The Big Rain and Herbicides (Prostko)

Most of Georgia received a significant rainfall event on April 24, 2021 (Figure 1).  Some areas received more than than 6".  Consequently, my phone has been ringing off the hook about the potential effects of this precipitation event on herbicides.  Here are a few thoughts:

1) The two biggest herbicide concerns with heavy rainfall events such as this are runoff and leaching.  

2) If a field received enough rainfall to physically move the soil from the field, herbicides were likely moved with it.  In this scenario, residual weed control would be reduced.  Tough luck here and nobody can prevent/predict an Act of God!!!

3) Herbicide leaching is a complicated interaction of many factors including soil type, OM, and certain chemical properties (i.e. water solubility and soil adsorption).  Very generally, herbicides with higher water solubility and lower soil adsorption characteristics are more likely to leach from the soil profile.  Check out Table 1 for a list of these properties. Note that dicamba has a very high water solubility and very low soil adsorption so it is very prone to leaching.  Although paraquat and glyphosate are very water soluble, they are strongly adsorbed to soils.

4) Most of the questions that I have been getting have had to do with Prowl (pendimethalin).  You will note in Table 1 that Prowl is not very soluble in water and is strongly adsorbed to soils.  Thus, it is less likely to leach in comparison to other herbicides so it should still be around in most situations.  

5) If a grower has already applied Prowl (on peanut land) and has observed significant soil movement/washing, I would suggest that he/she consider adding an additional 16 oz/A of Prowl in combination with Valor immediately after planting (i.e. behind the press wheel).  I would also suggest this in peanut fields where prepared beds must be reworked/remade/ refreshed before planting.

Table 1.  Herbicide Water Solubility and Soil Adsorption Properties for Common Herbicides Used in Georgia.

Trade Name	Common Name	Water Solubility (ppm)	Soil Adsorption (Koc)
Aatrex	atrazine	33	100
Callisto	mesotrione	2200	14-390
Dual Magnum	s-metolachlor	488	200
Engenia/Xtendimax	dicamba	4500	2
Gramoxone	paraquat	620,000	1,000,000
Impact	topramezone	0.69	22-172
Laudis	tembotrione	28.3	66
Liberty	glufosinate	1,370,000	100
Prowl	pendimethalin	0.275	17,200
Reflex	fomesafen	50	60
Roundup (IPA Salt)	glyphosate	900,000	24,000
Sonalan	ethalfluralin	0.3	5,000
Tricor	metribuzin	1100	60
Valor	flumioxazin	1.79	557
Zidua	pyroxasulfone	3.49	57-114

 

Using Pesticides Wisely 2021 and Paraquat Training Update (Stanley Culpepper - UGA and Jesse Kelly and Jennifer Wren - GDA).

Using Pesticides Wisely (UPW) 2021 virtual trainings are nearly completed with only three more opportunities available (table below). This training must be completed to be able to make labeled dicamba or 2,4-D in-crop cotton or soybean applications. 

April 5, 5:30 PM	https://zoom.us/webinar/register/WN_86HgfXsMRt64_dN_xz9b0g
April 8, 9 AM	https://zoom.us/webinar/register/WN_Nry9IN0HQSu7YgP5TOiC3g
April 12, 5:30 PM	https://zoom.us/webinar/register/WN_ox4YobtHSwW7N9OfjgnkBA

For those who have already attended UPW training, your attendance information will be posted at http://www.agr.georgia.gov/24c.aspx and available through the link highlighted in the picture below. Remember, it may take a few weeks after training competition before names will appear.

Before  mixing, loading, and/or applying paraquat, new labels require the completion of on-line training https://www.epa.gov/pesticide-worker-safety/paraquat-dichloride-training-certified-applicators approved by the U.S. EPA.  Thanks to the National Pesticide Safety Education Center, GDA has posted a list of those applicators completing training prior to 3/21/2021 at http://www.agr.georgia.gov/24c.aspx, link highlighted in slide below.  Periodic updates to the list will occur overtime.

When you complete your paraquat training you will receive a certificate. Regardless of the date in which you were trained, send your certificate to AgPest@agr.georgia.gov for 1 CEU of pesticide credit. 

Cold Temperatures and POST Field Corn Herbicide Applications (Prostko)

Over the next few days (April 1-4), low daily air temperatures are expected to drop below 50 and even 40 degrees in many areas.  Consequently, I would encourage any field corn grower who wants to make a POST herbicide application during this time period to consider waiting until next week when temperatures get warmer.  It has been my experience that when herbicides are applied in colder temperatures, weed control will likely be reduced/slowed and crop injury increased (i.e. reduced plant metabolism).  As of today, weather conditions for herbicide applications next week (April 5-9) look very favorable and weed growth from now until then would not be significant enough to negatively impact control.  In general, summer annual weeds do not grow as fast in April as they do in May/June.

A few years ago, I applied Halex GT + Atrazine + Induce early (V2 stage) during a cold period (8/15 days with low temps below 50 F) and observed significantly more crop injury than usual (Figure 1).  The good news is that the field corn recovered from this injury and final yields were NOT reduced by the 1X rate.  FYI, I am not picking on Halex GT (one of many awesome field corn herbicides) here since increased crop response could happen with almost any POST herbicide when applied in unfavorable environments.  

 

Figure 1.  Field corn injury from Halex GT + Atrazine + Induce applied at the V2 stage of growth during colder weather in 2018 (low air temperatures <50 F for 8/15 days).

   

Acuron GT For Weed Control in Field Corn (Prostko)

Syngenta recently received registration for a new postemergence field corn herbicide sold under the trade name of Acuron® GT.  Acuron® GT is very similar to Halex® GT but it contains an additional active ingredient (bicyclopyrone).  Syngenta has several similar field corn herbicides in the market and I have summarized them in Table 1.  I have only had the opportunity to evaluate Acuron® GT for 1 year (Figure 1) so I would encourage any interested GA growers to use it on a limited basis until I can get more data in 2021.  A complete copy of the Acuron® GT label can be downloaded here: https://www.syngenta-us.com/current-label/acuron_gt.   

Table 1. A comparison of Acuron, Acuron Flexi, Acuron GT, and Halex GT.

Trade Name	Active Ingredients (lbs/gal) (WSSA MOA)
	glyphosate (9)	mesotrione (27)	bicyclopyrone (27)	S-metolachlor (15)	atrazine (5)
Acuron	-	0.240	0.060	2.14	1.0
Acuron Flexi	-	0.320	0.080	2.86	-
Acuron GT	2.00	0.200	0.095	2.00	-
Halex GT	2.09	0.209	-	2.09	-

 

2021 Cotton Weed Management Circular is Ready for Agents! (Culpepper and Vance)

The cotton circular should be on-line (gaweed.com) by late February but if you would like them before then or if you would like them laminated, do the following:

E-mail Jenna Vance at jcsmith3@uga.edu and ask for one of the following options:

Option 1: Request laminated circulars to be mailed to you. Provide the number of circulars that you would like plus an address of where to send them.

Option 2: Request a pdf version.  An e-mail response will provide the PDF as an attachment.

Some Reminders Before Field Corn Planting (Prostko)

Based upon my 22 years of experience in Georgia, here are 3 things that I know will happen somewhere in a patch of field corn in 2021:

1) Herbicide carryover will be blamed for corn injury but low soil pH is the real problem (Figure 1). Favorable average soil test results and/or "grid-sampling" do not guarantee that there are no areas of low soil pH in a field.

2) Herbicide carry-over will be blamed for corn injury but nematodes are the real problem (Figure 2).  In my opinion, nematodes are much more of a problem than is currently perceived by many.

3) Valor (flumioxazin) injury, from either sprayer contamination (i.e. improper cleanout) or drift will occur (Figure 3).  Good news is that depending upon rate and stage of growth, field corn has some tolerance to Valor (Figures 4 and 5).

Enlist™ Soybean Variety Data – 2020 (Prostko)

UGA-OVT just recently released the results of their 2020 soybean yield trials.  In those trials, several Enlist™ (2,4-D choline tolerant) varieties were included.  There has not been much Georgia generated data about the performance of Enlist™ soybean varieties in our state.   A quick summary of those Enlist™ varieties is presented in the following table. 

Table 1.  Enlist Soybean Variety Performance in Georgia – 2020. 

Variety	Statewide Average Yield (Bu/A)	Maturity Group Average (Bu/A)
DM 48E73	48.3	47.9
AGS 48E19	54.1	47.9
MS 4800E	52.5	47.9
DM 59E01	65.1	62.5
ZS 5098E3	64.0	62.5
MS 5110E	60.7	62.5
AGS 51E19	61.9	62.5
DM 51E01	61.6	61.7

Five of the eight Enlist™ soybean varieties in these tests had higher yields than the maturity group average.  To get the full report of the preliminary 2020 UGA-OVT soybean yield results, check out this link: https://swvt.uga.edu/content/dam/caes-subsite/statewide-variety-testing/docs/performance-trials/2020/soybean-prelim-2020-tables.pdf