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.