MALTA STAR-THISTLE INVASION

MALTA STAR-THISTLE INVASION Malta star-thistle (Centaurea melitensis L.) was first found in Eddy County around 2003 or so along the truck by pass in Carlsbad. I carry a hoe in the truck for such occurrence and have rouged out a number of new invasive weed when I see them. I was too late for this one I did rouge out a patch only to find 20 or more down the highway. Since that time this weed has been the target of the Eddy County weed management group who have done their very best to stop this weed. But like the Russian thistle (tumble weed) it can now be found in the just about everywhere in the county and is moving from disturbed site such as road sides into fields and landscapes. It is a winter annual with a spiny yellow flowered head that reaches about 3 feet higher but under good growing condition can reach 4 feet. The spins are less than an 1.5 inches, which distinguishes it from its cousin yellow star-thistle. It reproduces by seed and can produce 1-60 seeds per flowering head. The leaves are withered usually by flowering time. This is a tricky weed though. It germinates in the fall, like the mustard, as soon as it has two true leaves it bolt and send up one flower that will have 1-5 seed in all less than 3 inches tall. So it is difficult to mow this flower off and it a guaranteed species survival for another year. There have been six biological control insects released for yellow star thistle. These insects feed on the seed thus reducing seed production. It is a wait and see if they will also help with Malta. Chemical control if applied at the right time of year works well. The systemic herbicides clopyralid or picloram work well when applied between December and April. Once the flower is set, chemical application don’t do the job. In alfalfa fields the use of the mustard herbicides when there are mustard weed present may help. Sheep and goat like to graze this weed until it get the spiny flower. It has no toxic effect but once the spine form they can lodge in the mouth and tong causing problems; however most animals will not try it. This weed is almost imposable to control by mechanical methods. So here it is the first part of June, the weed has set seed and the leaves are withered so they will not absorb herbicide. All you can do is hoe of cut the tops off catching the seed head and disposing them in a dumpster. Because of the flooding last year there is a lot of seed in the field and if you did not spry for mustard there is nothing you can do now. The seed will not germinate until late fall. Then you can control the mustard and this weed too hopefully. Subscribe to Eddy County Ag news at: http://nmsueddyag.blogspot.com/ Eddy County Extension Service, New Mexico State University is an equal opportunity/affirmative action employer and educator. All programs are available to everyone regardless of race, color, religion, sex, age, handicap, or national origin. New Mexico State University, U.S. Department of Agriculture, and the Eddy County Government Cooperating.