Warrant Receives Peanut Label (Prostko)

Warrant recently received both federal (January) and state (February) approvals for use on peanuts in Georgia. Here are a few of my thoughts regarding its potential use in 2014:

1) The current supplemental label only permits PRE and/or EPOST applications (before flowering).  

2) Of these 2 timings, I would prefer to see EPOST applications of Warrant tank-mixed with Gramoxone + Storm + NIS.  

3) At this point in time, I have NOT observed any real differences in weed control between Dual Magnum and Warrant based peanut weed control programs (Figure 1).  However, there is some data that suggests that Warrant might be a better choice for non-irrigated fields.

Figure 1.  Dual Magnum vs. Warrant Based Weed Control Programs

4)  A copy of the current supplemental Warrant peanut label can be viewed at the following location:

http://www.cdms.net/LDat/ld9KA011.pdf

5)  I have made some suggestions to Monsanto that hopefully will result in a better and more usable label in the near future.

Peanut Yields and Cobra + 2,4-DB (Prostko)

Frequently, peanut growers get concerned when they make herbicide applications that "burn" their crop.  One of the herbicides that can cause this type of injury is Cobra (Figure 1).   Recent results from tests conducted in Florida reconfirm that the injury caused by Cobra or Cobra + 2,4-DB is cosmetic in nature and does not negatively impact peanut yields (Figure 2).  In these tests, Cobra or Cobra + 2,4-DB treated plots yielded 97-105% of the non-treated check plots. Cobra or Ultra Blazer + 2,4-DB is recommended for the control of Palmer amaranth in peanut fields when Cadre is not a viable option due to ALS-resistance or crop rotation concerns (page 460 of 2014 UGA Pest Control Handbook). 

Figure 1.  Peanut leaf burn caused by Cobra.  

Berrien County Atrazine Resistance - Part 2 (Prostko)

In my last blog, I informed you of the recent discovery of atrazine-resistant (AR) Palmer amaranth in Berrien County.  After a more thorough investigation by Berrien County Agent Fast Eddie Beasley, it was discovered that the corn rotation in this field was shorter than expected (Figure 1).  Because this rotation is different from the fields where AR-Palmer was first confirmed in Georgia, there is some concern about how the resistance occurred.  Here are a few things that you might want to consider before thinking that the sky has fallen:

1) AR is not a brand new phenomenon.  The first (ever) reported case of herbicide resistance was AR-groundsel (Senecio vulgaris) way back in 1970 in the Pacific Northwest.

2) AR-Palmer was confirmed in Georgia in 2008 (Macon County).  Thus, the UGA Weed Group has had 6 years to work on this problem.  As indicated in the previous blog, numerous other herbicides are available for use in field corn that will provide outstanding pigweed control (page 155 of 2014 UGA Pest Control Handbook). However, atrazine is still very much needed in our corn weed control programs for troublesome weeds such as sicklepod and morningglory.

3) It is possible that AR-Palmer evolved in this field via pollen movement or physical seed movement (birds, equipment, animals, gnomes, etc.).

4) It might also be possible that AR-Palmer evolved in this field due to the fact that the resistance is metabolism-based rather than target-site based.  It has been documented in other weeds species with metabolism-based resistance that cross-resistance can occur in the absence of selection pressure.  This has been confirmed in some ACC-ase resistant Rigid ryegrass (Lolium rigidum) populations that were also cross-resistant to ALS herbicides that were never used in the field.  Mother Nature at its finest (i.e. genetics and evolution)!!!!

5) Herbicide resistance is a complicated issue for sure.  Consequently,  it is very important for our growers to be proactive and make every effort to delay the evolution of herbicide resistance in all of our crop production systems (tillage, cover crops, crop rotations, mode of action rotations, hand-weeding, soil seed-bank management, etc.).

Atrazine-Resistant Palmer Amaranth Confirmed in Berrien County (Prostko and Vencill)

Plants from a recently collected Palmer amaranth seed sample, submitted by Berrien County Extension Agent Eddie Beasley, have been confirmed to be resistant to atrazine (Figure 1). This population was also resistant to glyphosate but not Staple (pyrithiobac).  The discovery of atrazine-resistance (AR) in Berrien County is potentially very important since this seed sample was collected from a row-crop production region (i.e. not a dairy production region).  As far as we can tell at this point, the field in question was continuous corn for at least 10 years.  This would suggest that the AR evolved via selection pressure rather than pollen flow or physical seed movement.  

There are a couple of positives here.  Firstly, 5 lbs/A of atrazine controlled these plants which would indicate that the level of resistance is low (2X) in comparison to what we have observed with glyphosate (6-8X).  Secondly, this population was controlled with Evik (ametryn), another member of the triazine herbicide family.  This confirms results from our previous research which suggested that AR in Georgia is metabolism based rather than target-site based.   

How do we plan to address this issue?  In 2013, Dr. Vencill and several County Extension Agents collected various weed seeds from numerous locations across Georgia (Figure 2). These weeds are now being screened for resistance to multiple herbicides, including atrazine. Also, we are planning to collect additional Palmer amaranth seed this summer in the major corn growing counties.  The plants grown from these seed samples will be screened by Dr. Vencill for resistance to atrazine.     

Although this recent discovery is alarming, we do not think that it necessarily means that AR is widespread.  Results from the above mentioned surveys will answer this question.  At this point in time, growers using normal crop rotations likely need not worry about AR.  Fortunately, numerous other herbicides can be used in field corn to effectively control Palmer amaranth (Armezon, Callisto, Capreno, Dual Magnum, Impact, Laudis, Liberty, Realm Q, Status, Warrant, and Zidua).   Refer to page 155 of the 2014 UGA Pest Control Handbook for specific recommendations regarding the control of GR-ALS-AR-Palmer amaranth in Georgia field corn (http://www.ent.uga.edu/pmh/Comm-Field-Corn.pdf).

Figure 1.  2013 Berrien County Palmer Amaranth Population Treated with 1, 2, and 5 lbs ai/A of Atrazine.

Figure 2.  2013 Herbicide-Resistant Weed Survey (Dr. Bill Vencill).

Liberty-Link Soybean Varieties (Prostko)

Growers searching for Liberty-Link (LL) soybeans varieties that perform well in Georgia may find that this list is rather short at this time.  This is typical for new technologies as varieties tend to get better as the technology becomes more widely adopted over time and space.  Just think back to the 1st generation of RR soybean varieties.  These early RR varieties were not the racehorses of today.  The chart listed below is a summary of the rankings for LL soybean varieties grown in the official 2013 UGA OVT tests (irrigated).

You will note that only 3 LL soybean varieties were ranked in the top 10 (yield) at 3 of 6 locations.  These include HBK LL4950 (indeterminate), HBK LL5350, and Halo 5:45.  Our recently hired UGA soybean breeder, Dr. Zenglu Li, is also incorporating the LL technology into his breeding program.  Thus, it is very likely that Georgia-bred LL varieties will be available in the near future.

Late-Season Options for Morningglory Control in Peanut (Prostko)

Recently, I have been in several fields and have had numerous phone calls about late-season morningglory control in peanut (Figure 1).  Here a few thoughts to consider:

1) Depending upon the anticipated digging date, 2,4-DB can be used to slow down the spread/growth of annual morningglory.  However, this treatment will not provide any real control or result in complete weed death.  For convenience, 2,4-DB could be tank-mixed with a fungicide.  The pre-harvest interval (PHI) for 2,4-DB is 45-60 days depending upon the specific product label.  Only 2 applications/year of 2,4-DB are legal in peanut.

2) Aim 2EC (carfentrazone) can be used as a harvest-aid for annual morningglory in peanut (but not smallflower) .  Please refer to page 448 of the 2013 UGA Pest Control Handbook for more info about this particular treatment.  Applications of Aim will not provide complete control of large morningglories but Aim will make the stems brittle enough to improve harvest efficiency.  ET (pyraflufen-ethyl) could also be used in a similar manner but I have less experience with ET than Aim.  Both of these herbicides will cause minor peanut leaf burn.

3)  Top-mowing can be a very effective method for removing unwanted weed-growth and improving harvest efficiency.  The top few inches of the peanut plants can be mowed just prior to harvest.  However, excessive top-mowing will severely effect the flow of the peanut vines over/through the digger.  I prefer mowing with a flail mower (vertical blades) rather than a rotary mower (horizontal blades) since the rotary mower often leaves a bunch of debris on one side of the row which can cause problems.  Top-mowing is a common practice that I use in some of my weedy research plots.




Figure 1.  Late-season morningglory in peanut.

 

Reflex/Glyphosate Compatibility Issues in Soybeans (Prostko)

Just a quick reminder that there have been a few issues regarding tank-mixtures of glyphosate and Reflex.  Generally, some K-salt formulations of glyphosate have not mixed well with Reflex.  In order to prevent incompatibility problems, please refer to the following Syngenta document: