Fall Herbicide Treatments – Even More Important This Year?

Source: Dr. Mark Loux, OSU

If you have never applied herbicide in fall to burn down winter annuals, or done it only infrequently, this might be the year to make an investment in fall herbicides.  Fall treatments are an integral component of marestail management programs.  They also prevent problems with dense mats of winter annuals in the spring, which can prevent soil from drying out and warming up, interfere with tillage and planting, and harbor insects and soybean cyst nematode.  2019 was a generally tough year for weed control, leading to higher end of season weed populations in some fields.  A number of acres were never planted, and growers got to experience the difficulty in obtaining season-long control in the absence of a crop.  Reminds us all how important the crop canopy and shading of the soil is during the second half of the season.  Bottom line – there was substantial production of weed seed in some fields, and a replenishment of the soil seedbank by both winter annual and summer annual weeds.  The seed of winter annuals and marestail lacks dormancy so above-average weed seed production can lead to an immediate increase in fall-emerging weeds.  Applying herbicides this fall can compensate for increased weed populations and make life easier in the spring.

We have published information on fall herbicides fairly frequently, and our suggestions for fall treatments have not really changed much.  There is plenty of information on fall herbicide treatments in the C.O.R.N. newsletter archive and on other university websites.  Our philosophy on this has not changed much over the past decade.  A few brief reminders follow:

1.  When to spray?  Anytime between now and Thanksgiving will work, and possibly later.  We have applied into late December and still eventually controlled the weeds present at time of application.  Once hard freezes start to occur, there is usually a substantial change in the condition of certain weeds, such as dandelion and thistle, that renders them less sensitive to herbicides.  We discourage applications during periods of very cold weather which can occur starting about Thanksgiving, and also (obviously) when the ground is snow-covered.  The generally dry conditions we are experiencing have limited weed emergence so far this fall.  We anticipate that rain occurring now that leads to some sustained soil moisture near the surface will likely result in germination and emergence of the weeds that have been missing until now.  Our recommendation is to wait for rain and the additional weed emergence before applying any herbicide this fall.  The risk in this is that the weather turns wet, making it difficult to apply herbicide.  So it’s also possible to apply now and include a residual component to help with later fall emergence (which is the exception to the “no residual” recommendation in #4 below), such as simazine, a low rate of metribuzin or Canopy, or a Sharpen rate higher than 1 oz.

2.  What about all of the crop residue on the ground after harvest – won’t that cause problems?  We have not worried about this, and the herbicides seem to work regardless.  Most agronomists I have asked have the same impression.  On the other hand, it probably wouldn’t hurt to wait a while after harvest to let the residue settle down, and the weeds to poke through.  Dense crop residue usually prevents marestail from emerging anyway. Continue reading

Sorting Out the Soybean Herbicide Resistance Traits

Source:  Mark Loux, OSU

The world of soybean herbicide resistance traits has gotten more complex over the past several years.  The good news is that we have new options for control of herbicide-resistant weeds, although it can be a little difficult to sort out which one is best for a given situation and whether the possible downsides of certain traits are tolerable.  The following is a quick rundown of what’s available and some things to consider when selecting seed.  This is not meant to be an extensive evaluation/description of these systems because including all the possible configurations of herbicide use and the stewardship stuff would probably kill the possibility that anyone reads the rest of the article.  We also do not attempt to include all of the possible seed trade names.  For ratings of herbicide effectiveness on certain weeds, check the tables in the “Weed Control Guide for Ohio, Indiana, and Illinois”.

Roundup Ready (RR1, RR 2 Yield, etc.) – the original herbicide resistance trait.  Resistant to glyphosate which can be applied anytime up through R2

LibertyLink – resistant to glufosinate (Liberty, Interline, etc.) which can be applied anytime up to R1.

LL-GT27 (Freedom Plus, etc.) – resistant to glyphosate, glufosinate, and isoxaflutole (Balance), although there is currently no isoxaflutole product approved for use in these soybeans.

Enlist – resistant to glyphosate, glufosinate, and 2,4-D.  Enlist One (2,4-D choline) and Enlist Duo (2,4-D choline + glyphosate) are the only 2,4-D products approved for preemergence and postemergence use on this soybean, outside of the typical use of 2,4-D ester 7 or more days ahead of planting that works on any soybean.  These products can be used any time before or after planting Enlist soybeans without a waiting period as well as postemergence through R2

Roundup Ready Xtend – resistant to glyphosate and dicamba.  XtendiMax, FeXapan, and Engenia are the dicamba products approved for preemergence and postemergence use on this soybean.  These products can be applied any time before or after Xtend soybean planting without a waiting period, as well as postemergence (prior to R1 and no later than 45 days after planting).

Note:  Dicamba and 2,4-D are different herbicides.  Dicamba cannot be applied to Enlist soybeans and 2,4-D cannot be applied to Xtend soybeans.  Just like glyphosate cannot be applied to LibertyLink soybeans and glufosinate cannot be applied to Roundup Ready soybeans.  Seems obvious but it’s a surprisingly frequent question.

All of these soybean herbicide trait systems have utility in certain situations.  Factors determining this are the resistant weeds present and the type of tillage.  The primary resistant weed issues in Ohio, which require herbicides other than glyphosate, are marestail, giant and common ragweed, waterhemp, and Palmer amaranth.  A few things to consider here – all of which assume that some type of residual herbicides are being used, regardless of the specific weed issues: Continue reading

Reminders about Pre-harvest Herbicide Treatment

Source: Mark Loux, OSU

Information on preharvest herbicide treatments for field corn and soybeans can be found in the “Weed Control Guide for Ohio, Indiana, and Illinois”, at the end of these crop sections (pages 74 and 141 of the 2019 edition).  Products labeled for corn include Aim, glyphosate, and paraquat.  Products listed in the guide for soybeans include Aim, paraquat, glyphosate, and Sharpen.  Some dicamba products are also approved for preharvest use in all types of soybeans, which escaped our notice until now, so it is not listed in the guide.  The basic information for preharvest dicamba (for 4 lb./gal products):

Apply 8 – 32 oz/A as a broadcast or spot treatment after soybean pods have reached mature brown color and at least 75% leaf drop has occurred; soybeans may be harvested 14 days or more after a pre-harvest application; do not use preharvest-treated soybean for seed unless a germination test is performed on the seed with an acceptable result of 95% germination or better; do not feed soybean fodder or hay following a preharvest application of this product.

Preharvest herbicide treatments are primarily intended to suppress/kill and desiccate weeds that can make harvest more difficult.  Products with contact activity will cause faster desiccation and leaf drop of weeds but may be less effective at killing weeds compared with systemic products.  Effective desiccation with contact herbicides may still require a week or more following application.  Differences can vary by weed.  The maximum paraquat rate is well below the rate required to actually kill large weeds, but it is still probably most effective for desiccation of morninglory.  Glyphosate is not likely to be effective on marestail and waterhemp, and many giant ragweed populations, whereas dicamba may with enough time between application and harvest.  The first frost will usually provide the same results, so in a situation where crop maturity is delayed as is the case in many fields this year, consider whether an herbicide treatment is actually needed.

Preharvest treatments are not intended to be used to speed up crop maturity, and largely do not accomplish this.  The restrictions on preharvest treatments that specify how mature the crop must be at time of application are designed to minimize any effect of herbicides on crop maturation.  Applying earlier than specified could interfere with that process.  The residue tolerances for this use are also based on a certain application timing, and failure to follow label guidelines could result in illegal herbicide residues in grain.

No Pigweed Left Behind – Late-Season Scouting for Palmer Amaranth and Waterhemp

Source: Dr. Mark Loux (edited)

Remain vigilant!  We have Palmer and Waterhemp in Knox County!! Now is an excellent time to scout for these weeds, especially in bean fields. If you would like help with identification call John at 740-397-0401.

If you don’t already have to deal with waterhemp or Palmer amaranth, you don’t want it.  Ask anyone who does.  Neither one of these weeds is easy to manage, and both can cause substantial increases in the cost of herbicide programs, which have to be constantly changed to account for the multiple resistance that will develop over time (not “can”, “will”).  The trend across the country is for Palmer and waterhemp to develop resistance to any new herbicide sites of action that are used in POST treatments within about three cycles of use.  Preventing new infestations of these weeds should be of high priority for Ohio growers.  When not adequately controlled, Palmer amaranth can take over a field faster than any other annual weed we deal with, and waterhemp is a close second.  Taking the time to find and remove any Palmer and waterhemp plants from fields in late-season before they produce seed will go a long way toward maintaining the profitability of Ohio farm operations.  There is information on Palmer amaranth and waterhemp identification on most university websites, including ours –  u.osu.edu/osuweeds/ (go to “weeds” and then “Palmer amaranth”).  An excellent brief video on identification can be found there, along with an ID fact sheet.  The dead giveaway for Palmer amaranth as we move into late summer is the long seedhead, and those on female seed-bearing plants are extremely rough to the touch.  We recommend the following as we progress from now through crop harvest: Continue reading

Horseweed (marestail) control options in fallow prevent plant fields

Source: Christy Sprague, Michigan State University

The challenging conditions this spring have left many fields unplanted. Glyphosate- and multiple-resistant horseweed (marestail) dominates a majority of these fields. Horseweed and other weeds in these unplanted fields need to be controlled prior to setting seed to prevent future weed problems. To help determine some of the more effective options for horseweed control, we sprayed several treatments two weeks ago on 2 feet tall horseweed. Common lambsquarters, common ragweed and prickly lettuce were also present in this field. Below is a compilation of pictures of these treatments and a summary of the results.

Horseweed control results

Roundup PowerMax (glyphosate) alone was ineffective at controlling a majority of the horseweed plants in this field (Figure 1A), indicating this population is highly resistant to glyphosate. Glyphosate-resistant horseweed is extremely common in many Michigan fields and glyphosate alone should not be used. The addition of 2,4-D ester at 1 pint per acre (pt/A) or 1 quart per acre (qt/A), Enlist One at 1 pt/A or Clarity (dicamba) at 1 pt/A to Roundup PowerMax improved horseweed control. However, controlling horseweed with these treatments only ranged from 60–70% 14 days after treatment (Figure 1B). These treatments will not likely result in complete control of horseweed.

The addition of 2,4-D or dicamba also improved common lambsquarters and common ragweed control over Roundup PowerMax alone. While these may be some of the more inexpensive treatments, they were not the most effective and caution should be taken if 2,4-D ester or any of the dicamba formulations are used. Off-target movement by drift or volatility, especially under high temperature conditions and when sensitive crops are in the area, can occur these herbicides.

Horseweed control 2
Figure 2. Glyphosate-resistant horseweed control with (A) Liberty (glufosinate) at 32 fl oz/A plus AMS and (B) Sharpen at 1 fl oz/A plus Roundup PowerMax at 32 fl oz/A plus MSO plus AMS, 14 days after treatment. Photo by Christy Sprague, MSU.

The most effective treatments to control glyphosate-resistant horseweed were Liberty (glufosinate) at 32 fluid ounces per acre (fl oz/A) plus AMS (Figure 2A), or Sharpen at 1 fl oz/A or 2 fl oz/A plus Roundup PowerMax at 32 fl oz/A plus MSO plus AMS (Figure 2B). These treatments resulted in greater than 95% control of horseweed, common lambsquarters, common ragweed and prickly lettuce. A higher rate of Liberty (glufosinate) at 43 fl oz/A can also be used.

Initial control of glyphosate-resistant horseweed with Gramoxone 3L (new formulation) at 2.67 pt/A plus surfactant was 80%. However, by 14 days after treatment, horseweed started to regrow (Figure 3). Controlling common lambsquarters, common ragweed and prickly lettuce ranged from 70–75%.

Horseweed control 3
Figure 3. Glyphosate-resistant horseweed control with Gramoxone plus surfactant, 14 days after treatment. Photo by Christy Sprague, MSU.

Two additional treatments we examined included disking and mowing. Mowing reduced overall weed biomass, however it also removed the primary growing point and as horseweed started to regrow, additional shoots were produced. If mowing, multiple passes throughout the season will likely be required. A onetime mowing would likely be more beneficial later in the season prior to flowering and seed set. Tillage or disking did provide good horseweed control, however it will likely take multiple passes to keep the fields clean throughout the season.

Additional considerations

All these treatments were applied under good growing conditions (plenty of moisture and heat) and resulted in good herbicide activity. As weeds continue to grow and begin to flower, the effectiveness of these treatments will likely be reduced. Additionally, depending on the weed species, there could possibly be new emergence later in the season.

Crop rotation restrictions also need to be considered when choosing one of these herbicide treatments for horseweed and other weed control. Sharpen, 2,4-D and dicamba all have residual activity and could cause injury to certain cover crops and winter wheat if rotation restrictions are not followed. Winter wheat should not be planted earlier than one month after applying dicamba or 2,4-D (Enlist One). Sharpen at 1 or 2 fl oz/A can be applied any time before planting winter wheat. There is a 70-day rotation restriction between Liberty applications and planting winter wheat. Consult individual herbicide labels.

The Ohio Noxious Weed Law – A Tool in the Prevention of Waterhemp and Palmer Amaranth

Source: Dr. Mark Loux

Waterhemp and Palmer amaranth are both now listed on the Ohio noxious weed law, which means that landowners must take steps to control infestations and prevent further spread.  Since these are annual weeds, preventing spread is achieved by preventing plants from reaching maturity and producing seed.  This is the basis for our “No pigweed left behind” effort, for which the goal is to create an understanding that the only way to beat these weeds is to prevent seed.  Prevention needs to occur in any area that might be subject to infestation, such as roadsides, parks, conservation seedings, parks, etc, in addition to agricultural fields.  The entities managing these areas are responsible for recognizing and controlling infestations of waterhemp and Palmer amaranth, but this does not always occur.  Not everyone involved in crop production or land management is aware of the waterhemp/Palmer problem to begin with, and many managers are busy enough that preventing noxious weed problems has low priority.

Our advice is to pay attention to what’s happening in your area or in the areas that you farm, with the goal of becoming aware of new infestations early enough that plant maturity and seed can still be prevented, regardless of where they may be occurring.  We recommend as a first step contacting the land manager or owner to explain the issue, make them aware that they have an infestation, and request that action be taken.  However, where it’s not possible to have this conversation, or there is a refusal to take action, the Ohio noxious weed law can be used to try to force action.  A two-page summary of the noxious weed law that can be found here on the OSU Ag Law Blog, and also links directly to the law itself.

The basic idea here is that following an unsuccessful attempt to work with a landowner or manager, noxious weed issues should be reported to township trustees, and this must be done in writing.  The trustees then have the responsibility to deal with the issue, and the method for doing so varies depending upon what the land is used for and who is managing it.  If it’s necessary to use the noxious weed law, be sure to start the process early enough in summer, well before potential seed production.  There is a need to allow time for all of the steps in the process to occur, and for notifications to be received and acted on (or not).  Our experience is that not all landowners and managers will take action upon first notification, and in addition to action, their response to notification can include minimal response of protesting their need to act.  Waiting too late to start the process can result in lack of resolution of these issues in time to prevent plant maturity and seed production.  The noxious weed law has been used several times within the last two years to force managers to control Palmer amaranth, and could be used to accomplish the same for waterhemp, which was recently added to the list.  Consider the law a tool to prevent the establishment and spread of these weeds when other methods are ineffective.

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

No pigweed left behind

No pigweed left behind

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.