Palmer amaranth Field Research Tour July 30

The University of Illinois weed science program would like to extend an open invitation to join us on July 30, 2014 for a field tour and discussions at our Palmer amaranth research site, located approximately ½ mile east of the intersection of county roads 14000 west and 3000 north (see Google map following this article) near the community of Union Hill.  The tour will provide an excellent opportunity for farmers, input suppliers, members of the media, etc. to have a first-hand encounter with a Palmer amaranth population thriving just a few miles south of Illinois’ largest city.  The tour will feature four presentations by weed scientists that highlight the identification, biology, and management of Palmer amaranth, and also provide ample opportunity to view the numerous research plots.  Participants will receive a complimentary tour booklet that contains field research protocols and maps that will help guide them through the research plots.  The tour will begin at 9:00 a.m. and conclude with a catered lunch around noon.  Advanced registration can be accomplished by visiting  Everyone is welcome and there is no fee to attend this tour.  Credits for certified crop advisers will be available.

Figure 1.  Photographs taken at the Palmer amaranth location the day of planting (left) and six weeks after planting (right).


A brief synopsis of the four tour presentations follows:

Dr. Larry Steckel, extension weed scientist at the University of Tennessee, will provide tips on Palmer amaranth identification and also share his vast experience in managing this invasive and extremely competitive weed species in Tennessee

Dr. Pat Tranel, professor of molecular weed science at the University of Illinois, will discuss the current status of herbicide resistance among waterhemp and Palmer amaranth populations in Illinois, and also offer insights into how to best employ future technologies to manage these dioecious pigweeds

Dr. Aaron Hager, extension weed scientist at the University of Illinois, will discuss recommendations to manage Palmer amaranth in Illinois agronomic crops, including how to best utilize soil-residual herbicides in combination with intense crop scouting, timely applications of foliar-applied herbicides, and other mechanical and cultural methods

A representative of Bayer CropScience will provide an update on new Bayer traits and technologies under development to help manage Palmer amaranth and other troublesome weeds


Our Palmer amaranth field research activities and tour are in collaboration with scientists and researchers from Bayer CropScience.  We thank Bayer CropScience and all our research partners for providing the research support necessary to better understand and manage Palmer amaranth in Illinois.

Screening Waterhemp for Herbicide Resistance

Herbicide-resistant waterhemp populations continue to expand into more areas of Illinois each season.  Waterhemp has evolved resistance to herbicides encompassing more mechanisms of action than any other Illinois weed species, including resistance to inhibitors of acetolactate synthase (ALS), photosystem II (PSII), protoporphyrinogen oxidase (PPO), enolpyruvyl shikimate-3-phosphate synthase (EPSPS) and hydroxyphenyl pyruvate dioxygenase (HPPD).  Not every individual waterhemp plant is resistant to one or more herbicides, but the majority of field-level waterhemp populations contain one or more types of herbicide resistance.  Perhaps even more daunting is the occurrence of multiple herbicide resistances within individual plants and/or fields.

Since 2010, the Illinois Soybean Association has provided funding to screen waterhemp samples for herbicide resistance.  During the first three years of screening, approximately 1000 samples were submitted; in 2013 alone over 1200 samples were submitted.  These samples have allowed us to monitor the spread of herbicide resistance (and in particular glyphosate resistance) across Illinois (Figure 1).  One point of particular interest in 2013 was that the vast majority of samples were submitted from counties north of Champaign County.

We are pleased to announce that, with continued financial support from the Illinois Soybean Association and Pioneer, we are offering free screening for herbicide resistance in waterhemp during the 2014 growing season.  There is no fee for this service, but please understand that we cannot guarantee when results will be available. Also, because of the way in which we conduct our resistance tests, a test result of “sensitive” to glyphosate does not rule out the possibility that the plant actually is resistant, but by a mechanism that is different than for what we are testing. We would like to assure everyone that we will respect the privacy of those sending samples: we will not make the exact location of any samples, or names associated with samples, available to anyone without your permission. The sample submission form, including submission instructions, is available as a downloadable file. If you have any questions, feel free to contact Pat Tranel (217-333-1531;

Sample submission form 2014

Reminder…University of Illinois Weed Science Field Research Tour

We would like to take this opportunity to once again extend the invitation to attend the 2014 University of Illinois Weed Science Field Day, to be held next Wednesday, June 25th at the University of Illinois Crop Sciences Research and Education Center, located immediately south of the main campus.  Coffee and refreshments will be available under the shade trees near the Seed House beginning at 8:00 a.m.  The tour will provide ample opportunity to look at research plots and interact with weed science faculty, staff, and graduate students. Participants can compare their favorite corn and soybean herbicide programs to other commercial programs.  The tour will conclude around noon with a catered barbeque lunch at the Seed House.  Cost for the Urbana weed science field tour is $10, which will help defray the cost of the field tour book, refreshments and lunch.

We look forward to visiting with you at the Urbana weed science field day on June 25th.  Please contact us at 217-333-4424 if you have any questions.


University of Illinois to Offer Assistance Identifying Palmer Amaranth

Accurate identification of weedy Amaranthus species during early vegetative stages sometimes can be difficult.  Differentiating between smooth pigweed and waterhemp is relatively easy since one species (smooth pigweed) has pubescence on the stem and leaves while the other does not.   However, differentiating between waterhemp and Palmer amaranth during early vegetative stages can be much more difficult.  To assist weed management practitioners in accurately identifying Palmer amaranth, we will accept tissue samples from suspected Palmer amaranth plants and use tools of molecular biology to identify whether the plant is Palmer amaranth or another species of Amaranthus.  Information on how to collect and submit tissue samples from suspected Palmer amaranth plants can be found in the “Palmer Amaranth Identification” form that accompanies this article.  Please download this form, provide as much information as possible, and submit it along with the tissue samples to the address listed at the top of the form.

Palmer Amaranth ID Form

Soybean Injury from Soil-Applied Herbicides

Integrated weed management programs offer the greatest potential for long-term, sustainable solutions to weed populations demonstrating resistance to herbicides from multiple families.  Soil-residual herbicides are important components of integrated weed management programs and provide several benefits, including reducing the intensity of selection for resistance to foliar-applied herbicides.  Recent survey data indicate the percentage of Illinois soybean acres treated with soil-residual herbicides has increased during the past few years.

In the vast majority of instances, soil-applied herbicides control target weed species with little to no adverse effect on the crop.  However, soybean plants sometimes are injured by these herbicides. Questions about soybean injury caused by soil-applied herbicides recently have been posed, so this article will review some of the factors that can contribute to herbicide-induced soybean injury.

Herbicides vary in their inherent potential to cause soybean injury.  Many university-generated herbicide effectiveness rating tables also provide estimates of soybean injury potential.  Some herbicide active ingredients, such as cloransulam and clomazone, are often rated as having very low potential to cause soybean injury, whereas other active ingredients are rated as having a greater inherent potential to cause injury.  The rate at which the herbicide is applied can influence the potential for soybean injury by increasing or decreasing the amount of herbicide in a given volume of soil.

Most many cultivars are not overly sensitive to any particular herbicide, but other soybean cultivars can vary in their sensitivity to certain herbicides.  Data in the scientific literature and company-generated variety trials demonstrate cultivar sensitivity differences to various soil-residual herbicides.  Some cultivars demonstrate sensitivity to one active ingredient, whereas other cultivars can be sensitive to more than one active ingredient.

The environment has a large influence on the severity of soybean injury caused by soil-applied herbicides.  Environment-induced crop stress, often caused by cool, wet soil conditions, can enhance soybean injury from soil-applied herbicides.  In most cases, herbicide selectivity arises from the soybean plant’s ability to rapidly metabolize the herbicide to a nonphytotoxic form before it causes much visible injury.  Soybean plants growing under favorable conditions are able to adequately metabolize the herbicide before any injury symptoms are expressed.  However, when the soybean plant is under stress, its ability to metabolize the herbicide can be sufficiently reduced to the point at which injury symptoms develop.

Soil physical properties can increase or decrease the potential for soybean injury by impacting how much herbicide is available for plant uptake.  Soils with higher amounts of clay and organic matter have a greater ability to adsorb more herbicide onto these soil colloids.  Herbicide bound to soil colloids is not available for plant uptake.  In contrast, coarse-textured soils have less adsorptive capacity so more herbicide remains available for plant uptake.  Labels of soil-applied herbicides often contain precautionary language about the increased potential for soybean injury when the product is applied to sandy soils or soils low in organic matter.

The application timing of soil-residual herbicides also can impact the potential for soybean injury.  Applications made immediately before or after soybean planting result in a high concentration of herbicide near the emerging soybean plants.  In contrast, a herbicide is often more widely distributed within the soil profile by the time of soybean emergence when applications are made several days or weeks prior to planting.

The soil-applied PPO-inhibiting herbicides, including saflufenacil, flumioxazin, and sulfentrazone, are very effective for control of Amaranthus species.  These herbicides (and many others) also can cause soybean injury.  Our first experience with soybean injury from soil-applied PPO inhibitors occurred in 1996 while evaluating sulfentrazone for control of herbicide-resistant waterhemp.  Soybean injury symptoms caused by these soil-applied herbicides can vary depending on the soybean developmental stage when exposure occurred.  The most commonly encountered injury symptoms occur on the hypocotyl and cotyledons (Figure 1), often indicating the plants were exposed to a high concentration of herbicide as they were emerging.

Figure 1. Injury symptoms evident on emerging soybean plant.

Symptoms include necrotic lesions on the soybean hypocotyl near the soil surface and reddish-colored spots or lesions on the hypocotyl and/or cotyledons (Figures 2 and 3).  Lesions on the hypocotyl may not always kill the young soybean plants, but can create an area of weakened tissue that may lead to stems breaking during rain or high wind.  In severe cases, plants may actually die following emergence of the cotyledons.

Figure 2. Reddish-colored hypocotyl tissue near the soil surface.

Figure 3. Emerged soybean with damage to hypocotyl and cotyledons.

Plants with damage only to cotyledons usually develop normally (Figure 4).

Figure 4. Injury to cotyledons.

Other symptoms can occur after soybean emergence if treated soil is splashed into the soybean meristem by heavy precipitation.

There likely is no solitary reason for the recent instances of soybean injury from soil-applied PPO-inhibiting herbicides.  As previously mentioned, our first experience with this type of soybean injury occurred almost 20 years ago and we have continued to observe this type of injury intermittently ever since.  These herbicides have become very popular choices for the management of herbicide-resistant Amaranthus populations, and widespread application of these herbicides increases the probability of encountering soybean cultivars that inherently are more sensitive to one or more of these herbicides.  In many instances of soybean injury, the herbicide was applied after soybean fields were planted and a precipitation event occurred within a few days of soybean emergence.  Cool air and soil temperatures during the same interval can further increase injury potential by slowing the rate of herbicide metabolism.  A crusted soil surface can slow soybean emergence, increasing the time the hypocotyl and cotyledons remain in the zone of high herbicide concentration.  Once the herbicide is moved deeper into the soil profile, the potential to cause additional injury is greatly reduced.


It’s not too early to scout for Palmer amaranth

Planting progress may have been slowed by the recent precipitation, but weed emergence continues despite wet field conditions.  Be aware that Palmer amaranth has begun to emerge. We scouted our Palmer amaranth field location west of Kankakee on May 8 and observed emerged Palmer amaranth plants (Figure 1).

Figure 1. Emerged Palmer amaranth, May 8 near Kankakee


We returned to the field on May 15 to find a very robust Palmer amaranth population (Figure 2).  The largest Palmer amaranth plants found on May 15 were approximately 2 inches tall with 6 to 8 true leaves.

Figure 2. Emerged Palmer amaranth, May 15 near Kankakee


Some leaf petioles on older Palmer amaranth plants already had elongated to approximately twice the length of the leaf blade, but we did not find any leaves with chevrons or watermarks.  Extension weed scientists in Iowa and Ohio also have reported finding emerged Palmer amaranth plants in their respective states.

Completing corn and soybean planting will assume top priority when field conditions are again suitable, but please do not overlook the need to control emerged Palmer amaranth in fields already planted.  The return of warm air temperatures coupled with ample soil moisture will help emerged Palmer amaranth plants grow very rapidly.  Postemergence herbicides should be applied before Palmer amaranth plants are taller than 4 inches.  It is NOT advisable to delay the application of postemergence herbicides until additional Palmer amaranth plants emerge.  Delayed application of postemergence herbicides, whether by choice or due to adverse weather conditions, can lead to disastrous outcomes.

Palmer amaranth continues to germinate throughout much of the growing season, making it altogether likely that additional Palmer amaranth plants will emerge following the initial postemergence herbicide application.  Consider including a soil-residual herbicide with the postemergence herbicide to control additional Palmer amaranth emergence and allow the crop to gain a competitive advantage over later-emerging weeds.

Palmer Amaranth 2014 HI

University of Illinois Weed Science Field Research Tours

We invite you to attend the 2014 University of Illinois Weed Science Field Day on Wednesday, June 25th at the University of Illinois Crop Sciences Research and Education Center, located immediately south of the main campus.  Coffee and refreshments will be available under the shade trees near the Seed House beginning at 8:00 a.m.

Similar to past years, we will car pool to the fields where participants can join in a guided (but informal) tour format.  The tour will provide ample opportunity to look at research plots and interact with weed science faculty, staff, and graduate students. Participants can compare their favorite corn and soybean herbicide programs to other commercial programs and get an early look a few new products that soon will be on the market.  The tour will conclude around noon with a catered lunch at the Seed House.

Cost for the Urbana weed science field tour is $10, which will help defray the cost of the field tour book, refreshments and lunch.  We will apply for 2 hours of CCA credit under the IPM category.

We are continuing field research work at the Dekalb, Perry and Brownstown research centers.  There will not be formal weed science tours at these locations, but most of the weed science plots will be signed during the agronomy day field tours scheduled for these locations.  We are also planning to host a field tour at our Palmer amaranth field location west of Kankakee toward the later part of July.  We’ll provide additional information about this tour via the Bulletin when details have been finalized.

We look forward to visiting with you at the Urbana weed science field day on June 25th.  Please contact us at 217-333-4424 if you have any questions.

Visualizing the growth rate of Palmer amaranth

Recently, the weed science program at the University of Illinois published recommendations for the management of Palmer amaranth in Illinois agronomic crops.  One particular recommendation emphasizes the need for timely application of foliar-applied herbicides; in particular, foliar-applied herbicides must be applied before Palmer amaranth plants are taller than four inches.  Most weed management practitioners are very familiar with the growth rates of waterhemp and many other weed species, but perhaps are less familiar with the growth rate of Palmer amaranth.

Cody Evans, a weed science graduate student at the University of Illinois, initiated work in the greenhouse to compare the growth rate of waterhemp and Palmer amaranth.  This was not a replicated experiment, but simply a demonstration of the relative growth rate differences between these two species.  Both species emerged on the same day, and the plants were photographed every other day for a month.  As the photographs illustrate, Palmer amaranth plants reached a 4-inch height less than 10 days after emergence.

The growth rate comparison illustrated in the accompanying photographs was conducted under greenhouse conditions, but experience suggests a similar growth rate of Palmer amaranth should be expected under field conditions.  Timely applications of foliar-applied herbicides will require vigilant scouting throughout a large portion of the growing season.

Ready for Samples at the University of Illinois Plant Clinic

Welcome to another Diagnostics season! Samples have been steadily appearing this spring here at the Clinic in our 39th year of operation. On the field front, there have been concerns with virus disease diagnosis in wheat. On the home landscape front, there is a mountain of winter kill and windburn injury from the harsh winter just past.

The University of Illinois Plant Clinic began year-round operation in the fall of 2011. Our new location is in Jonathan Baldwin Turner Hall on the south end of the Urbana campus. During the winter, our hours are irregular due to trainings and winter meetings so call ahead. However, we resume regular business hours, 8am-12pm and 1pm-4:30pm, on Monday April 28th, 2014.

Example of a great sample: Sample form, symptomatic plant, protected root ball and payment

Plant Clinic services include plant and insect identification, diagnosis of disease, insect, weed and chemical injury observation (chemical injury on field crops only), nematode assays, and help with nutrient related problems, as well as management recommendations involving these diagnoses. Microscopic examinations, laboratory culturing, virus assays, and nematode assays are some of the techniques used in the clinic. Many samples can be diagnosed within a day or two. Should culturing be necessary, isolates may not be ready to make a final reading for as much as two weeks. Nematode processing also requires about 1-2 weeks depending on the procedure. We send your final diagnoses and invoices to you through both the US mail and email. If you provide your email address on the sample form you will get your information earlier.

Please refer to the Plant Clinic website for additional details on sampling, sample forms, fees and services offered. If you have questions about what, where, or how to sample call us at 217-333-0519. Whenever submitting a sample, provide as much information as possible on the pattern of injury in the planting, the pattern on individual affected plants, and details describing how symptoms have changed over time to cause you concern.

Our fees vary depending on the procedure necessary. General diagnosis including culturing is $15, ELISA and immunostrip testing is $25, Nematode analysis for SCN or PWN is $20, Specialty Nematode testing (such as corn) is $40.

Please include payment with the sample for diagnosis to be initiated. Checks should be made payable to the University of Illinois or to the Plant Clinic. Companies can setup an account, call and we will accommodate you. Call if uncertain of which test is needed.

Plant Clinic location, S-417 Turner Hall, 1102 S. Goodwin, Urbana IL 61801

Drop off a sample:

You can also drop off a sample at S-417 Turner Hall. Park in the metered lot F 28 on the east side of Turner or at the ACES library metered lot on the west side of Turner. Come in the South door. Take the elevator located in the SE corner of the building. Turn left when exiting the elevator; we are located along the SE corridor of the 4th floor. Please use the green drop box located just outside S-417 if we are temporarily out of the office.

Sending a sample thru US mail or delivery service address to:

University of Illinois Plant Clinic
1102 S. Goodwin, S-417 Turner Hall
Urbana, IL 61801

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