Published March 1974. Please look for up-to-date information in the OSU Extension Catalog: http://extension.oregonstate.edu/catalo

Oregon State University. Extension Service

University of Idaho. Agricultural Extension Service

Washington State University. Extension Service

Undetermined

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630.71Cr3 78pno.1C8c .3DOCUMECOLLECTIOREGOIOLLECTI'son Oak anLyTRARYDocrm ri ecliOflPOISON OAK - Rims diversiloba - Showingbranch with leaflets, individual leaf, maleflowers, top, and female flowers, center.PNW 108 March 1974Poison Oak and IvyPoison oak (Rhus diversiloba) isfound in open woods, hill pastures, cut-over forest lands, and rocky banks inmost western Oregon and Washingtoncounties, extending southward into Cali-fornia. Its near relative, poison ivy(Rhus toxicodendron), is common in drywoods and thickets in eastern Washing-ton and Oregon, and throughout Idahoand eastward. The two are similar intheir general appearance, growth habits,and effect on humans.This bulletin deals with poison oak,but since control measures for poisonivy are the same, it is applicable forboth plants.DescriptionPoison oak will not stand cultivation.It has some value as a browse plant forlivestock, especially goats and sheep,and is a source of good-quality honey.Its brilliantly colored fall foliage at-tracts, often to their sorrow, an annualnew group of children, city people, ornewcomers, who gather it for house dec-oration.The shrub grows from 3 to 10 feet tall,erect, thick, and woody, or may grow asa vine and twine around trees. It re-produces both by seed and rootstocks.It often has aerial rootlets that adhereto the trunks of trees. Leaflets are from1/2 to nearly 2 inches long, produced3 in a group on a common stem. Theleaflets somewhat resemble oak or ivyleaves. The leaf surface is glossy andmay have a blistered appearance. Flowergroups are about 1/4 inch across, green-ish-white, borne in clusters, on a slenderstem. The fruits are berry-like, glossy,and dry when ripe, with a striped stoneinside the papery shell.The entire plant contains at all sea-sons an oily substance extremely poi-sonous to some people, causing painfulirritation of the skin that appears sev-eral hours after contact. Humans varyfrom extreme susceptibility to near im-munity. A few cases have been reportedwhere the poison covered such largeareas of the body that death resulted.This is rare, but doctors should be con-sulted in all extreme cases. To causepoisoning, the skin usually must comeinto direct contact with the oil, eitherby touching the plant or by touchingsomething that has touched it, such asclothing, gloves, livestock, or firewood.However, the smoke from poison oakwood fires often poisons persons whothink they are immune.After exposure to poison oak, thehands and arms should be thoroughlywashed with strong soap and hot water.The soap should contain an excess oflye. A solution of water and alcohol inequal proportions will dissolve the poi-son, but the solution must be used lib-erally. Numerous lotions for relievingthe discomfort of poison oak are on themarket.Control MethodsFOLIAGE SPRAYS. Commonly usedbrush killers 2,4,5-T and mixtures of2,4,5-T and 2,4-D are effective for thecontrol of poison oak. Best control hasbeen obtained by using 3 to 4 pounds (3to 4 quarts product) of the acid equiva-lent in 100 gallons of water (1 cup in 5gallons of water). The foliage shouldbe covered thoroughly for good control.Foliage spraying should be done in thespring after the poison oak plants arefully leaved out. Regrowth and missedplants should be resprayed with a sim-ilar spray the following year. The2,4,5-T type sprays kill slowly and mustbe applied carefully in areas where sus-ceptible plants are growing. Consult thelabel for grazing restrictions and otherlimitations in use.Picloram is one of the more effectiveherbicides for controlling poison oakand poison ivy. Picloram is not regis-tered for use on crop or grazing land. Itcan be used on non-grazed or non-cropareas.Prepared by Oregon State University Extension weed control specialists in consultation with Extensionspecialists at Washington State University and the University of Idaho.Picloram, sold as Tordon, will controlpoison oak. The recommended rate is 1to 1-1/2 pounds of active picloram peracre. This is usually applied in about 100gallons of water per acre. The spray ma-terial should be applied after the plantsare fully leafed. Dry material should beapplied in the early fall, preferablyOctober.Picloram sprays or beads must be usedcarefully to prevent the spray materialsfrom drifting to desired plants or toprevent the material from moving withwater to nearby plants. Follow labelprecautions on the container.Amitrole, sometimes called ATA orATZ, with trade names of Amino Tn-azole, Weedazol, Amitrole T, and Cy-trol, will control poison oak. Amitroleshould be applied when the poison oakis in full leaf, preferably during themonth of June. Later applications areeffective but not as good as June appli-cations. Use at least 1 pound of the 50percent powdered form or 1 quart (1/2pound) of the liquid form for each 12gallons of water. The foliage of the poi-son oak should be thoroughly covered.One treatment usually eradicates poisonoak. However, should regrowth occur,it should be resprayed with amitrole thefollowing year. Amitrole will damagegrassy plants. This chemical is not reg-istered for use on crop or grazing lands.Ammate-X (Ammonium sulfamate) isan effective, rapid-killing chemical forpoison oak plants. This spray is mixedat the rate of 1 pound of Ammate-X pergallon of water. It should be appliedafter the plant is in full leaf. Ammate-Xcan be used successfully any time dur-ing the summer months. It is especiallyeffective around parks and playgroundswhere rapid plant kills are important.Animate does not volatilize, thus is safeto use in areas where 2,4,5-T suscepti-ble plants are growing. Ammate-X iscorrosive to spray equipment. Sprayersused for applying Animate should bewashed thoroughly after each use.Basal or dormant sprays. One gallon(4 pounds active) of 2,4,5-T, when mixedwith 25 gallons of diesel or stove oil,can be applied as a basal spray on poisonoak. This spray can be applied during thedormant season. The lower 30 inches ofthe plants are sprayed with this method.Winter or basal sprays are especiallywell adapted for spraying fence rowsand roadsides. They are generally ap-plied when there is a minimum chancefor injury to nearby susceptible plants.Soil sterilants. Soil sterilants such assodium chlorate, borate, and mixtures ofborate-chlorate will kill poison oak.These chemicals are not selective andshould not be used in areas where de-sired plants are growing, Sodium chlo-rate, after becoming wet, is a fire hazard.Soil sterilants must come in contactwith the root system of the plant. Inwestern Oregon and Washington thechemical should be applied in April. Ineastern Oregon and Washington and inIdaho, October applications are best.More uniform dry applications of soilsterilants can be obtained if poison oakis burned before treatment.Recommended RatesRate (poundsChemical product per sq. rod)Sodium chlorate 4-5Atlacide 5-6Borate 12-15Borate-chlorate mixture 8-100,thwezt cPublished and distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914, by the OregonState University Extension Service, Joseph R. Cox, director; the Washington State University ExtensionService, Arthur W. Peterson. acting director; the University of Idaho Agricultural Service, James L. Graves,director; and the United States Department of Agriculture, cooperating. OSU-4M; WSU-1OM; I-2M.

Poison oak and ivy [1974]

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Poison oak and ivy

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