Weed Science Update Follow-Up (Prostko)

1) Slides sets (field corn, soybean, peanut, grain sorghum/canola/sesame/tractor speed, UGA Herbicide Recommendations) from the December 9, 2015 Weed Science Update are now available at the following web-address:  http://gaweed.com/slides.html

2) There was much interest in the field corn herbicide tolerance charts.  Here is what is available as of today:

2015 Pioneer Corn Hybride Herbicide Management Guide
https://www.pioneer.com/CMRoot/Pioneer/US/products/stewardship/2015_corn_herbicide_guide_ProdList.pdf

Dekalb Corn Hybrid Information (Herbicide Safety Column)
https://www.dekalb.ca/eastern/en/corn

Grain Sorghum Dessication (Prostko)

Seems like I am getting more questions this year about the dessication of grain sorghum.  The change in the weather has everyone getting ants in their pants.  Growers need to know that the use of harvest-aids in grain sorghum has shown little effect in reducing grain moisture content.  A summary of 2 older papers is as follows:

1) Hurst, Harold.  1991.  The Use of Dessicants For Field Drying Grain Sorghum With and Without Weeds.  Mississippi Agricultural and Forestry Experiment Station Bulletin #974.

"Overall, these studies did not result in any distinct advantage for application of dessicants to reduce grain sorghum moisture."

2) Olson, B.L.S, T. Baughman, and J.W. Sij.  2001. Grain Sorghum Dessication with Sodium Chlorate and Paraquat in the Texas Rolling Plains.   Texas Journal of Agriculture and Natural Resources 14:80-83.

"Results from our 2-year study indicate that dessicant applications were generally ineffective (and most likely uneconomical) in reducing grain moisture in late-planted grain sorghum."

In my opinion, the major (only?) benefit of using a harvest-aid in grain sorghum would be to reduce the amount of green plant material that goes through the combine and might end up in the grain.  I know of only 3 things that will dry down grain sorghum seed: time, a hard freeze, and/or a grain dryer.

Wheat Weed Control 2015-2016 (Culpepper)

The circular for controlling annual ryegrass and wild radish has been finalized. You can access the circular on the UGA Weed Science Web-page.  The link is listed below   This publication is also included in this blog (if you click on the picture, it can be viewed in a larger format).  If you want laminated handouts for your growers send me an e-mail including 1) the number of copies that you want and 2) the address that you want them sent to.  I will have laminated copies for this circular and other circulars during our December 9^th training but I realize this will be too late for growers wanting to experiment with Zidua or Fierce.  I would encourage everyone to try a few acres of these new herbicides if ryegrass is a problem.

http://www.gaweed.com/HomepageFiles/2016%20wheat%20-%20Final%20-%20Oct%205.pdf

 PAGE 1

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New Section 24(c) Label for Fierce in Wheat (Culpepper, 2015) - For UGA Extension Agents Only

Fierce, active ingredient pyroxasulfone and flumioxazin, just obtained a new approval for postemergence applications in Georgia wheat as a Section 24(c) Special Local Need Label.  We did have a label for Fierce last year but we improved its use pattern for this 2015/2016 season.   

Our goal is to help growers struggling with ryegrass that is resistant to postemergence herbicides; although our research would also suggest that Fierce provides good to excellent wild radish control.  Our intentions for the 2015/2016 crop are to have a controlled use of Fierce allowing growers the chance to determine if the herbicide can be used to effectively manage problem weeds while having acceptable crop injury.  

Application of Fierce:

1.  Follow the label exactly (Figure 1).

2.  Wheat must be planted 1 to 1.5 inches deep and cannot be broadcast spread.

3.  Apply Fierce at 1.5 oz/A in ONLY CLEAN water when wheat is between the spike and 2-leaf stage; ryegrass needs to be ½ inch or hopefully much smaller.

4.  Apply Fierce only in water.  Notice I just mentioned twice that you cannot have anything in the tank other than clean water and the herbicide; no exception!

5.  Must use 10-15 GPA; prefer 15 GPA if weeds are emerged.

6.  Do not apply with airplane.

7.  Only for wheat!!  Again, only wheat.

8.  DO NOT USE ON SANDS!

Crop Injury:

1. Greatest potential for injury occurs when 1) label recommendations are not followed and 2) when open/cracked seed furrow allows herbicides to directly contact the seed, when seed are planted to shallow, or when seed are planted in a deep furrow that allows herbicide concentration after a rain/irrigation event while wheat is growing. 

2.  Even when following the label, injury will occur in some environments.  This is why we are taking such a conservative approach.  With that said, our research suggests the benefits in weed control far outweigh injury concerns when following the label; you guys need to tell us if the research is accurate or not.

3.  Strongly suggest growers try only few field acres; do not treat the whole farm!!!! 

Also, just a reminder about Zidua which is the other new ryegrass herbicide we have available.  See the 2015-2016 UGA Wheat Production Guide for the lastest weed control information.

Figure 1.  24(C) Special Local Need Label for Fierce use on wheat in Georgia.  

What's that Weed? (Prostko)

In the last few weeks, I have received a few samples of  the weed known as old world diamond flower or flat-top mille graines (Hedyotis corymbosa) (Figures 1 and 2).  Its not very common, at least in my world.  In fact, I only touched it for the first time last year in a corn field in Decatur County. This summer annual plant is a member of the Rubiaceae (Madder) family and is closely related to more common plants such as poorjoe and Virginia buttonweed.   

Can't find any control data for row crops but a bunch exists for turf.

Figure 1.  Old world diamond flower (Photo Source: C. Tyson - Tattnall County)

Figure 2.  Old world diamond flower

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.    

Prefix/Soybean Label Change (Prostko)

It recently has come to my attention the the POST application soybean label for Prefix has changed from what is currently printed in the 2015 UGA Pest Control Handbook (Page 579).  Not really sure what happened but I will take the full blame for not catching this earlier.  The old Prefix label reads as follows:

"Prefix herbicide may be applied at 2-2.33 pt/A as a postemergence application from cracking through the third trifoliate stage of soybeans (V3). "

The new label reads as follows:

"Prefix herbicide may be applied at 2-2.33 pt/A as an early postemergence application in soybeans."

According to my Syngenta contacts, the main purpose of this label change was to remove the 3rd trifoliate restriction.  

In order to clear up any confusion caused by this label change, I would recommend that any product that contains the active ingredient fomesafen (Dawn, Flexstar GT, Prefix, TopGun, Reflex) be applied on or after the V1 stage of growth (Figure 1).  Although it would be unlikely for earlier applications to cause significant crop injury, a soybean plant in the V1 stage will be better able to tolerate and recover from the the injury caused by fomesafen (Figure 2).  Since fomesafen is a contact herbicide, only the soybean leaves that are present at application will be injured.

Figure 1.  V1 soybean stage of growth.

Figure 2.  Roundup + Reflex + Dual Magnum applied to soybeans in the VC stage of growth @ 2 DAT (Photo courtesy of Eddie McGriff - Southern States)

Current Field Corn Weed Control Issues (Prostko)

The rainy weather this week has delayed many postemergence herbicide applications in field corn.   Consequently, growers will be forced to make some tough decisions when the weather clears.  Here are a few things to consider:

1) Refer to the 2015 UGA Pest Management Handbook pages 161-183 for information about the latest stage of growth that herbicides can be applied in field corn.  A stage of growth or height restriction is listed for every POST herbicide.  The label is the LAW regarding POST herbicide applications.

2) Results from 1 field trial conducted in 2014 in a high input environment with Roundup + Atrazine would suggest that there might be some yield problems if applied over-the-top after the V7 stage of growth (Figure 1).  This research is being repeated in 2015. Growers with corn fields in the V7 stage or later should strongly consider using a lay-by rig with this treatment.

Figure 1.  Field corn yield response to Roundup + Atrazine applied at various stages of growth in Georgia, 2014.

3) Do not use days after planting (DAP) as method to determine corn stage of growth or when herbicides can or cannot be applied.  Generally in south Georgia, more GDD's have been accumulated in 2015 than in 2013 and 2014.  During the period from March 1 to April 16, 2015 (Tifton), 717 GDD's have been accumulated. Only 375 and 430 GDD's were accumulated during this same time period in 2013 and 2014, respectively.

4) Growers who have used residual herbicides such as Dual, Warrant, or Zidua should be on the lookout for crop injury (Figure 2).  Injury from these herbicides is more likely to occur during cool, wet weather conditions.  Injury is also influenced by hybrid and rate.  Some formulations of metolachlor contain a crop safener such as benoxacor or dichlormid (i.e. Brawl II, Dual II Magnum, Me-To-Lachlor II, Parallel, Stalwart C).  Benoxacor and dichlormid will significantly improve the tolerance of corn to metolachlor but it will not completely eliminate all injury (Figure 3).

Figure 2.  Field corn injury caused by Dual.

Figure 3.  Corn response to metolachlor with and without crop safeners.  

Halex GT + Atrazine Tank-Mixtures (Prostko)

It has recently come to my attention that there might be some problems when tank-mixing atrazine with Halex GT for postemergence weed control in RR field corn.  Halex GT, from Syngenta, is a 3-way pre-mixture of glyphosate + mesotrione (Callisto) + s-metolachlor (Dual Magnum).  Please refer to the information listed below to help avoid problems with this tank-mix.

Sicklepod/Cadre Resistance Update (Prostko)

Just wanted to let you know that my MS/PhD graduate student (O. Wen Carter), Dr. Ted Webster-USDA/ARS, and I recently completed our first round of greenhouse experiments investigating potential Cadre resistance in sicklepod.  Since collecting the seed last fall, we have been able to test 8 populations (Figure 1).  We are very happy to report that NONE of these 8 populations appear to be resistant!!!!! (Figure 2).  We have 21 more populations to screen but will not likely tackle these until this fall (too busy in the field right now and greenhouse will be getting too hot).

Figure 1.  First 8 sicklepod populations tested for resistance to Cadre in Georgia.  None were resistant!

Figure 2.  Susceptible AZ1 population (L) and suspect Georgia population DC4 (R) response to Cadre @ 4 oz/A + COC @ 1% v/v - 21 DAT.  Both sicklepod populations had 93% fresh weight biomass reductions after the Cadre application.

Time of Day Impact on Herbicides (Culpepper)

Over the past few years, we have been studying the impact of application time of day on the postemergence activity of numerous herbicides. The table below is provided to help guide you in assisting your growers with timely applications.  Liberty remains, by far, the most sensitive herbicide to the time of day in which it is applied.  However, research is showing most herbicides applied early, late, or early and late may not perform at their optimum. 

Consistent results from numerous locations have been generated with Liberty, Roundup, Clarity, and 2,4-D.  For Reflex, Direx, and Gramoxone results provided are from a single location and the study will be repeated during 2015. Data results used to generate this table will be discussed in depth during the cotton section at Winter School on April 1, 2015.

Warrant/Peanut Label Changes (Prostko)

I just received "official" word about the latest changes in the Warrant/Peanut label. Please note the following important changes:

1) Preplant soil incorporated (PPI) applications together with Prowl, Sonalan, or Strongarm are not recommended due to the increased risk for crop injury and reduced weed control.

2) POST applications of Warrant can be made after peanut emergence up through the R1 stage (beginning bloom).  R1 ends when 50% of plants have reached the R2 stage (visible peg).

3) The supplemental label must be in possession of user at the time of application.