Pesticides

Cressleaf Groundsel (Packera glabella)

Source: Marcelo Zimmer and Bill Johnson, Purdue University

Every spring we receive several calls and e-mails about a certain 3-foot tall weed with yellow flowers (Figure 1). The most common yellow flowered weeds we have in Indiana are cressleaf groundsel, the buttercup species, and dandelion.  Occasionally we have some fields of canola or rapeseed in the state. But, by far the most prevalent specie we see in no-till corn and soybean fields, and occasionally pastures, is cressleaf groundsel.  I have only rarely observed wild mustard in Indiana.  Wild mustard is more common in the northern tier of states near the Canadian border.  This year, due to recent cooler weather, cressleaf groundsel is flowering later than it did last year.  This article is intended to provide information on the biology and life cycle of cressleaf groundsel, as well as how to control it in fields and pastures.

Biology and Identification

Cressleaf Groundsel is a winter annual weed that has become more prevalent in Indiana pastures and agronomic crop ground over the past 20 years.  The small seeds produced by this weed allow it to thrive in reduced and no-till systems as well as poorly established pastures.  Cool and wet springs of the past few years have also favored cressleaf groundsel, as it is a weed that prefers moist soils and typically struggles in hot and dry weather.

Much like most winter annual weeds, cressleaf groundsel emerges as a rosette in the fall then bolts, flowers, and produces seed in the spring.  Basal rosette leaves are deep pinnate serrations with roundly lobed leaf margins.  Leaves are typically 2 to 10 inches in length (Britton and Brown 1970).  Bolting stems are hollow and can reach up to three feet in height with inflorescences that contain six to twelve yellow ray flowers that are often compared to the flowers of common dandelion.  When looking for cressleaf groundsel in older weed id or taxonomic guides be aware that it has traditionally been placed in the Senecio genus and only recently was placed into the Packera genus.

Toxic Properties

The competitiveness of cressleaf groundsel with agronomic crops has not been researched, though its presence as a winter annual in no-till fields will have the same implications of slowing soil warming and drying as other winter annual weeds.  The presence of this weed in pastures and hay fields should be of more concern as it does contain toxic properties when ingested by livestock.  Leaves, flowers, and seeds of cressleaf groundsel contain alkaloids that will cause liver damage in livestock that is termed seneciosis and typically occurs on a chronic level (Kingsbury 1964).  Symptoms of seneciosis are loss of appetite, sluggish depressed behavioral patterns, and in extreme cases aimless walking without regard to fences or structures.  Although cressleaf groundsel is not as toxic as many of its relatives in the Packera genus, livestock producers encountering this weed in pastures or hay should take steps to avoid prolonged ingestion by animals.

Control

Herbicide applications for control of cressleaf groundsel are most effective when applied to plants in the rosette stage.  Plants that are larger, or bolting are very difficult to control with herbicides.  Infestations in pastures can be controlled with 2,4-D or a combination of 2,4-D and dicamba applied to rosettes in the fall or early spring prior to bolting.  Producers should be aware that applications of these herbicides will also kill favorable broadleaves (legumes) that are present in pastures.

Control recommendations for cressleaf groundsel in no-till agronomic crop fields has typically been to apply 2,4-D @ 1 qt/A to actively growing rosettes in the fall.  In fact, just about any broadleaf herbicide commonly applied in the fall in the eastern cornbelt will work well on controlling this weed.  However, we have observed that control of cressleaf groundsel with spring burndowns can be challenging if the plants are large and spray applications are made in cool weather.  In situations like this, we often observe severe injury and necrosis of leaves, but new growth will appear from live buds on the plant.  In some instances, resprays are needed to finish off the cressleaf groundsel. The best herbicide programs for spring burndowns are 2,4-D + dicamba, atrazine + paraquat + 2,4-D, something with chlorimuron in it, and Elevore + 2,4-D. for more information on spring burndown information, consult the burndown section in the Weed Control Guide for Ohio, Indiana, and Illinois (publication WS-16).

 

Adapting Burndown Programs to Late-Planted Situations

Source: Mark Loux, OSU Extension

It’s déjà vu all over again.  We have run this article every few years, and it seems like maybe the frequency is increasing as we deal with wet and cold weather that delays planting.  The questions about this have not changed much, and neither have the suggestions we provide here.  One of the most common questions, predictably, is how to kill glyphosate-resistant marestail and giant ragweed and generally big weeds in soybeans when it’s not possible to delay planting long enough to use 2,4-D ester (Enlist soybeans excluded since there is no wait to plant).  Overwintered marestail plants become tougher to kill in May, so this is an issue primarily in fields not treated last fall.  The good news is that we have more effective herbicide/trait options for help with burndown compared with a few years ago.  The bad news is that nothing we suggest here is going to be infallible on large marestail.

A burndown of glyphosate and 2,4-D struggles to control marestail in the spring anyway, especially in the absence of fall herbicide treatments.  Our standard recommendation, regardless of when spring treatments are applied, is to either replace the 2,4-D with something more effective, or to add another herbicide to supplement the 2,4-D.  Sharpen has been the frequent replacement/supplement, and we now have the option to use dicamba in the Xtend soybean system instead of 2,4-D.  While it’s possible to use higher 2,4-D rates in the Enlist soybean without waiting to plant, higher rates do not necessarily solve this issue based on our research, although a follow up POST treatment that includes glufosinate or 2,4-D usually finishes off plants that survive burndown.  There’s a list of suitable soybean burndown treatments in our marestail fact sheet, and also below – these are for fields not treated the prior fall.

  • Glyphosate + saflufenacil + 2,4-D (+ metribuzin if possible)
  • Gramoxone (3-4 pt) + 2,4-D + metribuzin
  • Glyphosate + dicamba (Xtend soybeans)
  • Glyphosate + dicamba + saflufenacil (Xtend soybeans)
  • Glufosinate + Sharpen (+ metribuzin if possible)

Salfufenacil herbicides include Sharpen, Zidua PRO, and Verdict.  It is possible to use a mix of glyphosate, saflufenacil, and metribuzin, omitting the 2,4-D, but control can be more variable.  We have observed some weakness also with the glyphosate/saflufenacil combination on dandelion, purple deadnettle, and larger giant ragweed.  There is usually going to be a benefit to keeping 2,4-D in the burndown where possible, as part of a more comprehensive mixture.  We advise against using Gramoxone unless it can be mixed with both 2,4-D and a metribuzin-containing herbicide.  One strategy would be to plant corn first as soon fields are fit, and delay soybean planting so that 2,4-D could still be used.  And a reminder – deciding to include saflufenacil at the last minute can result in a need to alter the residual herbicide program.   Labels allow mixtures of Sharpen/Verdict with herbicides that contain flumioxazin (Valor), sulfentrazone (Authority), or fomesafen (Reflex) only if applied 2 or more weeks before planting.

Some other things to consider in a delayed burndown situation:

1.  Aside from glyphosate-resistant weeds, increasing glyphosate rates may be one of the most effective ways to maintain effective control.  We suggest a rate of at least 1.5 lb ae/A, and higher rates could be warranted.  This will not improve marestail control, but should help with most other weeds, especially under (presumably) warmer May conditions. Continue reading →

Take Care When Washing Work Clothes Used Around Pesticides

Source: Elizabeth Danielson, ISU Extension

Pesticide applicators and handlers need to wear, at a minimum, the Personal Protective Equipment (PPE) specified on pesticide product labels. Most pesticide labels require a long-sleeved shirt and long pants. Proper laundering of work clothes that may be contaminated with pesticide residues is essential to reduce pesticide handlers’ short- and long-term exposure to pesticides and prevent the potential of residue cross-contamination onto other clothing.

Many pesticide labels provide limited instructions for cleaning work clothes. In situations where no instructions are provided, the following are guidelines for caring for and laundering pesticide contaminated clothing. A downloadable publication, Laundering Pesticide-contaminated Work Clothes, provides additional, more detailed information.

 

Roundup vs. Roundup vs. Roundup – REALLY??!

 

From a consumer standpoint this could quite possibly be the worst product marketing of ALL TIME!

 

 

Roundup has been around for a long time.  The active ingredient in “Roundup” is glyphosate.  Many of us know “Roundup” as a non-selective herbicide – i.e. it will kill all plants it contacts.

So what’s the problem?  With these products having a similar name, it’s quite possible to grab the wrong product from the shelf and thus risk harming or destroying the wrong (or all) plants.

The Solution.  Always read the label!  Products with similar names may have different active ingredients and therefore may not have the have the desired outcome.

Below is a general guide to the different Roundup products available to consumers.  Note that for many of these products there may be ready to use (RTU) and/or concentrate formulations available with different ratios or percentages of the same active ingredients.  Additional products are marketed for use in southern turfgrass.

Don’t be fooled by products that have a similar name . . . read the label!

 

Calibration for Rate Controlled Sprayers

Source: Erdal Ozkan, OSU Extension

I had an article in last week’s CORN newsletter encouraging growers to fine tune and calibrate their sprayers. I had mentioned that the next couple of weeks may be the last best time period to do this since planting season is just about to start. There would not be any better time to do this than now. The next day I got an email from a grower asking me this question that I get often: “I have a rate controller in the cab that regulates the flow rate of the sprayer regardless of the changes in sprayer ground speed. So, should I still calibrate the sprayer to find out the application rate?”. The answer is, Yes, you should. Although the rate controllers do an excellent job with regulating the flow rate of nozzles to keep the application rate constant, a manual calibration at least once a year is needed to ensure the rate controller is functioning properly.

Here is why we should confirm the accuracy of rate controllers: Unfortunately, electronic controllers usually cannot detect flow rate changes on each nozzle on the boom, and none can detect changes in spray pattern. If a nozzle is plugged, or extremely worn out, the rate controller cannot tell us this is happening. It will still try to maintain the constant application rate by changing the system pressure and force other nozzles to spray less or more to overcome the problem in one or several nozzles. If the ground speed sensor works based on revolutions of the tractor wheels, the ground speed determined may not be accurate, because of the slippage that may occur under some ground conditions. Even the tire pressure being off just a few psi may change the tire revolutions per minute leading to erroneous travel speed readings. Finally, Controllers don’t show changes in spray patterns that may happen when a nozzle is defective, plugged, or worn-out. So, we will have to continue manually checking the flow rate of the nozzles, and visually observing the changes in spray patterns until the technology is developed to do these observations remotely, and on-the-go.

As I mentioned in the article in last week’s CORN newsletter, it usually doesn’t take more than 30 minutes to calibrate a sprayer, and only three things are needed: a watch or smart phone to record the time when measuring the nozzle flow rate or the travel speed, a measuring tape, and a jar graduated in ounces. Please take a look at the Ohio State University Extension publication FABE-520 for an easy method to calibrate a boom-type sprayer.  Here is the URL for this publication: http:// ohioline.osu.edu/factsheet/fabe-520  

Not knowing limitations of rate controllers may create serious problems. I already mentioned how smoothly the rate controllers keep the application rate the same regardless of changes in travel speed. However, this convenience comes at a cost if the controller is forced to make drastic changes in the application rate as a result of too high or too low of a travel speed. As you know, to achieve best results from pesticides, the application rate, as well as the droplet size must remain relatively unchanged during the entire spraying. When sprayer speed goes up, to maintain the pre-set application rate, the controller requires the system pressure to go up to increase the nozzle flow rate. This, unfortunately results in more drift-prone droplets coming out of the nozzle, especially if the nozzle used is designed for low application rates within the recommended pressure ranges. Conversely, when the sprayer slows down, the opposite happens: the controller forces the system to lower the pressure, in order to reduce flow rate of nozzles. This will result in production of larger than the desired size of droplets, leading to inadequate coverage. If you are spraying Dicamba or 2,4-D herbicides, you need to pay even more attention to operation of rate controllers. As you know, only a small number of nozzles at specific ranges of pressure can be used to spray these products. Significant changes in ground speed may force the rate controller to make significant changes in spray pressure that may be outside the allowable legal pressure range required to spray these herbicides. Without you realizing it, you may find yourself in violation of the label. Make sure the nozzle size selected will allow the controllers to make necessary changes in the flow rates while still staying within a safe, applicable and allowable pressure range.

Now is the Time to Fine Tune Your Sprayer

Source: Erdal Ozkan, OSU Extension

Pesticides need to be applied accurately and uniformly. Too little pesticide results in poor pest control and reduced yields, while too much injures the crop, wastes chemicals and money, and increases the risk of polluting the environment. Achieving satisfactory results from pesticides depends heavily on five major factors:

  1. Positive identification of the pest.
  2. Choosing the least persistent and lowest toxicity pesticide that will work.
  3. Selecting the right equipment, particularly the right type and size of nozzle for the job.
  4. Applying pesticides accurately at the right time.
  5. Calibrating and maintaining equipment to make sure the amount recommended on the chemical label is applied.

Inspection of sprayers

Higher pesticide costs and new chemicals designed to be used in lower doses make accurate application more important than ever. There is no better time than early spring to take a closer look at your sprayer. Here are some of the things I would recommend you do this week if you don’t want to unexpectantly halt your spraying later in the season when you cannot afford delaying spraying and missing that most critical time to control weeds:

  • First, if you need new or one other type of nozzles on the boom this year, do not delay purchasing new nozzles. Do it now.
  • Double-check your sprayer for mechanical problems before you start using it.  You won’t have time to do this when planting is in full swing.
  • Clean the sprayer tank thoroughly and make sure all filters on the sprayer, especially the nozzle filters are clean.
  • Clean spray nozzles to make sure they are not partially plugged. Check their flow rates, and replace the ones that are spraying more than 10 percent of the original output at a given spray pressure.
  • Check the agitator in the tank to make sure it’s working properly. This is extremely important if you will be applying dry chemicals. Run water through the spray system to make sure everything is working properly.
  • Always carry a spare, excellent quality pressure gage (glycerin filled) in your shop, and check the accuracy of the pressure gage on the sprayer compared to the reading you see on this spare pressure gage. Your rate controller will not know if your pressure gage is bad, and the flow rate of nozzles will be adjusted by the rate controller using the bad pressure gage.
  • Once you are convinced that all sprayer parts are functioning properly, it is time to calibrate the sprayer.

Calibrate the sprayer

One can determine if the chemicals are applied at the proper rate (gallons per acre) only by carefully calibrating the sprayer. Calibration, perhaps more than anything else, will have a direct impact on achieving effective pest control and the cost of crop production. While applying too little pesticide may result in ineffective pest control, too much pesticide wastes money, may damage the crop and increases the potential risk of contaminating ground water and environment. Results of “Sprayer Calibration Clinics” I participated in Ohio a while back, and data from several other States show that only one out of three to four applicators are applying chemicals at a rate that is within 5 % (plus or minus) of their intended rate (an accuracy level recommended by USDA and EPA). For example, if your intended rate is 20 gallons per acre, the 5% tolerable difference will be 1 gallon (5% of 20). So, your actual application rate should be as close to 20 gpa as possible, but not outside the range of 19 to 21 gpa.

How do you calibrate the sprayer?

There are several ways to calibrate a sprayer. Regardless of which method you choose, you will end up measuring the nozzle flow rate (in ounces), and the actual travel speed in miles per hour to determine the actual chemical applied in gallons per acre. Once you determine the actual application rate, you should find out if the difference between the actual rate and the intended rate is greater than 5% of the intended rate (plus or minus). If the error is greater than the 5% tolerable error margin, you will need to reduce the error below 5% by doing one of three things: 1) Change the spraying pressure, 2) change the travel speed, and 3) change nozzles (get a different size) if the error cannot be reduced below 5% by making adjustments in either the pressure or the travel speed, or both.

It usually doesn’t take more than 30 minutes to calibrate a sprayer, and only three things are needed: a watch or smart phone to record the time when measuring the nozzle flow rate or the travel speed, a measuring tape, and a jar graduated in ounces. Please take a look at the Ohio State University Extension publication FABE-520 for an easy method for calibrating a field crop (with boom) sprayer.  Here is the URL for this publication: http://ohioline.osu.edu/factsheet/fabe-520 

New Private Pesticide Applicator Virtual Training

Source: Mark Badertscher, OSU Extension

Join OSU Extension for a virtual New Private Pesticide Applicator Training to help new pesticide applicators prepare for the Ohio Private Pesticide Applicator License scheduled for Tuesday, January 26 from 12:30-4:30 pm. The class will provide instruction in CORE, Grain, and Cereal Crops. For further study and to prepare for the test, books can be purchased from OSU Extension Publications online and shipped to your house at your expense.

Optional books for the online participants include:

Applying Pesticides Correctly (Core Manual)
https://extensionpubs.osu.edu/applying-pesticides-correctly-core-manual/

Ohio Pesticide Applicator Training: Core Student Workbook
https://extensionpubs.osu.edu/ohio-pesticide-applicator-training-core-student-workbook/

Ohio Pesticide Applicator Training: Field Crops Student Workbook
https://extensionpubs.osu.edu/ohio-pesticide-applicator-training-field-crops-student-workbook/

Register for this virtual event at https://go.osu.edu/virtualnewpesticideapplicatortraining-january26 and you will be sent a link for the class. There is no cost to participate and those who are unable to participate on the scheduled webinar date will be sent an email to watch the recording later if they register for the class. Following the class, participants can schedule an exam time at https://pested.osu.edu/PrivateApplicator/testing when they are ready to take the tests.

Dicamba Approved for Over-the-Top Use 2021 and Beyond

Source: Agweb.com

Tuesday, Oct. 27, 2020, the Environmental Protection Agency (EPA) announced it will approve three of the new dicamba formulations for over-the-top use for five years, according to EPA Administrator Andrew Wheeler. The herbicide is labeled for use in soybeans and cotton with the trait that confers tolerance to dicamba.

The specific formulations include Xtendimax VaporGrip Xtra, Engenia and Tavium. The registration starts next year (2021) and runs through 2025. The administrator said they opted for a five-year registration, which is typical for pesticides, instead of a two-year like dicamba has experienced in the past because they had more data to base this decision upon.

“EPA will register dicamba for over-the-top use on dicamba tolerant cotton and soybeans, this decision provides a five-year registration to provide certainty to growers,” Wheeler says. “EPA. has determined that these registrations address the concerns outlined in the June 9th Circuit Court of Appeals decision.”

The administration said it reviewed 65 new studies when making this decision, reviewed all literature and consulted with experts before making this decision.

In approving the herbicide for use in cotton and soybeans, EPA provided the following changes to the herbicide labels. These changes, and all label instructions, must be followed for legal use:

  • Downwind buffer of 240′ is required and a buffer of 310′ required where listed species are located.
  • Over-the-top application of dicamba of soybeans prohibited nationwide after June 30, and after July 30 in cotton.
  • An approved pH buffering agent will be required to be mixed for application to lower volatility. Buffering agents are registered with the EPA and must be documented each use.
  • Opportunities for growers to use hooded sprayers to reduce buffers.
  • States can expand over-the-top use to meet local needs by working with EPA.

“All of these efforts will help ensure there are not negative impacts on other farmers’ lands,” Wheeler continued. “States can further restrict, but they have to work with us and file the appropriate requests with EPA. We’re trying to have a national program here, we’re responding the the court’s concerns with a national cutoff.”

Dicamba’s use was hotly contested earlier this year. An appeals court vacated the product’s use in early June, which was followed by an exemption for use of stocks on-hand for farmers by EPA. The announcement brough confusion and brought dicamba’s compliance with the Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) under the microscope. EPA took those concerns into consideration while making this decision.

“The economic damage that would result from not being able to use dicamba herbicides would be tremendous,” said Ken Fountain, National Cotton Council chairman. “We greatly appreciate EPA’s timely issuance of a new five-year label for the critical crop protection product for cotton farmers.”

Some have already expressed concerns about EPA’s most recent announcement.

“Rather than evaluating the significant costs of dicamba drift as the 9th Circuit told them the law required, EPA rushed re-approval as a political prop just before the election, sentencing farmers and the environment to another five years of unacceptable damage,” said George Kimbrell, legal director at the Center for Food Safety. “Center for Food Safety will most certainly challenge these unlawful approvals.”

This story will be updated with quotes and information as it becomes available.

Herbicide Residue Considerations for Fall Cover Crop Establishment

Source: Alyssa Essman, Mark Loux, OSU

Herbicides with residual that are used in corn and soybeans can affect the establishment of fall-planted cover crops, and should be taken into account when planning cover crop practices and selecting species. Soil characteristics and weather also play a role in the persistence of residual herbicides, which can vary by field and year. More information is needed on rotational intervals for many cover crop species, and this information is often not included on herbicide labels. University weed scientists have studied the effect of residual herbicides on some of the most popular cover crop species in order to provide this information to growers. In general, residual herbicides that control grass weeds can hinder establishment of grass cover crop species. Broadleaf cover crop species are most impacted by group 2 (ALS inhibitors), 5 (PSII inhibitors), 14 (PPO inhibitors), and 27 (HPPD inhibitors) herbicides (Purdue University).

A multi-state study found that the general order of sensitivity of cover crops to herbicide carryover, from greatest to least sensitive, is:

  • Tillage radish > Austrian winter pea > crimson clover = annual ryegrass > winter wheat = winter oats > hairy vetch = cereal rye.

Soybean herbicides that tended to be most injurious were:

  • Fomesafen, pyroxasulfone, imazethapyr, acetochlor, and sulfentrazone.

Corn herbicide treatments that were most injurious to cover crops were:

  • Topramezone, mesotrione, clopyralid, isoxaflutole, pyroxasulfone, and nicosulfuron

(University of Missouri).

Below is a table of commonly used corn and soybean herbicides, the fall cover crops that are safe to plant in rotation, and cover crop species that may be injured following these herbicides (Adapted from Lingenfelter D. and Curran W., Penn State University).

 

 

Cover crops provide a multitude of benefits and their use is becoming an increasingly popular practice in Ohio. Including cover crops in rotation with agronomic crops to realize these benefits costs time and money. It is important to evaluate the potential risk of herbicide residue on the establishment of cover crops in order to ensure success. Residual herbicides applied at the time of planting typically interfere with cover crop establishment less than those applied POST. Weather can affect the persistence of herbicides also, especially rainfall in summer.  The risk of residual herbicides affecting cover establishment will be higher in areas that have been dry since herbicide application.  Risk will be lower where the herbicide application was followed by some wet weather to get herbicide degradation started, compared with an application during prolonged dry weather.  One of the least problematic cover crop species is cereal rye, which can be successfully established following a late corn or soybean harvest, and is tolerant to a most of the most commonly used corn and soybean herbicides. Weed control should continue to be the priority in selecting herbicides, and cover crop species selection should be based on potential injury and goals for the use of cover crops.  The introductory section of the “Weed Control Guide for Ohio, Indiana, and Illinois” has some of the same information presented here, and OSU weed scientists also summarize this in a video: https://www.youtube.com/watch?v=ylr0zGnXMfs

The following resources contain information on residual herbicides and cove crops also:

https://extension.psu.edu/corn-herbicides-and-rotation-to-cover-crops https://extension.psu.edu/soybean-herbicides-and-rotation-to-cover-crops

https://ipm.missouri.edu/IPCM/2020/3/coverCropTermination-KB/

https://ag.purdue.edu/btny/weedscience/Documents/covercropcarryover.pdf