Field Guide   pic  Weed Management   pic  Lady’s Thumb

Lady’s Thumb

(Polygonum persicaria L.)

Crop Impacts: Vegetables, barriers, grains and pastures

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About Lady’s Thumb:

Lady’s Thumb is a summer annual, competitive, broadleaf weed that reproduces by seeds. Almost every part of this weed is edible and best consumed from mid-spring to late fall. The stems, flowers and leaves can all be eaten cooked or raw, tasting similar to lettuce. Introduced from Europe, Lady’s Thumb can also be used for medical purposes. The leaves can be used as treatment for poison ivy and stomach pains. If you rub this weed on horses, it can be used as an insect repellant for them.

Family: Buckwheat or Smartweed Family (Polygonaceae)

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Lady’s Thumb Scouting and Prevention:

The seedlings of Lady’s Thumb have oblong to football shaped leaves that are about 8 to 12 mm long, and 1 to 3 mm wide. The leaves have small glandular hairs along the edge near the base, and are holding onto short stalks that are fused at the base. A mature Lady’s Thumb stands from 20 to 100 cm high, with a smooth, green or reddish, erect stem. The leaves sit one per node alternating up the stem, each leaf can be from 2 cm to 15 cm long. The top surfaces of the leaves are green. Typically, there is a blotch which is red to brownish or purplish in colour located on the top middle half of the leaf. The Lady’s Thumb weed produces small flowers that grow on a crowded spike, which are usually 1 to 4.5 cm long, sitting at the ends of branches and stems. Each flower is pinkish and sometimes white in colour with 5 sepals, blooming from June to September. The fruit produced by Lady’s Thumb are enclosed by the sepals of the flower when the plant is mature. These seeds are smooth, shiny, black, and ovate and are slightly thicker near the middle.

Common locations

  • Moist soil
  • Shaded areas
  • Pastures
  • Seasonal flooding area
  • Rice fields
  • Grain fields
  • Barley fields
  • Vegetable fields


Prevention of Lady’s Thumb is less expensive and less time-consuming than trying to control it. Make sure when you are seeding a new area, you are doing so with certified weed-free seeds. If there is an infested area on your property, be sure to drive around, instead of through it. Make sure to give all equipment that has been in infested fields a good clean, to make sure no seeds are transferred. Applying the chemical Dichobenil, as a pre-emergent herbicide, is an aggressive and effective prevention method. This process will have to be repeated several times for about a year or a little more to take noticeable control.

Lady’s Thumb Control:

Cultural Control

The best time to control Lady’s Thumb is when the plant is young and the soil is wet. During this time you will have a higher probability and an easier time removing the entire root system. If you do decide to pull a mature Lady’s Thumb by hand, be aware that it is very difficult to pull the taproot out, and it is likely that seeds will be dropped into the soil. If the plant is a little bigger but has yet to set seeds, which is the perfect time to take a hoe to it. After hand pick or herbicide control, lay down landscape fabric or polypropylene plastic, this blocks the sun from reaching the soil. The fabric does not provide 100% control against the weeds. If you put holes in the plastic or fabric for desirable plants to grow through, Lady’s Thumb may sneak in as well. Mulching is a good way to prevent regrowth. Mulch must be at least 3 inches deep, with synthetic materials underneath to once again block out the sun, and provide a barrier to restrict seed growth.

Chemical Control

There are numerous chemical control methods that can be used to manage Lady`s Thumb. The first method would be using systemic herbicides to kill the root system. Another option is using non-selective herbicides. For Lady’s Thumb, some of the best control methods work when applying products containing dicamba, 2,4-D or glyphosate.

Latin / Alternative Lady’s Thumb names:

  • Polygonum persicaria L
  • Renou?e persicaire
  • Red shank, Smartweed
  • Persicaire pied rouge
  • Persicaire

Additional Lady’s Thumb Resources'STHUMB_PAGE_FINAL.html