Mixing Order of Pesticides is Important (Prostko)

This is a friendly reminder to all young and old extension agents that the tank-mixing order/sequence of pesticides is very important.  I discussed this topic in a previous UGA Weed Science Blog (Tank-Mixing - April 4, 2018) so check that one out so I do not have to reinvent the wheel.   

Got a call from a industry tech rep today about some mixing problems with Roundup PowerMax3 and Zidua SC.  You can see in the slide below that when the Roundup was put in the plastic bottle first followed by the Zidua, that some problems (i.e. the formation of precipitates that could gum up a sprayer) occurred immediately but did not do so when the Zidua was mixed in the bottle first.  This simple demonstration was conducted using 1500 mls of water (0.396 gallons) so just imagine the potential mess in an 800 gallon sprayer.  This problem could have been easily avoided by reading page 13 of the Zidua SC label (https://s3-us-west-1.amazonaws.com/agrian-cg-fs1-production/pdfs/ZiduaR_SC1t_herbicide_Label.pdf).

Strongarm Carryover from Peanuts to Field Corn (Prostko)

The 2021 field corn production season has not been great.  Cold, cloudy, wet weather has many farmers scratching their heads about the way some of their fields look.  There are many possible causes of these problems (i.e. fertility, disease, insects, nematodes, weather, herbicide carryover, etc.).  My colleagues and I have tried to address these issues as needed.  With that in mind, I would like to give you my thoughts on the potential for Strongarm (diclosulam), applied to peanuts in 2020, to have carried over to field corn in 2021.

1) In general, I am of the opinion that the potential for herbicide carryover (assuming 1X rates were applied) for many herbicides in Georgia is low.  Why?  We have warm temperatures, lighter/low OM soils, abundant rainfall, and soils that never freeze (maybe in extreme North Georgia).  These are conditions that are very favorable for the microbial degradation of herbicides (the major breakdown method for most herbicides). 

2) The labeled rotation restriction for field corn following an application of Strongarm is 18 months.  Consequently, any grower/consultant/county agent who actually reads the label might automatically assume that this could be the cause of many field corn problems.  But, there is more to this story.

3) What does Strongarm injury to field corn look like?  See the pictures below.  These are from research trials that I conducted in 2013/2014 where I applied various rates of Strongarm to irrigated field corn immediately after planting (i.e. PRE). Remember that the labeled rate of Strongarm is 0.45 oz/A.  

4) The NOEL (no effect level) for Strongarm's influence on field corn yield (based upon 3 years of irrigated field trials in south Georgia) is 0.029 oz/A (1/16X rate).  

5) The greatest/longest reported half-life for Strongarm is 43 days (range of 13-43 days).  Thus, based upon our data, it would take 172 days or 5.7 months for the 0.45 oz/a rate to breakdown to this 0.029 oz/A rate. So, field corn planted after that time period would be unlikely to be affected by Strongarm carryover (in irrigated fields and normal weather patterns).

6) A few other random thoughts:

    a) Sweet corn is way more sensitive to Strongarm than field corn.

   b)  PRE applications of Strongarm would be more likely to carryover than POST applications (i.e. more herbicide reaches the soil).

   c) Much of the Strongarm used in Georgia peanuts is applied at reduced rates.  Many growers who use Strongarm PRE only apply 0.225 oz/A.  Many growers who apply Strongarm POST only use 0.30 oz/A.

    d) The potential for Strongarm carryover would be greater in dryland fields vs. irrigated fields.

7) I will never say never but it is my opinion that Strongarm applied at 0.45 oz/A or less to irrigated peanuts is unlikely to cause carryover problems in irrigated field corn planted more than 6 months (7+ months even safer) after application.  But, it is never a good idea to use Strongarm in dryland peanut fields that will be rotated to dryland field corn and never a good idea to use Strongarm in any peanut field (dryland/irrigated) rotated to sweet corn.

8) The label is the law so growers who choose to plant field corn earlier than 18 months after an application of Strongarm do so at their own risk.  It is not very likely that Corteva would ever change the current Strongarm field corn rotation restrictions based upon previous UGA test results. 

9) Soil/tissue tests for pH/fertility problems and a nematode test are always very helpful when diagnosing field problems since these types of problems can look very similar to herbicide injury. 

10) The refereed journal article for this research is as follows:  Prostko, E.P. and T.M. Webster.  2015.  Field corn response to diclosulam.  Crop, Forage, & Turfgrass Management 1:1-5.   

Glyphosate Residual Activity Impacts Vegetable Transplants (Culpepper)

Over the past several years, we have been discussing how glyphosate applied pre-transplant to vegetables can be problematic depending on rate applied, time interval between application and transplanting, and rainfall amount between application and transplanting. A current graduate student's project further stresses the importance of understanding this challenge (photos below) and the importance of following our new label (below) when transplanting into bare-ground or mulch production systems.  

For a better copy of this new label:

https://s3-us-west-1.amazonaws.com/agrian-cg-fs1-production/pdfs/Roundup_PowerMAX_II2t_Herbicide_2EE.pdf

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	-