More Pokeweed than Usual?

Jaime Cummings and Ken Wise (NYS IPM), Jeff Miller, Mike Hunter and Paul Cerosaletti (CCE)

We are receiving reports and more questions than usual on pokeweed incidence this season from various parts of the state.  Particularly with regards to it seemingly surviving glyphosate applications in fields.  Some of us are familiar with this large weed, and know that once established in your fields, it can be a serious challenge to eradicate.  And, sometimes by the time you notice it, it has already flowered and set fruit, and the birds are helping to spread it further.

Here are some quick questions and answers on pokeweed:

Why is pokeweed so challenging to manage?  It’s a perennial with a very large and persistent taproot, and is also a prolific seed producer with a wide emergence period.

Why is pokeweed becoming more prevalent?  Plowing and soil-applied residual herbicides were the typical management strategies for this weed.  With the widespread adoption of no-till or conservation tillage practices, and a move away from some of those residual herbicides in combination with less crop rotation diversity, we are experiencing a resurgence of pokeweed.

Why do I still have pokeweed in my fields that were treated with glyphosate?  Pokeweed seedlings can emerge from May – August, which means that you may have missed some of the later emerging seedlings during your typical early-season corn and soybean herbicide applications, especially if you didn’t include a residual herbicide in the mix.  And, since pokeweed is a perennial, you may be trying to kill plants that over-wintered and have established huge and hardy taproots.  It’s challenging to kill any weed with well-established taproots with a single herbicide application.

Pokeweed seedling emergence
Figure 1. Research at Penn State University illustrates seasonal patterns pokeweed seedling emergence. This figure can be found as part of a larger presentation, available at https://extension.psu.edu/pokeweed.

Pokeweed seedlings can emerge continuously throughout the summer, with a peak in May and ending in August (Fig. 1).  This long period of emergence makes it difficult to manage with a single-pass program of post-emergence herbicides alone.  And, it’s important to manage any seedlings that emerge later in the season, because although they are unlikely to set seed that season, they can produce a serious taproot to overwinter and pop up the following year (Fig. 2).  Research by K. Patches at Penn State University from 2011-2013 investigated the biology and management of pokeweed, and determined that many herbicides (including glyphosate and plant growth regulators) provided at least 80% control, when applied with either air induction or flat fan nozzles (Figs. 3 & 4).  And, in those trials, glyphosate applications after mid-June provided better control than applications made earlier in the season (Fig. 5).  This is because systemic herbicides applied at flowering on perennials are more likely to be translocated down to the roots to kill the taproot.  For increased later season pokeweed control, consider rotating into a small grain crop and applying herbicides in August to kill the seedlings that emerged after your typical soybean or corn herbicide applications.

Pokeweed seedling continual emergence
Figure 2. Pokeweed seedling continual emergence May – August, as observed in research (https://extension.psu.edu/pokeweed) at Penn State University. (Photos by K. Patches)
Chart showing effect of corn herbicides on pokeweed
Figure 3. Results from Penn State research trials on herbicide efficacy against pokeweed in corn 12 weeks after application. (Figure courtesy of Penn State University)
Chart showing effect of soybean herbicides on pokeweed
Figure 4. Results from Penn State research trials on herbicide efficacy against pokeweed in soybean 12 weeks after application. (Figure courtesy of Penn State University)
Effect of glyphosate application timing on pokeweed
Figure 5. Timing of glyphosate applications for controlling pokeweed in corn and soybean. (Figure courtesy of Penn State University)
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Tall Waterhemp and Herbicide Resistant Marestail found in Northern NY

Mike Hunter, North Country Regional Ag Team, Cornell University Cooperative Extension

We knew that it was only going to be a matter of time before we found herbicide resistant tall waterhemp and marestail in NNY.  In July, we confirmed two fields on two different Jefferson County farms that have herbicide resistant marestail and three fields on one farm that has tall waterhemp seedlings.

Tall waterhempUpon further investigation and doing some additional field testing we have strong evidence to believe that the two marestail populations are resistant to both Group 9 (glyphosate, i.e. Roundup) and Group 2 (ALS herbicides, i.e. Classic, FirstRate) herbicide Sites of Action.  This finding is not surprising due to the fact that the seeds of marestail are windblown and can be easily moved 50 to 100 miles.

The tall waterhemp (see photo) was found in three adjacent fields on a farm in Jefferson County.  Prior to this finding there were nine counties in NYS with confirmed populations of herbicide resistant tall waterhemp. While we cannot be sure that the tall waterhemp found in Jefferson County is resistant to any particular herbicide.  We can certainly assume that it will be resistant to Group 9 herbicides based on the fact that all current populations of tall waterhemp in NY is known to be resistant to this herbicide family.  We are currently working closely with this grower and will be doing additional testing to confirm its resistance to different herbicide families.

For additional information about marestail and tall waterhemp, I would encourage you to read an article on pages four and five of the CCE NCRAT North Country Ag Advisor May 2019 newsletter https://nydairyadmin.cce.cornell.edu/pdf/newsletter/pdf216_pdf.pdf

If you suspect you have one of these weeds on your farm or have a weed that is surviving applications of glyphosate please contact your local CCE Field Crop Specialist if you’re outside NNY or one of the CCE North Country Regional Field Crop Specialists Mike Hunter (315)788-8450 or Kitty O’Neil (315)854-1218.  Don’t be afraid to bring this to our attention because we will keep farm name and field locations confidential.

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The Muddy Boot Weed Seed Dispersal Method

Josh Putman, Field Crops Specialist, CCE SWNY Dairy, Livestock, and Field Crops Team

Tall waterhemp is one of the most problematic weed species throughout the Midwest and has now arrived and spread to eight counties in Upstate New York. Waterhemp can spread from field-to-field and farm-to-farm on equipment, clothing, application equipment, or via water from over flooded ditches and rivers. Following a recent field day event we wanted to demonstrate the amount of weed seed that could travel back with you.

Boots that were considered “clean” were not as clean as we had thought (Figure 1). A knife was used to clean the boots and break up any hard clots that were present. Once the boots were clean, tweezers were used to separate the weed seeds from the dirt (Figure 2). The pigweed/waterhemp seed was then separated from other weed seeds that were present, and pigweed seeds were counted (Figure 3). The clods of dirt were also checked, and one pigweed seed was found stuck to a clay particle (Figure 4).

Figure 1: Muddy boots
Figure 1: Muddy boots – Photo: Josh Putman
Figure 2: Tweezers used to separate weed seed from dirt
Figure 2: Tweezers used to separate weed seed from dirt – Photo: Josh Putman
Figure 3: Seeds were separated and counted; 17 total pigweed seeds
Figure 3: Seeds were separated and counted; 17 total pigweed seeds – Photo: Josh Putman
Figure 4: One pigweed seed hidden in a clay particle
Figure 4: One pigweed seed hidden in a clay particle – Photo: Josh Putman

An estimate of a 3 year establishment of waterhemp assuming 50% of the seeds were waterhemp and 100% were waterhemp was then calculated, respectively. The calculations are seen below:

16 pigweed seeds + 1 pigweed seed hiding in soil = 17 pigweed seeds from 2 boots.

Assuming only half of those are waterhemp and it can produce 250,000 seeds per female plant: 17/2 = 8.5 X 250,000 = 2.125 million seeds the following year in a field.

Assuming every seed on the bottom of the boots are waterhemp: 17 X 250,000 = 4.250 million seeds the following year.

Assuming 75% survival rate and reproduction in year 2: 4.250 million X 75% = 3.1875 million plants X 250,000 seeds per plant = |

**796,875,000,000 seeds going into the soil in year 3 (potentially)

In conclusion, correct and early identification is very important; learn the correct characteristics of the plants (Figure 5) and seeds. Proper cleaning and sanitation of equipment, clothing, and vehicles can help prevent spreading. Intense management and continuous scouting are vital to eradication of this weed species. Mechanical control such as plowing can bury the seed deep which might decrease seed bank numbers. And, if in doubt, contact your local CCE specialist for help with identification or other management practices.

Figure 5: Tall Waterhemp (left) vs. Smooth Pigweed
Figure 5: Tall Waterhemp (left) vs. Smooth Pigweed

 

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Waterhemp Herbicide Resistance Tests: Preliminary results

Bryan Brown, New York State Integrated Pest Management
Collaborators: Antonio DiTommaso, Kathleen Howard, Mike Hunter, Jeff Miller, Scott Morris, Jodi Putman, Peter Sikkema, Mike Stanyard

Waterhemp seedlings in greenhouse
Bryan Brown is coordinating a project testing waterhemp for resistance to herbicides.

Last summer, several populations of waterhemp (Amaranthus tuberculatus) survived herbicide applications in western NY corn and soybeans.

Growers asked if these weeds are actually resistant to certain herbicides. If so, which ones? And are all populations of western NY waterhemp resistant to the same herbicides, or do they differ?

To answer these questions, we collected seed from these surviving weeds at three locations in NY, grew them in a Cornell University greenhouse alongside a population of waterhemp that we know is susceptible to herbicides, and then used a spray chamber to apply a range of herbicides and rates.

The herbicides we used were glyphosate (i.e. Roundup, WSSA Group 9), atrazine (i.e. Aatrex, WSSA Group 5), lactofen (i.e. Cobra, WSSA Group 14), and imazethapyr (i.e. Pursuit, WSSA Group 2). The WSSA groups represented here are the ones waterhemp has developed the most resistance to in other states. For each herbicide, we used five different rates. Each rate was applied to five waterhemp plants from each population. Following the methods of other studies, plants were sprayed when they were around 5” tall. BASF Agricultural Solutions and Valent USA LLC supplied some of the materials for this study.

We’ll be doing a final analysis three weeks after spraying. But here’s how the NY populations look after only one week. At the full labelled rates, glyphosate resulted in 50% control and lactofen resulted in 99% control. Atrazine and imazethapyr resulted in poor control, but waterhemp plants were larger than the maximum size stated on the label.

But it’s the comparison of our three NY populations to the susceptible population that determines resistance. Final control ratings will be done in two weeks, but initial results indicate that two NY populations are potentially resistant to glyphosate, three are potentially resistant to atrazine, none are likely resistant to lactofen, and two are potentially resistant to imazethapyr. So herbicides in WSSA Groups 2, 9, and 5 shouldn’t be solely relied upon to control this weed.

Since there were some differences between NY populations, we’ve shared each farm’s results with the participating growers so they can make the necessary changes to their management plans.

So if you haven’t seen it already, keep an eye out for waterhemp this year. It looks similar to other NY pigweeds, except that it’s completely hairless and it has separate male (pollen-producing) and female (seed-producing) flowering heads. (A video comparison may be found from American Agriculturalist.) Since it can travel in seed, feed, and equipment ­– make sure they’re clean. And think about trying out some new weed control options.

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New Weed Control Options in Winter Wheat and Barley for NYS

By Mike Stanyard, NWNY Dairy, Livestock & Field Crops Team – Field Crops Specialist and Team Leader

It has always been encouraged to spray the earliest planted fields for winter annual weeds (purple deadnettle, chickweed, chamomile) in late fall. However, there are so many other things going on in the fall and your windows of opportunity for spraying can be slim to none. You never know what the weather will be like in the spring and timely weed control can be tricky. Here is an update on broadleaf and grass control products for this spring with two new products just registered in 2018.

Broadleaf Weeds. Harmony Extra and Harmony SC are still the backbone of many spray programs. Harmony Extra (Harmony + Express), controls a wider range of broadleaves and it is favored over other products because of its control of corn chamomile, wild garlic and chickweed. A recent point of concern has been the number of marestail/horseweed plants that are making it through until harvest. This may be an indication that you have an ALS resistant marestail population. Both of these products can be applied up until the flag leaf is visible (before Feeke’s stage 8).

Growth regulator products like Clarity, Banvel, MCPA and 2,4,-D are effective against many broadleaves and should take care of ALS resistant marestail. They are usually tankmixed with Harmony products for extra control of winter annuals and perennials. Application past Feek’s stage 6 (jointing) is not advised as it could lead to plant injury and yield reductions. Unfortunately, I have seen annual marestail emerge after this stage.

Huskie (Bayer Crop Science) just received a 24(c) Special Local Needs label for New York on March 2nd. It is a combination of pyrasulfotole (an active not labeled in NY yet) and two formulations of bromoxynil (ie Buctril). The SLN labeling is for marestail/horseweed control in wheat, barley, rye and triticale. Huskie can be used for control of marestail in winter malt barley as well. Talking with Dwight Lingenfelter, Penn State weed scientist, Huskie would be best tank-mixed with Harmony Extra for complete broadleaf control. In fallow ground trials over the past two seasons, Penn State has been seeing (90-95%) control of 8 inch marestail with Huskie at the highest rate. Huskie can be applied up until flag leaf emergence.

Grasses. NYS has a 24(c) Special Local Needs label for Osprey for control of roughstalk bluegrass and cheat in winter wheat. It expires at the end of 2018. Osprey can be applied in the fall and spring but must be applied early in the spring, prior to the jointing stage in winter wheat.

Prowl H2O can be applied to wheat and triticale in the fall and the spring but must be applied before weed seeds germinate. It is very effective on our annual grass spectrum and some of our annual broadleaves but must be applied early in the spring prior to weed emergence.

Axial XL (Syngenta) was just registered on January 12 in NYS and is labeled for the control of grasses in wheat and barley. The active ingredient is pinoxaden which is in Group 1 (ACCase mode of action). Axial can be applied to wheat and barley from the 2-leaf stage to pre-boot stage. It is labeled for Foxtail (giant, green and yellow), volunteer and wild oats, annual ryegrass, barnyardgrass and canarygrass. Axial XL can be used for annual grass control (foxtails most importantly) in spring malt barley. For optimal control, it is recommended to apply when grasses have between 1 and 5 leaves on the main stem or prior to emergence of the 3rd tiller. THIS PRODUCT IS NOT LABELED FOR OATS!!!

We are still advising growers not to mix your herbicide and nitrogen applications and spray separately. The leaf burning can cost us up to 10 bushels and could get worse as temperature and humidity increase.

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Oneida County Scouting Report – June 30, 2017

This week’s crop report (PDF).

The main issue is potato leaf hopper numbers over threshold in heavy alfalfa fields.
 
The second major issue is the potential for DON in wheat this year. Setting combines to blow out infected kernels and sampling for DON analysis.

Many soybean fields will need herbicide application soon

Many corn fields will need to be side dressed with N soon.

Jeffrey J. Miller
Cornell Cooperative Extension Oneida County
Ag Program Leader
Agronomist
315-269-5599
jjm14@cornell.edu
121 Second St., Oriskany, NY 13424

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Help locate Johnsongrass populations in New York State

Professor Toni DiTommaso is working on a nation-wide research project assessing the distribution and genetic diversity of the invasive perennial weed, Johnsongrass (Sorghum halepense). Currently, NY State is at the geographic northern-most limit of its range, but it is expected to increase in abundance in the state over the coming decades. He has included a brief description and several images of this species below to help with identification in case you are not familiar with it.

He is reaching out to you to help him locate Johnsongrass populations in NY State as he would like to collect seeds from these plants later this month and into early fall. These seeds along with seeds collected in other regions of the country will be grown in “common gardens” at locations across the country including here in central NY. This research will give us a good idea of how well adapted different populations of this invasive species are to growing in various regions of the country and in which regions it may become especially troublesome to manage.

If you know of Johnsongrass populations in NY State that have not yet been killed by herbicides or mowed (he needs to collect seeds), please e-mail Toni (ad97@cornell.edu) the precise location of the population (GPS coordinates, road intersections, etc.), the type of habitat it is found in (e.g. corn field, roadside, back of barn), and the approximate size of the population(s) (e.g. 10 ft x 15 ft). If you would like to take a few pictures of the plants and e-mail them to Toni, he could try to confirm that it is indeed Johnsongrass.

When this research is completed in a few years, he hopes to present his findings at various agricultural extension venues in the State.

Thank you for your help and he looks forward to hearing from you.

Toni DiTommaso (ad97@cornell.edu)
Weed Ecology & Management Lab
Soil and Crop Sciences
903 Bradfield Hall
Cornell University

BRIEF DESCRIPTION: Johnsongrass is a tall, coarse, grass with stout rhizomes. It grows in dense clumps or nearly solid stands and can reach 8 feet (2.4 meters) in height. Leaves are smooth, 6-20 inches (15.2-50.8 cm) long, and have a white midvein. Stems are pink to rusty red near the base. Panicles are large, loosely branched, purplish, and hairy. Spikelets occur in pairs or threes and each has a conspicuous awn. Seeds are reddish-brown and nearly 1/8 inch (0.3 cm) long.

Johnsongrass plants in flower
Mature Johnsongrass plants in flower
Johnsongrass seedheads 1
Seedheads
Johnsongrass seedheads 2
Seedheads

 

 

 

 

 

Note the prominent, white, midvein on a mature Johnsongrass leaf (LEFT) and root system with rhizomes (RIGHT)
Note the prominent, white, midvein on a mature Johnsongrass leaf (LEFT) and root system with rhizomes (RIGHT)

 

The ligules on Johnsongrass leaves (A) are membranous, while the ligules on Fall Panicum leaves (B) are a fringe of hairs. Barnyardgrass (C) lacks ligules.
The ligules on Johnsongrass leaves (A) are membranous, while the ligules on Fall Panicum leaves (B) are a fringe of hairs. Barnyardgrass (C) lacks ligules.

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