Purple Starthistle

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Purple starthistle (Centaurea calcitrapa) was detected in eastern Fresno County for the first time since 2007. Approximately 1.5 acres of the 32 acre site were treated. Purple starthistle was first detected at the site in May of 2001. From 2001 to 2007 the site has been surveyed all of the plants were hand pulled and disposed. No plants were detected in surveys from 2007 to 2010. In 2012 mature plants were detected at the same site. Management methods are currently ongoing. Purple starthistle is a B-rated invasive noxious weed. It is a biennial weed that will infest rangeland and open grasslands. Just like its close relative yellow starthistle, it can degrade the forage quality of rangeland and hinder access to humans and livestock. Mature plants can grow over 6 feet tall. The bracts of the flowers have toothpick like spines over one inch in length.

Mature Purple Starthistle Along Canal BankFlower Heads and Spines
Mature Purple Starthistle Along Canal Bank (Left) and Flower Heads and Spines (Right)

Purple Starthistle FlowerRoot System
Purple Starthistle Flower (Left) and Root System (Right)