Problem Weed Series for Apples: Common chickweed

Problem weed:

Common chickweed

Other names:

Stellaria media, STEME, annual chickweed

Growth habit:

Annual, or winter annual, prostrate stems which turn erect, holding opposite leaves that are mostly smooth with pointed tips. Chickweed prefers the cool temperatures of fall and spring, and some swear that it even grows under the snow! Its bright green colour is very distinctive.

Spreads by:

Only by seed, flowering from early spring, and continuing all summer. Each plant can produce thousands of seeds, which germinate from a shallow depth (prefers no-till situations like orchards, vineyards and no-till). Seeds are long-lived in soil.

Reasons for concern:

Germinates in the fall or early spring when herbicide residues are low; Grows thickly under trees; Peak growth during critical period for trees & vines; Hosts insect pests like tarnished plant bugs.

May be confused with:

1. Mouse-eared chickweed: which has a similar growth habit. However, the leaves of mouse-eared chickweed are more elongated and very hairy (like a mouse's ears!). Also mouse-eared chickweed is usually a perennial forming dense patches. Mouse-eared chickweed has similar flowers but they are in compact groups, while common chickweed has single flowers.
2. Grass-leaved stitchwort that is sometimes called narrow-leaved chickweed. It is a close relative but is a perennial with a square stem and very long narrow leaves.
3. Thyme-leaved sandwort that has smooth leaves like common chickweed, but much smaller, with a bluish-green appearance. The stems look rougher and branch mostly from the base. Also the flowers are green (white for chickweeds).

Chemical control:

• Well controlled with spring burndown applications (Amitrol, glyphosate, Gramoxone, Ignite) when weeds are small.
  
• Soil-applied herbicides (simazine, Sencor, Casoron, linuron, Dual Magnum, Treflan, Devrinol, Kerb) usually control chickweed for 8-12 weeks.
  
• Mid-summer burndown herbicides can work well if coverage is adequate, and weeds are not too tall. Check for Tarnished Plant Bugs first - chickweed is a good refugia and can keep them off the fruit.
  
• In orchards, 2,4-D Amine can be effective on common chickweed (but mouse-eared is mostly resistant), but use with care:
  
• Wait for calm, cool conditions to avoid both physical drift and vapour drift.
  
• Do not apply 2,4-D within 80 days of harvest
  
• Can be applied after harvest if late rains bring a new flush in August.
  
• Avoid 2,4-D use around vineyards.

Cultural control

Mechanical control methods (cultivation, flaming, mulching) are very effective on chickweed if done early. Mowing needs to be done very close to the ground, as side branches will grow and flower from mown plants.

Learn more

• Ontario Weed Gallery online
  
• Publication 505, Ontario Weeds, p. 73