46 FARM WEEDS OF CANADA 



* LADY'S THUMB (Polygonum Persicaria L.) 



Other English names: Persicary, Smartweed. 



Introduced from Europe. Annual, stem erect, fleshy, nearly 

 smooth, hairless. Leaves lance-shaped, pointed, nearly stalk- 

 less, the surface roughish, often dotted and marked with a dark 

 triangular or round spot near the centre. The mode of flowering 

 is an ovoid or short cylindrical spike, dense, erect, composed of 

 pink or dark purple flowers. 



The seed (Plate 72, fig. 10) is about 1 /12 of an inch in dia- 

 meter, ovate, heart-shaped, hollowed out on one side or roundly 

 triangular, jet black, shining. 



Time of flowering: July to September; seeds ripe by August. 



Propagation: By seeds. 



Occurrence: Common all over the country, especially in 

 low fields and meadows. 



Injury: Although Lady's Thumb and others of the Knot- 

 weeds and Smartweeds are widely distributed, they are not seri- 

 ously noxious in most field and garden crops. Knotweed is 

 most abundant in yards and along paths where the soil is well 

 trodden. Smartweeds thrive best in a rich, moist soil and 

 are usually plentiful in grain or clover fields where the crop has 

 killed out. The seeds of Lady's Thumb, in particular, are com- 

 mon in clover seeds. Smartweeds, like many other weeds, 

 help to perpetuate nuisances even more injurious than the weeds 

 themselves. They harbour insects, particularly plant lice, and 

 fungus diseases, such as mildews, smuts and rusts. 



Remedy: Lady's Thumb should not be permitted to seed. 

 The plants in clover seed crops should be hand-pulled or cut 

 before coming into full bloom. Destroy the screenings that 

 accumulate when grain is threshed or fanned. The seeds do not 

 retain their vitality long, and by cutting the plants two or three 

 times during the season for a few years the pest may be eliminated 

 from waste places. 



* Lady's Thumb very closely resembles Pale Persicary, illustrated on plate opposite 



