Screening Palmer Amaranth Samples for Liberty Resistance (Culpepper and Prostko)

Without question, the amount of Liberty (glufosinate) applied during 2015 was much greater than in previous years.  Unfortunately, overuse and abuse of the herbicide was also more prevalent.  If Liberty is lost to resistance, it is questionable if our agronomic growers will remain viable in the long-term.  We must work hard to help growers make better decisions with Liberty and we must also determine where resistance develops rapidly.

Therefore, we are committed to screening some pigweed samples taken by county agents this winter.  Fields treated numerous times with Liberty, fields treated with Liberty multiple years in a row, or fields in which you felt timely Liberty applications were made but control was inadequate are ideal situations. 

The screening process is only as effective as the sampling technique.  Some suggested guidelines for seed collection are as follows:

1.  Harvest at least 25 FEMALE seedheads when MATURE.

2.  Female seedheads are usually the prickly ones and, of course, have the seeds.

3.  At least 75% of the seeds must be completely dark black; if they are burgundy or lighter in color they are likely not viable.  To check seed color/maturity, shake seedhead over hand allowing seed and seed cover to fall in hand; rub aggressively and seed should dislodge from cover. 

4.  Place seedheads in a paper bag (suggest cutting seedheads in sections so the will lay down in bag). Do not use a plastic bag!

5.  Write GPS coordinates, county, and your name and/or grower name on bag.

6.  Carry samples back to office, open bag, and place them in dry area for a few days.

7.  Bring to Tifton when visiting or send with someone going to Tifton.

8.  Drop off at Dena Watson's office in Horticulture Building.

 Note: Palmer amaranth plants are currently mature in fields that were planted during late April or very early May and the pigweed emerged with the crop.  Pigweed emerging later in the season are probably still a few weeks from being mature.

Figure 1.  A large Palmer amaranth plant survives an untimely application of Liberty. Not good for long-term resistance management!!!!!!!  

Soybean Weed Control (Prostko)

On occasion, someone might come up to me and randomly say something like "When are you going to figure out how to control pigweed in soybeans?"  When I hear that, it makes me think about what planet that person has been living on the last few years.  As far as I am concerned, Georgia soybean growers have had all the tools needed to control herbicide-resistant Palmer amaranth since day one.  The problem has been getting folks to do what UGA has recommended. Check out the following picture from some of my soybean plots taken earlier this morning.  

Figure 1.  Soybean Weed Control Tests, Attapulgus, GA, August 31, 2015.  Asgrow 7934 planted on May 12.

The soybeans in the picture without any pigweed were managed the following way:

1) Started clean.
2) 2 residual herbicides (1 PRE + 1 POST).  For RR soybeans, I prefer Boundary or Dual Magnum or Warrant - PRE followed by Roundup + Reflex or Prefix (Reflex + Dual Magnum) - POST.  In 2016 , a new formulation of Warrant + Reflex (Warrant Ultra) will be available for those growers who prefer Warrant over Dual (FYI, I do not have  preference!!!!).  
3) POST applications were timely (24 DAP).
4) This particular soybean field was under grown under a center-pivot.  It is very unlikely that dryland soybean growers will be able to achieve optimum weed control on a consistent basis when relying on rainfall for the activation of residual herbicides.  That is one of the biggest perils of dryland farming. 
   

Pre-Harvest Applications of Aim or ET in Peanuts (Prostko)

Been getting many questions lately about late-season annual morningglory control in peanut.  I partially addressed this issue in a previous blog (August 29, 2013).  In most cases, it is too late in the year to legally apply herbicides.  Pre-harvest intervals (PHI) of peanut herbicides with POST activity on annual morningglory are as follows: Cadre = 90 days; Cobra = 45 days; Ultra Blazer = 75 days; 2,4-DB = 45-60 days.  In my opinion, the best thing a grower can do for annual morningglory this late in the season is to apply a pre-harvest application of either Aim or ET (i.e. 7 days before digging).  Both herbicides will provide sufficient dessication of annual morningglory plants (except smallflower) to improve peanut vine flow through a digger with minimal effect on the peanuts (Figures 1 and 2). It is very important that the peanuts be dug in 7 days after treatment (or as soon as possible after that time).  If digging is delayed, the morningglory vines could start to recover/regrow especially after a rainfall event.  Specific recommendations for these herbicides can be found on page 502 of the 2015 UGA Pest Control Handbook.   

Figure 1.  Annual morningglory response to Aim (5 DAT).

Figure 2.  Peanut injury caused by a pre-harvest application of Aim (5 DAT).

Clethodim Formulations (Prostko)

In order to minimize any confusion about the use of clethodim for postemergence grass control in peanuts, the following is a list of all the different formulations that are labeled (at least the ones that I could find).  Pay close attention to the lb ai/gal since this will influence specific use rates.

Trade Name	Clethodim (lb ai/gal)	Manufacturer (s)	Labeled Use Rate for Most Annual Grasses (oz/A)	Labeled  Adjuvant for Peanuts
Arrow	2	ADAMA/MANA	6-8	COC (1% v/v)
Clethodim 2EC	2	Albaugh, Amtide, Tide International, Willowood	6-8	COC (1% v/v)
Intensity	2	Loveland	6-8	COC (1% v/v)
Intensity One	0.97	Loveland	9-16	NIS (0.25% v/v) or COC/MSO (1% v/v)
Section	2	Winfield	6-8	COC (1% v/v)
Section Three	3	Winfield	4-5.33	COC (1% v/v)
Select	2	Valent	6-8	COC (1% v/v)
Select Max	0.97	Valent	9-16	NIS (0.25% v/v) or COC/MSO (1% v/v)
Shadow 2EC	2	Arysta	6-8	COC (1% v/v)
Shadow 3EC	3	Arysta	4-5.33	COC (1% v/v)
TapOut	0.97	Helena	9-16	NIS (0.25% v/v) or COC/MSO (1% v/v)
Volunteer	2	Tenkoz	6-8	COC (1% v/v)

Morningglory Identification - Prostko

Just got out of a peanut field with Tift County Agent, Scott Carlson.  We were talking about weed ID and general peanut stuff.  Many of the weeds that were present in this peanut field were various species of morningglory. Consequently, I thought you might benefit from some of the following information:

1) An old publication that helps with the identification of adult morningglory plants.  Great to keep in your truck!  

Figure 1.  Identifying Morningglory Species.  Source: Dr. Dick Oliver, University of Arkansas,  Weeds Today

2)  Some very good close-up pictures of seedling morningglory plants.  Pictures are from LSU and Virgina Tech.  Also, something good to keep in your truck (besides a sandwich and a Dr. Pepper).

3) Why is this important?  Not all morningglories are controlled equally by certain herbicides. Here are a few examples:

a) Gramoxone (paraquat) is generally good on most morningglory species but not smallflower. 

b) Basagran (bentazon) is generally not effective on most morningglory species but will control smallflower.

c) Staple (pyrithiobac) is generally considered to be an excellent morningglory herbicide but not on tall.

d) 2,4-DB is less effective on pitted morninglory than other species.

e) Aim (carfentrazone) is considered a good morningglory herbicide but not on smallflower. 

Peanut Weed Tips for July - Prostko

A few things to consider as we head into July:

1) Cobra or Ultra Blazer applications should be avoided if possible when the peanut plants are in the R5 (beginning seed) to R6 (full seed) stage of growth (Figure 1).   Results from a 9 location study conducted in 2005-2006 indicated that Cobra applied at this time could cause a significant peanut yield loss (~5%).  

Figure 1. Peanut Stages of Growth.

2) Nearly all 2,4-DB labels limit the official number of applications that can be made in peanut to 2.  Results from trials conducted in 1997 indicated that peanut plants (Florunner and GK-7) were tolerant of multiple applications (1, 2, or 3) of 2,4-DB.  Research is currently underway in 2015 to confirm these older results using GA-06G.  Check out Figure 2 for a list of how much and when 2,4-DB can be applied according to current labels.

Figure 2.  Summary of 2,4-DB labels for use in peanuts.

3) On more than 1 occasion this year, growers have accidently applied 2,4-D amine rather than 2,4-DB to peanut plants.  Fortunately, we have a good idea what could happen to peanut yields when this occurs (not that bad depending upon rate and peanut stage of growth).  Check out the following UGA Extension publication:

http://extension.uga.edu/publications/files/pdf/C%201036_1.PDF

"Not a rocket scientist for sure but I am thinking that is a great idea to read and check the label (or at least look at it) of any pesticide jug before dumping it into a spray tank.  As my father once told me, fast and ready sets the pace but slow and steady wins the race!"

4) I will be on vacation from July 4-11.  If you need to contact me, please send me an e-mail or text.  I will respond to e-mails and texts from 9 am-10 am during my vacation.  

5) From July 13-17, I will be attending the annual APRES Meeting in Charleston and will respond to any phone calls, texts, or e-mails as usual.

6) Now that my busy spray season is almost over, I would like to remind any county extension agent (seasoned or un-seasoned) that I would be more than happy to spend a day in your county just walking and talking.  All you need to do is call.  

Peanut Weed Control Update (Prostko)

It has been awhile since I had a chance to write a blog.  I have been very busy spraying plots, answering phone calls/e-mails/texts, and trouble-shooting.  Here a few things to consider based upon your questions and my experiences over the past few weeks:

1) Generally, Cadre almost always looks better after an EPOST (i.e. at-crack) application of paraquat + Basagran or Storm and this would be my preferred recommendation in most cases (Figure 1). With that said, there are some exceptions when paraquat + Basagran or Storm may not be justified including the following:

a) Irrigated fields that have been treated with a Prowl or Sonalan + Valor (+/- Strongarm) and these residuals are working well.

b) The only weed present is nutsedge.  

2) Peanut tolerance to Cadre is excellent at any stage of growth.   Crop injury has never really been an issue with this herbicide. 

3) You will note from the above figure that the average control of sicklepod with Cadre is 86% (~50 trials).  Thus, 100% control of sicklepod with Cadre is unrealistic but its the best we have.

4) Generally, I have no preference between Dual Magnum or Warrant when used in a complete peanut weed control program.  However, I have observed faster breakdown with Warrant  (i.e. does not last as long) in some of my research plots over the last few years (100% irrigated).  Culpepper has data to suggest that Warrant might be a better choice than Dual Magnum in dryland fields.  If a grower has a preference, I would not try to talk him/her out of it.