The Enemy: Maltese starthistle (Centaurea melitensis)

Strategy: This is a winter annual plant that reaches about 3 feet tall and can invade any landscape. It prefers open, disturbed soils. The invader branches at the base have three or more main stems. Leaf margins are smooth and lightly toothed or waxy. The leaf bases extend down the stems, giving them a winged appearance. It greatly resembles yellow starthistle, which has a narrow stem and exhibits a gray-green color. A rounded flower head has yellow flowers that have modified bracts that are needlelike and 1 inch long.

Attack: This nasty invader is completely inedible to livestock and wildlife, mostly due to the needlelike spines on the flower head. Also, the leaves usually disappear after flowering. It prefers disturbed sites with some open soil like most rangelands. With the spines, it makes it virtually impossible to walk through to your favorite fishing hole or hunting spot.

Crimes: As with all annuals, especially winter annuals, establishment is quick and spreading rapidly is imminent until the landscape has been destroyed. This plant is one of the newest invaders in the West, but has yet to be found in Idaho. It is spread by the wind as well as by simply dropping seeds on the ground. Animals are the greatest at spreading the seeds.

Defense: Mechanical control is effective if you can tolerate the spines on the seed heads. Many herbicides are effective. Early in the season, 2,4-D is adequate, but we need to switch to Tordon 22K (1 quart), Milestone (6 ounces), Opensight or a new product Method (in nongrazing areas only). Treatment is necessary in early fall or early spring. Once established, attack the plants with any of the other products listed.

To learn more, call Bonneville County Weed Superintendent Jeffrey Pettingill at 208-529-1397 or email