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 lamczyk@illinois.edu.


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 http://go.illinois.edu/soy-survey – if you want the fillable (PDF) forms please email me or email soyncsrp@illinois.edu 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 soyncsrp@illinois.edu 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 https://uofi.box.com/s/bizu6oz3re35v9boif784nz4zvy85gjc

 


New bacterial leaf disease “Bacterial leaf streak” identified in one northern Illinois County

Extension Staff Join with other Agencies to Survey Illinois for New Corn Disease 2016: The USDA just announced the presence of Bacterial leaf streak in corn, as determined by recent surveys of the Corn Belt states.  In Illinois, a cooperative survey was organized with APHIS-PPQ (Animal Plant Health Inspection Service), IDA (Illinois Department of Agriculture), CAPS (Illinois Natural History Survey’s Cooperative Agricultural Pest Survey) and University of Illinois Extension to provide a rapid response to determine distribution.

In a short time window, our surveyors examined randomly selected fields in transects across 68 of Illinois’s 102 counties. They looked for Bacterial leaf streak symptoms in approximately 340 fields across the state.  Leaves with suspicious symptoms were collected and have been sent to a USDA laboratory for evaluation.  The Extension surveyors consisted of volunteers from the Commercial Agriculture, Small Farms and Local Foods and the Energy and Environment teams.

One positive sample of Bacterial leaf streak was found in DeKalb County, IL and identification was verified by the USDA yesterday.  This is the only county in Illinois that has been verified to have the disease.  So far, Bacterial leaf streak has been identified in 9 states:  Colorado, Iowa, Illinois, Kansas, Minnesota, Nebraska, Oklahoma, South Dakota, and Texas, figure 1.

Figure1: Illinois surveyed counties for Bacterial leaf streak 2016

Bacterial leaf streak is caused by the pathogen Xanthomonas vasicola pv. vasculorum. The disease causes the formation of linear lesions between the veins on a corn leaf. The lesions look similar to gray leaf spot (GLS) symptoms. GLS lesions tend to be shorter, more rectangular and stay within their veinal borders. Bacterial leaf streak lesions are more irregular, often thinner and longer,  will “bleed” over the veinal border and may have a halo when held up to the light.

Xanthomonas1

Picture 1. Foliar symptoms of Bacterial leaf streak showing long lesions with wavy margins and halo visible with back-lighting. Photo courtesy of Nicole E. Furlan USDA-APHIS-PPQ

In many Great Plains states that have found the disease, symptoms first appear on the lower leaves and infection progresses up the plant. Typically these fields have been under pivot irrigation.  However later infections may occur and show up primarily in the upper canopy, as was the case for the positive DeKalb county sample.  There is currently very little known about this disease. Further research is needed to develop a complete understanding of this disease, its impact and strategies for long term management.  However, APHIS notes it is not believed to present a health risk to people or animals.

Picture 2: Late foliar symptoms of Bacterial leaf streak showing long lesions.  Photo courtesy of Scott Schirmer Illinois Department of Agriculture, State Plant Regulatory Official.

Picture 2: Late foliar symptoms of Bacterial leaf streak showing long lesions. Photo courtesy of Scott Schirmer Illinois Department of Agriculture, State Plant Regulatory Official.

Since this is a bacterial disease, fungicides cannot be expected to control or suppress this disease. Crop rotation and tillage are the best short-term management strategies if the disease is present in a field.  Differences in varietal susceptibility may point the way to sources of resistance.

If you suspect Bacterial leaf streak, submit a sample to the University of Illinois Plant Clinic http://web.extension.illinois.edu/plantclinic/ We would like to get a comprehensive idea of distribution in the state. For more information on Bacterial leaf streak,  biology, symptoms, or management, please visit: http://cropwatch.unl.edu/bacterial-leaf-streak from University of Illinois alumna Dr.Tamra Jackson-Ziems, Nebraska Extension Plant Pathologist, and http://broderslab.agsci.colostate.edu/corn-bacterial-leaf-streak/.

Authors: N. Dennis Bowman and Suzanne Bissonnette


“Tip-back” and the 2016 corn crop

Although my post last week reflected the current optimism about yield prospects for the 2016 Illinois corn crop, there has been some recent discussion about unfilled ear tips and whether or not this might mean lower yields than the appearance of the crop leads us to believe.

Corn ears with kernels missing at the outer end of the ear are often said to have “tip-back.” The term is a little obscure, but the idea is that the end of the cob has been exposed by lack of kernels there, and that something happened to cause the ear to adjust its kernel number downward so it won’t have as many kernels to fill.

The missing kernels can be aborted kernels – ones that were fertilized but stopped developing – or can be kernel initials that weren’t fertilized due to problems with the pollination process. Low sugar levels in the plant before, during, and after pollination are often associated with such loss of kernels.

Because kernel number is closely related to yield, missing kernels on an ear suggest to many people that yield has been lost. Drought stress, loss of leaf area to hail or disease, or lack of nitrogen all result in stress that lowers photosynthesis and so decreases the sugar supply. So we associate low kernel numbers with stress. If different hybrids show different amounts of tip-back, this is taken as an indication of their tolerance to stress.

While low kernels numbers per acre and low yields do go together, it’s important in a year like this to consider the overall condition of the crop and to focus on how many kernels are present before worrying about how many kernels seem to be missing. We often see some amount of tip-back even in good years, and this may have no effect on yield if kernel numbers are still high.

As an example, under outstanding pollination conditions in 2014, we saw almost no tip-back; ears were filled out to the very end of the cob. There was much more tip-back in 2015, but kernel counts per acre and yields were as high in many areas in 2015 as in 2014. While we don’t think that having some tip-back is necessary to show that the ear had “extra” room in case it was needed it, it’s much more common to see some tip-back than to see none, and we don’t consider tip-back to be a problem if kernels numbers are high.

What matters for yield is the number of kernels per acre that fill, along with the ability of the crop to fill them completely. So 34,000 ears each with 16 rows of kernels and 35 kernels per row should produce yields in the vicinity of 220 bushels, even if most cobs have “room” on the end for another 50 or 100 kernels. At high yield levels when all of the nutrients the plant produces go to fill kernels, having more kernels may mean that kernels stay smaller, and yield may not change much.

In looking at some of our corn on South Farm on August 3, I saw more variability in kernel number and some smaller ears than I expected. In one field planted at about 36,000 seeds on April 20, plants were about 10 ft. tall but stalks were small in diameter and ear placement was high and somewhat variable. Figure 1 shows some ears in this field. This crop came up well and has had the dark green leaves and uniform appearance that most fields in the area have shown since emergence. But there are only about 375 kernels per ear on average, and if kernels fill to normal weight, yield will be around 160 bushels per acre. Ears show a lot of tip-back, and having silks still attached suggest that most of this resulted from failure of pollination. Kernels were in the late milk stage which is in line with planting date, but otherwise the crop has the appearance of corn that was planted late.

Figure 1. Ears in corn planted at 36,000 per acre on April 20.

Figure 1. Ears in corn planted at 36,000 per acre on April 20.

In another field with similar soil planted at the same time with slightly lower population, plants were not quite as tall, stalks were larger in diameter, and ears were more uniform in both placement and size (Figure 2). These ears show a small amount of tip-back, but with an average of about 600 kernels per ear, this field should yield 225 bushels per acre or more.

Ears in corn planted at 34,000 on April 22

Ears in corn planted at 34,000 on April 22

There are no obvious reasons why similar fields planted at about the same time should have such different kernel numbers and yield potential. The hybrids are different, but the field with lower yield potential has a number of different hybrids and most seem to show some degree of the same problem.

Even when plants emerge well and looked uniform in size and canopy color during vegetative growth, variability in ear size and placement suggests that plant-to-plant competition began early and increased during vegetative growth, eventually showing up as non-uniform ear development and lower kernel numbers. We can only speculate about how this might have happened, and why fields differ as much as they do. With the exception of a couple of cool periods in May, temperatures in May and June were warm and there was a lot of sunshine. Rainfall both months was near normal, but the latter half of June was dry, which could have meant more underground competition.

It appears that the crop used a lot of resources to grow the plant, including roots as they grew deeper during dry weather in the weeks before pollination. Uniformly warm air and soil temperatures and rapid growth during that period might have meant some diversion of sugars away from ear growth and kernel set. It’s also possible that uptake of water was slightly lower in some soils due to texture or root growth and uptake, and that the crop in such soils experienced a little more stress.

Although we can’t do anything to change kernel numbers now, it is worthwhile to visit each field to note kernel number and other plant characteristics that can help explain what happened in different fields. While the Illinois corn crop condition overall remains good, some fields may have disappointing kernel numbers even on plants that continue to look very good. Note which hybrids show this, but given that this may be a one-time phenomenon, be cautious about discarding hybrids, especially those that have been top-yielding in the past.