Noxious Weeds in Cover Crop Seed and Seed Germination

Source: Alexander Lindsey, Laura Lindsey, Mark Loux, Anne Dorrance, Stan Smith, John Armstrong, OSU Extension

Seed quality is key to establishing a good crop (or cover crop). Some of the critical components of seed quality are percent germination, mechanical analysis for purity (% other crops, % inert, and % weeds), and a listing of noxious weeds identified by scientific/common name and quantity found. As producers are looking for seed sources to provide living cover on acreage this year that was previously earmarked for corn or soybeans, it is important to pay attention to the quality. These tests may also be required on seed lots for use in some relief programs as well. Commercial or certified seed used for cover crops should have a seed tag that shows variety and the seed quality measurements above. However, if the seed is sourced from out of state, the noxious weeds listed (or NOT listed) on the tag by name may differ from those had the seed been sourced from Ohio.

Only the noxious weeds for the state where the seed was originally going to be sold are required to be listed on the tag by name and quantity (Federal Seed Act, part 201.16). Each state determines which species are included on this list, and can differ from state to state. If seed is outside of Ohio for use on-farm, producers may want to have the seed tested for an “all state noxious-weed exam” prior to planting if this was not done previously on the seed lot. Only 1.1-1.2 lbs of seed is needed for the test, but it is critical the sample is representative of the lot to ensure quality test results. This test would screen the seed sample supplied for the weed contained in this list: https://www.ams.usda.gov/sites/default/files/media/StateNoxiousWeedsSeedList.pdf, and may serve as a more comprehensive exam than was conducted at the time of initial seed lot labeling. One service provider that can conduct this exam is Central Ohio Seed Testing (a subsidiary of the Ohio Seed Improvement Association; https://ohseed1.org/about-our-lab/). Samples can also be sent to ODA for an Ohio noxious weed exam (https://agri.ohio.gov/wps/portal/gov/oda/divisions/plant-health/grain-warehouse-feed-and-seed/). Depending on the source of seed and the planned use, a seed lot may be eligible to be tested for free through ODA between June and December (up to three per farmer). Conducting a noxious weed exam could help slow the movement of problematic weeds throughout the state and minimize future weed problems.

Another issue to consider is the quality of seed in storage that was not planted this year due to weather. Storing seed in an environment where the temperature (in F) plus the % relative humidity are less than 100 (Harrington’s rule) helps to minimize the rate of seed deterioration (or loss in germination and vigor). Seed germination is an important consideration for determining seeding rate to ensure the critical final stand for yield is achieved for crops like corn and soybeans. Most seed germination percentages on a seed tag for agricultural seeds (like corn and soybeans) are valid for 12 months from the last date of the month in which they were completed, with the exception being cool season grasses which are valid for 15 months beyond the month of testing (Ohio Revised Code, Chapter 907.07). Be sure to check the seed tag for both the date of the test as well as the germination when planning seeding rates.

You can search this blog for a complete description and pictures of all of the weeds on the Ohio Noxious weed list.

Recommended adjuvants for delayed preemergence/early postemergence herbicide applications.

Source:  Penn State University

Table 2.2-10 (from The Penn State Agronomy Guide) 

See specific herbicide label(s) for additional information on application. This type of application generally is used when weather conditions preclude the use of a standard pre­emergence program. For most products, do not apply in liquid fertilizer if com has emerged. Poor control from residual herbicides may result if annual grasses such as foxtail and panicum have emerged at the time of application; tank-mix with product that controls emerged grasses. Delayed preemergence/early postemergence programs can work well with herbicide-resistant corn hybrids now available (e.g., Roundup Ready and Libertylink). When tank-mixing with other pesticides, follow the most restrictive product label.

Recommended Adjuvants When Preemergence Herbicides Are Used Early Postemergence

Trade Name Recommended If Corn Has Emerged and Weeds Are Present Optional
Acuron1,2 NIS (0.25% v/v) or AMS 8.5 lb/100 gal
Acuron1,2 COC3 (1% v/v) AMS 8.5 lb/100 gal
Acuron Flexi NIS (0.25% v/v) or
Acuron Flexi COC3 (1% v/v)
Anthem ATZ/Anthem Flex/Anthem Maxx NIS (0.25% v/v) or
Anthem ATZ/Anthem Flex/Anthem Maxx COC (1–2 pt/A) or
Anthem ATZ/Anthem Flex/Anthem Maxx MSO (1–2 pt/A)
Atrazine label only mentions COC
Balance Flexx label states “Do not use COC or MSO or fully loaded glyphosate formulation”
Bicep II Magnum label mentions only NIS when tank-mixed with specific herbicides
Corvus label states: “Do not use COC or MSO”
FulTime NXT, TopNotch1, or Keystone NXT1 not addressed on label
Guardsman Max/G-Max Lite NIS (1–2 pt) or UAN (1–2 gal/100 gal)
Guardsman Max/G-Max Lite COC4 (1 qt/A) AMS (8–17 lb/100 gal)
Halex GT NIS (1–2 qt/100 gal) AMS (8.75–17 lb/100 gal) (required)
Harness MAX1,5 NIS (1 qt/100 gal) or UAN (rate not specified)
Harness MAX1,5 COC (1 gal/100 gal) AMS (rate not specified)
Harness Xtra or Degree Xtra not addressed on label
Instigate NIS or COC UAN or AMS (required)
Instigate rates not specified rates not specified
Lexar EZ1,2 NIS (0.25% v/v) or UAN (2.5% v/v) or
Lexar EZ1,2 COC (1% v/v) AMS (8.5 lb/100 gal)
Lumax EZ1,2 NIS (0.25% v/v) or UAN (2.5% v/v) or
Lumax EZ1,2 COC (1% v/v) AMS (8.5 lb/100 gal)
Python WDG/Accolade NIS (1 qt/100 gal) or UAN (2.5 gal/100 gal)
Python WDG/Accolade COC (1 gal/100 gal) AMS (2–4 lb/A)
Resicore NIS (1 qt/100 gal) or AMS only allowed with glyphosate or glufosinate herbicides
Resicore COC3 (1 gal/100 gal)
Zemax1,2 NIS (1 qt/100 gal) or UAN (rate not specified)
Zemax1,2 COC3 (1gal/100 gal) AMS (rate not specified)

1. Do not use either NIS or COC if tank-mixed with Liberty (AMS is allowed).
2. Do not use either NIS or COC if tank-mixed with a fully-loaded glyphosate (AMS is allowed); if glyphosate label recommends an adjuvant, add NIS and AMS.
3. Label cautions about crop injury.
4. Use COC only with Guardsman Max alone or tank-mixed with atrazine.
5. Do not use either NIS or COC if tank-mixed with glyphosate (AMS is allowed).

 

Spray Additives When Tank-mixed with Liberty (LibertyLink corn [LL]) or Glyphosate (Roundup Ready corn [RR])

Trade Name Specific Adjuvant Comments
2,4-D n/a**
Accent Q n/a
Aim/Cadet n/a
Atrazine n/a
Basagran n/a
Basis Blend n/a
Callisto/Callisto Xtra LL: Do not use COC
RR: Add AMS; if glyphosate calls for an adjuvant, add NIS (do not use UAN, COC or MSO)
Capreno LL: Do not use MSO or COC; only add AMS at 8.5 lb/100 gal
RR: Use of glyphosate compatible high surfactant oil concentrate (HSOC) is recommended with fully loaded glyphosate and required with partially loaded glyphosate; AMS is required; do not use COC or MSO
Curtail n/a
DiFlexx/DiFlexx Duo LL: Do not use MSO or COC; only add AMS at 8.5 lb/100 gal
RR: Label allows for additional adjuvant if resistant weeds are present
Halex GT LL: Not allowed
Harmony SG LL: n/a
RR: Add AMS; if glyphosate calls for an adjuvant, add NIS (1–2 pt/100 gal) (do not use UAN, COC, or MSO)
Impact/Armezon n/a
Laudis LL: Do not use MSO or COC; only add AMS at 8.5 lb/100 gal
RR: Label recommends additional adjuvant if fully loaded glyphosate is used; label requires additional adjuvant if partially loaded glyphosate is used
Maestro/Moxy n/a
Marksman n/a
NorthStar n/a
Permit Plus n/a
Permit/Sandea n/a
Realm Q LL: n/a
RR: When tank-mixed with glyphosate, ensure total adjuvant load is equivalent to the label recommendation
Resolve Q When tank-mixed with glyphosate or glufosinate, ensure total adjuvant load is equivalent to the label recommendation
Resource n/a
Revulin Q LL: n/a
RR: When tank-mixed with glyphosate, ensure total adjuvant load is equivalent to the label recommendation
Status n/a
Steadfast Q n/a
Stinger n/a
Stout n/a
Yukon n/a

*See also Table 2.2-16.
**n/a = adjuvants for LibertyLink or glyphosate not addressed.

 

Maximum Corn & Weed Size For Delayed Herbicide Applications

Source: Penn State University

Table 2.2-10 (from The Penn State Agronomy Guide) Maximum corn size, weed sizes for delayed preemergence/early postemergence herbicide applications.

See specific herbicide label(s) for additional information on application. This type of application generally is used when weather conditions preclude the use of a standard pre­emergence program. For most products, do not apply in liquid fertilizer if com has emerged. Poor control from residual herbicides may result if annual grasses such as foxtail and panicum have emerged at the time of application; tank-mix with product that controls emerged grasses. Delayed preemergence/early postemergence programs can work well with herbicide-resistant corn hybrids now available (e.g., Roundup Ready and Libertylink). When tank-mixing with other pesticides, follow the most restrictive product label.

Maximum Corn and Weed Sizes

Trade Name Maximum Corn Size Maximum Weed Size
Acuron 12 inches 3-inch broadleaves; inconsistent on emerged grasses
Acuron Flexi 30 inches 3-inch broadleaves
Anthem Maxx, Anthem ATZ 4 collars (V4) 2-inch broadleaves, before grass emergence
Atrazine 12 inches 1.5 inches
Axiom before emergence before emergence
Balance Flexx 2-leaf (V2) 1 true leaf stage
Bicep II Magnum 4-leaf or 2 collars 1- to 2-leaf
Corvus 2-leaf (V2) <2 inches (in general)
Dual 5 inches 2-leaf
Dual II Magnum, Bicep II Magnum, Bicep Lite II Magnum, Cinch ATZ Lite 5 inches 2-leaf
Fierce before emergence 2-inch broadleaves; by tank-mix partner for grasses
Guardsman Max/G-Max Lite 12 inches 1.5 inches broadleaves; before grass emergence
Halex GT 30 inches 4 inches
Harness, Harness MAX, Harness Xtra1, or Degree Xtra 11 inches or by tank-mix partner before broadleaf emergence, 2-leaf grasses or by tank-mix partner
Instigate 2-leaf (V2) 3 inches
Lexar EZ 12 inches 3-inch broadleaves; before grass emergence
Lumax EZ 12 inches 3-inch broadleaves; inconsistent on emerged grasses
Outlook 12 inches before emergence or by tank-mix partner
Prequel before emergence before emergence
Princep before emergence before emergence
Prowl H2O 30 inches before weed emergence
Python WDG/Accolade 20 inches (V6) before weed emergence
Resicore 11 inches 3-inch broadleaves
Resolve 12 inches 2-inch grasses; 3-inch broadleaves (in general)
SureStart II/TripleFLEX II11 inches 11 inches limited activity on 1-inch broadleaves; before grass emergence
Surpass NXT, FulTime NXT, TopNotch, or Keystone NXT, Breakfree NXT ATZ2 11 inches or by tank-mix partner before emergence or by tank-mix partner
Verdict before emergence before emergence
Zemax 30 inches (8-leaf) 3-inch broadleaves; before grass emergence
Zidua early postemergence before emergence or by tank-mix partner

1May be tank-mixed with Accent, atrazine (Harness), Banvel or Clarity, Marksman, Permit, or Roundup (Roundup Ready corn).
2May be tank-mixed with a number of different products, including Accent Q, Banvel or Clarity, Prowl, etc. See an herbicide label for specific information.

Current Weed Issues II: Revised Herbicide Management Strategies for Late Planting

Source: Dr. Mark Loux, OSU Extension

We’re running about a month behind in many cases, and with respect to weeds we are a month later than normal in implementing herbicide programs.  The most important thing to know about this is that we are well into the period of summer annual weed emergence, most of which occurs between early May and the end of June, which overall shortens the period of weed control that we need and allows earlier application of POST herbicides.  There are some advantages to this – here’s what it means for those fields just planted or that will still be planted within the next couple weeks:

Because we are this late, the burndown has become a major part of what is usually our in-season herbicide program, and is taking care of a good portion of the summer annuals that residual and POST herbicides would usually control.  The big glaring issue at this time is nasty burndown situations, and we provided some suggestions for this in previous articles.  Lots of pretty yellow fields due to cressleaf groundsel.  Keep in mind that this and other winter annuals that have flowered are ending their life cycles, so they have died or started dieing on their own anyway.  Focus should be more on the large giant ragweed, lambsquarters, marestail, etc that are present.  We are also late enough that waterhemp is part of the burndown mix in come fields.  Don’t skimp.

Herbicide programs do not have to last as long in crops planted late.  When we plant in early May, we need an herbicide program that controls weeds from then until the end of June or so, which is in part why we use residual herbicides and frequently apply POST herbicides 5 to 6 weeks after planting.  Applying the POST too early in a crop planted in early May introduces the risk of poor control of weeds that emerge soon after that application, before the crop is developed enough to control them on its own.  This is much less of an issue with a late-planted crop.  Since summer annual weed emergence tapers off as we move through June, the POST herbicides can be applied much sooner after planting without sacrificing control.  Planting soybeans this late can therefore allow earlier POST applications when weeds are small – more like 3 weeks after planting.  This can help minimize carryover concerns with fomesafen, and also provide a wider window to look for the right conditions to apply dicamba (see below).

In studies of reduced-rate POST applications that we conducted a couple decades ago, planting soybeans in late May or early June allowed us to use earlier POST applications (e.g 21 days after planting) at lower rates and still maintain control.  There were just fewer weeds emerging after planting and the duration of weed emergence after planting was also shorter.  It was not possible to achieve this in early-planted soybeans – we needed either two applications at reduced rate or a later application at full rates for control.

One issue with later POST sprays is the potential for herbicide carryover from products such as mesotrione and fomesafen (Flexstar, etc), among others.  Fomesafen carryover has been rare in the state but risk increases with later applications, especially if rainfall subsequently becomes limiting.  Where glyphosate and fomesafen are being combined in a late POST application to control ragweeds, it may become necessary to replace the fomesafen with lactofen (Cobra/Phoenix) as applications move into July.  Our research indicates that the lactofen products are less effective than fomesafen in this mix by about 10 to 20%.

Another concern would be POST applications of dicamba on Xtend soybeans shifted later into the hotter weather that occurs as we move from June into July.  The consensus of the weed science community is that both of the approved dicamba formulations have potential to move via volatilization, and the risk of this would increase with increasing temperatures and increased frequency and duration of inversions.  The current long-range forecast also indicates a trend for hotter than normal temperatures as we move into mid-summer.  Current labels allow application through 45 days after planting or prior to the R1 stage, whichever occurs first.  For soybeans planted early, the 45-day limit is often the main determinant, but later planted soybeans progress through growth stages more rapidly so the R1 stage may be the more frequent limitation.  Movement of dicamba onto other types of soybeans later in summer also has increased potential to reduce yield, since long-term effects of exposure to dicamba are more severe when soybeans have flowered.  Bottom line here is that there is less weather and time suitable for dicamba application with late-season applications, and movement and injury that does occur can have more substantial impact.  Planting within the next couple weeks and looking for the right conditions to spray starting about June 21 would provide more flexibility with regard to weather and weed size than deciding to wait until about July 10 to spray when it’s hotter and weeds are already large.

Can residual herbicides be omitted in late-planted soybeans?  Maybe.  Reduced weed populations could make this more feasible, but we really hesitate to recommend it.  Omitting residuals is never the right thing to do in fields with a history of weed control problems or high weed populations, or those with waterhemp and Palmer amaranth.  One advantage of omitting residuals would less risk of antagonism with burndown herbicides in mixtures.  Applying certain soybean residuals in June can increase risk of carryover.  The effectiveness of current soybean herbicide-tolerance trait systems makes this more of a possibility, but lack of residuals generally increases risk of problems and selection for resistant weeds, and makes timing of POST herbicides more critical.  The latter point is important because with a compressed season, applicators can be required to cover a lot of acres within a short period of time.  Keeping residuals in the program allows for more flexibility overall.

In late-planted corn, residual herbicides may be effective enough to reduce need for POST herbicides.  Or the residuals could be applied early POST, after the rush to plant is over (keeping rotation guidelines in mind).  Some corn fields are already in this situation, planted without any herbicide applied yet.  The table below shows restrictions on POST use of residual corn herbicides (source – U of Illinois).  This information can also be found in the herbicide descriptions in the Weed Control Guide , and is also summarized in this PSU newsletter article and this table from the MSU weed control guide.  Reminder that use of 28% UAN as a spray carrier is prohibited for POST application of herbicides with the exception of Degree Xtra.

 

 

It’s All About the Weed Seedbank – Part 1: Where Has All the Marestail Gone?

Source: Mark Loux

For the second year in a row, we are scrounging to find enough marestail at the OARDC Western Ag Station to conduct the research we had planned on this weed.  After years of having plenty of marestail, we have had to look around for off-site fields where there is still a high enough population.  Which, since we are scientists after all, or at least make our best attempts, left us thinking about reasons for the lack of marestail, and our overall marestail situation, and seedbanks.

While the short game in weed management is about getting good enough control to prevent weeds from being a yield-limiting factor and interfering with harvest, the long game is about preventing seed production and managing the soil seedbank.  One of the characteristics shared by marestail, giant ragweed, and the nasty pigweeds, waterhemp and Palmer amaranth, is a rapid decline in seed viability in the soil within the first year, and an overall decline to 5% or less viable seed within 3 to 4 years.  Another characteristic of marestail and pigweed seed is a relative lack of dormancy, which results in the potential for an almost immediate increase in population the year following a year of substantial escapes and seed production.  How big that increase is depends upon how many plants go to seed and how many seeds are produced per plant, with the potential of up to about 200,000 seeds per marestail plant and one million per waterhemp or Palmer amaranth plant.  The net result of these two characteristics, though, is that these weeds can ramp up population fast following a year of poor control, but populations can also decline rapidly with good control that prevents seed.

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Adapting Burndown Herbicide Programs to Wet Weather Delays

Source:  Dr Mark Loux, OSU

While it’s not terribly late yet, the wet soils and wet forecast could keep most of us out of the fields for a while.  The questions about how to deal with burndown herbicide treatments in delayed planting situations are rolling in.  One of the most common ones, 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).  While we wrote last week about marestail populations being on the decline, this does not mean it’s gone by any means.  Overwintered marestail plants become tougher to kill in May, and the fact that fall weather was not conducive for herbicide applications makes the situation worse in some fields.  The good news is that we have some additional herbicide/trait options for help with burndown since the last time we wrote an article covering this in 2016, although our experience is that nothing we suggest here is 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.  We also would not expect the addition of Elevore to consistently solve this issue either, and it requires a 14 day wait to plant any soybean.  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.

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Spring Herbicide Applications on Winter Wheat – Part 2 Labeled Herbicides

Source: Purdue University (Edited)

If weed infestations are severe enough to require a herbicide application, the use of liquid nitrogen fertilizer solution as a carrier is a popular option for applying herbicides and topdressing the wheat crop in a single pass over the field.  Caution should be taken when using a liquid fertilizer as a herbicide carrier as moderate to severe crop injury can result, especially in saturated conditions.  Many post applied wheat herbicide labels allow for liquid nitrogen carriers, but require different rates and types of surfactants than if the herbicide was applied with water as the carrier.  Table 1 includes precautions to be taken when applying wheat herbicides using liquid fertilizer as a carrier; further details and directions can be acquired from the herbicide label.

Another consideration growers should take into account when planning early spring herbicide applications is the plant back restrictions to double crop soybeans.  A large percentage of the herbicides listed in Table 1, especially those with activity on Ryegrass and Brome, have soybean plant back restrictions greater than the typical three month time period between spring applications and double crop soybean planting.  The soybean plant back restrictions greatly reduce the number of options available to wheat producers who double crop soybeans after wheat.  Refer to Table 1 for more specific plant back timing restrictions.Click Here For Complete Table

Spring Herbicide Applications on Winter Wheat – Part 1 Growth Stages

Source: Purdue University (Edited)

The winter is finally winding down and we are bound to have warmer days and spring in the near future. As we look towards the warmer weather there a few field activities that are going to start quickly, including winter wheat greenup herbicide applications and winter annual weed burndown applications in no-till fields. There are few things to keep in mind as these activities are added to the calendar. Many wheat producers, especially in the southern regions of Indiana will soon be or already are topdressing their wheat.  Those looking into topdressing need to also be scouting for weeds and determining if a herbicide application is necessary on any existing winter annual weeds.  The following information will outline winter annual weeds to look out for, weed scouting tips, crop stage restrictions, and herbicide recommendations.

Some common broadleaf weeds to scout for in your winter wheat are dandelion, purple deadnettle, henbit, chickweed, Canada thistle, and wild garlic.  These winter annual species that emerge in the fall can remain relatively inconspicuous through the winter and become competitive and troublesome during the spring if not controlled early in the spring.  Summer annual weeds such as ragweed will be of less concern in the early spring and will be outcompeted by the wheat crop if managed properly.  Grass weeds to be aware of and scouting for are: annual bluegrass, annual ryegrass, cheat, and downy brome.

Determining the severity of weed infestations in your wheat fields is key in determining the necessity of a herbicide application.  As with all agronomic crops, you should scout your entire field to determine what weed management practices need to be implemented and determine any areas of severe weed infestations.  Wheat fields that contain uniform infestations of at least one broadleaf weed and/or three grass weeds per square foot should be taken into consideration for a herbicide application to avoid yield loss and harvest interference problems.  Some fields that have less uniform infestations, but rather pockets of severe infestation should be managed to reduce weed seed production and future infestations.

When determining your herbicide program for spring applications, the stage of the wheat crop should be considered.  The majority of wheat herbicides are labeled for application at certain wheat growth stages and some commonly used herbicides have very short windows in which they can be applied.  The popular broadleaf weed herbicides 2,4-D and MCPA are efficient and economical, but can only be applied for a short period of time between tillering and prior to jointing in the early spring.  Wheat growth stages and herbicide timing restriction are outlined in Figure 1 above.

The LL-GT27 soybean – what’s legal?

Source: Dr. Mark Loux, OSU Extension

We are starting to see the availability of soybean varieties with more than two herbicide resistance traits, which can expand the herbicide options, improve control, and allow multiple site of action tank mixes that reduce the rate of selection for resistance.  One of these is the Enlist soybean, with resistance to glyphosate, glufosinate, and 2,4-D.  As of this writing, full approval for the Enlist soybean is still being held up by the Philippines (because they can apparently).  The other is the LL-GT27 soybean, which has resistance to glyphosate, glufosinate, and isoxaflutole (Balance).  There is no label for use of isoxaflutole on this soybean yet, but it is legal to apply both glyphosate and glufosinate.  In Ohio, as long as neither label prohibits applying a mixture of two herbicides labeled for a specific use, it’s legal to apply the mixture.  So, it’s also legal to apply a mixture of glyphosate and glufosinate to the LL-GT27 soybean.  There is no label that actually mentions or provides guidance for this mixture, which does not affect legality, but could affect who assumes liability for the recommendation to apply a mixture if that matters to you.  Some seed companies are making the recommendation for POST application of the mix of glyphosate and glufosinate to the LL-GT27 soybean in printed materials.  Our interpretation after discussion with ODA, is that these materials are essentially supplements to labels, and so the seed company would assume some liability for the recommendation.

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Achieving Full-season Waterhemp Control in Soybeans

Dr. Bob Hartzler and Meaghan Anderson, Integrated Crop Management News, and Iowa State University Extension and Outreach.

Although there are many ways weeds escape control in crop fields, one of the leading causes of waterhemp control failures is emergence of plants following postemergence herbicide (POST) treatments.

Waterhemp requires more than twice as many growing degree days to reach 50% emergence as giant foxtail or velvetleaf (Figure 1), resulting in much of the population emerging after mid-June.

The layered residual system is one of the best ways to reduce late-season waterhemp escapes in soybean. It involves a split application of herbicides with residual activity – the first application is made at or near planting, and then additional residual is included with the POST application (Figure 2). The additional residual herbicide extends activity later into the season than a single application, and is especially beneficial in years with heavy rains following planting.

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