Problem Weed of the Month: Poison Ivy

Problem weed:

Poison ivy

Other names:

Rhus radicans, poison creeper, three-leaved ivy, sometimes incorrectly called poison oak. Actually a member of the Cashew family.

Growth habit:

Woody perennial. Extremely variable in both its habit of growth and kinds of habitat.

Description:

Stems are woody and grow either along the ground, or as a climbing vine with aerial roots, reaching to tree tops. "Leaflets three - Let it be!" Always has 3 leaflets alternate at the nodes, with the middle leaflet having a longer stalk (petiolule). Leaves are generally shiny with varying types of margins. Leaves turn a bright red in autumn.

Leaves are generally shiny with varying types of margin

Stems are woody and grow either along the ground

Spreads by:

Seeds and by woody rhizomes. Birds spread the seeds from the white berries.

Reasons for concern:

All parts of the poison ivy plant are poisonous, producing a major skin rash. The toxic compounds can be spread by smoke or by direct contact with the oils in the plant. About 2/3 of the population are sensitive to poison ivy. Pets, tools and clothing can spread the oils at any time through the year. Usually invades from field edges, but often occurs in growing in fruit trees and vines. Listed as a noxious weed under the Ontario Weed Control Act.

May be confused with:

• Virginia creeper: also a woody vine common in orchards and fence rows, but has 5 or 7 leaflets. Berries are blue, and are also poisonous.
  
• Manitoba maple: may have 3 leaflets instead of the usual 5, but has leaves opposite on each node. Seeds are like maple keys instead of in berries.
  
• Clematis : also a climbing or trailing vine but has opposite leaves (2 compound leaves come from each node on the stem) and larger white or blue flowers.
  
• Hog-peanut and ground nut: also vines with alternate leaves (like poison-ivy) but with clusters of small whitish to purplish or brownish flowers like those of the sweet pea.
  
• Poison oak: also has very coarsely toothed leaflets, but does not occur in Canada.

Cultural control:

• Easily controlled by repeated cultivation.
  
• Cutting and burning can be done with care. Find someone who is not sensitive to poison ivy - not me! However, it is almost impossible to remove every piece of underground stem so regrowth is likely to occur. Ensure that the oils in the smoke and contaminated clothing do not come in contact with sensitive people.
  
• Cutting flowers before they set berries will reduce the spread by birds.

Chemical control:

• Remember that herbicides will also damage desirable plants. Good coverage is essential, and repeat treatments are usually necessary, likely over several years.
  
• These herbicides will give some control of poison ivy: systemic herbicides like amitrole or glyphosate (may be mixed with simazine), or hormone herbicides like 2,4-D, mecoprop, dicamba. In non-crop areas, dichloroprop, Arsenal (imazapyr) or Garlon (triclopyr) can be effective.
  
• The most effective treatment time is June 15 -July 31, but anytime plants are actively growing can be useful.
  
• A small sprayer to treat cut stumps can also be useful for spot treatments.

Learn more:

• Publication 75, Guide to Weed Control, p. 313, Poison Ivy Control
  
• Publication 505, Ontario Weeds, p. 136-137
  
• Ontario Weed Gallery online
  
• Poison Ivy, OMAFRA Factsheet 99-015
  
• Noxious Weeds Profile - Poison Ivy
  

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