Cover Crop Termination

The following information about cover crop termination is taken from the 2016 Weed Control Guide for Ohio, Indiana and Illinois.  The information was originally written by extension weed scientists at Purdue University.

Cover crops are unique in that most are planted primarily to reduce soil erosion and otherwise enhance soil quality, and are not harvested for their seed, fruit, or forage (although some are grazed or used as forage). Instead, cover crops are terminated before planting of summer annual grain crops such as soybeans and corn. When not effectively terminated, cover crops have the potential to become weeds in the grain crop and can slow soil drying and warming in the spring. Many cover crop species have characteristics that make them both desirable as cover crops, and troublesome as weed species. Weedy cover crop escapes not only affect the current production crop, but also can produce seeds and establish a seed bank that will result in future weed problems.

Cover crops can be terminated by a number of meth­ods, although herbicide application is the most common method. When selecting a herbicide program for termi­nation of a cover crop, consider:

  • the cover crop species
  • the cover crop growth stage
  • other weed species present
  • the production crop to be planted
  • the weather conditions at application

Cover Crop Species. Cover crop systems that contain only grass species or only broadleaf species can be terminated using selective grass or broadleaf herbicides. However, producers will often grow combi­nations of grass, legumes, and non-legume broadleaf species together to receive the maximum benefits that each group presents. Successfully terminating a cover crop that contains grasses and broadleaves will require a nonselective herbicide such as glyphosate, glufos­inate, or paraquat. It is possible to combine a selective grass herbicide (sethoxydim, clethodim, quizalifop, fluazifop) and selective broadleaf herbicide (2,4-D, dicamba) to terminate a mixed crop, but it is not advisable because many of these combina­tions can be antagonistic and poor control will result. Combining glyphosate with either 2,4-D or dicamba can ensure more complete termination of broadleaf spe­cies than spraying glyphosate, 2,4-D, or dicamba alone. Effective herbicide control of grasses and broadleaves varies by species. Consult a weed control guide or herbicide label to ensure the herbicide will be effective on a particular cover crop species. See species-specific recommendations below for herbicide programs for some common cover crops.

Cover Crop Growth Stage. The growth stage and height of the cover crop at the time of termination is critical in determining what herbicide and rate will be most effective. Crops that are bolting, jointing, or pro­ducing reproductive structures can be difficult to control with herbicides and may require other termination meth­ods. Always take cover crop heights into consideration because taller, more mature plants may require higher herbicide rates than smaller, less mature plants.

Other Weed Species Present. Before choosing a herbicide to terminate a cover crop, carefully consider all the plant species that are present — including weeds. Decide on a herbicide plan before planting or seeding the cover crop, and then amend the plan according to any additional weed species that occur.

Cash Crop to Be Planted. When planning a herbi­cide termination program, use only herbicides that are labeled for burndown or preplant applications with the summer annual crop you will plant. Be sure you also observe crop rotational restrictions. For example, there is a 14-day restriction when planting soybean after us­ing high rates of 2,4-D in a cover crop termination. The rotational restrictions for corn after applications of selec­tive grass herbicides (sethoxydim, clethodim, quizalifop, fluazifop) range from 30 to 120 days.

Weather Conditions at Application. Environmental conditions affect herbicide performance, and unfortu­nately these are factors that cannot be controlled or predicted. Typically, cover crop terminations take place in the early spring, so while the exact weather may vary, temperatures tend to be cool with variable cloudiness and high soil moisture. Take these typical weather con­ditions into account when planning an herbicide termi­nation program — cool, cloudy conditions slow the rate at which herbicides kill plants. Wet soil can also keep sprayers out of fields, which delays spray applications and allows cover crops to reach undesirable heights and growth stages.

A wide variety of cover crop species are available and recommended for specific cropping systems, soil types, and regions. The following section provides herbicide termination recommendations for the cover crop species most commonly planted in Indiana, Ohio and Illinois.

Annual ryegrass (Lolium multiflorum), also called Ital­ian ryegrass or common ryegrass, has become a very popular cover crop throughout the Midwest. Do not confuse annual ryegrass with cereal rye (Secal cereal). Annual ryegrass is a good cover crop because of its ability to rapidly germinate in the fall, grow aggressively in the spring, and add substantial root and forage mass to the soil profile. However, this plant’s aggressive and competitive nature can also make it a weed problem in grain crops. The introduction of annual ryegrass as a cover crop in Indiana and the possibility of it escaping as a weed is a concern. Annual ryegrass has established itself as a weed in orchards, vineyards, and grain crops throughout the western and southern United States and is recognized by multiple scientific weed societies as an invasive weed species. Annual ryegrass is also able to quickly adapt to herbicide selection pressure. The International Survey of Herbicide Resistant Weeds (Heap 2015) reports herbicide-resistant annual ryegrass populations in ten states and across six herbicide sites of actions. Follow these guidelines for successful termi­nation of annual ryegrass cover crops:

  • Make applications prior to 8″ plant height
  • Glyphosate rates of at least 1.25 lb ae/A are required, although 2.5 lb is preferred for annual ryegrass termi­nation
  • Ryegrass must be actively growing, and it is recom­mended that applications occur only following three consecutive days when air temperatures have been above 45 F
  • The addition of saflufenacil to glyphosate can improve control of annual ryegrass
  • Combinations of paraquat, metribuzin and 2,4-D or dicamba can control small ryegrass (<6″ in height), but are not recommended for control of larger plants
  • Avoid using PSII herbicides (atrazine & metribuzin) in mixtures with glyphosate, as they can cause antago­nism and poor control of annual ryegrass.

Cereal rye and oats. Glyphosate at a rate of 0.75 lb ae/A will effectively control both species up to 18 inches tall. Mixtures of glyphosate plus 2,4-D, chlorimuron, chloransulam, atrazine, or saflufenacil can also be ap­plied for additional control of other cover crop species (specifically broadleaf species) and residual control of summer annual broadleaf weeds. The nonselective her­bicides paraquat and glufosinate are less effective than glyphosate on these species.

Crimson clover and Austrian winter peas are two popular legume species used as cover crops that typi­cally do not winter kill and require a spring termina­tion. Escapes and failed control of crimson clover and Austrian peas have been documented as rare, so they pose less threat as potential weed species in production crops than annual ryegrass. Information on control of these species with herbicides is limited, but cover crop guides advise that glyphosate and 2,4-D easily control crimson clover and winter peas.

Dicamba-resistant soybean varieties

On February 3, Monsanto announced its commercial launch plans for soybean varieties resistant to the herbicides dicamba and glyphosate (designated Roundup Ready 2 Xtend varieties). This announcement followed China’s decision to import grain from these varieties. Many weed management practitioners hope this new technology package will provided improved control of problematic weed populations, including those with evolved resistance to glyphosate and herbicides from other site-of-action families. The weed science program at the University of Illinois has evaluated this technology for several years, conducting field research that has helped us better understand the technology and how it might be best utilized in Illinois soybean production systems.

We believe the technology can be a useful new tool for weed management, but are less confident that soybean farmers can realize its full utility during the 2016 growing season. Currently, there are no federal or state labels for any dicamba-containing product that allow applications at soybean planting (preemergence) or after the soybean crop has emerged (postemergence). Furthermore, there is uncertainty about whether approved federal and state labels will be granted in time to allow application of dicamba-containing products on these varieties during the early portion of, or perhaps even much of, the 2016 growing season. Without approved labels, applying a dicamba-containing product to these soybean varieties would constitute a violation of both state and federal laws.

Some have posed the question of whether or not dicamba can be applied prior to planting dicamba-resistant soybean varieties. The answer is “yes”, but remember this type of application must follow the herbicide label guidelines regardless of the soybean variety planted. For example, following the application of Clarity for control of existing vegetation prior to planting (including soybean varieties resistant to dicamba) and one inch of accumulated precipitation, a waiting interval of 14 days is required for up to 8 ounces of Clarity and 28 days for up to 16 ounces. This use pattern is governed by the herbicide label, not by the soybean variety planted.

Herbicide-resistant weed populations continue to be a common occurrence across most areas of Illinois. Waterhemp and horseweed (marestail) are the two most common herbicide-resistant weed species in Illinois, and observations during 2015 suggest these species are likely to remain prevalent in 2016. More than 1300 waterhemp samples (representing 236 fields) were submitted to the University of Illinois Plant Clinic in 2015 for herbicide resistance screening. The sheer number of samples submitted suggests herbicide-resistant waterhemp continues to be a significant management challenge for farmers. Waterhemp plants and/or populations resistant to herbicides from more than one site-of-action group are increasingly common, and we do not foresee this changing. Recent survey data indicated resistance occurred in close to 90% of the fields sampled, and multiple resistance to glyphosate and PPO inhibitors was confirmed in 54% of the fields sampled.

Soybean producers planning to rely on dicamba and dicamba-resistant soybean in their 2016 weed management programs for control of waterhemp populations resistant to both glyphosate and PPO inhibitors are encouraged to consider utilizing alternative strategies. The Enlist soybean trait technology and the complementary Enlist Duo herbicide formulation have received regulatory clearances, but without export approval to China it remains unclear how widely available these varieties will be in 2016. Alternative strategies to manage weed populations with resistance to multiple soybean herbicides include rotating fields to a different crop, or planting soybean varieties resistant to glufosinate (i.e., Liberty Link) and utilizing glufosinate as a postemergence herbicide. Please keep in mind, however, that regardless of the crop planted, the variety selected, or the herbicide applied, the most sustainable solution to the challenges of herbicide-resistant weeds is an integrated weed management system that utilizes both chemical and non-chemical tactics to eliminate weed seed production throughout the growing season.

2016 Weed Control Guide Now Available

The 2016 Weed Control Guide for Ohio, Indiana and Illinois contains 224 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 2016 Weed Control Guide is available to download, and a printed version of the guide can be ordered at:


2016 Ohio, Indiana and Illinois Weed Control Guide

Considerations for Weed Management in 2016

Here is the final installment of considerations for weed management in 2016.


Steps for Successful Weed Management in Glufosinate-Resistant (Liberty Link) Soybean


Step 1:

Plant Liberty Link soybean seed into a weed-free seedbed

Achieve a weed-free seedbed through the use of:

                          1) Preplant tillage

                          2) Effective burndown herbicide(s)

                          3) A combination of tillage and burndown herbicides


Step 2:

Select and apply within 14 days of planting a soil-residual herbicide that targets your most problematic weed species.

For waterhemp or Palmer amaranth, select a product containing the active ingredients from one of the following categories of control:

Excellent                                 Good                                                 Acceptable

sulfentrazone                         pyroxasulfone                                   S-metolachlor/metolachlor

flumioxazin                             metribuzin                                         acetochlor

                                              fomesafen+metolachlor                     dimethenamid


*Excellent: greatest efficacy on Amaranthus species and longest residual control

Good: good efficacy on Amaranthus species, residual control generally not as long

Acceptable: stronger on grass species but with some activity on Amaranthus species


Step 3:

Apply Liberty at 32 fluid ounces per acre when waterhemp or Palmer amaranth are less than 4 inches tall. Be sure to apply in a minimum of 15 gallons per acre carrier volume with nozzles that produce a medium droplet. Include AMS (8.5 lb/100 gallons) with all applications. Add lactofen-, fomesafen-, or acifluorfen-containing products for a second site of action against PPO-susceptible Amaranthus species.


Step 4:

Scout treated fields within 7 days after application. If control of waterhemp or Palmer amaranth was not complete, or if another flush has emerged, retreat with 22-29 fl oz plus AMS. Rogue any survivors from the field before the plants begin to flower.




Helpful reminders:

1) Liberty is NOT Roundup. Applying Liberty with the same equipment set-up used for applying Roundup increases the likelihood of performance complaints.

2) Liberty works best with bright sunshine and high humidity. Avoid spraying after 6:00 p.m.

3) Ensure thorough coverage of weeds with carrier volumes between 15–20 gallons per acre. Applications made at higher gallons per acre result in fewer performance complaints.

4) AMS is the most reliable spray additive. Add a minimum of 8.5 lb/100 gallons.


Considerations for Weed Management in 2016


Here is the third installment with additional considerations for weed management in 2016.  The final installment will be posted tomorrow.


Multiple or Effective

The continuing and expanding challenges imposed on agronomic cropping systems by weed populations resistant to various herbicides has led to renewed interest in utilizing multiple modes of herbicide action in weed management programs. Indeed, articles written about and advertisements for products that contain multiple modes of action populate many farm media publications. But, simply because a herbicide premix or tankmix combination includes herbicides representing more than one mode of action doesn’t necessarily mean that each component in the premix or tankmix will be effective against the target weed species of greatest concern. There are many instances when multiple modes of action and effective modes of action are not synonymous. For example, two-component premixes of soil-applied herbicides containing a PPO inhibitor and ALS inhibitor do not contain two effective modes of action against ALS-resistant waterhemp. Tankmixtures or premixtures of glyphosate and dicamba do not contain two effective modes of action against glyphosate-resistant waterhemp.


Traits and timelines

Soybean varieties with traits conferring resistance to 2,4-D or dicamba have received USDA approvals for commercialization, but as of this writing neither trait has received approvals in certain export markets. Additionally, dicamba-containing products have not received federal or state labels for in-crop application in commercial soybean fields. Much interest exists about utilizing these new technologies to manage challenging weed populations, but uncertainty remains if these technologies will be broadly planted in 2016. Those who are planning to rely on these traits and technologies in their 2016 weed management programs are encouraged to develop contingency programs in the event these technologies are not broadly available in 2016.

Considerations for Weed Management in 2016

Here is the second installment with additional considerations for weed management in 2016.

Resistance remains

Herbicide-resistant weed populations continue to be a common occurrence across most areas of Illinois. Waterhemp and horseweed (marestail) are the two most common herbicide-resistant weed species in Illinois, and observations during 2015 suggest these species are likely to remain prevalent in 2016. Approximately 1700 waterhemp samples (representing 338 fields) were submitted to the University of Illinois Plant Clinic in 2015 for herbicide resistance screening. Although summary data for these samples are not yet available, the sheer number of samples submitted suggests herbicide-resistant waterhemp continues to be a significant management challenge for farmers. Waterhemp plants and/or populations resistant to herbicides from more than one site-of-action group are not uncommon, and we anticipate this phenomenon will continue. Data from 2014 indicated resistance occurred in close to 90% of the fields sampled, and multiple resistance to glyphosate and PPO inhibitors was confirmed in 52% of the fields sampled.


It’s not just the POST herbicides

Soil-applied PPO-inhibiting herbicides (sulfentrazone, flumioxazin, saflufenacil, etc.) can be effective against several small-seeded broadleaf weed species. These active ingredients are often selected to provide residual control of pigweed species in soybean, and frequently are applied with other active ingredients to broaden the weed-control spectrum. The foliar-applied PPO-inhibiting herbicides (lactofen, fomesafen, acifluorfen) constitute one site-of-action group for postemergence control of waterhemp and Palmer amaranth in soybean. As previously mentioned, resistance to PPO-inhibiting herbicides in waterhemp is becoming more common across Illinois. Some mistakenly believe this type of resistance is only to the foliar-applied PPO inhibitors, but resistance to PPO inhibitors occurs regardless of whether the herbicide is applied to the soil or to plant foliage. A more comprehensive article on this topic, first published in 2013, can be found at:


Considerations for Weed Management in 2016

One of the founding fathers of the United States is often credited as the source of the phrase “in this world nothing can be certain, except death and taxes.” Scholars and pundits alike have added other “certainties” to this relatively short original list, so perhaps we can enjoy a sense of serenity to suggest another: weeds. Even with all the time and resources expended to control weeds in 2015, one can be reasonably confident this persistent foe will again plague Illinois fields in 2016. As weed management practitioners begin to contemplate plans and programs for next season, a review of weed management in 2015 could provide a bit of sage counsel.  We will publish several short blogs over the next several days that both review 2015 and provide suggestions for 2016.

Challenges caused by weather

Weather patterns during portions of the 2015 growing season once again demonstrated the inherent perils of weed management programs that rely exclusively on one tool or tactic. These perils were often highlighted in soybean fields not treated with soil-residual herbicides. Applications of postemergence herbicides were often delayed by frequent precipitation and persistently wet field conditions until well beyond the point when weed interference began to reduce soybean yield. This provides a reminder of a very important central tenent of weed management: resources expended to keep weeds under control do not increase crop yield. Increases in crop yields are accomplished though plant breeding; weed management, on the other hand, preserves the genetic yield potential achieved through breeding. Put another way, weeds and crop plants require the same resources for growth. Any resource consumed by competing weeds becomes a resource unavailable for the crop to use to express its genetic yield potential. Once weed interference has persisted long enough to adversely impact crop yields, nothing can restore the lost yield.

Be cautious about which expenditures you trim

Lower commodity prices have many contemplating ways to reduce input costs in 2016. There are several viable options to reduce herbicide costs, but remember that hybrids and varieties, even those with the highest yield potential, will not realize their yield potential if weeds are not adequately and timely controlled. For example, assume a soybean farmer did not realize (or refuses to accept the fact) that glyphosate-resistant waterhemp infests a particular 60-acre field. The decision is made not to invest in an effective soil-residual herbicide; the farmer believes glyphosate alone will control the waterhemp. Following the in-crop application of glyphosate, two outcomes of this decision become rather obvious: poor control of waterhemp, and weed interference that continues to reduce soybean yield for much of the growing season. With a soybean yield potential of 65 bushels per acre, a modest yield loss of 20% due to weed interference, and a soybean market price of $9 per bushel, the decision to save a few dollars in weed control costs at the beginning of the season actually resulted in a revenue loss of over $100 per acre through reduced soybean yield. Keep in mind, especially while planning 2016 weed management programs, that wise investments to manage weeds before interference reduces crop yields will realize a return through more bushels harvested at the end of the growing season. An investment in high-yielding hybrids and varieties should be coupled with an investment in weed management that adequately protects yield potential.

Ewing Demonstration Center Fall Field Day – September 10th

The University of Illinois Extension will host its annual Ewing Demonstration Center Fall Field Day on Thursday, September 10, 2015 at 9:00 a.m.  The Ewing Demonstration Center is located in southern Illinois about 20 miles south of Mt. Vernon at 16132 N. Ewing Rd; Ewing, IL 62836.  It is on the north edge of the village of Ewing, north of the Ewing Grade School on north Ewing Road.  Watch for signs.

The ongoing research this year includes trials on soybean cover crops, nitrogen management in corn, corn maturity, corn seeding rates, soybean seed treatments, and a pumpkin variety trial.


The topics to be discussed at Field Day include:


Soybean Weed Management

  • Ron Krausz, Manager, SIU Belleville Research Center

2015 Cropping Season Challenges

  • Emerson Nafziger, Extension Crop Specialist, University of Illinois

Planning Ahead for the 2016 Wheat Crop

  • Robert Bellm, Extension Educator, University of Illinois

Results of 2015 Corn and Soybean Insect Surveys: Implications for 2016

  • Mike Gray, Extension Entomologist, University of Illinois

Making the Most of Prevent Plant Acres with Cover Crops

  • 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 (CM –  1.0, PM – 1.0, SW – 0.5).  For additional information, contact Nathan Johanning (618-687-1727; or Marc Lamczyk (618-439-3178;

The End of an Era

In early 1998, Extension specialists in the Department of Crop Sciences (Drs. Kevin Steffey, Mike Gray, Bob Hoeft, and Emerson Nafziger) launched a new educational program dubbed the Corn & Soybean Classic. The program consisted of a series of regional meetings at which extension specialists shared with those in attendance the most current and relevant information related to crop production, pest management, and farm economics. Annually for 18 years, 7 to 10 specialists spent many long hours compiling the information generated from applied and basic research programs into a format that was shared with an audience that ranged in size from 800 to over 1300. An estimate conducted during a recent Classic series suggested those attending that year represented approximately 8 million of Illinois’ agronomic crop producing acres.

The Classic changed and evolved over the years: several meeting venues around Illinois were tried; 29 different specialists from the University of Illinois spoke at one or more Classic meeting; leadership of the program began with Dr. Bob Hoeft, who upon becoming department head passed the mantel of leadership to Dr. Kevin Steffey, who upon his retirement from the University of Illinois passed it along to me. Sharon Conatser and Kris Ritter provided the behind-the-scenes support for the program during its early years, which later transitioned to Sandy Osterbur who became coordinator of the program. Even with these and the numerous other changes that occurred over the years, the individuals involved with putting together the program always remained committed to providing a research-based program that was the best possible.

The adage that all good things must come to an end now also applies to the Corn & Soybean Classic; the 2015 program was the last. As extension faculty retire or move on from the University of Illinois, their positions are not being refilled with tenure-track extension faculty. Those few of us who remain feel that we can no longer maintain the standard of excellence that was the hallmark of the Classic. We currently are exploring alternative formats for conveying our research results and recommendations, but to date have not reached any decisions.

Similar challenges have led to changes in another of our programs, the University of Illinois AGMasters. Recently, we partnered with the Illinois Certified Crop Advisor (CCA) program to transition the AGMasters to a one-day format that will be held in Springfield on December 3, the day following the annual CCA conference. We sincerely appreciate the Illinois CCA program’s willingness to assist us with this educational program.

On behalf of my colleagues, thank you for your support of the University of Illinois Corn & Soybean Classic and AGMasters.

Brownstown Agronomy Research Center Field Day – August 5, 2015

The 2015 Brownstown Agronomy Research Center Field Day, presented by the University Of Illinois Department Of Crop Sciences, will be held on Wednesday, August 5. Extension researchers and specialists will address issues pertinent to the current growing season. The tour will start at 8 a.m. and will last approximately three hours. It will be followed by lunch provided by U of I Extension. 2.5 hours of Certified Crop Adviser CEUs have been approved.

Shaded tour wagons will take participants to each stop. These topics will be addressed:

  • 2015 Cropping Season Challenges – Dr. Emerson Nafziger, U of I
  • Weed Management: The Simple Days are Over – Dr. Aaron Hager, U of I
  • Soybean Sudden Death Syndrome – Dr. Angie Peltier, U of I
  • Update on Statewide Insect Surveys & Potential Implications – Dr. Mike Gray, U of I
  • Factors Contributing to a Healthy Soil – Russ Higgins, U of I

The 208-acre Brownstown Agronomy Research Center has been conducting crop research on the claypan soils of southern Illinois since 1937. More than 30 research and demonstration projects are conducted at the Center each year. Visitors are always welcome.

The research center is located south of Brownstown on IL Route 185, approximately 4 miles east of the IL Route 40/185 junction.

For more information, contact Robert Bellm (618-427-3349);
Visit us on the web at