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Hemp Leaf Spot: Bipolaris spp. Causing Severe Losses

1. New Species New Fungus Hemp Leaf Spot: Questions Outpace Answers Desiree Szarka, Graduate Student Nicole W Gauthier, Assoc Professor of Extension University of…
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  • 1. New Species New Fungus Hemp Leaf Spot: Questions Outpace Answers Desiree Szarka, Graduate Student Nicole W Gauthier, Assoc Professor of Extension University of Kentucky College of Agriculture
  • 2. Hemp Leaf Spot • Reported in 2014 – SE KY • Samples collected in 2015 • Reports increased each year • Confirmations in 9 counties in 2018 • First symptoms early-July • Yield losses up to 100% • Detailed reports in at least 2 neighboring states • Hemp, only
  • 3. Bipolaris sp. Causal Fungus Large spores (macroconidia) Small spores (microconidia) Sclerotia or proto-perithecia Fungal morphology DOES matter: • Airborne or rain driven? • Survival structures? • Sexual recombination?
  • 4. Molecular Identification & Whole Genome Sequencing
  • 5. Host Ranges of Bipolaris sp. • Rice • Corn • Barley • Wheat • Poa, grasses • Banana • Coconut
  • 6. Alternative Hosts (KY)
  • 7. Alternative Hosts (KY) Four alternative hosts • False nettle (Boehmeria cylindrica) • Hophornbeam copperleaf (Acalypha ostryifolia) • Velvetleaf (Abutilon theophrasti) • Virginia copperleaf (Acalypha virginica) Dicots, not monocots! Primary source or secondary infection?
  • 8. Populations & Recombination
  • 9. Unrelated Populations • Source for inoculum? • Relatedness of populations? • Primary host? Spread from hemp field to hemp field unlikely • Not clone-transmitted • Not seed-transmitted
  • 10. Hemp Leaf Spot – Still… More Questions than Answers! KyHempDisease.com
  • 11. Management using Fungicides Lab analysis • Poison plates – amended agar • Exposure analysis – comix • Inhibition plates Detached leaf analysis – pending Results following are NOT recommendations.
  • 12. Management using Fungicides, Amended Media
  • 13. Management using Fungicides, Comix Susp
  • 14. Management using Fungicides, Inhibition
  • 15. Management using Fungicides Lab analysis Detached leaf analysis – pending Field trials – multiple sites & years needed before recommendations or publications.
  • 16. Hemp Leaf Spot – Still… More Questions than Answers! KyHempDisease.com
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