Overview. Effects of Phenoxy Herbicides on Landscape Trees & Shrubs. Familiar Brands. Phenoxy Chemical Class. Phenoxy Herbicide fate

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1 Overview Effects of Phenoxy Herbicides on Landscape Trees & Shrubs By: Paul J. Pugliese, MPPPM UGA Extension Coordinator Bartow County Phenoxy Herbicide Class and MOA Fate of herbicides in soil How to read Herbicide Labels Case study real world examples Who s to blame? How to protect your business Integrated Weed Management Phenoxy Chemical Class Mode of action: Acts as a plant growth regulator (synthetic auxin hormone) Uncontrolled cell division and growth Selectively kills broadleaf weeds (trees & shrubs) Used in lawns & pasture forage grasses (low toxicity) Phenoxy Acids: 2,4 D; 2,4 DP; MCPA; MCPP Benzoic Acids: Dicamba Carboxylic Acids (Pyridinoxy): Picloram, Clopyralid, Triclopyr, Aminopyralid, Fluroxypyr Often combined chemical formulations Familiar Brands Three Way and Triplet (2,4 D + MCPP + dicamba) Escalade (2,4 D + fluroxypyr + dicamba) Spotlight Phenoxy Herbicide fate in soil Break down in warm, moist soil from microbial action and photodegradation within 3 6 months During cool or dry conditions, can persist in soil for several months; high leachability Surface applications usually do not penetrate more than 1 inch into clay soils Irrigation can wash into mulched areas If applied to very dry soils, may be washed into soil cracks by rain or irrigation Phenoxy Herbicide fate Many broadleaf herbicides contain combinations of pheonxy chemicals in the amine salt form: Makes them less volatile More soluble and more soil mobile Label usually warns against: spraying solution near desirable plants spraying the root zone of trees and shrubs exceeding the recommended rate within drip lines 1

2 Herbicide Damage Symptoms 2,4 D: Twisting of the leaf petiole (epinasty), turning or curling the leaf upside down Downward cupping of leaves Narrow strap like leaves on youngest growth May resemble injury from certain sap feeding insects, but petiole wouldn t be twisted. Certain virus diseases may also look similar Phenoxy Herbicide Injury Phenoxy Herbicide Injury Oak Herbicide Damage Symptoms Dicamba: Leaf curling and twisting Parallel leaf venation Leaves tend to cup upward rather than downward Proliferation of short shoots (witch s broom) Swelling of shoots Abnormal elongation of leaf margins Phenoxy Herbicide Injury 2

3 Triclopyr Injury Poplar Herbicide Injury Diagnosis Soil Testing for phenoxy herbicide group ($100) Plant tissue analysis for phenoxy herbicide group ($100) Field Diagnostics: Timing of injury within a few days or weeks of application(s): May see a delayed effect with newly planted trees/shrubs until roots reach treated areas. Likely find adjacent plants with similar symptoms: Look for injury on two or more species Location of injured plants to areas treated Areas of Concern Dripline of a tree s canopy is highest risk: Older, established trees have a more extensive root zone as much as 2 to 3 times canopy width. Research shows absorption roots may extend more than 2 times tree height More than 50% of tree roots extend beyond the dripline Grass clippings? Compost? Hay? Manure? Sensitive tree species: Boxelder, birch, catalpa, honeylocust, apple (crabapple), spruce, poplar, oaks, lilacs Case Study: Typical Spray Schedule for Commercial Lawn Care? Pictures taken in May 2011 Development about 5 years old 40 oz. = 2.5 pints per acre 2.5 pints x 4 apps. = 10 pints in 7 months + spot treatment 10 pints = 1.25 gal. x 2.38 lbs. ae/gal. = 3 lbs. ae/acre 3

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5 Lab Results of Phenoxyherbicide Residue Foliage Sample The lowest residue of 2,4 D that will produce symptoms in susceptible tree species is 0.02ppm Plant Recovery from Phenoxy Damage Depends on overall health and vigor of plants Plants may recover from low doses with time If lethal doses are absorbed, may persist in plants (and symptoms appear) for the next two or three seasons. Exposure early in the growing season will be more severe (herbicide moves upward) than later in the year. Plant Recovery from Phenoxy Damage Irrigation can help leach herbicides and avoid drought stress Don t fertilize for one season after injury Delay pruning for one year to fully assess injury Activated charcoal only helps tie up residues, but must be applied before damage occurs. Remove trees that don t improve within 1 year Test soil for residual herbicides before replanting Who s to blame? Landscape designer? Herbicide manufacturer/epa vague labels? Local tree ordinances landscaping mandates? Home Owner s Association expectations? Turfgrass manager/herbicide applicator? 5

6 Tips for Avoiding Damage Do not apply broadleaf herbicides during hot, windy conditions. Avoid spraying near mulched trees and shrubs Do not spray before heavy rainfall is expected Don t exceed labeled rate or application frequency Rotate chemical classes (less dependent on phenoxy) Carefully consider herbicides appropriate for site use Avoid broadcast spraying during spring Herbicide Modes of Action (Group 4 = Synthetic auxin) 1 ACCase inhibition 2 ALS or AHAS inhibition 3 Inhibit Microtubule Structure and Function 4 Synthetic auxin 5 Photosystem II inhibition (different binding site than Groups 6 and 7) 6 Photosystem II inhibition (different binding site than Groups 5 and 7) 7 Photosystem II inhibition (different binding site than Groups 5 and 6) 8 Fatty Acid and Lipid Biosynthesis Inhibitors 9 ESP synthase inhibition 10 Glutamine synthase inhibition 11 Carotenoid Biosynthesis Inhibitors 12 Carotenoid Biosynthesis Inhibitors 13 Carotenoid Biosynthesis Inhibitors 14 PPO inhibition 15 Inhibit Very Long Chain Fatty Acid (VLCFA) Synthesis 16 Fatty Acid and Lipid Biosynthesis Inhibitors 17 Potential Nucleic Acid Inhibitors or Non Descript Mode of Action 18 Dihydropteroate Synthetase Inhibitors 19 Auxin transport inhibition 20 Cellulose Inhibitors 21 Cellulose Inhibitors 22 Photosystem I Inhibitors 23 Inhibit Cell Division and Microtubule Organization and Polymerization 24 Oxidative Phosphorylation Uncouplers 25 Potential Nucleic Acid Inhibitors or Non Descript Mode of Action 26 Potential Nucleic Acid Inhibitors or Non Descript Mode of Action 27 Carotenoid Biosynthesis Inhibitors 28 Cellulose Inhibitors or Potential Nucleic Acid Inhibitors or Non Descript Mode of Action Note: This table was originally prepared by Dr. Alan York, North Carolina State University and was updated by Drs. Eric Prostko, Stanley Culpepper, Tim Murphy, and Patrick McCullough, The University of Georgia, October Broadleaf Weed Herbicides (Check labels for turf species) Common Name Trade Name (Examples) 2,4-D (Various) bentazon Basagran chlorsulfuron Corsair clopyralid Lontrel dicamba Vanquish fluroxypyr Spotlight MCPP Mecoprop metsulfuron Blade, Escort, or Manor sulfentrazone Dismiss triclopyr Turflon trifloxysulfuron Monument Herbicide Combination Products Common Names Trade Name (Examples) 2,4-D + dicamba + MCPP Trimec Classic 2,4-D + dicamba + MCPP + Trimec Plus MSMA 2,4-D + triclopyr Chaser carfentrazone + 2,4-D + Speed Zone dicamba + MCPP carfentrazone + dicamba + Power Zone MCPP + MCPA clopyralid + triclopyr Confront clopyralid + 2,4-D + dicamba Millennium Ultra Bookmark Now! 6

7 Tips for Avoiding Damage Integrated Weed Management: Rely more on timely pre emergent apps. Rotate to avoid resistant weeds Identify weeds and spray more selectively Keep turfgrass thick and healthy to avoid weeds Spot spray rather than broadcast spray Read and follow herbicide labels very closely! Keep detailed records of herbicide applications Train your employees! Calibrate sprayers! Books for Weed ID $14 Call UGA Office of Communications to order books at or online at Download Apps Today! References