Reductions in Grass Control in 2018? (Prostko)

Getting plenty of calls about perceived reductions in grass control after applications of ACC-ase inhibiting herbicides, such as Select (clethodim) or Poast (sethoxydim), have been applied.  Some folks first reaction to this "lack" of control is that we suddenly have widespread ACC-ase resistance.  When its comes to the issue of resistance, I will never say never.  But, before traveling down that bumpy road, I would like for you and your growers to consider the following:

1) Currently, only 2 grass species have been "officially" confirmed to have evolved ACC-ase resistance in Georgia including large crabgrass and Italian ryegrass. Scientific confirmation of herbicide resistance takes lots of time, manpower, and greenhouse space.

2) Labeled heights for optimum control of various common grasses with Select, including crabgrass, Texas panicum crowfootgrass, and goosegrass, are 2"- 6".  

3) The following is some data illustrating the effect of Select rate and timing on the control of goosegrass.  Please note that goosegrass control was reduced by 16-23%, depending upon rate, when applied at the 4-6 tiller stage of growth.

Figure 1.  Goosegrass control with Select applied at different rates and timings.

4) If Cadre (imazapic) was applied prior to the grass herbicide application, it is very likely that grass control will be reduced.   Research has shown that Cadre can reduce the photosynthetic rate of goosegrass which then reduces the sensitivity of the ACC-ase enzyme to clethodim (Burke and Wilcut.  2003.  Physiological basis for antagonism of clethodim by imazapic on goosegrass.  Pesticide Biochemistry & Physiology) 

5) At this time of the year, peanut plants are kinda tall (> 12").  Thus, any grass plants peaking out of the top of the peanut canopy are not likely to be adequately controlled due to size and coverage issues.

6) Before dropping the R-bomb, please double-check use rates, stages of growth, adjuvants, rain-free periods, and field history.  The threat of herbicide resistance is definitely real but it does not happen in one night.

Peanut Tank-Mix Thoughts (Prostko)

     Rain delays and/or late planting have resulted in continual inquiries about peanut herbicide + fungicide tank-mixes and their potential effects on weed control and crop injury. UGA will never be able to adequately address all concerns with 90,000+ potential tank-mixtures in peanuts.   Here is a quick review of some of the published data:

1) When 2,4-DB is tank-mixed with a postemergence graminicide, grass control can be reduced by 8% to 15% approximately 45% of the time.

2) When averaged across 5 grass species, Cadre (imazapic) + Select (clethodim) tank-mixtures provided 19% less effective grass control than Select alone.

3)  Abound (azoxystrobin), Absolute (tebuconazole + trifloxystrobin), Bravo (chlorothalonil) and Headline (pyraclostrobin) are 4 fungicides that have caused significant grass antagonism when tank-mixed with Select (~12% to 30% reductions in grass control).

4) Grass efficacy with Poast (sethoxydim) and Select has not been consistently reduced by tebuconazole (various trade names including Folicur, Orius, TriSum, Integral, Ebustar, Muscle, Tebuzol).  However, when reductions have been significant, grass control was reduced by 4% to 13% with tebuconazole mixes.

5) Palmer amaranth (PA) control was not reduced when 2,4-DB was tank-mixed with Bravo, Provost (prothioconazole + tebuconazole), Headline, or Absolute.  But, 2,4-DB is not that great on PA anyway though?

6)  Sicklepod control with 2,4-DB was reduced by 14% when applied with Abound but not with Bravo or tebuconazole.  

Tropical Spiderwort/Benghal Dayflower (TSW/BD) Control in Peanuts (Prostko)

Been getting quite a few phone calls about TSW/BD in peanuts.  This particular plant loves wet weather so I am not surprised.  Here are few thoughts to consider especially since many of you were not employed by UGA back when TSW/BD was Public Enemy #1.

1) The backbone of all TSW/BD programs has been Dual Magnum.  Over the years, Dual Magnum has provided some of the most consistent residual control of this weed.  When Culpepper, Flanders, and I were frantically searching for control strategies back in the early 2000's, Warrant and Zidua were not yet players in this game.  Warrant and Zidua have good activity on TSW/BD but I have more data/experience with Dual Magnum.  

2) Paraquat + Dual Magnum + Basagran or Storm is an excellent EPOST treatment for the control of TSW/BD, assuming the peanut field is still within the labeled paraquat application window of ~33-38 DAP.

Figure 1.  Tropical spiderwort/Benghal dayflower control with paraquat + Basagran + Dual Magnum.

3) If growers miss the paraquat application window, the best POST treatment for TSW/BD is Strongarm.  Growers who apply Strongarm POST in peanut need to pay close attention to the labeled crop rotation restrictions.   

Figure 2.  Tropical spiderwort/Benghal dayflower control with POST applied Strongarm.

Weed Science Update - May 29 (Prostko)

Yes, it has been raining every day since May 12, Valor damage (peanut) is everywhere, and growers need to apply POST treatments and cannot get in the field.  What do I think?  

1) Most areas in Georgia have received at least 4" of rain or more since May 12 (Figure 1).  This has resulted in many problems including Valor injury (no surprise) and/or the failure to get PRE herbicides applied.

Figure 1.  2018 Georgia Rainfall Totals - May 12 to May 28

2) Peanut growers who were planning on spraying Gramoxone + Storm/Basagran + Dual/Warrant/Zidua will very likely miss the ~33-38 DAP (28 DAC) labeled application window.  If they miss that window, they need to pull the trigger on something else (#3 below).  The following is some weed-free data I collected a few years ago regarding the response of GA-06G to various timings of Gramoxone + Basagran (Figure 2):

Figure 2.  GA-06G Yield Response to Gramoxone + Basagran

3) Peanut growers who have missed the Gramoxone window should consider applying the following as soon as the weather permits:

a) Cadre + 2,4-DB + Dual/Warrant/Zidua (assuming ALS-resistance is NOT present and crop rotations are acceptable) or 
b) Cobra or Ultra Blazer + 2,4-DB + Dual/Warrant/Zidua (assuming ALS resistance is present).  Check out Figure 3 for a recent picture of Ultra Blazer's effectiveness on pigweed when applied correctly (rate, timing, GPA, nozzle, speed).  I would expect the very same from Cobra.

Figure 3.  Palmer amaranth control with Ultra Blazer + 2,4-DB - 2018

c) Some peanut growers have tank-mixed Cadre + Cobra/Ultra Blazer + 2,4-DB + Dual/Warrant/Zidua and have not had any major problems.  But, I do not have a ton of data to support this 4-way mixture (1 test) but currently have another trial in the field right now to investigate.  Hope to spray that this week.  

4) Soybean growers who have run into some weather troubles might want to consider the following:

a) Avoid herbicide applications when soybeans are cracking.  For whatever reason, soybeans tend to be more sensitive to injury from herbicides during this stage of growth and current environmental conditions (i.e. wet), including residual herbicides such as Valor, Prowl, and Zidua.
b) My preference would be for POST herbicide applications in soybean to occur at the V1 stage (1 trifoliolate leaf) or later (Figure 4).

Figure 4.  V1 soybean stage of growth.  Source: Iowa State University.

c) The following would be good POST + residual weed control options for soybean fields in need:

RR soybeans: glyphosate + Reflex or Prefix or Warrant Ultra

LL soybeans: Liberty + Reflex or Dual Magnum or Warrant

Xtend soybeans:  glyphosate + Xtendimax or Engenia or Fexapan + Warrant or Dual Magnum [check current web-sites for drift reducing adjuvant (DRA) requirements]

Weed Science Update - May 18 (Prostko)

A few things based upon my telephone calls and e-mails this week:

1) Growers must not cut corners when cleaning a sprayer after Valor has been used.  Heard someone say this week that if you cut out the corners, you just go in circles.  I have discussed this tank-cleaning issue in a previous blog (June 3, 2013).

2) Field corn growers might be able to use a lay-by rig for cleaning up some messes or improving annual morningglory control.  In the past, I have talked alot about Evik (ametryn) but I have had some trouble with the formulation this year.  If a grower decides to use Evik, he/she must pre-slurry, have aggressive tank agitation, use 20 GPA, and get new product.  There have been some older and bad batches of Evik out there.  There are other lay-by options such as Gramoxone (paraquat) and Aim (carfentrazone).  Currently, I am investigating the potential for Laudis (tembotrione) to be used in a lay-by rig. 

3)  Growers who are considering using a dicamba product for pigweed or morningglory control in field corn need to be reminded that the use rate in field corn (0.25 lb ae/A) is 1/2 of the use rate in Xtend cotton/soybean (0.50 lb ae/A). Thus, it is highly unlikely that dicamba in field corn will control a large escaped pigweed plant (>3" tall).     

4) Zidua, Zidua, Zidua???????  Tons of questions about this new peanut product.  Based upon all the work I have done since 1997, I have seen no differences in performance between Dual Magnum, Warrant, and Zidua when used in our recommended peanut weed control programs.  I have also discussed this topic in a previous blog (May 23, 2017).  There might be some minor differences between these herbicides on individual weed species but these differences tend to disappear when a complete weed control program is used.  

Zidua in Peanuts (Prostko)

It appears as though the following statement on the supplemental Zidua peanut label has many people confused:

"Apply Zidua as a broadcast spray to peanut from "at-cracking" stage to first true leaf stage through beginning of pod development."

A few points to consider:

a) For whatever reason, most people do not talk about peanut stages of growth as frequently as they do with other crops such as soybean and corn.  However, there are some "official" stages of growth for peanuts (Figure 1).

Figure 1.  Peanut stages of growth (K.J. Boote.  1982.  Peanut Science 9:35-40).

a) Zidua is not labeled for PRE use in peanut for good reason.  Peanuts do not have a 2X tolerance to PRE applications.  In my research since 1997, PRE applications of 2X rates have caused peanut yield losses ranging from 7% to 25%.  The 1X rate of Zidua is 1.5-2.0 oz/A (85WG) or 2.50-3.25 oz/A (4.17SC).

b) I have applied Zidua as early as V2-V3 (10 DAP) and as late as R6 (90 DAP) with no yield loss.  However, applications made at V2-V3 did cause more peanut injury than later applications but this injury did not result in yield loss.

c) I have applied the equivalent of 8 oz/A of 85DG or 13 oz/A of 4.17SC (4X rate) at 44-51 DAP (R1 to R2 stage) with no yield loss.  Not suggesting that growers do this but this is a good indicator of the tolerance of peanuts to POST applications of Zidua.

d) **Bottom line, growers should never apply Zidua PRE and POST applications can be made from the V2 through R3 stages of growth.

Tank-Mixing (Prostko)

Tank-mixing pesticides can be rather complicated especially when numerous products will be mixed.  Here are a few questions and answers based upon some recent inquiries that I have received:

1) Can I tank-mix Prowl EC and Prowl H20?

I have never have done this in my research plots but I recently conducted a small tank-mix test (Figure 1).  With good agitation, I did not observe any problems.  Do not mix these two herbicides together before putting in water.  They should be put in spray tank (already filled with water) separately.

Figure 1.  Prowl H20 3.8ASC + Prowl 3.33EC Tank-Mix (32 oz/A of each in 15 GPA, Prowl H20 was put in 1st)

2) Can I tank-mix dry and liquid Valor formulations together in a spray tank?

I have never done this either in my research plots but I conducted another small tank-mix test (Figure 2).  With good agitation, I did not observe any problems.  Remember, it is always a good idea to pre-slurry dry formulations in water before dumping into a large spray tank.

Figure 2.  Valor SX 51WG + Valor EZ 4L Tank-Mix (3 oz/A of each in 15 GPA)

3)  When tank-mixing various pesticides, what is the correct mixing order?  

The general formulation science mixing order is as follows:

a) water soluble bags (WSB)
b) water soluble granules (WSG)
c) water dispersible granules (WG, XP, DF)
d) wettable powders (WP)
e) water based suspension concentrates/aqueous flowables (SC, F)
f) water soluble concentrates (SL)
g) suspoemulsions (SE)
h) oil-based suspension concentrates (OD)
i) emulsifiable concentrates (EC)
j) surfactants, oils, adjuvants
k) soluble fertilizers
l) drift retardants

For those Millennials out there that sleep with their cell phones taped to their head or hands, there is an app called Mix-Tank (Precision Laboratories) that you might find useful (http://www.mixtankapp.com/). There might be some other apps out there that I am not yet aware of?

4) How do I mix Reflex and Gramoxone?

a) add 1/2 of the required amount of clean water into the spray tank
b) start up and maintain tank agitation
c) add NIS
d) add Reflex
e) add Gramoxone
f) add remaining amount of clean water

5) How do I mix Atrazine and Halex GT?

a) add 1/2 of the required amount of clean water into the spray tank and start/maintain agitation
b) add AMS (**only if water quality sample indicates need)
c) add NIS
d) add atrazine (make sure atrazine is fully dispersed before adding other products)
e) add Halex GT
f) add remaining amount of clean water