It’s been a “fun” couple weeks to be a weed scientist. While on vacation we were getting calls about new Palmer amaranth finds and had to make the recommendation to mow down one field of soybeans in SW Ohio to prevent an even bigger mess next year. Another field in that same area had enough plants to justify localized mowing where the plants were. The initial introduction of Palmer appeared to be due to purchase of a combine from Georgia, which was used in several operations. Early this week we visited several soybean fields in NE Ohio that had also been mowed down due to dense Palmer infestations after an OSU county educator talked to the growers. A couple more fields nearby probably should have been mowed down as well. Photos of some of the mowed and unmowed fields below. A central thing about Palmer amaranth has been reinforced through all of this. The message that we got from our counterparts in the south several years ago when Palmer started to rear it’s ugly head here was – “you have to get across to growers that if seed production is not stopped when there are just a few plants, this weed will take over a field faster than any other weed they have dealt with.” This is due to the extremely prolific seed production that can be well upwards of 200,000 seeds per plant. And this was readily apparent for the fields that had to be mowed down. We know that Palmer was in these fields last year, but apparently not at a level to raise concern. And this year it’s essentially game over. Be warned. It’s also apparent that mowing of large plants with seedheads will usually have to be followed with some type of aggressive tillage that cuts up plants well so that they cannot recover and still produce seed. We also observed plenty of new Palmer plants emerging still, and this season-long emergence is another trait that makes it so tough to manage.
As promised in the C.O.R.N. newsletter, we have added a link on the marestail page (or click here) to access some of our research results on control in wheat stubble and a couple other tough situations. The first page shows four scenarios: sites 1 and 2 are the same population but site 2 was where it had survived a previous glyphosate application; site 3 where plants regrew following mowing (similar to cutter bar on a combine); and site 4 had plants that had survived tillage. The results pretty clearly show how much more difficult it was to control the plants in sites 3 and 4. The second page shows results of a wheat stubble study, where plants had been low growing and mostly unaffected by the cutter bar, and then grew following wheat harvest. There were two application timings, and the results show the benefit of the earlier application for some treatments. The generally high level of control in this study probably overestimates control that will be obtained in many fields where plants have regrown following cutter bar damage.
We spent some time windshield scouting fields northeast of Columbus this week after being called out to determine whether a mystery weed was Palmer amaranth. There were only a few plants of this mystery weed in the field, and it tuned out to be common mullein. The inflorescence stalk on mullein can resemble a long Palmer seed head from a distance, but upon closer examination it’s difficult to confuse the two weeds. Mullein has a single stalk inflorescence while Palmer can have many, and the rest of the mullein plant doesn’t resemble an amaranth at all. Mullein rarely shows up in large numbers in corn and soybean fields, being primarily a weed of more undisturbed places. Use of the “images” tool in a Google search will allow you to pull up photos of both and see for yourself. Also take a look at the video on amaranth identification in the Palmer amaranth section of this website under the “weeds” tab. A couple photos below of mullein (left) and Palmer (right) to prove the point – the mullein photo was from the field in question:
In the soybeans behind the mullein, symptoms of PPO herbicide application were evident (fomesafen), which was intended to control giant ragweed and I suppose possibly marestail. The giant ragweed was pretty well controlled and the marestail unaffected. We have received more calls than usual asking for any possible solutions to control marestail in Roundup Ready soybeans, and there still aren’t any. Money spent on PPO inhibitors (fomesafen, Cobra, Cadet, etc) or 2,4-DB in an attempt to control marestail is just wasted in our opinion. Reports of glyphosate resistance in giant ragweed and common ragweed have also been on the rise. There has been much use of fomesafen remediate this, although expectations of effectiveness are often too high. Fomesafen is about an 85% herbicide on small giant ragweed plants, and this number decreases with plant size. Keep in mind also that when fomesafen is the primary herbicide in the mix for control of glyphosate-resistant ragweed, the rate, adjuvants, and application volume need to be optimized for fomesafen. This means use of the highest rate possible per geographic area, inclusion of COC or MSO, and upwards of 15 gpa.
We also found an infestation of waterhemp on this trip, in a field of LibertyLink soybeans. The LibertyLink system can be effective for management of waterhemp, but the plants in this field were already up to 20 inches tall. The field was supposed to be treated with glufosinate “soon”, which still was way too LATE. Glufosinate won’t control waterhemp plants this tall, and we suggested the addition of fomesafen, which still might not be enough. And finally, one of our educators sent us the following photo of waterhemp in soybeans (I think there are soybeans in there):
These plants are of course well beyond any control measures that involve herbicides. The grower has decided at this point that continuous soybeans and use of only glyphosate may not be the best course, and is thinking about residual herbicides and corn and cover crops for next year. Some people will change when the sky actually falls on them I guess.
The weed science group at U of Missouri has released a new publication, “Weed Identification and Herbicide Injury Guide”. It’s available for $18 at http://extension.missouri.edu – search for “IPM1007”. It’s well done, so consider adding to your library or folder of materials carried around to aid in problem solving and making recommendations. Cover and sample pages shown below.
We are currently in our first year of research to determine the safest and most effective herbicide programs for spring barley in Ohio. This research is briefly described in the video below. We don’t have any prior experience with weed control in spring barley. Summer annual weeds such as ragweeds, lambsquarters, pigweeds, and foxtails are the primary weed problem in spring-planted crops, and the competitiveness of the crop with weeds will be affected by planting date and stand density, among other things. There are a number of herbicides registered for use in barley, but not all labels specifically mention spring barley. Control of foxtails in barley can be obtained only by POST application of an Axial product, such as Axial XL or Axial Star, and labels for these products just mention “barley”. Axial Star controls ragweeds in addition to foxtails, since the premix contains fluroxypyr (Starane) in addition to the pinoxaden (Axial XL). Axial products can be applied up to the pre-boot stage, when grass weeds have 1 to 5 leaves and less than 3 tillers. There is no mention of a need for adjuvants on Axial XL and Star labels, but mixtures with certain broadleaf herbicides may require nonionic surfactant (check labels). Labels for the following broadleaf herbicides specifically mention spring barley: 2,4-D, MCPA, bromoxynil (Moxy, etc), dicamba (Clarity, etc), Huskie, Peak, Pulsar, and Starane. Labels for another group of broadleaf herbicides do not specifically mention spring barley, just “barley”: Aim, Cleansweep, Orion, Widematch, tribenuron (Express, etc), and thifensulfuron/tribenuron premix (Harmony Xtra, etc). We have descriptions and ratings for all of these on summer annual weeds in the “Weed Control Guide for Ohio, Indiana, and Illinois” (page 139-149 of 2016 edition).
There are still some tough burndown situations in the state due to weeks of less than ideal weather conditions. Controlling large marestail is probably the biggest challenge, especially when there’s not much time between herbicide application and soybean planting. This situation is discussed in the video below. We realized too late however that while we showed examples of areas where marestail were still alive following an early burndown, we didn’t cover what the options were for a second burndown to control these and newly emerging plants where soybeans have yet to be planted. Options here depend upon what was already applied earlier in spring. Where a mixture of glyphosate, 2,4-D and residual herbicides was applied early, a follow up burndown of Sharpen plus glyphosate or glufosinate or Gramoxone would be adequate to control the marestail and small grasses and ragweeds that have emerged. It’s probably possible to just apply Gramoxone or glufosinate in these situations, along with a few ounces of metribuzin. Where residual herbicides were applied early, it may also be beneficial to include another reduced rate of residuals in any second burndown. This can improve the chances of: 1) controlling marestail until the soybean canopy can take over and provide late-season control; and 2) controlling giant ragweed, grasses, and other weeds until soybeans get somewhat established and the POST herbicides can be applied.
Results of a national survey of weed scientists and practitioners conducted by the national and regional weed science societies are in. Probably no surprise to all of us here in Ohio that marestail was identified as the most troublesome weed in soybeans. The other four weeds mentioned most frequently as hard to control in soybeans were Palmer amaranth, waterhemp, and giant and common ragweed. Nationally, over all crops, weeds designated as most troublesome, starting with the one listed the most times, were: Palmer amaranth, morningglory, lambsquarters, waterhemp, marestail, nutsedges, kochia, giant ragweed, Canada thistle, and foxtails.
Link to the WSSA newsletter that contains a summary of the survey – http://wssa.net/wp-content/uploads/WSSA_April_2016.pdf.
The amazing marestail plant – is there anywhere it can’t grow?
Our latest video covers pigweed identification. We compare four aspects of pigweed biology that we use to differentiate between redroot pigweed, waterhemp, and Palmer amaranth – pubescence, petiole length, leaf shape, and inflorescence (seedhead) characteristics.
Yes I know – it’s not officially spring yet. Here are some poems about the resilient and adaptable dandelion anyway.
The Dandelion’s pallid tube – Emily Dickinson
The Dandelion’s pallid tube
Astonishes the Grass,
And Winter instantly becomes
An infinite Alas —
The tube uplifts a signal Bud
And then a shouting Flower, —
The Proclamation of the Suns
That sepulture is o’er.
The First Dandelion – Walt Whitman
Simple and fresh and fair from winter’s close emerging,
As if no artifice of fashion, business, politics, had ever been,
Forth from its sunny nook of shelter’d grass–innocent, golden, calm
as the dawn,
The spring’s first dandelion shows its trustful face.
From “A Rhapsody” (excerpt) – John Clare
Tis May; and yet the March flower Dandelion
Is still in bloom among the emerald grass,
Shining like guineas with the sun’s warm eye on–
We almost think they are gold as we pass,
Or fallen stars in a green sea of grass.
They shine in fields, or waste grounds near the town.
They closed like painter’s brush when even was.
At length they turn to nothing else but down,
While the rude winds blow off each shadowy crown