Identification of Palmer amaranth in Illinois

Palmer amaranth continued to expand its presence in Illinois during 2014. Palmer amaranth populations have been confirmed in counties colored orange or blue in Figure 1; orange designates glyphosate-resistant populations are present in these counties. It should be neither construed nor assumed that Palmer amaranth populations occur only in the counties colored on this map. It is altogether likely that Palmer amaranth populations are present in many other counties. Emerged Palmer amaranth plants were observed on May 7 at our field research location west of Kankakee.

Palmer amaranth distribution May 2015

Once again, we will assist Illinois 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 sample 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.

Also, please note that screening for herbicide resistance in waterhemp is now a service offered by the University of Illinois Plant Clinic and requires a different sample submission form.  More details about sample submission for herbicide resistance screening is available at: http://bulletin.ipm.illinois.edu/?p=3224

Palmer Amaranth Identification


A Quick Pigweed Identification Exercise

A scouting trip last Thursday to our Palmer amaranth research location west of Kankakee revealed that Palmer amaranth plants had begun to emerge a few days before our arrival. Early and accurate identification of Palmer amaranth plants is an important component of an integrated management program, but differentiating among seedling-stage Amaranthus plants sometimes can be difficult. As plants become larger and reproductive structures are present, identification becomes increasingly easier. The following photographs might help renew your Amaranthus species identification skills. See how many you can identify from these photographs, and in a few days we’ll repost this story with the species identified.

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Palmer amaranth

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Waterhemp

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Waterhemp

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Palmer amaranth

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Palmer amaranth

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Waterhemp

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Waterhemp

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Palmer amaranth

Cody's waterhemp populations

Waterhemp

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Redroot pigweed

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Smooth pigweed

Powell amaranth inflorescence

Powell amaranth

Spiny amaranth 4

Spiny amaranth

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Palmer amaranth


2015 Season at the University of Illinois Plant Clinic

What pests will the 2015 growing season feature? Let the Plant Clinic help you diagnose them. Samples havePreview been gradually filling up the lab here at the Clinic in our 40th year of operation. On the field front, there have been concerns with root and virus disease diagnosis in wheat. On the home landscape front, there has been a steady influx of fungal disease.

 
The University of Illinois Plant Clinic accepts samples year-round. We are located in the Jonathan Baldwin Turner Hall building on the south end of the Urbana campus. 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, herbicide resistance testing for glyphosate and PPO inhibitors in pigweed, 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 our website http://web.extension.illinois.edu/plantclinic/ 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, leave a voicemail if you can’t get through. 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.

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Photo 1:Example of a great sample: Sample form, symptomatic plant, protected root ball and payment

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

Email: We have a new email address plantclinic@illinois.edu. Use this address to send .jpg pictures to accompany your samples or to contact a diagnostician.

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 Hall 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.

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

Photo 2: Plant Clinic location, S-417 Turner Hall, 1102 S. Goodwin, Urbana IL 61801

Suzanne Bissonnette


University of Illinois Weed Science Field Research Tour

We invite you to attend the 2015 University of Illinois Weed Science Field Day on Wednesday, June 24th 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.

Mr. Doug Maxwell, long-time manager of the herbicide evaluation program at the University of Illinois, has announced his plans to retire sometime after the end of the 2015 growing season.  Doug has been an outstanding manager of this program for many years, and his leadership, vision, and attention to detail will be greatly missed.  We plan to refill this position, but realize we cannot replace Doug.  We hope you will take the opportunity to visit with Doug and wish him all the best for his retirement.

We look forward to visiting with you at the Urbana weed science field day on June 24th. Please contact us at 217-333-4424 if you have any questions.

 

 


Applying Soil-Residual Herbicides to Emerged Corn

The rapid progress of corn planting sometimes can outpace the application of soil-residual herbicides.  In most instances these herbicides are applied within a few days after planting, but weather-and equipment-related factors can delay applications until after corn has emerged.

Most, but not all, soil residual herbicides can be applied after corn has emerged.  Products such as Balance Pro, Radius, Fierce, Prequel, Sharpen and Verdict must be applied before corn begins to emerge; applications of these products to emerged corn can result in significant corn injury.  Be cautious about applying a soil-residual herbicide in UAN carrier if corn has emerged as this can increase the potential for corn injury.  Also, be sure to consult the respective product label for tankmix and spray additive recommendations or prohibitions.

Labels usually indicate a maximum corn growth stage beyond which applications should not occur.  These growth stages can range from as early as two leaf collars to as late as 40-inch tall corn, so be sure to consult the respective product labels.  Products containing atrazine must be applied before corn exceeds 12-inches tall, although the labels of some atrazine-containing products specify a smaller height.

 


Slowing the Evolution of Weed Resistance to Herbicides

Many individuals involved in production agriculture have first-hand experience with the numerous challenges caused by herbicide-resistant weeds.  The magnitude of herbicide resistance is best measured on a worldwide scale.  The most recent summary indicates 450 unique cases of herbicide resistance—encompassing 245 species—occur globally.  Approximately 11–12 cases of unique resistance are discovered each year.  Methods employed to detect and study the evolution of herbicide resistance have improved greatly over time, but our understanding of the epidemiology of herbicide resistance has lagged.

Recommendations to slow the evolution of herbicide-resistant weeds have been promoted by university and industry personnel for many years.  A common element of these recommendations has been to diversify the herbicide mechanisms of action (MOA) to which weed populations are exposed.  Herbicide rotations (within and between years) and tank-mixtures are two strategies recommended to achieve this diversification, but few quantitative data describe the effectiveness of these approaches at a landscape level.  So the question that largely remains unanswered is: does rotating herbicide MOA annually, or exposing weeds to multiple MOA simultaneously (i.e., tank-mixtures), do more to slow the evolution of herbicide resistance?

A recently completed research project sought to answer this critically important question.  In April 2015, USDA/ARS and University of Illinois weed scientists published the results from a project that studied the evolution of glyphosate-resistant waterhemp.  The research examined factors related to landscape, weed, and management from 105 Illinois grain fields, including over 500 site-years of herbicide application records. The researchers employed a statistical analysis known as CART (classification and regression tree) to identify relationships between the presence of glyphosate-resistant waterhemp and 66 variables related to environment, soil, landscape, weed community, and weed management.

Results of this landscape-level analysis indicated that management practices were the best predictors of glyphosate-resistant waterhemp among all 66 variables included in the analysis.  The occurrence of glyphosate-resistant waterhemp was greatest in fields where glyphosate had been used in over 75% of the seasons included in the analysis, where fewer MOA were used each year, and where herbicide rotation occurred annually.  Simply rotating herbicide MOA actually increased the frequency of resistance.

On the other hand, exposing populations to multiple MOA through tank-mixtures greatly reduced the selection for glyphosate-resistant waterhemp.  A field in which 2.5 MOA per application were used was 83 times less likely to select glyphosate-resistant waterhemp within 4–6 years than a field in which only 1.5 MOA per application were used.  But the researchers stressed that this strategy will work only if each component of the tank-mixture is effective against the target species.  They also emphasized that effective, long-term weed management will require even more diverse management practices.

What are some possible implications of these results as Illinois farmers continue to struggle with herbicide-resistant weeds?  The data indicate lack of effective tank-mixtures, not lack of residual herbicides, was the best predictor of glyphosate-resistant waterhemp.  In other words, each application made to a population, whether that be before emergence or after, should expose the population to more than one effective MOA.  A soil-residual herbicide applied before or after planting followed by single postemergence herbicide is unlikely to be a sustainable resistance management approach.

What about other and future herbicide-resistant traits?  Simply switching from a Roundup Ready system to Liberty Link, Enlist, or Extend is unlikely to provide a long-term solution.  If glyphosate-resistant weeds are already present in fields planted with varieties containing these other traits, we will begin selection for resistance to glufosinate, 2,4-D, and dicamba, respectively, if we don’t carefully consider how to best steward these traits.   These alternative herbicide-resistance traits are often touted as a “solution” to existing herbicide-resistant populations, but these types of marketing slogans unfortunately might serve to shorten the effective lifespan of these traits.  Long-term, sustainable solutions to herbicide resistance are unlikely to be “simple” or “convenient.”

One of the encouraging findings of the study was that, as previously stated, management practices were the most important predictors of glyphosate-resistant waterhemp. Proximity to infected fields, or weed population densities within a given field, were not important predictors of resistance.  In other words, even if you have large populations of waterhemp in your field, or a neighbor with glyphosate-resistant waterhemp in their field, you can keep glyphosate-resistant waterhemp at bay if you implement appropriate weed management strategies.


Don’t Forget about Marestail

The harsh realities of poor marestail control with burndown herbicides applied before soybean planting were widespread during the 2013 growing season.  We anticipated even more challenges with this species for the 2014 growing season, but by and large the forecasted marestail “train wreck” did not materialize in much of the state.  Fall herbicide applications coupled with a harsh winter that caused a high degree of mortality to winter annual weed species probably contributed to a reduced population of marestail last spring.  However, it is unwise to assume that a lower marestail population last year will translate into a low marestail population this year.

It’s not too early to apply herbicides to control emerged marestail in fields that will be planted to soybean.  The small marestail plants we have currently will be much easier to control than the larger plants that will be encountered in several weeks.  Consider an early herbicide application targeted for marestail control, and application of soil-residual herbicides for summer annual weeds closer to soybean planting.  Dr. Mark Loux, extension weed scientist at The Ohio State University, recently published suggestions to improve marestail control with burndown herbicides; you can read these suggestions at http://corn.osu.edu/newsletters/2015/2015-08/managing-marestail-this-spring-2013-the-perfect-storm

 


Decisions About Winter Wheat and Weeds

The most recent report on the condition of the Illinois winter wheat crop indicated approximately 10% of the crop was rated poor or very poor, while close to 90% was rated fair to excellent.  It appears likely that much of the wheat crop will remain intact, but in other instances farmers might elect to terminate poorer stands and plant corn or soybean.  If the decision is made to plant corn or soybean into wheat stands where some plants remain alive, it is advisable to control any remaining wheat plants prior to planting either corn or soybean.  Controlling existing wheat stands may be accomplished through the use of tillage, herbicides, or a combination of these.

If the wheat field was previously treated with a herbicide, be sure to check for any applicable crop rotational intervals.  These could determine whether or not corn or soybean could be planted.  If a combination of herbicides and tillage will be used to terminate an existing stand, improved control might be achieved if the herbicide application occurs prior to the tillage operation, compared with the opposite order.  Regardless of what herbicide you use to control wheat plants, there should be an interval of at least 3 to 5 days (or more) between application and tillage to allow the herbicide to work within the plant.

It is altogether possible that other weed species, such as maturing winter annuals, early summer annuals, biennials, or perennials, also might be present in existing wheat fields.  If so, select a herbicide or herbicide combination that will provide broad-spectrum control of both grass and broadleaf weed species.  If 2,4-D is included in the tankmix, be cognizant of the intervals that must elapse between application and planting (especially for soybean, but also for corn with some formulations).

Several herbicides could be used to control existing wheat plants.  Glyphosate is very effective on grasses, including wheat.  The label suggests using 0.56 lb ae to control overwintered wheat up to 6 inches tall, 0.77 lb ae to control wheat up to 12 inches tall, and 1.125 lb ae for wheat up to 18 inches tall.  Gramoxone SL is a rapidly-acting contact herbicide.  Efficacy on wheat can be improved when atrazine or metribuzin is tankmixed with Gramoxone SL.  A crop oil concentrate or nonionic surfactant should be included, and thorough spray coverage is essential for good control.  The labels of the ACCase-inhibiting herbicides (Poast, Assure II, Select Max, Fusilade DX, and Fusion) indicate these products are effective against volunteer wheat.  However, each product label also indicates a specific rotational interval between application and planting corn.  Poast is labeled for preplant applications, but applications must be made at least 30 days before planting corn.  The labels of Select Max, Fusion, Fusilade DX, and Assure II indicate rotational intervals of 30, 60, 60, and 120 days, respectively, between application and planting corn.

Herbicide applications to control weeds in wheat must be properly timed to provide good weed control and minimize the potential for crop injury.  Applications made to actively growing weeds and during periods of warm air temperatures generally provide more effective and complete weed control as compared with applications made during cold, cloudy conditions.

The labels of all herbicides commonly used for weed control in Illinois wheat have application restrictions based on wheat developmental stage.  The labels of most herbicides commonly used in Illinois indicate applications must be made before the wheat jointing or boot stage.  Figure 1 contains information derived from the herbicides labeled for use in small grains.  Before making any herbicide application, consult the respective herbicide label for additional information.

If you are considering applying a herbicide with liquid nitrogen as the carrier, be sure to consult the herbicide label prior to making this type of application.  Not all herbicides allow applications with liquid nitrogen as the carrier, and those that do allow this might have specific recommendations with respect to including/excluding other spray additives or their application rates.

Figure 1. Wheat growth stages and herbicide application (from 2015 Weed Control Guide for Ohio, Indiana and Illinois).


Spring Cover Crop Field Day March 26th – Ewing Demonstration Center

Join us on Thursday, March 26th, 2015 for the  Spring Cover Crop Field Day at the University of Illinois Extension Ewing Demonstration Center.  Registration will start at 8:30 a.m. and the program will begin at 9:00 a.m., rain or shine.  The Ewing Demonstration Center is 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.

Cover crops have many benefits to the soil, environment, and overall crop production and management.  Topics covered during this field day program include:

Challenges of Grazing Lush Spring Forage

–          Travis Meteer, Extension Educator, U of I Extension

Techniques for Planting into Cover Crop Residue

–          Mike Plumer, Private Consultant

Understanding the Soil Profile Beneath Your Feet

–          Bryan Fitch, Resource Soil Scientist, NRCS

Which One to Choose? Cover Crop Species Selection and Demonstration Trial Tour

–          Nathan Johanning, Extension Educator, U of I Extension

Some of the program highlights will be the demonstration trial planting of cover crops, including 17 different cover crops and combinations illustrating first hand the characteristics of the cover crops and what benefits they bring to your soil and crop production system.  Also, (weather and soil conditions permitting) we will have a soil pit dug, exposing the soil profile, where NRCS Resource Soil Scientist, Bryan Fitch will lead us through the characteristics of our southern Illinois soils to enhance understanding of the importance of a healthy soil.  Also Certified Crop Advisor CEU credits will be available (2.0 Soil & Water Management & 1.0 Crop Management) for the program.

This field day will be free and open to anyone interested in learning more about cover crops.  A light lunch will be provided and this is a great way to talk to fellow growers to learn more from their challenges and successes incorporating cover crops into their cropping systems.  Please call the Franklin County Extension Office at 618-439-3178 for more information and to register by March 24th.  We hope to see you there!


2015 Weed Control Guide Now Available

The 2008 edition of the Illinois Agricultural Pest Management Handbook was the final edition of a publication that served pest management practitioners for many decades. Herbicide information and annual updates of product performance ratings were mainstays of that publication.  Since 2008 we periodically have published herbicide performance ratings, but admittingly not with a great deal of consistency.  Recently, the weed science programs at The Ohio State University and Purdue University extended an invitation to the University of Illinois weed science program to join them in the production of their joint weed control publication.  The 2015 Weed Control Guide for Ohio, Indiana and Illinois contains 212 pages of weed management information, including weed response ratings for corn and soybean herbicides.  Information and recommendations for managing weeds in small grains and forages is included, along with more specific information about and control recommendations for several problem weed species.  A pdf of the 2015 Weed Control Guide is available to download, and a printed version of the guide can be ordered at: http://estore.osu-extension.org/productdetails.cfm?PC=2860