Commodities: Fieldcrops: Peanuts: 2007 Peanut Update

2007 Peanut Weed Control Update

Eric P. Prostko

What is New For 2007?

Firestorm:  Firestorm is a new formulation of paraquat sold by Chemtura Corp.  Chemtura Corp. was formed via the merger of Great Lakes Chemical Corp. + Crompton Corp.  This formulation of paraquat is similar to the old Gramoxone Max formulation (3 lb ai/gallon).  Normal use rates for peanut are 5.5-10.8 oz/A.   A copy of the current label can be obtained from the following web-address: http://www.cdms.net/ldat/ld7ET000.pdf

Aim: Aim is now registered for use as a preplant burndown herbicide in peanuts.  Aim can be applied up to 24 hours after planting.   Aim should be tank-mixed with glyphosate particularly when large annual morningglories are present at planting. Use rates range from 1-2 oz/A.  A copy of the supplemental label can be obtained at the following web-address: http://www.cdms.net/ldat/ld5L1003.pdf

Impose:  Impose is a generic formulation of imazapic (Cadre) that will be marketed by Makhteshim Agan of North America (MANA).  In UGA field trials, there have been no differences in crop or weed response between Cadre and Impose. 

ALS-RESISTANT PALMER AMARANTH (PIGWEED) MANAGEMENT

Results of the 2005/2006 UGA ALS-resistant Palmer amaranth survey indicated that more than 80% of the plants screened were resistant to Cadre (imazapic).  Consequently, growers who have experienced ineffective pigweed control over the past few years need to seriously consider alternative management programs. (Table 1).   A few other thoughts to consider with regards to Palmer amaranth management include the following:

1. Growers who farm large acreages must seriously consider using residual herbicides.  Depending upon the crop planted, residual herbicides would include the following: Valor, Dual Magnum/generics, and Outlook/Propel.  More often than not, large acreage growers don’t/can’t get back in their fields on a timely basis to make an early postemergence herbicide application.  Remember, preemergence herbicides must be activated by 0.5-1.0 inches of rainfall/irrigation within 7-10 days after application or they will not work.
2. In one of my field trials in 2006, Palmer amaranth grew 16 inches in one week! Thus, postemergence control recommendations that are delayed or not implemented immediately will be less effective due to weed size.  The #1 enemy of postemergence herbicide applications is large weeds!!!!!!!!! (FYI, dry weather would be a close 2nd)
3. Postemergence herbicides such as Cobra or Ultra Blazer are not the final answers for large pigweed problems.  Yes, they will control small pigweed plants but they provide no residual control.  Cobra and Ultra Blazer will have to be used in a total program that includes residual herbicides. 
4. In peanuts, a sequential application of 2,4-DB + crop oil followed by Cobra + crop oil (1% v/v) 4 days later was more effective than either herbicide applied alone or in a tank-mix .
5. Many pigweed problems that exist are due to the fact that the plants were not adequately controlled at planting by either tillage or burndown herbicide programs.   It is imperative that seedbeds be weed-free at planting to obtain optimum pigweed control.
6. To the best of my knowledge, there have been no reported cases of steel, hoe or hand-resistant pigweed in the world.  Cultivation can be an effective weed management tool.  However, high diesel fuel prices and future farm legislation may hinder its rebirth.
7. ALS-resistant Palmer amaranth will force producers to spend more money on control programs.  However, improved control of Palmer amaranth should also result in improved yields that could potentially pay for these increased production costs.  New research from North Carolina has shown that Palmer amaranth has the potential to reduce peanut yields by 28 to 66%, depending upon density, if left uncontrolled.

Table 1.  Suggested Herbicide Programs for Managing ALS-resistant Palmer Amaranth in Georgia Peanut. 1

1. 1 ALS-resistant Palmer amaranth is a very serious concern. An aggressive, broad-based management program is necessary to slow spread of the resistant biotypes and to reduce selection pressure in areas currently not infested with resistant biotypes.  A combination of soil residual and postemergence herbicides will be required for optimum control.
2. Strongarm is not included in this table because it is an ALS-inhibiting herbicide.  However, it can be used for the control of other broadleaf weeds.  If Strongarm is used preemergence, Cadre or Pursuit should NOT be applied postemergence.
3. Apply cracking or early postemergence treatment only if weeds have emerged.
4. Cadre or Pursuit may be tank-mixed with Cobra or Ultra Blazer if needed for control of other weed species. Cadre and Pursuit are ALS- inhibitors. Because of concerns with weed resistance to ALS-inhibitors, a mixture of Cobra or Ultra Blazer with Cadre or Pursuit  would be preferred over Cadre or Pursuit alone.  When using Cadre or Pursuit, follow all labeled crop rotation restrictions.
5. Generic brands of Prowl (pendimethalin) are available and perform similarly.  Prowl or Sonalan can be used preemergence if 0.5-0.75" of water can be applied within 48 hours of application.  They can be tank-mixed with Valor, Dual Magnum, or Outlook in this situation.  Dual Magnum and Outlook may also be applied preplant incorporated in combination with Prowl or Sonalan if desired.
6. If Valor is properly activated with 0.5-0.75" of rainfall or irrigation within 7 days of application, it is unlikely that an “at-cracking” treatment will be required.  However, if control with Valor is unacceptable, an “at-cracking” treatment of paraquat + Basagran + Dual Magnum or Outlook should be applied.
7. Valor, Cobra, Storm, and Ultra Blazer have the same mode of action (PPO inhibitor).  Consequently, no more than a total of 2 applications of these herbicides should be used in a season.
8. Generic brands of metolachlor are available (Stalwart, Parallel PCS, Me-Too-Lachlor). However, these generic brands have not provided the same length of residual control as Dual Magnum (S-metolachlor) in some UGA field trials.
9. Paraquat is sold under the trade names of Gramoxone Inteon or Firestorm.

IMPROVING THE PERFORMANCE OF PARAQUAT

Over the last few years, there have been several changes in the formulations of paraquat.  In 2007, paraquat will be available in 2 formulations, Gramoxone Inteon (2 lb ai/gal) and Firestorm (3 lb ai/gal).  When these formulation changes have occurred, there has been some concern about their performance in comparison to the older formulations.  In numerous UGA field trials, a difference in weed control performance between old and new formulations of paraquat has not been observed.  The following tips may be helpful for improving the performance of paraquat applications in peanut:

1. If Florida beggarweed, sicklepod, and Texas panicum are the main weed problems, use paraquat by itself.  When applied alone, paraquat should be applied before 14 days after cracking.  Tank-mixes with Basagran or Storm will reduce the control of these weeds.  Although, peanut injury will also be reduced by the addition of Basagran or Storm, the effects of paraquat on peanut are mainly cosmetic in nature.
2. Use at least 15 GPA.  Lower spray volumes = less spray coverage.  Increasing water volumes from 10 to 15 GPA can result in increases of spray coverage by as much as 45%. 
3. Use slower tractor speeds.  Faster tractor speeds = less spray coverage.  Also, slower tractor speeds may produce less dust which can tie up paraquat and make it less effective
4. Do not use whirl-jet nozzle tips. Flat-fan nozzle tips are preferred.  In 2006 UGA tests, whirl-jet nozzle tips provided 42 to 53% less spray coverage than flat-fan nozzle tips.

top