Blessed Milkthistle

Pest: Blessed Milkthistle (Silybum marianum)

Pest Type: Annual, biennial Broadleaf Weed

Major Identifying Features: Thick succulent cotyledons that are egg shaped, hairless, mature plants are stiff, erect, sparsely branched and have prickly, white-marked leaves, stem branches are thick, hollow, ribbed, sparsely hariy, 2-6.5 feet tall, spiny leaves and deeply lobed, white marbling around veins, pink to purple flowers

Life Cycle: Winter or summer annual, biennial, flowers from April through July, reproduces by seeds

Pest Rating: Limited

Management Rating: Moderate

Host/Season/Outbreak Information: Grows on the North Coast in California, Central Valley, San Francisco Bay area, South Coast Ranges, Channel Island, to about 1600 feet, grows on agricultural land and other disturbed areas, can be found on pastures, orchards, trail margins

Damage Information: Leaves can accumulate toxic nitrate levels for cattle under stressful conditions, can also be used as a medical herb

Management Options: Biological control with weevels, see other thistles

Sources:

http://www.ipm.ucdavis.edu

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