Commodities: Fieldcrops: Peanuts: 2008 Peanut Update

2008 Peanut Update

2008 Peanut Weed Control Update

Eric P. Prostko

• What is new in 2008??
• Keys to Managing Palmer Amaranth (Pigweed) in 2008
• Fungicide Tank-Mix Concerns
• Suggested Herbicide Programs for Managing ALS-Resistant Palmer Amaranth in Peanut. 1

What is new in 2008??

AIM EC – Peanut Harvest Aid Label

Late in 2007, Aim EC received a registration for use as a harvest aid in peanut.  Aim EC can be applied at 1-2 ozs/A at least 7 days before harvest.  Aim will defoliate/desiccate annual morningglories, pigweed, and tropical spiderwort to help facilitate easier digging and harvesting.  When using Aim EC as a harvest aid, include either a NIS (0.25% v/v) or COC (1% v/v).

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Keys to Managing Palmer Amaranth (Pigweed) in 2008

1. Palmer amaranth is a unique plant that can be very difficult to control.  Palmer amaranth produces a large amount of seed (400,000 seeds/plant), grows at least 1-3” per day, and is very competitive with peanuts.
2. Determine if Palmer amaranth populations are ALS or glyphosate resistant.  Check with your County Extension Agent about the confirmation of resistance in your county or area.
3. Use one or more residual herbicides in your peanut weed management program.  For more information, refer to table listed at the end of this section (page x).
4. Make postemergence herbicide applications when weeds are small (2-4’’).
5. If possible, avoid overusing the PPO herbicides in all crops (Valor, Cobra, Ultra Blazer, Reflex, Storm, etc.)

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Fungicide Tank-Mix Concerns

In 2007, a few growers experienced tank-mix problems with the new fungicide sold under the trade name of Provost (Proline + Folicur).  In numerous field trials, Provost has provided excellent disease control and minimal crop injury when applied alone.  Most of the field problems that were observed in 2007 were related to the fact that Provost was applied in 3 and 4 way combinations with herbicides, fertilizers, and spray adjuvants.  UGA scientists do not recommend the use of any 3 or 4 way tank-mix on peanuts.  The risk for crop injury is too great with these mixes and there is no reasonable method to test all the potential combinations.  The best information available regarding the combinations of herbicides with fungicides and other chemicals can be found in the following publication:

Tank-Mixing Chemicals Applied to Peanuts:  Are the chemicals compatible?
This publication is available on-line at:

• http://www.peanut.ncsu.edu/ag653_web.pdf

Growers who wish to use Provost in their 2008 fungicide program should refer to the newest label which lists several restrictions regarding tank-mixes.

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Suggested Herbicide Programs for Managing ALS-Resistant Palmer Amaranth in Peanut. 1

1ALS-resistant Palmer amaranth is a very serious concern. An aggressive 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.

2Strongarm 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.

3Apply cracking or early postemergence treatment only if weeds have emerged.

4Cadre 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.

5Generic 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 in this situation.

6If 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 + Storm + Dual Magnum or Outlook should be applied.

7Valor, Cobra, Storm, and Ultra Blazer have the same mode of action (PPO inhibitor).  Consequently, no more than 2 applications of these herbicides should be used in a season.

8Generic 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.

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