high in many fields, and it appears that seed size will be at least normal. For both soybeans and corn, Illinois is to some extent the “garden spot” for soybean in 2018, compared to most other production regions in the U.S.

Some have noticed the modest decline in crop ratings for both corn and soybeans, and have wondered (or hoped) that this might mean lower yields than expected. Good + excellent ratings for corn in the U.S. are at about 68% now, above those of a year ago but less than those of 2014 and 2016. The fact that the crop is so far along this year means that recent (and small) changes in ratings don’t mean very much, in my opinion. In 2017, ratings began to climb only in late September after the crop was mature and as harvest got underway. These ratings were likely influenced by actual yields more than by the appearance of the crop.

Soybean ratings have also slipped a little over the past month, but they remain high, at 75% G+E in Illinois and about 66% for the U.S. As with corn, it’s likely that much of this is coming from the unexpectedly early start to maturity and loss of canopy color rather than to actual problems in the field.

As is always the case, we’ll have to wait for the combines to tell us what yields really are. In relative terms, soybean pod counts have been a little better than corn kernel counts this year, and some producers report that they expect soybeans to do relatively better than corn this year. Corn ears tend not to have the length that we have seen in some years, but kernel counts are high due to high ear counts, and so far I see no indication that kernels will be smaller than normal.

We’ve seen substantial numbers of both corn and soybean plants emerge following a rain after harvest in recent years, especially when grain moisture at harvest has been low. It only takes about 2 corn kernels and 4 soybean seeds per square foot to put a bushel of grain per acre on the ground rather than in the bin. Combine adjustments, including reel speed for soybeans and stripper plate adjustments for corn, can lower this loss some, but if corn is at 17-18% moisture or less and soybeans are at less than 10-11% moisture, losses can mount quickly. Harvesting corn in the afternoon and soybeans in the morning and evening might help some. Soybeans will take on moisture quickly enough to make this practical; corn moisture tends to go back up only during extended wet periods not form afternoon to evening like soybean.

I’ll be interested to hear some yields as harvest gets underway. The few that I’ve heard so far don’t provide much ammunition for those who hope lower yields will bring higher prices.


Corn disease updates

This week there has been a slight uptick in the amount of foliar disease reports in corn, likely as many people are actively scouting prior to making a fungicide application decision.  The most common disease, as you may expect is Grey leaf spot.  This disease is present to varying degrees in most fields.  No big surprise there.

We have seen and received several reports and samples of Diplodia leaf streak.  This disease can be caused by two different species of Diplodia, D. macrospora and D. maydis.  We have thusfar identified those samples where we were able to acquire spores as D. macrospora, but we have many more samples to assess.  Diplodia leaf streak can easily be misdiagnosed as Grey leaf spot, Northern corn leaf blight, or other foliar diseases and disorders.  Characteristic foliar symptoms include oblong, irregular lesions with green/yellow edges.  Occasionally, blocky lesions are observed.  Often “targets” can be seen in the lesions, where the initial infections occurred (Figure 1).   Older lesions contain black pycnidia, which resemble tiny pinheads or dots.  You will not see these in Grey leaf spot or Northern corn leaf blight lesions.

Diplodia infections can appear blocky. Sometimes targets can be observed within the lesions. Photo E. Alinger.


The other disease that we have started to look for more intensely is Southern rust.  Everyone should be familiar with this one, as it hammered parts of Illinois in 2016.  Remember, that year the corn was not as far along, and there was a period of persistent heavy rains throughout many parts of the state.  The disease likes it wet and warm, typically 80 F or more, and the earlier it arrives on a plant the more damage is can cause.  Thus, the need for spraying also is related to when it arrives in a given field (Table 1).  Remember, Southern rust does not overwinter here.  It needs to blow in every year from the south.  When stripe rust arrives early, (VT or earlier), and warm, wet weather occurs, severe epidemics can result.  If the disease arrives late (R3 or later) the amount of potential damage and yield impacts are reduced.  Under the correct conditions the Southern rust fungus reproduces rapidly, producing  spores that can infect new tissues or plants (Figure 2).

Table 1.  The amount of damage and yield impact due to stripe rust is related to the time of arrival on the crop. From Crop Protection Network

Through the Southern rust iPiPe map,  we can see where Southern rust is located, preventing it from sneaking up on us without notice.   The only item that is not included in the map is the incidence and severity of the Southern rust reports, which provide additional information for determining the risk of disease.  For example, a single leaf with a few Southern rust pustules  OR a field with severe Southern rust infestations result in the the county being turned red on the iPiPe map (Figure 4).  For this reason, it is important to stay on top of reports and scout when you notice Southern rust is nearby.

Figure 2.  The Southern Rust Life cycle. Photo Crop Protection Network

This year conditions have not been very conducive for Southern rust in the United States.  Until a few days ago, no reports of the disease were present.  Over the last week, more reports have occurred, and extremely low levels of the disease were detected yesterday and today in Franklin and Bond Counties in Illinois.  Most corn in those areas was well past R1 and close to R3 in many areas.  In both cases, the disease was only detected in a single field in each county and was extremely difficult to locate.

Figure 4 The Southern Rust iPiPe map as of 7/19. Red=detected. Green = scouted none detected. Yellow = suspected, not confirmed


Signs of Southern rust include pustules, typically somewhat bunched on the foliage, what often have a light brown to orange color.  Pustules are circular, and tend to be found mostly on the upper side of the leaf blade, and may be surrounded by chlorotic halos.  Occasionally you can find the fungus infecting stalks.  When you touch a pustule of Southern rust with your hand, you will notice it having a dusty, rusty appearance (hence the name rust).  Common rust, which is rarely impactful to corn production in Illinois, produces scattered, red to brown pustules.  Pustules are often somewhat elongated, and can be located on both sides of the leaf surface.  It is important to be able to distinguish Southern rust from Common rust due to their different potential impacts on crop yield.


Southern rust pustules are often circular, orange, and located on the upperside of the leaf. Note the halos surrounding the lesion. Photo N Kleczewski


Although Southern rust currently is not considered to be a significant threat to the corn crop, it is important to continue to scout, as changes in the environment could cause the situation to change.  If you think you may have found Southern rust, email me at or tag me on the picture on twitter @ILplantdoc with an indication of the severity (amount of pustules on leaves) and incidence (approximate number of plants with symptoms).  Additional information on this disease can be found on the Crop Protection Network.

Managing Japanese Beetles in Corn and Soybean

It is proving to be a big year for Japanese beetles in Illinois, and while populations should be starting to decline in much of the state, there is still a lot of feeding going on. The damage these insects cause can be eye-catching, especially on the edges of fields where Japanese beetles tend to congregate; however, before you decide to put out an insecticide, you want to be sure that decision is justified by the economics of the system. The economic threshold is the level of insect pests or damage at which a control should be implemented to prevent economic damage from occurring.

Japanese beetles captured using a sweep net in soybean.

Corn. Silk clipping by Japanese beetle feeding can impact pollination; however, this damage often appears worse than it is. The economic threshold for this damage is 3 or more beetles per ear with silks clipped to ½” or less while pollen shed is <50% complete. In many cases silk clipping is observed on ears that have already been pollinated, and if an insecticide is put out at that point it will only be good for “revenge.”

Soybean. The economic threshold for defoliation of soybean (whether caused by Japanese beetle and/or other defoliating species) is 30% defoliation prior to bloom and 20% after bloom, with the target insect still present in the field and actively feeding. Defoliation is easy to over-estimate, so be sure to train your eyes to get an accurate estimate.


Soybean defoliation caused by Japanese beetles ranging from 2-40% of the leaf area


If an insecticide is justified, initial control with a pyrethroid or carbamate insecticide is not difficult to achieve. However, be aware that the residual activity of these materials is short-lived. I have heard anecdotal reports of fields being sprayed multiple times for Japanese beetles – a frustrating situation given that the economic threshold was likely never reached. Scouting fields thoroughly and using economic thresholds to guide treatment decisions helps to ensure that these inputs are used only in situations where they are likely to provide a positive return on investment.


Dr. Nick Seiter

Research Assistant Professor, Field Crop Entomology

The 2018 Illinois Corn Crop at Mid-Season

The crop progress report from NASS showed that on July 1, 40 percent of the Illinois corn crop was silking, the crop rating was 85 percent good + excellent (G + E), and more than 85 percent of Illinois was reported as having adequate or surplus soil moisture. While this combination is very supportive of prospects for high yields, questions remain about whether the crop is actually as good as it looks, and about how dry weather in the coming weeks might affect crop prospects.

Do high crop ratings point to high yields? In a series of articles on Farmdoc, Scott Irwin and Todd Hubbs have pointed out that U.S. crop ratings become better predictors of final yield as the season progresses, with the highest correlation reached by about the third week of July. They also showed that when high early ratings drop, most of this drop tends to occur by the time the crop pollinates, which is normally in mid-July.

The largest drop in the Illinois corn ratings we have seen in recent decades was in 2012, when 79% G+E on May 20 dropped to 26% on July 1, and to 5% by the end of July. That was the year of the worst drought since 1988, and by July 1 of that year, only 10% of Illinois soils were judged as having adequate moisture.

In only one of the past five years did Illinois corn condition ratings drop between late May and mid-July; that was in 2015, when very wet June weather resulted in ratings going from the upper 70s in late May to the mid-50s by mid-July. In 2014 and 2016, ratings rose from the low 70s in late May to the lower 80s by mid-July, while in 2013 and 2017, ratings rose from the upper 50s to the mid-60s over the same period. With the help of the very low rating and low yield (105 bushels per acre) in 2012, correlation between mid-July rating and yield was fairly good over the past 6 years: yields were in the mid-170s in 2013 and 2015, and close to 200 the other three years. The most “out of line” year was 2017, when cool weather in August canceled out the mediocre crop ratings to give Illinois the highest average yield on record.

In the five years before 2012, early ratings were high only in 2007, and they stayed high that year. Ratings bounced around some in the other four years, and in 2011 went from the 60s in early June to 40% by August. But in none of the last 11 years did high ratings in late June or early July turn into low ratings by August, followed by low yields. So we have no precedent for expecting the crop rating to come crashing down this year, and for yields to be low. When we have had low yields, crop ratings at the time of pollination have usually predicted that this is going to happen. Nothing about the crop in 2018 suggests that this year will be different.

After a cool April, the weather turned warm in early May and has stayed warm ever since. As a result, growing degree day accumulation rates have been very high: GDD totals through the end of June were some 300 above average in Illinois, totaling about 1,200 since May 1 in northern Illinois, 1,400 in central Illinois, and 1,500 in southern Illinois. With about 1,400 GDD needed to reach pollination in most hybrids, the 40 percent figure for silking reported for July 1 was probably low, and by July 8 we should see silks on 75% or more of Illinois fields.

GDDs used to track corn development have 86 degrees as the cutoff, meaning that with the same night temperature, a daytime high temperature of 95 degrees produces the same GDD as a high of 86 degrees. This means that above-normal GDD accumulations during the summer result more from above-normal night temperatures than from high daytime temperatures. With night temperatures running in the 70s as July gets underway, we have been adding about 200 GDD per week. This will moderate some with slightly cooler temperatures forecast for July 6-8, but unless the temperature pattern turns consistently cooler soon, we are on pace to reach the 2,700 or so GDD required for mid-season hybrids to reach maturity by the third week of August in central Illinois: 1,400 GDD by July 1 plus 180 per week (a little higher than the average for July) means only about 7 more weeks to crop maturity. A couple of stretches of below-normal temperatures like we saw in 2017 would delay maturity, but would very likely add some yield. This weekend will be such a stretch, but a very modest one.

High temperatures have meant rapid crop development, and while the crop currently has good leaf color and is in good condition in most fields, will continued high temperatures cause problems and lower yields? Good plant height and good crop color now indicate that high temperatures have not been a problem so far. Sunshine amounts were above normal in most of Illinois in June, which helped boost growth. And periods of dry weather have resulted in good root growth, except where water has stood in wetter parts of the state.

This is a good time to remember that plants aren’t people – corn plants have no problem with high temperatures in the 90s, and they are more or less unaffected by what the “heat index” might be. Low temperatures in the 70s mean high dewpoints, which can mean wetter leaves in the morning and higher nighttime respiration, both of which are negatives. Good nitrogen uptake as gauged by leaf color (except where water has stood) and lots of sunshine have been positives, though, and on balance the crop condition and our eyes tell us that the 2018 corn crop is in great shape over most of Illinois.

The worry persists that rains will stop and that heat will build, causing rapid deterioration of the crop and stopping grainfill before maturity. We can’t rule this out, especially in the region with a radius of about 50 miles centered on Quincy, where June rainfall was less than normal. Elsewhere, the water in the soil now will, in fields with medium or heavier-textured soils, provide good protection against crop water shortages in the coming weeks. The crop coefficient, which is the percentage of evaporation that goes through the crop and out the leaves as water vapor, is at its maximum of about 80% at pollination. It will remain high for a few weeks before starting to decline.

Daily evaporation amounts on hot, sunny days are in the range of 0.25 to 0.3 inches, so crop water use (transpiration) on such days with the crop at full canopy like it is now is about 0.2 to 0.25 inches. A quarter acre-inch of water is about 6,750 gallons, so in one day each plant in a field with 35,000 plants per acre takes up and transpires about 3 pints of water. While we sometimes say that plants “lose” this amount of water, having the stomata wide open to allow water vapor to exit also means allowing maximum amounts of carbon dioxide into the leaf, where the carbon is used to make dry matter through the process of photosynthesis. Dry matter production can exceed 500 pounds per acre on a good day, so losing water means making yield.

Our deeper prairie soils hold as much as 8 to 9 inches of plant-available water within reach of healthy roots systems. That amount would supply the crop for a month of high-demand days. So unless there’s no rain at all over the next month, a lot of the Illinois corn crop already has enough water in the soil to set kernels in the coming weeks and to begin the filling process that will end with maturity.

While we know from experience that unexpected problems can come up that threaten to decrease yields, it’s hard to imagine having Illinois yields end up being below normal after the first half of the season we’ve had in 2018. Leaf diseases haven’t blown up in most fields, and as the crop moves past pollination and into grainfilling, the threat of disease outbreaks decreases. Insects such as corn rootworm adults and Japanese beetles will emerge too late to affect pollination. Weather threats like hail have occurred and will occur again, but the size of affected areas is normally small, and hail means rain, whose benefits usually exceed losses from hail over a wide area. With a crop that should be mature by early September, frost is a non-issue. Finally, the fact that it has rained in places in the last few days means that the pattern has not yet turned as dry as some feared that it might.

As is always the case, we will know the potential for yield once we can count developing kernels, by the third week of July in the early-pollinating fields. We won’t reiterate the process here, but it’s a simple one: ear number per acre x kernel number per ear gives kernels per acre. If that number is 16 to 20 million, good yields will likely follow.

Illinois to host crop sciences field day near Monmouth in July

MONMOUTH, Ill. – The Northwestern Illinois Agricultural Research and Demonstration Center near Monmouth has scheduled a field day for July 18. University of Illinois crop sciences faculty, researchers, students, and Extension specialists will address issues pertinent to the 2018 growing season.

The program will begin promptly at 8 a.m. on Wednesday, July 18, and is open to the public at no cost.

Weather permitting, presentations will take place outside next to research plots. Participants will board buses to tour portions of the farm.

Field day topics include:

  • A chip off the ole block: What kind of woodchips are best for a woodchip bioreactor? – Presented by Hannah Dougherty, Niranga Wickramarathne, and Laura Christianson
  • Insect management in corn and soybean – Presented by Nick Seiter
  • Damage from above and below: Managing SCN and white mold in soybeans – Presented by Nathan Kleczewski
  • 2018 Weed Control Update – Presented by Doug Maxwell and Charlie Mitsdarfer

Certified Crop Advisors may earn two continuing education units (0.5 – SW, 1.5 – IPM).

The Northwestern Illinois Agricultural Research and Demonstration Center is a 320-acre facility, established in 1980. The center is located 1 mile north and 4 miles west of Monmouth at 321 210th Avenue. Each year, more than 40 projects are conducted by campus-based project leaders and the center superintendent.

Please contact Greg Steckel (309-734-7459, ) if you have any questions about the field day.

Crop conditions and potential in mid-June

Warm temperatures continue in Illinois, with growing degree day (GDD) accumulations since May 1 running from 150 above average in northern Illinois to about 250 GDD above average in the rest of the state. With GDD accumulations of 900 to 1,000 since May 1, the corn crop planted in early May is at V10 to V14, about 30 to 60 inches tall, and needing only about 350 to 450 more GDD to tassel and silking. With daily accumulations at about 25 GDD, much of the crop will be showing tassels and silks by the end of June and first days of July.

The corn crop condition ratings as of June 10 were 83% good + excellent, one of the highest early-season ratings we’ve ever had. In most fields, the crop looks outstanding, with probably the best stands we’ve ever had, and in most cases very good crop canopy development and color. On the other hand, plants are showing leaf curling in the afternoon in some areas, indicating that the water supply in the soil is not high enough to sustain maximum rates of photosynthesis now.

A lot of the rain over the past month has been from thunderstorms rather than broad movement of fronts; as a result, its distribution has been very uneven. During the first half of June, rainfall ranged from less than a half inch in parts of western and southwestern Illinois to more than six inches in southeastern Illinois. Even in those areas showing average or above-average rainfall, there are places that the storms missed, and where soil water is starting to run short. The US drought monitor shows “abnormally dry” conditions in several western Illinois counties, and in a small pocket in northeastern Illinois.

While the well-watered areas with deep soils have enough soil water now to get the crop through pollination, normal to below-normal temperatures will assure that the crop has high potential to set the kernel numbers needed for high yields. In areas where plants are showing stress in the afternoon now, we expect that this will set in a little earlier, and last a little longer, each day that temperatures remain high and there’s no rainfall. Canopy development is good so far, but a good canopy also means faster water usage, and a crop that’s head-high has a “crop coefficient” (the proportion of evaporation that the crop takes up) of about 0.7. This value reaches a maximum of about 0.8 at full crop canopy.

That means that if evaporation (also called “potential evapotranspiration” or PET) on a warm, sunny day is 0.25 inches – PET has been high as 0.3 inches on the warmest days in Illinois in recent weeks – the crop takes up 0.25 x 0.7 = 0.18 inches of water. Our best soils can store as much as 10 to 12 inches of plant-available water in the top three feet, so at field capacity the water supply can last six weeks or more without rainfall. That’s under ideal conditions, though – the crop will often show stress effects before the soil water is completely depleted. It’s been dry enough in parts of Illinois that the soil water supply is not enough to keep the crop well-supplied now.

As pollination approaches, the effect of water stress on the crop will increase. If it rained everywhere today, the crop could probably recover its full yield potential in most fields. But if leaf rolling starts by noon, the crop is producing less than half the normal amount of sugars through photosynthesis on that day, and the closer the crop gets to pollination the larger the effect of lost sugars will be. Today’s hybrids are bred to produce silks, pollen, and some fertilized kernels under stress conditions, but if it stays dry over the next weeks where the crop is already showing stress, kernel numbers will be lowered. Lower kernel numbers mean lower yield potential.

Corn plants that develop under high temperatures and with plenty of water tend to be taller than usual. In areas where the crop has been showing stress symptoms in the past week or two, though, we can expect plants to end up shorter than normal. Any water stress during rapid stem elongation – between V8 and tasseling – results in less elongation of cells in those internodes that are expanding during that time, and this results in shortened internodes and plants. As we saw in 2017, shorter plants can still yield very well, but that requires that they get adequate water by a week or so before tasseling to assure that the pollination process can proceed normally.

On a more positive note, the benefits of relatively dry weather include the development of good root systems, a good supply of soil nitrogen, and little development of diseases. The dark green leaf color shows that the N supply has been adequate. Where it has rained the soils have not stayed wet except in low-lying areas, and so there has been little potential for N loss. Some rains have been so intense that much of the water runs off, and dry period before the rain meant that the soils could take in several inches of water before they became saturated. Where water has stood or is standing now in fields, though, we can expect both some root damage and some denitrification, with the potential of considerable yield loss in those areas. Fortunately, this area is not as large in size as it’s been in some recent years.

By now the question of whether the corn crop needs more N to follow normal rates applied earlier should be answered: the deep green leaf color of the crop means that it’s not likely to run out of N so well-supplied with N as shown by its canopy color, there’s almost no chance that it will need more N than is on the soil now. Our N-tracking results from this spring confirm what the crop is telling us – that it has plenty of N. Those who put on a normal amount early with the idea that they’d come back to apply more if the yield potential looks good can skip the additional application this year.

The Illinois soybean crop in mid-June has the same high crop condition rating as the corn crop. Stands are good in most fields, and plants have begun to develop rapidly, after the usual lag that we often see, which in some cases might have been lengthened by application of certain herbicides. In a planting date study we have here at Urbana, early varieties planted on April 25 are at V6-V7 and 15-18 inches tall, with a lot of flowers now. As is the case in corn, canopy health is very good. Growth so far has been good even in dry areas, because soybean plants don’t use water very fast when they’re small so more water remains in the soil.

We see flowers appear before the longest day of the year when soybeans are planted relatively early, and when temperatures are warm in June. The appearance of flowers requires a certain night length, and if it takes 10 days after the longest day (June 21) to reach that night length, then that night length also occurs 10 days before June 21. But if plants aren’t past stage V3 or if nights are relatively cool, soybean plants won’t flower before the summer solstice. Even when they do flower in mid-June, limited numbers of flowers might turn into pods. We will need a lot of flowers appearing after June 21 along with good growing conditions in order to set the number of pods needed for high yields.

Our best hope now is for a return to normal temperatures and rainfall by July to get both corn and soybeans on the way to reaching their current potential for high yields. Little potential has been lost so far, but the next weeks will spell the difference between average and very good crops.

A fast start for the 2018 crop

We worried our way through the cool month of April, with 32 percent of corn and only 7 percent of soybean acres planted by April 29, and nothing emerged. During the first two weeks of May, the weather was warmer and drier than normal, and adding together corn and soybeans, Illinois farmers planted more than a million acres for each of the 10.3 “days suitable for fieldwork” between April 29 and May 13.

By May 13, 90 percent of the corn was planted and 63 percent had emerged; the numbers for soybean were 66 percent planted and 24 percent. The soybean stands I’ve seen so far are good, and corn stands are truly outstanding – among the best we’ve seen in Illinois. Warm temperatures brought the crop up quickly and uniformly, and one would have needed a stopwatch to find differences in emergence time between plants down the row this year. If, as some like to claim, uniform emergence is the key to high yields, we’re in for a great year.

Cool soils dry slowly, and soils did not have enough time to dry out very much between tillage and planting this year, even with warm and windy conditions. This helped fields emerge quickly and uniformly despite lack of rain. The once-upon-a-time worry that soils will dry out fast enough to delay emergence is almost a thing of the past due to fewer tillage trips, less time between tillage and planting, and better seed placement by today’s planters.

Temperatures have been above average every day in May so far, with an average of more than 18 GDD per day accumulating in Illinois. The average under normal temperatures is only about 12 GDD per day for the first half of May. So corn planted on May 1, that would normally take 10-11 days to accumulate the 115 or so GDD needed to emerge, took less than a week to emerge this year. That temperature trend continues, and we’re on track to reach about 600 GDD for the month of May. That will have most corn fields at the V5-V6 stage by the end of May, ready to begin rapid growth. If June brings the normal 650 to 700 GDD, we’ll see tassels and silks in many fields before the July 4 fireworks.

Some might have noticed that the 5-year averages used as the basis for comparing this year’s planting and crop development progress seem to have changed since last year. That’s because the past five years (2013-17) no longer include 2012, which was the year with the earliest planting on record, followed by rapid crop development, but also drought and low yields. So we can expect to be ahead of average a little more often over the next few years.

High-Crown Syndrome?

Warm weather after planting can increase the potential for so-called “high-crown syndrome” in corn. We think this comes from having the coleoptile (the pointed structure we see when the corn is “spiking through”) growing so quickly that it grows above the soil surface before the coleoptile gets the signal – from sunlight striking its tip – to stop growing. It might even make a difference if emergence begins near the end of the day and the night is warm, in which case the tip of the coleoptile might be a half inch or more above the soil surface by the time sunlight hits it the next morning.

When the coleoptile stops growing, the crown (the base of the stem) establishes about an inch below the tip of the coleoptile. Normally, the tip of the coleoptile may be an eighth to a quarter of an inch above the soil surface, and the crown sets at least three-quarters of an inch below the soil surface. If the coleoptile tip is a half inch above the soil surface instead, the crown may set only a half inch deep – the “high-crown syndrome.” I have not heard of any of this in 2018 so far, but the temperatures have been favorable for its development, and it’s not something we see unless we look for it.

The major concern when the crown is shallow is the possibility that the nodal roots, which originate at the crown, might be unable to grow out into the bulk soil soon enough to provide water, nutrients, and support for plant growth. If the surface soil is very dry and loose, or a no-till furrow remains open with dry, hard surfaces, nodal roots can struggle, or even fail entirely, to grow; the result can be “rootless” corn. Plants may stay alive to stage V4 or V5 with just the seminal root system that grows from the seed at germination, but they need a nodal root system – the “permanent” root system – in order to continue to grow. In the worst cases, plants without nodal roots fall over and can detach from their roots and die.

I don’t want to raise an alarm about the potential for high crown placement this year – we’ve more often anticipated this problem than we’ve actually seen it. Enough rain that comes early enough to get the nodal roots to take hold and start growing will often mean no noticeable yield loss from this. Short of replanting, which no one wants to (or probably should) consider with a near-perfect stand, rain to get the roots growing is the only cure. Today’s fast-growing hybrids can do the rest.


One question I’ve heard a few times in recent weeks is whether there’s any need to worry about how much nitrogen remains in the soil as the crop approaches the stage of rapid N uptake. With below-normal rainfall in April and so far in May, and below-normal temperatures in April, and no extended winter thaw, we think that N that was properly applied anytime since last fall should be present. The only wet period we’ve really had in Illinois was odd mid-February system that dropped 5 inches or more in places, but that was during a time of cool soils and water did not stand very long.

Samples taken over recent weeks confirm that the applied N is still there, and also hint that mineralization began early, as we’d expect given the conditions this year. According to data from the WARM network of the Illinois State Water Survey, current soil moisture at the 4-inch depth is in the mid-20s (% of soil that’s water – less that 20% is starting to get dry, more than 35% is wet) over much of the state except for the northern and southern ends of Illinois, which are wet. Soil temperatures at 4 inches are in the upper 60s to lower 70s, well above normal for mid-May.

An early start to mineralization and lack of saturated soils are indicators that roots starting to develop on corn seedlings should get early (and easy) access to N in the soil. There will still be some lag in leaf color as growth gets underway, but if the sun shines and temperatures stay warm, we should see the leaves start to darken by the time plants have 4 or 5 leaf collars visible. And when the supply of N from the soil is good, that usually means good root growth and good supplies of other nutrients as well.