Using Herbicides to Manage Invasive Weeds

Herbicide Development Stimulus: realized chemical environment of plant easier to manipulate than climatic, edaphic, or biotic environments in which they grow

Herbicide Classification Many Schemes Degree of response among plants: selective controls some species in presence of others non-selective controls all species

Herbicide Classification Method of application: foliar applied soil applied broadcast entire area spot restricted area band

Herbicide Classification Length of soil persistence: persistent injure follow crop normal rotation residual injure/kill germinating weeds short time 1 growing season or less long residual control several growing seasons

Herbicide Classification Chemistry/herbicide family: inorganics organics

Herbicide Classification Organics: phenoxy-, benzoic-, pyridine-, quinolinecarboxylic acids sulfonylureas, imidazolinones, triazolopyrimidine triazines, substituted ureas, uracils thiocarbamates, halogenated acids dinitroanilines, carbamates, phosphoric amides aryloxyphenoxypropionates, cyclohexanediones nitrodiphenyl ethers those with no particular family

Herbicide Classification Plant related characteristics: systemic translocates throughout plant contact no translocation mode/mechanism of action

Herbicide Classification Mode/mechanism of action: amino acid biosynthesis inhibitors Escort, Amber, Plateau, Roundup auxin-like Tordon, Curtail, 2,4-D, Vanquish/Clarity photosynthetic inhibitors Velpar, Karmex, Krovar, Spike cell division inhibitors Treflan, Prowl lipid biosynthesis inhibitors Poast, Fusilade

Herbicide Formulations Form solutions: soluble liquids Tordon, Plateau, 2,4-D amine Form emulsions: emulsifiable concentrates 2,4-D ester, Treflan

Herbicide Formulations Form suspensions (need agitation): water dispersible granules Escort, Amber flowables Sencor wettable powders Karmex, Krovar Dry solids: pellets Spike

Methods of Application Broadcast: aerial or ground low volume liquid granules or pellets Spot treatment: typically by ground high or low volume liquid Band:

Herbicide Application Rule Number 1: Read and follow the label directions!! Rule Number 2: see Rule Number 1

Factors Influencing Herbicide Performance Plant factors: Weed ID Weed phenology/physiological status life cycle monocot v dicot location of meristems growth stage cuticle leaf number, shape, orientation, & pubescence metabolism Competition from desirable plants

Factors Influencing Herbicide Performance Herbicide factors: formulation volatility absorption dose placement retention use of adjuvant

Factors Influencing Herbicide Performance Climate: precipitation & relative humidity temperature wind light

Factors Influencing Herbicide Performance Edaphic (soil) factors: adsorption, degradation, leaching, volatility, availability for absorption texture organic matter pH moisture temperature

Factors Influencing Herbicide Performance Other factors: topography application efficiency sprayer calibration knowledge of operator Water Use clean water

Commonly Used Herbicides Rangeland & Non-crop

2,4-D - Many Trade Names Auxin-like, systemic, selective ester and amine formulations Short residual in soil average half-life 10 days Broadleaf herbicide many annual broadleaf weeds notably weak on kochia often tank-mixed High volatility

Dicamba - Vanquish/Clarity/Overdrive Auxin-like, systemic, selective Relatively short soil residual < 14 days good conditions metabolism low to medium leaching potential, weakly adsorbed Broadleaf herbicide many annuals, biennials, perennials thistles and knapweeds weak on toadflaxes & Russian knapweed Don’t use near water or trees/shrubs buffalograss sensitive to injury

Picloram - Tordon 22K, Picloram 22K Auxin-like, systemic, selective Residual herbicide average half-life 90 days high leach potential, weakly adsorbed Broadleaf herbicide thistles, knapweeds, leafy spurge, houndstongue, toadflaxes, bindweed, locoweed, larkspur, lupines … Grazon P+D is picloram + 2,4-D very weak kochia & some mustards Don’t use near water, trees/shrubs smoothbrome sensitive to injury

Aminopyralid Milestone, Milestone VM, Forefront R&P Auxin-like, systemic, selective Short residual average half-life 34.5 days in North America Lab studies show potential movement; limited movement in field Broadleaf herbicide - odd spectrum thistles, knapweeds, hawkweeds, oxeye daisy, dandelion, absinth wormwood … Forefront R&P is aminopyralid + 2,4-D Can spray to water’s edge Half-life in water 0.6 days Safe around some trees/shrubs

Clopyralid Transline, Clopyralid 3 Auxin-like, systemic, selective Short residual average half-life 40 days moderate leaching, weakly adsorbed Broadleaf herbicide - odd spectrum thistles, knapweeds, hawkweeds, oxeye daisy, dandelion, locoweeds … Curtail is clopyralid + 2,4-D only control emerged weeds Don’t use around water Safe around trees/shrubs

Metsulfuron – Escort/MSM 60/Cimarron Plus; Amino acid biosynthesis inhibitor systemic, selective Moderate residual typical half-life 30 days persistence increases with soil pH Broadleaf herbicide perennial mustards, biennial thistles, arrowgrass, locoweed, halogeton, houndstongue, camelthorn, African rue … weak on toadflaxes, Canada thistle, diffuse knapweed must use a surfactant!!

Chlorsulfuron – Telar/Chlorsulfuron 75 Cimarron Plus Amino acid biosynthesis inhibitor systemic, selective Residual average half-life 40 days persistence increases with soil pH Broadleaf herbicide perennial mustards, Russian knapweed, Canada thistle RK, CT high rates and fall best must use surfactant!! Fall applications more injurious to some grass species

Imazapic Plateau, Panoramic Amino acid biosynthesis inhibitor systemic, selective Residual most “imis” persistent e.g. imazapyr 1-4 months Broadleaf and grass leafy spurge, bindweed, houndstongue, cheatgrass, foxtail barley … must use methylated seed oil!! Cool-season grass injury fall applications for leafy spurge

Glyphosate - Roundup, Campaign, Rodeo, Aquamaster Amino acid biosynthesis inhibitor systemic, non-selective Campaign is glyphosate + 2,4-D Rodeo is aquatic formulation Moderate persistence average half-life 47 days strongly adsorbed, no soil activity Broadleaf and grass many annuals, biennials, perennials Campaign good control perennial pepperweed

Aminocyclopyrachlor Perspective, Method Perspective - noncrop Telar + aminocylopyrachlor Method - noncrop aminocyclpyrachlor Amino-acid biosynthesis inhibitor + Auxin-like; systemic, selective Short to long residual Aminocylcopyrachlor half-life range 5-164 days in North America Lab studies show potential movement; limited movement in field Broadleaf herbicide - odd spectrum thistles, knapweeds, leafy spurge, mustards (Telar) …