Herbicide Resistance in Waterhemp: PPO inhibitor and Glyphosate Testing University of Illinois Plant Clinic 2016

What is your waterhemp doing ? Waterhemp glyphosate and PPO inhibitor resistance testing was offered by the Plant Clinic for the first time in 2015. Due to the strong demand for this testing, we are offering it again this year. We adapted protocols developed by Dr. Tranel’s lab in the Dept. of Crop Sciences to transition the molecular protocols for glyphosate and for PPO Inhibitor resistance from a research laboratory to a service lab offering. In 2015, we screened plants from 338 fields (approx. 1350 plants) in 5 states, including 240 fields from Illinois. To the best of our knowledge, we are the only Plant Clinic in the country offering this service.

The data  generated showed that the majority of the fields sampled contained waterhemp resistant to at least one of these two classes of herbicides. The Plant Clinic was sponsored by the Regional Crop Management Extension Conferences to purchase some of the necessary equipment for this endeavor.

2015 Counties with waterhemp samples testing positive for PPO inhibitor or glyphosate resistance, University of Illinois Plant Clinic.

2015 Counties with waterhemp samples testing positive for PPO inhibitor or glyphosate resistance, University of Illinois Plant Clinic.

To submit waterhemp samples for testing: After applying herbicide, select up to 5 waterhemp survivors. Remove the top inch or two from each plant (containing young, newly-emerged, healthy leaves. Older leaves and leaves that are damaged by herbicide will be more difficult for us to work with), and seal it in a sandwich-sized tip-top plastic bag. Use a separate bag for each plant. Place the bags in an envelope and send via overnight delivery to the University of Illinois Plant Clinic, along with a Waterhemp Testing sample submission form (see below). Ideally samples should be sent the same day they’re collected, but if necessary they can be stored for a day or two in a refrigerator. Do not freeze the samples. Do not send samples on Friday or Saturday.

Select top few inches from the waterhemp  for testing

Select top few inches from the waterhemp for testing

Sample submission forms are available for download on our website: http://web.extension.illinois.edu/plantclinic/downloads/WaterhempForm.pdf Fill out a new form for each field. There is a $50 fee for the testing, which includes both the glyphosate and PPO-inhibitor resistance tests. Authors: Suzanne Bissonnette and Diane Plewa


University of Illinois Plant Clinic: Celebrating 40 Years of Service to Illinois

Anniversary Overview of Plant Clinic: Welcome to another year of service at the Plant Clinic! Since 1976, the University of Illinois Extension Plant Clinic has served as a clearinghouse for plant problems. Housed first in the Department of Plant Pathology and now Crop Sciences, the Plant Clinic was originally developed to help County Cooperative Extension staff and campus-based Extension specialists with requests for diagnoses on a wide variety of plants. By acting as a centralized diagnostic laboratory, the Plant Clinic  serves as a source of information about plant problems in Illinois.  While our primary mission is to provide diagnostic service to Illinois,  the Clinic maintains permits to receive plant, pest, and soil samples from the continental US and territories.

For most of its existence, the Plant Clinic was open from May through October. In 2010, we began year round operation.  During the off-season diagnostic staff write grants, compile reports, write fact sheets, and present at conferences and meetings around the state to support the outreach mission.  Our Nematology diagnostic clinic staff process samples and bioassays year round. The Plant Clinic has taken a lead role in the Illinois First Detector Invasive Species Workshops which started in 2013, as a part of our NIFA CPPM-EIP grant that supports IPM and diagnostics outreach. The workshops are held every year in various locations across Illinois and educate green professionals, city and municipal employees, and concerned public about invasive plants, insects, and diseases that threaten Illinois horticulture and agriculture.

U of I Plant Clinic Diagnostic Lab

U of I Plant Clinic Diagnostic Lab

For the past several years, the Plant Clinic has processed over 4,000 plant and soil samples annually. The vast majority of the plant samples are analyzed for disease and insect problems, though plant and insect identification is also performed. The soil samples are analyzed for nematode populations, including Soybean Cyst Nematode and vermiform pathogenic nematodes. Last year a new service testing for herbicide resistance in waterhemp was offered. Protocols for molecular testing for glyphosate and PPO-inhibitor resistance were adapted from ones developed in Dr. Tranel’s laboratory at the University of Illinois, 338 fields (representing 1350 plants) were analyzed. Plants were submitted from Illinois and 4 other Midwestern states.

The Plant Clinic works with the National Plant Diagnostic Network, Illinois Department of Agriculture and the National Sentinel Plant Network to stay aware of new threats in Illinois. Last year we found several new pests in Illinois, including jumping worms (an invasive earthworm) in northern Illinois, and tar spot of corn in north/central Illinois (this disease was found in Illinois and Indiana in 2015 and was a first find in the country). The Plant Clinic also works with the Illinois Department of Agriculture and Illinois Crop Improvement Association to certify diseases present crops for export, and has a partnership with the Illinois Department of Natural Resources to monitor the health of natural areas in Illinois.

The Plant Clinic employs undergraduate and graduate students, providing them with hands-on experience working in a plant diagnostic laboratory and expanding their outreach skills. Staff write articles for various online newsletters, including the Home, Yard, and Garden Pest Newsletter (http://hyg.ipm.illinois.edu/) and The Bulletin (http://bulletin.ipm.illinois.edu/). The Plant Clinic participated in the ACES Family Academies in 2015, where youth ages 6-13 got a chance to use microscopes, inoculate plants, and wash soil to collect nematode eggs. Departmental service includes opening the laboratory for tours and hands-on activities for students, and outreach at events such as Agronomy Day held every August.

Sample Information for the 2016  Season: Plant Clinic services include plant and insect identification, diagnosis of disease, insect, weed, and chemical injury problems (chemical injury on field crops only), nematode assays, herbicide resistance testing of waterhemp to PPO and glypohsate, and help with nutrient related problems, as well as recommendations involving these diagnoses. Microscopic examinations, laboratory culturing, virus assays, qPCR, ELISA and nematode assays are some of the techniques used at the Plant Clinic. Many samples can be diagnosed within a few days. Should culturing be necessary, isolates may not be ready to make a final reading for 10-14 days. Standard nematode processing also requires 1-2 weeks depending on the procedure. Some nematode bio-assays can take up to 4 months. We send your final diagnosis and invoice to you through both the US mail and email.

Please refer to our website at http://web.extension.illinois.edu/plantclinic/ for additional details on samples, sample forms, fees, and services offered. If you have questions about what, where, when, or how to sample call us at 217-333-0519. When submitting a sample, please 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. Pictures of the affected plants or areas can also be sent with the sample to give us a better idea of what is occurring in the environment.

Our fees vary depending on the procedure necessary. General diagnosis including culturing is $15, ELISA and other serological testing is $25, nematode analysis for SCN or PWN is $20, specialty nematode testing (such as corn) is $40. Call ahead for other specialty nematode testing or bio-assays. Checks should be made payable to the University of Illinois Plant Clinic. Please contact us if you are uncertain of which test is needed.

For more information about the Plant Clinic, including how to contact us and submit a sample, please see our website at: http://web.extension.illinois.edu/plantclinic/. We are celebrating 40 years of service to the state of Illinois all season long on our Facebook page (https://www.facebook.com/UofIPlantClinic/) and are looking forward to another 40 years of helping people with their plant problems!  authors Suzanne Bissonnette and Diane Plewa


What is That Yellow-Flowered Plant?

The springtime color scheme provided by winter annual weed species in many no-till fields has shifted from the hearty purple of flowering henbit and purple deadnettle to the bright yellow flowers of two species.  Yellow rocket and cressleaf groundsel (a.k.a. butterweed) both produce bright yellow flowers and are common across much of the southern half of Illinois.  Although flower color is similar, the plants are distinct species.  Most of the yellow-flowered plants currently in fields is butterweed.

Native to the United States, butterweed (Packera glabella) can be found from Texas east to Florida, northward along the Atlantic coast to Virginia, and west to Nebraska.  Herbarium specimens from the Illinois Natural History Survey indicate that butterweed specimens were collected in Illinois as early as 1932.  The earliest herbarium specimens of butterweed generally originated from counties in southern Illinois.  During the 1980s and 90s, the Illinois Natural History Survey augmented their collection with specimens from more northern counties, such as Champaign and Vermillion.  While scouting fields in Kankakee County recently, butterweed was easy to find.  Typically favoring moist to saturated soils, butterweed thrives in areas such as wastelands, pastures, fence-rows, and roadsides.  With the increased adoption of no-till and reduced tillage conservation practices, butterweed has become more prevalent in areas devoted to agronomic crop production.

Butterweed completes its life cycle within one year (an annual growth habit).  Field research was conducted from fall 2004 through spring 2006 at the University of Illinois to determine the emergence timing and growth characteristics of butterweed in no-till fields.  Butterweed emergence was predominately during the fall months and was essentially completed by November, although some emergence occurred in the spring.  From these results, we generally consider butterweed to be a winter annual species.

Following emergence, the formation of rosettes occurs prior to overwintering.  The rosette leaves have petioles that connect the leaves to the stem.  Often the under side of the rosette leaves are deep purple.  Bolting (stem elongation), flowering and seed production occurs the following spring, often during late April to early May.  The stem of butterweed is glaborous and hollow.  After bolting, petioles are absent from leaves on the upper part of the plant.  The leaves are pubescent, generally irregular in shape, and are deeply cut to the midrib.  The elongated stem often has a purplish tint. A member of the Asteraceae family, butterweed produces two types of composite flowers.  The outside portion of the flower contains ray florets while the center part contains disk florets.  The flowers are bright yellow and grouped in clusters that are located on several flowering stalks of the plant.  Seeds are easily disseminated via wind due to the white hairs (pappus) on the apex of the achene.

Yellow rocket (Barbarea vulgaris) is a winter annual species in the mustard (Brassicaceae) plant family.  The plant can produce numerous stems that grow from a basal crown surrounded by a rosette of deeply green leaves.   These basal leaves range in length from approximately 2–8 inches and have a large terminal lobe that is somewhat heart-shaped at its base.  Stem leaves are arranged alternately and become progressively shorter toward the top of the plant.  Flowers are produced on spike-like racemes and consist of four petals that form a cross.  Seed pods (siliques) are about 1 inch long and nearly square in cross section.

Yellow rocket and butterweed side-by-side

Yellow rocket and butterweed flowers

https://www.youtube.com/embed/zHKurkaGEQE?rel=0


University of Illinois Weed Science Field Research Tour

We invite you to attend the 2016 University of Illinois Weed Science Field Day on Wednesday, June 29th 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 look forward to visiting with you at the Urbana weed science field day on June 29th. Please contact us at 217-265-0344 or 217-333-9646 if you have any questions.


Marestail Control Prior to Planting

Marestail can be one of the most challenging weeds to control prior to planting no-till soybean.  Already this season some have reported poor marestail control following applications of glyphosate plus 2,4-D.  Poor control can be caused by several factors, including large plant size and resistance to glyphosate.  If a marestail population is resistant to glyphosate, a pint of 2,4-D in the spring is generally inconsistent/ineffective when it’s the only product in a tankmix active on the resistant population.

Adding Sharpen or metribuzin to glyphosate plus 2,4-D can improve marestail control.  Include MSO with Sharpen and be sure to adhere to planting intervals in treated fields where another soil-applied PPO inhibitor will be used.  Glufosinate (Liberty, Interline, etc.) or Gramoxone SL are other options to control marestail before planting.  Control is often improved when these products are tankmixed with metribuzin and 2,4-D.  Both glufosinate and Gramoxone are contact herbicides, so be sure to adjust application equipment (nozzles, spray volume, etc.) to ensure thorough spray coverage.

Tillage is another option to control emerged marestail.  Delay tillage until field conditions are suitable and be sure to till deep enough to completely uproot all existing vegetation.


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: http://estore.osu-extension.org/2016-Ohio-Indiana-and-Illinois-Weed-Control-Guide-P433.aspx

 

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

                                                                                                        pendimethalin

*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.