Ewing Demonstration Center Fall Field Day – September 10th

The University of Illinois Extension will host its annual Ewing Demonstration Center Fall Field Day on Thursday, September 10, 2015 at 9:00 a.m.  The Ewing Demonstration Center is located in southern Illinois about 20 miles south of Mt. Vernon at 16132 N. Ewing Rd; Ewing, IL 62836.  It is on the north edge of the village of Ewing, north of the Ewing Grade School on north Ewing Road.  Watch for signs.

The ongoing research this year includes trials on soybean cover crops, nitrogen management in corn, corn maturity, corn seeding rates, soybean seed treatments, and a pumpkin variety trial.


The topics to be discussed at Field Day include:


Soybean Weed Management

  • Ron Krausz, Manager, SIU Belleville Research Center

2015 Cropping Season Challenges

  • Emerson Nafziger, Extension Crop Specialist, University of Illinois

Planning Ahead for the 2016 Wheat Crop

  • Robert Bellm, Extension Educator, University of Illinois

Results of 2015 Corn and Soybean Insect Surveys: Implications for 2016

  • Mike Gray, Extension Entomologist, University of Illinois

Making the Most of Prevent Plant Acres with Cover Crops

  • Nathan Johanning, Extension Educator, University of Illinois


The field day is free and open to anyone interested and lunch will be provided.  Certified Crop Advisor CEUs will also be offered (CM –  1.0, PM – 1.0, SW – 0.5).  For additional information, contact Nathan Johanning (618-687-1727; njohann@illinois.edu) or Marc Lamczyk (618-439-3178; lamczyk@illinois.edu).

Brownstown Agronomy Research Center Field Day – August 5, 2015

The 2015 Brownstown Agronomy Research Center Field Day, presented by the University Of Illinois Department Of Crop Sciences, will be held on Wednesday, August 5. Extension researchers and specialists will address issues pertinent to the current growing season. The tour will start at 8 a.m. and will last approximately three hours. It will be followed by lunch provided by U of I Extension. 2.5 hours of Certified Crop Adviser CEUs have been approved.

Shaded tour wagons will take participants to each stop. These topics will be addressed:

  • 2015 Cropping Season Challenges – Dr. Emerson Nafziger, U of I
  • Weed Management: The Simple Days are Over – Dr. Aaron Hager, U of I
  • Soybean Sudden Death Syndrome – Dr. Angie Peltier, U of I
  • Update on Statewide Insect Surveys & Potential Implications – Dr. Mike Gray, U of I
  • Factors Contributing to a Healthy Soil – Russ Higgins, U of I

The 208-acre Brownstown Agronomy Research Center has been conducting crop research on the claypan soils of southern Illinois since 1937. More than 30 research and demonstration projects are conducted at the Center each year. Visitors are always welcome.

The research center is located south of Brownstown on IL Route 185, approximately 4 miles east of the IL Route 40/185 junction.

For more information, contact Robert Bellm (618-427-3349); rcbellm@illinois.edu
Visit us on the web at http://web.extension.illinois.edu/barc/

Corn disease update and farewell

Last week, I visited all of the University of Illinois corn variety trials in the northern half of the state.  Gray leaf spot and northern leaf blight were beginning to appear in most of the locations, but were the most obvious at the trial located near Perry, IL (Pike County).


“Young” lesions of northern leaf blight beginning to develop on a corn leaf.


Gray leaf spot lesions developing on a corn leaf.

With the amount of rainfall received in the past few weeks, it is not surprising that these diseases were beginning to appear.  Since hybrids differ in their level of susceptibility to these diseases, not all hybrids in the trials had symptoms.  If the rainy conditions continue, then a foliar fungicide application sometime between tassel emergence and silking may need to be considered on hybrids that are the most susceptible.  Some general guidelines that may help make a foliar fungicide application decision follow:

  • On susceptible to moderately-susceptible hybrids:  consider a foliar fungicide if disease is present on the third leaf below the ear or higher on 50% of the plants prior to tasseling.
  • On intermediate hybrids:  consider a foliar fungicide if the field has a history of disease, if the previous crop was corn with at least 35% of the ground covered with residue, if disease is present on the third leaf below the ear or higher on 50% of the plants prior to tasseling, and if warm and humid weather has persisted.
  • On moderately-resistant to resistant hybrids:  foliar fungicides generally are not recommended, but scouting is important to confirm that diseases are not present.

The presence of diseases does make a difference in how profitable a fungicide application may or may not be.  From trials conducted at the University of Illinois from 2008 to 2014 at many environments (45 total environments) in Illinois, the results indicate that the overall yield response to foliar fungicides was 5.3 bushels/acre (see chart below).  However, this yield response was 9.5 bushels per acre when disease developed to affect at least 10% of the leaf area in untreated controls (in 17 of the environments).  In situations with low disease severity (disease developed to less than 10% of the leaf area in untreated controls), the average yield response was only 2.8 bushels per acre (in 28 of the environments).  Obviously, the marketing price of corn and the fungicide and application costs will determine if fungicide applications were profitable.  The chart below shows the profitability of fungicide applications under different yield response goals (3, 5, 8, and 11 bushels per acre).  The bottom line is that it takes a higher yield response to be profitable when corn marketing prices are lower.

Corn fung results 2014

Results from University of Illinois corn fungicide trials conducted from 2008 to 2014. All applications were made at tassel emergence (VT).

On a final note, my last day at the University of Illinois is today (June 30).  I will be moving to a similar position at the University of Kentucky, and will be based out of the Princeton Research and Education Center in the western part of Kentucky.  I want to thank the University of Illinois for my opportunities here and thank many of you for your support and interest.  There are no current plans to replace my position as Extension Plant Pathologist at the University of Illinois.  If you have field crop disease questions, the following contacts may be useful:

University of Illinois Plant Clinic

1102 S. Goodwin Ave.

Urbana, IL 61801

Tel: 217-333-0519

Email: plantclinic@illinois.edu


Commercial Agriculture Extension Educators:

Robert Bellm

Brownstown Agronomy Research Center

1588 IL 185

Brownstown, IL 62418

Tel: 618-427-3349

Email: rcbellm@illinois.edu


Dennis Bowman

Crop Sciences Research and Education Center

1102 S. Goodwin Ave.

Urbana, IL 61801

Tel: 217-244-0851

Email: ndbowman@illinois.edu


Russ Higgins

Northern Illinois Agronomy Research Center

14509 University Road

Shabbona, IL 60550

Tel: 815-824-2029

Email: rahiggin@illinois.edu


Angie Peltier

1000 North Main Street

PO Box 227

Monmouth, IL 61462

Tel: 309-734-5161

Email: apeltier@illinois.edu

Corn and Nitrogen as Rains Continue

Some rain has fallen somewhere in Illinois nearly every day for the past 3 weeks, and rainfall totals for this period exceed 7 inches – two to three times normal – over more than half of the state (Figure 1). This has a lot of people wondering if enough nitrogen remains in the soil to supply the corn crop.

Figure 1. Illinois rainfall from May 26 through June 18, 2015.

Figure 1. Illinois rainfall from May 26 through June 18, 2015.

Daily high temperatures have averaged close to normal over the past three weeks, while night temperatures have been 3 to 4 degrees above normal, so growing degree accumulation rates remain high. Sunshine amounts have been marginal, but growing conditions have been good enough to keep the crop coming along rapidly. Fields that were planted in April in central Illinois have 10 to 13 leaves, and the crop is 4 to 5 feet tall or more and growing rapidly, adding 3 or more inches of height per day and adding a new leaf every two days or so. With warm temperatures during June and plenty of water, we can expect corn plants to be tall this year.

Except where roots have been in water for a week or more, fields and parts of fields where crop roots are still supplied with oxygen continue to show good canopy color. Much of the early-planted crop is in or about to enter the rapid N uptake period – from about V9 through tasseling – during which the crop takes up as much as 6 or 7 lb of N per acre per day.

We are continuing to monitor soil N in the N-tracking study that I described here on May 30 http://bulletin.ipm.illinois.edu/?p=3241. The most recent samples for which we have numbers were taken last week, before the end of the current deluge. Table 1 gives rainfall amounts and changes in soil N between samples taken May 20-22 and those taken 18 to 20 days later. The 340 lb found following fall application on the first date at Urbana is 85 lb more than was found 9 days earlier, and is likely a result of sampling variability.

Table 1. Rainfall and changes in soil N between two dates at three Illinois sites in 2015.

Table 1. Rainfall and changes in soil N between two dates at three Illinois sites in 2015.

We know these numbers are variable and that we need to be cautious in using them, but the fact that soil N didn’t decrease sharply, especially at Urbana where so much rain fell, provides some confidence that losses have not been very high. The crop at Urbana is ahead of those at the other two sites, and so has taken up more N; I would estimate N uptake by the time of the second sampling (June 12) at about 40 lb of N per acre.

Fig 1 soil NThe percentage of N found as ammonium increased over this period at DeKalb and Urbana, but not at Monmouth, where ammonium percentage was higher on the first date than at the other sites. This may reflect an increase in mineralization as soils warmed up, and could also reflect some loss of nitrate. Mineralization is the likely cause of the uptick in soil N in the zero-N checks as well.

As plants begin to take up N at a rapid rate, we can expect soil N to drop, though N losses and mineralization will both affect the rate of change. Over the next few weeks, we expect that the plants (canopy color) will be a better gauge of N availability to the plant than will amounts of N we measure in the soil. The question that remains, without a solid answer, is whether N levels might slip below those needed to maintain crop growth before uptake starts to slow. From what we’re seeing so far that seems unlikely, at least if rains slow before too many more days.

A more immediate question is whether the pale green or yellow spots in fields need N applied now in order to prevent serious yield loss. Rapid loss of color in places where water stands comes from loss of root ability to take up N, not from loss of N from the soil. We know this because parts of fields where roots are in aerated soil are not showing deficiency.

We won’t know the extent to which roots of plants in wet or flooded soils will recover until soils dry and re-aerate enough for root function to return. Adding N before then will do nothing for the plants, and if soils remain wet or flooded, some of this N will be lost before the plant has a chance to take it up. Aerial application of urea is not inexpensive, and while it can test our patience, waiting until soils dry out for a week or more before deciding that more N is needed is the best course of action. Our hope is that a lot of acres will return to green once soils dry out. Even if that happens, we expect such areas to have lost yield potential, and the larger the plants were when first flooded and the longer soils stay wet, the larger will be the loss. Adding N now will do nothing to fix this.

As plant size and leaf area increase, the ability of the crop to help move water from the soil to the air will increase as well, so the crop itself will help to dry the soils and will speed progress toward aerated soil conditions. Water loss in yellow, root-damaged corn that is standing in wet soils is very slow, so we won’t see much help there. Our best hope is to get two weeks of weather without much rain and with average temperatures to help get the crop back on track. It won’t be an easy wait.

Tracking Soil Nitrogen – Does Corn Have Enough N?

Rainfall in April and May has been about average through most of Illinois, at least until the downpours the last days of May. This has allowed timely planting and a good start to the crop in most areas, and has allowed nitrogen management to be carried out more or less as planned by most producers. Warm temperatures during some weeks of May are moving crop development along, and much of the N planned for application after crop emergence has already been applied.

Much of the rainfall has come with low or moderate intensity; there have been few multiple-inch downpours leading to standing water and fears of crop damage and of loss of nitrogen, though rain on May 30 has been heavy in places. But reapplying N late or using higher rates due to expectations of N loss happen every year, and while that might be less common this year, it remains a consideration.

To find out if more N is justified, we initiated a new study this year, funded by NREC, to “track” N applied at different times and forms to see how much N remains in the soil and available to the crop through the vegetative growth period. At four research center sites in central and northern Illinois, we applied 200 lb of N in four different ways: 1) as NH3 applied in November 2014; 2) as 100 lb NH3 last fall + 50 lb UAN at planting + 50 lb UAN as V5-V6 sidedress; 3) as NH3 applied in early-mid April; and 4) as 50 lb UAN at planting + 150 lb UAN at V5-V6 sidedress. The 200-lb rate is higher than the N rate calculator rate, which is about 160 lb N for corn following soybean; our objective is to track N over time. Beginning after the fall application and about every 10 days this spring, we have been sampling soil to 2 feet deep, with samples analyzed for both nitrate and ammonium.

Figure 1 shows how much soil N (nitrate plus ammonium) we’ve found at the Urbana site in samples taken so far. Sampling like this always finds a fair amount of variability – we don’t know exactly where the N ended up in the soil, and soil probes don’t always get a representative sample. But we did find more N in plots where we had applied N, and we are able to see changes in soil N as the soils have warmed up and mineralization has kicked in. About as much fall-applied NH3 remains available as spring-applied NH3; both show at least 250 lb of available N in the top two feet on May 22. We think this confirms that N losses have been small since last fall.

Figure 1. Soil N at different sampling times in an N-tracking trial at Urbana in 2015. Fall NH3 was applied before the November 14 sampling, early spring NH3 before the April 7 sampling, and planting-time applications (as UAN) were made before the April 24 sampling. Pl is planting time and SD is sidedress, which was done after the May 22 sampling. The 2014 crop was soybean, and corn was planted on April 23.

Figure 1. Soil N at different sampling times in an N-tracking trial at Urbana in 2015. Fall NH3 was applied before the November 14 sampling, early spring NH3 before the April 7 sampling, and planting-time applications (as UAN) were made before the April 24 sampling. Pl is planting time and SD is sidedress, which was done after the May 22 sampling. The 2014 crop was soybean, and corn was planted on April 23.

One surprise at this site has been the relatively large amount of N found in the soil where no fertilizer N was applied. In soils with a good amount of organic matter we never expect to find zero N, but we would not have expected to find the 130 to 180 lb of N that we found in the last three (May) samples. Still, getting yields of 125 to 150 bushels per acre in corn following soybean without N fertilizer is not unusual, and so finding this amount of N may not be abnormal.
The findings at DeKalb and Monmouth are similar to those at Urbana, though the soil N levels are a little lower at the other sites, in part because they were last sampled a little earlier than at Urbana. Soil N without N fertilizer has yet reached only about 100 lb per acre at those two sites. At the Perry site, with soils lower in organic matter, levels of soil N we have been finding are considerably less than at the other three sites; at the May 22 sampling at Perry, we found only about 150 lb of soil N in both the fall- and spring-applied NH3.

The majority of the soil N is now in the nitrate form, regardless of what form was applied (Figure 2.) This is more or less as we expected for fall-applied NH3 and for spring-applied UAN, but by about six weeks after early spring NH3 application (done on April 6) we might have expected a little more of the N to still be in the ammonium form. As expected, most of the N found in plots without N fertilizer was in the nitrate form regardless of when sampling was done. Mineralization releases ammonium, but under the soil temperatures that increase mineralization rates, the ammonium converts to nitrate quickly.

Percentage of soil N present as nitrate following different N treatments and at different sampling times at Urbana. The rest of the N was present as ammonium.

Percentage of soil N present as nitrate following different N treatments and at different sampling times at Urbana. The rest of the N was present as ammonium.

The takeaway message from what we’ve found so far in this project is that we see no reason to adjust upward the total amount of N applied due to concerns about N loss. The fertilizer N that was applied is mostly present as plant uptakes begins, and we can add to that the N coming from soil organic matter. It’s also encouraging that the amount we’re finding has continued to increase as we move into the N uptake period. Last year we found that the crop took up a total of less than 1 lb of N per bushel of yield, so we don’t see a shortage for the crop coming anytime soon.

As part of this project we are also working with Dan Schaefer (IFCA) to sample several on-farm sites with similar treatments, and we’re sampling following spring N applications at two southern Illinois sites. We’ll keep you posted on what we find in the coming weeks.

2015 Field Day Events in Illinois

Fields days organized by Crop Sciences and Extension at the University of Illinois and by other institutions will focus on crops and pests, with speakers talking about current crop issues along with information from previous research. Each event will offer CEUs for CCAs.

Following is the schedule of crop-related 2015 field days organized by University of Illinois Crop Sciences and by several other institutions.

Event Date – start time Food Contact
Urbana – Weeds June 24 – 8:00 AM lunch Doug Maxwell (217) 265-0344 dmaxwell@illinois.edu
Macomb – WIUa June 25 – 12:00 N lunch Mark Bernards (309) 313-5917 ml-bernards@wiu.edu
DeKalb July 9 – 9:00 AM lunch Russ Higgins (815) 274-1343   rahiggin@illinois.edu
Belleville – SIUb July 9 – 9:00 AM lunch Ron Krausz (618) 566-4761 rkrausz@siu.edu
Orr Center, Perry July 22 – 9:00 AM lunch Mike Vose (271) 236-4911   mvose@illinois.edu
Monmouth July 28 – 8:00 AM snack Angie Peltier (309) 734-5161 apeltier@illinois.edu
Brownstown August 5 – 8:00 AM lunch Robert Bellm (618) 427-3349   rcbellm@illinois.edu
Dixon Springs August 6 – 9:00 AM lunch John Pike (618) 695-2790   jpike@illinois.edu
Urbana August 20 – 7:00 AM lunch Bob Dunker (217) 244-5444 r-dunker@illinois.edu
Urbana August 31 – 8:00 AM International Agronomy Day: http://internationalagronomyday.org
Ewingc Sept. 10 – 9:00 AM lunch Mark Lamczyk (618) 439-3178   lamczyk@illinois.edu
aWestern Illinois University conducts this field day at its Macomb research farm.
bBelleville is a research center operated by Southern Illinois University–Carbondale.
cEwing Field is operated by University of Illinois Extension in southern Illinois.


Stripe rust and Fusarium head blight (scab) concerns in Illinois

Stripe rust of wheat has been observed in different parts of Illinois within the last week. Although some varieties have very good resistance to stripe rust, there are still several varieties that are susceptible. Stripe rust is able to flourish under the cooler temperatures we’ve had over the last few days. With rain in the forecast in parts of the state over the next few days, favorable conditions for this disease likely will continue.

Although some wheat fields in the state are already past the critical period for applying a fungicide for protection against Fusarium head blight (a.k.a. scab) (beginning flowering up to 6 days after beginning flowering), some fields in the state are just beginning to flower or will within the next week. For the fields that are just beginning to flower or will within the next week, an application of Prosaro or Caramba fungicide should be considered for protection against Fusarium head blight and stripe rust. Multi-state university research has indicated that Prosaro and Caramba are the best products available for managing Fusarium head blight and the associated mycotoxin, deoxynivalenol (DON; a.k.a. vomitoxin). Both of these fungicide products also have efficacy against the stripe rust pathogen.

Light-orange colored stripe rust pustules on wheat leaves (Photo by C. Bradley).

Light-orange colored stripe rust pustules on wheat leaves (Photo by C. Bradley).


Wheat disease outlook

As the weather begins to warm up, wheat is beginning to grow at a faster pace.  Symptoms of some diseases also are beginning to appear or will likely be appearing soon.  Below are some diseases to look for right now.

Stagonospora and Septoria leaf blotch: Although caused by two different pathogens, symptoms of these two foliar diseases look very similar and both can be managed with an appropriate foliar fungicide application.  Most results from University of Illinois wheat foliar fungicide trials conducted since 2008 have shown that an application of an effective fungicide for control of Fusarium head blight (scab) when wheat is beginning to flower also provides good protection against common foliar fungal diseases on the flag leaf.  However, if a variety is very susceptible and if conditions are favorable (frequent rainfall / damp conditions), then an application of a fungicide when the flag leaf emerges may be needed.  On a side-note, the 2015 multi-state university foliar fungicide efficacy table for wheat diseases can be found here: NCERA 184 Wheat fungicide table 2015_V3.

Septoria leaf blotch symptoms on a wheat leaf. (Photo by C. Bradley)

Virus diseases: Surveys of viruses affecting wheat in Illinois conducted in recent years indicate that Barley yellow dwarf virus (BYDV) is the most commonly detected virus affecting wheat in the state.  However, other viruses, such as Wheat spindle streak mosaic virus (WSSMV), Soilborne wheat mosaic virus (SBWMV), Wheat streak mosaic virus (WSMV), and a few others also have been detected.  Virus symptoms (yellowing, purpling, yellow streaks, etc.) can be confused with other disorders, and it can be extremely difficult identifying a virus disease by symptoms alone.  Therefore, specific laboratory tests must be conducted to determine if a virus is responsible for these symptoms.  The University of Illinois Plant Clinic (https://web.extension.illinois.edu/plantclinic/) does not currently test for viruses in wheat, but can help make a determination if virus testing is needed.  Plant virus testing can be done at the Purdue University Plant & Pest Diagnostic Laboratory (http://www.ppdl.purdue.edu/ppdl/index.html) and at a private lab known as Agdia, which is located in Elkhart, IN (https://www.agdia.com/).  Unfortunately, no in-season control options are available for managing virus diseases.

Symptoms caused by Barley yellow dwarf virus on wheat. (Photo by C. Bradley)

Symptoms caused by Soilborne wheat mosaic virus on wheat. (Photo by C. Bradley)

Stripe rust: To my knowledge, stripe rust has not yet been detected in Illinois during the 2015 season.  However, there have been reports of stripe rust from states to the south of Illinois, such as Arkansas and Tennessee.  Since rust spores have the capability of moving many miles, stripe rust could be on its way to southern Illinois.  If stripe rust is observed on plants, a foliar fungicide may be needed to protect the flag leaf, depending on the susceptibility of the variety.  Applications at early flowering for control of Fusarium head blight also may be effective in managing stripe rust; however, an earlier application of a fungicide may be needed if stripe rust is found prior to heading and if disease is developing rapidly.

Early symptoms of stripe rust on a wheat leaf. (Photo by C. Bradley)

Orange-colored pustules of the stripe rust fungus on a wheat leaf. (Photo by C. Bradley)

Fusarium head blight (scab): Although it cannot be observed yet, Fusarium head blight is the most important wheat disease in Illinois, and thinking about how to manage this disease cannot occur too early.  In years in which weather is favorable for infection (frequent rains, moderate temperatures, and cloudy weather – such as 2014 for southern IL producers), this disease can wreak havoc.  This is especially true because the fungus that causes this disease also produces toxins, such as deoxynivalenol (DON; also known as “vomitoxin) that will contaminate grain and will result into major dockage when grain is delivered to the elevator.  Infection of the scab fungus occurs when wheat heads begin to flower.  The beginning flowering stage also is the best timing for applying an effective fungicide to managing Fusarium head blight and DON.  Results of university fungicide trials across multiple states have shown that Prosaro (Bayer CropScience) and Caramba (BASF) are the best products currently available for reducing Fusarium head blight and DON in grain.  One thing to keep in mind with these fungicides is that 100% control cannot be achieved, and susceptible varieties cannot be “fixed” by applying a fungicide when conditions are very favorable for Fusarium head blight.  University research has shown that Fusarium head blight and DON can be reduced by approximately 40%-60% with Prosaro or Caramba (relative to a non-treated check); therefore, the bottom line is that fungicides will reduce disease and DON levels in grain, but don’t expect a complete reduction with fungicides alone.  The forecasted risk of Fusarium head blight can be observed by going to the Fusarium head blight Prediction Center website (http://www.wheatscab.psu.edu/).

Fusarium head blight (scab) affecting a wheat field. (Photo by C. Bradley)

Planting into Cool Soils – Yes or No?

While research shows that the last 10 days of April is on average the best time to plant corn in Illinois, expectations of below-normal temperatures in most of Illinois during the last week of April has some wondering if it makes sense to plant now or to wait until temperatures warm up.

Averaged over the past 22 years, Illinois corn producers have planted 16% of the crop by April 20. NASS reported that 15% of the crop was planted by April 19 this year, so planting progress to date is right at the average. There will be some progress to report this week, though rainfall coupled with cooler temperatures will limit the rate at which fields get ready to plant in some areas. Still, we may be on track to maintain planting progress at the average rate, which would mean having close to 40% planted by April 30.

Research tells us that planting before May 1 almost always yields more than planting later, with yield loss accelerating with delays past early May. Planting date and yields over years for the whole state often give a different picture, however.  Over the past 22 years, in fact, there has been no correlation between the date by which 50% of the corn crop was planted and statewide yield, measured as departure from trendline yield in order to correct for the upward yield trend over time.

In 2014, 36% of the Illinois corn crop was planted by April 30, and the average yield was 200 bushels per acre. In contrast, 81% of the crop was planted by April 30 in 2012, but the average yield was only 105 bushels per acre. Two of the latest-planted crops in recent years – 2009 and 2013, with hardly any corn was planted by April 30 – produced yields more than 10 bushels above trendline yields. So it is clear that what happens with weather during the season can override when the crop was planted, at least over a large area.

But for each individual field we still need to try to plant as early as conditions allow. Even if planting a week or two later would have little effect on yield in that field that year, we need to “start so we can finish” – getting all fields planted by early May is a goal as we try to maximize yield potential. But might this year be an exception, with potential for harm from planting into cool soils in the last week of April, with the weather forecast indicating that temperatures may stay low for the next week?

As a principle, waiting until soil is dry enough to allow planting into good seedbed and rooting (less-compacted) conditions is more important when soils are cool than when they are warm. We never want to work soils wet and plant under wet soil conditions if we can help it, but we certainly do not want to do that in April, especially when soil temperatures are less than normal.

So our first question should be whether or not the soil is dry enough; if the answer is no, then we wait. Cool soils dry slowly, and wet soils warm slowly, so waiting might take an extra measure of patience, especially if a neighbor brings out the planter. There is some comfort in the fact that germination and emergence are slow in cool soils, so planting a few days earlier when it’s cool makes very little difference in how far along the crop will be on a given date later in the season.

According to the Illinois State Water Survey, minimum temperatures 2 inches beneath bare soil on April 21 averaged about 40 degrees in the northern half of Illinois and in the upper 40s in southern Illinois. That’s a drop of more than 10 degrees over four days. And the weather forecast indicates that soils may not warm up much by the end of April. If we go by the old standard recommendation that corn should be planted only after the minimum soil temperature 2 inches deep exceeds 50 degrees, we would have planted for perhaps half the days in April through April 19, but none since then. Maximum temperatures 2 inches deep reached the 80s on April 17, but only averaged in the low 60s on April 21.

It takes soil temperatures of 50 or above to get the germination process underway, but does this mean that we should avoid planting corn into soils where temperature at seeding depth averages less than 50? Based on a lot of planting date work, we would say that the danger from doing this in minimal. It takes about 115 or so growing degree days (GDD, based on air temperature) after planting to get corn plants to emerge, and emergence has usually been good even when it has taken 3 weeks for this number of GDD to accumulate. Planting date has had little or no effect on emergence in most of these trials.

Normal GDD accumulation in the month of April ranges from about 180 in northern Illinois to 220 in central Illinois to 300 in southern Illinois. So far in April 2015, we have had about 200 GDD accumulate at Urbana. With the slowdown this week, the total will end up somewhere around the average for this month. We made our first planting here in the planting date trial on April 1, and it emerged more or less on schedule, around April 16. We can expect corn planted on April 22 or 23 to take at least this long to emerge, and longer if temperatures don’t rebound next week.

The chances of getting good emergence when planting into cool soils are higher if here is little or no rain between planting and emergence. Cool soils bring slow germination and emergence, but they may lower the chance of emergence problems due to soil crusting or to saturated soil. Crusting problems usually develop after intense rainfall followed by warm, dry conditions that help “bake” the crust. Warm soils mean more rapid growth of seedlings, which can mean running out of oxygen sooner if soils become saturated. So while we would prefer warmer and relatively dry soils, next best is having cool and dry soils. Most stand problems occur when soils are warmer, simply because that’s when the plants are trying to grow faster. Still, warm soils help bring the crop up, and we hope that they start to warm soon.

Heavy rainfall is not predicted for this coming week or so, which is a positive. Taking the longer view, temperatures in May will inevitably start to rise at some point in time, and this will speed up emergence. Taking all the factors together, I would suggest that planting proceed as long as soil conditions are good, even if the germination process will be slow due to cool soils in the near term.

One of the concerns being mentioned is “imbibitional chilling injury” that has been reported when seeds and seedling take up water that is colder than 40 degrees. This can stiffen plant cell membranes and lead to damage, in some cases distorting growth and reducing emergence. This has usually been linked with melting snow or very cold rainfall after planting. It’s something to keep in mind, but it has been rare in Illinois (we think there was some in corn planted around April 20-25 in western Illinois in 2011) and it should probably not keep us from planting in the last week of April. Higher, drier fields are less likely to suffer from this, and should be planted first.