New Species, New Fungus. Hemp Leaf Spot: Questions Outpace Answers. An update on hemp leaf spot, 2019.

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

6. 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?

9. Molecular
Identification &
Whole Genome
Sequencing

10. Host Ranges of Bipolaris sp.
• Rice
• Corn
• Barley
• Wheat
• Poa, grasses
• Banana
• Coconut

11. Alternative Hosts (KY)

12. 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?

14. Populations &
Recombination

15. Unrelated Populations
• Source for inoculum?
• Relatedness of populations?
• Primary host?
Spread from hemp field to hemp field unlikely
• Not clone-transmitted
• Not seed-transmitted

16. Hemp Leaf Spot –
Still… More Questions than Answers!
KyHempDisease.com

17. Management using
Fungicides
Lab analysis
• Poison plates – amended agar
• Exposure analysis – comix
• Inhibition plates
Detached leaf analysis – pending
Results following are NOT recommendations.

18. Management using Fungicides, Amended Media

19. Management using Fungicides, Comix Susp

20. Management using Fungicides, Inhibition

21. Management using
Fungicides
Lab analysis
Detached leaf analysis – pending
Field trials – multiple sites & years needed before
recommendations or publications.

22. Hemp Leaf Spot –
Still… More Questions than Answers!
KyHempDisease.com