Yellow Starthistle Biology, Impacts, and Management in the Western United States

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Yellow Starthistle Biology, Impacts, and
Management in the Western United States

• Stephen Enloe, Joe DiTomaso Mark Renz

http//wric.ucdavis.edu/yst/yst.html
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Objectives

• Review Introduction, spread and current
  distribution of Centaurea solstitialis L.
• Discuss life history stages, impacts, and
  relevance to management strategies
• Discuss current control strategies and the
  importance of IPM for long term success

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IMPACTS

• Reduces forage quality
• livestock and wildlife avoid grazing in heavily
  infested areas
• Infested areas had less crude protein and total
  digestible nutrients
• Toxic to horses (chewing disease), no cure
• Reduce access to recreational areas
• Displace native plants, and decrease native plant
  and animal diversity
• Depletes soil moisture
• In CAloss of 16 to 56 million in water/year.
• Bee industry

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YST Seeds and Seedlings
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YST Seedbank Dynamics

• Produces gt 100,000 seeds/plant
• Seed longevity is 3-5 years
• Requires light, moisture and temps. lt 90 F
• Germination/death appears to be 60-80 per year
• Germination is highest immediately after rainfall

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Shoot Root biology

• Seedlings typically germinate in late fall or
  early winter and overwinter as rosettes.
• Root growth is preferential in early season
• Shoots do not bolt until late spring
• Flowering does not occur until summer months

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• Strong allocation to early root growth
• YST roots grew six feet in two months

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Timing of Control Determined by YST Phenology

• Temperature, rainfall, and growth stage will vary
  across the Western US
• Mowing, burning
• Late spiny - 2 flowering stage
• Grazing, hand pulling
• bolting stage
• Chemical (varies by herbicide)
• seedling - 2 flowering

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Growth form of YST affects mowing success
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Biological Control

• Distribution 5 biological control agents
• None released in NM
• All available agents feed in developing flowers
• Agents have not yet proven to be highly effective
  for reducing infestations
• 70 of the seed may be consumed
• Future releases in NM are planned

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Hairy weevil Eustenopus villosus
False Peacock Fly Chaetorellia succinea
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Chemical Control of YST

• Early season clopyralid, picloram
• Late season (Bolting - early flowering)
• Clopyralid (1.5 - 4 oz ae / A) applications must
  be before buds emerge to prevent viable seed
• Picloram (0.25-0.375 lbs ae/A) rosette to bud
• Will not harm established grasses
• Effective control for 2-3 years
• Glyphosate (1 lbs ae/A)
• Effective bolting through early flowering unless
  plants show signs of drought stress
• Can be strategically applied following senescence
  of desirable grasses to prevent grass injury
• Spot applications of 1 v/v
• 2,4-D, triclopyr not recommended for late season
• Dicamba effective to bolting stage (0.5 lbs ae/
  A)

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Prescribed fire and Clopyralid Strategy over two
years

• Yellow starthistle
• Excellent control with two years of Transline or
  burning (if second year burn in complete) and
  with burning followed by Transline
• Noxious annual grasses
• Incorporating a burn can greatly reduce noxious
  annual grass populations
• Legumes
• Repeated Transline treatments reduce overall
  legume populations
• Plant diversity
• Overall diversity not dramatically effected by
  any treatment, but population shifts can occur

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Revegetation/Restoration

• Generally requires herbicide / reseeding
  techniques
• Most work has focused on cool season forage
  grasses
• Grazing management may be tricky

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