Slug Management in Illinois Field Crops

Authors: Nick Seiter, Talon Becker, and Nathan Johanning

Slugs can be a difficult pest to manage when conditions are favorable for them, which has been the case often (particularly in southern Illinois) over the last couple of years. These mollusks can damage both corn and soybean early in the season, along with a variety of other crops; however, they have the potential to be especially problematic in soybean, where they can kill the cotyledons and ultimately reduce stands. There are a few management points to consider for slugs in field crops:

  • Monitor slugs before planting to estimate the severity of the problem. Slugs can be monitored by inspecting residue, or by creating artificial shelters (made from shingles or other flat materials placed in the field to create a dark, damp environment) and inspecting them periodically before planting and during early stand establishment.1

    A slug found under a shingle trap placed in a field prior to planting in southern Illinois. Photo: Talon Becker.

  • Cool, wet weather during stand establishment results in greater slug problems. Slugs require a moist environment to survive, and they perform best when conditions are wet. Cooler temperatures extend soil drying time and delay plant development, leaving seedlings vulnerable to slug feeding damage for a longer period of time. Discussions with several CCAs in southern Illinois highlighted the fact that, while slug damage is a fairly normal occurrence on a small scale in most years, particularly in no-till fields, the mild winter of 2017 followed by wet and cool conditions in the spring after many acres had already been planted likely contributed to the greater incidence of slug damage last season. It appears that soybeans were most affected last season in southern Illinois, with several thousand acres of replanting reported.
  • Reduced tillage and/or certain cover crop systems can lead to larger slug populations. Higher levels of residue retain water and provide harborage for slugs, resulting in an increased probability of slugs reaching damaging levels. Reports from southern Illinois indicate that most problem fields last spring had a cereal rye cover crop that had not been terminated before producing excessive growth, creating a favorable environment for slugs. It is important to manage residue in cover cropped fields, particularly if they are no-till. If you had a problem with slugs last year, or have found concerning levels under your “shingle traps” in the field, make it a priority to terminate the cover crop before too much above ground biomass has accumulated (generally less than 1 ft. of growth). Cover croppers may also consider decreasing their seeding rate or planting a cover crop mix which includes species that winter-kill along with their favorite over-wintering species.
  • Avoid open seed furrows. When planter closing wheels fail to seal the furrow, the resulting trench provides an ideal environment for slugs and allows them to consume developing cotyledons as the seed germinates.
  • Chemical control options are limited. Slugs are not insects, and insecticides do not provide effective control. There are slug-specific baits available, but they tend to be expensive. Note that several formulations of the active ingredient metaldehyde (e.g., Deadline®) are labeled for use in corn, but this molluscicide is not currently labeled for soybean in Illinois.

Ultimately, the most reliable management tactic for slugs is to plant into a warm, dry seed bed, which is not always an option. However, by understanding conditions which are likely to lead to slug problems, you can be better prepared to address them when and where they occur.


Nick Seiter: – Research Assistant Professor, Field Crop Entomologist, University of Illinois Department of Crop Sciences

Talon Becker: – Extension Educator, Agriculture and Natural Resources, Illinois Extension

Nathan Johanning: – Extension Educator, Agriculture and Natural Resources, Illinois Extension

1 Douglas, M. R. and Tooker, J. F. 2012. Journal of Integrated Pest Management 3(1) DOI:

One More Call for Soybean Production Information

A number of times over the past 30 months I’ve asked Illinois soybean producers for help in gathering field-level information on soybean fields to feed into a study, led by the University of Nebraska and funded by the North Central Soybean Research Program, looking at weather, soil, and management effects soybean yield over the Corn Belt.

The last growing season from which we are collecting information is 2017, so this is probably the last time I’ll ask. As we have done for the last year, we are offering a $50 gift card for those who fill out and return forms from 2016 and 2017.

We are not asking for detailed information – only the location of each field, yield level, and a little production information such as planting date, seeding rate, etc. We’d like information on four fields from each of the past two season from each producer if possible.

If you can help us in this effort, please download the PDF forms at – there are four pages, one an example with a little explanation, one is the gift card request form, and there is one page each for 2016 and 2017, with space on each for information from four fields. If it’s easier, you can email me and I’ll email the forms . We can send also forms by mail if anyone needs that.

Forms can be filled on the computer or printed and filled out by hand, then scanned and returned as email attachments or sent by mail.

We have fallen short of the number of fields in this project each of the first three years, and I’d really appreciate everyone’s help to get to reach goal this time. We’d like information from fields all over Illinois. Students (who might have special interest in the gift card), vo-ag classes, farmers, company agronomists, sales people – all can help with this effort.

Thanks in advance for your help on this. Let me know if you have questions.

Issues as Harvest Approaches

It is looking like at least some harvest surprises may be positive after an up-and-down 2017 season in Illinois. The September 1 yield predictions released by the USDA this week are for Illinois corn yield to average 189 bushels per acre, up a bushel from the August 1 estimate. The soybean yield estimate is unchanged at 58 bushels per acre. Both would be outstanding after the tough start to the year and dry weather at times over much of the state.

Many soybean fields in east central Illinois are dropping their leaves, and harvest is getting underway. While we don’t expect as many 80+ bushel yields this year as we had in 2016, pod numbers look better than many had expected after dry weather in August and September. Rain now might boost yields by a little, but only in fields planted late or with late-maturing varieties where plants are still green. Cool temperatures in recent weeks have lowered water use rates, though, and we aren’t seeing the premature leaf drop that sometimes signals an early end to seedfilling due to lack of water.

With high temperatures in the 80s now and expected for the next week or more, the process of shedding leaves and drying down will accelerate, and it will be important to try to harvest soybeans at seed moisture above 10 percent. While some rain would help lawns and still-green crops, it would be better for the pod integrity if it stayed dry until after harvest, especially if temperatures stay high.

With high temperatures, seeds and pods following maturity will dry within hours instead of days, and we need to be alert and ready to harvest as soon as plants can be cut and seed moisture is at 12 or 13 percent. If moisture drops to 10 percent or less during harvest, it might be worth stopping until pods and seeds take on some moisture in the evening or overnight. Breeding and the use of improved combine headers have reduced pod shatter, but seeds less than 10 to 11 percent moisture can crack more easily. This might be one of those years with frequent switching between soybeans and corn harvest.

The corn crop in many fields is also looking a little better than expected as the leaves dry down and ears start to drop. As of September 10, two percent of the state’s corn crop had been harvested, mostly in southern Illinois. Yield reported so far range from low to high, reflecting differences in planting (or replanting) time, ability of soil to hold water for the crop, and whether rain fell or didn’t fall at critical times.

Nearly all of Illinois had below-normal rainfall in August, and little or no rain has fallen over most of Illinois during the first half of September. Dry soils during grainfill can decrease leaf photosynthesis, and when that happens, sugars are pulled out of the stalk into the ear to fill the grain. This leaves the stalks more susceptible to stalk-rotting fungi, and so more subject to lodging. So fields – especially those where leaves dried up earlier than expected – should be checked for stalk strength. Good growing conditions in July can increase the deposition of stalk-strengthening lignin, however, making stalks less likely to break even if sugars are pulled out. So as long as winds stay relatively calm, lodging is not expected to be much of a threat, especially in those parts of the state that received more rainfall in July and August.

Below-normal temperatures in recent weeks – most of central and northern Illinois are now about 150 GDD behind normal since May 1 – have slowed grainfilling rates and delayed maturity of the corn crop. The cooler temperatures have probably been positive for yields, by extending the water supply into mid-September. But the mid-August predictions that early-planted fields would mature by late August or early September didn’t happen. With GDD accumulation rates now above normal, a lot of fields will reach physiological maturity quickly, and grain will start to dry down. High temperatures mean rapid grain moisture loss; we’ve seen moisture loss as high one percent per day under high temperatures, especially if it’s breezy.

Dry conditions over the past month have limited the spread of ear rots. Most kernels now have the bright yellow color we like to see at harvest, and if the grain reaches maturity and can be harvested without an extended period of wet weather, we can expect grain quality to be good. Harvesting at high moisture and drying at high temperatures, or storing grain without proper care, can all compromise quality, however, and can mean getting a lower price for the crop.

One issue that often comes up for discussion during corn harvest is that of corn test weight. If test weight turns out to be lower than the standard of 56 pounds per bushel, many people consider that a sign that something went wrong during grainfill, leaving yield less than it could have been. And, test weights in the high 50s or above are often taken as a sign that kernels filled extraordinarily well, and that yield was maximized. Neither of these is very accurate –high yields often have test weights less than 56 pounds, and grain from lower-yielding fields can have high test weights.

Test weight is bulk density – it measures the weight of grain in 1.24 cubic feet, which is the volume of a bushel. Kernel density is the weight of a kernel divided by its volume, so does not include air like bulk density does. Kernel density is a more useful measure of soundness and quality than is test weight, but is harder to measure. A typical kernel density might be 91 pounds per 1.24 cubic feet of actual kernel volume. So a bushel of corn grain is about 56/91 = 62 percent kernel weight; the other 38 percent of the volume is air. Kernels with higher density tend to produce higher test weights, but only if they fit together without a lot of air space. Popcorn, as an example, has small, high-density kernels that fit together well, and a typical test weight of 65 pounds per bushel.

Hybrid genetics, growing conditions, and grain moisture at which test weight is measured can all affect test weight. If kernels appear to be well-filled, without a shrunken base that can signal that grainfill ended prematurely, it’s likely that they filled to their capacity and that yield was not compromised even if test weight is less than 56 pounds per bushel. For reasons that go back to an earlier time, though, corn needs to have a test weight of at least 54 pounds per bushel in order to be sold as U.S. No. 2 corn, which is the most common market class. Corn with a test weight of 52 or 53 might not be docked in price if it can be blended with higher test weight corn to reach the minimum. That’s much easier to do in a year when test weights are generally good. We expect that 2017 might be such a year.

Join us for the Ewing Agronomy Field Day on Thursday, July 27, 2017

The University of Illinois Extension will host the Ewing Demonstration Center Agronomy Field Day on Thursday, July 27, 2017 at 9 a.m.  Every growing season presents challenges to production, and this year is no exception!  We are happy to host this summer field day to share with local growers current, ongoing agronomy research in southern Illinois, including cover crop trials on corn and soybeans, nitrogen management in corn, weed management in soybean, and our continuous no-till field, now in its 49th year of continuous no-till production.


The topics to be discussed at Field Day include:


Managing Nitrogen for Corn & 2017 Growing Season Overview

  • Emerson Nafziger, Extension Crop Specialist, University of Illinois

Management Strategies for PPO-resistance

  • Karla Gage, Assistant Professor—Weed Science, Southern Illinois University

Southern Rust Management in Corn

  • Talon Becker, Extension Educator, University of Illinois

Insect Headlines in 2017

  • Kelly Estes, State Survey Coordinator, Illinois Cooperative Agriculture Pest Survey Program

Cover Crops:  The Good, The Bad, and The Practical

  • 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.  The Ewing Demonstration Center is about 20 minutes south of Mt. Vernon located at 16132 N. Ewing Rd; Ewing, IL 62836, on the north edge of the village of Ewing, north of the Ewing Grade School on north Ewing Road.  Watch for signs.  To help us provide adequate lunch and materials, please RSVP to the University of Illinois Extension Office in Franklin County at 618-439-3178 by Monday, July 24.  For additional information on the field day, contact Marc Lamczyk at the number above or

Crunch time for corn

While the record will show that corn planting progressed at a more or less normal rate this spring in Illinois, wet, cool conditions that developed after nearly half of the crop had been planted resulted in a great deal of replanting, especially in the flat-soil areas of Illinois. Some fields damaged by water and some that were too wet to plant before late May likely were planted to soybeans instead of corn. The June 30 acreage report shows Illinois corn acreage dropping by 500,000 from 2016 to 2017 (to 11.1 million acres) and soybean acreage increasing by 290,000 acres, to 10.4 million acres in 2017.

The Illinois corn crop condition ratings (from NASS) reflect both the poor growing conditions during the first weeks of May and the fact that so much replanting took place. The May 14 rating showed that only 42 percent of the corn crop was in good or excellent condition. This rose to 52 percent by May 28, and to 59 percent by June 4. It has remained around 60 percent for the past month, and was 62 percent on June 25. That’s lower than in any of the previous four years, and is lower than the 70 percent or more that is typical for a corn crop on its way to high yields.

The weather so far in the 2017 growing season will look more or less average in retrospect, but has been more variable than usual. April was relatively warm with average rainfall, and May was wetter to much wetter, and a bit cooler than normal. The first half of June was dry with temperatures 2 to 5 degrees above normal, while during the second half of June, rainfall varied from below to above normal, and temperatures were 2 to 3 degrees below normal. Even though they took a roundabout way to get there, growing degree day (GDD) accumulations were close to normal by the end of June, and corn planted in mid-April in central Illinois had accumulated enough GDD to be at or near silking.

One notable feature of the corn crop as we approach the critical pollination period is the short plant height in most fields. Plants in some fields are only five feet tall or so as tassels begin to emerge. This is widespread in central Illinois, though the degree of shortening depends some on how much rain has fallen in the past few weeks. I traveled in southwestern Illinoi early last week, and early-planted fields there were of normal height (about 6 feet tall) right before tassel emergence. Those in northern Illinois have a little more time before they tassel, and they might get to more normal height as well, especially if they were planted in May.

Why are early-planted plants short this year? It’s an unusual combination of factors, starting with cool, wet soils in May that both restricted root growth and slowed plant growth, causing roots to grow slowly out into the bulk soil. Then came warm and dry weather in early June, with widespread afternoon leaf-rolling caused by high evaporative demand and root systems unable to take up water fast enough to meet the demand. Having leaves roll indicates a shortage of water in the plant, and cells in any internodes that were developing at that time were not able to compete very well for water. Such cells elongated less than they normally would, and once the cell walls hardened after that, these internodes stayed short.

Low temperatures during vegetative growth in June also worked to keep internodes short, even if there was adequate water. Night temperatures fell into the upper 40s for a day or two during the last week of June, and coming after the high temperatures and lack of rainfall earlier in the month, this likely contributed to having some upper internodes stay shorter than usual. If we look at internode length after pollination (when plant height is fixed) we will be able to tell when stress occurred by which internodes are shortened.

Is below-normal plant height in corn a problem? If the plant has a normal amount of healthy leaf area (at 32,000 plants per acre that would be in the neighborhood of 6 square feet of leaves per plant), high yields would be possible with plants only 6 feet tall or so after pollination. But leaves have to compete for water in order to enlarge just like stems have to compete for water to elongate, so leaf area on short plants is often less than it is in taller plants. Because the sun is never directly overhead, having leaves a little farther apart on the stem (that is, longer internodes and so taller plants) also improves light interception a little bit.

Most people who have watched the corn crop for many years observe that, while good yields are possible on short plants, really high yields (250 bushels per acre or more) are, all else being equal, more likely on plants that are 8 or 9 feet tall than on plants that are 6 or 7 feet tall. In the same way that short plants have likely experienced some stress that might affect yield, early-planted corn that grows tall has experienced little if any stress. That means it has been able to maximize its size and its ability to produce high kernel counts based on the leaf area, roots, and stalks that it has developed.

That is not to say that tall corn always yields more than short corn. Late-planted corn often grows taller than early-planted corn because it’s warmer when the stem is elongating. Some replanted corn this year will escape the conditions that shortened early-planted corn, and so may be a lot taller than early-planted corn. But just being taller does not mean higher-yielding – late-planted plants tend to have less dry weight by the time of pollination than early-planted plants, and so less capability for forming and filling the large number of kernels that high yields require.

The concern about loss of nitrogen and not having enough N for the crop has faded over the past month, as leaf color has deepened under warmer conditions and as plant growth has taken off. By mid-June, our measurements of soil N have shown levels almost as high as we saw in mid-June in 2016. There is a little less growth of the crop this year than last year, so a little more N yet may need to be taken up this year. But soil N levels aren’t low enough to ring any alarm bells, and as pollination approaches and canopy color remains good, it’s unlikely that the crop is going to run out of N, especially if soil water supplies remain adequate. Adequate water not only carries N to the roots for uptake, but also helps maintain mineralization needed to make N available from soil organic matter.

The largest concern now, as it almost always is at this time of year, is having enough water and sunshine to maintain photosynthetic rates in order to get the high kernel numbers we need to produce high yields. It is possible that the rollercoaster conditions over the past two months have had a negative effect on how many kernels will set per ear. Any such effects would likely be subtle, often related to such factors as leaf area or effects of stress on the number of kernel rows now developing.

Very good pollination conditions – plenty of rainfall, good sunshine, and average temperatures – can overcome such pre-tassel effects, but will need to last for two weeks or so after pollination to keep kernels from aborting. We simply can’t know how this will end until we can count kernels and assess the state of the canopy by the time kernels start to add dry weight, about a month from now. We remain optimistic.

A Little Drier, But Not Yet Warm

Very little corn or soybean planting took place in Illinois over the past week, and while planting progress is not far behind average for the end of the first week of May, crop development is starting to lag as temperatures remain cool. Crop emergence has been slow, with only less than half of the corn crop that was planted by the end of April emerged by May 7.

One of the most visible consequences of the cool weather has been the poor corn crop color of recent days. Night temperatures in the 30s and low 40s cause physiological damage in young leaves, and such leaves can’t absorb light properly, so bright sunlight causes loss of color. In most cases, the sickly, yellowish leaf color is fairly uniform across the field, which indicates that it’s low-temperature damage rather than frost, which tends to be unevenly distributed. These symptoms should improve once air temperatures return to normal, but much of the green color may have to come from newly-emerged leaf area rather than repair of older leaves.

The cool temperatures also mean slow drying of the soil. This is delaying the improvement of soil conditions where the crop has been planted, and is also delaying planting, including replanting. In areas that received 5 or more inches of rain between April 26 and May 4, ponding was extensive, and seeds that spent more than a day or two under water did not survive.

Replanting will be widespread, and the first decision in many fields will be whether to replant the entire field or only the ponds after they dry up. Repair-planting – dropping the planter in to replant the most-damaged areas – has gotten more difficult to manage as planters have gotten larger; when only three or four rows are damaged, 24 rows may need to be planted. This also brings the complication of ending up with too many plants in much of the field. If replant seed cost is low, then destroying the existing stand and replanting the whole field might be the preferred option.

It will take patience to wait until soils are dry enough to get back into the fields, either to replant or to plant the first time. It’s more accurate to think of planting delays in terms of growing degree days than in terms of calendar days; in other words, planting delays are less sever when the weather is cool. Once it does warm up (and history says it always does), drying rates will increase and planting will resume.

Even though it will be difficult to wait, remember that planting into wet soils can mean compromised soil conditions, and depending on the weather, this can turn into a season-long problem. The longer-term forecast (accuracy unknown) is for a return to warmer, drier conditions soon, and we can still be optimistic that 2017 will turn into a good season.

Calling Illinois Soybean Growers-Again

In January I posted about the large project we are part of, funded by the North Central Soybean Research using soybean checkoff funds, to gather information on some 500 soybean fields in Illinois for each crop year from 2014 through 2017. The response has not been as enthusiastic as I had hoped, so I’m again calling for help on this. With 10 million acres of soybean in Illinois, 500 fields is less than a quarter of a percent of fields. And since we’re requesting information on up to 4 fields per grower, having only 2 or 3 producers in each soybean-growing county do this would get it done.

The most useful way I’ve heard this project described is as a “search to find what we should work on next” with regard to soybean research. The goal is to have thousands of fields in a large database, then to see how soil, weather, and management interact to produce yield.

To help, download the forms and other information at – if you want the fillable (PDF) forms please email me or email The forms can be emailed back or printed and returned by mail.

We will provide a $50 gift card as an incentive for people to fill out forms. The gift card request form is included in the group of forms, and can be returned with them. It would be great if FFA and college students (maybe those on spring break) could get experience taking part in a scientific study and also earn a reward for their efforts.

If you have questions about this, or if you’d like forms mailed instead of downloading them, please contact or me by email.

Thanks in advance for your help.

Extension Bi-State Crops Conferences in and near Western Illinois

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


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

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

Hosts: Iowa State University and University of Illinois Extension

More Information: Click here to access the flier.

Online Registration: Click here to register


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

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

Hosts: Iowa State University and University of Illinois Extension

More Information: Click here to access the flier.

Online Registration: Click here to register.


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

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

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

More Information: Click here to access the flier.

Online Registration: Click here to register.

Nitrogen on Corn in 2016: A First Look

The 2016 cropping season was a good one in Illinois, with planting a little ahead of normal and good May moisture and temperatures to get the crop off to a good start. June was warm and, in most parts of Illinois, drier than normal; parts of western Illinois received less than an inch of rainfall for the month. Temperatures and rainfall returned to normal in July and August, though there was the usual variability from region to region, including much-above-normal rainfall in the southern end of the State.

With good May soil conditions, mineralization got off to a fast start, and the crop in most fields was dark green by the end of May and starting to grow rapidly. Without N loss conditions in June, N from both fertilizer and mineralization stayed in the rooting zone, and N availability to the crop was outstanding. Even no- or low-N strips stayed dark green in trials into the middle of June, much later than we normally see N deficiency developing.

The retention of N in the soil and its availability to the crop carried through the season to diminish the need for fertilizer N. Figure 1 shows a response to N in an on-farm trial in DeWitt County, Illinois. Not only did about 150 lb. of N maximize yield at 230 bushels per acre, but it made almost no difference whether the N was applied in the fall or in the spring. We know from our N tracking that most of the N was in the nitrate form by the time crop uptake started in late May; we can see here that in the absence of N loss (wet) conditions, nitrate stays in the soil and is available for plant uptake just like ammonium.

Figure 1. N responses from fall- and spring-applied anhydrous ammonia in an on-farm trial in DeWitt County, Illinois in 2016. Optimum points are the N rate and yield at the point where the last addition of N provides just enough yield increase to pay for that N.

Figure 1. N responses from fall- and spring-applied anhydrous ammonia in an on-farm trial in DeWitt County, Illinois in 2016. Optimum points are the N rate and yield at the point where the last addition of N provides just enough yield increase to pay for that N.


Dan Schaefer of IFCA coordinated dozens of on-farm trials similar to the one shown in Figure 1. Some had fall versus spring N timing comparisons, some had all early versus some early plus sidedress, and others just compared yields at different N rates. Figure 2 shows results from 26 trials conducted across central Illinois in 2016.


Figure 2. N responses from 26 N rate trials in corn following soybean in central Illinois, 2016. Each line connects the data points from one trial, and the optimum points (triangles) are calculated from curves (not shown) fitted to the data. The MRTN points are calculated as the yield at 175 lb N/acre, which is the MRTN (optimum N rate) calculated for central Illinois corn following soybeans at a N to corn price ratio of 0.1 ($0.375/lb. of N and $3.75/bushel of corn.)

Figure 2. N responses from 26 N rate trials in corn following soybean in central Illinois, 2016. Each line connects the data points from one trial, and the optimum points (triangles) are calculated from curves (not shown) fitted to the data. The MRTN points are calculated as the yield at 175 lb N/acre, which is the MRTN (optimum N rate) calculated for central Illinois corn following soybeans at a N to corn price ratio of 0.1 ($0.375/lb. of N and $3.75/bushel of corn.)

In 2015, high N loss conditions and damage from standing water resulted in high optimum N rates. In 2016 we found just the opposite: Figure 2 shows that relatively low rates of N were needed to maximize yield in nearly every case. Of the 26 trials, only five had an optimum N rate higher than the MRTN rate, and on average across trials, only 150 lb. of N was needed to produce an average yield at the optimum N rate of 225 bushels per acre. Some like to calculate “efficiency” of (fertilizer) N by dividing yield by N rate; here, we calculate a very high efficiency of 2/3rds of a lb. of N per bushel of yield, or 1.5 bushels per lb. of N used.

We ran a new study at a number of sites this year to compare the application of N rates at planting to keeping 50 lb. of N back and applying it dribbled next to the row at tasseling. Figure 3 shows the results of the corn following soybean trial at Urbana.


Figure 3. Response to N applied as UAN at planting (early) compared to applying all but 50 lb. of N at planting them dribbling the remaining 50 lb. next to the row at tasseling.

Figure 3. Response to N applied as UAN at planting (early) compared to applying all but 50 lb. of N at planting them dribbling the remaining 50 lb. next to the row at tasseling.

Responses to late-split timing of N at other sites were all similar to that in the trial shown in Figure 3. We had three corn following corn trials and four corn following soybean trials, and in none of them did keeping back 50 lb. of N to apply late provide a benefit to either yield or return to N; that is, late-split application did not pay the added application cost. This makes sense given the low N loss conditions in 2016. We would expect to see some loss and possible response to late supplemental N following a wet June, though we did not see much response to a single treatment (150 lb. N early versus 100 early and 50 at tasseling) in 2015.

We’re seeing N “at its best” in 2016; it was there in abundance when the crop needed it, and adding the supply of N from soil organic matter meant that the crop needed less fertilizer N than it has typically needed, even at high yield levels. We can’t depend on this to happen in 2017, but we see clearly that the common idea that “high yields require high N rates” often does not hold true. There is certainly no need to raise rates for next year, and fields that received more N than was needed in 2016 (according to N response curves that is probably most fields) might have added to the pool of soil N that can be tapped by the 2017 crop, whether that’s corn or soybean. Keep in mind, though, that what we saw in 2016 was mostly a response to the (June) weather and crop off to a good start; we will need to watch how things develop in the spring of 2017 to know if we’ll have a repeat.


2016 Tar Spot again found on corn in Northern Illinois

Corn leaf samples from LaSalle county have been positively identified by the University of Illinois Plant Clinic to be infected with Tar Spot Phyllachora maydis.  Commercial Agriculture Extension Educator Russ Higgins found the disease while field scouting.  The fungal leaf blight was identified in numerous northern Illinois and northern Indiana counties in 2015.

Tar Spot has distinctive signs and symptoms. The fungal fruiting body, called an ascomata, looks like an actual spot of tar on the leaf.  Lesions are black, oval to circular.  They can be small flecks of about 1/64” up to about 5/64”.   The lesions can merge together to produce an affected area up to 3/8”.  If you run your finger across the leaf you will feel tiny bumps.

Picture 1. Distinctive black fruiting bodies of Tar Spot on corn leaf 2016. Photo courtesy of Russ Higgins, University of Illinois Extension

Prior to 2015, Tar Spot was known to occur only in cool humid areas at high elevations in Latin America.  Tar Spot can form a complex with another fungus. The 2 fungi that cause ‘Tar Spot disease complex’ on corn are  Phyllachora maydis and Monographella maydisWhen  Monographella maydis is in association with  Phyllachora maydis  the complex has been demonstrated to cause economic yield losses in Latin America. Phyllachora maydis alone is not known to significantly reduce yield.  When the two are in combination a distinctive symptom is seen.  The black Tar Spot will be surrounded by a tan lesion so the two together resemble a ‘fish-eye’.

Other pathogens may be confused with Tar Spot, especially the overwintering teliospore (black) phase of corn rust.  Also, there are many fungi, called saprophytes that feed on dead corn tissue and form black splotches on the leaves.

To date only one of the pathogens, Phyllachora maydis, has been found in IL in 2015 and 2016, and IN in 2015.  If you suspect Tar Spot please submit a sample to The University of Illinois Plant Clinic.  We are cooperating with USDA-APHIS-CAPS to get a comprehensive idea of distribution in the state.  Illinois producers can participate at no cost, see how at this link