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Bolted Scotch Thistle Plant Prior Flowering

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Scotch Thistle Head Prior to Flowering

Invasive weeds are an issue anywhere people travel or transport things. Every month, I will highlight a weed that is either not established or is in low abundance in Lyon County. Verified records of these weeds are very helpful to weed managers and Nevada Department of Agriculture. If you see these plants, you can report them directly to Nevada Department of Agriculture, using the app EDDmaps, or email me photos and a location. Invasive weeds are everyone’s problem, so help keep them from invading your neighborhood and report them.

Scotch thistle, Onopordum acanthium, is a large spiny plant with pink to purple flowers. Thistles are difficult to identify, so confirm your identification before destroying thistles. Native thistle plants are declining for many reasons and need to be protected. Like most thistles, Scotch thistle is biennial and is a rosette of leaves the first year and bolts into a tall plant with flowers the second year. The rosette stage is difficult to identify. The bolted plant can be very tall, up to 6 feet. Characteristics of the leaves, flowers or seeds can distinguish it from other thistles.

Current distribution maps (EDDmaps or USDA Plant Database)of scotch thistle is broad across the United States. EDDmaps reports Scotch Thistle in Lyon county. I observed it while hiking in southern Lyon county. It is listed as a category B weed by Nevada Department of Agriculture. Scotch thistle can be controlled by pulling up the plant or removing the flower heads by cutting or mowing before it goes to seed. Nevada Department of Agriculture has recommendations for chemical control of Scotch thistle.