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Weed Scientist Dean Lee Research and Extension Center LSU AgCenter

Italian ryegrass is everywhere! Do not forget about it this fall.

Italian ryegrass is everywhere! Do not forget about it this fall. published on No Comments on Italian ryegrass is everywhere! Do not forget about it this fall.

How many of you had an issue with glyphosate-resistant Italian ryegrass this spring?  Did you expect clethodim to solve the problem and then found it did not?  Did you apply paraquat and were not satisfied?  Many farmers, consultants, and dealers commented to me since late January that the Italian ryegrass problem has exploded in Louisiana.  Honestly, this is not surprising because we have not been addressing this pest properly.  Mississippi has had this issue for longer than Louisiana has.  Mississippi State University weed scientists determined a good strategy to manage glyphosate-resistant Italian ryegrass five or six years ago.  LSU AgCenter weed scientists adopted their strategies and began disseminating that plan.  It starts with tillage or a residual herbicide application in the fall, which has not been adopted by many producers in Louisiana.  This article will not go into detail about Mississippi State University’s glyphosate-resistant Italian ryegrass management plan in this article, BUT it will be covered at length later this year.

I am writing this article because I would like for Louisiana farmers, consultants, dealers, and ag lenders to notice that glyphosate-resistant Italian ryegrass is still present in corn, cotton, and soybean fields on May 1st.  It may be brown following herbicide applications, but it is still competing with crops as you can see in the photo (Figure 1).

Do not take glyphosate-resistant Italian ryegrass lightly.  Remember what crop fields look like in the spring so that you will be motivated to implement good management strategies in the future.  More to come later.  If you have questions, please contact your LSU AgCenter parish agent.  Feel free to contact me at 318-308-7225.  Have a great day.

Figure 1.  Italian ryegrass competing with seedling soybean
Figure 1. Italian ryegrass competing with seedling soybean

Weed Management Thoughts: Planting cotton and soybean in 2 to 3 weeks

Weed Management Thoughts: Planting cotton and soybean in 2 to 3 weeks published on No Comments on Weed Management Thoughts: Planting cotton and soybean in 2 to 3 weeks

To manage weeds preplant, meaning two to three weeks prior, or preemergence, an application of paraquat at 0.5 to 0.75 lb/A plus a residual herbicide is needed to remove existing weeds and maintain fields weed-free.  If paraquat is applied preplant, a second application may need to be applied at planting to remove any remaining green vegetation.

If 2,4-D, dicamba, Elevore, and others may be applied, read the label because there are planting restrictions for cotton and soybean.  However, there are no planting restrictions for Enlist Duo and Enlist One in Enlist crops or Engenia, FeXapan, Tavium, and XtendiMax in Xtend crops.

Choosing a residual herbicide, whether applied preplant and/or preemergence, depends on the crop to be planted and the weed spectrum.  There are numerous choices of residual herbicides labeled preplant/preemergence in cotton, but research has shown that Cotoran at 2 pints/A is a good choice for control of numerous grass and broadleaf weeds.  If glyphosate-resistant Palmer amaranth and waterhemp are a major concern, Brake plus Cotoran, both at 1 pint/A, is an excellent choice.

In soybean, there are numerous residual herbicide options.  Many will provide control of glyphosate-resistant pigweeds; however, they differ in the other weeds they will control.  For example, if pigweed, yellow nutsedge, and grasses are the targets, Boundary at 1.5 to 2 pints/A is a good choice.  But, if morningglory or smellmelon are also an issue, herbicide formulations that contain sulfentrazone (Authority formulations, Sonic, BroadAxe, etc.) or Canopy DF at 4 to 6 oz/A plus S-metolachlor at 0.95 lb/A would provide control.  Please contact your local LSU AgCenter agent to discuss your specific weed spectrum and residual herbicide options.

The length of maximum control provided by a residual herbicide is usually 3 to 4 weeks when properly activated.  So, if applied 2 weeks prior to planting, one may only expect 1 to 2 weeks of residual control in-crop.  In contrast, if the residual is applied preemergence, 3 to 4 weeks of control may be expected in-crop.  So, the choice of preplant or preemergence residual herbicide application will influence when the first in-crop postemergence application should occur.  Remember, seedling cotton and soybean must be protected from weed competition to help maximize yield potential, so plan accordingly.

Methods to control corn prior to replanting

Methods to control corn prior to replanting published on No Comments on Methods to control corn prior to replanting

Many producers are having to replant corn due to poor stands. There are three main ways to remove a failed corn stand.

  1. Use tillage equipment to physically remove the existing corn.
  2. Apply 0.0469 lb clethodim/acre and wait six days before planting the second corn crop. That equals 6 ounces of a 1 lb/gal clethodim, 3 ounces of a 2 lb/gal clethodim or 2 ounces of a 3 lb/gal clethodim. Waiting six days before planting is critical to prevent injury.
  3. Apply 0.625 lb paraquat/acre plus atrazine at 1 pint/A or diuron at 1 pint/A or metribuzin at 3 oz/A. Good coverage is essential. Even then, don’t expect outstanding control with this choice.

 

Call 318-308-7225 with any questions.

Control Weeds Prior to Planting Corn

Control Weeds Prior to Planting Corn published on No Comments on Control Weeds Prior to Planting Corn

Dr. Daniel Stephenson, LSU AgCenter Dean Lee Research and Extension Center

Dr. Donnie Miller, LSU AgCenter Northeast Research Station

As the snow and ice melt, fields begin to dry, and the extended forecast predicts better conditions for weed management strategies, burndown applications will be going out.  Research has shown that burndown applications need to be applied four to six weeks prior to planting to prevent physical competition between weeds and crop as well as reduce the chance of damage from insects such as cutworms.  Louisiana corn producers historically have desired to plant corn in late February through early March, so the time is now.

Research has shown that corn yield was 15 to 25% greater when weeds were removed 4 weeks prior to planting compared to 2 weeks.  Unfortunately, the cold weather over the last two or three weeks has prevented producers from applying burndown herbicides; therefore, it is likely that many producers will be planting corn in fields that have not been burned-down or were sprayed only one to two weeks prior.  In addition to weed competition and possible insect infestation, plant-back restrictions to corn for many herbicides are very important.  The standard burndown treatment for many Louisiana corn producers is glyphosate plus 2,4-D or dicamba.  There are no labeled plant-back restrictions for glyphosate, 2,4-D, or dicamba, but the LSU AgCenter suggest not more than 0.5 lb ai/acre of 2,4-D be applied within 2 weeks of planting.  Products such as Leadoff (generic formulations included), which is often times added by producers to their burndown tank-mix of glyphosate plus 2,4-D for residual control of weeds, does not have a plant-back restriction either.  However, a burndown application containing glyphosate, 2,4-D, dicamba, or Leadoff requires at least two to four weeks for maximum activity, which may not prevent physical competition between weeds and corn or control the vegetation in a timely fashion to prevent insect damage if corn is planted within the two to four week window.  Products such as Valor and Goal, when tank-mixed with glyphosate, offer some foliar activity on weeds, but they’re primarily utilized for residual control of winter annual weeds when applied as a burndown.  However, Valor has a 30 day plant-back interval in conventional tillage corn and a 14 day plant-back interval in minimal tillage corn.  If Goal is applied at least 30 days prior to corn planting and at least three rainfalls of 0.25-inches are received, then corn can be planted without worry.  If applied within 30 days of planting, Goal needs to be incorporated into the soil to a depth of two or more inches prior to planting.  Therefore, if a producer is within two to four weeks of corn planting, burndown applications containing glyphosate, 2,4-D, dicamba, Leadoff, Valor, or Goal are not optimal  options based on the issues discussed earlier.

What does a Louisiana corn producer do for burndown if they desire to plant as soon as it dries up?  Products that contain paraquat (Gramoxone SL and other generics) or Sharpen should be considered.  Both products offer rapid desiccation of weed vegetation and no plant-back restrictions to corn.  The positives and negatives of paraquat are well understood by producers and should be utilized properly.  Sharpen at 1 oz/A plus 1% v/v methylated seed oil (MSO) is good for burning vegetation down, but increasing the rate to 2 to 3 oz/A will provide residual control of many broadleaf weeds in addition to controlling existing vegetation.  Research has shown that tank-mixing Sharpen with glyphosate will control a broader spectrum of weeds and if Sharpen is mixed with a brand name glyphosate (i.e. Roundup PowerMax), then the addition of MSO is not needed for winter annual control.  However, if Sharpen is applied alone, addition of MSO is critical to achieve expected weed management.  It should be noted that activity of paraquat and Sharpen can be influenced by sunlight, temperature, and coverage; therefore, sunny days and warm temperatures at application with good sprayer output (higher the better) will increase the chances of good weed control.  Another thing to consider is an application of a product that contains atrazine at planting following the first burndown application.  Atrazine at planting is not a substitute for a burndown application discussed earlier.  However, if a producer is forced to apply a burndown application within two weeks of planting, applying atrazine (or a product containing atrazine) will provide good control of weeds that were not completely controlled by the first burndown application.

Ultimately, it is best to burn down winter vegetation four to six weeks before planting, but a producer may not have that option.  Therefore, use good judgment when selecting herbicides for burndown.  Don’t just assume that glyphosate plus 2,4-D will work if applied within two weeks of planting.  It is crucial that weeds be removed so they don’t negatively influence yield.  If you have specific questions, please call your local LSU AgCenter county agent or weed scientist.

Programs for Control of Suspected Glyphosate-Resistant Italian Ryegrass in Louisiana

Programs for Control of Suspected Glyphosate-Resistant Italian Ryegrass in Louisiana published on No Comments on Programs for Control of Suspected Glyphosate-Resistant Italian Ryegrass in Louisiana

Glyphosate-resistant (GR) Italian ryegrass has been documented in Mississippi and growers have been forced to adopt practices to manage it.  GR Italian ryegrass has been shown to significantly reduce corn yield and is troublesome in cotton and soybean if not controlled.  LSU AgCenter weed scientists currently have samples from multiple locations in Louisiana where glyphosate did not control the Italian ryegrass populations this past spring.  Preliminary data indicates that GR Italian ryegrass is present in Louisiana.  As a consequence, Louisiana crop producers need to begin mitigation/management programs.

Drs. Jason Bond and Tom Eubank, weed scientists with Mississippi State University, have published excellent programs to control GR Italian ryegrass in corn, cotton, soybean, and rice.  The programs can be found at http://msucares.com/pubs/infosheets_research/i1355.pdf.  Their research has shown that fall applications of Dual Magnum at 1.33-1.67 pints/acre (corn, cotton, soybean), trifluralin at 3 pt/A (cotton, soybean), Boundary at 2 pints/acre (soybean), or Command at 2 pints/acre (rice) provide excellent control of GR Italian ryegrass.  Boundary has received a 24c label for fall application in Louisiana.

All afore mentioned fall-applied herbicides should be tank-mixed with paraquat at 0.5-0.75 lbs. a.i./acre to kill any emerged Italian ryegrass.  Their research also showed that double-disking in the fall is another option.  In mid-January to mid-February, either 12-16 oz./acre of Select Max or the equivalent rate of a 2 lb/gallon clethodim is needed if Italian ryegrass begins to emerge, but a 30 day preplant interval is required if corn or rice will be planted.  In the spring, if glyphosate applied as a burndown is not effective for control of Italian ryegrass, their research indicates that two applications of paraquat at 0.75-1.0 lb a.i./acre spaced 14 days apart will be required for control.  Adding either atrazine (corn) at 1 quart/acre, metribuzin (soybean) at 4 oz./acre, or diuron (cotton) at 1.5 pints/acre with the first paraquat application will increase efficacy of paraquat against GR Italian ryegrass.

Steps should be taken to mitigate and/or manage GR Italian ryegrass.  If you have questions, please call your local LSU AgCenter county agent or Dr. Daniel Stephenson (318-308-7225) or Dr. Donnie Miller (318-614-4044).

24c Granted for Fall-Application of Boundary 6.5 EC in Louisiana for Control of Suspected Glyphosate-Resistant Italian Ryegrass

24c Granted for Fall-Application of Boundary 6.5 EC in Louisiana for Control of Suspected Glyphosate-Resistant Italian Ryegrass published on No Comments on 24c Granted for Fall-Application of Boundary 6.5 EC in Louisiana for Control of Suspected Glyphosate-Resistant Italian Ryegrass

A 24c label has been granted for fall-application of Boundary 6.5 EC in Louisiana.  This will provide producers another tool to mitigate/manage Italian ryegrass in the fall.  24c label is linked below.

LABoundaryItalianRyegrassFinalSLNLbl

If you have any questions, please call:

Dr. Daniel Stephenson (318-308-7225)

Dr. Donnie Miller (318-614-4044)