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.