Adjacent and Neighboring: How Far is That?

An article posted to the Bulletin last November outlined several changes made by the United States Environmental Protection Agency to the labels of XtendiMax, Engenia, and FeXapan.  The intent of these label amendments is to reduce sensitive plant species exposure to dicamba primarily through physical movement (i.e., drift during the application or particle movement during temperature inversions) and via dicamba residues dislodged from application equipment.  Those in Illinois who have completed the required dicamba training being conducted by registrant personnel likely heard repeatedly that preventing off-target movement during the application is solely and completely the responsibility of the applicator.  But what is less-than-clear is how far from the treated field off-target extends.

The following statements can be found on the current labels of XtendiMax/FeXapan and Engenia, respectively:

“Do not apply this product when the wind is blowing toward adjacent non-dicamba tolerant susceptible crops; this includes non-dicamba tolerant soybean and cotton.”

“Do not apply when wind is blowing in the direction of neighboring sensitive crops.”

The labels clearly specify that applications may be made only when wind speed is between 3 and 10 miles per hour, meaning there always will be a downwind side(s).  Problematically, however, neither product label defines “adjacent” or “neighboring” with respect to distance from the treated field.  In instances where no downwind areas can be included in a buffer (corn field, paved road, building, etc.), there always will be some sensitive crop at some distance downwind.  Is a sensitive soybean crop adjacent or neighboring if it is less than 10 feet from the treated field?  What about 100 feet from the treated field?  What if the sensitive soybean field is one mile from the treated field?  “Adjacent” and “neighboring” can be defined by a dictionary, but no dictionary can provide the distance(s) considered adjacent or neighboring for these products.

Registrants of dicamba-containing products labeled for use in dicamba-resistant soybean varieties have indicated they have no intention to include distances that define adjacent and neighboring on the labels.  Rather, manufacturers intend to leave the decision to spray or not to spray at the discretion of the applicator.  However, inspectors with the Illinois Department of Agriculture (IDOA) ultimately will have the final determination of distance to adjacent and neighboring sensitive crops during investigations.  If an inspector’s interpretation of adjacent or neighboring is different from the applicator’s interpretation, penalties and fines against the applicator could result.

A request was made of the IDOA to define how agency personnel will interpret adjacent and neighboring with respect to distance.  The following paragraph, reproduced in its entirety and with permission, is the response from IDOA:

“Every situation is unique and numerous factors must be considered when evaluating whether an application is appropriate.  The Department interprets this label provision (“adjacent” or “neighboring”) to go beyond “side by side” but we do not have a specific distance limitation. Users are instructed to “survey the application site for neighboring non-target susceptible crops”. Based on this survey, they make their spray/no spray decision. It is not just a simple 1-mile, 2-mile, 3-mile measurement because every situation, including local topography, weather conditions, etc., is unique.”

So, how will an applicator determine whether or not an application should be made when the wind is blowing toward a dicamba-sensitive crop that is 5, 10, or 5280 feet adjacent or neighboring the field to be treated?  The answer remains critically important but rather elusive.

Test Your Integrated Weed Management Knowledge!

Test your knowledge of integrated weed management (IWM) with this short quiz ( The quiz is anonymous, and the answers will be revealed at the end.

Effective long-term weed management requires integrating multiple effective techniques, as opposed to relying solely on one or two tactics. This is particularly true as troublesome herbicide-resistant weeds continue to develop and spread throughout the US. Diversifying weed management tactics, preventing the introduction of new weeds, and varying herbicide modes of action reduces the spread and establishment of resistant weeds. This brief, anonymous, 20-question quiz will test your IWM chops and help us give due credit to how farmers are using IWM throughout the US. All answers are completely anonymous and optional. Answers are score are revealed after clicking “Submit.” Click here to take the quiz:

The quiz was written by weed scientists from 14 universities with funding from the USDA Agricultural Research Service and is being distributed in states all over the US. Find more information on IWM and herbicide resistant weeds at

Precautions for Dicamba Use in Xtend Soybeans

The extension weed science programs at The Ohio State University, Purdue University, and the University of Illinois recently collaborated to produce suggestions and precautions for use of dicamba in dicamba-resistant soybean.  The United States Environmental Protection Agency issued amendments to the Xtendimax, Engenia, and FeXapan labels last October, and this new extension weed science publication offers additional suggestions to help further reduce off-target dicamba movement.  Dicamba Precautions

Label Changes for XtendiMax, Engenia, and FeXapan

On October 13, the United States Environmental Agency (EPA) issued several amendments to the XtendiMax, Engenia, and FeXapan labels that will impact all purchases and applications of these products in 2018 and beyond.  These amendments can be summarized as:

1) XtendiMax, Engenia, and FeXapan are now restricted use products (RUP), permitting only certified applicators to purchase and/or apply these products.

2) Prior to applying these products in 2018, applicators must complete dicamba or auxin-specific training.  Two of the labels further specify training will be required annually.

3) Record keeping is required for applications of these products.  See the updated labels for the entire list of records that must be completed within 14 days of each application and retained for a period of two years.

4) All applications, regardless of application timing, are limited to when maximum wind speeds are not greater than 10 miles per hour (reduced from 15 miles per hour).  Wind speed and direction are to be recorded at boom height.

5) All applications are limited to between sunrise and sunset.

6) A record of compliance with spray system cleanout procedures, as per label guidelines, is required.

7) Enhanced language pertaining to susceptible crops; for example: “DO NOT APPLY this product when the wind is blowing toward adjacent non-dicamba tolerant susceptible crops; this includes NON-DICAMBA TOLERANT SOYBEAN AND COTTON.”

The intent of these label amendments is to reduce sensitive plant species exposure to dicamba primarily through physical movement (i.e., drift during the application or particle movement during temperature inversions) or via dicamba residues dislodged from application equipment.  These amendments, however, do not address exposure through volatility.

The RUP classification of these products requires anyone who purchases or applies them to be licensed by the State of Illinois as either private or commercial applicators.  A private applicator license is required if you apply RUPs on lands you own or control in the production of an agricultural commodity, whereas a commercial license is required for persons who apply pesticides for hire, apply pesticides to the property of their employer only, or for government employees who apply pesticides during the normal course of duty.

Dicamba or auxin-specific training must be completed prior to application of these products in 2018.  The training is required for any labeled application of these products (i.e., not only for application to dicamba-resistant soybean varieties).  The Illinois agricultural organizations are working to assist the industry with meeting the training requirement prior to the 2018 crop season. Go to after November 15 for a list of scheduled training events around Illinois, and the register for these events.

Weed Seed Destructor Field Demonstration Reminder

Here is a great opportunity to see a novel weed management tool!  Dr. Adam Davis, USDA/ARS weed ecologist at the University of Illinois, will host a field demonstration of the Harrington Seed Destructor (HSD) on October 12.  The HSD will be run several times during the tour, so please attend even if you are not able to arrive exactly at 1:00 p.m.  The following news release, written by Lauren Quinn, provides more details about the field demonstration.


Weed seed destructor demonstration planned at Illinois

URBANA, Ill. – Farmers battling herbicide resistant weeds could add a new weapon to their arsenal, but it’s not a chemical. The Harrington Seed Destructor destroys this year’s weed seeds during harvest, preventing establishment in the spring. Farmers can see it in action Oct. 12 at the University of Illinois.

“I’ll admit I was a bit skeptical about whether the HSD would work on waterhemp, but using it during last year’s harvest reduced waterhemp populations in this year’s crops,” says Adam Davis, ecologist in the Department of Crop Sciences and with the USDA Agricultural Research Service.

The field tour will begin at 1 p.m. at the Crop Sciences South First Street Facility at 4202 South 1st Street in Savoy. The tour will also include visits to two nearby field sites.

Attendees are not required to register, and all are welcome. For more information on the Harrington Seed Destructor, visit, or contact Taylor Stewart at 217-300-6299 or

The Dicamba Dilemma in Illinois: Facts and Speculations

Only a short time ago, many agricultural professionals were optimistic Illinois would somehow be “spared” the incidents of off-target damage caused by dicamba that continue to plague several states to our south.  The recent preponderance of evidence (observations made traveling the state, stories on social media, an increasing number of pesticide misuse complaints filed with the Illinois Department of Agriculture (IDOA), etc.), suggests otherwise.  Instances of soybean demonstrating symptoms of exposure to dicamba have greatly increased over the past two weeks and it’s nearly certain the number of affected acres will continue to rise.  To estimate the extent of this using the number of complaints filed with the IDOA as the sole metric would be to grossly underestimate the current reality.

Some might be surprised to learn that instances of soybean exposure to dicamba have been an annual occurrence in Illinois since dicamba was first commercialized almost 50 years ago.  One of the first experiments that described soybean’s sensitivity to dicamba was conducted by Dr. Loyd Wax at the University of Illinois in 1966–19671.  The stated objective of the experiments “…was to determine the response of soybeans to soil and foliar applications of dicamba, picloram, and 2,4-D to assess the potential hazard of using these herbicides in crops in rotation with soybean and in areas adjacent to soybean fields.”  The symptoms of soybean exposure to dicamba described by these researchers 50 years ago are nearly identical to those currently being observed.

The widespread adoption of glyphosate-resistant corn hybrids in Illinois during the first decade of the 21st century was accompanied by a decrease in dicamba use in corn, resulting in relatively few complaints of soybean exposure during the last 10 years.  With more dicamba currently being applied, it’s not surprising the instances of soybean exposure have increased. Whether applied in corn or dicamba-resistant soybean, the fact remains that few dicot species in the Illinois landscape are more sensitive to dicamba than soybean.

Symptoms of exposure:

There appears to be some confusion about symptoms of exposure to dicamba compared with leaf symptoms caused by non-dicamba factors.  Dr. Wax and his colleagues described the effects of dicamba on soybean leaves as “…cupped and crinkled,” which are terms still commonly used today.  Other factors can cause leaf distortions, but I am not aware of anything other than dicamba that causes the following symptoms collectively:

1) ) extreme cupping of trifoliolate leaves, most pronounced on the upper trifoliolates (Figure 1)

2) veins of affected leaves tend to assume a parallel orientation instead of the usual net venation pattern (Figure 2)

3) tips of cupped leaves with parallel veins are often brown or cream-colored

4) plants are stunted as compared to plants not demonstrating the aforementioned symptoms; these plants may sometimes remain stunted the remainder of the season

5) depending on time and dose of exposure, pod development can be adversely affected

While the symptoms of exposure to dicamba are apparent, identifying how the exposure occurred is not always obvious.  Speculations and “explanations” from some industry personnel have included almost everything except the Russians (stay tuned…that one might be next).  Soybean’s extreme sensitivity to dicamba sometimes complicates accurately identifying the source of exposure.  Recent research published by Dr. Kevin Bradley, weed scientist at the University of Missouri, indicated symptoms of exposure to dicamba could be induced at 1/20,000 of a 1x (0.5 lb ae/acre) field use rate.  Additionally, symptoms generally do not develop immediately after exposure; we have observed instances where 21 days elapsed between exposure and symptom development.

Possible routes of exposure:

1) Physical drift of spray particles during the actual application.

This route of exposure might be the easiest to identify based on field observations.  Symptoms are usually most pronounced along the edge of the field adjacent to the drift source, and lessen as the distance from the source increases (Figure 3).  Remember, the symptoms of exposure to dicamba depend largely on the dose.  Symptoms are different on soybean directly sprayed with dicamba (often dead plants) compared with soybean exposed to a very low concentration (leaf cupping, etc.) farther from the source.  Exposure from physical drift has been observed this year, but it does not appear to account for the majority of off-target exposure instances to date.

2) Residues remaining in/on the spray equipment from previous applications are applied at low concentrations with the POST soybean herbicide.

These symptoms are often most pronounced around the perimeter of the field and along the edge where the applicator began spraying the remainder of the field.  Symptoms often become less pronounced as the sprayer moves farther across the field away from the side where the application began (Figure 4).  Contamination has been touted by some as an explanation for cupping of Liberty Link varieties, but it seems odd that it hasn’t been mentioned much as an explanation for cupping of Roundup Ready varieties.

3) Herbicide vapors on the plant or soil surface move out of the treated field (vapor drift).

The volatility of a herbicide (i.e., tendency to change from a liquid to a gas) is a function of several factors related to the formulation of the herbicide and to prevailing environmental conditions.  Vapor pressure is a measure of the tendency of a herbicide to volatilize.  As the vapor pressure of a herbicide increases, the potential for volatility also increases. Volatility tends to increase as soil moisture and temperature increase.  As soil moisture decreases, the amount of herbicide adsorbed to soil colloids can increase and reduce the amount of herbicide available to volatilize.  All commercially-available formulations of dicamba have the potential to volatilize.

4) Applications made during temperature inversion conditions.

Small droplets can remain suspended in the air when pesticides are applied during temperature inversion conditions.  These particles then move out of the target area when winds begin to move the following morning.  Where and how far they move depends primarily on wind direction and speed.  Labels of dicamba-containing products approved for in-crop application to dicamba-resistant soybean restrict applications during temperature inversions.  Some have speculated applications made at night (when inversions occur) have been responsible for off-target damage, but does anyone have actual data on how many acres are treated when headlights are needed on the applicators?

Leaf distortions:

There has been much conversation about leaf symptoms that likely were not caused by exposure to dicamba.  As mentioned previously, symptoms of dicamba exposure can vary according to the dose of exposure and stage of soybean development.  However, the symptoms of low-dose exposure tend to be fairly consistent.  Can other herbicides cause leaf distortions?  Yes, but these symptoms are different from those caused by dicamba.  Foliar-applied PPO inhibitors can cause leaf distortions, but the degree of “cupping” is generally much less than that caused by dicamba and the symptoms appear on leaves treated with the application (Figure 5).  In contrast, cupping caused by dicamba is generally seen on leaves that emerge after the exposure occurred.  We also have observed distorted leaves following POST application of soil-residual herbicides (Figure 6), but these symptoms are very different from those caused by dicamba.

Effects on soybean yield:

If cupped soybean plants were actually exposed to dicamba, will yield be adversely effected?   The answer is that it is absolutely NOT possible at this point of the season to predict whether or not yield will be impacted.  Published literature suggests this injury does not always result in soybean yield loss, but several factors are involved in determining if yield loss will occur.  In particular, soybean growth stage at the time of exposure, dosage of exposure, and growing conditions for the remainder of the growing season are important factors that determine if yield loss does or does not occur.  Much of the available literature suggests that if minor exposure occurs during early vegetative development, yield loss is less likely to occur than if exposure occurs when soybean have entered reproductive development.  However, there are no data that describe yield effects on soybean exposed to dicamba more than once.

Comments heard from the field and industry:

I have attempted to describe the current situation in Illinois as accurately as possible, and to provide data-derived information related to soybean exposure to dicamba.  As mentioned previously, soybean injury from dicamba has occurred each year in Illinois since the product was first commercialized.  However, the response of some individuals from companies who market formulations approved for use in dicamba-resistant varieties has been unlike anything I’ve experienced during my 24-year tenure at the University of Illinois.  Some comments heard from the field, social media, and industry are, in my opinion, quite troubling.

“Only a negligible percentage of soybean acres are affected”

I doubt anyone has completely accurate data on the actual number of soybean acres that have been impacted by dicamba.  Even if those data support the aforementioned statement, I haven’t spoken with many farmers who consider themselves or their acres as “negligible.”  Merely counting official reports filed with the IDOA does not accurately reflect the extent of acres impacted.

“Thoroughly investigate before drawing conclusions”

Excellent advice, especially when followed.  Without question, there have been instances of symptom misidentification.  I attempted to describe some of these in this article.  However, it seems that other factors are repeatedly being mentioned as able to cause leaf cupping.  Environmental conditions are frequently mentioned as inducing leaf cupping, yet I cannot find any peer-reviewed literature that specify or describe these conditions.  If these conditions exist, one would speculate they could be replicated under controlled conditions to confirm their impact on symptom development.  Also curious to me is that I have yet to see or have anyone report cupping of dicamba-resistant varieties.  Are these varieties somehow immune to these environmental conditions?

“The instances of volatility likely are due to applying older, non-approved formulations”

Again I ask, where are the data that indicate older formulations are being applied?  If we should “thoroughly investigate before drawing conclusions,” it seems premature to me to conclude the instances of volatility are wholly attributable to older dicamba formulations.  Much discussion has been made about the newer formulations that are purportedly lower volatility formulations.  These statements will have to be taken at face value, as I am aware of only one university that has evaluated volatility of only one commercial formulation.  Please keep in mind that low volatility is not the same as no volatility.  The new formulations are still volatile, albeit less volatile than older formulations.  Symptoms in many affected fields do NOT follow patterns associated with physical drift or contaminated application equipment, and exposure though volatility remains a very possible source of exposure.

“It is unlikely yield will be reduced.  You might even see a yield increase.”

This is perhaps the most troubling statement I have heard.  In my opinion, statements similar to these are unprofessional and unethical.  These individuals do NOT have the necessary data to make such bold predictions, which includes:

1) when the exposure occurred

2) the dose of the exposure

3) what the growing conditions will be like the remainder of the season

When dicamba is applied in a state that grows soybean, the occurrence of off-target symptoms is not a question of “if,”, but rather “scale.”  Some suggest the solution is to plant all soybean acres to dicamba-resistant varieties.  That might solve issues associated with soybean, but would likely increase the incidents of damage to other dicot species across the Illinois landscape.

Literature cited:

 Wax LM, Knuth LA, Slife FW (1969)  Response of soybean to 2,4-D, dicamba, and picloram.  Weed Sci 17:388–393.


Figure 1.  Cupping of young trifoliolate leaves following exposure to dicamba.

Figure 1. Cupping of young trifoliolate leaves following exposure to dicamba.


Figure 2.  Veins of young, affected leaves assume a parallel orientation following exposure to dicamba.

Figure 2. Veins of young, affected leaves assume a parallel orientation following exposure to dicamba.


Figure 3.  Physical spray drift from the soybean field to the left onto the soybean field to the right.

Figure 3. Physical spray drift from the soybean field to the left onto the soybean field to the right.


Figure 4.  Damage to soybean from dicamba residues dislodged from spray equipment.

Figure 4. Damage to soybean from dicamba residues dislodged from spray equipment.


Figure 5.  Leaf distortion caused by a foliar-applied PPO-inhibiting herbicide.

Figure 5. Leaf distortion caused by a foliar-applied PPO-inhibiting herbicide.


Figure 6.  Leaf distortion following  the POST application of a soil-residual herbicide.

Figure 6. Leaf distortion following the POST application of a soil-residual herbicide.

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

Palmer Amaranth ID of seed or plant tissue and Herbicide Resistance Testing at the University of Illinois Plant Clinic

Are you having trouble with Palmer amaranth? We have something new for you.

NEW Palmer ID test available this year: We spent a long winter optimizing a new assay in collaboration with Dr. Pat Tranel’s lab to aide in Palmer amaranth ID. Contamination of seed mixes with Palmer amaranth became a wide-spread issue last year. Efforts to determine if a seed mixture is contaminated can be hampered by low germination rates and slow grow outs in greenhouse tests. A new molecular assay to confirm the presence or absence of Palmer amaranth in sample seed or leaf tissue is now being offered by the University of Illinois Plant Clinic. Up to 100 Amaranthus spp. seeds, or 5 plants, can be tested as a single mixed sample. To submit plant tissue, remove the top two inches of young, healthy, newly-emerged leaves from suspect Palmer amaranth plants. Only Amaranthus spp. seeds are accepted for testing; if you have a seed sample containing forbes, grasses, etc., please contact the Illinois Crop Improvement Association at (217) 356-4053 for assistance in separating the Amaranthus seed.

Figure 1:

Figure 1:  Waterhemp leaf extract prior to DNA extraction. University of Illinois Plant Clinic photo

Herbicide Resistance testing: The University of Illinois Plant Clinic also continues to offer herbicide resistance testing in waterhemp and Palmer amaranth in 2017, Figure 1. This is the third year the service has been offered at the Plant Clinic. Samples are tested using molecular assays for common modes of action for both glyphosate and PPO-inhibitor herbicide resistance. Currently, only waterhemp and Palmer amaranth are accepted for this type of testing. To sample, remove the top two inches of plants that have survived an application of glyphosate and/or PPO-inhibitor herbicides. Young, healthy, newly-emerged leaves are ideal for submissions. We recommend submitting five plants per field. Results are given on a per-field basis.

For results from last year’s tests, please see:

The fee for each service is $50 per sample. For additional information about how to sample, please see our flyer: and the molecular sample submission form:

Authors: Diane Plewa and Suzanne Bissonnette

What to do if you suspect herbicide drift

Each year, the Illinois Department of Agriculture (IDOA) receives approximately 120 pesticide misuse complaints, of which 60% are pesticide drift complaints.  Neighborly discussions before pesticides are applied are important so applicators understand if sensitive plants are growing near the application site.  In the unfortunate case that drift has occurred, it’s a good idea to know the basics of the complaint process and what resources are available to you.

Before doing anything, both parties should make an effort to discuss the suspected drift incident and rule out other possible causes of the damage.  In cases where the cause of the damage remains unclear or where the parties will not work together, a formal complaint may be necessary.

The IDOA and University of Illinois Extension have important but different roles in assisting citizens of Illinois in dealing with pesticides. These roles are based on the IDOA’s responsibilities to administer and enforce the laws related to the use of pesticides and University of Illinois Extension’s responsibilities to educate and solve problems.

You may send affected plant samples to the University of Illinois Plant Clinic. For information on how to do so, go to Be sure to include as much relevant information as possible. Keep in mind that the Plant Clinic does not perform pesticide residue tests, and without such tests, the cause of a symptom cannot be attributed to pesticide drift with 100% certainty. However, it is possible for Clinic staff and specialists to rule out other possible causes and establish whether the likely cause is drift.

The IDOA has three roles that impact its handling of pesticide-drift complaints. These roles are (1) education and licensing of applicators and operators via the Pesticide Safety Education Program, (2) investigation of complaints, and (3) enforcement of pesticide laws. The roles of IDOA are determined by laws and statutes passed by the Illinois legislature or the federal government.

If you choose to file a complaint with IDOA, time is of the essence. The pesticide drift complaint process is started by filling out a complaint form which can be found at: or by calling IDOA’s Bureau of Environmental Programs at 1-800-641-3934 (voice and TDD) or 217-785-2427.  Additional information on pesticide uses and misuses can be found on the agency’s website at:

Complaint forms must be received by IDOA within 30 days of the incident or within 30 days of when the damage was first noticed. Complaints filed after that will be kept on record, but no administrative action can be taken.

The complaint process

Once a complaint is filed with the department, a field inspector is assigned the case. In most cases, the inspector will interview the complainant and inspect the site. Various types of samples, such as plants, water, or soil, may be collected for analysis at an approved laboratory.

The inspector may also interview applicators in the area, examine pesticide records and collect weather data in an attempt to determine the nature and cause of the damage. The field investigator will then submit a report to the Department for review.

Both parties will receive written notification if the Department finds a violation and takes an enforcement action. Penalties range from advisory or warning letters to monetary penalties of $750 to $10,000, depending on the type and severity of the violation. Penalties are determined through a point system defined in the Illinois Pesticide Act.

Even if a violation of the Illinois Pesticide Act cannot be substantiated, both the complainant and the alleged violator will be notified in writing of the complaint’s status. Remember, the Department’s role in pesticide misuse incidents is limited to determining whether a violation has occurred. IDOA cannot help complainants recover damages.

Certainly, it is easiest and best to prevent herbicide drift from occurring.  Drift can be extremely expensive and often results in poor neighbor relations.

Additional information for use when handling potential drift injury

A useful resource that includes information and helpful tips on preventing and dealing with the off-target movement of herbicide applications is an online module titled,

“Herbicide Tolerant Crop Stewardship”.   Especially useful would be chapter 5, “Avoiding/Handling Injury.”  While it was created with producers in mind, it would also be beneficial to homeowners, gardeners, and anyone who grows plants and it’s free.  It can be found at:

Aaron Hager and Michelle Wiesbrook

Postemergence Herbicides in Corn

The 2017 Illinois corn crop currently is at various stages of development.  Applications of postemergence corn herbicides continue to be made across areas of Illinois, although the recent precipitation has delayed applications in some areas.  Even though applications may be delayed, adequate soil moisture coupled with warm temperatures will certainly promote rapid growth of emerged weeds.

Properly timing the application of the postemergence herbicide is critical toward achieving the goal of removing weed interference from the corn crop before the weeds adversely impact (i.e., reduce) corn grain yield.  Unfortunately, it’s not possible to accurately predict the specific day after planting or emergence when weed interference begins to reduce corn yield.  This interval is influenced by many factors and can vary based upon the weed spectrum, the density of certain species, available soil moisture, etc. Weed scientists generally suggest an interval, based either on weed size (in inches) or days after crop/weed emergence, during which postemergence herbicides should be applied to avoid crop yield loss via weed interference.  In corn, it is often recommended to remove weeds before they exceed 2 inches tall.  The longer weeds are allowed to remain with the crop the greater the likelihood of crop yield loss.

It’s important to remember that the labels of most postemergence corn herbicides allow applications at various crop growth stages, but almost all product labels indicate a maximum growth stage beyond which broadcast applications should not be made, and a few even a state minimum growth stage before which applications should not be made.  These growth stages are usually indicated as a particular plant height or leaf stage; sometimes both of these are listed.  For product labels that indicate a specific corn height and growth state, be sure to follow the more restrictive of the two.  Application restrictions exist for several reasons, but of particular importance is the increased likelihood of crop injury if applications are made outside a specified growth stage or range.

As mentioned, corn plant height is commonly used on many herbicide labels but plant height may not always provide an accurate indication of the plant’s true physiological maturity.  Determining plant height may seem relatively straightforward, but using different benchmarks for measurement can lead to different plant heights.  Generally, corn plant height is determined by measuring from the soil surface to the arch of the uppermost leaf that is at least 50% emerged from the whorl.  Be sure to measure several plants in a given field and average the numbers.  Plant height is obviously influenced by many factors, including genetics and the growing environment.  Adverse environmental conditions, such as cool air/soil temperatures, hail, etc., can greatly retard plant height and result in corn plants that are physiologically older than their height suggests.

Many agronomists agree that leaf number is a more accurate measurement of corn developmental stage.  Counting leaves and counting leaf collars are the two primary techniques used.  Leaf counting begins with the short first leaf (the one with a rounded tip) and ends with the leaf that is at least 40–50% emerged from the whorl.  Counting leaf collars also begins with the short first leaf, but includes only leaves with a visible collar (the light-colored band where the leaf joins the stem).  Leaves in the whorl or those without a fully developed collar are not counted.  The leaf collar method quite often stages a corn plant at one leaf less than the leaf counting method.

Corn plants under stress conditions may be more prone to injury from postemergence herbicides. Stress can arise from a number of factors, including cool temperatures and wet soils.  Be sure to consult the product label when selecting spray additives to include with postemergence herbicides.  Many labels suggest changing from one type of additive to another type when the corn crop is under stressful growing conditions.  Attempting to save a trip across the field by applying a postemergence corn herbicide with a liquid nitrogen fertilizer solution (such as 28% UAN) as the carrier is not advisable.  While applying high rates of UAN by itself can cause corn injury, adding a postemergence herbicide can greatly increase corn injury.

Labels of several postemergence corn herbicides (most commonly ALS-inhibiting herbicides but also some HPPD-inhibiting herbicides) include restrictions with respect to applying the product to corn previously treated with certain soil insecticides.  Be sure to consult the respective herbicide label for other restrictions and limitations.