Using Herbicides Safely Around Woody Plants Off-site Movement of Herbicides 2013 Washington State Weed Conference By: Paula Dinius, Urban Horticulturist WSU Chelan County Extension

Fate of Herbicides after Application Image source:

Using Herbicides Around Trees & Shrubs Mechanisms of Off-site Herbicide Movement Symptoms of Herbicide Injury Case Studies

Using Herbicides Around Trees & Shrubs Plant injury is usually caused by not following label directions. ◦Using around sensitive plants ◦Improper rate or method of application ◦Spraying during adverse weather conditions ◦Over/under irrigation

Using Herbicides Around Trees &Shrubs Off-site movement is when any herbicide misses or moves from the intended treatment area.

Mechanisms of Off-Site Movement Movement via air ◦Volatilization - vapor ◦Drift – droplet and granule dust Movement via soil water ◦Leaching ◦Run-off

Off-site Movement ~ Volatilization High temperatures + low humidity = gas (vapor) Fumes travel for long distances Herbicide can volatilize right off plant or soil Dependent on molecular weight of herbicide

Off-Site Movement Drift ~ Droplet Droplet drift is affected by Weather conditions ◦Wind speed and direction ◦Temperature and humidity Droplet size ◦Nozzle type, size & height ◦Spray pressure Carrier ◦Type and volume

Influence of Droplet Size on Potential Distance of Drift Droplet Diameter (Microns) Type of Droplet Time Required to Fall 10 ft. Lateral Distance Droplets Travel Falling 10 ft. in 3 mph winds 5Fog 66 min. 3 miles 20 Very fine spray 4.2 min. 1,100 ft. 100 Fine spray 10 sec. 44 ft. 240 Medium spray 6 sec. 28 ft. 400 Coarse spray 2 sec. 8.5 ft. 1,000 Fine rain 1 sec. 4.7 ft. Source - University of North Dakota

Off-site Movement Drift ~ Dust/Granular Dust and Granular Formulations ◦Dust can drift farther and for longer duration than liquid. ◦Granular have less drift potential due to pellet size/weight. Image source:

Wind Speed Indicators Drift Potential Field ObservationProbable Wind Speed (mph) Smoke rises, air motionless0 Smoke drifts, air rises1-3 Leaves quietly rustle4-7 Leaves and twigs move8-12 Branches move13-18 Small trees sway19-24 Large branches move25-31 Whole trees move32-38 Source: Herbicide Application Handbook Monsanto

Chronic Exposure to Phenoxy Herbicide Drift (Dicamba, 2,4-D, MCPP, etc.) Buffer Strip

Off-Site Movement ~ Soil Water Leaching ◦Vertical Run-off ◦Horizontal

Off-site Movement ~ Leaching & Run-off Rainfall or irrigation water can move herbicides down through or off the soil. Potential depends on: ◦Solubility of herbicide ◦Adsorption to soil particles ◦Persistence of herbicide ◦Soil texture and structure ◦Amount and frequency of rainfall/irrigation

Herbicide Movement in Soil Herbicide Characteristics ◦Solubility: Highly soluble herbicides are more likely to run-off or leach Image source:

Herbicide Water Solubility PesticideSolubility (mg/l) Dichlobenil (Casoron) 21.2 Benefin (Balan) 0.1 Glyphosate (Round-up) 900,000 2,4 - D dimethyamine 796,000 Pendimethalin (Prowl) Dicamba salt (Banvel) 400,000 Oryzalin (Surflan) 0.7 Trifluralin (Treflan) 0.3 Isoxaben (Gallery) 1.0 Picloram (Tordon) 200,000 Source: OSU Extension Pesticide Properties Database No endorsement of products intended, used for example purpose only.

Herbicide Movement in Soil Herbicide Characteristics Absorbency – vegetation uptake Adsorbency – binding of a chemical to soil particles

Herbicide Movement in Soil Herbicide Characteristics ◦Persistence = resistance to breakdown in soil. (Half-life of herbicide in the soil)  Degradation occurs mainly in O & A Horizon  Factors influencing degradation : ◦ Microbes ◦ Soil chemical reactions ◦ Sunlight/temperature Image source:

Persistence in Soil ChemicalHalf-life in MonthsHalf-life in Days Dicamba (Banvel)2 – Dichlobenil (Casoron)4 – Glyphosate (Roundup)130 Pendimethalin (Prowl)3 – Picloram (Tordon) Trifluralin (Treflan) ,4-D (Weedar 64)130 Oryzalin (Surflan)<120 Benefin (Balan)1.540 Isoxaben (Gallery) Source: No endorsement of products intended, used for example purpose only.

Herbicide Movement in Soil Herbicide Movement in Soil Soil Profile Herbicide Characteristics (Ad)Sorption Coefficient:

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Herbicide Movement in Soil Soil Characteristics Soil texture:  Sandy soils much more prone to leaching.  Compacted clay soils are prone to runoff.  Well aggregated loamy soils reduce herbicide movement. Image source:

Herbicide Movement in Soil Soil Characteristics Organic matter: Soils high in OM have:  Increased microbial activity  Greater water holding capacity  Greater adsorption capacity Image source: &

Herbicide Movement in Soil Site Characteristics Slope: Greater the slope, greater potential of herbicide movement

Awareness of Root Systems

Herbicide Movement in Soil National Pesticide Information Center ◦OSU Extension Pesticide Properties Database ◦Based on Solubility, Koc, and Half-life ◦Pesticide Movement Rating  Very high – Very low

National Pesticide Information Center ◦Pesticide Movement Rating ◦ Pendimethalin (Prowl) = Very low ◦ Dichlobenil (Casoron) = Moderate ◦ Oryzalin (Surflan) = Low ◦ 2,4 –D amine (Weedar 64) = Moderate ◦ Isoxaben (Gallery) = Low ◦ Dicamba (Banvel) = Very high ◦ Picloram (Tordon) = Very high ◦ Glyphosate (Roundup) = Extremely low ◦ Benefin (Balan) = Extremely low Herbicide Movement in Soil Source

Herbicide Injury Symptoms

Seedling Growth Inhibitor Herbicides Root & Shoot ~ Stunting & Distortion Newly planted woody plants ◦Root tips enlarge into rounded structures and shoots can swell and be stunted. Established woody plants ◦Stems enlarge and become brittle ean/ ean/documents/herbicideinjury_05.pdf

Seedling Growth Inhibitor Herbicides Root & Shoot Inhibitors ◦Benefin – Balan ◦Pendimethalin – Pendulum, Prowl ◦Trifluralin – Treflan ◦Oryzalin – Surflan ◦Isoxaben – Gallery ◦Prodiamine – Barricade Trifluralin damage to spruce

Growth Regulator Herbicides Malformed or Distorted ~ Leaves or Shoots Systemic herbicides Symptoms usually on new growth Leaf cupping, twisting or strapping of leaves, splitting or cracking of bark Prone to drift and can move with leading edge of soil water. Dicamba damage on Linden

Growth Regulator Herbicides 2,4-D, MCPP, MCPA Dicamba Triclopyr, picloram, clopyralid Dicamba/2,4-D Damage on Pin Oak

Phenoxy Damage on Conifers Phenoxy Damage on Conifers 2,4-D damage to pine & fir Invasive.org, Minnesota Department of Natural Resources ArchiveInvasive.org, Minnesota Department of Natural Resources Archive,

Phenoxy Growth Regulator Herbicide ◦Irregular contours herbicide damage on honey locust trunk (2,4-D, Dicamba, MCPP, etc.)

Herbicide Injury Symptoms Leaf Chlorosis or Necrosis Inhibition of photosynthesis causes various patterns of chlorosis. Pre-emergence systemic herbicides absorbed by roots translocated to leaves. Post emergent systemic Symptoms more severe on side of herbicide placement. Glyphosate damage

Leaf Chlorosis or Necrosis Herbicide At high rates, necrosis can occur without chlorosis. Symptoms may persist for more than a year. Symptoms may be confused with salt burn, drought, or freeze damage. Picloram damage to maple

Diuron = Karmex Diruon + bromacil = Krovar Imazapyr = Arsenal Diquat and paraquat = Ortho Diquat, Reward Oxyfluorfen = Goal Paraquat Damage on Pecan; Krovar damage on Zelkova Leaf Chlorosis or Necrosis Herbicides

Distorted Growth and Chlorosis Glyphosate damage (sublethal dose) ◦Chlorosis to necrosis ◦Shortened internodes ◦Stunted growth ◦Witches broom effect ◦Loss of apical dominance ◦Branch dieback Glyphosate Damage on Rose

Case Studies Dichlobenil Picloram Trifluralin

Dichlobenil (Casoron) and the Flowering Cherry Trees

Flowering Cherry Tree Casoron Damage

Picloram and the Curb Cleaner

Trifluralin and the Conifer Conundrum

Summary Always Thoroughly Read & Follow All Pesticide Label Directions Study present & future weather conditions ◦Temperature ◦Wind speed & direction ◦Humidity ◦Rainfall Study plants found in surrounding area ◦Identify species ◦Tree and shrub root zone area ◦Slope Choose herbicide to fit site conditions with considerations of potential movement

Sources Washington State University Turf & Ornamental Weed Management Principles. MISC0170 Washington & Oregon State University & University of Idaho Pacific Northwest Weed Management Handbook. Starbuck, Chris Turfgrass Research & Information Report. University of Missouri-Columbia Turfgrass Research. Cornell University Dicamba (Banvel) Herbicide Profile 10/ Dexter A.G Herbicide Spray Drift A-657 (Revised). North Dakota State University & University of Minnesota Ohio State University. Newsletter. Do “Drift Retardant” Chemicals Really Work? C.O.R.N – html#linkg 15.html#linkg Costello, Perry, Matheny, Henry, & Geisel University of California. Abiotic Disorders of Landscape Plants A diagnostic Guide. Publ Sinclair, Lyon. & Johnson Cornell University. Diseases of Trees and Shrubs Voge, Derle, and Jenkins Oregon State University Extension. OSU Extension Pesticide properties Database. National Pesticide Information Center.