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.
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.
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).
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!
Source: Dr. Mark Loux, OSU
Current forecast is for fairly warm temperatures through late evening Tuesday evening, followed by a substantial drop in temperatures and chance of snow, followed by cold/cool temperatures through the weekend. Primary question concerning this scenario seems to be whether it is okay to apply wheat or burndown herbicides prior to this cold snap. Some things we know about herbicides and cold weather:
– Herbicides applied to an emerged crop just prior to or during cold weather may be more injurious compared with favorable weather conditions. During cold weather when plants are not actively growing or growing slowly, the rate of translocation and metabolism of herbicide by the plant slows down, which can mean an accumulation of herbicide that is not being metabolized. This can increase the risk of crop injury since metabolism of herbicide by the crop, or conversion to an inactive form, is what allows that herbicide to be safely used on the crop in the first place. For some herbicides, there is such a large margin of safety with regard to crop safety that this is all inconsequential. For others the margin is narrower and issues such as cold weather and sprayer overlaps are more important. The inclusion of safeners in herbicide formulations reduces the risk of injury, usually be increasing the rate of metabolism, but may not completely solve issues that arise because of adverse weather or too high a dose. So with regard to this week and risk of injury to wheat, we would recommend avoid applying herbicide once the cold weather starts (from Wednesday on), until warm weather resumes.
– There is less certainty in making a recommendation about whether to treat wheat on Tuesday prior to the cold weather. We have seen instances in corn where application just prior to cold weather has resulted in greater injury. Wheat is actively growing now under favorable weather, and should readily translocate and metabolize herbicides. Much of this process occurs within the first few hours of application. Temperatures do not really start to plunge until early Wednesday morning per the forecast. While it’s somewhat of a guess, it seems that application during the first part of Tuesday would be possibly safer to the crop than later in the day. Past experience has shown us that some wheat herbicides are just generally safer than others, so one option would be to omit the ones that have stricter growth stage guidelines or have more of a history of causing injury. Having said this, in our research we have really not experienced injury from small grain herbicides applied per label.
– With regard to efficacy of burndown herbicides and cold weather, some of the same principles apply. Applying herbicide from Wednesday through the weekend, when weeds are not actively growing, is not recommended due to the likely loss of activity. Susceptible weeds metabolize herbicide slowly anyway, so the issue is a lack of translocation within the plant and the inability of herbicide to do it’s thing at the active site when plant processes are shut down. This is the type of cold weather we referenced in the recent article about dandelions, when we have observed control of this weed to plummet. We have also observed extremely slow control of overwintered annual weeds during cold weather.
– We would recommend going ahead with burndown herbicide applications on Tuesday, prior to the cold. As with wheat, weeds are actively growing under favorable weather so we assume herbicides will work. It’s still a bit of a guess, but it could be a while before field conditions and weather are suitable for application again.
– This is the type of scenario that makes us want to remind everyone again that a few dollars of herbicide in the fall can help avoid some of the nasty burndown issues that develop when spring conditions are less than optimum. Just saying.
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:
- Positive identification of the pest.
- Choosing the least persistent and lowest toxicity pesticide that will work.
- Selecting the right equipment, particularly the right type and size of nozzle for the job.
- Applying pesticides accurately at the right time.
- 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
Source: Mark Loux, Curtis Young, OSU Extension
Poison hemlock remains one of the more persistent and prevalent poisonous weeds that we deal with in Ohio. It’s most typically a biennial plant (sometimes perennial), emerging from seed in year one and developing into a low-growing rosette by late fall. The rosette overwinters and then resumes growth in the spring of year two. Stem elongation initiates sooner in spring than many other biennials, and this is followed by continued growth and development into the often very tall plant with substantial overall size. Flowering and seed production occur in summer.
Failure to control poison hemlock occurs partly because, while it often grows in edges and fencerows around crop fields, no one really pays much attention to it until it does reach this large size when it’s less susceptible to herbicides. And everyone is busy getting crops planted in spring anyway so control of hemlock gets low priority. Stages in the poison hemlock life cycle when it is most susceptible to control with herbicides are: 1) fall, when in the low-growing rosette stage; and 2) early spring before stem elongation occurs. It’s most easily controlled in fall, but several products can work well in spring. Herbicide effectiveness ratings for poison hemlock can be found in Table 21 of the current Weed Control Guide for Ohio, Indiana, and Illinois. Herbicides rated 8 or 9 on poison hemlock include the following: 9 – Crossbow, Remedy Ultra; 8 – Cimarron Max, Curtail, dicamba, glyphosate. Mixing glyphosate and dicamba can improve control compared with either applied alone.
Several online resources cover poison hemlock more comprehensively than this article does, including this one from the University of Missouri. Information on toxicity can also be found via an internet search or by contacting OSU Extension if help is needed to resolve a specific concern.
Source: Mark Loux, OSU Extension
Waterhemp populations across the Midwest continue to develop more complex variations of herbicide resistance. Multiple resistance to an increasing number of herbicide sites of action is the norm in many populations in states west of Ohio. Waterhemp has on the whole developed resistance to seven sites of action, including the following:
Group 2 – ALS inhibitors – chlorimuron, imazethapyr, etc
Group 4 – Synthetic auxins – 2,4-D, dicamba, etc
Group 5 – Photosystem II inhibitors – atrazine, metribuzin, etc
Group 9 – EPSP synthase inhibitor – glyphosate
Group 14 – PPO inhibitors – fomesafen, flumioxazin, sulfentrazone, etc
Group 15 – long chain fatty acid inhibitors – metolachlor, pyroxasulfone, etc
Group 27 – HPPD inhibitors – mesotrione, isoxaflutole, topramezone, etc
Individual populations with resistance to three or more sites of action are common. Mutations are occurring that confer resistance to several of these sites of action simultaneously, through a resistance mechanism that enhances the metabolism and inactivation of the herbicides by the plant. For example, there appears to be a linkage in the resistance to mesotrione and atrazine, where resistance to one means it’s likely that resistance to the other occurs also. Weed scientists have concluded that this weed is capable of developing resistance to any herbicide site of action used against it. We aren’t actually sure what the correct recommendation is for stewardship of herbicides once a single mutation can confer resistance to multiple sites of action. Which is the reason we stress the need to take steps in mid to late season to prevent seed from plants that survive management strategies.
The Agronomic Crops Team will host a virtual Corn College and Soybean School on February 11, 2021. Corn College is in the morning, from 9:00 – 12:00pm, with Soybean School in the afternoon from 1:00-4:00pm. Each program will feature updates from OSU Specialists. CCA CEUs are available. The schedule for the day is as follows:
Corn College, 9:00am-12:00pm
- Corn Management for 2021, Peter Thomison, 1.0 CM CCA CEUs
- Meeting Nutrient Needs in Corn, Steve Culman, 1.0 NM CCA CEUs
- Disease Management, Pierce Paul, 1.0 PM CCA CEUs
- Insect Management, Andy Michel, 1.0 PM CCA CEUs
Soybean School, 1:00-4:00pm
- Soybean Management for 2021, Laura Lindsey, 1.0 CM CCA CEUs
- Weed Management, Mark Loux, 1.0 PM CCA CEUs
- Disease Management, Anne Dorrance, 1.0 PM CCA CEUs
- Insect Management, Kelley Tilmon, 1.0 PM CCA CEUs
This program is free to attend. Register at www.go.osu.edu/agronomyschools.
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)
Ohio Pesticide Applicator Training: Core Student Workbook
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.