Seedling disease is running rampant across Illinois soybeans. Many producers are wondering why. Afterall, you used a fungicide treatment. Well, there are many things that could be at play. I describe these in this weeks Field Crop Disease Blog (click here). Remember to sign up for updates!
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.
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.
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.
Black cutworm moth flights continue across much of Illinois. Several counties reported second -and even third- significant moth flights (Madison, Champaign, and Lee). Several counties had near significant flights (Piatt and Coles). It is important to remember that lack of a reported significant flight and subsequent projected cutting dates does not take black cutworm out of the equation in your area. I have had reported of 1st-2nd instar feeding and even a report of 3rd-4th instar cutting in a couple areas of the state. These reports have been isolated, and under recommended thresholds for rescue treatments.
While spring storms and southern winds brought black cutworm moths to many areas of Illinois, that is not the case for true armyworm. Trap counts remained low across the state for a second week in a row.
Weekly Moth Total
(May 5-May 11)
|Northern (Lee County)||2|
|West Central (Warren County)||4|
|East Central (Champaign County)||5|
We remain several weeks from corn rootworm hatch in Illinois. Soil temperatures are warm and degree-day accumulations reflect totals that are slightly ahead of the historical average. We will continue to monitor degree-days and egg hatch.
No reports of alfalfa weevil feeding have made their way to the office this week, but varying life stages are possible across the state. A quick refresher on biology, injury and management can be found on the alfalfa weevil factsheet.
While we won’t begin trapping for corn earworm for a couple of weeks, Purdue University reports the first 2018 moth catch of the year in Indiana. At this time of year, the catch has little significance on field crops, but is a reminder that spring is truly here and we will be transitioning for our early season insect pests to summer insect pests soon.
Spring insect activity is off to a slow start, but is expected to pick up with the recent warming trend.
Piatt, Madison, Montgomery, and Sangamon counties all recorded significant moth flights this week. Projected potential cutting dates are identified in the map below. Remember, these dates are just estimates, scouting should occur before and after the potential cutting dates.
True armyworm numbers have been very low. Armyworm traps are just getting going, so reports for this week are broken down into a general area of the state.
Matt Montgomery, Pioneer, reported alfalfa weevil activity in Shelby county this week. Degree-day accumulations indicate that early instar alfalfa weevils may be present in the southern third of the state. Injury may consist of pinhole size feeding on the leaves.
We have published the 2018 small grain fungicide recommendation guide. Please find a link to the guide and more information at the Illinois Field Crop Disease blog, which can be accessed by clicking here
Email alerts to new posts on the Illinois Field Crop Disease Blog can be found by subscribing for updates, which is located at the right side of the webpage.
Parts of Illinois received some precipitation for the third Sunday in a row (starting with Easter) on April 15, and in a few places, also for the third Sunday in a row, it came partly in the form of snow. That streak should end this weekend, and less rain and warmer temperatures are predicted to move in for the rest of April.
Some ammonia went on late last week and there was planting activity in places, but NASS reported no (meaning less than 1 percent) of the corn or soybean crop planted by April 15. It rained again over much of Illinois on April 13 to 15, and cool temperatures and slow drying of soils continue to delay the start of planting.
One concern when corn is planted into cool soils is the uptake of cold water as germination begins. When the first water moving into a dry seed is at a temperature below the mid-40s, “imbibitional chilling injury” (ICI) can result. Rain and lower air temperatures that followed planting in some fields on April 13 or 14, such injury is a possibility. We expect to see such damage more often than we actually see it, but low-moisture seed takes up (cold) water quickly, and moisture of planted seed planting might influence the amount of damage. If seed has a chance to take up warmer water before cold rain comes, such damage will probably no occur. Cold water makes membranes in the seed more brittle, and can cause cell death.
ICI damage usually shows up as abnormal seedling growth, often with “corkscrew” roots and shoots. The practical effect of this is that it lowers emergence. Unlike death of seeds from lack of oxygen, which was widespread following heavy rainfall after planting in 2017, ICI symptoms aren’t necessarily more common in low-lying parts of a field. There’s no fix for ICI – if it lowers stands enough, replanting may be necessary. But if affected seedlings are able to emerge, they may develop normally.
Almost every year in some part of Illinois, corn is planted into good soil conditions, but then it rains and turns colder, causing emergence problems. People tend to remember this as a “window” during which they should have held off planting until the forecast was more favorable. Such hindsight is usually good, but it’s rarely the case that the forecast is so accurate that waiting to plant, at least after the third week of April, turns out to be the best decision.
At the same time, as long as soil and air temperatures remain cool, the early-planting advantage will be smaller than usual this year. It takes about 115 growing degree days from planting to corn emergence. Fewer than half that many GDD have accumulated since April 1 in most of Illinois, and with daily accumulations in single digits this week (a low of 50 or less and a high of 60 degrees provides only 5 GDD), planted corn isn’t growing a lot faster than corn seed still stored in the shed.
While cool temperatures have slowed surface drying, April rainfall, with the exception of a number of counties in east central Illinois, has been at or below normal to date. That has allowed excess water to move out of surface soils, and once the weather starts to warm, the surface soil will start to dry and conditions for planting will improve quickly. We need to wait until the seedbed is in good condition, but if predictions hold, we could see planting begin by this weekend, and accelerate next week. There’s no great advantage to planting on April 30 instead of May 1, but a strong start to planting as April ends will do a lot to restore our hopes that the 2018 season will be a good one.
If we can plant either corn or soybean, next week, which crop do we start with? If two planters can run at the same time, “both” would be a good answer. If it has to be one or the other, I’d still give a small edge to corn, only because it can emerge a little more consistently than soybeans if plant into cool soils. If we don’t get heavy rainfall before emergence, though, both crops should get off to a good, albeit somewhat delayed, start.
Since my article last week in which I mentioned that some people had planted soybeans very early (mostly in mid-March) this year, I’ve received several more reports, some indicating that hundreds of acres of soybeans were planted that early. If any of those fields establish good stands, please let me know and we can record this as the miracle it would be. I also saw in the recent newsletter from the Illinois Crop Improvement Association that both warm and cold germination percentages of soybean seed are not as high this year as they were last year.
If soybean planting (and replanting) is into cool soils, it might be worthwhile to bump up seeding rates to account for the possibility of lower germination. If you know the cold score, you might consider dividing the desired plant population (say 115,000 per acre) by the cold score minus 5 points to give seeding rate; as an example, if the cold score is 85%, divide 115,000 by 0.85 – 0.05 = 0.8 to give a seeding rate of about 144,000. If a cold score isn’t available, divide by warm germination minus 10 instead. If planting into warm soils, divide by the warm germination minus 5 points to make the adjustment.
Last month (March 2018) we used data from 2017 N rate response trials to update the N rate calculator that provides best-estimate N rate guidelines for different regions and previous crops (corn or soybean) in Illinois. The updating process, which is currently being done by spring each year in Illinois, involves adding the new data and taking out some of the older data.
Many people understand the idea of using data from previous research to try to predict how a management factor will work the next time (in this case, in fields in 2018) – after all, that’s what applied research is all about. But responses to N are highly variable across even nearby fields within a year, and that can make it difficult to place a lot of confidence in the results as a predictor of what will happen the next year. Which N response curve from last year would we expect to do the best job of telling us how much N to use this year?
Let’s use the data from Illinois trials in which corn followed soybean in 2017 to illustrate this. These data (shown in Figure 1) represent a large amount of work; many of these trials were done on farmer fields, organized and conducted by Dan Schaefer of the Illinois Fertilizer & Chemical Association, and some are done within our N research projects at University of Illinois sites. Both IFCA’s and my research projects are supported by the fertilizer checkoff, administered by the Illinois Nutrient Research & Education Council.
In order to show actual corn yields at different N rates, Figure 1 has straight lines connecting the yields, each of which is an average over three or four reps at each N rate. To work with the data, we have the computer calculate a “best-fit” line for each set of data, and the equation for this line produces a smooth curve. That equation is also used to calculate what N rate is required to maximize yield, and what that yield is. We can’t possibly hope to set N rates so that one of them is the “best” rate – we have to produce the shape of the response defined by the actual data points, then work with that.
Each set of N response data shown in Figure 1 has two symbols associated with it. One is a yellow triangle that marks the N rate – and yield at that rate – where the last pound of N produced just enough additional yield to pay for that pound of N. We call this rate the “economic optimum N rate” or EONR. As a default, we often set the cost of 10 pounds of N as equal to the price of one bushel of corn – for example, N might be $0.40 per pound and corn $4.00 per bushel. In that case the EONR is the N rate at which the last pound of N produces a tenth of a bushel of yield. Above that N rate, the cost of added N is not covered by the additional yield; below that rate, each pound of N adds more yield than it takes to cover its cost. In both cases, the return to N is less than it is at the EONR.
Each set of response data also has a green circle (like the EONR triangles, many of these are not exactly on the line because the lines aren’t the fitted curves) that gives the “maximum return to N” (MRTN) N rate calculated by the N rate calculator (the 2017 version, which ran using data through 2016), and the yield at that N rate for that response curve. There are three vertical arrays of the green circles, each corresponding to the Illinois region in which the trials were conducted; MRTN values produced by the N rate calculator decrease from the north (those on the left) to central (middle set of circles) to southern (circles on the right) regions of Illinois for corn following soybean. The green circle shows how well using the MRTN rate would have done in that field in 2017 compared to what we now know (because we had an N rate trial there) was the actual best rate (the EONR, shown by the yellow triangle) in that field in 2017.
At first glance, the fact that the EONR values (yellow triangles) on Figure 1 are so spread out, and that most of them are not very close to the green circle on the same curve, looks like the MRTN rate failed to predict the best N rate for that field in 2017. Of the 51 sites, the actual EONR is to the right of the green circle – that is, the MRTN rate wasn’t high enough – at 21 sites. At the other 30 sites, the MRTN rate was higher than the actual EONR – the yellow triangles are to the left of the green circles. Across all 51 trials, the average MRTN was 172 pounds N per acre, and the average EONR was about 168 pounds N per acre – the difference was only 4 pounds of N. The average yield at the MRTN rate was 226 bushels per acre, and at the EONR was 229 bushels per acre, or 3 bushels more. Using N and corn prices of $0.35 per pound and $3.50 per bushel, using the EONR (which, of course, we couldn’t have known before the season) in each field would have returned about $12.50 per acre more than using the MRTN rate in each field. The two sites with the highest EONR values (those farthest right in Figure 1) by themselves added almost 4 pounds to the average EONR value and almost $3 to the higher return from using the EONR. Though we seldom see such high EONR values, we leave them in the database because they represent possible (future) outcomes, and we can’t justify leaving them out.
Focusing on the yellow triangles in Figure 1 makes clear what we discovered some years ago – that there is no correlation between EONR and the yield at the EONR across a set of N response trials. In fact, a trendline drawn through the EONR values slopes down slightly, meaning that across this set of trials, higher yields needed a little less N than lower yields. The only explanation for this that makes sense is that moisture and temperature conditions that resulted in high yields also increased the amount of N provided by mineralization of sol organic matter, and may also have increased the ability of the roots to get access to that N. At the extremes, in one trial the yield was 278 bushels at 101 pounds of N, and in another the yield was 203 bushels at 226 pounds of fertilizer N. We estimate that corn needs to take up about one pound of N for each bushel it yields. If so, fertilizer provided only 101/278 = 36 percent of the N needed in the first trial, but 226/203 = 111% of the N needed in the second trial.
Even though on average the MRTN performed well in 2017, it clearly did not do so in every trial field, or even in most of these fields. This points out a fundamental difficulty that dogs every attempt to predict “best” N rates for a field or for different parts of a field: nothing we have been able to measure predicts with any accuracy how much N from fertilizer a given field will need at the start of a given season. With yield goal as a basis for N need pretty much sidelined by the finding that higher yields don’t need more N than lower yields, and with both yields and N responses highly influenced by (unpredictable) weather, what can we use to predict how much fertilizer N a field will need?
One such possibility is a way to predict how much N will come from mineralization of soil organic N, which by subtraction could help estimate how much fertilizer might be needed in a field. Another is a way to estimate how much N is lost due to unfavorably wet weather before the plant has a chance to take it up. These attempts have so far not been very successful; we still don’t have a way to know, in May or June, whether the crop in a field needs 120 pounds of N or twice that much to produce the yield it will produce this season. Our best guess today is the MRTN, perhaps tweaked up or down depending on circumstances. Each MRTN value has a range of about 15 pounds of N on either side over which we expect return to N to be very close (within $1 per acre) of the return at the MRTN.
Updating the N rate calculator with recent data and dropping out some older data doesn’t change its output by very much in Illinois, because we have so much data already there: there are 267 N responses for corn following soybean in the database for central Illinois alone. The update this spring added about 3 pounds of N to most MRTN values using current N and corn prices. At $500 per ton of ammonia and with corn at $3.85, the MRTN for corn following soybean in central Illinois is 183 pounds per acre. That rate is expected to produce 99% of maximum yield; by definition, the optimum N rate never produces maximum yield because the last N has to pay for itself, and only if N were free would that be at the rate needed to produce maximum yield. The range over which the return to N would be expected to be within one dollar per acre of the maximum is 168 to 200 pounds of N per acre.
Other numbers produced by the calculator include the cost of N at the MRTN ($54.90/acre), the amount of material needed (223 pounds of ammonia), and the net return to N at the MRTN ($314.62 per acre.) Note that the calculator subtracts the yield without N from each N response – the return to N is only the yield added by fertilizer N times the corn price minus the MRTN N rate times the price of N. With the N cost of $54.90 per acre and the gross return of $314.62 + $54.90 = $369.52, we can calculate that this amount of N increased yield by $369.50/acre ÷ $3.80/bushel = 97 bushels per acre. The “true” nitrogen use efficiency (NUE) is the MRTN divided by the amount of yield added by N, or in this case 183 lb. N/acre ÷ 97 bushels/acre = 1.9 pounds of N for each bushel added from using N fertilizer. We often just divide N rate by yield for a field because we can’t know what the yield was without N, so when yields are high and N rates reasonable, we typically have NUE values of only 0.7 or 0.8 lb. N per bushel. That’s helpful in that it helps us see that we don’t need such high N rates to get high yields. But it includes the N supplied by the soil, not just that added as fertilizer.
I received notice of stripe rust in S. Illinois today. Stripe rust is an important disease affecting wheat. Please find an article on this disease and management by clicking here.
If you locate stripe rust in your field please tweet a picture to me (@ILplantdoc) or email (firstname.lastname@example.org) with the wheat variety, growth stage, and approximate percent of field infected. This information will be useful to IL wheat producers this year and in upcoming seasons.
If the old saying that rain on Easter means that it will rain on the next seven Sundays applies to snow, we’re in trouble – it snowed across a wide swath of Illinois on Easter Sunday (April 1) and also on April 8.
We had enough dry weather in March to allow some ammonia to go on early, but there has been little opportunity for field work over the last six weeks. Rainfall over the past month has been below normal for the northern third of Illinois and above-normal in the southern half of the state, especially along I-70. Even though it’s not sopping wet in many areas, below-normal temperatures in recent weeks means very slow drying of soils. While we know that conditions can change quickly – even as I write this the forecast has improved for the rest of this week – it’s clear that the spring of 2018 is not going to be one that allows a very early start for field operations.
Soybean following soybean
With soybean acreage in Illinois expected to increase some and corn acreage to fall this year, some soybeans in 2018 will follow soybeans. As I’ve written before, there is no particular concern in planting soybeans after soybeans, except perhaps to avoid doing this if soybean cyst nematode egg counts are high. We have no reason to expect that SCN counts are unusually high, but if this will be the third year of soybean in the same field or if there was any hint of SCN damage in the 2017 crop, it might be worth taking a count yet this spring. SCN-resistant varieties are a must in any case.
The yield penalty for soybeans that follow soybeans instead of corn varies some by site and year, but most of our research shows this penalty to be modest, usually less than 10%. Averaged over three trial sites and two years (2016 and 2017), soybean following: 1) continuous corn yielded 76.9 bushels per acre; 2) two years of corn yielded 71.4 bushels; 3) one year of corn yielded 69.2 bushels, and; one year of soybean yielded 68.0 bushels per acre. In 2017 we had soybean following two years of soybean, and averaged over three sites, these yielded about 2.5 bushels less than those following one year of soybean.
In two long-running studies in western Illinois, tillage has had either no effect on yield of soybean following soybean, or has decreased yield. If the soybean stubble was not tilled last fall, it would probably be better to plant soybeans without tillage this spring. We did see a slow start to no-till soybeans under the cool, wet conditions of 2015, and at the Monmouth site that year, no-till soybeans following soybeans yielded 5 bushels less than tilled. This differences was even larger in soybean following corn that year. Soybean following corn tends to yield a little more when tilled than with no-till, in fact, though the difference averaged over years is not enough to pay for tillage operations.
Other than normal scouting for disease and weed management, though, there are few other management considerations specific to growing soybeans after soybeans.
Cover crop management
Cereal rye planted into corn stalks last fall has made much less growth than normal, especially in comparison to 2017, when February temperature averaged nearly 10 degrees warmer than in 2018 and the cover crop grew for a couple of months before April. The slow growth this year will continue as long as soil temperatures remain in the upper 30s to low 40s as they are now. But rye is a cool-season crop, and will start to grow rapidly once it warms up.
Conditions have not been good to kill the cover crop with herbicide, so slow growth may be preferable to rapid growth for now. But a choice will need to be made in the coming weeks about how long to let the rye grow before spraying to kill it. We want enough growth to produce the benefits for which we planted the cover crop, but we also need to manage it so it doesn’t interfere with soybean establishment. If soybean seed can be placed into soil well, this shouldn’t be a big concern. But as long as the weather and soils stay cool, soils will dry slowly, especially once the rye is killed and is no longer taking up water. Lower amounts of residue due to slow growth will help some, but soybean seed placement and crop emergence could still be a challenge, especially if soils continue to dry slowly or the weather turns wetter. Clearing residue off the row will help, if that’s an option.
In the spring of 2017, soil conditions and temperatures were so favorable early that some people planted a “test” area of soybeans in February to see how they’d do. They did well – soybean are quite tolerant of frost as long as they haven’t emerged yet or have emerged and their “neck” has straightened out to bring leaves and cotyledons to the horizontal. So the period in mid-March with temperatures in the 20s last year didn’t kill the crop, and some of these soybeans yielded as much as those planted in late April.
This year, soils in some areas were dry enough to plant by mid-March, and some people again planted soybean then. [Some corn got planted as well, but that no longer attracts the attention that super-early soybean planting does.] Conditions since have been much less favorable than they were a year ago, and this has kept the early-planted crop from emerging, at least in most fields. Only about 30 growing degree days (base 50) have accumulated over the past month at Champaign – that’s maybe a fourth of the number of GDD needed for the crop to emerge. It will be surprising if soybean seed that has been in cold, wet soils for the past month is still viable, but we won’t know for sure until soils warm up. For the curious, digging up seeds and putting them in a damp paper towel in a warm room for a few days will show whether they’re still alive. Even if they’re alive there’s no guarantee that they’ll be able to emerge and become healthy plants.
Lost in the attention given to the survival of soybeans planted very early is the question about such early planting – provided the crop survives – affects soybean yield. Given how rare it is that soybeans can be planted by or before mid-March, we have not done trials on this. We mostly have anecdotes, and those may be skewed towards those times when the crop survived. We have seen a few cases, especially in the very dry spring of 2012, when planting in early April was followed by stressful (cool or dry) conditions that limited plant height and yield compared to soybeans planted later. Even if soil conditions allow a March-planted crop to emerge, there is virtually no chance that it will yield more than a crop planted in the same field in late April, and some chance (if it survives) that it will yield less.
Overall, our data across 26 soybean planting date trials show that soybeans produce full yield if planted anytime between the second week of April and the end of April. The rate of yield loss with planting delay accelerates into May, reaching about 2/10ths of a bushel per day by the end of the first week of May, a quarter of a bushel per day by mid-May, a third of a bushel by the end of May, and 4/10ths of a bushel per day by June 10. These are lower loss rates than we often see presented elsewhere, most of which are based on a limited number of trials. That doesn’t mean we shouldn’t try to plant as early as we can to get full yields, but it does show what most farmers know from experience – that high soybean yields depend more on what happens during the season than on when the crop gets planted, although planting by mid-May increases the chance that the crop will be able to respond to favorable conditions later. A corollary to that observation is that planting soybean into poor soil conditions just to get them planted early can decrease the ability of the crop to respond to favorable conditions later, and thereby end up costing yield.
While 100,000 or even fewer plants per acre will maximize yield in many cases, our research shows that this is not always enough plants. Trying to minimize the seeding rate can end up costing yield and losing money, especially in those cases when emergence and stand establishment are lowered by conditions at or after planting. While responses to plant stand do vary across trials, we have found that 115,000 to 120,000 plants (not seeds) per acre are often needed to produce the highest dollar return on the seed investment. If we plant good seed into good conditions we can expect 85% stand establishment, in which case we should plant about 140,000 seeds per acre, which for most seed companies today is one unit of seed.
Despite that fact that most trials in Corn Belt states in recent years – including our trials in Illinois – have shown little or no yield increase from applications of 45 to 90 pounds of N (100 to 200 pounds of urea) during the growing season, this practice continues to draw a lot of interest. In a set of trials we just finished, applying 45 or 100 pounds of N at planting time produced large increases in yield two years in a row on an irrigated loam soil near the Illinois River at Chillicothe, Illinois. Planting-time N had no effect on yield in most other trials in heavier, higher-organic-matter soils. We did find yield increases in a number of trials when we applied the same amount of N four different times, from planting through early podfilling. While repeated use of N may help explain some “contest” yields, the yield increase from four applications was not enough to pay even half the cost of these applications. Putting that much N on also means a lot of N left in the soil at the end of the season, so more N loss through tile.
With so many voices today claiming that N application on soybean “can” increase yield and others saying that it still won’t increase profits, what should producers do? In an ideal world, 500 Illinois farmers would put out a set of N strips (next to strips without N) in a field or two each year, and results would be brought together to produce data-backed expectations of how profitable this practice is on different soil types and across years. One of the reasons that’s difficult today is that so many soybean fields are harvested on an angle to the rows, making yield data collection difficult or impossible. There is also no one to organize such work and little noticeable interest by those who might fund such a project. “Trying” N by applying it to a field or two is sometimes suggested by those who feel that this is a profitable practice. This approach, of course, provides no information on whether or not applying N did anything.
For those interested in a “lite” N trial on soybean
Both times that we’ve seen a large yield increase from N on soybeans were on lighter-textured soil with N applied at planting. Applying N at planting typically makes leaves and cotyledons of small plants darker green in color compared to plants without N. In cases where N ends up increasing yield, this darker green color persists into vegetative stages, and plants tend to show increased growth and more green through most of the rest of the season. Where planting-time N doesn’t increase yield, the difference in green color between plants with N and those without N disappears as the plants make vegetative growth, and as their roots get more access to N from the soil and from N fixation in nodules. By the time plants are 6 to 8 inches tall, the effects of planting–time N are often no longer visible.
Based on what we’ve seen, I’m suggesting a low-cost alternative to large-scale application of N as a way to see where and how often N might have the potential increase soybean yields. Here’s the outline:
- After planting and before emergence, choose a uniform spot at least 20 feet away from endrows or edge of the field, and put flags in the corners of an area 15 feet x 15 feet square. We expect to see N effects more often on soils that are lighter in texture and lower in organic matter, so place this accordingly, in two or three fields or parts of fields with contrasting soil types if that’s an option. If possible record GPS coordinates for each site.
- Weigh out enough N fertilizer – urea or lawn fertilizer (without herbicide) – to provide 50 pounds of N per acre on the 225 square feet you flagged out. Calculate this by dividing the number 25.83 by the percentage of N in the product (urea may be 46-0-0, or 46% N; lawn fertilizer might be something like 27-0-4, or 27% N) to give the amount of product needed. As an example, if using urea (46% N), you would need 25.83/46 = 0.56 lb. of product. Multiply this by 16 to get number of ounces, or by 453.6 to give number of grams, if you have a gram scale. If you have a measuring cup but not a scale, urea weighs roughly 3/4ths as much as the same volume of water, so a cup (8 fluid ounces) of urea weighs about 6 ounces.
- Apply the fertilizer carefully, by hand or using a hand spin-spreader, uniformly over the soil inside the square.
- The “data” to be taken can, for most people, just be a photograph with the image split between the area with N and an area (outside the square) without N. I suggest taking a photo at about the V2 stage (two full trifoliolate leaves present), and another one about a month later, at perhaps V6-V7, when plants may be a foot tall or so. Find the side of the square that gives the best contrast under existing light conditions. Feel free to supplement the photo by noting what you can see (or not see) by eye.
- If the second photo shows no difference in greenness of plant size between those that received N and those that didn’t, the experiment could end there, with the conclusion that N probably made no lasting difference on growth, and so is unlikely to increase yield. If the plants with N are still greener and/or larger than those without N, that would be a signal to come back once or twice more, to see if the differences persists to the podfilling stages in mid- to late August, and again before leaves drop.
- If plants inside the treated square are visibly different than those outside, and there’s enough ambition and curiosity, you could harvest 15 or 20 randomly-selected plants inside the treated area and outside the treated area, and take a photo with the two sets of plants next to one another to show any visual effects on height or pod number. Those interested could count the number of pods, or even thresh the plants (in burlap bags works best) and weigh seed to estimate yield. Calculating yield would require an estimate of number of plants per foot of row. Yield estimated this way are highly variable, so they may not line up with what we thought we’d see based on plant size and appearance.
I’d be happy to look at photos from such comparisons; if there’s enough interest I could also develop a small reporting form to make a record for each trial. I’ll also be glad to send a layout for anyone interested in doing a strip trial with and without N. I can be contacted by email (link below, on my name) or my cellphone number is (217) 369-1997.