Research and More information on Yellow Starthistle

Overview references:
Yellow Starthistle Management Guide  Published by the California Invasive Plant Council, 2006.  Comprehensive guide broken into sections of Introduction and Spread, Impact, Biology and Ecology, Mechanical Control, Cultural Control, Biological Control, Chemical Control, and Developing a Strategic Management Plan.

StarThistle Pest Notes  UCCE Pest Notes, 2007.  Provides brief overview of Yellow Starthistle (YST) from identification, biology, and management options.

Biology References:
Reproductive biology of yellow starthistle, maximizing late-season control  Weed Science journal article, 2001.  Seed viability was examined at different flowering stages of YST.  It was found that to reduce the amount of viable seeds, late-season control methods should be timed before the YST population has advanced beyond the 2% flower initiation stage.  Examining the seed bank, after the first growing season, over 80% of the seeds were either damaged or degraded.  It is estimated that over 97% of the total seeds were removed from the seed bank after two growing seasons.

Effect of light and density on yellow starthistle (Centaurea solstitialis) root growth and soil moisture use  Weed Science journal article, 2003.  The article examines how root growth is reduced by shade; soil moisture is depleted by density of YST.

Soil water dynamics differ among rangeland plant communities dominated by yellow starthistle (Centaurea solstitialis), annual grasses, or perennial grasses  Weed Science journal article, 2004.  Soil water depletion by annual grasses, perennial grasses, and YST was examined for four years.  The soil moisture was driest in the YST plots, and the most moisture was in the annual grasses.  YST also depleted soil moisture later in the season and at deeper depths than the two grass communities.  Invasion of YST can alter the soil moisture of rangelands.

Spatio-Temporal Relationship between Water Depletion and Root Distribution Patterns of Centaurea solstitialis and Two Native Perennials  Restoration Ecology journal article, 2010.  The research project examined root growth and soil moisture depletion of YST and two native perennials during a wet year and a dry year.  During the wet year, YST roots functioned similar to the native perennials, but during the dry year the roots functioned more like annual grasses, depleting shallow soil moisture.  During native plant restoration, it is critical to control YST early in the growing season before shallow soil moisture is depleted.

Biological Control References:
Effects of the rust Puccinia jaceae var. solstitialis on Centaurea solstitialis (yellow starthistle) growth and competition  Biological Control journal article, 2010.  Introduced in 2003, the rust fungus was examined for the control potential of YST.  While there was some success in reducing YST biomass, the rust fungus appears to be a minor biological significance and would be unlikely to cause major declines in YST.

The effect of Puccinia jaceae var. solstitialis on the yellow starthistle biological  Biological Control journal article, 2010.  With the introduction of the rust fungus, this article examines if there is any interaction of the rust fungus and other biological controls.  There was found no effect of the rust on seedhead attack rates of other biological control insects.

Burning References:
Instability in a grassland community after the control of yellow starthistle (Centaurea solstitialis) with prescribed burning  Weed Science journal article, 2002.  After three years of fire, YST seedbank, seedling density, and mature vegetative cover were reduced by 99, 99, and 91% respectively.  The plant community also had a great species diversity and species richness.  The area was monitored for four years, during which time the YST population recovered.  After reducing YST, some change in management needs to continue to maintain a low population of YST in annual grasslands.

Mowing References:
Success of mowing to control yellow starthistle depends on timing  Cal Ag article, 1999.  Successful control of YST by mowing depends on both proper timing and the plant's form of growth and branching.  Erect, high-branching populations can be controlled with single mowing at early flowering.  Sprawling, low-branching plants were not controlled even by multiple mowings.  Mowing should be an effective tool in an integrated approach.

Chemical References:
New growth regulator herbicide provides excellent control of yellow starthistle  Cal Ag article, 1999.  Comparison of herbicides to control YST.  The then just registered clopyralid provided excellent control of YST at low rates and worked equally as well whether applied to leaves or to soil to control germinating seedlings and had residual activity throughout the season.  Complete YST control was achieved with applications made from December through April.  February treatments maximized desirable forage production, especially grasses.  Late-season applications to glyphosate and clopyralid were effective for control of YST plants in late rosette and bolting stages.

Integrated Approaches References:
Integrating prescribed burning and clopyralid for the management of yellow starthistle  Weed Science journal article, 2006.  Both prescribed burning and clopyralid are very effective tools for managing YST, but not practical for repeated use.  Five different possible treatments were examined: a control of no treatments, 2 consecutive years clopyralid, 2 consecutive years of prescribed burning, first-year of clopyralid followed by second year of prescribed burning, and first-year prescribed burning followed by second year of clopyralid.  2 years of clopyralid and prescribed fire followed by clopyralid consistently reduced YST the following year by 92 to 100%.  A treatment with fire in the last year seemed to stimulate germination of remaining soil seedbank.

Perennial Grass Establishment Integrated with Clopyralid Treatment for Yellow Starthistle Management on Annual Range  Weed Technology journal, 2005. Examines using clopyralid to control YST in addition to planting a perennial (wheatgrass).  Clopyralid was able to significantly reduce YST and allow wheatgrass establishment in one treatment.  Annual grasses and forbs dominated clopyralid treatment only plots, allowing for reestablishment of YST.  The wheatgrass and clopyralid treatment plots provided long term YST suppression, indicating the importance of revegetating the infected area as part of a control strategy.

Restoration References:
Functionally Similar Species Confer Greater Resistance to Invasion Implications for  Restoration Ecology journal article, 2009. Examines the ability of different plant communities to resist the invasion of YST.  Early season forbs and grasses were not able to prevent the invasion of YST  Late season native perennials were able to resist the invasion of YST, not allowing more than 10% cover of YST.  Two late season native perennials, blue wild rye, Elymus glaucus, and Great Valley gumweed, Grindelia camporum, are functionally similar to YST.  Blue wild rye quickly spread to all plots and communities containing blue wild rye were better at resisting invasion of YST.  However, Great Valley gumweed failed to survive the project's 5 years.  When selecting a species to restore a grassland, care should be taken to ensure that not only does the species you are planting function similarly to the invading species, but that it is also easy to establish, will be competitive, and survive.

The Role of Light and Soil Moisture in Plant Community Resistance to Invasion by Yellow Starthistle (Centaurea solstitialis)  Restoration Ecology journal article, 2010.  Different native winter annual forbs, non-native annual grasses, native perennials, and a combination the native forbs and perennials were examined for their ability to withstand YST invasion.  Native perennial grasses, such as blue wildrye (Elymus glaucus) is functionally similar to YST, using deeper soil moisture later in the season compared to shallow rooted forbs and annual grasses.  Blue wildrye established quickly and resisted YST invasion.