Common chickweed (Stellaria media)
by Dr. Bob Blackshaw
Common chickweed is a cool season annual plant found most frequently in high rainfall zones. Its distribution in Alberta is primarily along the Highway 2 corridor from Calgary to Edmonton where it is a troublesome weed in barley, canola, and field peas. Although not widespread in farm fields in southern Alberta, it is present in urban gardens in our region and bears being on our weed watch list.
Common chickweed can be identified by having bright green ovate-pointed leaves, a distinctive line of hairs along its stem, and small white star-shaped flowers with five petals. It has a prostrate growth habit and rarely attains a height more than 30-50 cm. The low growing stems have the ability to root at each node thus allowing it to form dense succulent mats of vegetation.
Common chickweed has egg-shaped seed pods that contain small reddish-brown seed and seed production can be up to 15,000 seeds per plant. Optimum germination occurs at soil temperatures of 12-20 C; thus it primarily emerges in early spring but can continue to emerge throughout the growing season under wet conditions. Seed has little dormancy and usually will not persist in the soil more than a couple of years.
Common chickweed competes with crops by shading and smothering young seedlings with its mat-like growth. It also takes up considerable amounts of soil nutrients that otherwise would be available to the crop. Plants often remain green in the fall and can pose harvesting problems if dense infestations exist.
Control measures include cultural practices such as higher crop seeding rates that will shade out later emerging flushes plus a combination of preseed burndown and in-crop herbicides. Group 2 herbicide-resistant chickweed populations have been documented in Alberta, Saskatchewan and Manitoba; thus herbicide programs should utilize different herbicide groups within and over cropping years.