Glyphosate and Peanut Yield (Prostko)

In the May/June 2013 issue of the Southeastern Peanut Farmer (page 16), there is an article that suggests that applying low rates of glyphosate to peanut late in the season will improve yields.  This research work is being conducted by scientists at the National Peanut Lab in Dawson.

A few years ago (2006-2007), I conducted similar research with glyphosate (Figure 1).  In my research, there was no positive benefit from applying glyphosate at 105 DAP.  In fact, peanut yields were significantly reduced by several glyphosate treatments.   Because glyphosate is not labeled for such a use in peanut and there are contradictory results regarding the benefits/risks, please encourage your growers to NOT use glyphosate for this purpose.

Figure 1.  Peanut Response to Roundup WeatherMax Applied 105 DAP in Georgia, 2006-2007.

Keep Gramoxone (Paraquat) in the Peanut Mix (Prostko)

Peanut growers need to be reminded (gently, bluntly, harshly, your choice) that Cadre is almost always better following an EPOST (cracking) application of paraquat (Figure 1).  Growers should only consider not using a cracking treatment of paraquat (+ Basagran or Storm) if weather conditions have prevented a timely application (< 28 days after peanut emergence) and/or when there is not enough weed growth to justify the application (i.e. no weeds).

Reflex Injury on Soybean (Prostko)

Many soybean growers are in the process of applying their 1st postemergence (POST) herbicide.  One of the most popular POST soybean herbicide used in Georgia is Reflex (fomesafen).  Reflex can be mixed with glyphosate (avoid K+ salt formulations of glyphosate though) and will provide both POST and residual control of Palmer amaranth.  Growers who have not used Reflex in the past need to be aware of the fact that this herbicide will cause temporary crop injury (Figure 1).  Since Reflex is a contact herbicide, the injury will only be observed on the leaves that were present at application and yield should not be affected.  Any new soybean growth should not exhibit Reflex injury symptoms.  Other PPO-inhibitor herbicides, including Cobra (lactofen) and Ultra Blazer (acifluorfen), will cause similar soybean injury symptoms.



Figure 1.  Fomesafen injury on soybean, 7 DAT, Ty Ty, GA 2013.

Valor Injury on Peanut (Prostko)

Last night, I received 1.7" of rainfall in about 1-1.5 hours.  If this type of rainfall occurred in your county, be prepared for phone calls about potential Valor injury on peanuts.  Any Valor treated peanut plants that were cracking or ~2 weeks old will likely exhibit some damage (Figures 1 and 2).  The good news is that the peanut plants will likely recover without suffering yield loss (Figure 3).  The yield results presented in Figure 3 occurred after observing significant crop injury in Figure 2 (i.e. the same test).

Figure 1.  Valor Injury on Peanut.

 

Figure 2.  Valor Injury on Peanut.

 

Figure 3.  Peanut Yield Response to Valor After Observing Significant Crop Injury -
Pooled Over 3 Cultivars (GA Green, GA-06G, GA-07W) - PE-08-09.

 

Cleaning Valor From Sprayers (Prostko)

In the last 2 weeks, I have received 2 inquiries from county agents regarding field corn injury symptoms caused by POST applications of Roundup + Atrazine (+/- Warrant).  In both cases, the symptoms resembled a "burning" or "spotting" type of injury (Figure 1).  These symptoms are not typical of Roundup + Atrazine.  Another common theme in both situations was that Valor and been recently used in the sprayer.  Historically, Valor has caused numerous headaches in regards to sprayer contamination problems even when "properly" cleaned.  I am not saying with 100% certainty that these problems were caused by Valor.  However, I am suggesting that if sprayers are not cleaned according to Valent's directions (Figure 2), weird, perhaps unexplainable, things can happen.  These types of symptoms could also be caused by Reflex, Direx, or Liberty if they were accidently included in a mixture.  


Figure 1.  Corn injury from recent application of Glyphosate + Atrazine (maybe Warrant).

Figure 2.  Valor Sprayer Cleanout Procedure (Valent)