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.