Cadre (imazapic) Carryover and Oats (Prostko)

I had 2 inquiries earlier this week about the potential of Cadre, when normally applied to peanuts during the growing season, to cause injury to fall planted oats.  This was one issue I tackled very early on in my career here at UGA.  Here are a few things for you to consider: 

1) According to a recent (2018) USDA/NASS survey of pesticide use in peanut, Cadre is used on 59% of the peanut acres in Georgia.

2) The official labeled rotation restriction for oats after an application of Cadre is 18 months!

3) Field research conducted in Georgia indicated that the rotation for oats could potentially be reduced to 4 months (like other small grains) but the label was never changed (and will not be changed) due to the limited amount of oat acres planted.  Oats were planted on 70,000 acres in Georgia in 2019. U.S. total planted oat acres were 2,810,000 in 2019.

4) Oats planted less than 4 months after a Cadre application could very likely be injured (Figure 1).  Note that Cadre injury to oats also looks very much like phosphorus deficiency and/or cold injury so these potential problems would need to be investigated as well.  We had at least 1 freeze event here in Tifton around November 13.   

5) When Cadre was applied to bare-ground (a worse case scenario, i.e. 100% of Cadre reaching the soil surface and no peanut uptake/metabolism) either 5, 4, 3, 2, or 1 month(s) before oat planting, total forage yield was only significantly reduced by the 1 and 2 month timings (61.6% and 22.4% forage yield losses, respectively).  Interestingly, oat grain yields were not reduced by any pre-plant application of Cadre.

6) I do not have any hard data to back this statement up but it makes sense that oat injury could be worse in short-planted fields where Cadre-treated dryland peanuts were grown.  

7) Complete results of this Cadre/oat research can be obtained from the following paper:

Prostko, E.P., T.L. Grey, R.N. Morgan, and J.W. Davis.  2005.  Oat (Avena sativa) response to imazapic residues.  Weed Technology 19:875-878.

8) Culpepper is the small grain weed guy so he would be more than happy to walk any and all small grain fields including oats!!!!!!

Figure 1.  Cadre injury symptoms on oats.

Direx 4L FIFRA 24(c) Special Local Need Label Approved for Georgia Cotton Growers (Culpepper).

At the recent Weed Science Update in Tifton, we discussed that federal diuron labels only allow applications between 15 and 45 days prior to planting cotton and that our state label providing a more flexible and effective use of diuron at burndown had expired. Thanks to the help of ADAMA, the Georgia Department of Agriculture, and the U.S. EPA, our growers once again have a state diuron label with flexible and effective use patterns to combat Palmer amaranth and other problematic weeds just prior to planting. Make sure growers understand that “strip-till” by our definition includes a ripper shank.  ***Direx 4L by ADAMA is the only diuron product available in Georgia with the shortened plant-back interval.  The 24(c)-SLN label is presented below (click on pictures to view better quality picture and/or download):

Syngenta's New Gramoxone 3SL (paraquat) Formulation (Prostko)

Syngenta recently received a label for their new formulation of paraquat sold under the trade name of Gramoxone 3SL (3 lb ai/gal).  As you may recall from a previous blog (March 10, 2019), many rules regarding the purchase, handling, and application of paraquat are changing.  Most notably, all non-bulk paraquat products (with new labels) must adhere to closed-system packaging requirements set forth by the EPA's Paraquat Dichloride Human Health Mitigation Decision by November 2020.  Also, all paraquat applicators are required to complete an EPA-approved training module before applying.

In my recent discussions with both Syngenta and AMVAC field personnel, there will still be some of the older labeled paraquat formulations (2SL and 3SL) in the marketplace for 2020 but these will disappear when supplies are exhausted.  Thus, growers need to be very aware of the label requirements of the container(s) they have in their possession.

A couple of quick links for you to review and share with your growers:

1) New Gramoxone 3SL label:
http://www.syngenta-us.com/current-label/gramoxone_sl_3.0

2) Current bulk handling systems already meet the new closed-system packaging requirements.  Tank adaptors for new closed system 2.5 gallon containers should be available from dealers and/or manufacturers?????  In my opinion, this headache will likely push more growers to bulk handling systems.  

3) EPA-Approved Paraquat Training Information:
https://www.epa.gov/pesticide-worker-safety/paraquat-dichloride-training-certified-applicators

4) Generally, research results from my 2019 field trials with the new Gramoxone 3SL formulation have been very positive (see below).

Grain Sorghum After Watermelons Treated with Reflex (Prostko)

Been getting a few questions about planting grain sorghum following watermelons that were previously treated with Reflex.  Here are a few things to think about:

1) The "official and legal" rotation restriction for grain sorghum after an application of Reflex is 10 months.  Watermelons are roughly a 90 day (3 month crop).

2) I have heard that some test strips (i.e. not for sale or entry into the market) of grain sorghum have been planted after Reflex with no problems and others have seen some major problems.  Herbicide carryover is a complicated issue that depends upon many factors including rate, soil type, moisture, temperature, tillage, and where the Reflex was applied (bare-ground, on/over plastic much, under plastic mulch).  In general, carryover potential to rotational crops would be greater when Reflex was applied under plastic mulch.

3) I have a test in the field right now at the UGA Ponder Farm where I applied Reflex at various rates to bare-ground 90 days before planting (DBP) grain sorghum.  The typical use rate of Reflex in watermelons is 12 oz/A.  In these plots, 12 oz/A of Reflex has caused significant injury and reduced sorghum height/biomass.  If I can keep the birds out of these plots, I might be able to get some good yield data as well (but I have not been able to do that with sorghum in 20 years though).  See pics below:

Cowpea Control (Prostko)

Every so often, I get a few inquiries about herbicides for the control of cowpea (Vigna unguiculata) (Figure 1). Unfortunately, cowpea (also known southern pea, black-eye pea, or crowder pea) can be a very difficult plant to control and not much research data is out there.  In preparing our UGA Weed Science graduate students for the upcoming 2019 National Weed Science Contest, I was able to collect some good data for various herbicides (Table 1).  

In summary, the following herbicides could be used for the control of cowpea depending upon the planted crop:  PRE = Atrazine, Balance Flex (isoxaflutole), and Tricor (metribuzin); POST = Classic (chlorimuron), Engenia (dicamba), Enlist One (2,4-D), Envoke (trifloxysulfruon), Gramoxone (paraquat), Liberty (glufosinate), Osprey (mesosulfuron), Roundup (glyphosate), Sharpen (saflufenacil), and Stinger (clopyralid).  

Figure 1.  Cowpea

Table 1.  Cowpea (‘Top Pick Pinkeye Purple’) control with PRE and POST herbicides, TyTy, Georgia, 2019.¹

Herbicide	Rate/A (oz)	Application Method (PRE or POST)	Test 1 Control (%)		Test 2 Control (%)
			15 DAT3 (Prostko)	20 DAT (Culpepper)	14 DAT (Prostko)
Harness 7EC	22	PRE	0	0	0
Atrazine 4L	64	PRE	100	100	100
Diuron 4L	26	PRE	0	0	0
Valor SX 51WG	3	PRE	0	10	20
Pursuit 2SL	4	PRE	0	8	0
Balance Flexx 2SC	6	PRE	100	100	100
Callisto 4SC	3	PRE	60	65	0
Prowl H20 3.8ASC	48	PRE	0	5	0
Zidua 85WG	1	PRE	0	10	0
Dual Magnum 7.62EC	21	PRE	0	12	0
Spartan 4L	1	PRE	0	0	0
Tricor 4L	24	PRE	100	100	100
Enlist One 3.8SL	13	POST	95	95	100
Buctril 4EC	12	POST	50	70	30
Classic 25DG + COC4	0.5	POST	95	95	85
Select Max 0.97SC + NIS	25	POST	0	10	0
Stinger 3SL	8	POST	95	100	80
Engenia 5SL	6.4	POST	95	95	85
Fusilade DX 2EC + COC	12	POST	0	10	0
Resource 0.86EC + COC	4	POST	0	0	0
Reflex 2SL + NIS	12	POST	50	50	50
Liberty 2.34SL + N-Pak AMS (2% v/v)	22	POST	100	93	85
Sandea 75DG + NIS	0.66	POST	40	25	30
Osprey 4.5DG + MSO	4.6	POST	70	88	85
Accent 75DG + COC	0.66	POST	65	75	60
Gramoxone 2SL + NIS	32	POST	100	95	90
Facet 75DG + MSO	16	POST	50	60	55
Sharpen 2.85SC +  MSO	2.5	POST	95	92	80
Laudis 3.5SC + MSO	3.5	POST	65	68	60
Envoke 75DG + NIS	0.09	POST	85	88	90
Roundup PowerMax 5.5SL	22	POST	100	97	90

¹Test 1: Planting Date = May 28; PRE = May 29; POST = June 13 (~8” tall cowpea).

²Test 2: Planting Date = June 17; PRE = June 18; POST = July 8 (~8” tall cowpea).

³DAT = days after POST treatment.

⁴COC = Agridex @ 1% v/v; NIS = Induce @ 0.25% v/v; MSO = MES 100 @ 1% v/v.