Weed Science Update - June 16 (Prostko)

Just got done rating some of my soybean weed control plots.  Thought I would pass along these few thoughts.

1) Not sure what to say when someone asks me "When are you guys going to figure out how to control pigweed?"  I am pretty confident that we have but not everyone listens or can get it done! (Figure 1).

  

Figure 1.  General overview of 2017 soybean weed control plots in Ty Ty, GA.   Notice weedy-checks in comparison to other plots (started clean + activated residual + timely POST).

2) I fear that some are thinking that the new auxin technologies are the greatest thing since sliced bread.  That would be very stale sliced bread since 2,4-D has been around since the 1940's and dicamba since the 1960's.  I am still getting great results with other chemistries (Figure 2).

Figure 2.  Soybean weed control in 2017 with Tricor (metribuzin) followed by Roundup PowerMax (glyphosate)+ Reflex (fomesafen).

3) If growers decide that they must use the auxin weed control systems, I cannot over emphasize the need for residual herbicides in these programs (Figure 3).

Figure 3.  Weed regrowth/emergence (1 sq. ft.) 25 days after a single application of Roundup PowerMax (28 oz/A) + Xtendimax with VaporGrip (22 oz/A).

  

Valor Injury or The Sky Is Falling (Prostko)

My right ear is currently bleeding due to the numerous telephone calls that I have received over the last few days about Valor injury in peanuts.  Peanuts that were planted approximately 10 days ago or so were in a great place to get hammered from Valor because of the recent rainfall events (Figure 1).   Everyone seems to be panicking as though this was a surprise??????  If it rains on Valor treated peanuts when they are cracking and small (~2 weeks after cracking), injury will occur.  Peanuts typically recover from this injury without a yield penalty.  Check out Figures 2 and 3 from some of my research back in 2009.  In this trial, more than 5" of rainfall occurred in the 30 day period after peanut planting.  Peanut injury was significant but yields were not reduced even at a 2X rate.  Not sure what else I can say or do at this point???

Zidua Peanut Label (Prostko)

On Friday afternoon, May 19, I received word from BASF that Zidua (pyroxasulfone) was labeled for use in peanut.  I have been conducting peanut research with pyroxasulfone for more than 10 years (over 47 field trials).  In a nutshell (no pun intended), Zidua will compete with Dual Magnum or Warrant in our POST peanut herbicide programs for the residual control of Palmer amaranth and a few other weeds (Figure 1). Some advantages for Zidua include its lower use rate (1.5 oz/A-2.1 oz/A) and improved control of other broadleaf weeds such as Florida beggarweed.  Generally, I have observed no real differences in performance/yield between Zidua, Dual Magnum, and Warrant when used in a complete peanut weed control program (Table 1). A copy of the supplmental peanut label can be obtained at the following web-address: http://www.cdms.net/ldat/ldAMK017.pdf

Figure 1.  Zidua vs. Dual Magnum Programs in Peanut - 2016.

Table 1.  Dual Magnum/Warrant/Zidua Peanut Weed Control Programs - 2014.

Common Cocklebur in Peanut (Prostko)

Chris Tyson (Tattnall County) recently sent me a picture of a common cocklebur seedling (Figure 1).  In 2016, Brian Hayes (Grady County) had a peanut grower with a very serious cocklebur problem (Figure 2).  In fact, that peanut field in Grady County was probably the first time that I ever made a recommendation just for that specific weed.  At one time though, cocklebur used to be a more widespread weed problem but sorta disappeared during the "glyphosate era".   Peanut herbicides with good to excellent activity on cocklebur include the following: 2,4-DB, Basagran, Cadre, Cobra, Gramoxone (paraquat), Pursuit, Storm, Strongarm, and Ultra Blazer.  On the downside, Valor is not very effective on this weed so don't be surprised if you see cocklebur in a Valor treated field. The fruiting structure of cocklebur (i.e. the big bur that sticks to your favorite shirt or hunting dog) contains 2 seeds, one for now and one for later.   

Figure 1.  Common cocklebur seedling (Source: Chris Tyson)

Figure 2.  Common cocklebur infestation in a Grady County peanut field, 2016.

Peanut Injury Likely (Prostko)

Rainfall events today will likely result in the development of Valor injury on peanut, especially in fields where the peanut plants are just beginning to emerge/crack.  In preparation for any upcoming questions, please refer to my Weed Science Blog on May 20, 2014.  This should help refresh your memory.  No need to re-invent the wheel.

http://ugaweedscience.blogspot.com/2014/05/peanut-injury-update-prostko.html

Field Corn Weed Control Update (Prostko)

Field corn weed control does not have to be difficult.  Just about any of the herbicide programs that growers are using in Georgia do a good job of controlling most weeds, especially Palmer amaranth, when applied to small plants (<3" tall). Want some proof? Check out the following pictures from my field corn plots that I rated earlier today (click on pictures to make them larger).  Just so you know, these herbicide treatments were applied 17 days after planting with a CO2-powered backpack sprayer calibrated to deliver 15 GPA at 3.5 MPH using AIXR 11002 nozzles.

The most troublesome weed in Georgia field corn, in my opinion, is annual morningglory.  Field corn growers who struggle with morningglory should seriously consider a post-directed/lay-by application of Evik (ametryn) sometime after their initial POST treatment was applied.  Check out page 70 of the 2017 UGA Pest Control Handbook for more information about Evik.  The minimum corn height for post-directed applications of Evik is 12".  If Evik is tank-mixed with glyphosate, post-directed applications can be applied up until 48" tall corn (RR2 hybrids).

Glyphosate/Atrazine/Adjuvants in Field Corn (Prostko)

A common question this week from field corn growers is "Do I need to add a crop oil concentrate (COC) when applying glyphosate + atrazine?"  For you Roundup babies out there, Atrazine + Prowl + COC was one of the most common and effective field corn herbicide treatments in Georgia before the introduction of RR-crops.  Thus, it is tough for seasoned field corn growers to consider not using a COC.  With that said, there is no need to use a COC when a fully "loaded" formulation of glyphosate is used.  Fully "loaded" glyphosate formulations already contain enough adjuvants.  In fact, COC's have been known to cause antagonism when mixed with glyphosate.  

Fully "loaded" glyphosate formulations include the following:  Abundit, Barbarian Max, Buccaneer Plus, Cornerstone 5 Plus, Credit/41Extra, Credit Xtreme, Duramax, Durango DMA, Gly-Fos Xtra, Glysort Plus, Gly Gold Extra, Gly Star Plus, Helosate Plus, Helosate 70, Mad Dog Plus, Makaze, Roundup PowerMax, Roundup WeatherMax, Showdown, Touchdown CT, Touchdown IQ, Touchdown Total.

In my own research program, I have not been using additional adjuvants with Roundup + Atrazine for a very long time (Figure 1).

If a grower uses a glyphosate formulation that is not loaded at all or is partially loaded, then he/she should consider adding a non-ionic surfactant (NIS) @ 0.25% v/v or 1 qt/100 gal.

Figure 1. A common field corn weed control program.  No adjuvants were used with the POST treatment of Roundup PowerMax + Atrazine.  FYI, this entire herbicide program costs approximately $16.50/A (excluding application costs).