How to Kill Goatheads and Star Thistle

Comment to the Josephine County Commissioners and Grants Pass City Council, 8-30-12

There are two noxious weeds that are growing throughout our town: goatheads, AKA puncture vine, tack vine, bullthorns and caltrops; and star thistle, a thistle that has thorns only on its flower buds.  They are both weeds of non-residential commercial and public landscapes, because most people don’t tolerate them where they live, even if they put up with all kinds of other weeds.  In 12 years of professional gardening, I have seen them at exactly one residence.  Working there made me get a flat-free wheelbarrow tire.

 

                                         Goathead flower

Meanwhile, I have watched bullheads move onto downtown properties like the three across F Street from the Growers’ Market parking lot, and star thistle taking over vacant lots and the underused edges of public properties.  They are mostly weeds of organizations that do not love their neighbours by obeying our city’s nuisance codes.

Unlike windblown weeds, these do not travel far or fast.  Goathead seeds spread on bike tires, wheelbarrows, and riding mowers; high speed travel apparently crushes them, and few people or dogs carry them far on their feet.  One would think that star thistle would spread on the wind, like other thistles, but they don’t.  They cling to the plant and are picked up on clothing and spread by mowers as well.

                                 goathead seeds

This year, I am getting a lot of practice killing these two weeds on the City’s Water Reclamation Plant property at the end of Greenwood, in preparation for the dog park that the City, at my suggestion, wants to build east of the walking path to the Reinhart Volunteer Park.  I spend about 20 minutes a day on the task, before and while I walk my dog.  The ground is very dry and hard, and they don’t pull, my normal weeding method, so I have been cutting them under the crown, which appears to work well.

 

  Star Thistle:  http://cameronkopf.blogspot.com/2011_09_01_archive.html

Annual weeds like goatheads and star thistle build up food in their roots until they flower, and then move that energy into their crowns and tops as they flower and seed.  Cutting to two inches high, the height at which most people mow and whack weeds, only slows down flowering above mower height, and doesn’t touch flowers below that point.  The tall ones like star thistle grow right back above it; the crawlers like goatheads are not affected, except that mowers spread their seed.  Cutting annuals below the crown takes out the source of flowers, and the roots cannot recover.

   Young star thistle (http://www.dpi.vic.gov.au/agriculture/pests-diseases-and-weeds/weeds/other-declared-weeds/star-thistle)

Whacking either weed all the way to the ground can take out most of the crowns, but spreads any ripe goathead seeds.  Pruning scissors are more effective; allow one to pick up the ripe goatheads; and may even be faster, though one has to stoop to do the work, because it takes a lot of whacking to kill a crown or cut below it.  Star thistles have tough stems, but their crowns are often 2 inches or more off the ground, and are readily cut even with dull scissors, which they will be after much cutting in the dirt.

         

Rycke Brown, Natural Gardener         541-955-9040    rycke@gardener.com