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Fall and Spring Burndown Considerations

Fall and Spring Burndown Considerations published on No Comments on Fall and Spring Burndown Considerations

Fall and Spring Burndown Considerations

Josh Copes, Daniel Stephenson, and Donnie Miller

 

This time of year, especially when it is dry, brings about questions concerning a fall burndown application that contains a residual herbicide.  As with any field operation, fall burndown should provide a monetary benefit.  A lot of time and money is spent after harvest preparing fields for planting next spring.  Producers should realize that some fall-applied residual herbicides will provide control of most winter annuals which may result in excess soil and bed erosion.  So, you may be asking why apply a fall burndown?  If glyphosate-resistant Italian ryegrass along with some other winter annual weeds like henbit are an issue, research has shown that a fall residual herbicide application will provide good to excellent control the following spring.  The table below is a glyphosate-resistant Italian ryegrass weed control program developed by Mississippi State University weed scientists that LSU AgCenter weed scientists have adopted.  The fall-applied herbicides listed in the table will provide some control of henbit as well.

To combat glyphosate-resistant Italian ryegrass, many producers tank-mix Select Max/clethodim in their spring burndown.  Unfortunately, several phone calls were received this past spring concerning Italian ryegrass control failures following Select Max/clethodim application.  If controlling Italian ryegrass has been an issue and control failures with clethodim products has occurred, one of the Fall programs in the Table 1 should be utilized.

Regardless of the crop planted in the spring, the LSU AgCenter suggest applying a spring burndown 4 to 6 weeks prior to planting.  This gives plenty of time for weeds to die and break the “green bridge” and for soil residual herbicides, if applied, will keep the fields weed free until planting.  If planting corn, a soil residual herbicide applied in the fall may provide weed control until corn planting time.  Therefore, a fall residual herbicide can pay and keep the field weed free until planting.  If you plan on planting soybeans or cotton however, a fall-applied soil residual herbicide may not be the best choice.  In some years, soil residual herbicides can provide weed control up to 120 days.  If applied in early-December, you could expect good weed control until mid to late March.  We must remember that if a fall-applied residual herbicide is applied in December with the hopes of skipping a spring burndown, you are making a mistake.  Don’t assume a fall-applied residual herbicide will hold through spring.  Fields must be scouted.

When burning down fields near planting, herbicide selection and rate and spray coverage are very important to ensure complete control.  If mare’s-tail, henbit, cutleaf evening-primrose, and sowthistle are present, be sure to apply 2,4-D at 1 lb of acid equivalent per acre.  In many instances, when weed control is unsatisfactory from spring burndown, it is because 2,4-D rates that were too low or 2,4-D was not applied at all.

The main goal of any burndown operation is to be weed free at the time of planting.  Choice of fall or spring burndown will depend on what crop you intend to plant, if Italian ryegrass an issue, and if soil and bed erosion a problem.  Spending more money than necessary is a big concern when deciding on burndown.

 

Glyphosate-resistant Italian ryegrass control recommendations. Adopted from Mississippi State University.

 Crop Fall Winter Spring
Corn Dual Magnum @ 1.33 pt/A or Zidua @ 2.5 oz/A double disk Select Max @ 12-16 oz/A or equivalent rate of 2 lb clethodim formulation Paraquat @ 0.75-1.0 lb of a.i. or two applications 10-14 days apart
Cotton Dual Magnum @ 1.33 pt/A or

trifluralin @ 3 pt/A or double disk

Select Max @ 12-16 oz/A or equivalent rate of 2 lb clethodim formulation Paraquat @ 0.75-1.0 lb of a.i. or two applications 10-14 days apart
Soybean Dual Magnum @ 1.33 pt/A or

Boundary @ 2 pt/A or trifluralin @ 3 pt/A or double disk

Select Max @ 12-16 oz/A or equivalent rate of 2 lb clethodim formulation Paraquat @ 0.75-1.0 lb of a.i. or two applications 10-14 days apart
Rice Command @ 2 pt/A or double disk Select Max @ 12-16 oz/A or equivalent rate of 2 lb clethodim formulation Paraquat @ 0.75-1.0 lb of a.i. or two applications 10-14 days apart

http://mafes.msstate.edu/publications/information-sheets/i1359.pdf

 

Please feel free to contact us with any concerns or questions.

 

Josh Copes

Cell: 318-334-0401

Office: 318-766-4607

jcopes@agcenter.lsu.edu

 

Donnie Miller

Cell: 318-334-0401

Office: 318-766-4607

dmiller@agcenter.lsu.edu

 

Daniel Stephenson

Cell: 318-308-7225

Office: 318-473-6590

dstephenson@agcenter.lsu.edu

Weeds: Problematic Year-Round

Weeds: Problematic Year-Round published on No Comments on Weeds: Problematic Year-Round

Weeds: Problematic Year-Round

Josh Copes, Daniel Stephenson, Donnie Miller, and Lauren Lazaro

 

Prolonged rains coupled with the high temperatures during August delayed harvest, caused crop damage, and environmental conditions were optimal for weed growth. We have received several phone calls concerning weeds requiring a herbicide application to better facilitate harvest. Once the crop dries down, weeds will begin to receive adequate sunlight allowing for rapid growth and development. If harvest is delayed for too long weeds, in particular vines, will quickly limit harvest efficiency. Paraquat (1 to 2 pints/acre), Aim (1 to 2 oz/acre), and sodium chlorate (4.8 quarts/acre) are labeled as harvest aids in corn. Labels require 7, 3, and 14 days for paraquat, Aim, and soidium chlorate, respectively, between application and harvest. Seven days or more will be required for adequate weed desiccation. Maximum water volume (gallons of water per acre) should be utilized as large weed size and growth habit within and on top of crop will limit herbicide coverage and desiccation efficacy. After the weeds have dried sufficiently to allow for harvest (and label requirements have passed), harvest as soon as possible to reduce the risk of weed re-growth.

Calls have also been received regarding control options for weeds post-harvest. Earlier harvest trends have resulted in adequate time for weeds to set seed between harvest and a killing frost. This time period can range from 1 to 4 months. The average first frost date in North and Central Louisiana is November 15 and 25, respectively. Since a lot of money and effort is spent in controlling weeds during the growing season to negate yield loss, timely weed control practices following harvest is important. These practices can reduce weed seed return to the soil seedbank, thus ensuring fewer weeds to fight in future cropping seasons. Post-harvest weed control is especially important in fields containing herbicide resistant weeds. A good example to illustrate the importance of post-harvest weed management is the ability of glyphosate-resistant Palmer amaranth to produce mature seed in as little as 30 days after emergence during late summer and early fall. Many other grass and broadleaf weeds are capable of setting viable seed in a similar time frame.

For weeds that are present in the field at harvest time, mowing and/or tillage should be conducted as soon as possible upon harvest to ensure viable seed set is reduced. Rainfall will influence subsequent germination of weed seed and therefore the need for additional weed control. Furthermore, rainfall following cultivation could increase weed seed germination, however, if the weeds are controlled, the soil seedbank would be reduced. Producers in no-till systems will have to rely on mowing and herbicides to prevent weed seed production.

Other methods of weed control include the use of herbicides. Herbicide applications should be targeted from late-September through October when the time period from application to first killing frost is shortened. Multiple herbicide applications for post-harvest control of summer annual weeds should be avoided. Residual herbicides such as S-metolachlor, pyroxasulfone, linuron, and diuron, among others, can be applied in the fall following harvest. However, rotation interval restrictions must be followed and length of residual control will be influenced by soil temperature and saturation. Glyphosate plus 2,4-D and/or dicamba or paraquat plus diuron and/or linuron are some choices for late-fall post-harvest applications. Diuron and linuron will offer soil residual; however, if soil temperatures are warm and rainfall frequent, do not expect long residual from these products. Likewise the lack of rainfall to properly activate residual herbicides to minimize weed germination can negatively impact treatment effectiveness.  Maximize water volume to ensure good weed coverage, as this is critical for good weed control, especially for paraquat plus diuron and/or linuron.

To reiterate, some weeds are capable of setting viable seed within 30 days after emergence during late summer and early fall. Post-harvest weed control is especially important when combatting glyphosate-resistant weeds such as Palmer amaranth, waterhemp, or johnsongrass. Problem fields should be identified and receive top priority for preventing seed return to the soil seedbank. Once harvested these problem fields should be mowed or tilled shortly after harvest to prevent and/or reduce seed set. Fields should then be regularly scouted for emerging weeds and additional control tactics applied prior to seed set. This will require close inspection of weed species to determine when they are flowering. Once a weed species is observed flowering a weed control operation should be implemented. Depending on weather conditions following harvest, weed control tactics may need to be implemented approximately every 3 to 4 weeks until a killing frost has occurred. If glyphosate-resistant Palmer amaranth or waterhemp is an issue, a management tactic (i.e. mowing, tillage, herbicide application) should be employed every 3 to 4 weeks.

Fall herbicide applications can be made for control of perennial weed species such as johnsongrass, bermudagrass, alligatorweed, and redvine. Studies conducted by LSU AgCenter weed scientist have determined that fall applications should be made from September 15 to October 15 when environmental conditions favor weed growth (http://www.lsuagcenter.com/portals/communications/publications/agmag/archive/2006/summer/longterm-management-of-perennial-weeds-starts-in-the-fall). For johnsongrass, bermudagrass and alligatorweed control, 1.0 lb ai/acre of glyphosate should be applied. Two lb ai/acre of glyphosate or dicamba are effective control options for redvine. Glyphosate (2.0 lb ai/acre) plus dicamba (1.0 lb ai/acre) can also be an effective control option. Fields should be scouted the fall following herbicide application to determine whether an additional application is needed. Do not mow or till fields for several weeks following herbicide application.

If you have any questions please contact us.

Josh Copes

Cell: 318-334-0401

Office: 318-766-4607

jcopes@agcenter.lsu.edu

 

Donnie Miller

Cell: 318-614-4044

Office: 318-766-4607

dmiller@agcenter.lsu.edu

 

Daniel Stephenson

Cell: 318-308-7225

Office: 318-473-6590

dstephenson@agcenter.lsu.edu

 

Lauren Lazaro

Cell: 210-562-0878

Office: 225-578-2724

llazaro@agcenter.lsu.edu

Mitigating and/or Managing Herbicide-Resistant Weeds

Mitigating and/or Managing Herbicide-Resistant Weeds published on No Comments on Mitigating and/or Managing Herbicide-Resistant Weeds

Drs. Daniel Stephenson and Josh Copes

LSU AgCenter

 

Herbicide-resistant weeds, especially glyphosate-resistance, is not a new topic.  Glyphosate-resistant (GR) Palmer amaranth was documented in Louisiana in 2010.  GR waterhemp was documented in 2015.  As of today, glyphosate-resistant Palmer amaranth can be found in virtually every row crop parish in Louisiana.  I’m not saying it has infested every field in every parish, but those fields having infestations range from a few plants to an extreme number of plants.  GR johnsongrass and Italian ryegrass have been documented too.  Although we haven’t officially documented GR horseweed (mare’s-tail) in Louisiana, I am certain it infests many acres in northern Louisiana.  Therefore, Louisiana producers must implement strategies to mitigate and/or manage this extremely troublesome pest.

 

In 2015, the LSU AgCenter published an extension publication entitled “Herbicide Programs for Managing Glyphosate-Resistant Palmer Amaranth and Common Waterhemp in Louisiana Corn, Cotton, and Soybean”.  It can be found at http://www.lsuagcenter.com/~/media/system/c/7/5/a/c75a63bba3f758d391b8c91871076ba6/pub3522herbicideprogramsformanagingglyphosateresis.pdf.  This publication provides suggested programs that can help mitigate and/or manage glyphosate-resistant pigweeds.  In addition, if these programs are implemented, they offer control of many if not all of the other grass and broadleaf weeds Louisiana crop producers deal with every year.

 

I’m not going to discuss the programs in this article in depth, so I ask that you view the document.  If you have questions, please call.  However, I will highlight the main focus of all programs.  The main, primary, essential thing to remember in designing a program to manage glyphosate-resistant weeds is residual herbicides.  Let’s break it down.

Step 1:  It is crucial for producers to apply a residual herbicide just prior to planting, at planting, or preemergence.  Paraquat at 0.5 to 1 lb ai/A (i.e 1 to 2 quarts/A of Gramoxome SL or 0.67 to 1.33 quarts of a generic 3 lb ai/gal paraquat) needs to be tank-mixed with this preemergence residual herbicide to kill any emerged weeds to ensure that the crop emerges in a weed-free seedbed.  All the residual herbicides listed in the preemergence section of the publication will provide residual control of pigweed following proper activation.  The choice of preemergence herbicide depends upon other weed species found in the field.  I won’t go into each different situation, so please call us to discuss if needed.

Step 2:  The next crucial step is to apply a residual herbicide tank-mixed with a non-selective herbicide 3 to 4 weeks after planting.  Examples of herbicides that offer residual control when applied POST are Dual Magnum (or many generics at proper rates), Prefix, Warrant, or Zidua.  Tank-mix one of them with glyphosate in Roundup Ready crops or with Liberty in Liberty Link crops.

 

Implementing steps 1 and 2 overlays residual herbicides during the early growing season, which protects the crop from early season competition.  The best time to kill a pigweed is when it is emerging or when it is very small (less than 3-inches).  Residual herbicides will kill the pigweed as it germinates or while it is emerging.  In addition, research has shown that maintaining soybean weed-free for the first five weeks after emergence maximizes yield, assuming proper growing conditions and insects/diseases are managed.

 

Between burndown and planting, pigweed and other weeds could emerge and reach heights too large to kill with an at-planting application of any labeled non-selective herbicide, specifically paraquat.  This situation usually occurs in fields that received a burndown application greater than 4 weeks prior to planting or when a burndown application didn’t include a residual herbicide.  Remember, Palmer amaranth has the potential to grow one-inch in height per day.  Therefore, it is critical that emerged Palmer amaranth or any other weed species be controlled when they are small with either tillage or a non-selective herbicide before planting.  Tank-mixing a residual herbicide with this preplant application will help to maintain your field weed-free up to planting.  However, do not think that applying a residual herbicide weeks prior to planting will be sufficient for residual control in-crop.  A preemergence residual herbicide will still be needed to maintain the crop weed-free until the first postemergence application.

 

In many states to our north, PPO-resistant Palmer amaranth and waterhemp have been documented.  To date, the LSU AgCenter has not documented any PPO-resistant pigweed in Louisiana.  However, we are screening some populations, so the potential for this is there.  You are probably wondering what are PPO’s?  PPO-inhibiting herbicides include Valor, Envive, Enlite, Valor XLT, Rowel, Rowel FX, all the Authority products, BroadAxe, Prefix, Flexstar, Flexstar GT, Reflex, Cobra, Ultra Blazer, Resource, ET, Cadet, and many more.  Honestly, this worries me as a weed scientist more than glyphosate resistance!  In Louisiana, the most common weed is morningglory.  Producers historically rely upon one of these herbicides to control morningglory.  It was always a big positive that they controlled pigweed and other weeds such as hemp sesbania, sicklepod, Texasweed, smellmelon, and others too.  We all should remember the articles in popular press articles showing the devastating effects of uncontrolled Palmer amaranth on a crop.  Imagine spraying a PPO-inhibiting herbicide for morningglory, hemp sesbania, AND Palmer amaranth control and you get little to no control of pigweed.  In this situation, I would have no suggestion for a herbicide application to help you.  In the presence of glyphosate and PPO-resistance Palmer amaranth, we will still have products that contain Dual Magum and other metolachlor products, metribuzin and products that contain it, Zidua, Warrant, Classic, and Liberty, but use of only these products would severely limit a producers ability to effectively manage herbicide-resistant weeds and all the numerous weed species Louisiana producers struggle with.  I’m not trying to be “chicken little” and claim the sky is falling.  I just want the reader to understand that this isn’t something to play with and a plan should be developed and implemented to prevent it.

 

Use of residual herbicides before crop emergence and in the first postemergence application is vital for weed management in Louisiana corn, cotton, and soybean.  In cotton, a residual herbicide is most likely needed in the second postemergence application too.  To mitigate and/or manage glyphosate-resistance and/or PPO-resistance, we have to use residual herbicides, rotate crops, tank-mix multiple herbicidal modes of action in a single application, don’t use similar herbicidal modes of action every year, and if you see a weed that should have died after application, go pull it up and burn it.  Those steps will help in the fight against herbicide resistance.  If you have any questions, please call your local county agent.  Good luck.

Getting ready to plant – Burndown considerations

Getting ready to plant – Burndown considerations published on No Comments on Getting ready to plant – Burndown considerations

Drs. Daniel Stephenson and Josh Copes

LSU AgCenter

 

 

I have received many calls concerning burndown over the past couple of weeks.  The warm weather we have experienced recently has most farmers itching to get started.  Research has shown that the optimum time to burndown winter vegetation is 4 to 6 weeks prior to planting.  This is primarily to reduce the risk of insect damage to seedling crops.  Think of it this way, winter vegetation in the field is like a buffet for the worms.  Removing the buffet 4 to 6 weeks prior to planting will cause the worms to die or move on to another food source.  If a crop is planted into green or dying vegetation, the possibility of those worms feeding on the seedling crop is very high.  Also, removal of winter vegetation 4 to 6 weeks prior to planting reduces the risk of physical competition between the weed and the crop.  Corn, for example, is determining its yield as it is spiking and if growth is hampered by any physical competition, i.e. weeds, then yield will be reduced.  Acreage that had a burndown application greater than 6 weeks prior to planting may need to be sprayed again prior to planting, especially if a residual herbicide was not applied with the burndown.  The take home message is simple, plant into a clean, weed-free seed bed.

 

Use of residual herbicides tank-mixed with the burndown application is pretty common.  Many herbicides utilized for residual control in a burndown application need to contact bare soil to provide residual.  If a field is completely covered by winter vegetation (cannot see much bare soil), that vegetation will intercept the burndown application cocktail, thus the “residual” herbicide may only act as a foliar herbicide and offer little to no residual herbicide.  Metolachlor or S-metolachlor are examples of herbicides that are tightly bound by plant biomass, so don’t expect residual control if it doesn’t reach the soil surface.

 

Research has shown that glyphosate plus 2,4-D at 1 lb ae/A is the best broad spectrum burndown treatment.  Notice I wrote 1 lb ae/A, not 0.5 or 0.75 lb ae/A.  For a 4 lb ae/gal 2,4-D formulation, 1 lb ae/A of 2,4-D equals 1 quart/A.  In my opinion, this holds true no matter if you add another herbicide like Sharpen, Goal, LeadOff, etc. to the burndown application.  Essentially, if you are going to make the trip to apply the herbicide, why not apply enough 2,4-D that research has shown will kill almost all of the winter weeds Louisiana farmers deal with.

 

If a producer does not want to or can’t use 2,4-D in their burndown application, then the choice of burndown herbicide depends upon weed spectrum.  I’m not going to go through every scenario because there can be many options.  Give your local county agent a call for help in this situation.

 

In conclusion, the main item all consultants and producers need to strive for with burndown is to ensure that any crop is planted into a weed-free seedbed.  Good luck and please call us if you need any help.

Post-harvest Weed Control

Post-harvest Weed Control published on No Comments on Post-harvest Weed Control

Assessment of Weed Control Programs and Post-harvest Weed Control in Problem Fields.

Josh Copes, Donnie Miller, and Daniel Stephenson

 

Assessment of weed control programs.

With corn harvest underway and soybean and cotton fields approaching maturity, this is a great time to evaluate this year’s weed control programs. Things to consider include: what herbicides were applied, when they were applied in respect to crop and weed growth stages, what were weather conditions like before and after application, and what weed species are present after final weed control efforts. In addition, knowing which fields contain glyphosate-resistant weeds and other difficult to control species that escaped control can help us better plan and budget for more effective herbicide programs. These factors will help critically evaluate weed control programs and may offer insights into becoming more effective at herbicide selection, improving application timing, and how environmental conditions may dictate the need for more aggressive weed control tactics in certain fields.

 

Post-harvest weed control.

The time period from corn harvest and the first killing frost can range from 1 to 4 months. The average first frost date in North and Central Louisiana is November 15 and 25, respectively. A lot of money and effort is spent in controlling weeds during the growing season to negate yield loss. With the extended window from harvest to first frost, weeds will continue to emerge and produce seed. Timely weed control practices following harvest (post-harvest weed control) can reduce weed seed return to the soil, thus ensuring fewer weeds to fight in future cropping seasons. Post-harvest weed control is especially important in fields containing herbicide resistant weeds. A good example to illustrate the importance of post-harvest weed management is the ability of glyphosate-resistant Palmer amaranth to produce mature seed in as little as 30 days after emergence during late summer and early fall. Many other grass and broadleaf weeds are capable of setting viable seed in a similar time frame.

For weeds that are present in the field at harvest time, mowing and/or tillage should be conducted as soon as possible upon harvest to ensure viable seed set is eliminated or reduced. Rainfall will influence subsequent germination of weed seed and therefore the need for additional weed control. Furthermore, rainfall following cultivation could increase weed seed germination, however, if the weeds are controlled the soil seedbank would be reduced.

Other methods of weed control include the use of herbicides. Herbicide applications should be targeted from late-September through October when the time period from application to first killing frost is shortened. Multiple herbicide applications for post-harvest control of summer annual weeds should be avoided. Residual herbicides such as S-metolachlor, pyroxasulfone, linuron, and diuron, among others, can be applied in the fall following harvest. However, rotation interval restrictions must be followed and length of residual control will be influenced by soil temperature and saturation. Glyphosate plus 2,4-D and/or dicamba or paraquat plus diuron and/or linuron are some choices for late-fall post-harvest applications. Diuron and linuron will offer soil residual; however, if soil temperatures are warm and rainfall frequent, do not expect long residual from these products. Likewise the lack of rainfall to properly activate residual herbicides to minimize weed germination can negatively impact treatment effectiveness.  Maximize water volume to ensure good weed coverage as this is critical for good weed control, especially for paraquat plus diuron and/or linuron.

To reiterate, weeds are capable of setting viable seed within 30 days after emergence during late summer and early fall. Post-harvest weed control is especially important when combatting glyphosate-resistant weeds such as Palmer amaranth, waterhemp, or johnsongrass. Problem fields should be identified and receive top priority for preventing seed return. Once harvested these problem fields should be mowed or tilled shortly after harvest to prevent and/or reduce seed set. Fields should then be regularly scouted for emerging weeds and additional control tactics applied prior to seed set. This will require close inspection of weed species to determine when they are flowering. Once a weed species is observed flowering a weed control operation should be implemented. Depending on weather conditions following harvest, weed control tactics may need to be implemented approximately every 3 to 4 weeks until a killing frost has occurred. If glyphosate-resistant Palmer amaranth or waterhemp is an issue, a management tactic (i.e. mowing, tillage, herbicide application) should be done every 3 to 4 weeks.

 

If you have any questions please contact us.

Josh Copes

Cell: 318-334-0401

Office: 318-766-4607

jcopes@agcenter.lsu.edu

 

Donnie Miller

Cell: 318-334-0401

Office: 318-766-4607

dmiller@agcenter.lsu.edu

 

Daniel Stephenson

Cell: 318-308-7225

Office: 318-473-6590

dstephenson@agcenter.lsu.edu

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