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.