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Louisiana Rice Notes #7

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This edition covers current crop issues including the rise in sheath blight in south Louisiana, effect of midday rain on flowering rice, leaf miners, the black rice bug.

Louisiana Rice Notes #6

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This edition covers current crop progress and issues, recommended fungicide rates and timings, shortage of Sercadis, and stink bug BMP’s.

Louisiana Rice Field Notes #5

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This edition covers current crop progress and issues, effect of time of flooding on rice at PD, how to identify Cercospora, and proper fungicide timing.

Louisiana Rice Notes – May 4th

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This edition covers the current weather concerns, hail damage on rice, rice survival under submerged conditions, stretched rice management, estimating lost N from draining submerged rice, and the retirement of Dr. Levy the state soybean extension specialist.

Thrips Management in Cotton

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With the abnormally warm winter and spring, cotton planting in Louisiana has gotten off to an early start. In Louisiana, and across most of cotton states, thrips are considered the number one early season insect pest. The species we encounter greater than 85% of the time is tobacco thrips with western flower thrips typically comprising the other 15%.

Thrips control options are limited to seed treatments, in-furrow applications and foliar sprays. Over the past few years, control of tobacco thrips with thiamethoxam (Avicta, Cruiser, etc) has been declining and resistance has been confirmed through bioassays. As a result, we have switched almost exclusively to imidacloprid products (Aeris, Gaucho, Acceleron F1) and no longer recommend thiamethoxam (alone) as a seed treatment in cotton. Aeris treated seed contains imidacloprid + thiodicarb and performs very well in our thrips trials and in the field. The use of imidacloprid alone is another option; however, it may not perform as well as Aeris or imidacloprid + an acephate overtreatment. Overtreatment with acephate is an economical option that has demonstrated increased thrips control when applied on top of imidacloprid. Acephate alone controls thrips but the residual is significantly shorter than currently used products and increases the likelihood of foliar follow up applications.

The use of in-furrow applications of imidacloprid and AgLogic 15G are also options that work well for controlling thrips and other early season insects in cotton. AgLogic 15G is an aldicarb based replacement for Temik that is available in either gypsum or corn cob grit formulations with performance very similar to Temik when used at the appropriate rate.

Finally, foliar rescue treatments are utilized when seed treatments have played out. Foliar treatments should be made when immature thrips are present and/or when large numbers of adults are present and damage is occurring. The presence of immature thrips often signifies that the insecticide seed treatment has lost its efficacy. Avoid spraying solely based on plant injury since the damage has already occurred. Below are some considerations when deciding what foliar insecticide to use.

Dimethoate:

Positives: Relatively inexpensive, good efficacy at high rates, less likely to flare spider mites and aphids than acephate

Negatives: Ineffective towards western flower thrips, less effective than acephate or bidrin when applied at lower rates

Acephate

Positives: Relatively inexpensive, effective towards western flower thrips

Negatives: May flare spider mites and aphids if present, may be weaker against tobacco thrips in certain circumstances

Bidrin

Positives: Effective, less likely to flare spider mites and aphids than acephate

Negatives: Less flexibility with applications early season

Radiant

Positives: Effective, least likely to flare spider mites and aphids

Negatives:  More expensive, requires adjuvant

Insecticide choice depends on a number of factors such as cost, impact on secondary pests and spectrum of thrips species present. If a foliar thrips treatment is justified, do not wait for a herbicide application and only spray when necessary to avoid flaring spider mites and aphids.

Louisiana Rice Notes – March 30, 2017

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This is the third installment of the Louisiana Rice Notes newsletter for  2017.  This edition covers planting progress and the quick start to the rice season in southwest Louisiana, accumulated DD50 heat units so far, rice seedling development, the importance of Clearfield Stewardship Guidelines, starter N fertilizer guidelines, and planning your 2017 disease management program. This edition can also be found on the LSU AgCenter’r rice website (click here to view).

Louisiana Rice Notes – March 22, 2017

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This slightly longer than normal edition covers planting progress, current weather and soil temperatures, a shift in blackbird pressure this year, effect of treating only half of your seed with AV-1011, economic evaluation of using AV-1011 versus replanting, a change to the FirstShot label, a survey and solicitation for information about pyrethroid use in rice, a welcome to Dr. Blake Wilson who was hired as the AgCenter’s new extension rice and sugarcane entomologist, and how to choose the right insecticidal seed treatment in rice for your individual situation.

Louisiana Rice Notes – Feb 23, 2017

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This edition covers the low germination issue, how to adjust seeding rates due to the low germination issue, AV-1011, Kaput feral hog bait, burndown plant back restrictions and other useful information.

 

 

Mitigating and/or Managing Herbicide-Resistant Weeds

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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

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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.

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