Glyphosate Use in RR Field Corn (Prostko)

There were 2 trait events, discovered by Monsanto, that lead to the development of RR corn hybrids.  GA21 was the first event used to develop the original RR corn hybrids.  These hybrids were commercialized in 1998.  A later trait event, NK603, resulted in increased tolerance to glyphosate and the subsequent commercial release of RR2 corn hybrids in 2001. 

It has recently come to my attention that not all field corn hybrids planted in Georgia are RR2 corn hybrids.  There are some corn hybrids that contain the original RR event, including Pioneer’s new racehorse, 2023BVT.  This is very important for those of us who make public recommendations since certain formulations of glyphosate are not currently labeled for use on RR corn hybrids.   Corn growers should check with their seed salesman to determine if their planted hybrids are RR or RR2 before making a POST application of glyphosate.

Syngenta corn hybrids (Northrup King) that have the glyphosate-tolerance trait are being sold as Agrisure® GT hybrids.  The event used in these hybrids was GA21, thus they could be considered RR hybrids.  Pioneer 2023BVT has the Agrisure® GT trait. 

The following is a summary of various glyphosate products that can be used on glyphosate-tolerant corn hybrids:

Glyphosate Formulation	Manufacturer	Product  Rate/A (ozs)		RR Corn Hybrids	RR2 Corn Hybrids
		0.75 lb ae	1.12 lb ae
Buccaneer Plus	Tenkoz	32	48	Yes	Yes
Credit 41 Extra	NuFarm	32	48	Yes	Yes (?)*
Gly Star Plus	Albaugh	32	48	Yes	Yes
Gly-4 Plus	UCPA	32	48	Yes	Yes (?)*
Glyfos X-tra	Cheminova	32	48	Yes	Yes
Honcho Plus	Monsanto	32	48	No	Yes
Roundup PowerMax	Monsanto	22	32	No	Yes
Roundup WeatherMax	Monsanto	22	32	No	Yes
Touchdown HiTech	Syngenta	19	29	Yes	Yes
Touchdown Total	Syngenta	23	34	Yes	Yes

*These generic labels make no specific distinction between RR and RR2 hybrids. 

The next issue of concern is what application rate of glyphosate can legally be used on RR and RR2 corn hybrids?  Generally, RR corn hybrids can receive 2 in-crop applications of glyphosate at 0.75 lb ae/A from emergence through the V8 stage or 30” in height (whichever occurs first).  RR2 corn hybrids can receive 2 in-crop applications of 1.12 lb ae/A from emergence through V8 or 30”.  Glyphosate can also be applied on RR2 corn hybrids when the corn is 30-48” tall with drop nozzles.

There is one exception to these rules.  The labels of Syngenta’s Touchdown products make no rate/timing distinctions between RR and RR2 corn hybrids.

If this makes absolutely no sense at all to you, join the club.  I have spent numerous hours over the last week trying to determine what is legal or not.  Also, it is very likely that Monsanto will amend their glyphosate labels in the very near future to include RR corn hybrids.

Bottom line, growers need to know if their corn hybrids are RR or RR2 and they must READ their specific glyphosate label to determine if, when, and how much can be applied.

 

  

 

Zidua Labeled for Use in Soybean (Prostko)

Zidua 85WG (pyroxasulfone) recently received a registration for use in soybean.  You may recall that back on January 10, I published some information on this blog about its potential uses in field corn.  Zidua provides residual control of certain annual grass and broadleaf weeds, including Palmer amaranth (Figure 1).  Zidua can be applied PPI, PRE, or EPOST at rates ranging between 1.0 to 2.1 oz/A on coarse soil types (~$6.50/A to $13.65/A).  Zidua should NOT be applied from soybean emergence (cracking) through the unifoliolate stage of growth or unacceptable crop injury may occur. A copy of the complete supplemental soybean label can be found at the following location: http://www.cdms.net/LDat/ldAMK004.pdf

Additionally, there have been revisions to the crop rotation restrictions for Zidua.  Current crop rotation restrictions for Zidua can be viewed at the following location:
http://www.cdms.net/LDat/ldAMK003.pdf

Figure 1.  Weed Control in Soybean with Zidua 85WG @ 2 oz/A.

Fierce Labeled for Use in Soybean (Prostko)

Fierce 76WG recently received a label for preemergence (PRE) use in soybean.  Fierce 76WG is a combination of 33.5% Valor (flumioxazin) + 42.5% Zidua (pyroxasulfone).  The normal use rate of Fierce for coarse soil types is 3 oz/A.  Fierce 76WG @ 3 oz/A is equivalent to Valor 51WG @ 2 oz/A + Zidua 85WG @ 1.5 oz/A.  Generally, Fierce has looked impressive in my field trials (Figure 1).  A copy of the supplemental Fierce soybean label can be found at the following location:
http://www.valent.com/Data/Labels/2013-FIE-0013%20Fierce%20Soybean.pdf

Figure 1.  Fierce for Weed Control in Soybean - 2012

Currently, there are several PRE soybean herbicides that contain the active ingredient flumioxazin (Envive, Fierce, Valor, Valor XLT).  There is no question that one of the most effective herbicide programs for the control of Palmer amaranth in soybean would be to use one of these flumioxazin-containing products (PRE) then follow with Reflex (POST).  However, this progam should not be encouraged since all of these herbicides have the same mode of action (PPO-inhibitor).  Growers in a soybean/corn rotation might get away with this program since Reflex and Valor are not being overused.  But, growers in a cotton/peanut rotation, who are relying heavily on Valor and Reflex, should avoid their overuse in soybean.  Some specific recommendation's for soybean growers who want to protect Valor and Reflex are presented in Figure 2. 

Figure 2.  Soybean Herbicide Options That Help Protect Valor and Reflex



Counter/Herbicide Interactions in Field Corn (Prostko)

It is very important to remember that if a field corn grower wants/needs to use an in-furrow application of Counter 20G, he cannot use certain herbicides (Figure 1).  This negative insecticide/herbicide interaction is more commonly associated with the ALS-inhibiting herbicides (Accent, Beacon, Steadfast Q) but can also occur with certain HPPD-inhibitors (Callisto, Halex GT) and PPO-inhibitors (Sharpen, Verdict).  In one of my field corn trials conducted in 2012, a Counter/Steadfast interaction resulted in a 40% yield loss.  The manufacturers of Counter 20G (AMVAC) have put together a excellent publication to address this issue (Figure 2).  

Figure 1.  Field Corn Injury Caused By Counter/ALS Herbicide Interaction.

 



Figure 2.  AMVAC Counter/Herbicide Publication

Postemergence Field Corn Herbicides (Prostko)

Not sure what happened, but the table below was accidently left out of the 2013 UGA Pest Control Handbook.  It should help you address questions about times of application in field corn.

 

Table 1.  Times of Application/PHI for Postemergence Herbicide Labeled for Use in Field.
 

Herbicide	Field Corn Stage of Growth		PHI (DAYS)	Grazing, Feed, Forage, Hay, Silage Interval (days)
	Earliest	Latest
Accent Q	1-2 leaf	20” or V6 20-36” or V10 - drops		30
Aim	spike	V8 V8-14 leaf collars - drops	14 leaf collars	14
Atrazine	PPI/PRE	12”		grazing = 21 forage = 60
Basagran	1-2 leaf	NL		12
Callisto	pre	30” tall or 8 leaf stage	45	45
Capreno	V1	V6 V6-V7- drops		45
Clarity	1-2 leaf	5th leaf or 8” tall 8-36” tall drops
Dual Magnum	PPI/PRE	40” tall		30
ET	Spike	V4 V4-V8 - drops	90	50
Halex GT	Spike	30” or V8	45	45
Impact/Armezon	spike	??	45	45
Laudis	1-2 leaf	V8		45
Liberty	spike	24” or V7 24-36” - drops	70	60
Prowl H20	spike	30” or V8		21
Realm Q	1-2 leaf	20” or V7	70	45
Resolve Q	1-2 leaf	20” or V7		30
Roundup	spike	30” or V8 30-48” - drops	50	50
Sandea/Permit	spike	layby		30
Status	V2	5th leaf or 8” 8-36” or V10 - drops	72	32
Steadfast Q	1-2 leaf	20” or V6		30
Warrant	spike	24” 24-30” - drops		40
Zidua	spike	V4

¹NL = none specifically listed on the label. 

 

Valor Application Method (Prostko)

Not sure what's going on in some counties so here is a friendly reminder that UGA does not recommend that Valor be applied preplant incorporated (PPI) in peanut for 2 very good reasons: 1) Valor is not labeled for this type of application and 2) PPI applications provide significantly less control of of Palmer amaranth than PRE applications (Figure 1).

Gramoxone/Reflex Tank-Mixtures (Prostko)

Over the last few years, growers have experienced a few problems when tank-mixing Gramoxone (paraquat) + Reflex (fomesafen).  In order to prevent these potential compatibility problems, consider the following recommendations developed by Syngenta:

1) When tank-mixing Gramoxone and Reflex, use a non-ionic surfactant (NIS) that contains a minimum of 80% active ingredient.

2) With spray volumes of 10 GPA or more, use NIS at 2 qt/100 gal (0.5% v/v).  Use 1 gal/100 gal (1% v/v) when spraying less than 10 GPA.

3) Mix chemicals in the following order:

a) Add half of the required amount of clean water to the spray tank.

b) Start the sprayer agitation system and continue agitation throughout mixing and spraying.

c) Add the required amount of non-ionic surfactant to the spray tank.

d) Add the required amount of Reflex to the spray tank.

e) Add the required amount of Gramoxone brands to the spray tank.

f) Add the remaining amount of clean water to the spray tank.