Perennial Sowthistle

Sonchus arvensis ssp. arvensis

Class C Noxious Weed

General

Native to Europe, Asia and Northern Africa.
Can cause economic losses in croplands due to reduced yields, increased cultivation and herbicide costs.
Perennial sowthistle is a host of several economically important plant pests.
It can also invade marine and freshwater shorelines and river mouths, where it outcompetes and displaces native groundcover and grass communities with a monoculture.

Identification

Deep-rooted perennial herb. Ranging in height from 1.5 to 6 feet tall.
Leaves are alternate with prickly edges, pointed lobes and vary in size becoming smaller and less lobed moving up the stem. Leaves are lanceolate, oblong, or ovate in shape. The upper surface of each leaf is hairless and smooth. Lower leaves can be up to a foot long. Stem leaves are clasping without stalks.
Upright, hollow stems with bitter, milky juice; branch only at the top of the plant.
Bright yellow flowers, 1.5 to 2 inches wide when in bloom. Flowers open 2-3 hours after sunrise and close around noon. Flowers bloom from June to September, usually only a few flower at the same time.
Flowers, stalks, and bracts are covered with gland-tipped sticky hairs.
Seeds are small, around 0.1 inches long with ridges on each side. Seeds are reddish-brown, attached to white parachute-like hairs that can carry them in the wind.
The root system consist of a stout taproot that can penetrate 9 feet into the ground and produces long spreading rhizomes (horizontal underground stems).

Photos

Habitat

Prefers low, fine-textured soils, especially loams. Prefers alkaline or neutral conditions over acidic conditions.
Found in a variety of habitats including cultivated fields, waste areas, meadows, sloughs, woods, lawns, roadsides, beaches, ditches, and river and lake shores.

Reproduction and Spread

Reproduces by seeds and creeping roots.
Perennial sowthistle spreads rapidly via its spreading root system, which allows it to quickly establish in new areas and persist under cultivation. The rhizomes can spread more than 6 feet in one growing season.
Seed production is highly variable, but a plant may produce nearly 10,000 seeds per year, which are dispersed by wind. The parachute-like hairs also allow them to stick to clothes, fur, vehicles and farm implements.
Shoots and new roots begin to form around April; seeds also germinate around this time. Plants form rosettes early in development. Most plants do not flower during their first-year.

Control

Prevention is the most cost effective approach. Vehicles, farm, outdoor recreation and construction equipment can transport seeds and fragments of rhizomes. Clean all equipment and clothing before moving from an infested area.
Small isolated populations (6 to 8 plants) can be carefully dug up, but root fragments left in the soil can produce new shoots. Collect and bag all plant material and dispose of in trash.
Dead heading, or cutting all budding/flowering/seeding parts of the plant tops, and carefully bagging and disposing of them will control seed production. This method is very effective in combination with an application of herbicide.
Tillage during the 7 to 9 leaf rosette stage seems to work best for reducing the reproductive capacity of the roots.
Replanting or seeding areas after control work is completed will reduce perennial sowthistle numbers in subsequent seasons, and prevent establishment of other invasive weed species. Perennial sowthistle rarely thrives where competing species are well established and maintained.

Herbicide Control

Herbicide control is best done in combination with other control methods as perennial sowthistle is relatively resistant to many common broadleaf herbicides.
Herbicides with the following active ingredients are effective on perennial sowthistle:
- Triclopyr
  - Product name Garlon 3A.
  - Selective, non-residual herbicide.
  - Foliar application, apply at a 1.5% to 2 % solution.
  - Apply in the spring when plants are actively growing; in the pre-bud to early bud growth stage.
- Aminopyralid
  - Selective herbicide with residual soil activity.
  - Product name Milestone. Refer to label as this product can only be used in specific areas listed on the label.
  - Apply at a rate of 3 to 5 fluid ounces per acre. (0.05% to 0.08% solution. Do not exceed 7 fluid ounces per acre per year.
  - Apply in the spring when plants are actively growing and in the pre-bud to early bud growth stage.
- 2,4 –D
  - Apply at a rate of 2 lb acid equivalent per acre.
  - Apply in spring during bud stage and to regrowth 8 to 10 inches high. Repeat applications are necessary.