Control and Ecological Studies of Scotch Thistle

Abstract
The range weed, Scotch thistle (Onopordum acanthium L.), is an increasing problem in the western United States. It competes with desirable forage plants and the flower stalks are a barrier to livestock movement. Prolific production of viable but dormant achenes makes this species a persistent pest. Applications of 4-amino-3,5,6-trichloropicolinic acid (picloram) in the spring or fall, at rates as low as 0.03 lb/A, gave control of Scotch thistle.

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