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.

Counter/Herbicide Interactions in Field Corn (Prostko)

In a previous blog (March 1, 2013), I discussed the potential problems associated with the the use of Counter and certain postemergence herbicides in field corn. The following are some answers to questions you might get asked about this problem at this time of year:

1) Why can't certain herbicides be used after an in-furrow (INFR) application of Counter in field corn?

Organophosphate (OP) insecticides, amino acid synthesis (ALS) and certain pigment (HPPD) inhibitors are metabolized in field corn by the same enzyme system (cytochrome P450 monooxygenase).  When these pesticides are used sequentially (INFR + POST) in field corn, this enzyme system cannot successfully metabolize both active ingredients.

2) How bad would corn yields be affected if this accidentally happened?

Research results from 2012 would suggest that yield losses could exceed 40% if an inappropriate herbicide was used following an INFR application of Counter.

Figure 1.  Corn yield response to the interaction of Counter (INFR) and Steadfast (POST).

3) What herbicides can be applied in field corn if Counter is used INFR?

The following herbicides, commonly used in GA field corn production systems, are safe to use if Counter is applied INFR:

Aim, Atrazine, Clarity, Dual Magnum, glyphosate, Impact, Laudis, Liberty, Prowl, Status, Warrant, 2,4-D, and any pre-mix containing these ingredients.

 

Third Party Indemnified Reflex or Dual Magnum Labels for GA Vegetables (Culpepper)

Agents, I am getting a significant number of calls from growers regarding new Reflex and Dual Magnum vegetable labels.  Consider helping your growers by asking them to come in and visit with you to get their label. This is a great opportunity for young/new agents to obtain face time with our clientele!!

Agents MUST NOT give growers any indemnified label; however, agents can help them through the process but must make sure the grower clicks the “I ACCEPT” liability waver.

Obtaining the label for First Time:

1.  Go to www.farmassist.com

2.  Register the grower (or if you want a label register yourself); “register” is located on the 2nd tool bar in top middle of page.  After filling in information; click I accept at bottom.

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3.  The next page that pops up asks about you; you do not have to fill this out if you do not want.

4.  Select products along top bar.

6.  Select indemnified labels (4^th one down).

7.  For state, select Georgia and for product, select Dual Magnum or Reflex (play around and see our other labels) and then submit.

8.  Select the Dual Magnum or Reflex crop of interest and submit.

9.  Accept waiver; this is the process making the label an indemnified label.  GROWER MUST CLICK THE I ACCEPT KEY TO GET THEIR LABEL!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

10.  Print label and have present during application.