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.

Zidua® Herbicide (Prostko)

Just got through looking at some popular press articles and noticed that there were several advertisements for a new herbicide sold under the trade name of Zidua®.  The UGA Weed Science Team has been evaluating this herbicide for several years so we have some good data for sure.  Here are a few things you might need to know about this new product:

Trade Name: Zidua®

Active Ingredient: pyroxasulfone (It was tested under experimental number KIH-485)

Manufacturer: BASF

Mode of Action:  Inhibits the synthesis of very long chain fatty acids.  Same mode of action as Dual and Warrant. (MOA = 15)

Formulation: 85WDG

Typical Use Rate: 1-2 oz/A

Estimated Cost: $6.50/oz

Current Registrations: Field Corn (Zidua® is listed in Field Corn section of the 2013 UGA Pest Control Handbook)

Future Registrations: soybean, sunflower, wheat, cotton (?), peanut (?)

Field Corn Application Methods:  PPI, PRE, or POST but does not have POST activity.  Only provides residual control.

Weeds Controlled:  Small seeded broadleaf weeds and annual grasses.  In UGA tests, it has provided excellent control of Palmer amaranth

General Comments:

Zidua will compete for market share against similar herbicides such as Dual Magnum or Warrant.  The one big advantage that this herbicide has over these is that its use rate in much lower.  I am not expecting Zidua to change the world but it does give growers another residual herbicide option to choose from.  The active ingredient, pyroxasulfone, will also be available in the following herbicide pre-mixes:

Anthem = pyroxasulfone + Cadet (FMC)

Anthem ATZ = pyroxasulfone + Cadet + Atrazine (FMC)

Fierce = pyroxasulfone + Valor (Valent)

Registrations for the above herbicides are pending.  For a copy of the current Zidua label, please refer to the following link:

http://www.cdms.net/LDat/ldAMK000.pdf

Check out the following Zidua® pictures from my 2012 field research:

Managing Weeds in Wheat (A. Stanley Culpepper)

With a warm December, numerous winter weeds are up and growing aggressively.  For wheat that was planted timely, herbicide applications are usually needed around Christmas.

Broadleaf weeds are common in wheat but can be managed effectively if herbicide applications are timely. Numerous herbicide options exist and six of these options are shown below.

Herbicide Option	Wheat Stage of Growth	Weeds
Harmony Extra1 + MCPA2 or Harmony Extra1 + 2,4-D2	Fully tillered	Wild radish, henbit, chickweed, primrose, and most other broadleaf weeds.
Harmony Extra1 followed by MCPA or 2,4-D	After 2 leaf & before flag leaf followed by fully tillered
Harmony Extra1	After 2 leaf & before flag leaf	Henbit, chickweed, most other broadleaf weeds EXCEPT primrose and radish larger than 1”.
2,4-D or MCPA	Fully tillered	Wild radish and primrose.
PowerFlex	Three leaf but before jointing	Wild radish, ryegrass and less than 1.5” henbit or chickweed
Osprey	Emerged but before jointing	Ryegrass, annual bluegrass, and less than 2” henbit or chickweed

¹Harmony Extra, Harmony Extra Total (Sol) and generic products are available, use correct rate.

²MCPA or 2,4-D can be applied at 12-16 oz/A; MCPA is “softer” on wheat.

Annual ryegrass is a serious pest of wheat, especially in middle and North Georgia, primarily due to herbicide resistance.  Growers must rotate herbicide chemistry. Osprey and PowerFlex have the same mode of action thus rotating these herbicides is not an effective approach in rotating herbicide chemistry.  Osprey/PowerFlex should be rotated with Axial; a piece of land should never be treated two years in a row with PowerFlex/Osprey OR Axial.  In addition to rotating herbicides, one must implement cultural practices such as tillage (deep tillage helps considerably) and crop rotation (allowing use of other herbicides such as Roundup) in a ryegrass management program.  There are Georgia growers with ryegrass resistant to Axial, PowerFlex, Osprey, and Hoelon and the production of small grains is no longer economically feasible.  Ryegrass will develop resistance to herbicides more quickly than any other known plant.

All “ryegrass” herbicides should be applied prior to 2 tiller ryegrass!  Mixtures with Harmony will improve broadleaf weed control; however, do not mix these products with 2,4-D or MCPA.

Herbicide Option	Wheat Stage of Growth	Weeds in Addition to Ryegrass
Axial XL	Two leaf up to pre-boot.	None
PowerFlex	Three leaf up to before jointing.	Wild radish < 6”, henbit and chickweed < 1.5”
Osprey	Before jointing.	Annual bluegrass; wild radish < 4”, henbit or chickweed < 2”

Should Growers Be Concerned About Diuron Carryover to Wheat (Culpepper)?

Growers are strongly encouraged to apply diuron + MSMA at cotton layby for the control of Palmer amaranth.   With rapid adoption of diuron use at layby in cotton, many growers are now questioning the potential for diuron injury to a subsequent wheat crop.   The following restriction is made clear on the Direx label when it is applied at cotton layby: “Cotton, corn, and grain sorghum can be planted during the next spring.  Do not replant treated areas to any other crop within 1 year after the last application, as injury to subsequent crops may result.”

Therefore, the Direx label prohibits planting wheat following a layby application of Direx.  So is this restriction based on sound science or is this proposed potential for damage simply not fully understood?  Our initial research suggests that the potential for damage is simply not understood.  During last winter, we applied Direx from 8 oz/A up to 32 oz/A preemergence on wheat and followed immediately with heavy irrigation.   Injury was not detected with 8 oz/A and less than 10% injury was noted with 16 oz/A.  Therefore, our INITIAL research suggest diuron applied at layby in cotton should pose little to no risk to the following wheat crop as long as at least 90 days has passed (Table 1).  Significant (23 to 43%) wheat injury was noted with 24 to 32 oz/A Direx applied PRE to wheat.  It is important to note that this study was conducted on a soil with less than 1% organic matter which increases the potential for injury as compared to soils with greater than 1% organic matter.

Table 1.  Wheat tolerance to Direx applied PRE.
Rate of Direx applied PRE to Wheat	Maximum Wheat Injury
Direx  8 oz/A	0% d
Direx 16 oz/A	8% c
Direx 24 oz/A	23% b
Direx 32 oz/A	43% a
Experiment conducted in TyTy, GA during the 2010 and 2011 season.  Values with the same letter are not different at P = 0.05.

It is important to remember to always follow all herbicide label restrictions.  Our goal is to work with MANA to address rotational restrictions for Direx to wheat.

Post-Harvest Control of Benghal Dayflower (Tropical Spiderwort) (Prostko)

Although much of our attention and effort has been focused on Palmer amaranth control, other weeds are still problematic in Georgia.  While driving around recently, I noticed many harvested corn fields that were covered with Benghal dayflower a.k.a. tropical spiderwort (Figure 1).  Like Palmer amaranth, it is very important to control these fall populations of Benghal dayflower since plants can go from seed to seed in about 40 days.  Here are a few reminders:

1) Tillage is just as effective as herbicides in controlling post-harvest populations of Benghal dayflower.
2) Herbicides that can be used for the control of post-harvest populations include 2,4-D, paraquat, and Aim.  Please refer to page 56 of 2012 UGA Pest Control Handbook for more information.
3) Plants larger than 6" tall will need split applications of herbicides (Figure 2).

Post-Harvest Control of Palmer Amaranth (Prostko)

I have been getting numerous telephone calls lately regarding the post-harvest (i.e. after field corn) control of Palmer amaranth.  It is extremely important to control this fall population of Palmer plants before they produce more seed which can be added to the soil seed-bank.  A year's worth of good control could go down the drain if these populations are allowed to produce seed! In case you were unaware, I have very specific recommendations for this particular situation on page 62 of the 2012 UGA Pest Control Handbook.  It is critical that growers pay close attention to the size of the Palmer.  If paraquat is applied to weeds larger than 6", control will be poor and this lack of control may even help contribute to the future development of paraquat resistance.  I often suspect that some folks think that I make this stuff up.  However, if you or your growers do not believe me, please refer to Figure 1.  Increasing the paraquat rate and tank-mixtures with 2,4-D or dicamba would help but not enough for me to say that it is a great idea to spray pigweed plants greater than 6" tall.

Herbicide Options for Double-Cropped Soybeans

With the current high price of soybeans, many GA growers are planting soybeans after field corn.  Thus, I have received many questions about weed control options for this situation.  Please consider the following:

1) My recommendations for weed control at this point in time are very different from early/normal planted soybeans. 
2) My primary concern is crop rotation.  If wheat is to be planted this fall or field corn is to be planted next spring, herbicide options may be limited depending upon the application date.
3) Table 1 lists the current labeled crop rotation restrictions for common soybean herbicides.
4) In order to prevent any major crop rotation problems, I would suggest a PRE application of Dual Magnum (or generic) followed by an EPOST application of glyphosate + Cobra or Ultra Blazer (RR soybeans).
5) Valor would be an excellent choice in fields where a POST application of Cobra, Prefix, Reflex, and Ultra Blazer may not be needed.  If we are going to protect Valor, growers must avoid PRE applications of Valor followed by POST applications of Cobra/Prefix/Reflex/Ultra Blazer. PPO abuse for sure!
6) If field corn will be planted next spring (~8 months), avoid the use of Canopy, Envive, Prefix, Pursuit, and Reflex.