Weed Update - August 19, 2016 (Prostko)

It has been a while since my last blog.  In the last 60 days, I was out of commission for at least 27 days for various reasons (vacation time, 3 professional meetings, and 2 college moves).   However, the telephone calls kept rolling in!  Here are a few things to consider based upon recent calls:

1) Glyphosate will not adequately control sicklepod plants that have emerged thru the top of a soybean canopy.  However, glyphosate might have some effect on seed rain depending upon the sicklepod stage of growth at application and how much of the plant actually gets treated (Figure 1).  However, I would not expect as much seed reduction as depicted in this graph if only a few inches of the sicklepod plant actually gets treated with glyphosate. 

Figure 1.  Late-season response of sicklepod to glyphosate @ 0.75 ai ae/A as influenced by application timing.

2) Growers who have planted ultra-late soybeans need to be more conscious of herbicide crop rotation restrictions.  For example, Reflex, Prefix, or Warrant Ultra all have a field corn rotation restriction of 10 months (yes, this is real!!).  Thus, these herbicides should be avoided if field corn will be planted early next spring.  POST soybean herbicides with minimal crop rotation restrictions include Liberty, Cobra, or Ultra Blazer.  

3) At this time of year, there are NO miracle cures or magical silver bullets for escaped morninglory, Texas panicum, or sicklepod in any crop.  Growers will need to rely on harvest aids or non-selective applicators when appropriate and/or labeled.  What's the best strategy for controlling a 12-24" weed?  Treating it when its 3" tall!!!!!!!!!!!!!!  Sometimes a difficult but necessary pill to swallow.

4) Growers need to stay vigilant in their post-harvest (corn) weed control efforts to minimize weed seed-rain back into production fields.  It would only take a few escaped, seed-producing plants to mess up multiple years of good weed control.  Please refer to pages 74 and 87 of the 2016 UGA Pest Control Handbook for more information about post-harvest weed control strategies.

5) As a reminder, I would be more than happy to spend some time in any county at this time of year at your request!  

Weed Science Update - Week of July 4, 2016

1) This is what an IPhone 6 + LifeProof case looks like after mowing with a Massey Ferguson 2615 (50 HP) + 6' rotary mower.  I have a new phone now so please feel free to call me as usual.  

2) Earlier this week, I had some questions about peanut fungicide tank-mixes with Cobra and Strongarm.  Here is what I know based upon some older data (not much though):

a) Cobra + Fungicides:  Results from a field trial conducted in 2005 suggested no problems with Cobra + Bravo or Folicur.  When Abound was tank-mixed with Cobra, Florida beggarweed control was reduced by 12%. When Headline was tank-mixed with Cobra, annual morningglory control was reduced by 8%. All treatments also included COC @ 1% v/v. Peanut injury was not increased with Cobra + fungicide tank-mixtures. All treatments were applied to Georgia Green at 28 DAP.   

b) Strongarm + Fungicides:  From another field trial conducted in 2005, annual morningglory control was not reduced when Strongarm was tank-mixed with Bravo WS, Abound, Folicur, and Headline.  Florida beggarweed control with POST applications of Strongarm was poor in general (<70%) and control was further reduced by 15% when tank-mixed with Headline.  NIS @ 0.25% v/v was included with all treatments.  Peanut injury was not increased with Strongarm + fungicide tank-mixtures.  All treatments were applied to Georgia Green at 23 DAP.

3) Someone asked me about the tolerance of soybeans to dicamba drift.  As with most drift situations, it all depends upon rate and stage of growth.  Generally, soybeans are less tolerant of dicamba drift at reproductive stages of growth.  

Peanut Tank-Mix Time (Prostko)

Now is the time of year that most of us will get numerous questions about the various tank-mixes that peanut growers would like to try.  Here are a few reminders:

1) With over 90,000 potential peanut tank-mixtures, it is impossible for UGA or anyone else to have all the answers.  If a  grower puts more than 2 chemicals in a spray tank, it is very likely that that specific mixture will not have been adequately tested.

2) Just because a specific tank-mixture may not have caused peanut injury on one day, it does not mean it will not cause injury at another time.  Peanut response to tank-mixtures is a function of many factors including temperature, humidity, leaf wetness, and overall plant health.

2) The following is a good publication to keep handy at this time:  Tank-Mixing Chemicals Applied to Peanut Crops: Are the Chemicals Compatible?.  This publication can be accessed from the web at the following location:

http://www.peanut.ncsu.edu/pdffiles/004993/tank_mixing_chemicals_applied_to_peanut_crops.pdf

3) Recent research from NC State University indicated that manganese did not affect the efficacy of Select, Poast, Cadre, Pursuit, 2,4-DB, Abound, Bravo, Headline, or Folicur. Common ragweed control with Cobra was reduced 6% by dry Mn sulfate but not liquid Mn.   (Peanut Science 2012 39:1-8)

4) Here a few slides of some tank-mixtures that I have tried or seen in the field.

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Peanut Tips - Week of May 23 (Prostko)

A few comments based upon some frequent questions that I have received this week:

1) Generally, there should be no major problems mixing Orthene (acephate) with paraquat cracking treatments (Peanut Science 2014 41:58-64).

2) UPI is in a sold out position for Storm 4SL herbicide.  However, Storm is in UPI's production schedule for next year.  No worries though since growers can make their own Storm if need be.  1.5 pt/A of Storm would be equivalent to 1 pt/A of Ultra Blazer 2SL +  1 pt/A of Basagran 4SL.  FYI, when making your own Storm cocktail for mixing with paraquat, I prefer 1 pt/A of Ultra Blazer + 0.5 pt/A of Basagran.  0.5 pt/A of Basagran still helps "safen" the peanuts but this new ratio will be slightly more active on the weeds.  

3) Helena has been actively promoting a product called ENC (Ele-Max Nutrient Concentrate) to be used in combination with paraquat cracking sprays.  According to Helena, the use of ENC will help the peanuts recover faster from paraquat injury.  As far as I can tell, ENC is a fertilizer solution (11-8-5 + various micros).  We are currently evaluating this product and its potential benefits.  Preliminary results from 1 trial in Attapulgus this year would suggest that the use of ENC resulted in less peanut injury (leaf burn) at 3 DAT (Figure 1) but no differences were detected at 7 DAT (Figure 2).  Way too early for a yea or nay recommendation at this point!!!  More to follow as additional data is collected.  

Figure 1.  Influence of ENC on peanut leaf burn - 3 DAT - 2016.

Figure 2.   Influence of ENC on peanut leaf burn - 7 DAT - 2016.

4) Guess what?  When it rains on peanuts that were treated with Valor, especially at cracking, you get crop injury.  It happens all the time, regardless if they were irrigated immediately after application or not.  Unless something funky has happened (i.e. sprayer problems, excessive rates, misapplication, etc.), research results and on-farm experiences since 2001 would suggest that is very likely that the peanut plants will recover from Valor injury with no yield loss.  For more info and injury pictures, refer to my June 3, 2013 blog on this very same issue.

Liquid Flumioxazin Mixing Problems (Prostko)

Panther 4SC (NuFarm) is a new liquid formulation of the active ingredient flumioxazin (i.e. Valor). This week, I have heard a few complaints about some tank-mixes with this new formulation. Growers who use this liquid formulation must follow the mixing order described below in order to minimize potential tank-mix problems:

Check out the following YouTube video for some cool visuals about Panther 4SC.  FYI, I have not sprayed a single drop of Panther 4SC so I have no experience or data at this point with this new formulation.

https://www.youtube.com/watch?v=PvpsOI7C50M

Metribuzin on Soybeans (Prostko)

As many of you know, I have been trying my very best to prevent the overuse of Valor and Reflex in soybeans, especially for growers who also plant cotton and peanuts.  Growers who want to protect Valor and Reflex (PPO's) have many other PRE options including Dual, Warrant, and metribuzin.  For you Roundup babies out there, let me remind you of a few things about metribuzin.

1) Metribuzin used to be sold under the trade names of Sencor (Bayer) or Lexone (DuPont).  Many moons ago, about 20% of the US soybean crop was treated with metribuzin.  

2) Current trade names for metribuzin include the following: Tricor, Metribuzin, Dimetric.

3) Metribuzin is also a component of many soybean pre-mixes including the following: Authority MTZ (metribuzin + Spartan), Boundary (metribuzin + Dual Magnum), Canopy or Canopy Blend (metribuzin + Classic) ), Intimidator (metribuzin + Reflex + Dual Magnum), and Trivence (metribuzin + Valor + Classic). 

4) When using metribuzin in soybeans, soil type, OM and pH are very important.  Metribuzin should not be used on coarse soils (i.e. sandy loam or loamy sand) with less than 1% OM and/or in soils with a pH greater than 7.5.  Refer to the individual product labels for more specific information about use rates, soil types, and organic matter restrictions.

5) Metribuzin should not be used on sensitive soybean varieties.  Check out page 268 of the 2016 UGA Pest Control Handbook for a partial list of soybean varieties that have been screened for tolerance.  Also, check out the following publication from the University of Arkansas ( http://mssoy.org/wp-content/uploads/2014/12/2014-SOYBEAN-VARIETY-METRIBUZIN-SCREENING-UA1.pdf).  

6) Metribuzin is in the same herbicide family as atrazine (triazine). Metribuzin is a PS II inhibitor (WSSA Group 5).

7) Metribuzin injury symptoms on soybeans are presented in Figures 3 and 4.  

Figure 3.  Metribuzin injury on soybeans.

Figure 4.  Metribuzin injury on soybeans.

Prowl vs. Sonalan in Peanuts (Prostko)

Recent price increases in Sonalan 3EC (ethalfluralin) have many growers taking a closer look at the cheaper priced pendimethalin formulations (Generic Prowl 3.3EC and Prowl H2O 3.8ASC) for use in peanuts.  With the exception of use in reduced tillage systems (i.e. Prowl is preferred there), there have been no consistent differences in peanut tolerance and weed efficacy between Sonalan and Prowl in peanut (Table 1).  It has always been my position that I have no preference between these two herbicides and that every peanut acre in Georgia should be treated with one of them.  If a grower is trying to save a few bucks on input costs, there is no reason not to use a cheaper formulation.

A couple of other comments about this issue:

1) The Weed Science Group at UGA has not been able to detect any major differences in the performance between Prowl 3.3EC and Prowl H20 3.8ASC.
2) 2016 estimated costs for 1 qt/A are as follows:  Sonalan 3EC = $10.50; Generic Prowl 3.3EC = $6.75; and Prowl H2O 3.8ASC = $8.75.
3) The lb ai/A for each formulation are slightly different at the 1 qt/A typical use rate as follows:  Sonalan 3EC = 0.75 lb ai/A; Generic Prowl 3.3EC = 0.83 lb ai/A; and Prowl H2O 3.8ASC = 0.95 lb ai/A.  This might need to be considered when figuring the true cost differences per acre.