Managing Weeds in Oregon Mint

Production

Andy Hulting541-737-5098

andrew.hulting@oregonstate.edu

Dept. of Crop and Soil ScienceOSU

Corvallis

Afternoon Outline

• Review importance of weed management in mint

• Update on several OSU research trials– Results and proposed future work

• summer annual broadleaf control• evaluate herbicides that may have a fit in mint production

• OSU Extension Resources-websites and publications

• Discussion on environmental fate of herbicides

• Specific questions ?– We value your input on current/future weed management needs

Peppermint Yield

• Weeds reduce peppermint biomass through competition for resources

– sunlight, water and nutrients

• Weeds may reduce the life of the stand

– problem perennial weed species

Weeds Impact Peppermint Yield

Adapted from Schmitt (1996)

Peppermint Oil Quality

• Weeds present at harvest impact oil quality– undesirable odor (organoleptic quality) and

color– may reduce commercial value of oil

• Broadleaf weeds reduce oil quality more than grass weeds– often more difficult to manage

Weed Species Impact Quality

Adapted from Schmitt (1996)

Weed Management• Management of both grass and broadleaf weed

species critical to maintain yield and quality

• Costs must be weighed against potential gains in yield and quality

– Some species warrant greater efforts than others

• groundsel, pigweed spp., marestail, wild garlic, wild onion, prickly lettuce

• species of greatest importance vary be region

Historical OSU Weed Science Focus• Optimize labeled uses and develop new chemical control

uses in mint that benefit mint growers– new and older herbicide products– explore rates and timings– document weed control spectrum and crop safety– summer annual broadleaf management a recent priority

• pyroxasulfone (Zidua and other trade names TBD)• carfentrazone (Aim or Shark)• MCPB (Thistrol) tank mix options• others

– not all these treatments are currently registered for use in mint– see PNW Weed Management Handbook for currently registered

treatments

Broadleaf Weed Control in Established Mint

MCPB-Based Tank MixesCrop Safety

Yield

GroundselRating Type % Control Fresh wt Oil yieldRating Date 6/15/2011 6/27/2011 6/27/2011 8/17/2011 8/29/2011Treatment Rate Appl. lb/ 2 yd2 lb/A

lb ai/A codecheck 0 0 0 17 69MCPB 0.375 A 1 6 13 17 68MCPB + 0.375 A 1 9 5 16 65  terbicil 0.8MCPB + 0.375 A 3 6 38 18 81  bromoxynil 0.25MCPB + 0.375 A 33 33 5 14 63  carfentrazone 0.015MCPB + 0.375 A 1 8 43 17 81  bentazon 0.75MCPB + 0.375 A 20 33 85 17 67  fluroxypyr‐florasulam 0.092bentazon 0.75 A 3 1 38 17 81bentazon + 0.75 A 3 1 43 16 75  terbacilbentazon + 0.75 A 4 3 95 16 78  bromoxynil 0.25bentazon + 0.75 A 40 35 5 15 76  carfentrazone 0.25fluroxypyr‐florasulam 0.092 A 20 30 80 14 60LSD (P=0.05) NS NSCV 11.51 16.42

‐‐‐‐‐‐‐% Injury‐‐‐‐‐‐‐Peppermint

A ‐ Applied 6‐8‐2011, 14‐18 inch peppermint 

Peppermint

Untreated Control

Buctril + Basagran

Thistrol + Aim

Thistrol + Starane Flex

Broadleaf Weed Control with Peppermint HerbicidesHerbicide Evaluation in a Non Crop Study-Problem Summer

Annuals

plot area over-seeded with broadleaf weeds

Pigweed Control With Postemergence Peppermint Herbicides, Corvallis, Oregon, 2011

Sharp.Fluvellin RR Pigweed Powell Amaranth

-------------------------------------------------% Control-------------------------------

Rating Date Rate Appl. 8/5/2011 8/5/2011 8/19/2011 8/5/2011 8/19/2011

Treatment lb ai/A code

check 0 0 0 0 0

MCPB 0.25 A 17 33 43 33 43

carfentrazone 0.012 A 20 43 47 63 60

MCPB + carfentrazone

0.25 +0.012 A 47 57 63 77 80

bentazon + 0.5 A 37 33 27 33 23

carfentrazone 0.012

A - Applied 7-29-2011 to 4 leaf Redroot Pigweed and 6 inch Powell Amaranth

Broadleaf Weed Control in Established Mint

Evaluation of CarfentrazoneCrop Safety

Yield

Rating Type InjuryRating Date 5/2/2011 5/31/2011 6/27/2011Treatment Rate Appl.

lb ai/A codecheck 0 0 0carfentrazone 0.015 A 0 0 0carfentrazone 0.015 B 5 0 3carfentrazone 0.015 C 12.5 10 4carfentrazone 0.015 D 0 30 10carfentrazone 0.015 E 0 0 15

C ‐ Applied 4‐19‐2011, 4 inch peppermintD ‐ Applied 5‐19‐2011, 8 inch peppermintE ‐ Applied 6‐16‐2011, 18 inch peppermint

‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐%‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

Peppermint

A ‐ Applied  2‐2‐2011, dormant peppermintB ‐ Applied 3‐22‐2011, 1/4 ‐1/2 inch peppermint  

Rating Type Injury Fresh wt Oil YieldRating Date 5/2/2011 5/31/2011 6/27/2011 8/17/2011 8/29/2011Treatment Rate Appl. lb/2 yd2 lb/A

lb ai/A codecheck 0 0 0 12.5 52.2carfentrazone 0.015 A 0 0 0 13 44.4carfentrazone 0.015 B 10 0 0 13.4 51.6carfentrazone 0.015 C 12.5 7.5 0 13.5 55.5carfentrazone 0.015 D 0 30 5 12.4 55.7carfentrazone 0.015 E 0 0 30 11 47.2LSD (P=0.05) NS NSCV 16 21

E ‐ Applied 6‐16‐2011, 18 inch peppermint

A ‐ Applied  2‐2‐2011, dormant peppermintB ‐ Applied 3‐22‐2011, 1/4 ‐1/2 inch peppermint  

‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐%‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐

Peppermint

C ‐ Applied 4‐19‐2011, 4 inch peppermintD ‐ Applied 5‐19‐2011, 8 inch peppermint

10 days-2 weeks following 1 oz/A Aim EC

~ 1 month following 1 oz/A Aim EC

Broadleaf and Grass Weed Control in Dormant Established

MintPyroxasulfone

pyroxasulfone• Preemergence herbicide developed by Kumiai

– Marketed by several companies• BASF-Zidua• Valent and FMC also have pyroxasulfone products in the pipeline

• Effective on grass and broadleaf weeds in many crops– OSU working with it in mint, grass seed and winter wheat

• > 90 % pigweed control in our 2010 study– May application

• 2011 timing study– Feb –March application dates– No visual mint injury– 2012 studies will include more timings and oil yield measurements

• double cut systems• tank mixes with carfentrazone?

Untreated Check

Zidua 0.184 lb ai/A (2X rate?)

Axiom 0.42 lb ai/A

Herbicide Evaluation Summary• Pyroxasulfone has the potential to be a mint

herbicide– good crop safety-dormant and double cut– effective on a wide range of grass and broadleaf

species

• Carfentrazone (Aim or Shark) use patterns– will injure mint at late POST timings, but mint recovers– earlier timings/replacement for paraquat?– small weed size is critical, will improve pigweed

control • tank mixes with MCPB (Thistrol) look promising

OSU Extension Resources• 2012 PNW Weed Handbook

– Mint Chapter– http://pnwhandbooks.org/weed/

• EM 8774 Weed Management in Mint– weed ID poster and mint herbicide application rates– call or email me if you want a copy/copies

• Annual reports at OSU Research Stations

Dec. 2010

Thoughts on herbicide persistence…• What is herbicide persistence?

Context of the farming/cropping system Must have something to do with the herbicide appliedMust have something to do with soil environment

• Why is it an important production consideration?

Maximize economic return from weed managementMinimize risk to rotational crops

Understand carryover symptomologyMinimize unintended consequences of herbicide use

Movement offsiteSelection pressure

• Define herbicide persistence

• General factors that influence herbicide persistence

• Talk through some considerations for common herbicides

Thoughts on herbicide persistence…

What is herbicide persistence• Herbicides are applied for specific reasons at specific times

• Ideally, they do their job and then dissipate– Expressed in terms of herbicide half-life (days, weeks,

years)

• Often times and for a variety or reasons herbicides can persist in the environment

• Plantback restrictions, minimum recrop intervals and herbicide carryover issues become important

Factors influencing persistence…

Factors influencing persistence…• Chemical characteristics determine

behavior in soils– Acidic or basic nature of the compound– Water solubility– Volatility

• Soil Characteristics– Texture– Organic matter content– pH– Soil temp, topography, water holding capacity

Factors influencing persistence…• Chemical characteristics determine behavior in soils

– Acidic or basic nature of the compound• In general, similar pH between soil/water and the

compound = tightly bound (little leaching, less available for uptake, degradation)

• Dissimilar pH between soil/water and the compound = less tightly bound (subject to leaching, more available for uptake, degradation)

– Water solubility• How readily the herbicide dissolves in water

– Volatility• Tendency of the herbicide molecule to become a vapor

Factors influencing persistence…• Soil Characteristics

– Texture• Soil particle distribution plays an important role in

herbicide adsorption

• clay > silt > sand

– Organic matter content• Higher organic matter soils have more reactive sites for

herbicide adsorption

Factors influencing persistence…• Soil Characteristics

– pH• affects the way herbicides bind to the soil particles

• can affect chemical degradation pathways (process and rate)

– Soil temp, topography, water holding capacity• influences microbial degradation• a major mechanism for herbicide dissipation in soils• warm, adequate soil moisture, high organic matter =

high degradation

Summary of some factors…

Synthetic Auxins-Group 4Mode of Action– These herbicides disrupt hormone balance andprotein synthesis in plants, leading to a variety ofplant growth abnormalities

Chemical Families– Phenoxy Acetic Acids: 2,4-D, 2,4-DB (Thistrol), MCP– Benzoic Acids: dicamba (Banvel/Clarity)– Pyridines: aminopyralid (Milestone), fluroxypyr (Starane),

picloram (Tordon), clopyralid (Stinger), triclopyr (Garlon)

High acidity, maximum soil adsorption under acidic conditions, tightly bound to OM, mostly limited to moderate persistence except for Milestone, Tordon, Garlon and Stinger, microbial breakdown is major degradation pathway

Amino Acid Synthesis Inhibitors-Group 2 ALS Inhibitors

Mode of Action– Inhibit a specific enzyme (single site) which prevents production of

essential amino acids

Chemical Families

– Imidazolinones: imazethapyr (Pursuit), imazamox (Beyond)

highly acidic, maximum soil adsorption under acidic conditions, persistence ranges from short to long, microbial dissipation

– Sulfonylureas: mesosulfuron (Osprey), nicosulfuron (Accent), primisulfuron (Beacon), thifensulfuron + tribenuron (Harmony/Affinity), halosulfuron (Sandea), chlorsulfuron (Glean/Telar), sulfosulfuron (Maverick)

retention directly related to soil organic matter, persistence ranges from short to long, both chemical and microbial degradation important, more persistent under basic soil conditions

Lipid Synthesis Inhibitors – Group 1Mode of Action– Prevents the formation of fatty acids, which areessential for the production of lipids. Lipids arevital in the integrity of cell membranes and thusnew plant growth

Chemical Families– Cyclohexanediones: clethodim (Select Max), sethoxydim (Poast)

– Aryloxyphenoxypropionates: quizalifop (Assure II), fenoxaprop (Puma/Tacoma)

– Phenylpyrazolines: pinoxaden (Axial XL)

Generally no persistence issues

Mobile Photosynthetic Inhibitors-Group 5

Mode of Action– These herbicides block the photosyntheticprocess, thereby preventing the conversion ofsunlight into chemical energy

Translocation– Moved upward from roots via xylem, uptake byroots, shoots, and leaves– No movement out of leaves

Chemical Families– Triazines: atrazine (various), metribuzin (Metri/Sencor)– Uracils: terbacil (Sinbar)

low solubility, very low volatility, high pH soils =low binding=increased potential for crop injury and leachinghowever, degradation generally faster under acidic soil conditions and is primarily through chemical means

Non-Mobile Photosynthetic Inhibitors-Group 6

– Foliar applied, so uptake by leaves– No soil activity– No translocation, but some redistribution within leaf– For these reasons, sometimes called “contact herbicides”

Chemical Families– Benzothiadiazoles: bentazon (Basagran)– Nitriles: bromoxynil (Buctril)

No persistence issues

Cell Membrane Disrupters-Groups 14 and 22

Mode of Action– These herbicides disrupt cell membranes

Chemical Families– Bipyridyliums: paraquat (Gramoxone Inteon/Firestorm), diquat (Reglone)

tightly bound to OM and clay, highly persistent-but plant unavailable-same can be said for glyphosate (but different MOA-Group 9)

– Diphenylethers: oxyfluorfen (Goal)– N-phenylphthalimides: flumioxazin (Chateau/Valor/Payload)– Aryltriazolinones: carfentrazone-ethyl (Aim), sulfentrazone (Spartan) – Pyrimidinedione: saflufenacil (Sharpen Powered by Kixor)

Rates of soil-applied products determined by soil type and OM contentStrongly absorbed to soil and organic matterSoil half lives (in general): sulfentrazone>oxyfluorfen > flumioxazinPlant back restrictions vary by herbicide and rotational crop

Summary• Potential for herbicide persistence

depends on complex interactions– chemistry of herbicide applied– cropping system context-soils, crops, etc– the environment

• Some herbicide families are more likely to exhibit persistence than others

• Some crops are more sensitive than others

Discussion

• Know your cropping systems, know your soils, have a basic understanding of herbicide chemistry, review labels

• Match the correct herbicide to its intended site/use

• Questions ?

Helpful References

http://extension.oregonstate.edu/ catalog

Google: “PNW 437”

Acknowledgements

• OSU Weed Research Group

– Barbara Hinds-Cook, Dan Curtis, Kyle Roerig and Bill Brewster

• Oregon Mint Commission

• Industry Partners and Field Personnel

• Cooperating Growers