A Good Free Weed ID Resource
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DSource: Dr. Mark Loux, OSU
Ohio Department of Agriculture: Dicamba use in Ohio ends June 30, 2020
On June 3, the US 9th Circuit Court of Appeals issued a decision in a case concerning the use of dicamba on Xtend soybeans. This decision voided the labels for XtendiMax, Engenia, and FeXapan that allows use on Xtend soybeans. Tavium was not included in this decision, because it was not approved for use when the case was initially filed. Several excellent articles covering this decision can be found here on the OSU Ag Law blog (https://farmoffice.osu.edu/blog). EPA stated on June 8, providing further guidance about what this decision means for the use of dicamba for the rest of this season. The gist of this decision was the following:
“EPA’s order addresses sale, distribution, and use of existing stocks of the three affected dicamba products – XtendiMax with vapor grip technology, Engenia, and FeXapan.
ODA subsequently issued a statement regarding the registration and use of these products in Ohio, stating that any application must happen before July 1, 2020. Partial text from this statement:
“The registration of these products (XtendiMax, FeXapan, and Engenia) in Ohio expires on June 30, 2020. After careful evaluation of the court’s ruling, US EPA’s Final Cancellation Order, and the Ohio Revised Code and Administrative Code, as of July 1, 2020, these products will no longer be registered or available for use in Ohio unless otherwise ordered by the courts.
Source: Dr. Mark Loux
The maps that accompany this article show our current knowledge of waterhemp and Palmer amaranth distribution in Ohio. These are based on information from a survey of OSU Extension County Educators, along with information we had from samples submitted, direct contacts, etc. We still consider any new introductions of Palmer amaranth to be from an external source (brought in from outside Ohio) – hay or feed, infested equipment, CRP/cover/wildlife seedings. Palmer is not really spreading around the state, and as the map shows, we have had a number of introductions that were immediately remediated. The number of counties where an infestation(s) is being managed is still low, and within those counties, the outbreak occurs in only a few fields still. Waterhemp is much more widespread in Ohio and is spreading rapidly within the state from existing infestations to new areas via equipment, water, animals, etc. We do not have Ag Educators in all counties, and even where we do, infestations can occur without us knowing about them. Feel free to contact us with new information to update the maps.
Among the weed photos sent to the Agronomy Team members for identification, a fair number lately has been for the purposes of “pigweed” identification. “Pigweed” as used here can refer to waterhemp, Palmer amaranth, spiny amaranth, Powell amaranth, and redroot/smooth pigweed (these two are mostly the same for ID/control purposes). It’s almost impossible to tell these apart when they are very small, but this gets easier by the time they are 4 inches tall. Waterhemp and Smooth/redroot pigweed are still the most common. Waterhemp is smooth all over with a somewhat elongated leaf with smooth edges, and leaves sometimes can be a darker and glossier green than pigweed. Smooth/redroot pigweed will have a hairy/rough stem (more defined as it gets larger), with relatively nonglossy leaves that are widest in the middle with “rougher” edges. Various resources are available to help with identification, including our pigweed ID fact sheet and Youtube video. Identification of pigweeds is not necessarily straight forward, so feel free to contact your local extension educator or OSU weed scientists (firstname.lastname@example.org or email@example.com) for help with identification.
Source: Mark Loux, OSU
Depending upon where you are in the state, it’s possible right now to be experiencing delays in getting anything done, progress in planting but delays in herbicide application, weather too dry to activate residual herbicides, and/or reduced burndown herbicide effectiveness on big weeds due to cold weather. What’s become a typical Ohio spring. Some information relative to questions that OSU Extension educators have passed on to us:
1. Residual herbicides and rainfall. Residual herbicides do vary in the relative amounts of rain needed for “activation”, or adequate movement into the soil to reach germinating seeds. Most growers are applying mixtures or premixes of several products, so we’re not sure these differences are as important as the overriding principle here. Residual herbicide treatments need to receive a half to one inch of rain within a week or so after tillage or an effective burndown treatment, to control weeds that can will start to emerge at that time. This varies with timing of application and weather. Summer annual weeds are the target here, and their emergence ramps up in early May, although cold weather can slow this down. So residual herbicides applied in mid-April, prior to most of the summer annual weed emergence, may not need rain as soon after application, compared with herbicides applied in May. Aside from this, residual herbicide activity is not really dependent upon soil reaching a certain temperature. Under more marginal rainfall conditions, it’s possible that herbicides may control the small-seeded weeds that emerge at or just below the soil surface, but be less effective on larger-seeded weeds that can emerge from deeper. In a tilled situation, a timely rotary hoe can be used to remove some of the weeds that are about to emerge (the “white stage”) and buy some time for rain. The good news here is that we have effective POST herbicides to remedy many situations where the residual herbicides are not completely effective.
2. Residual herbicides and crop injury. The concerns here seem to be more about soybean herbicides, which may partly reflect the overall greater safety of residual corn herbicides. Several residual soybean herbicides can cause injury, depending upon when they are applied relative to planting, rainfall, soil type, seeding depth, etc. These include products that contain metribuzin, sulfentrazone, flumioxazin, and chlorimuron. One of the things that has reduced our risk of injury from all of these herbicides is that in no-till soybeans they have usually been applied a week or more prior to planting to accommodate restrictions on 2,4-D ester and dicamba. Application at or after planting increases the risk of injury, as does use in tilled situations. We have increased metribuzin use substantially over the past decade, but injury has been extremely rare due to application prior to planting and use of relatively low rates in combination with other products. We hear more about injury or suspected injury from flumioxazin and sulfentrazone when wet weather delays planting and forces application of residual herbicides after planting. It’s worth noting here also that the Xtend and Enlist soybean systems do away with the wait to plant soybeans for dicamba and 2,4-D, respectively, and more growers may be waiting until after planting to apply burndown/residual herbicides.
In brief, symptoms of these are as follows: chlorimuron – slowed development, stunting, yellowing; flumioxazin and sulfentrazone – necrosis on young leaves and stem, stunting; metribuzin – usually delayed until first trifoliate, yellowing and possibly necrosis on margins of older leaves. Cloransulam, imazethapyr, and imazaquin are generally safer on soybeans than chlorimuron, in situations where injury is a concern. Activity of metribuzin varies considerably with soil texture and organic matter content, so using the labeled rate for soil type is important. Injury from any of these may be more likely when herbicide application is delayed for several days after planting, followed by substantial rain as the soybeans are about to emerge. Labels for products containing flumioxazin state that soybeans should be planted 1 ½ inches deep and herbicide should be applied no later than three days after planting, in an attempt to avoid this situation (does not always work). The good news here is that early injury to soybeans usually does not reduce stand, but may slow early growth and rate of crop canopy development and leave soybeans open to the effect of other stresses. In some of these situations, it can be difficult to sort out how much of the damage is due to herbicide and how much is due to other factors. Yield loss is probably infrequent based on the soybean plant’s ability to compensate for these types of factors.
3. Cold weather and burndown herbicides. We had a fairly warm winter and early spring, followed by the recent month of colder than normal weather. The net result of this is large winter annual weeds, and weather that is currently not terribly conducive for burndown activity. There is not much specific guidance on herbicide labels about cold weather, just general statements about how effectiveness can be reduced under adverse conditions that include cold weather. We expect many experienced applicators may have their own set of rough guidelines on this, or at least gut feelings. Under cold conditions, the rate of herbicide activity declines and also the overall effectiveness. It’s more difficult to define the weather conditions when herbicide should not be applied. These would certainly include periods when frost or freeze is occurring overnight and daytime weather is cool and cloudy (less than about 50). One night of frost followed by a warm sunny day may still allow for decent herbicide activity, if weeds appear sufficiently recovered from the frost. Aside from this we could make a general recommendation to keep applying as long as night and day temperatures are at least 40 and 60 to 70, respectively, although this is still not ideal compared with day temperatures higher than 70 with sun. One way of dealing with this problem is to just wait for a return to warm, sunny weather before applying burndown herbicides. Another is to increase herbicide rates and use a more comprehensive herbicide mixture. For example, adding Sharpen to a mixture of glyphosate plus 2,4-D or dicamba. As with the less than effective residual herbicides under dry weather, burndown herbicide problems can sometimes be resolved with an effective POST treatment of glyphosate, 2,4-D, or dicamba, depending upon the trait system.
4. Reminder about the value of fall herbicides. Fall herbicides are an essential tool for marestail management, but given our current situation of dense, big weeds in no-till fields and potential problems with burndown herbicide effectiveness, it’s worth reminding all of us why fall herbicides started being used in the first place. In the late 1990’s, growers were experiencing problems with dense stands of winter annual weeds such as chickweed that interfered with tillage and planting. One contributor to this was the occasional reduced activity of spring-applied burndown herbicides in cool weather, which resulted in too slow death and dry down of weeds to prevent the problems the weeds caused. Fall-applied herbicides became a solution to this, since they result in almost weedfree spring seedbeds up until the point when giant ragweed and other summer annuals emerge (early May for most of these). As anyone knows who has used fall herbicides, their effectiveness reduces the overall importance of the spring-applied burndown, since it does not have to control a mess of large, overwintered weeds. It’s all just way easier. And issues with cold weather and spring-applied burndown herbicides are therefore less important. For as little as $6 worth of fall-applied herbicide. Something to think about moving forward.
Preemergence herbicides are the foundation of herbicide-based weed management systems, and effective use of these products is essential to protect crop yields and reduce selection pressure for herbicide resistant weeds. In a perfect world, applying preemergence herbicides immediately after planting would provide the greatest likelihood of maximum performance, but equipment and labor availability limit many farms from using this approach. This article will provide a brief overview of the pros and cons of different application strategies.
|Early preplant: Applications made more than 7 to 10 days prior to planting.|
When the news broke that we would need to retreat to our homes due to Coronavirus-19, the run on milk, eggs, bread and toilet paper began at our local grocery stores. I have been especially fascinated by the hoarding of toilet paper. Every time I have been out to get food and supplies, the toilet paper shelves have been completely bare.
As my wife Emily and I were out taking a Sunday evening walk, I noticed along the ditches some green, soft-looking plants which appeared to be the lambs-ear plant, with which many of us are familiar. After closer inspection, the plant we were looking at was Common mullein or Verbascum thapsus. Emily was quick to respond that locals refer to the plant as Cowboy’s Toilet Paper. Then the light bulb went off—could this be Mother Nature’s answer to our COVID-19 toilet paper shortage?
Besides Cowboy’s Toilet Paper, you may have heard it referred to as Quaker’s rouge, candle wick, flannel leaf, velvet dock, big taper, bunny’s ear, miner’s candle, or poor man’s blanket. These names commonly reflect some characteristic the plant exhibits, such as the flower stalk or leaf texture. If you read survival guides, this plant is mentioned as an emergency roadside toilet paper due to the large, fuzzy leaf of this botanical wonder. One word of caution however, the fuzzy leaf may cause some skin irritation when used as toilet paper.
The history of this plant is fascinating. Common mullein traces its roots back to Europe as it was planted in gardens for its medicinal purposes as an expectorant, diuretic, pain relief and healing of abrasions. Interesting enough, since Quaker women weren’t allowed to wear make-up, they would rub the hairy leaves on their cheeks to create a homemade blush look. Hence the name Quaker’s Rouge. However, its major claim to fame is definitely its use as a toilet paper.
According to our network of sources, the effectiveness of new soybean trait systems has some growers once again thinking about omitting preemergence residual herbicides from their weed management programs. Some people apparently need to learn the same lessons over and over again. Having gone through this once in the early 2000’s when Roundup Ready soybeans had taken over and we all sprayed only glyphosate all day every day, we think we’re pretty sure where it leads. We’re sensitive to concerns about the cost of production, but the cost-benefit analysis for residual herbicides is way in the positive column. We’re not the ones who ultimately have to convince growers to keep using residual herbicides, and we respect those of you who do have to fight this battle. Back in the first round of this when we were advocating for use of residuals, while the developers of RR soybeans were undermining us and telling everyone that residuals would reduce yield etc, we used to have people tell us “My agronomist/salesman is recommending that I use residuals, but I think he/she is just trying to get more money out of me”. Our response at that time of course was “no pretty sure he/she is just trying save your **** and make sure you control your weeds so that your whole farm isn’t one big infestation of glyphosate-resistant marestail.” And that answer probably works today too – maybe substituting waterhemp for marestail.
We need to state here that a good number of growers kept residual herbicides in their programs through all of this, and we assume they aren’t tempted to omit them now either. For everyone else – maybe interventions are called for. Where the recalcitrant person is repeatedly thumped with a stick while being reminded of what happened last time, until they change their minds.
Weed scientist: so you’re going to use residual herbicides right?
Soybean grower: no
WS: remember what happened last time – lambsquarters became a problem when every residual herbicide would have controlled it. Change your mind yet?
WS: remember when the weather didn’t cooperate and you ended up spraying 2 foot tall weeds because of no initial control? Do you want this again?
WS: so you’re going to use residuals?
SG: not sure
WS: and you expect your local dealer to clean up whatever mess occurs when you don’t use residuals?
WS: remember when you burnt out the FirstRate on marestail and then the glyphosate wouldn’t work? Do you want this to happen with dicamba, 2,4-D and glufosinate?”
WS: well then
Gentler persuasive tap
WS: You know how bad a weed waterhemp is right?
WS: what if residuals will help prevent waterhemp infestations
SG: Ok then – yes
WS: ok then
Note: we considered a number of sound effects here – thump, zap, whack…. Thump won out for no particular reason. We could not decide whether getting hit by a stick was more or less acceptable than getting shocked in this context.
The bottom line is that residual herbicides provide both short- and long-term risk management in weed management for a relatively low cost. A non-inclusive list of these:
– reduces weed populations overall and slows weed growth, resulting in more flexibility in the POST application window.
– Reduced risk of yield loss if weather interferes with timely POST application. In the absence of residual herbicides, soybean yield loss can occur when weeds reach a height of 6 inches.
– increases the number of different sites of action used within a season, slowing the rate of resistance development
– reduces the number of weeds that are treated by POST herbicides, which also slows the rate of herbicide resistance development
– residuals control lambsquarters which is not well-controlled by POST herbicides
– the most significant weed problems in Ohio soybean production – waterhemp, giant ragweed, and marestail – cannot be consistently controlled with POST herbicides alone. They require a comprehensive herbicide program that includes residual and POST herbicides. It may be possible to make a total POST system work some years or for a while, but in the end this approach will result in problems with control and speed up the development of resistance.
This whole subject of omitting residual herbicides makes us cranky because we don’t have to guess what will happen. We’ve made our best case here. It’s up to you of course, but we suggest that we not have to come back and have this discussion again. Because next time we’re bringing a few friends, a bigger stick, and a gorilla.
Disclaimer: Parts of this article are meant in pure jest. We would certainly never advocate in earnest the use of physical harm or other methods of persuasion to change the behavior of herbicide users. This goes against everything that the discipline of weed science stands for, and also OSU. Plus – we don’t even know where to rent a gorilla.